Air diffusion biocathode with CueO as electrocatalyst adsorbed on carbon particle-modified electrodes.

The current density of biofuel cells which use dissolved O(2) as electron acceptor is limited by O(2) supply to the electrode surface due to the low solubility and small diffusion coefficient of O(2) in the electrolyte solution. In order to increase the current density, we constructed an air diffusion biocathode which uses O(2) directly from the air. As cathodic biocatalyst, we utilized CueO from Escherichia coli, which belongs to the family of multi-copper oxidases. O(2) reduction was catalyzed by CueO adsorbed on Ketjen black-modified carbon paper electrodes. The hydrophobic electrode surface was obtained by optimizing the weight ratio of polytetrafluoroethylene binder to Ketjen black. The current density of O(2) reduction reached values as high as 20 mA cm(-2) at 0 V vs. Ag|AgCl, KCl(sat.) in a citrate buffer (1.0 M, pH 5.0, 25 degrees C).