Methanol tolerance of a mediated, biocatalytic oxygen cathode

The methanol tolerance of a mediated enzymatic oxygen-reducing cathode employing the enzyme laccase from Coriolus hirsutus and two types of electron-mediating redox polymer hydrogels is evaluated and shown to be greater than that of a platinum electrode. In the 0–1 M methanol concentration range, the loss of current density at constant potential demonstrated by such electrodes is shown to depend on the ionic charge of the redox polymer backbone, which controls deswelling of the mediator hydrogel due to the inclusion of methanol as a solvent. This interpretation is confirmed by comparison of apparent diffusion coefficient and water uptake (via electrochemical quartz crystal microbalance) of a cationic and neutral redox hydrogel in the presence and absence of 1 M methanol. The reduced electron transport properties and increased deswelling observed in the cationic polymer due to the presence of methanol is related to counterion condensation with the polymer in the presence of solvent with reduced dielectric constant.