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].