Carbon electrodes for direct electron transfer type laccase cathodes investigated by current density-cathode potential behavior.

Direct electron transfer from carbon electrodes to adsorbed laccase (EC 1.10.3.2) from Trametes versicolor is widely used to enable mediatorless enzymatic biofuel cell cathodes. However, data published so far are poorly comparable in terms of oxygen reduction performance. We thus present a comparative characterization of carbon-based electrode materials as cathode in half-cell configuration, employing adsorbed laccase as oxygen reduction catalyst. Open circuit potentials and performances were significantly increased by laccase adsorption, indicating the occurrence of direct electron transfer. At a potential of 0.5 V vs. SCE volume-normalized current densities of approximately 10, 37, 40, 70, and 77 μA cm(-3) were measured for cathodes nanotubes, carbon nanofibers and multi-walled carbon nanotubes, respectively. In addition, we could show that both, carbon nanotubes and porous carbon tubes exhibit dramatically lower current densities compared to graphite felt and carbon nanofibers when normalized to BET surface instead of electrode volume. Further work will be required to clarify whether this stems from material-dependent interaction of enzyme and electrode surface or constricted enzyme adsorption due to agglomeration of the nanotubes. In case of the latter, an improved dispersion of the nanotubes upon electrode fabrication may greatly enhance their performance.