Modelling of Reaction and Diffusion Processes in a High-surface-area Biofuel Cell Electrode Made of Redox Polymer-grafted Carbon

A mathematical model considering reaction and diffusion processes in biofuel cells, such as enzyme reactions, apparent electron diffusion in the redox polymer, and diffusion of a substrate in a redox polymer film, verified the effectiveness of a high-surface-area biofuel cell electrode with a thin, grafted redox polymer layer. The model calculation shows that the rate-limiting step of apparent electron diffusion can be overcome by using the electrode with a thin redox polymer, even when the redox polymer used has a low apparent electron diffusion coefficient. In the electrode, increase in the second-order rate constant for the reaction between an enzyme and a mediator above a certain value does not increase the current density, and thus the mediator used in the electrode should have an adequate second-order rate constant and a more negative redox potential. In addition, increase in the turnover rate of the enzyme and the surface coverage of the enzyme allows an increase in the current density; the surface coverage of the enzyme has the most influence. Based on these calculations, it is important to realise high-surface-area electrodes with a thin redox polymer, and with high enzyme loading.