Electroreduction of O(2) 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 approximately 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 approximately 100 microA 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].