Attainment of high power density in biocatalyzed fuel cells will require careful attention to electrode design. Enzyme electrocatalysts immobilized on high-surface-area porous supports can achieve high utilization and current density, as long as (1) the microscopic surface area is large, (2) the enzyme interacts with the surface in an way that is conducive to both activity and stability, and (3) transport of electrons and reactants is facilitated adequately.

This talk will review the many approaches to achieving these conditions that appear the literature, and will discuss our own efforts to create high-current density enzyme electrodes. We have designed a multi-scale carbon material that can be used to efficiently support and achieve electrical contact with enzymes. The material is produced by growing carbon nanotubes on carbon fibers using chemical vapor deposition (CVD). With this technique, an increase of more than two orders of magnitude in the surface area available for enzyme immobilization was obtained, resulting in a ten-fold increase in achievable current density using a glucose oxidase-catalyzed glucose electrode.

We have modelled this electrode as supported electrode using a macrohomogeneous approach that considers an active, high surface area film supported on cylindrical carbon fibers. Electrode morphology and biocatalytic film volume are known, and bi-bi ping-pong enzyme kinetics are assumed. We will discuss the use of such a model to study catalyst distribution and predict performance of the multiscale biocatlyzed electrode.