Electroreduction of O2 to water at 0.6 V (SHE) at pH 7 on the 'wired' Pleurotus ostreatus laccase cathode

O-2 was electroreduced to water at 0.6 V (SHE) near neutral pH on the 'wired' Pleurotus ostreatus laccase cathode. We previously reported high-current density (5 mA cm(-2)), four-electron electroreduction of O-2 to water on a 'wired' Coriolus hirsutus laccase electrode at +0.7 V (SHE) in pH 5 in citrate buffer. Since the enzyme was inhibited by chloride and because its activity declined steeply when the pH was raised to neutral, the rate of O-2 electroreduction in a physiological buffer solution was only similar to 1% of that at pH 5 in absence of chloride. Here we show that substitution of the C hirsutus laccase by laccase from P. ostreatus allows the upward extension of the pH range of O-2 electroreduction. The current density of the electrode made with laccase from P. ostreatus in pH 7 citrate buffer was similar to 100 muA cm-2 and at pH 7 and in phosphate buffered NaCl (PBS, 20 mM phosphate, 0.1 M NaCl) it still retained 6% of its maximal (1 mA cm(-2)) current density at pH 5 in citrate buffer. The electrocatalyst consisted of the crosslinked P. ostreatus laccase and the electron conducting redox polymer PVI-Os(dmebpy)(tpy)(2+/3+) [PVI = poly(N-vinyl imidazole) with about 1/5th of the rings complexed with (Os-dmebpy-tpy)(2+/3+); dmebpy = 4,4'-dimethyl-2,2'-bipyridine; tpy = 2,2 6 2 -terpyridine]. (C) 2002 Elsevier Science B.V. All rights reserved.