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

O2 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 O2 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 O2 electroreduction in a physiological buffer solution was only ∼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 O2 electroreduction. The current density of the electrode made with laccase from P. ostreatus in pH 7 citrate buffer was ∼100 μA 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]. [Copyright &y& Elsevier]