Bioelectrocatalysis is an expanding research area due to the use of this type of electrocatalysis in electrochemical biosensors, biofuel cells, bioelectrochemical cells, and biosolar cells. This feature article discusses recent advancements in tailoring the biointerface between electrodes and biocatalysts for facile electrocatalysis. This includes the design of pyrene moieties for directing the orientation of biocatalysts on electrode surfaces and mediation as well as the rational design of redox polymers for self-exchange-based electron transport to/from biocatalysts and the electrode and the use of bioscaffolding techniques for designing the bioelectrode structure. However, recent advances in the past decade have shown the importance of hybrid bioelectrocatalytic systems, and future work will be needed to use these same pyrene, redox polymer, and bioscaffolding techniques for hybrid bioelectrocatalysis.

Small implantable electronic devices require biologically compatible energy sources that are capable of delivering quick high-energy pulses. Combining batteries and supercapacitors allows for high power and energy density while providing both small size and biocompatibility. Here, we report a hybrid supercapacitor/biobattery whereby an oxygen-reducing cathode of bilirubin oxidase immobilized with anthracene-modified carbon nanotubes and tetrabutylammonium bromide-modified Nafion is coupled with a glucose bioanode of flavin adenine dinucleotide-dependent glucose dehydrogenase. The redox polymer, dimethylferrocene-modified linear poly­(ethylenimine), used at the bioanode simultaneously immobilizes enzyme, mediates electron transfer, and acts as a pseudocapacitor where capacitance of the anode scales with increased polymer loading. Both multiwalled carbon nanotubes and carbon felt incorporated into the anode construction improve polymer conductivity, subsequently resulting in further improved anodic capacitance. A supercapacitor/biobattery device of the above configuration results in a specific capacitance of 300 ± 100 F/g, which is over 4 times higher than that of other reported biologically derived supercapacitors.

and Matt Lovander for their friendship and support. I thank the University of Iowa Department of Chemistry and the National Science Foundation for …nancial support. I am thankful to my family, my parents, Randy and Becky Knoche, my sister Jennifer Knoche, and my brother Travis Knoche, for their love and inspiration through the years. I thank my college roommate Aidan Leddy for her awesome friendship and my love Shuvra Gupta for his inspiration and amazing con…dence in me.

Quantitative characterization of uniform density, electrochemically inert films on electrodes is achieved by cyclic voltammetry (CV) of a redox probe that partitions from electrolyte into the film. Electrochemically inert films generate no faradaic current in the voltammetric window of the probe. In simulation models, probes pre-equilibrate into films, electrolyze at electrodes, diffuse in film and solution, and extract across film solution interfaces. Film thickness is ℓ. Diffusion length δ approximates distance from the electrode where voltammetry perturbs probe concentration; δ∝ν− 1/2 for scan rate ν. At high ν, δ < ℓ and voltammetric morphologies are typical of semi-infinite linear diffusion. As ν slows, δ ≳ ℓ and CV morphologies can change with relative probe flux in the film and solution. For higher solution flux, voltammograms assume sigmoidal (S-shaped) characteristics; higher film flux generates gaussian (thin layer CV) characteristics. For film and solution diffusion coefficients Df and Ds and κ the equilibrium ratio of probe concentration in film to solution, diagnostics yield κ√(Df/Ds) and ℓ2/Df. Because diagnostics apply for all ν, films are fully parameterized by CV alone. Without these diagnostics, full characterization requires a second, steady state voltammetric measurement. Diagnostics are vetted with [Ru(bpy)3]2 + (probe) in inert polymer films of Nafion and of poly(styrenesulfonate).

No abstract