Layer-by-layer self assembled osmium polymer-mediated laccase oxygen cathodes for biofuel cells: The role of hydrogen peroxide.

P. SCODELLER; R. CARBALLO; R. SZAMOCKI; L. LEVIN; F. FORCHIASSIN; E.J. CALVO

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

AMER CHEMICAL SOC

Año: 2010 vol. 132 p. 11132 - 11140

0002-7863

High potential purified Trametes trogii laccase has been studied as biocatalyst for oxygen cathodes comprised of layer-by-layer self-assembled thin films by sequential immersion of mercaptopropanesulfonate modified Au electrode surfaces in solutions containing laccase and osmium-complex bound to poly (allylamine), (PAH-Os). The polycation backbone carries the Os redox relay and the polyanion is the enzyme adsorbed from a solution of a suitable pH so that the protein carries a net negative charge. Enzyme thin films were characterized by quartz crystal microbalance, ellipsometry, cyclic voltammetry and oxygen reduction electrocatalysis under variable oxygen partial pressure with rotating disc electrode. New kinetic evidence relevant to biofuel cells is presented on the detection of traces of H2O2, intermediate in the O2 reduction, with scanning electrochemical microscopy (SECM). Furthermore the inhibiting effect of peroxide on the biocatalytic current resulted in abnormal current dependence on the O2 partial pressure and peak shape with hysteresis in the polarization curves under stagnant conditions, which is offset upon stirring with the RDE. While fine control has been achieved over the film thickness, laccase and osmium surface concentrations with the layer-by-layer self-assembly technique, combination of the approximate analytical expressions with digital simulation to fit the data using the relaxation method and the simplex optimization algorithm to find best fit parameters allowed a complete kinetic analysis. The new kinetic evidence reported in the present work is very relevant for the operation of bio-fuel cells under stagnant conditions of O2 mass transport.