Enhanced Urea Oxidation Reaction through Layered Double Hydroxides:
Insights from ZIF-67-Derived Nanostructures
Abstract
Layered double hydroxides (LDHs) are ionic layered compounds
characterized by anion-containing intermediate regions within positively
charged brucite-like layers. LDHs have shown high electrochemical
activity in energy conversion systems such as batteries and fuel cells.
In this study, we developed a hierarchically porous nanostructure
derived from zeolitic imidazolate framework-67, which was subsequently
transformed into an LDH structure with varying Ni concentrations. We
precisely controlled the Ni-to-Co ratio within the LDH structure and
investigated how different mole fractions of Co and Ni influence
catalytic activity and selectivity for the electrochemical urea
oxidation reaction (UOR). LDH structures with low Ni content (up to
40%) demonstrated high activity and selectivity for O 2
due to their structural instability and the predominant oxygen evolution
reaction (OER) originating from ZIF-67. In contrast, LDHs with high Ni
content (over 60%) supressed OER and exhibited enhanced activity for
UOR. The resulting hollow structure with an expanded electrochemically
active surface in LDHs with high Ni content could improve mass transport
and diffusion at the electrode interface, leading to better reaction
kinetics and higher current densities. These findings provide a
foundational design guideline for metal–organic framework-derived
nanostructure in UOR.