3.2 Batteries and Energy Storage
Batteries produce current via chemical reactions on the surface of electrodes, which is limited by the available surface area [3]. To generate the currents needed to power modern electronic devices, metal coated TMV virions can be vertically oriented on top of a gold substrate to form a carpet-like nanoforest structure (Figure 2). The vertical attachment is achieved by introducing a cysteine residue at the amino terminus of CP to produce TMV1cys virions [3, 6]. Most cysteines in TMV are partially recessed and thus are incapable of metal binding; however, the N-terminal residue is fully exposed allowing for near-vertical assembly of the biotemplate on a gold substrate via covalent interactions between the gold and the thiol group of the cysteine. Subsequent coating with nickel and/or cobalt increases the active electrode surface area more than ten-fold with a doubling in electrode discharge capacity (or current generation) [3]. Similarly, Pd/Ni/Si-coated TMV anodes in lithium ion batteries can increase the discharge capacity by nearly ten-fold compared to then available graphite anodes [6]. Finally, incorporating TMV in sodium-ion batteries as a carbon/tin/nickel-coated TMV anode can increase battery cycling lifespan with little degradation in charge capacity over 150 deep charging cycles. This capability made it the longest-cycling nano-Sn anode material for Na-ion batteries at the time [27]. Coated TMV patterned with a similar nanoforest structure has also been shown to increase the performance of micro supercapacitors (Figure 2), which also rely on surface area to store charges [57].