Bioelectrocatalytic Oxygen Reduction by Laccase Immobilized on Various Carbon Carriers

Laccase is an enzyme that is used for fabricating cathodes of biofuel cells. Many studies have been aimed at searching the ways for enhancing specific electrochemical characteristics of cathode with the laccase- based catalyst. The electroreduction of oxygen on the electrode with immobilized laccase proceeds under the conditions of direct electron transfer between the electrode and active enzyme center. In this work, the effect of oxygen partial pressure on the electrocatalytic activity of laccase is studied. It is shown that, at the concentrations of oxygen dissolved in the electrolyte higher than 0.28 mM, the process is controlled by the kinetics of the formation of laccase-oxygen complex, whereas at lower concentrations and a polarization higher than 0.3 V, the process is limited by the oxygen diffusion. A wide range of carbon materials are studied as the carriers for laccase immobilization: carbon black and nanotubes with various BET specific surface areas. The conditions, which provide the highest surface coverage of carbon material with enzyme in the course of spontaneous adsorptive immobilization and the highest specific characteristics when using a "floating" electrode simulating a gas-diffusion electrode, are determined: 0.2 M phosphate-acetate buffer solution; oxygen atmosphere; the carrier material (nanotubes with a BET surface area of 210 m(2)/g and a mesopore volume of 3.8 cm(3)/g); and the composition of active mass on the electrode (50 wt % of carbon material + 50 wt % of hydrophobized carbon black).