Influence of Mediator Redox Potential on Fuel Sensitivity of Mediated Laccase Oxygen Reduction Electrodes.

The impact of methanol on oxygen reduction activity is studied using a mediated biocathode catalyzed by laccase from Trametes versicolor. The sensitivity of oxygen reduction current density to the presence of methanol at such electrodes depends strongly on mediator redox potential. This study demonstrates that the selectivity of laccase cathodes toward oxygen reduction can allow methanol feed concentration up to 5 M in direct methanol fuel cells. Within the 0-5 M concentration range, methanol primarily affects enzyme kinetics and not the electron transport via the mediator. For methanol concentrations of 0-2.5 M, laccase activity toward oxygen was largely maintained; approximately 30% loss of activity occurred in the 2.5-5 M range, and irreversible loss of enzyme activity was observed beyond 7.5 M. The presence of methanol primarily decreases the turnover number of the enzyme rather than altering substrate binding, suggesting a noncompetitive inhibition mechanism. It is proposed that this reduction occurs due to changes in the electron transfer environment near the T1 binding pocket due to the presence of methanol. [ABSTRACT FROM AUTHOR]