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\begin{document}

\title{Recent research progress of paper-based supercapacitors based on
cellulose}



\author[1]{chuanyin xiong}%
\author[1]{Tianxu Wang}%
\author[1]{Tianxu Wang}%
\author[2]{Jing Han}%
\author[1]{Zhao Zhang}%
\author[3]{Yonghao Ni}%
\affil[1]{Shaanxi University of Science and Technology}%
\affil[2]{Tianjin Polytechnic University}%
\affil[3]{University of New Brunswick}%


\vspace{-1em}



  
  \date{June 16, 2024}


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\selectlanguage{english}
\begin{abstract}
With the rapid development of science and technology, paper-based
functional materials have become the core of the field of new materials.
Recently, they have received extensive attention in the field of energy
storage due to their advantages of rich and adjustable porous network
structure, good flexibility. As an important energy storage device,
paper-based supercapacitors have important application prospects in many
fields, and have also received extensive attention from researchers in
recent years. At present, researchers have modified and regulated
paper-based materials by different means such as structural design and
material composition to enhance their electrochemical storage capacity.
The development of paper-based supercapacitors provides an important
direction for the development of green and sustainable energy.
Therefore, it is of great significance to summarize the relevant work of
paper-based supercapacitors for their rapid development and application.
In this review, the recent research progress of paper-based
supercapacitors based on cellulose was summarized in terms of various
cellulose-based composites, preparation skills and electrochemical
performance. Finally, some opinions on the problems in the development
of this field and the future development trend were proposed. It is
hoped that this review can provide valuable references and ideas for the
rapid development of paper-based energy storage devices.%
\end{abstract}%



\sloppy


\textbf{1. Introduction}

With the development of electronic devices and people's yearning for
electronic devices in the intelligent era {[}1-6{]}, flexible electronic
devices have shown great application potential in the future portable
consumer electronics and wearable devices {[}7-12{]}. Traditional
flexible electronic equipment uses flexible substrates such as metal
{[}13-15{]} (copper foil, aluminum foil, etc.) and plastic {[}16-18{]}
(such as polyethylene terephthalate, polyethylene, polypropylene, etc.).
Although these flexible substrates can endow flexible energy storage
equipment with excellent mechanical properties, metal and plastic
substrates have their own shortcomings. For example, metal and plastic
are both hard materials with poor bending performance. Moreover, due to
the weak binding force between the substrate and the active material,
the active material will fall off during the use of flexible devices,
resulting in poor cycle stability, which is not friendly to the life of
flexible devices. Therefore, it is very important to develop new
flexible materials with excellent flexibility and strong adhesion with
active materials.

Cellulose is passed by glucose unit \selectlanguage{greek}β-\selectlanguage{english}1,4 glycosidic bond linked natural
polymer {[}19-21{]}. Its general molecular formula is
(C\textsubscript{6}H\textsubscript{10}O\textsubscript{5})\textsubscript{n},
which is the most extensive and renewable biomass resource in nature and
can be extracted from trees, algae, bacteria and other substances. Its
structure can be seen from atomic, molecular and macro scales
(Figure1A). Its excellent aspect ratio and porous structure have
important application value in the energy storage field of cellulose
paper based supercapacitors {[}22-24{]}. Cellulose has attracted
extensive attention in the field of flexible supercapacitors
{[}25-27{]}. On the one hand, it is because cellulose is a kind of
material with rich content, excellent mechanical properties, sustainable
and cheap. On the other hand, the cellulose based paper supercapacitor
electrode has a controllable porous structure and pore size
distribution, which is very important for the rapid transfer of
electrolyte ions during energy storage. For the flexible supercapacitor,
the most important thing is the design and preparation of its electrode
material structure. In recent years, cellulose, including nano
cellulose, bacterial cellulose, cellulose fiber pulp and cellulose
paper, has been used to prepare high-performance cellulose paper based
supercapacitor electrode materials {[}28-32{]}. In this field, different
paper based supercapacitors show different emphasis on performance.
Therefore, it is very important to choose an appropriate preparation
method to prepare paper based electrodes. In this paper, the preparation
methods of cellulose based paper based supercapacitors in recent years
are systematically summarized and classified for the first time. As
shown in Figure1B, vacuum filtration {[}33,34{]}, in-situ polymerization
{[}35,36{]} and printing technology {[}37, 38{]} based on the division
of multi-component mixing are the main technologies for preparing
cellulose paper-based electrodes at present. In addition, commercially
mature papermaking process {[}39,40{]}, carbonization {[}41,42{]},
impregnation {[}43,44{]} and laser induced graphene technology
{[}45,46{]} are also used to prepare paper based supercapacitors. In
conclusion, this review is intended to provide convenient reference
materials for researchers in the field of paper-based supercapacitors,
so as to promote the rapid development of paper-based energy storage
devices.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

Figure1. (A) Cellulose and its composites at different levels and
scales.{[}22,23,24,25,60{]} (B) Main preparation methods of cellulose
based paper
electrodes{[}59,60,65,81,85,93,98,103,106,109,110,112,118{]}.

\textbf{2 Various preparation skills}

\textbf{2.1 Vacuum filtration}

According to the reported work on cellulose paper based electrode
materials for supercapacitors, vacuum filtration is the most widely used
and relatively simple method for preparing paper based electrode
materials from cellulose {[}47{]}. The method is to filter the solvent
(mostly water) in the homogenous electrode material slurry by pressure
difference, and then form 2D cellulose paper-based electrode material
through the interaction between materials. In the vacuum filtration
process, the structural design between cellulose and active materials is
the key to determine the energy storage performance of cellulose based
paper based supercapacitors. In the work related to this preparation
process, most of the work is focused on the structural design of
cellulose and carbon materials (activated carbon, graphene, carbon
nanotubes and graphene quantum dots, etc.) {[}48-51{]}, polyaniline
{[}52, 53{]}, MXene {[}54, 55{]} and other electrically active
substances {[}56-58{]}. Then, the electrochemical energy storage
performance is enhanced by introducing the third component active
substance or electropolymerization.

In the application of traditional electrode materials, carbon based
electrode materials are prepared by mixing the binder and conductive
carbon black. When used as a device, the specific surface area of the
active material involved in the electrochemical reaction will be reduced
due to the adhesion of the adhesive on the surface of the active
material, which severely limits the energy storage performance of the
active material. Cellulose, as a good binder, can provide sufficient
specific capacitance and good conductivity after being compounded with
active materials. Cellulose provides excellent mechanical properties and
porous structure. This makes the cellulose paper based supercapacitor
have good mechanical and electrochemical properties.

\textbf{2.1.1 Cellulose/activated carbon paper based composite
electrode}

In the field of supercapacitors, typical activated carbon materials with
double electric layers have been widely used due to their low cost,
extensive sources and mature preparation process. However, when
traditional activated carbon based electrode materials are assembled
into devices, it is inevitable to combine them with inactive binders
(such as polytetrafluoroethylene), conductive substances (such as carbon
black) and collectors (such as foam nickel). The preparation process is
not only complicated, but also the prepared electrode materials lack a
certain flexibility, which limits its application in flexible electronic
devices. To solve this problem, Chen et al. {[}59{]} prepared porous
carbon (PC)/MXene/nano cellulose (CNF) paper based composite electrode
materials through simple vacuum filtration. As shown in Figure 2A, the
preparation process of CNF/PC/Mxene paper-based material is shown. The
paper-based electrode is first prepared by simple mixing and dispersion,
and then by vacuum assisted filtration process. As shown in Fig. 2B, the
author points out that the densified structure formed by vacuum
filtration is the key to the excellent performance of the material. This
provides a strong interface interaction between the oxygen-containing
groups on the surfaces of CNF, PC and MXene, which makes paper based
materials have obvious mechanical advantages. It can be seen from the
microscopic image of the composite (Figure2C) that it is inside the
material. Mxene provides excellent conductivity (83.1S
cm\textsuperscript{-1}), ensuring fast electron transfer. On the other
hand, PC provides excellent double layer capacitors for the composite.
And the PCs are evenly distributed between the network structures built
by MXene and CNF. This also further avoids the stacking effect between
two-dimensional MXene and CNF, which makes the paper based material form
an intercalation structure extremely conducive to the rapid movement of
electrolyte ions, and shortens the diffusion distance of ions. The test
results show that the excellent structure of the paper-based material
gives it excellent electrochemical performance, such as the area
specific capacitance of 143mF cm\textsuperscript{-2} (current density
0.1mA cm\textsuperscript{-2}, thickness 0.2mm) and 2.4\selectlanguage{greek}μ\selectlanguage{english}Wh
cm\textsuperscript{-2} area energy density.

As mentioned above, the adhesive similar to PTFE will coat the surface
of some activated carbon, resulting in insufficient activation of
electrochemical performance. In the cellulose/activated carbon paper
based composite electrode materials prepared by vacuum filtration
similar to the above research work, cellulose molecules are only used as
the adhesive and structural support of an active substance in the
device. In the electrochemical reaction process, it can not provide a
transfer path for electron transfer. Therefore, in paper based electrode
materials, it is particularly important to build cellulose with
excellent electrical conductivity and mechanical properties. Luo et al.
{[}60{]} constructed BC/AB/AC paper based composite electrode materials
by vacuum filtration of bacterial cellulose (BC), acetylene black (AB)
and activated carbon (AC). Figure 2D shows the TEM image of the
paper-based material. It can be seen that due to the existence of a
large number of hydroxyl and carboxyl groups with electronegativity on
the molecular face of BC, the electrically neutral AB particles can be
adsorbed on its surface during the ultrasonic dispersion process, thus
building conductive cellulose on the microstructure. This provides an
excellent path for electron transfer in the electrochemical reaction
process (Figure 2E), which greatly enhances the energy storage
performance of paper based materials. As shown in Figure 2F, the author
also discussed the performance difference between PVDF as the binder and
BC as the binder. It can be seen from the figure that compared with
PVDF, the paper based electrode material constructed by BC has excellent
porous structure and AC has more active sites for electrochemical
reaction. The paper based electrode shows excellent energy storage
performance (the specific capacitance is 275F g\textsuperscript{-1} at
current density of 1A g\textsuperscript{-1}). This work provides a
simple and efficient method for the construction of paper based
electrode materials with excellent mechanical properties by non
carbonization method, and provides an idea for the wide application of
paper based electrode materials.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

Figure2. (A) Preparation process of CNF/PC/Mxene paper-based
supercapacitor. (B) Structural diagram of CNF/PC/Mxene paper-based
electrode. (C) SEM image of CNF/PC/Mxene electrode.{[}59{]} (D) TEM
image of BC/AB/AC electrode. (E) Schematic diagram of electron and ion
migration. (F) Comparison of electrochemical performance of BC based
paper-based electrode and PVDF based binder electrode. {[}60{]}

\textbf{2.1.2 Cellulose/graphene paper based composite electrode}

Graphene is a two-dimensional carbon material with hexagonal honeycomb
lattice structure, which is connected by carbon atoms with
sp\textsuperscript{2} hybridization{[}61{]}. Because of its excellent
conductivity, ultra-high theoretical specific surface area, high
mechanical strength and good thermal conductivity, it has attracted
extensive attention from researchers around the world. At present,
graphene has been widely used in many fields such as energy storage,
sensing, electromagnetic shielding, wave absorption and environment.
However, the van der Waals force and \selectlanguage{greek}π-π \selectlanguage{english}bond force exist between 2D
graphene sheets{[}62{]}. The electrode plates directly prepared from
graphene into supercapacitors will have stacking effect, which will lead
to the reduction of electrochemical reaction sites. And it is not
conducive to the rapid movement of electrolyte ions, which seriously
affects the performance of energy storage devices. Cellulose has a large
number of hydrophilic groups, such as hydroxyl and carboxyl
groups{[}63,64{]}, which can interact with graphene to promote the
dispersion of graphene in the solute and act as a perfect spacer between
2D graphene sheets. He et al.{[}65{]}prepared a self supporting flexible
paper based electrode material with excellent mechanical properties and
energy storage properties by vacuum filtration of CNF and reduced
graphene oxide (RGO). Figure 3A is a schematic diagram of the
preparation process of CNF/RGO paper-based electrical materials. The
influence of different mass ratios of CNF to RGO on the energy storage
performance of paper based electrode materials was discussed. As shown
in Figure 3B, when the ratio between CNF and RGO is 1:2, the composite
material shows an excellent laminated structure. This shows that at this
ratio, the existence of CNF weakens the force between graphene layers to
the greatest extent and limits the accumulation of RGO. And as expected,
the composite also showed the best performance, with a specific
capacitance of 146mF cm\textsuperscript{-2}, tensile strength of 83Mpa
and excellent conductivity (202.94S m\textsuperscript{-1}) at a current
density of 5mA cm\textsuperscript{-2}. Since RGO can only provide
certain energy storage characteristics of double electric layers, the
paper based energy storage materials prepared in this study have room
for improvement. For example, the introduction of the third component
with excellent energy storage performance. On the basis of the former
research, Qiang et al.{[}66{]}prepared CNF/RGO/polypyrrole (PPy) paper
electrode materials with sandwich structure by vacuum filtration. Figure
3C shows the preparation process of the composite. First, CNF/RGO paper
matrix composite was obtained by vacuum filtration. Then immerse it in
Fe(ClO\textsubscript{4}) solution. Finally, the pyrrole monomer was
dispersed on the CNF/RGO surface by spraying and polymerized for 30 min
to obtain the CNF/RGO/PPy paper based electrode. Thanks to the porous
structure of the CNF/RGO layer and the pseudocapacitance characteristics
of PPy, the paper based electrode shows excellent specific capacitance
(195.8F g\textsuperscript{-1}, 915mF cm\textsuperscript{-1}), excellent
energy density (13.04 Wh kg\textsuperscript{-1}) and power density
(200.6 Wkg\textsuperscript{-1}). Figure 3D shows the ion and electron
transfer model inside CNF/RGO/PPy electrode. The author points out that
thanks to the porous structure of CNF/RGO, the paper based electrode
material shortens the diffusion channel of electrolyte ions in the
electrochemical reaction. Moreover, the highly conductive polypyrrole
layers assembled layer by layer provide sufficient pseudo capacitance.
Using CNF/RGO paper-based materials obtained by vacuum filtration as the
substrate, the process of introducing pseudocapacitors through in-situ
polymerization similar to the above work is relatively cumbersome. The
electropolymerization law is a relatively quick method. For example,
Xiong et al.{[}67{]}used CNF/RGO prepared by vacuum filtration as the
substrate to introduce polyaniline into composite paper based materials
by means of electropolymerization (Figure 3E). Figure 3F shows the CV
curve of the composite. It can be clearly seen that due to the
introduction of high pseudo capacitance PANi, the paper based electrode
shows greater energy storage characteristics. From the above two works,
it can be seen that the cellulose/graphene paper based composite
obtained by vacuum filtration can not only be directly used as the
electrode material of supercapacitors, but also be used as an effective
substrate material to introduce other components to prepare cellulose
paper based electrode materials with better performance.

In addition to conducting polymers, metal oxides also exhibit excellent
pseudo capacitive properties, which can show high energy density through
reversible redox reactions. Therefore, introducing metal oxides into
CNF/RGO paper based materials is also a way to improve their
electrochemical performance. For example, Zou et al.{[}68{]}prepared
cellulose/RGO/Ag paper matrix composites with high conductivity through
vacuum filtration. Then, a paper based electrode material with high
conductivity and double electroactive substances was obtained by
depositing Fe2O3 on its surface (Figure 3G). The test results show that
the symmetrical supercapacitor device assembled with this paper based
electrode achieves a large area capacitance (1132mF
cm\textsuperscript{-1}) and energy density (226.4\selectlanguage{greek}μ\selectlanguage{english}Wh
cm\textsuperscript{-2}).Moreover, the device does not need additional
collectors, and it also shows excellent flexibility. Therefore, the
material has broad application prospects in the field of flexible
supercapacitor. In a word, the addition of metal oxides has an obvious
effect on improving the electrochemical performance of paper based
supercapacitors.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

Figure3. (A)CNF/RGO paper-based electrode preparation process. (B)SEM
images of CNF/RGO electrodes.{[}65{]}(C)The CNF/RGO/PPy paper based
electrode with sandwich structure was prepared.(D)CNF/RGO/PPy electrode
diagram. {[}66{]} (E)SEM images of CNF/RGO/PANi electrodes.
(F)Comparison of electrochemical performance before and after loading
PANi. {[}67{]} (G)Cellulose/RGO/Ag paper based supercapacitor picture
and light bulb. {[}68{]}

\textbf{2.1.3 Cellulose/carbon nanotube paper based composite electrode}

Carbon nanotubes (CNTs) have been widely concerned by researchers
because their unique 1D structure endows them with excellent mechanical
strength, electronic conduction efficiency, heat transfer efficiency and
stable chemical properties{[}69{]}. And CNT has a large aspect ratio and
easy surface modification{[}70{]}, which has great advantages for its
application in supercapacitors. Among them, the large aspect ratio makes
it possible to form a good conductive network without using adhesives.
However, CNT and graphene have the same defect, that is, due to the
strong interaction between CNTs, it is a fatal defect for electrode
materials{[}71{]}. Therefore, it is particularly important to find a
material that can disperse CNT evenly. It is a best of both worlds
method to prepare paper based composite materials by mixing with
cellulose materials. For example, Fang et al.{[}72{]}prepared BC/CNT
paper-based electrode materials by vacuum filtration. Figure 4A shows
the preparation process of the paper-based material. It is worth
mentioning that the author used juglone to chemically modify the surface
of CNT, because it is difficult for unmodified CNT to show high energy
density. Some studies have shown that the organic quinones rich in redox
carbonyls have high theoretical capacity, so the chemically modified CNT
surface has a large number of juglone molecules. The test results showed
that the conductivity of the paper matrix composite prepared by juglone
modified CNT was 1674S m\textsuperscript{-1} (the conductivity of the
unmodified composite was 1111S m\textsuperscript{-1}). At the same time,
the influence of the content of juglone molecules on the conductivity of
paper matrix composites was also discussed. As shown in Figure 4B, when
the content of juglone molecules is low, electrons can only have
discrete jumps between the molecules. When the content is high, due to
the crowding between molecules, electrons jump randomly in disorder
during conduction. Therefore, when juglone molecules are uniformly
distributed on the surface of CNT, the conductivity and energy storage
performance of the composite are greatly improved thanks to the
coordination between the uniformly arranged quinone molecules and CNT.
The electrochemical test results of the paper based electrode showed
that the modified BC/CNT paper based electrode showed a specific
capacitance of 461.8F g\textsuperscript{-1} at 0.5 A
g\textsuperscript{-1} (this value was five times that of the non
chemically modified electrode). The paper based electrode materials
prepared in this work have better performance than most reported CNT and
paper based electrode materials prepared by vacuum filtration. In
conclusion, this work provides an excellent strategy for preparing
high-performance paper based electrode materials by vacuum filtration.

As shown in Figure 4C, Jyothibasu et al. {[}73{]} first treated the CNT
surface with nitric acid to obtain CNT (f-CNT) loaded with a large
number of hydroxyl groups. The prepared cellulose is then uniformly
dispersed with the cellulose and then subjected to vacuum filtration.
Finally, the cellulose/f-CNT paper based film was obtained after drying.
In order to enhance its electrochemical performance, the author soaked
the paper based film in the mixed solution of potassium permanganate and
sulfuric acid to load manganese dioxide. The test results showed that
after 120 min of loading reaction, the solid paper based device
assembled by cellulose/CNT/MnO\textsubscript{2} paper based electrode
showed an excellent specific capacitance of 1812mF
cm\textsuperscript{-2}. This work shows that the cellulose/CNT paper
based material obtained by vacuum filtration is also a good conductive
substrate, and its electrochemical performance can be improved by
introducing the third component. This provides a perfect solution for
customizing high-performance flexible paper based supercapacitors.

\textbf{2.1.4 Cellulose/graphene quantum dot paper based composite
electrode}

Graphene quantum dots refer to a quasi zero dimensional material with
graphene sheet size less than 100 nm and sheet size less than
10{[}74{]}. Since its discovery in 2008{[}75{]}, GQD has attracted
extensive attention due to its excellent optical and electrical
properties. And it has been applied to energy storage, sensing,
catalysis, environment and other fields. Among them, GQD has ultra-fine
size and ultra-high specific surface area because its dimensions in the
three dimensions are at the nanometer level{[}76{]}. These superior
properties make it a new rising star of electrode materials for
supercapacitors. The composite of GQD and cellulose can overcome the
shortcomings of limited specific surface area, poor conductivity and low
utilization rate of cellulose. For example, Xiong et al.{[}77{]}obtained
CNF/GQD paper-based composites by vacuum filtration for the first time.
First, GQD was prepared by electrolysis and dialysis purification with a
stone mill (Figure 4D). Then, CNF/GQD paper-based electrode is obtained
by mixing GQD and CNF uniformly and vacuum filtering (Figure 4E). Figure
4F shows SEM and TEM images of CNF/GQD. It can be seen from the figure
that GQD is evenly distributed on the CNF surface. Moreover, CNF
crosslinked with each other to form a porous structure. This provides a
fast transport path for electrolyte ions in the electrochemical energy
storage process. The test results show that the paper based material can
maintain an area capacitance of 118mF cm\textsuperscript{-2} even at a
high scanning rate of 1000mV s\textsuperscript{-1}, indicating that it
has excellent magnification performance. This is mainly due to the
excellent energy storage characteristics of GQD itself and the porous
structure of CNF providing sufficient load sites for GQD.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

Figure4. (A)Preparation process of BC/CNT paper-based electrode modified
by juglone. (B)The mechanism of electrical transfer of juglone auxiliary
electrons on CNT. {[}72{]} (C)Flow chart of cellulose/f-CNT paper-based
electrode and loaded MnO\textsubscript{2}.{[}73{]} (D)GQD preparation
process. (E)CNF/GQD paper based electrode preparation process. (F)TEM
image of CNF/GQD. {[}77{]}

\textbf{2.1.5 Cellulose/MXene paper based composite electrode}

As a 2D material with high specific surface area and high conductivity,
MXene has shown great prospects in the field of supercapacitor energy
storage{[}78{]}. In recent years, the composite paper based electrode
materials prepared by vacuum filtration of cellulose and Mxene have been
fully studied. This section summarizes cellulose/MXene paper based
electrode materials. When 2DMxene chips are used as supercapacitors and
electrode materials of supercapacitors, stacking between layers is easy
to occur. In order to solve this problem, scientists also tried to use
1D carbon nanotubes and other carbon materials as spacers to prevent
their stacking. However, the preparation process of these carbon
materials is complex and costly. Cellulose, as a green and sustainable
renewable resource, is the first choice as a 2D active material spacer.
For example, Jiao et al. {[}79{]} first prepared BC/MXene composite
paper with excellent new mechanical properties and electrochemical
properties through vacuum pumping power. In addition, stretchable and
patterned paper based electrode materials are prepared by laser cutting
process to adapt to various use environments (Figure5A). Thanks to the
close stacking structure between BC fiber and Mxene lamellae (Figure5B).
The prepared paper based electrode was assembled into an all solid state
paper based supercapacitor, showing an area capacitance of 115mF
cm\textsuperscript{-2} and flexible mechanical properties. This work
provides a promising method for designing and manufacturing flexible
electronic equipment used in different environments through the
patterned scheme of laser cutting. Similarly, Tian et al. {[}80{]}
prepared CNF/Mexene paper-based electrodes by vacuum filtration, which
also showed excellent electrochemical performance (298F
g\textsuperscript{-1}). The above two works show that the
cellulose/MXene paper-based electrode prepared by simple vacuum
filtration process has a very broad application prospect.

Although the paper based electrode obtained by direct filtration of
cellulose and Mxene has good performance, it can not meet people's needs
under certain conditions. Therefore, it is very necessary to improve the
energy storage performance of paper-based materials through certain
methods. For example, the introduction of the third component or the
surface modification of MXene can improve its energy storage
performance. In order to improve the electron transfer rate of MXene in
paper based materials, as shown in Figure 5C, it is inspired by the
structure of plant leaves. Tang et al. {[}81{]} prepared a paper based
composite material with leaf like structure by vacuum filtration of
cellulose, Mxene and silver nanowires (AgNWs). As shown in Figure5D, the
structure diagram of natural leaf veins and prepared
cellulose/Mxene/AgNWs paper based electrode (PMxAg) is similar to leaf
veins. Among them, cellulose as the main pulse provides excellent
mechanical properties for paper based materials and provides a transport
channel for electrolyte ions. Secondly, AgNWs as the secondary pulse
provides a fast channel for electron transfer. Finally, as the
''mesophyll'', Mxene provides sufficient energy storage capacity for
composite materials. Thanks to the ''blade like structure'', the paper
based electrode shows a specific capacitance of up to 505F g-1. In
addition, the author also successfully prepared large area composite
paper by using paper machine. The batch preparation of this flexible
supercapacitor provides a solution. In addition, surface treatment of
MXene is also an effective method to improve the electrochemical
performance. Previous research shows that the energy storage performance
of MXene mainly comes from the=O group, while the -F and -OH groups in
it have no contribution to the energy storage performance, and even more
content will affect the energy storage performance. For this method,
Chen et al. {[}82{]} modified the surface of MXene by KOH and high
temperature treatment to reduce the -F and -OH groups on its surface.
Subsequently, NFC/Mxene paper based composite electrode was prepared by
combining nano fibrillar cellulose (NFC) prepared from soybean straw
with modified Mxene through vacuum filtration process. The preparation
process is shown in Figure 5E. The test results show that the paper
electrode based supercapacitor has a specific capacitance of 303.1F
g\textsuperscript{-1} at 1mA cm\textsuperscript{-2} and a capacitance
retention of 92.84\% after 10000 cycles. As shown in Figure 5F, Cai et
al. {[}83{]} prepared SnS2 on the surface of MXene by hydrothermal
method Mxene@SnS\textsubscript{2} Nanosheets, then CNF was prepared by
vacuum filtration/ Mxene@SnS2 Paper based composite materials. To
illustrate Mxene@SnS\textsubscript{2} The contribution of nano sheets to
the electrochemical performance of composite materials is shown in
Figure5G. The author compares CNF/MXene,
CNF/MXene/SnS\textsubscript{2}and CNF/ Mxene@SnS\textsubscript{2} Energy
storage performance among the three. CNF/ Mxene@SnS\textsubscript{2} The
specific capacitance of 171.6F g-1 is significantly higher than that of
CNF/Mxene (163.3F g-1) and CNF/Mxene/SnS\textsubscript{2} (130F g-1). At
the same time, because of the light heat conversion function of
SnS\textsubscript{2}, the assembled supercapacitor has the function of
solar energy driving. As shown in Figure 5H, the discharge time of the
paper-based supercapacitor increases with the increase of light
intensity (under the light intensity of 1kW m-2, the energy storage
performance of the device is improved by 60\%).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

Figure5 (A) BC-Mxene composite paper and laser cutting patterning
scheme. (B) SEM image of BC/MXene composite paper section. {[}79{]} (C)
PmxAg preparation process. (D) The design diagram of the micro network
structure in the blade and the paper material with similar structure ion
channels.{[}81{]} (E) NFC/MXene paper based electrode preparation
process.{[}82{]} (F) CNF/ Mxene@SnS\textsubscript{2} Paper based
electrode preparation process. (G) CNF/MXene,
CNF/MXene/SnS\textsubscript{2} and CNF/ MXene@SnS\textsubscript{2} GCD
curve at current density of 1A g\textsuperscript{-1}. (H) CNF at
different solar intensities/ MXene@SnS\textsubscript{2} GCD curve of
paper-based devices. {[}83{]}

\textbf{2.1.6 Cellulose/PANi paper based composite electrode}

Polyaniline is a kind of conductive polymer material with excellent
pseudo capacitance energy storage performance. However, when it is used
as electrode material of supercapacitor, serious volume shrinkage and
expansion will occur, resulting in obvious brittleness of pure
polyaniline electrode material. As a 1D material with excellent
mechanical properties, cellulose and polyaniline can compensate for the
brittleness of polyaniline, and polyaniline provides excellent
conductivity and energy storage properties. Sun et al. {[}84{]} first
introduced RGO into polyaniline polymerization to obtain PANi/RGO
composites. Then the cellulose/PANi/RGO paper based composite electrode
material was prepared by vacuum filtration of cellulose and the
composite material. Among them, the energy storage performance of the
paper-based electrode was significantly improved due to the addition of
RGO (the specific capacitance was 79.71F g\textsuperscript{-1}).
Although the specific capacitance value of the electrode is not as good
as that of the paper-based electrical base. However, as an excellent
pseudo capacitive electrode material, conducting polymers should be
tried to construct structures conducive to improving electrochemical
performance through vacuum filtration in future research. Cellulose and
other conductive polymer materials are used to prepare
cellulose/conductive polymer paper based electrode with more excellent
performance through vacuum filtration.

Based on the above discussion on the preparation of paper based
electrode materials by vacuum filtration. Due to the simple preparation,
strong controllability and similar to papermaking process, scientists
have also prepared a variety of paper-based electrical materials through
this process. Table 1 compares the main parameters of paper based
electrodes prepared by vacuum filtration. It is obvious from the
classification in the table that the process is still mainly focused on
the composite between cellulose and carbon materials and MXene, and
there is still a lack of research on the relationship between cellulose
and conductive polymers and metal oxides. For example, cellulose and
nanowire metal oxides (such as MnO\textsubscript{2}) can also be used to
prepare paper based electrode materials with excellent performance.
Therefore, in future research on preparation of the paper based
supercapacitor electrode materials by vacuum filtration. We can actively
broaden our vision and combine more electrochemical active substances
with cellulose through this simple preparation process to prepare
cellulose paper based electrode materials with excellent performance. At
the same time, in the era of rapid development of flexible electronics,
we should also pay attention to the use of this process to achieve mass
production. Among them, mature papermaking process should be the first
choice. For example, Tang et al. {[}81{]}realized the batch production
through the laboratory vacuum filtration results through the
manufacturing process, which provides a mature guidance scheme for the
production of cellulose paper based supercapacitors. In the 2.4.1
section, we will summarize the application of papermaking technology in
cellulose paper based supercapacitors in detail.

Table1 Performance Parameters of Cellulose Paper Based Electrode Blended
with Multi component Based on Vacuum Filtration\selectlanguage{english}
\begin{longtable}[]{@{}llllll@{}}
\toprule
\begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
Electrode\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
Electrolyte\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
Capacity\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
Energy density at power density\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
Cycles\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
Reference\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
CNF/PC/Mxene\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
KOH/PVA\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
143mF cm\textsuperscript{-2} at 0.1mA cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.4\selectlanguage{greek}μ\selectlanguage{english}Wh cm\textsuperscript{-2} at 17.5\selectlanguage{greek}μ\selectlanguage{english}W cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
90\%, 10000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
59\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
BC/AB/AC\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
6.0M KOH\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
276F g\textsuperscript{-1} at 1A g\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
5.3W h kg\textsuperscript{-1} at 163W kg\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
100\%, 10000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
60\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
CNF/RGO\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.1M H\textsubscript{2}SO\textsubscript{4}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
146mF cm\textsuperscript{-2} at 5mA cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
83.7\%, 2000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
65\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
CNF/RGO/ PPy\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1M H\textsubscript{2}SO\textsubscript{4}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
195.8 F g\textsuperscript{-1} at 0.1mA cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
13.04Wh kg\textsuperscript{-1} at 200.6W kg\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
96.6\%, 2000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
66\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
CNF/RGO/PANi\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
H\textsubscript{3}PO\textsubscript{4}/PVA\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
67\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
cellulose/RGO/ silver/Fe\textsubscript{2}O\textsubscript{3}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
LiCl/PVA\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
1132mF cm\textsuperscript{-1} at 2 mA cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
226.4\selectlanguage{greek}μ\selectlanguage{english}Wh cm\textsuperscript{-2} at 1.2mW cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
100\%, 10000\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
68\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
BC/CNT\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1M H\textsubscript{2}SO\textsubscript{4}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
461.8F g\textsuperscript{-1} at 0.5 A g\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
41.9 Wh kg\textsuperscript{-1} at 1.0 kW kg\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
82.4\%, 10000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
72\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
cellulose/f-CNT/MnO\textsubscript{2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1M Na\textsubscript{2}SO\textsubscript{4}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1812 mF cm\textsuperscript{-2} at 1 mA cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
251.6\selectlanguage{greek}μ\selectlanguage{english}Whcm\textsuperscript{-2} at 0.51mW cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
79\%, 10000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
73\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
CNF/GQD\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1.5M Li\textsubscript{2}SO\textsubscript{4}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
118mF cm\textsuperscript{-2} at 1000mV s\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
596\selectlanguage{greek}μ\selectlanguage{english}Wh cm\textsuperscript{-2}and 782mW cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
90\%, 5000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
77\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
BC/Mxene\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
H\textsubscript{2}SO\textsubscript{4}/PVA\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
115mF cm\textsuperscript{-2} at 1 mA cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.00419mWh cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
79\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
CNF/Mxene\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
3M H\textsubscript{2}SO\textsubscript{4}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
298F g\textsuperscript{-1} at 5mV s\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.08\selectlanguage{greek}µ \selectlanguage{english}Wh cm\textsuperscript{-2} at 145\selectlanguage{greek}µ\selectlanguage{english}W cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
100\%, 10000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
80\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
cellulose/Mxene/ AgNWs\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1M H\textsubscript{2}SO\textsubscript{4}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
505F g\textsuperscript{-1} at 5A g\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
90.9\%, 500\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
81\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
NFC/Mxene\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1M H\textsubscript{2}SO\textsubscript{4}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
303.1F g\textsuperscript{-1} at 1mA cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
92.84, 10000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
82\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
CNF/Mxene@SnS\textsubscript{2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1M H\textsubscript{2}SO\textsubscript{4}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
171.6F g\textsuperscript{-1} at 10mV s\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
6.7\selectlanguage{greek}μ\selectlanguage{english}Wh cm\textsuperscript{-2} at 1206\selectlanguage{greek}μ\selectlanguage{english}W cm\textsuperscript{-2}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
91.5\%, 40000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
83\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
cellulose/PANi/RGO\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1M H\textsubscript{2}SO\textsubscript{4}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
79.71F g\textsuperscript{-1} at 0.1 A g\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
4.03Wh kg\textsuperscript{-1} at 10.40W kg\textsuperscript{-1}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
84.8\%, 1000\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
84\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

\textbf{2.2 In-situ polymerization}

Cellulose, as a natural 1D flexible material with high specific surface
area, is only used as a binder of electrochemical active substances,
which does not make full use of its surface space. Electroactive
substances such as metals, metal oxides and conductive polymers are
polymerized and deposited on the cellulose surface through in-situ
polymerization. Compared with the paper-based electrode where cellulose
is only used as the binder, this can effectively reduce the volume of
electrode material and increase the utilization rate of cellulose. In
the cellulose paper based electrode prepared by this method, cellulose
not only provides mechanical properties, but also provides an electron
transfer path for the cellulose composite fiber deposited with active
substances, which can make outstanding contributions to electrochemical
energy storage.

At present, the work of depositing active materials on cellulose surface
can be roughly divided into two types. The first is by mixing the
cellulose dispersion with the precursor of the active substance. Then
the active substance is polymerized and deposited on the surface of the
cellulose fiber to form 1D cellulose composite fiber. Finally, these 1D
composite fibers were filtered through vacuum to obtain paper based
electrodes. It should be clearly pointed out here that cellulose in the
paper-based electrode summarized in the vacuum filtration section of
this paper is only used as the binder. However, the paper based
electrode obtained by in-situ polymerization of active substances
polymerized and deposited on the cellulose surface, and then filtered by
vacuum suction, is significantly different from the previous section.
Therefore, it is necessary to classify 1D cellulose composite fibers
into a single category. The second type is to directly put the prepared
2D cellulose paper into the precursor solution of the active substance,
and directly polymerize and deposit the active substance on the 2D
cellulose paper. This section summarizes and classifies the different
loading modes of active substances in the preparation process, including
the paper based electrode based on 1D cellulose composite fiber and the
paper based composite electrode based on 2D cellulose paper. Table 2
summarizes the performance parameters of related work.

Table2 Performance parameters of cellulose paper based electrode
prepared by in-situ polymerization\selectlanguage{english}
\begin{longtable}[]{@{}llllll@{}}
\toprule
Electrode & Electrolyte & Capacity & Energy density at power density &
Cycles & Reference\tabularnewline
\midrule
\endhead
CNF@c-MOF & 3M KCl & 125F g\textsuperscript{-1} at 0.33A
g\textsuperscript{-1} & - & 99\%, 10000 & 85\tabularnewline
CuS-NCs/QCD /CNF & 6M KOH & 314.3F g\textsuperscript{-1} at 1A
g\textsuperscript{-1} & - & 88.8\%, 5000 & 86\tabularnewline
1D-CNF@ZnO & KOH/PVA & 220F g\textsuperscript{-1} at 1A
g\textsuperscript{-1} & 30.2W h kg\textsuperscript{-1} at 1kW
kg\textsuperscript{-1} & 88\%, 8000 & 87\tabularnewline
PPy@BC/Mxene & 3M H\textsubscript{2}SO\textsubscript{4} & 879mF
cm\textsuperscript{-2} at 5mV s\textsuperscript{-1} & 33.1W h
kg\textsuperscript{-1} at 243W kg\textsuperscript{-1} & 83.5\%, 10000 &
88\tabularnewline
PPy@cobalt oxyhydroxide/cellulose & 0.6M
H\textsubscript{2}SO\textsubscript{4} & 571.3F g\textsuperscript{-1} at
0.2A g\textsuperscript{-1} & - & 93.02\%,10000 & 89\tabularnewline
PEDOT-ARS paper & ARS/H\textsubscript{2}SO\textsubscript{4} & 2191.3mF
cm\textsuperscript{-2} at 5 mA cm\textsuperscript{-2} & 4.87 mWh
cm\textsuperscript{-3} at 36 mW cm\textsuperscript{-3} & 82.21\%, 1000 &
90\tabularnewline
PPy:PSS/CNP & 1M H\textsubscript{2}SO\textsubscript{4} & 3.8F
cm\textsuperscript{-2} at 10mV s\textsuperscript{-1} & 122\selectlanguage{greek}μ\selectlanguage{english}W h
cm\textsuperscript{-2} at 4.4mW cm\textsuperscript{-2} & 80.9\%,5000 &
91\tabularnewline
PANI: PSS/CNP & 1M H\textsubscript{2}SO\textsubscript{4} & 2.56F
cm\textsuperscript{-2} at 2m A cm\textsuperscript{-2} & 40.9\selectlanguage{greek}μ \selectlanguage{english}Wh
cm\textsuperscript{-2} and 100.5\selectlanguage{greek}μ \selectlanguage{english}W cm\textsuperscript{-2} & 81.5\%,5000
& 92\tabularnewline
PEDOT:PSS/CNP & 1M H\textsubscript{2}SO\textsubscript{4} & 854.4mF
cm\textsuperscript{-2} at 5mV s\textsuperscript{-1} & 30.86\selectlanguage{greek}μ \selectlanguage{english}Wh
cm\textsuperscript{-2} at 28.27mW cm\textsuperscript{-2} & 95.8\%, 10000
& 93\tabularnewline
CP/Ni/Au & 1M Na\textsubscript{2}SO\textsubscript{4} & 49.1F
g\textsuperscript{-1} at1A g\textsuperscript{-1} & - & 92.1\%, 10000 &
94\tabularnewline
Ni-paper-MnO2 & 1M Na\textsubscript{2}SO\textsubscript{4} & 1095mF
cm\textsuperscript{-2} at 1mA cm\textsuperscript{-2} & - & 73\%, 2000 &
95\tabularnewline
MnO2-Au-Paper & 1M Na\textsubscript{2}SO\textsubscript{4} & 560.2mF
cm\textsuperscript{-2} at 0.2mA cm\textsuperscript{-2} & 28.74mWh
cm\textsuperscript{-2} and 1.597mW cm\textsuperscript{-2} & 96.1\%, 5000
& 96\tabularnewline
MnO2-Au-Paper(Vertically Layered Multi-Pair Interdigital Electrodes) &
1M Na\textsubscript{2}SO\textsubscript{4} & 0.974F
cm\textsuperscript{-2} at 0.1mA cm\textsuperscript{-2} & 86.58\selectlanguage{greek}μ \selectlanguage{english}Wh
cm\textsuperscript{-2} and 0.8mW cm\textsuperscript{-2} & 98\%, 6000 &
97\tabularnewline
MnO\textsubscript{2}-Au-Paper(Vertically integrated multi electrodes in
a single sheet of paper) & Na\textsubscript{2}SO\textsubscript{4}/PVA &
315.96F g\textsuperscript{-1} at 5mV s\textsuperscript{-1} & 13.73\selectlanguage{greek}µ\selectlanguage{english}W h
cm\textsuperscript{-2} and 1.6\selectlanguage{greek}µ\selectlanguage{english}W cm\textsuperscript{-2} & 84\%, 6000 &
98\tabularnewline
PEDOT/CP & H\textsubscript{2}SO\textsubscript{4}/PVA & 13.7F
cm\textsuperscript{-3} at 10mV s\textsuperscript{-1} & 0.76mWh
cm\textsuperscript{-3} at 0.01W cm\textsuperscript{-3} & 77\%, 1000 &
99\tabularnewline
PC-KHP & H\textsubscript{2}SO\textsubscript{4}/PVA & 6576mF
cm\textsuperscript{-3} at 25 mV s\textsuperscript{-1} & - & 84\%, 10000
& 100\tabularnewline
PPy/Cellulose Paper & H\textsubscript{2}SO\textsubscript{4}/PVA & 90.1mF
cm\textsuperscript{-2} at 0.25mA cm\textsuperscript{-2} & - & 86.7\%,
2000 & 101\tabularnewline
Paper/PPy/rGO & 1M HCl & 1685mF cm\textsuperscript{-2} at 2mA
cm\textsuperscript{-2} & 147\selectlanguage{greek}μ\selectlanguage{english}Wh cm\textsuperscript{-2} at 0.63mW
cm\textsuperscript{-2} & 92.8\%, 5000 & 102\tabularnewline
ACF/PPS/MWCNT-PPy & 3M HCl & 3205mF cm\textsuperscript{-2} at 5mA
cm\textsuperscript{-2} & - & 93\%, 5000 & 103\tabularnewline
\bottomrule
\end{longtable}

\textbf{2.2.1 Paper based electrode based on 1D cellulose composite
fiber}

\textbf{2.2.1.1 Cellulose/metal paper based composite electrode}

Metals and their compounds are considered as promising electrode
materials for supercapacitors because of their excellent point and
storage application prospects. Due to the large number of modifiable
hydroxyl groups in cellulose molecules, it provides a good platform for
the construction of polymerization and deposition of metals and their
metal compounds. Recent studies have shown that metals and their
compounds can be well combined with cellulose fibers or polymerized and
deposited on their surfaces to form 1D cellulose composite fibers with
excellent energy storage properties. Finally, paper based composite
electrode materials can be obtained by vacuum filtration. Zhou et al.
{[}85{]} used CNF as a substrate and deposited a conductive
metal-organic framework(c-MOF) with excellent electrical conductivity
through interfacial polymerization on its surface, and obtained
CNF@c-MOF nanofibers. Figure 6A shows the preparation process of
CNF@c-MOF, first introducing carboxyl groups to the surface of CNF
through TEMPO oxidation, then exchanging carboxylated CNF with
Ni\textsuperscript{2+} ions, and finally adding organic ligands to
obtain CNF@c-MOF nanofibers. CNF@c-MOF paper-based electrodes are
obtained by vacuum filtration. In addition, the authors discuss the
differences in the electrochemical performance of CNF@c-MOF paper-based
electrodes prepared by two different organic ligands, HITP
(2,3,6,7,10,11-hexaiminotriphenylene) and HHTP
(2,3,6,7,10,11-hexahydroxytriphenylene). Figure 6B shows a comparison of
the weight ratio capacitance of two different CNF@c-MOF paper-based
electrodes. It is evident that the CNF@Ni-HITP electrode prepared by
HITP has a weight capacitance of 125F g\textsuperscript{-1}. This is
mainly due to the continuous Ni-HITP nanolayers tightly wrapped around
the CNFs (Figure 6C). The authors note that the continuous nucleation of
c-MOF nanometers on CNF and the hierarchical porous high conductivity
structure provide a fast pathway for electrolyte transport and charge
transfer for CNF@c-MOF paper-based electrodes (Figure 6D). It is worth
mentioning that the authors also discuss the performance of CNF@c-MOF
paper-based electrodes of different thicknesses, and the results show
that the increase in thickness has almost no effect on the
electrochemical performance of the paper-based electrode. This opens up
the possibility of customizing paper-based electrodes of different
thicknesses.

Huang et al.{[}86{]}used quaternized chitosan (QCS) as the connection
stabilizer between CNF and copper sulfate nanocrystals (CuS-NCs). Figure
6E shows the contribution of QCS to CuS NCs deposition on CNF fiber
surface. In the absence of QCS, the deposition of CuS is mainly through
the electrostatic adsorption between the electronegative CNF and
{[}Cu(NH\textsubscript{3})\textsubscript{4}{]}\textsuperscript{2+}in the
precursor solution of CuS-NCs. At the same time,
S\textsuperscript{2-}will lead to rapid prototyping of CuS NCs, which
will lead to uneven distribution of CuS NCs on the CNF surface (Fig.
6F). When S\textsuperscript{2-} and QCS are added to the CNF/{[}Cu
(NH\textsubscript{3})\textsubscript{4}{]}\textsuperscript{2+}precursor
solution, CuS NCs are well anchored on the CNF surface (Fig. 6G) due to
the electrostatic attraction formed between the positively charged QCS
and CNF. In order to more intuitively check the contribution of QCS to
the stable deposition of CuS NCs on the CNF surface, as shown in Figure
6H, CuS-NCs/CNF and CuS-NCs/QCD/CNF were respectively immersed in KOH
electrolyte for 48h. It can be clearly observed from the figure that the
paper-based electronic base shows excellent stability due to the
addition of QCD. However, CuS NCs in the paper-based electrode without
QCD fell off obviously. The test results showed that CuS-NCs/QCD/CNF
paper based electrode exhibited 314.3F g-1 high specific capacitance and
high cycle stability (the capacitance retention rate was 88.8\% after
5000 cycles). Rabani et al. {[}87{]} used the sol-gel method to deposit
zinc oxide (ZnO) in 1D-CNF to obtain 1D-CNF@ZnO nanometer composite
fibers, and then further assembled the 1D-CNF@ZnO into an
all-solid-state flexible paper-based supercapacitor. As shown in Figure
6I, ZnO nanoparticles perfectly cover the 1D-CNF surface at suitable
concentrations of ZnO precursors, which is essential for their
application to energy storage electrodes. In order to better illustrate
the excellent electrochemical performance of this paper-based electrode.
As shown in Figure 6J, the authors compared 1D-CNF, ZnO, and 1D-CNF@ZnO
paper-based electrodes. It is clear from the figure that the 1D-CNF@ZnO
electrode has a larger CV area and energy storage characteristics for
discharge time.

Based on the above summary of the work related to metal compounds
deposited on 1D cellulose, we can see that the current work is mainly
focused on non-metallic oxide pseudocapacitor materials. This may be due
to the non conductivity of metal oxides. As an excellent pseudo
capacitor material, metal oxides can be used to prepare cellulose/metal
oxide composite fibers through the above process in future research.
Then, the paper based electrode material with excellent performance is
prepared by compounding with the electroactive material with excellent
conductivity.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

Figure6. (A) Preparation process of CNF@c-MOF nanocomposite fibers. (B)
Weight capacitance of CNF@c-MOF electrode. (C) TEM image of CNF@Ni-HITP
nanocomposite fibers. (D) Schematic diagram of charge transfer and
electrolyte ion transport in a CNF@c-MOF paper-based electrode.{[}85{]}
(E) Schematic diagram of CuS-NCs precipitating QCS as stabilizers and
binders in situ on CNF. (F) SEM image of CuS-NCs/CNF. (G) SEM image of
CuS-NCs/QCD/CNF. (H) CuS-NCs/QCD/CNF paper-based electrode stability
test.{[}86{]} (I) SEM image of 1D-CNF@ZnO nanocomposite fibers. (J)
Electrochemical performance of CNF@ZnO electrodes. {[}87{]}

\textbf{2.2.1.2 Cellulose/conductive polymer paper based composite
electrode}

1D composite fiber prepared by composite of conductive polymer and 1D
cellulose has been reported so far. Electrodes depositing polyaniline
(PANi), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT)
on the surface of 1D cellulose by in-situ polymerization have been
prepared. However, due to the low solubility and unstable structure of
conductive polymers in solvents, the energy storage performance of
electrodes directly compounded with cellulose is not excellent. At
present, scientists prepare paper based electrodes with excellent
electrochemical performance by adding surfactants or blending 1D
cellulose composite fibers based on conductive polymers with other
pseudo capacitive materials. As shown in Figure 7A, Song et al. {[}88{]}
used the in-situ polymerization method to uniformly deposit PPy on the
surface of BC fiber to obtain 1DPPy@BC composite fiber, and then
prepared PPy@BC/Mxene composite paper-based electrode by vacuum
filtration of the dispersion of PPy@BC and Mxene. Firstly, 1DBC fibers
as effective templates provide abundant space for the deposition of Ppy.
Secondly, the hierarchical porous structure formed by the assembly of
PPy@BC fibers and Mxene provides sufficient sites for electrochemical
reactions. This is very important for the electrochemical performance of
this paper-based electrode. Thanks to the above two points, the
PPy@BC/Mxene composite paper-based electrode exhibits a mass ratio
capacitance of 550F g\textsuperscript{-1} and an area ratio capacitance
of 879mF cm\textsuperscript{-2.} The work is to prepare high-performance
paper-based electrodes by blending 1D composite fibers with Mxene.
Although satisfactory electrochemical performance can be obtained by
this method, the thickness of the electrode will always be increased by
blending the two components, which is detrimental to flexible
microelectronic devices. It is a feasible method to introduce the second
component directly into the 1D composite fiber by in-situ
polymerization. Yang et al. {[}89{]} prepared 1DPPy@ cobalt
hydroxyoxide/cellulose composite fiber (1DPCC fiber) by liquid phase
reduction. Figure 7B shows the preparation process of this paper-based
electrode. First, cobalt hydroxyoxide is reduced to
CoCl\textsubscript{2}\selectlanguage{ngerman}·6H\textsubscript{2}O by NaBH\textsubscript{4} and
cobalt hydroxyoxide is loaded on the surface of 1D cellulose in situ.
1DPCC fibers are then obtained by in situ oxidative polymerization of
PPy. Finally, PCC paper-based composite electrode was obtained by vacuum
filtration. Electrochemical test results show that PCC paper-based
electrodes have a specific capacitance of up to 571.3F
g\textsuperscript{-1} and a capacitance retention rate of more than 93\%
(1000 cycles). In this work, 1D cellulose composite fibers with
excellent performance were prepared by two-step in-situ polymerization.
The paper-based electrode also exhibited excellent energy storage
characteristics, which provided a simple and fast method for preparing
paper-based composite flexible energy storage electrode.

Recent studies have found that the use of redox small molecules to treat
paper-based composite electrodes can also improve electrochemical energy
storage performance. Small organic molecules with specific
intramolecular conjugated structures, such as quinones, can be a
substance that enhances the electrochemical performance of composite
materials with an ideal valence. As shown in Figure 7C, Chang et al.
{[}90{]} effectively improved the energy storage performance of PEDOT
paper-based electrode by sodium alizarin sulfonate (sodium
1,2-dihydroxyanthraquinone-3-sulfonate) (ARS).
ARS/H\textsubscript{2}SO\textsubscript{4} composite electrolyte was
prepared. The results show that the supercapacitor device assembled by
ARS-treated electrode and electrolyte shows excellent electrochemical
performance (area ratio capacitance 2191.3mF cm\textsuperscript{-2},
energy density 4.87mWh cm\textsuperscript{-3}). This is a significant
improvement over the 348 mF cm\textsuperscript{-2} area ratio
capacitance of a paper-based electrode without ARS treatment. Figure 7D
shows the energy storage mechanism in the charging and discharging
process of the device. Among them, the addition of ARS promotes the
regeneration of PEDOT and reuses in redox reaction, which plays an
important role in improving the electrochemical performance of the
device. The water-soluble sulfonated polymer surfactant polystyrene
sulfonate (PSS) has attracted extensive attention from researchers due
to its excellent mechanical flexibility and adjustable conductivity. In
this paper, three recent works on the improvement of conductive polymer
1D cellulose composite fibers using PSS are summarized. As shown in
Figure 7E, Zhang et al. {[}91{]} added PSS to a mixed solution of
pyrrole monomer and CNF, and improved the loading of polypyrrole on the
surface of CNF through PSS. The results show that the paper-based
electrode PPy:PSS/CNP with PSS exhibits a specific capacitance of 240F
g\textsuperscript{-1}. Similarly, Zhang et al. {[}92,93{]} also used PSS
to improve the loading of PANi as well as PEDOT on the CNF surface.
Figure 7F and 7G are schematic diagrams of the preparation process of
PANi: PSS/CNP and PEDOT:PSS/CNP paper-based electrodes. It is worth
mentioning that the addition of PSS in these three works effectively
improves the cellulose loading of conductive polymers and promotes the
construction of high-performance paper-based electrodes. It provides a
good idea for the preparation of conductive polymer-based paper-based
composite electrodes.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image7/image7}

\end{center}
\end{figure}

Figure7. (A) PPy@BC/Mxene paper-based electrode preparation process.
{[}88{]} (B) Preparation process of PPy@cobalt hydroxyoxide/cellulose
composite flexible electrode materials. {[}89{]} (C) Preparation process
of ARS modified PEDOT paper-based electrode. (D) Schematic diagram of
the electrochemical energy storage mechanism of ARS modified PEDOT
paper-based electrode in a three-electrode system. {[}90{]}
(E)PPy:PSS/CNP paper-based electrode preparation process. {[}91{]} (F)
PANi:PSS/CNP paper-based electrode preparation process. {[}92{]} (G)
PEDOT:PSS/CNP paper-based electrode preparation process. {[}93{]}

\textbf{2.2.2 Paper-based composite electrode based on 2D cellulose
paper}

\textbf{2.2.2.1 Cellulose/metal paper-based composite electrodes}

Due to its excellent porous structure, low cost, easy degradation and
renewable, 2D cellulose paper is considered to be an ideal flexible
substrate in the field of flexible supercapacitors. Zhang et al.
{[}94{]} prepared cellulose paper (CP)/Ni/Au paper-based electrodes by
loading nickel/gold bimetals on vitamin paper. Figure 8A shows the
preparation process of this paper-based electrode. Thanks to the
hydrophilic group and porous structure of CP, CP immersion in nickel
salt solution can adsorb a large number of nickel ions. The metal Ni is
then loaded in CP by NaBH4 reduction. Then, CP loaded with nickel metal
is entered into the electroless plating solution of Au to obtain
CP/Ni/Au paper-based current collector. Finally, the carbon-based active
material is deposited on its surface by electrophoretic deposition to
obtain a paper-based supercapacitor electrode. The results show that
thanks to the flexibility of cellulose paper, the CP/Ni/Au paper-based
electrode still maintains 92.1\% of the initial capacitance after 2000
bending cycles, showing excellent mechanical properties. Li et al.
{[}95{]} also prepared Ni-paper by loading the filter paper with Ni
metal, and then soaked it in KMnO\textsubscript{4}/HCl solution to
obtain a Ni-paper-MnO\textsubscript{2} paper-based electrode (Figure
8B). In order to show the excellent mechanical properties of Ni-paper as
an electrode material. After 5000 consecutive bending of the Ni-paper,
the resistance of the film only increased from the initial 0.8 \selectlanguage{greek}Ω
\selectlanguage{english}cm\textsuperscript{-2} to 2.7 \selectlanguage{greek}Ω \selectlanguage{english}cm\textsuperscript{-2}. When
MnO\textsubscript{2} is used as the active material, this paper-based
electrode exhibits an area specific capacitance of 1095mF cm-2 at a
current density of 1mA cm-2. This is mainly due to the hierarchical
porous fiber structure in the Ni-paper-MnO2 electrode and the high
conductivity of Ni, which greatly contribute to the electrochemical
performance of the electrode.

General flexible energy storage devices must assemble independent
electrodes, current collectors, and diaphragms. This is not only complex
but also increases the size of the device. Combining all units of the
device in a single substrate to build an all-in-one flexible energy
storage device is a promising approach. Recently, Chang et al.
{[}96-98{]} from Chung-Ang University in South Korea cleverly designed a
series of integrated paper-based supercapacitors with excellent
performance using paraffin heating-assisted in situ polymerization of
Au. As shown in Figure 8C, the team first designed a single-layer
integrated porous paper-based supercapacitor. The preparation of the
device is divided into three steps, the first step is to fill the inside
of cellulose paper by printing solid paraffin wax on the surface of the
paper (Figure 8D(i)), then heating it to a molten state and filling it
inside the cellulose paper (Figure 8D(ii)). In the second step, AgNPs
are deposited on the upper and lower surfaces of the cellulose paper by
drop-casting process (Figure 8D(iii)). The paraffin is then removed by
methanol (Figure 8D(iv)). In the third step, the paper loaded with AgNPs
gold source is soaked in Ag growth solution (HauCl4 and hydroxylamine
hydrochloride mixed solution) to obtain the Au-Paper electrode (Figure
8D(vi)). Finally, MnO\textsubscript{2}-Au-Paper paper-based integrated
electrode is obtained by electrodeposition by loading
MnO\textsubscript{2} on the surface of Au-Paper (Figure 8E). Devices
assembled by combining a paper-based electric base with a gel
electrolyte exhibit a specific capacitance of 252.2F
g\textsuperscript{-1}. To achieve a high potential window of the device,
the team used the technique to fabricate five supercapacitors connected
in series on a sheet of paper. The devices connected in series can
exhibit a high voltage window of 4.0V, easily lighting the blue LED
operating at 2.65V. As shown in Figure 8F, this technique is used to
print the pattern by changing the paraffin wax as well as the heating
temperature. The team prepared three vertically arranged parallel
interdigital electrodes on a sheet of cellulose paper. Compared to
devices assembled with single-layer interdigital electrodes. The three
devices connected in parallel exhibit a larger CV curve area and a
specific capacitance for discharge time. The detailed preparation
process invites the reader to read the original article, which makes it
easier to understand the working principle of the device. Building on
the former's work, the team fabricated vertically integrated planar
multielectrode devices on a single sheet of paper. The highly integrated
multi-electrode, diaphragm, and current collector exist only on one
sheet of paper, and once again a device that expands the electrochemical
window is cleverly designed on a single sheet. Figure 8G shows a
schematic diagram of multilayer device integration and its corresponding
circuit diagram. Multilayer paper-based devices can exhibit greater
discharge times and CV curve areas in the same voltage window than
during a single layer. And it can still maintain excellent energy
storage performance under a higher electrochemical window. This series
of work provides an innovative idea for the ingenious design of
paper-based electrodes, which is of great significance to the
development of paper-based supercapacitors.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image8/image8}

\end{center}
\end{figure}

Figure8. (A)Schematic diagram of CP/Ni/Au paper-based electrode
preparation process and metal deposition.{[}94{]} (B)Schematic diagram
of the preparation process of Ni-paper-MnO\textsubscript{2} paper-based
electrode.{[}95{]} (C)Schematic diagram of the manufacturing process of
vertically layered Au-Paper electrode in a single sheet of paper and its
corresponding. (D)Optical photographs. (E)MnO\textsubscript{2}-Au-Paper
electrode preparation process.{[}96{]} (F)Schematic diagram of the
preparation of three-layer Au-paper interdigital electrodes in a single
sheet.{[}97{]} (G)Schematic diagram of series and parallel connection of
vertical multilayer Au-Paper electrodes in a single sheet and their
corresponding electrochemical properties.{[}98{]}

\textbf{2.2.2.2 Cellulose/conductive polymer paper-based composite
electrode}

In view of the excellent flexibility and modifiable properties of 2D
cellulose paper, two conductive polymers, PEDOT and PPy, have been
widely used in 2D cellulose paper by in-situ polymerization.Li et al.
{[}99{]} constructed a PEDOT/CP paper-based composite electrode by
successfully loading PEDOT in cellulose paper (CP) by gas phase
polymerization. Figure 9A shows a schematic diagram of the preparation
of a paper-based electrode. The Fe\textsuperscript{3+} oxidant is first
added dropwise to the CP, and then the CP adsorbed
Fe\textsuperscript{3+} is placed in a vapor phase polymerization vessel.
Finally, PEDOT/CP paper-based electrode was obtained by washing and
drying. The authors prepared paper-based electrodes with different PEDOT
loading amounts by controlling the number of gas-phase polymerization.
The results show that the electrode (PEDOT/CP-10) after 10
polymerization shows excellent conductivity (14 \selectlanguage{greek}Ω/\selectlanguage{english}square) and a volume
ratio capacitance of 13.7F cm\textsuperscript{-3}. Similarly, Heo et al.
{[}100{]} obtained conductive KHO (C-KHP) by loading Korean conventional
paper (KHP) with a loaded conductive ink. Then the PEODT is loaded on
C-KHP by gas phase polymerization to obtain PC-KHP paper-based composite
electrode material. Finally,1D paper-based yarn electrode was prepared
by mechanical winding of PC-KHP (Figure 9B). A power supply unit formed
by connecting six independent devices in series successfully charges a
smart device operating at 3.6V (Figure 9C). This work provides a
conceptual reference for the practical application and large-scale
production of 2D paper-based electrodes, and promotes the development of
a new generation of flexible paper-based electronic devices.

In recent years, simple paper-based flexible energy storage devices have
been difficult to meet people's living needs. As a device for collecting
tiny energy, nanogenerators have received widespread attention. Shi et
al. {[}101{]} prepared PPy/Cellulose Paper (PCC) by in-situ
polymerization as the main component units of flexible supercapacitors
and friction nanogenerators, respectively. As shown in Figure 9D, the
TENG consists of a Cellulose Paper substrate, a negative triboelectric
layer Nitrocellulose Membrane, and a PCC that acts as both a positive
triboelectric layer and an electrode. Supercapacitors consist of two
symmetrical PCCs, PVA/H2SO4 electrolytes, and a Cellulose Paper
substrate. The TENG exhibits an output voltage of up to 60V and a power
density of 0.83W m\textsuperscript{-2}. SC exhibits a specific
capacitance of 90.1mF cm\textsuperscript{-2}. The two devices were
successfully assembled into a miniaturized electronic energy storage
device (Figure 9E). To obtain paper-based high-performance electrodes
under high-quality loads. After the traditional in-situ polymerization
process, the addition of electric double-layer graphene can improve
energy storage performance (Figure 9F) {[}102{]}. The paper-based
electrode exhibits a specific capacitance of 1685mF
cm\textsuperscript{-2} and a cycle stability of 92.8\% (5000 cycles). In
addition, the assembled solid-state paper-based device exhibits an area
capacitance of 1408mF cm\textsuperscript{-2} and a high area energy
density of 147\selectlanguage{greek}μ\selectlanguage{english}Wh cm\textsuperscript{-2}.

Aramid fiber has attracted the attention of researchers due to its
excellent mechanical properties and chemical stability. In recent years,
multifunctional paper-based materials prepared from aramid fibers have
been widely used in various fields of social life. Yu et al. {[}103{]}
formed ACF/PPS/MWCNT composites by papermaking processes with adhesive
polyphenylene sulfide (PPS), MWCNTs and aramid chopped fibers. The PPS
is then used as a binder for ACF and MWCNT after heating. Finally, the
ACF/PPS/MWCNT-PPy paper-based electrode was obtained by in situ
polymerization of PPy (Figure 9G). The synergies between PPy thanks to
flexible ACF fibers, highly conductive MWCNTs and excellent
pseudocapacitance properties. The paper-based electrode exhibits high
specific capacitance (3205mF cm\textsuperscript{-2} current density at
5mA cm\textsuperscript{-2}) and excellent cycle stability (93\%
capacitance retention after 5000 cycles). In addition, ACF/PPS/MWCNT-PPy
also exhibits excellent flame retardant properties (Figure 9H). In
conclusion, bifunctional paper-based materials with excellent energy
storage performance and good flame retardant performance were prepared.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image9/image9}

\end{center}
\end{figure}

Figure 9. (A) Preparation process of PEDOT/CP paper-based composite
electrode. {[}99{]} (B) PC-KHP paper-based electrode. (C) PC-KHP
paper-based devices connected in series light the LEDs.{[}100{]} (D)
Schematic diagram of the preparation of PCC paper-based materials and
their self-charging devices. (E) PCC-based self-charging device.
{[}101{]} (F) Schematic diagram of rGO/PPy/paper composite electrode
material. {[}102{]} (G) Schematic diagram of the preparation process and
microstructure of acf/pps/MWCNT paper-based electrode. (H) Change of
specific capacitance of paper-based electrode after different
temperature treatment.{[}103{]}

\textbf{2.3 Printing technology}

In order to realize the rapid commercial application of flexible
electronic devices, mature printed electronic technology has received
widespread attention. Printed electronics provides a simple, efficient
and environmentally friendly manufacturing technology for the design of
flexible supercapacitors. It has been widely developed in the field of
flexible supercapacitors and has shown great potential. As a common
printing substrate in daily life, paper is naturally favored by the
majority of scientists. At present, a variety of printing technologies,
including screen printing, inkjet printing, coating, writing and 3D
printing, are used to prepare paper-based supercapacitors. This section
summarizes the development of printing technology in paper-based
supercapacitors. Table 3 summarizes the performance parameters of
cellulose paper-based electrodes prepared by different printing
technologies, so that readers can intuitively understand the application
of this technology in the field of paper-based supercapacitors.

Table3 Performance parameters of cellulose paper-based electrodes
prepared by different printing technologies\selectlanguage{english}
\begin{longtable}[]{@{}llllll@{}}
\toprule
Electrode & Electrolyte & Capacity & Energy density at power density &
Cycles & Reference\tabularnewline
\midrule
\endhead
\textbf{writing} & & & & &\tabularnewline
Cellulose paper/Graphitic/PPy &
H\textsubscript{2}SO\textsubscript{4}/PVA & 270.32mF
cm\textsuperscript{-2} at 0.5mA cm\textsuperscript{-2} & 24.03\selectlanguage{greek}μ\selectlanguage{english}Wh
cm\textsuperscript{-2} at 101.96\selectlanguage{greek}μ\selectlanguage{english}W cm\textsuperscript{-2} & 87\%, 2000 &
104\tabularnewline
Cellulose paper/Graphitic/PANi &
H\textsubscript{2}SO\textsubscript{4}/PVA & 93.64mF
cm\textsuperscript{-2} at 0.1mA cm\textsuperscript{-2} & 8.32\selectlanguage{greek}μ\selectlanguage{english}W h
cm\textsuperscript{-2} at 39.97\selectlanguage{greek}μ\selectlanguage{english}W cm\textsuperscript{-2} & 134.28\%,5000
& 105\tabularnewline
OPD@PN-V & 1M H\textsubscript{2}SO\textsubscript{4} & - & 785\selectlanguage{greek}μ\selectlanguage{english}Wh
cm\textsuperscript{-2} and 286mW cm\textsuperscript{-2} & 95\%, 5000 &
106\tabularnewline
MSCs & H\textsubscript{2}SO\textsubscript{4}/PVA & 4-8F
cm\textsuperscript{-3} & 0.36 \selectlanguage{greek}μ\selectlanguage{english}Wh cm\textsuperscript{-2} and 0.21 mW
cm\textsuperscript{-2} & 89\%, 5000 & 107\tabularnewline
paper/CNT/Ag & 1M Na2SO4 & 72.8F cm\textsuperscript{-3} at 0.5mA
cm\textsuperscript{-2} & 9.08mWh cm\textsuperscript{-3} at 0.22W
cm\textsuperscript{-3} & 75.92\%, 1000 & 108\tabularnewline
\textbf{Screen printing} & & & & &\tabularnewline
IP@PN-V & 1.5M H2SO4 & - & 39Wh kg\textsuperscript{-1} at 69kW
kg\textsuperscript{-1} & 90\%, 5000 & 109\tabularnewline
paper/Gr/AC & H\textsubscript{2}SO\textsubscript{4}/PVA & 12.5 mF
cm\textsuperscript{-2} at 0.01mA cm\textsuperscript{-2} & 1.07\selectlanguage{greek}μ\selectlanguage{english}Wh
cm\textsuperscript{-2} and 0.004 mW cm\textsuperscript{-2} & 88.1\%,
5000 & 110\tabularnewline
paper/Mxene & H\textsubscript{2}SO\textsubscript{4}/PVA & 158 mF
cm\textsuperscript{-2} at 0.08 mA cm\textsuperscript{-2} & 1.64\selectlanguage{greek}µ\selectlanguage{english}Wh
cm\textsuperscript{-2} at 778.3\selectlanguage{greek}µ\selectlanguage{english}W cm\textsuperscript{-2} & 95.8\%, 17000
& 111\tabularnewline
\textbf{Inkjet printing} & & & & &\tabularnewline
paper/Mxene & H2SO4/PVA & 23.4mF cm\textsuperscript{-2} at 0.05mA
cm\textsuperscript{-2} & 1.48mWh cm\textsuperscript{-3} at 189.9mW
cm\textsuperscript{-3} & 92.4\%, 5000 & 112\tabularnewline
paper/AC-Bi\textsubscript{2}O\textsubscript{3}/rGO-MnO\textsubscript{2}
& KOH/PVA & 455.05 mF cm\textsuperscript{-2} at 25 mV
s\textsuperscript{-1} & 13.28mWh cm\textsuperscript{-3} at 4.5W
cm\textsuperscript{-3} & 92.2\%, 20000 & 113\tabularnewline
paper/Ox-SWCNT & H\textsubscript{2}SO\textsubscript{4}/PVA & 33.0 mF
cm\textsuperscript{-2} at 0.1mA cm\textsuperscript{-2} & 0.51\selectlanguage{greek}μ\selectlanguage{english}Wh
cm\textsuperscript{-2} at 0.59mW cm\textsuperscript{-2} & 100\%, 10000 &
114\tabularnewline
PEDOT:PSS/CNF & - & 5.2mF cm\textsuperscript{-2} at 1A
g\textsuperscript{-1} & 0.27\selectlanguage{greek}µ\selectlanguage{english}Wh cm\textsuperscript{-2} at 10.5mW
cm\textsuperscript{-2} & 92\%, 2000 & 115\tabularnewline
PEDOT:PSS/CNF & - & 2.60mF cm\textsuperscript{-2} at 0.05 mA
cm\textsuperscript{-2} & 0.13\selectlanguage{greek}μ\selectlanguage{english}Wh cm\textsuperscript{-2} at 11mW
cm\textsuperscript{-2} & 95\%, 5000 & 116\tabularnewline
\textbf{3D printing} & & & & &\tabularnewline
CNF/AC/ graphite & CNC/ glycerol/NaCl & 25.6F g\textsuperscript{-1} at
1mV s\textsuperscript{-1} & 0.88Wh kg\textsuperscript{-1} at 830W
kg\textsuperscript{-1} & 99\%, 2000 & 118\tabularnewline
\bottomrule
\end{longtable}

\textbf{2.3.1 Writing}

The pencil as a very common writing instrument in life. Due to friction,
the graphite particles generated by writing on the paper by the graphite
rod inside it adhere to the surface of the cellulose paper. And with the
pencil you can draw a variety of shapes of conductive paper, this
conductive paper substrate provides an easy way to build. This
pencil-based conductive paper has been used to prepare flexible
supercapacitors. Zang et al. {[}104{]} used waste newspaper as a
flexible substrate and bought a patterned graphite substrate through a
pencil on its watch. Finally, PPy was deposited on its surface by
electrochemical polymerization to obtain a paper-based composite
electrode of newspaper/graphite/PPy (NGP) (Figure 10A). The electrode
drawn by pencil exhibits a specific capacitance of 270.32mF
cm\textsuperscript{-2} and an energy density of 24.03 \selectlanguage{greek}μ\selectlanguage{english}Wh
cm\textsuperscript{-2}. This work shows that graphite layer paper
constructed by pencil drawing can serve as a substrate for the active
substance. Since then, Yeasmin et al. {[}105{]} have successfully
introduced polyaniline on the surface of a paper-based material drawn by
electrochemical polymerization, and the electrode exhibits an area
capacitance of 93.64mF cm\textsuperscript{-2} and a specific capacitance
of 28.37F g\textsuperscript{-1}. With the popularity of flexible energy
storage equipment, it is inevitable that there will be damage and
deformation during use. This can seriously affect the performance of
flexible energy storage devices. Therefore, sustainable use is
particularly important for flexible devices. In response to this
problem, Xiong et al. {[}106{]} introduced Vitrimer with shape memory
and self-healing function into paper-based electrode, and prepared the
first paper-based electrode material with shape memory and self-healing
function. Figure 10B shows the preparation process of the paper-based
material. A OPD@PN-V paper-based electrode material is obtained by
polymerizing Vitrimer on conductive paper (OPD@PN) supported with
polyaniline. The original shape can be restored by giving the initial
paper-based electrode a certain shape and then processing it with a
blower (Figure 10C). And after external force damage, it can also be
self-repaired by blower treatment (Figure 10D). In addition, the
composite exhibits excellent sensing properties. In conclusion, the
introduction of Vitrimer into paper-based electrodes is a novel method
for the preparation of multifunctional intelligent energy storage
devices.

In order to increase the service life of the device and realize the
sustainable use of flexible energy storage devices. Ma et al. {[}107{]}
integrated TENG with a miniature supercapacitor (MSC) on a sheet of
paper. Figure 10E shows the preparation process of the integrated
device. First, interfinger-like 200 nm thick gold nanoparticles are
deposited on the paper-based surface by magnetron sputtering. For the
MSC unit, the gold surface is applied to functionalize its surface. The
pencil-drawn paper-based electrode is then soaked in 8-Amino-2-naphthol
solution for 1h. Finally, a PCA/H\textsubscript{2}SO\textsubscript{4}gel
electrolyte is applied to the patterning unit to obtain MCS. The TENG
consists of a sliding module and a stator (the stator on a piece of
paper with the MCS). When the stator moves across the stator covered by
the FEP membrane, the TENG releases current to charge the MSC for
continuous use of the device. As shown in Figure 10F, the TENG can
charge three MSCs in series to 2.6V in 465s and successfully drive the
electronics to operate. In conclusion, this work successfully prepared
self-charging paper-based supercapacitors. It provides a good design
idea for the integration of paper-based self-charging power supply and
paper-based energy storage device in the future.

In addition to the introduction of active materials after building a
conductive layer by drawing with a pencil, it is inspired by writing ink
pens. Guang et al. {[}108{]} prepared an energy storage ink that can be
written directly. The ink consists of CNT and Ag. As shown in Figure
10G, by assembling the ink in a ballpoint pen, the device controls its
writing and provides pressure to it. Finally, the written electrode is
placed at 60 \selectlanguage{ngerman}°C to completely dry the ink. The results show that the
prepared CNT/Ag paper-based electrode has a resistivity of 5.1×10-4\selectlanguage{greek}Ω
\selectlanguage{english}cm\textsuperscript{-1} and a specific capacitance of 72.8F
cm\textsuperscript{-3}. And after bending test, there is no effect on
the electrochemical properties (Figure 10H), showing excellent
mechanical stability.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image10/image10}

\end{center}
\end{figure}

Figure10. (A) NGP electrode preparation process.{[}104{]} (B) Schematic
diagram of OPD@PN-V paper-based electrode preparation. (C) OPD@PN-V
shape memory process. (D) OPD@PN-V self-healing process. {[}106{]} (E)
Preparation of paper-based TENG and MSC. (F) Three series of MSC
self-charging and GCD curves for power supply and applications.
{[}107{]} (G) Write CNT/Ag ink directly on the surface of the paper. (H)
Electrochemical performance of CNT/Ag paper-based electrodes. {[}108{]}

\textbf{2.3.2 Screen printing}

Screen printing is made by placing ink on a template, and then applying
a certain pressure to the screen template through a scraper, after which
the ink is squeezed on the surface of the substrate (such as paper)
through the template during the process. Among them, the pressure
exerted in the printing process and the number of printing times will
have a certain impact on the product performance. As shown in Figure
11A, Xiong et al. {[}109{]} printed conductive ink on the surface of
original blank paper (OP) by screen printing technology on the basis of
the former research. Then, polyaniline and Vitrimer were introduced into
the paper-based electrode by electrochemical polymerization and in-situ
polymerization to obtain conductive ink@polyaniline-Vitrimer(IP@PN-V)
paper-based electrode. Similarly, the electrode exhibits excellent
self-healing and shape memory properties. And at the same time it shows
excellent photothermal conversion and electromagnetic shielding
performance.

Compared with the method of introducing active materials after building
a conductive layer through screen printing, it is very convenient and
fast to directly prepare inks with excellent energy storage performance
and directly construct paper-based supercapacitors through screen
printing. Chen et al. {[}110{]} blended two-dimensional graphene with
activated carbon nanofiller to prepare a composite ink (Gr/AC-ink) for
screen printing. Among them, Gr/AC-ink printed on paper shows excellent
energy storage performance. This is mainly due to the presence of AC to
effectively prevent the stacking of two-dimensional graphene nanosheets.
Figure 11B shows the synergistic effect between graphene nanosheets and
AC. Compared to Gr and AC electrodes alone, this electrode exhibits
excellent ion storage performance due to the distinct layered structure
in the Gr/AC electrode. It can be seen from the paper-based
supercapacitor built by this work. The key to the preparation of
paper-based supercapacitors by screen printing lies in the design and
preparation of energy storage inks. In recent years, Mxene, a
two-dimensional material with excellent energy storage performance, has
also been used in screen printing to prepare paper-based electrodes. In
the traditional Mxene etching process, the products are generally
divided into a few layers of Mxene and unetched and unstripped Mxene.
The latter are generally discarded as waste, which undoubtedly increases
the cost of Mxene-based supercapacitors. Abdolhosseinzadeh et al.
{[}111{]} prepared paper-based supercapacitors with excellent
performance by using unetched and peeled Mxene precipitate and a few
layers of Mxene as screen-printed inks (Figure 11C). Among them, a few
layers of Mxene nanosheets act as conductive pathways between the
precipitates and act as conductive binders in the ink of paper-based
electrodes, thereby ensuring the metal conductive network. Finally, the
paper-based electrode prepared by screen printing of the ink exhibits a
specific capacitance of 158mF cm\textsuperscript{-2} and an energy
density of 1.64\selectlanguage{greek}μ\selectlanguage{english}Wh cm\textsuperscript{-2}. And the eight paper-based
devices connected in series exhibited an electrochemical window of more
than 4V and successfully lit the LED lamp (Figure 11D), which is already
one of the best performances of Mxene and graphene screen-printed energy
storage devices. In conclusion, this work provides a low-cost idea for
the preparation of this performance screen-printed paper-based
supercapacitor. In particular, the ''turning waste into treasure'' of
Mxene sediment in this work has a certain reference in the high-value
utilization of energy storage.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image11/image11}

\end{center}
\end{figure}

Figure11. (A)IP@PN-V Schematic diagram of preparation of paper-based
electronic base.{[}109{]} (B)Synergistic effect of Gr and AC. {[}110{]}
(C)Schematic diagram of MXene ink preparation and its application in
screen printing to prepare paper based supercapacitor. (D)GCD curves of
eight series connected MXene paper based supercapacitors. (E)The Mxene
paper based super capacitor connected in series lights up the LED lamp.
{[}111{]}

\textbf{2.3.3 Ink jet printing}

Ink-jet printing is a digital printing technology. The ink can be
deposited on the substrate according to the designed pattern. Compared
with screen printing, ink-jet printing ink is sprayed through
quantitative digital control. Therefore, the distribution and thickness
of the active material of the paper-based electrode prepared by the
technology are more controllable. Huang et al.{[}112{]}directly sprayed
a large area of MXene conductive ink on the paper surface. Then the
interdigital electrode with a certain width was prepared by ultraviolet
laser (Figure 12A). The geometry of interdigital electrode was optimized
by UV laser. Finally, the paper based device showed 23.4mF
cm\textsuperscript{-2} area specific capacitance and good magnification
performance. In order to expand the voltage window and power supply time
of the device, the author directly prepared series and parallel
paper-based devices through inkjet (Figure 12B). The results show that
the voltage window of the device after series connection can reach 1.2V
without affecting the discharge time. At the same time, the discharge
time of the two devices in parallel also increases by 100\%. Compared
with symmetrical supercapacitors, asymmetric electrode supercapacitors
have larger voltage window and energy density. Based on this, in order
to improve the voltage window of the device,Sundriyal et
al.{[}113{]}prepared an asymmetric miniature paper-based supercapacitor
through continuous ink-jet printing. As shown in Figure 12C, the device
preparation process is shown. Firstly, rGO ink interdigital electrode is
printed on paper. Then active
carbon-Bi\textsubscript{2}O\textsubscript{3} ink and
rGO-MnO\textsubscript{2} ink are printed on the corresponding separate
interdigital electrodes as cathode and anode respectively. Finally,
PVA/KOH gel electrolyte is also printed on the electrode surface in the
form of ink. Thanks to the asymmetric electrodes, the device shows a
high voltage window of 1.8V. Similarly,different series and parallel
devices are designed in this work, and the LED lamp with the working
voltage of 3.2V is successfully lit. Similarly, after ink-jet printing,
its energy storage characteristics can be improved through
post-processing. For example, Jo et al. {[}114{]} prepared a water-based
additive free oxidized single-walled carbon nanotube slurry for ink-jet
printing. It is worth mentioning that in this work, the ink of ink-jet
printing is treated with strong pulsed light to improve the
electrochemical energy storage performance of the paper-based electrode.
As shown in Figure 12D, under the treatment of intense pulsed light, the
released gas generated by the rapid elimination of oxygen containing
groups on the surface of carbon nanotubes can produce microporous
structures in the ink. This is very beneficial to the diffusion of
electrolyte ions and the storage of electrons. In addition, the ink is
also suitable for screen printing process. In a word, this work provides
a feasible method for the preparation of energy storage porous carbon
based ink.

In addition to the construction of paper based supercapacitor by
spraying active ink on cellulose paper, the preparation of cellulose
based conductive ink has also been studied in recent years. For example,
Engquist et al. {[}115,116{]} from Link\selectlanguage{ngerman}öping University in Sweden
reported two research efforts on inkjet printing of cellulose-based
inks. As shown in Figure 12E, the team prepared a printable cellulose
based ink by mixing CNF with conductive polymer PEDOT:PSS. Firstly, ink
is sprayed on PET/Al/Carbon collector by ink-jet printing to form a
paper-based electrode. Then the gel electrolyte is deposited on the
electrode by the rod coating method. Finally, the two cured paper
electrodes are combined into a supercapacitor. It is worth mentioning
that in order to prevent the brittleness of the ink after forming, the
author perfectly solved this problem by adding an appropriate amount of
glycerin. On the basis of this work, the team improved the molding of
cellulose/PEDOT:PSS ink again. As shown in Figure 12F, this work
prepared a paper based supercapacitor with controllable thickness and
large area through air atomization spraying of ink and screen printing
of gel electrolyte. In addition, the device is combined with the
flexible solar cell module to successfully prepare a self charging
flexible paper based supercapacitor based on solar energy (Figure12G).
As shown in Figure 3H, the integrated device irradiated by sunlight can
charge the paper based supercapacitor to 0.6V in 2000s.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image12/image12}

\end{center}
\end{figure}

Figure 12. (A)Mxene/paper electrode preparation process based on inkjet
printing. (B) Electrochemical performance of Mxene/paper electrodes.
{[}112{]} (C)Preparation process of asymmetric paper-based
supercapacitors.{[}113{]} (D)SEM image of CNT ink after intense pulsed
light processing.{[}114{]} (E)PEDOT: PSS/CNF paper-based device
preparation. {[}115{]} (F) PEDOT: PSS/CNF paper-based device
preparation. (G)Based on the schematic diagram of solar self-charging
equipment. (H)Electrochemical performance test of self-charging devices.
{[}116{]}

\textbf{2.3.4 3D printing}

3D printing, also known as additive manufacturing, can continuously
deposit materials to produce various structures under digital
design{[}117{]}. This makes it possible to accurately fabricate flexible
devices with complex structures in a short time. Aeby et al. {[}118{]}
prepared a cellulose based ink for one-time 3D printing. Electrode ink
is composed of CNF, water, CNC, glycerin, activated carbon and graphite
particles. Electrolyte ink is composed of CNC, glycerin and NaCl. As
shown in Figure 13A, the design of 3D printing paper based
supercapacitor is shown. The two printed devices are folded together to
form a paper based supercapacitor. In addition, the author tried to
print six paper based supercapacitors in series on curved substrate
(Figure 13B). And it realizes the power supply for the alarm clock with
the working voltage of 3V. The paper based device also shows excellent
biodegradability. After more than half of the weight can be decomposed
in 9 weeks, the remaining carbon based materials can be recycled (Figure
13C). In a word, this work has made considerable reference in the field
of 3D printing paper-based supercapacitors.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image13/image13}

\end{center}
\end{figure}

Figure 13. (A) Paper based devices for 3D printing. (B) 3D printed
paper-based devices provide energy for electronic watches. (C) The
degradable and recyclable process of paper-based devices. {[}118{]}

\textbf{2.4 Others}

In addition to the manufacturing process of paper-based supercapacitors
summarized above, papermaking process, impregnation, carbonization and
laser induced graphene technology are also used to prepare paper-based
supercapacitors. Table 4 summarizes the performance parameters of the
above preparation process related research work.

Table 4. Performance parameters of paper based supercapacitor\selectlanguage{english}
\begin{longtable}[]{@{}llllll@{}}
\toprule
Electrode & Electrolyte & Capacity & Energy density at power density &
Cycles & Reference\tabularnewline
\midrule
\endhead
\textbf{papermaking process} & & & & &\tabularnewline
PANi@paper & H\textsubscript{2}SO\textsubscript{4}/PVA & 282F
g\textsuperscript{-1} at 1A g\textsuperscript{-1} & 2.5W h
kg\textsuperscript{-1} and 0.3kW kg\textsuperscript{-1} & 86.1\%, 1000 &
119\tabularnewline
PPy@paper & H\textsubscript{2}SO\textsubscript{4}/PVA & 3600mF
cm\textsuperscript{-2} at 1mA cm\textsuperscript{-2} & 3.1mWh
cm\textsuperscript{-3} and 414.9mW cm\textsuperscript{-3} & 81.7\%, 1000
& 120\tabularnewline
cellulose-based ACFPs & 1M Na\textsubscript{2}SO\textsubscript{4} &
24.1F cm\textsuperscript{-3} at 0.5 mA cm\textsuperscript{-2} & - &
100\%, 10000 & 121\tabularnewline
\textbf{Pouring molding} & & & & &\tabularnewline
MFC/rGO/SnO\textsubscript{2} & NaCl/PVA & 53F g\textsuperscript{-1} at
10mV s\textsuperscript{-1} & - & 90\%, 1000 & 122\tabularnewline
PEDOT:/CNF/ARS & - & 435F g\textsuperscript{-1} at 0.5A
g\textsuperscript{-1} & 8.9Wh kg\textsuperscript{-1} at 459W
kg\textsuperscript{-1} & 92\%, 1500 & 123\tabularnewline
\textbf{carbonization} & & & & &\tabularnewline
FCP-NiCO\textsubscript{2}O\textsubscript{4} & KOH/PVA & 3115mF
cm\textsuperscript{-2} at 2mA cm\textsuperscript{-2} & 1.2mWh
cm\textsuperscript{-3} at 58.16 mW cm\textsuperscript{-3} & 103\%, 5000
& 124\tabularnewline
CNF/ Co\textsubscript{3}O\textsubscript{4} & 3M KOH & 214F
g\textsuperscript{-1} at 1A g\textsuperscript{-1} & 3.03Wh
kg\textsuperscript{-1} at 203.1W kg\textsuperscript{-1} & 94\%, 5000 &
125\tabularnewline
impregnation & & & & &\tabularnewline
Cellulose fibre/BC/CNTs & 1M H\textsubscript{2}SO\textsubscript{4} &
77.5F g\textsuperscript{-1} at 1A g\textsuperscript{-1} & 22.5Wh
kg\textsuperscript{-1} and 873kW kg\textsuperscript{-1} & 98.4\%, 15000
& 126\tabularnewline
\textbf{laser induced graphene technology} & & & & &\tabularnewline
Paper/LIG/sodium tetraborate & H\textsubscript{2}SO\textsubscript{4}/PVA
& 4.6mF cm\textsuperscript{-2} at 0.015mA cm\textsuperscript{-2} &
0.30\selectlanguage{greek}μ\selectlanguage{english}Wh cm\textsuperscript{-2} at 4.5\selectlanguage{greek}μ\selectlanguage{english}W cm\textsuperscript{-2} & 99.6\%,
10000 & 128\tabularnewline
Paper/LIG/ NaHCO\textsubscript{3} &
H\textsubscript{2}SO\textsubscript{4}/PVA & 23.8 mF
cm\textsuperscript{-2} at 0.015mA cm\textsuperscript{-2} & 2.64\selectlanguage{greek}μ\selectlanguage{english}Wh
cm\textsuperscript{-2} & 97\%, 10000 & 129\tabularnewline
\bottomrule
\end{longtable}

\textbf{2.4.1 Papermaking process}

Thanks to the long history of paper making technology, the paper making
technology in modern society is mature enough. At present, all kinds of
special paper are developed by people through papermaking process. As
shown in Figure 14A, Huang et al. {[}119{]} prepared a kind of cellulose
based on the disposal arrangement of polyaniline, and then prepared a
paper based composite electrode through the papermaking process. The
preparation of the electrode is mainly divided into three steps: first,
a large number of small branches are generated by high-speed mechanical
stirring of cellulose pulp, so that more hydroxyl groups conducive to
polyaniline polymerization are exposed on more cellulose surfaces.
Secondly, polyaniline is polymerized on the cellulose surface to form
PANi@cellulose. Finally, the PANi@paper composite electrode is obtained
through an industrial paper forming machine. As shown in Figure 14B, the
TEM image of PANi fiber shows that polyaniline grows vertically and
tightly on the surface of cellulose. This provides a faster redox
kinetics for electron/ion transfer and charge storage in the
electrochemical process. And the vertically arranged PANi structure also
gives the paper based electrode excellent capacitive characteristics.
The PANi@paper electrode exhibits an excellent specific capacitance of
296F g\textsuperscript{-1} at 1A g\textsuperscript{-1}. More
importantly, the solid paper based energy storage device assembled by
the PANi @ paper electrode also has a specific capacitance of 282F
g\textsuperscript{-1}, and still maintains excellent and stable
electrochemical performance under different bending angles (Figure 14C).
The large-scale preparation of paper-based electrode materials by
papermaking technology is exciting. However, the prepared paper-based
materials also require manual assembly of solid-state devices when
applied, which undoubtedly increases production costs and time. In
response to this problem, the team achieved large-scale production of
integrated paper-based supercapacitors by improving the process
technology {[}120{]}. As shown in Figure 14D, this technique uses
cellulose from orderly stacking PPy as the raw material for paper-based
electrodes. After continuous molding, pressing and drying, an integrated
supercapacitor is obtained. Figure 14E shows a schematic diagram of the
detailed preparation process. Firstly, the 1DPPy/cellulose pulp fiber is
passed through the sheet molding machine to obtain the non-dry state
PPy@paper, and then the two pieces of PPy@paper are assembled
sequentially with the cellulose diaphragm obtained by pure cellulose
pulp to form a sandwich structure. Finally, an all-paper-based
supercapacitor device is obtained by hot pressing, drying, and
impregnating the electrolyte (Figure 14F). The all-in-one paper-based
device has a mass ratio capacitance of 360F g\textsuperscript{-1} at
0.1A g\textsuperscript{-1} and a capacitance retention rate of 81.7\%
after 1000 cycles. It is worth mentioning that by controlling the
thickness of the pulp raw material in different electrodes, an
integrated device with different areas of capacitance can be obtained. A
series of paper-based devices in the 562-2507mF
cm\textsuperscript{-2}range of area ratio capacitance were designed.
This provides a fast and efficient way to industrialize mass
customization of paper-based devices.

Chen et al. {[}121{]} prepared a carbon fiber (CFs)-reinforced
cellulose-based activated carbon paper-based electrode (cellulose-based
ACFPs) by wet papermaking, carbonization and activation. Figure 14G
shows the preparation process of this electrode. Firstly, CFs were mixed
with fibrillated pulp fibers evenly, and carbonized precursor paper
matrix composites were prepared by papermaking process. This composite
is then soaked in H\textsubscript{3P}O\textsubscript{4} solution.
Finally, cellulose-based ACFPs paper-based electrodes were obtained by
H\textsubscript{3}PO\textsubscript{4} and CO\textsubscript{2} double
activation process. Among them, CFs in paper-based materials have a low
coefficient of thermal expansion and high chemical stability, which
provides excellent mechanical properties for paper-based electrodes
(Figure 14H).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image14/image14}

\end{center}
\end{figure}

Figure 14. (A) PANi @paper preparation process. (B) TEM image of PANi
@paper. (C) PANi @paper CV curves at different bending angles. {[}119{]}
(D) Preparation process of PPy pulp fiber. (E) PPy@paper preparation
process. (F) SEM image of a PPy@paper paper-based device.{[}120{]} (G)
cellulose-based ACFPs paper-based electrode preparation process. (H)
Physical photographs of cellulose-based ACFPs electrodes and
electron/ion transport mechanisms. {[}121{]}

\textbf{2.4.2 Pouring molding}

Due to its high specific surface area, excellent hydrophilicity and
excellent rigid structure, cellulose is widely used in self-assembly
film forming technology. In the field of flexible paper-based
supercapacitors, scientists have also tried to blend the active material
with cellulose and then prepare paper-based electrodes by pouring them
in a mold by using the electrostatic layer self-assembly method. For
example, Garino et al. {[}122{]} poured
rGO/SnO\textsubscript{2}synthesized by hydrothermal method with
microfibrimmated cellulose (MFC) blend in a PP mold. Self-assembled
paper-based electrodes were then obtained after holding in air for 24 h
to remove solvent moisture. Figure 15A shows an SEM image of a
paper-based electrode. It is clear from the figure that MFC and
rGO/SnO\textsubscript{2} tablets are perfectly combined. This is very
important for the mechanical properties of the composite electrode.
Edberg et al. {[}123{]} also prepared a cellulose-based paper-based
electrode based on PEDOT by pouring molding in a mold. After testing,
the paper-based electrode assembled energy storage device exhibits a
specific capacitance of more than 400F g\textsuperscript{-1}, showing
very excellent energy storage characteristics.

\textbf{2.4.3 Carbonization}

As a renewable biomass material rich in a large amount of carbon,
cellulose is activated to prepare carbon-based fibers that also exhibit
excellent electric double layer performance. However, the performance of
directly using the prepared cellulose-based carbon fiber for energy
storage devices is not very good. In recent years, paper-based
supercapacitors prepared by compounding cellulose-based carbon fibers
with substances with high energy storage activity have also shown
excellent performance. Wu et al. {[}124{]} loaded carbonized
cellulose-based tissue paper (FCP) with
NiCO\textsubscript{2}O\textsubscript{4} by hydrothermal method to obtain
FCP-NiCO\textsubscript{2}O\textsubscript{4} paper-based electrode
(Figure 15B). On the one hand, carbonized FCP provides abundant sites
for the loading of highly conductive
NiCO\textsubscript{2}O\textsubscript{4}. On the other hand, carbonized
FCP favors the rapid movement of electrons during electrochemical
reactions. Thanks to the synergistic effect of carbonized FCP and
NiCO\textsubscript{2}O\textsubscript{4}, the
FCP-NiCO\textsubscript{2}O\textsubscript{4} paper-based electrode showed
excellent area specific capacitance (3115mF cm\textsuperscript{-2}) and
excellent energy density (1.2 mWh cm\textsuperscript{-3}) and power
density (58.16 mW cm\textsuperscript{-3}). As shown in Figure 15C,
Rabani et al. {[}125{]} uniformly grow cobalt oxide
(Co\textsubscript{3}O\textsubscript{4}) nanoparticles on the surface of
1DCNF. Then the resulting composite fiber is molded to obtain
CNF/Co\textsubscript{3}O\textsubscript{4} paper matrix composite.
Finally, CNF/Co\textsubscript{3}O\textsubscript{4} paper-based electrode
was obtained by carbonization treatment at 200\selectlanguage{ngerman}°C. Thanks to the
excellent performance of CNF fiber and
Co\textsubscript{3}O\textsubscript{4} after carbonization treatment. The
paper-based energy storage device assembled with this electrode can
provide a high specific capacitance of 214F g\textsuperscript{-1} at 1A
g\textsuperscript{-1}.

\textbf{2.4.4 Impregnation}

The excellent porous structure and large specific surface area of
cellulose paper are considered suitable carriers for loading active
materials. Among them, bacterial cellulose (BC) has an excellent
length-to-diameter ratio and a network of interwoven fibers. However,
after impregnation, the conductive substance and the paper-based film
made of pure BC have poor mechanical properties. As shown in Figure 15D,
Wu et al. {[}126{]} prepared a flexible and strong paper-based substrate
by mixing cellulose fibers with BC. It is then impregnated in CNT
solution. Due to the surface modification of BC by polyimide, a large
number of amine groups are generated on the BC surface. The adsorption
of this CNT provides excellent prerequisites. From the SEM image of the
paper-based electrode, it is clear that the cellulose fibers provide the
skeleton of the composite, and the CNT is uniformly loaded inside the
material. The results show that the electrode has a conductivity of
0.59S cm\textsuperscript{-1} and a specific capacitance of 77.5F
g\textsuperscript{-1}. It is worth mentioning that after 15,000
ultra-long cycles, its electrochemical performance is still maintained
at 98.4\% of the initial state, showing excellent durability and
stability.

\textbf{2.4.5 Laser-induced graphene}

In 2014, Tour et al.{[}127{]} successfully prepared macroporous
laser-induced graphene (LIG) by treating polyimide membranes with
CO\textsubscript{2} lasers. Since then, LIGs prepared by various
substrates have been widely used in various fields such as energy
storage and sensing. Among them, paper-based materials have proven to be
excellent precursor substrates for LIG, but because untreated cellulose
paper burns easily when treated at high temperatures in air, it needs to
undergo chemical treatment. Lu et al.{[}128{]} soaked the paper in 0.1 M
flame retardant solution sodium tetraborate for pretreatment. This is to
prevent combustion when the laser processes the paper and better produce
LIG. Figure 15E shows SEM images of cellulose paper and LIG. When used
as a supercapacitor, the paper-based LIG exhibits a specific capacitance
of 4.6mF cm\textsuperscript{-2}, and the voltage and energy output of
these devices can be controlled by connecting them in series and
parallel. Although the LIG obtained by the paper-based material treated
with flame retardant has been successfully applied to the field of
supercapacitors, the capacitance performance of the device obtained by
this method is still not very good. Lin et al. {[}129{]} The paper-based
device prepared by combining chemical foaming and LIG exhibits a
specific capacitance of 23.8mF cm\textsuperscript{-2}. Figure 15G shows
the preparation process of this paper-based electrode. The paper is
first soaked in the inorganic salt NaHCO\textsubscript{3} for
processing. Then, the treated paper is patterned and scanned by a
CO\textsubscript{2} laser to obtain a paper-based electrode. Finally,
gel electrolyte is added to obtain a paper-based LIG device. It is worth
mentioning that thanks to the foaming effect of
NaHCO\textsubscript{3}(Figure 15F), the CO\textsubscript{2} laser
produces a large number of porous LIG on the paper when processing it.
This structure facilitates the migration of electrons and ions during
electrochemical energy storage.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image15/image15}

\end{center}
\end{figure}

Figure 15. (A) SEM image of MFC/rGO/SnO\textsubscript{2} paper-based
electrode.{[}122{]} (B) Preparation process and physical photo of
FCP-NiCO\textsubscript{2}O\textsubscript{4} paper-based electrode.
{[}124{]} (C) Preparation process of
CNF/Co\textsubscript{3}O\textsubscript{4} paper-based electrode.
{[}125{]} (D) Paper-based electrode prepared based on CNT impregnation.
{[}126{]} (E) SEM images of paper and LIG. {[}128{]} (F) Preparation
process of paper-based LIG devices. (G) NaHCO\textsubscript{3} chemical
foaming mechanism and CV curves of paper-based devices. {[}129{]}

\textbf{3. Summary and outlook}

As a biomass resource with biorenewable, easily degradable and excellent
mechanical flexibility, cellulose is considered to be the most
attractive green material for the preparation of flexible supercapacitor
electrodes. Especially in the context of global efforts to reduce
environmental pollution, cellulose paper-based supercapacitor energy
storage devices have become a current research hotspot. Among them, the
porous structure of cellulose gives paper-based supercapacitors unique
advantages, including high energy density, designability of thickness,
design of porous structure conducive to the rapid movement of
electrolyte ions, and preparation of integrated devices. In addition,
the application of printing technology makes the large-scale and
commercialization of paper-based energy storage devices a possibility.
This paper summarizes the latest research progress of electrode related
preparation methods of cellulose paper-based supercapacitors in recent
years, and classifies and summarizes them to provide a rich reference
for their development. Although scientists have done a lot of excellent
research in the field of the preparation of cellulose paper-based
electrodes. However, many problems and challenges require further
research and breakthroughs (Figure 16). (1) Although cellulose
paper-based electrodes prepared by different preparation methods have
been used in many fields. But these methods have a common problem with
energy storage. As a flexible energy storage device, the improvement of
electrochemical energy storage performance (specific capacitance, energy
density and power density) and designability are problems that need to
be further explored and studied in these preparation processes. (2)
Large-scale preparation is the most important problem restricting the
development of flexible supercapacitors. The relevant research work
reported so far is limited to laboratories and has not been demonstrated
on a large scale. Among them, mature papermaking technology and low-cost
printing technology have become the most effective way to achieve
large-scale preparation. In future research, the preparation of pulp
composite active fiber by blending pulp cellulose with active materials
or by in-situ polymerization is a research direction with high
feasibility of large-scale preparation. In addition, the development of
electroactive inks in printing technology is also a highly feasible
method for large-scale preparation of high-performance paper-based
supercapacitor devices. (3) In the preparation process of paper-based
electrodes other than flat printing technology and LIG technology, the
control of the material structure and pore size of the electrode by the
long-diameter ratio of cellulose is also a very worthy of study. For
example, cellulose materials with different length-diameter ratios and
composite forms with active materials have an impact on the pore
structure inside the electrode material. Therefore, controlling these
porosities by choosing the appropriate preparation method remains a
challenge. (4) The preparation of high-performance paper-based
electrodes assisted by computational simulation theory has also been
gradually applied. For example, COMSOL is used to carry out theoretical
simulation calculations on the movement of electrolyte ions in the pores
inside the electrode, and the influence of pore structure on energy
storage performance is studied more intuitively. And with the help of
simulation, the preparation process of paper-based electrodes can be
continuously optimized and referenced. In addition, advanced finite
element simulation can also be used to establish the relationship
between paper-based electrode structure and mechanical properties. (5)
The designability of the energy storage performance of paper-based
electrodes by related preparation methods is a topic that has not been
widely studied. For example, the change of thickness during vacuum
filtration, the control of polymerization conditions in in-situ
polymerization, and the thickness of ink in printing technology will
have a certain impact on the energy storage performance of paper-based
devices. Therefore, the controllable design of paper-based electrode
energy storage performance by using these technologies also has an
important impact on the preparation of high-performance paper-based
supercapacitor energy storage devices. (6) The development trend of
flexible electronics in the future when intelligent integrated
equipment. The introduction of self-charging, electrochromics,
self-healing and shape memory into paper-based supercapacitors, and the
development of integrated multifunction devices are critical to the
future development of paper-based supercapacitors. In summary, the
development of cellulose paper-based electrodes in the field of energy
storage of flexible supercapacitors is worthy of further exploration and
breakthrough. Finally, the future of cellulose paper-based
supercapacitor devices will definitely have a very promising market. We
also need to continue to work hard and expect paper-based energy storage
devices to enter an era of widespread application.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image16/image16}

\end{center}
\end{figure}

Figure 16. Future development prospects of cellulose-based paper-based
supercapacitor electrode materials.

\textbf{Acknowledgments}

This work was supported by Supported by the fund of National Natural
Science Foundation of China (22078184; 22171170). China Postdoctoral
Science Foundation (2019M653853XB). Natural science advance research
foundation of Shaanxi University of Science and Technology
(2018QNBJ-03). Major scientific and technological innovation projects in
Shandong Province (2019TSLH0316).

\textbf{References}

{[}1{]} G. Chen, X. Xiao, X. Zhao, T. Tat, M. Bick, J. Chen, Chem. Rev.
2022, 122, 3259-3291.

{[}2{]} M. Peng, L. Wang, L. Li, Z. Peng, X. Tang,T. Hu, K. Yuan, Y.
Chen, eScience. 2021, 1, 83-90.

{[}3{]} C. Xiong, T. Wang, Z. Zhao, Y. Ni, Smartmat. 2023, 4, e1158.

{[}4{]} Y. Ren, Z. He, H. Zhao, T. Zhu, Rare Metals. 2022, 41, 830-835.

{[}5{]} W. Chen, R. Zhang, Y. Sun, J. Wang, Y. Fan, B. Liu, Advanced
Powder Materials. 2023, 2, 100080.

{[}6{]} C. Vu,T. Truong, J. Kim, Mater. Today Phys. 2022, 27, 100795.

{[}7{]} J. Qiu, H. Zhao, Y. Lei, Smartmat. 2022, 3, 447-473.

{[}8{]} C. Zhu, J. Wu,J. Yan, X. Liu, Adv. Fiber Mater. 2022,
10.1007/s42765-022-00212-0.

{[}9{]} L. Zhao, Z. Qu, J. Energy Chem. 2022, 71, 112-128.

{[}10{]} A. Ahmed, S. Sharma, B. Adak, M. Hossain, A. LaChance, S.
Mukhopadhyay, L. Sun, Infomat. 2022, 4, e12295.

{[}11{]} C. Gu, A. Jia, Y. Zhang, S .Zhang, Chem. Rev. 2022, 122,
14679-14721.

{[}12{]} X. Jia, R. Guo, B. Tay, X. Yan, Adv. Funct. Mater. 2022, 32,
2205933.

{[}13{]} X. Xiong, W. Yan, Y. Zhu, L. Liu, L. Fu, Y. Chen, N. Yu, Y. Wu,
B. Wang, R. Xiao, Adv. Energy Mater. 2022, 12, 2103112.

{[}14{]} C. Chae, J. Han, S. Lee, Y. Choi, T. Kim, S. Jeong, Adv. Funct.
Mater. 2020, 30, 2000715.

{[}15{]} G. Zhang, J. Hu, Y. Nie, Y. Zhao, L. Wang, Y. Li, H. Liu, L.
Tang, X. Zhang, D. Li, L. Sun, H. Duan, Adv. Funct. Mater.. 2021, 31,
2100290.

{[}16{]} S. Selvam, Y. Park, J. Yim, Adv. Sci. 2022, 9, 2201890.

{[}17{]} K. Chen, C. Gao, B. Lu, X. Jin, C. Shao, J. Wang, W. Wu, L. Qu,
Y. Zhao, J. Power Sources 2022, 532, 231346.

{[}18{]} J. Du, Z. Wang, J. Yu, S Ullah, B. Yang, C. Li, N. Zhao, B.
Fei, C. Zhu, J. Xu, Adv. Funct. Mater. 2018, 28, 1707351.

{[}19{]} W. Zhang, X. Ji, M. Ma, Chem. Eng. J. 2023,458, 141402.

{[}20{]} A. Etale, A. Onyianta, S. Turner, S. Eichhorn, Chem. Rev. 2023,
10.1021/acs.chemrev.2c00477.

{[}21{]} Z. Sun, K. Qu, Y. You, Z. Huang, S. Liu, J. Li, Q. Hu, Z. Guo,
J. Mater. Chem. A 2021, 9, 7278-7300.

{[}22{]} W. Liu, K. Liu, H. Du, T. Zheng, N. Zhang, T. Xu, B. Pang, X.
Zhang, C. Si, K. Zhang, Nano-Micro Lett. 2022, 14, 104.

{[}23{]} J. Zhou, Y. Yuan, J. Tang, W. Tang, Energy Stor. Mater. 2019,
23, 594-601.

{[}24{]} A. Isogai, Y. Zhou, Curr. Opin. Solid State Mater. Sci. 2019,
23, 101-106.

{[}25{]} L. Xia, X. Li,Y. Wu, S. Hu, Y Liao, L. Huang, Y. Qing, X. Lu,
Chem. Eng. J. 2019, 379, 122325.

{[}26{]} Z. Wang, Y. Lee, S. Kim, J. Seo, S. Lee, L. Nyholm, Adv. Mater.
2021, 33, 2000892.

{[}27{]} H. Liu, H. Du, T. Zheng, K. Liu, X. Ji, T. Xu, X. Zhang, C. Si,
Chem. Eng. J. 2021, 426, 130817.

{[}28{]} R. Guo, L. Zhang, Y. Lu, X. Zhang, D. Yang, J. Energy Chem.
2020, 51, 342-361.

{[}29{]} W. Zhu, F. Yi, P. Huang, H. Zhang, Z. Tang, Y. Fu, Y. Wang, J.
Huang, G. Dong, Y. Li, S. Fu, J. Mater. Chem. A 2021, 9, 26758-26766.

{[}30{]} Y. Ko,M. Kwon,W. Bae,B. Lee,S. Lee,J. Cho, Nat. Commun. 2017,
8, 536.

{[}31{]} J. Wei, Y. Teng, T. Meng, X. Bu, H. Du, D. Li, J. Mater. Chem.
A 2020, 8, 24620-24634.

{[}32{]} Q. Huang,Y. Yang, R. Chen, X. Wang, Ecomat. 2021, 3, e12076.

{[}33{]} Y Jiang, J Ou, Z. Luo, Y. Chen, Z. Wu, H. Wu, X. Fu, S. Luo, Y.
Huang, Small 2022, 18, 2201377.

{[}34{]} Y. Wang , N. Chen, Y. Liu , X. Zhou, B. Pu, Qing Y, M. Zhang,
X. Jiang, J. Huang, Q. Tang, B. Zhou, W. Yang, Chem. Eng. J. 2022, 450,
138398.

{[}35{]} J. Huang, S. Han, D. Zhu, Q. Wu, H. Chen, A. Chen, J. Zhang, B.
Huang, X. Yang, L. Guan, Adv. Funct. Mater. 2022, 32, 2205708.

{[}36{]} R. Ma, X. Zhang, J. Zhuo, L. Cao, Y. Song, Y. Yin, X. Wang, G.
Yang, F. Yi, Acs Nano 2022, 16, 9713-9727.

{[}37{]} M. Li, S. Zhou, L. Cheng, F. Mo, L. Chen, S. Yu, J. Wei, Adv.
Funct. Mater. 2022, 10.1002/adfm.202208034.

{[}38{]} J. Liang, C. Jiang, W. Wu, Appl. Phys. Rev. 2021, 8, 021319.

{[}39{]} L. Tan, Z. Li, R. Shi, F. Quan, B. Wang, X. Ma, Q. Ji, X. Tian,
Y. Xia, ACS Appl. Mater. Interfaces 2020, 12, 38175-38182.

{[}40{]} C. Liao,X . Mu, L. Han, Z. Li, Y. Zhu, J. Lu, H. Wang, L. Song,
Y. Kan, Y. Hu, Energy Stor. Mater. 2022, 48, 123-132.

{[}41{]} A. Baskar, G. Singh, A. Ruban, J. Davidraj, R. Bahadur, P.
Sooriyakumar, P. Kumar, A. Karakoti, J. Yi, A. Vinu, Adv. Funct. Mater.
2022, 10.1002/adfm.202208349.

{[}42{]} W. Chen, K. Yang, M. Luo, D. Zhang, Z. Li, C. Liu, X. Zhou,
Ecomat 2023, 5, e12271.

{[}43{]} H. Wang, H. Yang, Y. Diao, Y. Lu, K. Chrulski, J. D'Arcy, Acs
Nano 2021, 15, 7799-7810.

{[}44{]} A. Maitra, R. Bera, L. Halder, A. Bera, S. Paria, S. Karan, S.
Si, A. De, S. Ojha, B. Khatua, Renew. Sust. Energ. Rev. 2021, 151,
111595.

{[}45{]} Z. Wan, N. Nguyen, Y. Gao, Q. Li, Sustain. Mater. Techno. 2020,
25, e00205.

{[}46{]} R. Rodriguez, S. Shchadenko, G. Murastov, A. Lipovka, M.
Fatkullin, I. Petrov, T. Tran, A. Khalelov, M. Saqib, N. Villa, V.
Bogoslovskiy, Y. Wang, C. Hu, A. Zinovyev, W. Sheng, J. Chen, I. Amin,
E. Sheremet, Adv. Funct. Mater. 2021, 31, 2008818.

{[}47{]} J. Li, H. Jia, S. Ma, L. Xie, X. Wei, L. Dai, H. Wang, F. Su,
C. Chen, ACS Energy Lett. 2023, 8, 56-78.

{[}48{]} M. Zhong, M. Zhang, X. Li, Carbon Energy 2022, 4, 950-985.

{[}49{]} N. Mohamed, M. El-Kady, R. Kaner, Adv. Funct. Mater. 2022, 32,
2203101.

{[}50{]} Y. Yuan, L. Jiang, X. Li, P. Zuo, X. Zhang, Y. Lian, Y. Ma, M.
Liang, Y. Zhao, L. Qu, Adv. Mater. 2022, 34, 2110013.

{[}51{]} Q. Zhang, C. Deng, Z. Huang, Q. Zhang, X. Chai, D. Yi, Y. Fang,
M. Wu, X. Wang, Y. Tang, Y. Wang, Small 2023, 10.1002/smll.202205725.

{[}52{]} X. Liu, C. Liu, S. Xu, T. Cheng, S. Wang, Y. Lai, W. Huang,
Chem. Soc. Rev. 2022, 51, 3181-3225.

{[}53{]} R. Chen, H. Tang, Y. Dai, W. Zong, W. Zhang, G. He, X. Wang,
Acs Nano 2022, 16, 19124-19132.

{[}54{]} Y. Zhu, J. Ma, P. Das, S. Wang, Z. Wu, Small methods 2023,
10.1002/smtd.202201609.

{[}55{]} Z. Cao, H. Hu, D. Ho, Adv. Funct. Mater. 2022, 32, 2111805.

{[}56{]} S. Jayaraman, T. Rawson, M. Belyustina, Energ. Environ. Sci.
2022, 15, 2948-2957.

{[}57{]} P. Lokhande, S. Kulkarni, S. Chakrabarti, H. Pathan, M. Sindhu,
D. Kumar, J. Singh, A. Kumar, Y. Mishra, D. Toncu, M. Syvajarvi, A.
Sharma, A. Tiwari, Coord. Chem. Rev. 2022, 473, 214771.

{[}58{]} J. Lee, G. Yang, C. Kim, R. Mahajan, S. Lee, S. Park, Energ.
Environ. Sci. 2022, 15, 2233-2258.

{[}59{]} W. Chen, D. Zhang, K. Yang, M. Luo, P. Yang, X. Zhou, Chem.
Eng. J. 2021, 413, 127524.

{[}60{]} W. Luo, N. Guo, L. Wang, Y. Cao, M. Xu, D. Jia, S. Feng, X.
Gong, S. Zhang, Electrochim. Acta 2021, 387, 138560.

{[}61{]} Z. Sun, S. Fang, Y. Hu, Chem. Rev. 2020, 120, 10336-10453.

{[}62{]} C. Xiong, B. Li, X. Lin, H. Liu, Y. Xu, J. Mao, C. Duan, T. Li,
Y. Ni, Compos. B. Eng. 2019, 165, 10-46.

{[}63{]} M. Zhong, X. Li, X. Chu, H. Gui, S. Zuo, C. Yao, Z. Li, Y.
Chen, Appl. Catal. B-Environ. 2022, 317, 121718.

{[}64{]} J. Qian, Q. Dong, K. Chun, D. Zhu, X. Zhang, Y. Mao, J. Culver,
S. Tai, J. German, D. Dean, J. Miller, L. Wang, T. Wu, T. Li, A.
Brozena, R. Briber, D. Milton, W. Bentley, L. Hu. Nat. Nanotechnol.
2023, 10.1038/s41565-022-01278-y.

{[}65{]} W. He, B. Wu, M. Lu, Z. Li, H. Qiang, Molecules 2020, 25, 2793.

{[}66{]} H. Qiang, W. He, F. Guo, J. Cao, R. Wang, Z. Guo, ACS Appl.
Nano Mater. 2022, 5, 6305-6315.

{[}67{]} C. Xiong, C. Zheng, S. Nie, C.Qin, L. Dai, Y. Xu, Y. Ni,
Cellulose 2021, 28, 3733-3743.

{[}68{]} Z. Zou, W. Xiao, Y. Zhang, H. Yu, W. Zhou, Appl. Surf. Sci.
2020, 500, 144244.

{[}69{]} A. Lopez-Moreno, J. Villalva, E. Perez, Chem. Soc. Rev. 2022,
51, 9433-9444.

{[}70{]} M. Geng, H. Yang, C. Shang, Adv. Sci. 2022, 9, 2204561.

{[}71{]} Q. Yin, M. Ye, H. Jia, A. Melo, Q. Ji, J. Mater. Chem. A 2022,
10, 21430-21445.

{[}72{]} D. Fang, J. Zhou, L. Sheng, W. Tang , J. Tang, Chem. Eng. J.
2020, 396, 125325.

{[}73{]} J. Jyothibasu, R. Wang , K. Ong, J. Ong, R. Lee, Cellulose
2021, 28, 3549-3567.

{[}74{]} A. Ghaffarkhah, E. Hosseini, M. Kamkar, A. Sehat, S.
Dordanihaghighi, A. Allahbakhsh, C. Kuur , M. Arjmand, Small 2022, 18,
2102683.

{[}75{]} L. Ponomarenko , F. Schedin, M. Katsnelson, R. Yang, E. Hill,
K. Novoselov, A. Geim, Science 2008, 320, 356-358.

{[}76{]} L. Shi, B. Wang, S. Lu, Matter 2023,
10.1016/j.matt.2023.01.003.

{[}77{]} C. Xiong, J. Xu, Q. Han, C. Qin, L. Dai, Y. Ni, Cellulose 2021,
28, 10359-10372.

{[}78{]} C. Ma, M. Ma, C. Si, X. Ji, P. Wan, Adv. Funct. Mater. 2021,
31, 2009524.

{[}79{]} S. Jiao, A. Zhou, M. Wu, H. Hu, Adv. Sci. 2019, 6, 1900529.

{[}80{]} W. Tian, A. VahidMohammadi, M. Reid, Z. Wang, L. Ouyang, J.
Erlandsson, T. Pettersson, L. Wagberg, M. Beidaghi, M. Hamedi, Adv.
Mater. 2019, 31, 1902977.

{[}81{]} H. Tang, R. Chen, Q. Huang, W. Ge, X. Zhang, Y. Yang, X. Wang,
Ecomat, 2022, 4, e12247.

{[}82{]} J. Chen, H. Chen, M. Chen, W. Zhou, Q. Tian, C. Wong, Chem.
Eng. J. 2022, 428, 131380.

{[}83{]} C. Cai, W. Zhou, Y. Fu, Chem. Eng. J. 2021, 418, 129275.

{[}84{]} H. Hsu, A. Khosrozadeh, B. Li, G. Luo, M. Xing, W. Zhong, ACS
Sustain. Chem. Eng. 2019, 7, 4766-4776.

{[}85{]} S. Zhou, X. Kong, B. Zheng, F. Huo, M. Stromme, C. Xu, ACS Nano
2019, 13, 9578-9586.

{[}86{]} X. Huang,B. Luo,C. Liu,L. Zhong,D. Ye,X. Wang, Nano Res. 2021,
14, 2390-2397.

{[}87{]} I. Rabani,J. Yoo,C. Bathula,S. Hussain,Y. Seo, J. Mater. Chem.
A 2021, 9, 11580-11594.

{[}88{]} Q. Song, Z. Zhan, B. Chen, Z. Zhou, C. Lu, Cellulose. 2020, 27,
7475-7488.

{[}89{]} S. Yang, L. Sun, X. An, X. Qian, Carbohydr. Polym. 2020, 229,
115455.

{[}90{]} Z. Chang, A. Huang, X. An, X. Qian, Carbohydr. Polym. 2020,
244, 116442.

{[}91{]} Y. Liang, Z. Wei, H. Wang, R. Wang, X. Zhang, Sci. China Mater.
2022, 10.1007/s40843-022-2225-x.

{[}92{]} Y. Liang, Z. Wei, H. Wang, M. Flores, R. Wang, X. Zhang, J.
Power Sources 2022, 548, 232071.

{[}93{]} H.D, M. Zhang, K. Liu, M. Parit, Z. Jiang, X. Zhang, B. Li, C.
Si, Chem. Eng. J. 2022, 428, 131994.

{[}94{]} Q. Zhang, L. Kang, J. Zou, C. Huang, Z. Gong, J, Zhang, Mater.
Design 2021, 205, 109742.

{[}95{]} Y. Li, Q. Wang, Y. Wang, M. Ba, J Shao, H Ji, H. Feng, J.
Zhang, X. Ma, W. Zhao, Dalton Trans. 2019, 48, 7659-7665.

{[}96{]} I. Oh, S. Lee, Y. Kim, S. Choi, I. Nam, S. Chang, J. Mater.
Chem. A 2021, 9, 27672-27683.

{[}97{]} K. Yeon Woo, O. In Hyeok, C. Suk Tai,Batteries \& Supercaps
2022, 10.1002/batt.202200407.

{[}98{]} Y. Kim, I. Oh, S. Choi, I. Nam, S. Chang, Chem. Eng. J. 2023,
454, 140117.

{[}99{]} B. Li, H. Lopez-Beltran, C. Siu, K. Skorenko, H. Zhou, W.
Bernier, M. Whittingham, W. Jones,Acs Appl. Energy Mater. 2020, 3,
1559-1568.

{[}100{]} Y. Heo, J. Lee, S. Kim, S. Mun, S. Lee, S. Park, ACS Appl.
Mater. Interfaces 2022, 14, 42671-42682.

{[}101{]} X. Shi, S. Chen, H. Zhang, J. Jiang, Z. Ma, S. Gong, ACS
Sustain. Chem. Eng. 2019, 7, 18657-18666.

{[}102{]} C. Ma, W. Cao, W. Xin, J. Bian, M. Ma, Ind. Eng. Chem. Res.
2019, 58, 12018-12027.

{[}103{]} Y. Yu, D. Pan, L. Zhao, S. Huang, P. Lin, Z. Wang, Y. Jia, H.
Wang, L. Wang, Adv. Fiber Mater. 2022, 4, 1246-1255.

{[}104{]} L. Zang, X. Qiao, Q. Liu, C. Yang, L. Hu, J. Yang, Z. Ma,
Cellulose 2020, 27, 1033-1042.

{[}105{]} S. Yeasmin, S. Talukdar, D. Mahanta, Electrochim. Acta 2021,
389, 138660.

{[}106{]} C Xiong, M. Li, W. Zhao, C. Duan, L. Dai, M. Shen, Y. Xu, Y.
Ni, Chem. Eng. J. 2020, 396, 125318.

{[}107{]} W. Ma, M. Zhang, W. Yan, J. Zhu, J. Liu, W. Song, Nano Energy
2022, 101, 107601.

{[}108{]} X, Guan, L. Cao, Q. Huang, D. Kong, P. Zhang, H. Lin, W. Li,
Z. Lin, H. Yuan, Polymers. 2019, 11, 973.

{[}109{]} C. Xiong, M. Li, Q. Han, W. Zhao, L. Dai, Y. Ni, J. Mater.
Sci. Technol. 2022, 97, 190-200.

{[}110{]} H. Chen, S. Chen, Y. Zhang, H. Ren, X. Hu, Y, Bai. ACS Appl.
Mater. Interfaces 2020, 12, 56319-56329.

{[}111{]} S. Abdolhosseinzadeh, R. Schneider, A. Verma, J. Heier, F.
Nuesch, C. Zhang, Adv. Mater. 2020, 32, 2000716.

{[}112{]} H. Huang, X. Chu, H. Su, H. Zhang, Y. Xie, W. Deng, N. Chen,
F. Liu, H. Zhang, B. Gu, W. Deng, W. Yang, J. Power Sources 2019, 415,
1-7.

{[}113{]} P. Sundriyal, S. Bhattacharya, Acs Appl. Energy Mater.. 2019,
2, 1876-1890.

{[}114{]} A. Jo, S. Chung, P. Kim, J. Lee, H. Lee, H. Yang, T. Ha, J.
Kim, Y. Lee, H. Jeong, S. Seo, S. Jeong, G. Lee, K. Baeg, J. Han, J.
Park, Acs Appl. Energy Mater.. 2021, 4, 13666-13675.

{[}115{]} M. Say, R. Brooke, J. Edberg, A. Grimoldi, D. Belaineh, I.
Engquist, M. Berggren, Npj Flex. Electron. 2020, 4, 14.

{[}116{]} M. Say, C. Brett, J. Edberg, S Roth, L. Soderberg, I.
Engquist, M. Berggren, ACS Appl. Mater. Interfaces.
2023,10.1021/acsami.2c15514.

{[}117{]} Y. Zhu, J. Qin, G. Shi, C. Sun, M. Ingram, S. Qian, J. Lu, S.
Zhang, Y. Zhong, Carbon Energy 2022, 4, 1242-1261.

{[}118{]} X. Aeby, A. Poulin, G. Siqueira, M. Hausmann, G. Nystrom, Adv.
Mater. 2021, 33, 2101328.

{[}119{]} H. Huang, S. Abbas, Q. Deng, Y. Ni, S. Cao, X. Ma, J. Power
Sources 2021, 498, 229886.

{[}120{]} H. Huang, C. Lin, Z. Hua, J. Guo, D. Lu, Y. Ni, S. Cao, X. Ma,
Chem. Eng. J. 2022, 448, 137589.

{[}121{]} J, Chen, J. Xie, C. Jia, C. Song, J. Hu, H. Li, Chem. Eng. J.
2022, 450, 137938.

{[}122{]} N. Garino, A. Lamberti, S. Stassi, M. Castellino, M. Fontana,
I. Roppolo, A. Sacco, C. Pirri, A. Chiappone, Electrochim. Acta 2019,
306, 420-426.

{[}123{]} J. Edberg, R. Brooke, H. Granberg, I. Engquist, M. Berggren,
Adv. Sustain. Syst. 2019, 3, 1900050.

{[}124{]} H. Wu, J. Bi, Y. Li, L. Wang, X. Pang, C. Xiong, Z. Li, J.
Materiomics 2021, 7, 166-176.

{[}125{]} I. Rabani, J. Yoo, H. Kim, D. Lam, S. Hussain, K. Karuppasamy,
Y. Seo, Nanoscale 2021, 13, 355-370.

{[}126{]} X. Wu, M. Zhang, T. Song, H. Mou, Z. Xiang, H. Qi, ACS Appl.
Mater. Interfaces 2020, 12, 13096-13106.

{[}127{]} J. Lin, Z. Peng, Y. Liu, F. Ruiz-Zepeda, R. Ye, E. Samuel, M.
Yacaman, B. Yakobson, J. Tour, Nat. Commun. 2014, 5, 5714.

{[}128{]} J. Coelho, R. Correia F, S. Silvestre, T. Pinheiro, A.
Marques, M. Correia, J. Pinto, E. Fortunato, R. Martins, Mikrochim. Acta
2022, 190, 40.

{[}129{]} K. Lu, Y. Ma, J. Ye, J. Power Sources 2022, 535, 231488.

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