Improvement of Electrochemical Performance of Bilirubin Oxidase Modified Gas Diffusion Biocathode by Hydrophilic Binder

Abstract

Performance of bilirubin oxidase (BOD) modified gas diffusion biocathode has been highly improved by incorporating a hydrophilic polymer as binder to form effective Ketjen black (KB)-immobilized structure for the enzyme reaction on carbon paper electrode. An aqueous dispersion of styrene-butadiene rubber latex with sodium carboxymethylcellulose (SBR/CMC) was employed as hydrophilic binder. In direct electron transfer system, the biocathode with SBR/CMC binder exhibited larger O2 reduction current in phosphate buffer solution (PBS, pH 7.0) at room temperature, compared with that of a poly(vinylidine fluoride) binder electrode, which is a typical hydrophobic polymer. Performance of the biocathode was further improved by utilizing mediator electron transfer system, and the maximum current density of ∼27 mA cm−2 was achieved in pH 5.0 PBS. These improvements are believed to be due to hydrophilic property of the KB-immobilized electrode surface by the SBR/CMC binder, leading to high-dispersion of BOD on the surface and also stable interface formation of O2 gas / enzyme / electrolyte during the reaction. Furthermore, we fabricated a glucose/O2 cell composed of the biocathode and an opposite bioanode with glucose oxidase. The full-cell successfully achieved mW-class power density of 5.22 mW cm−2 with an open-circuit voltage of 0.61 V in pH 7.0 PBS.