Identifying MnVII-oxo Species during Electrochemical Water Oxidation by Manganese Oxide

Abstract

Identifying surface active intermediate species is essential to reveal the catalytic mechanism of water oxidation by metal-oxides-based catalysts and to develop more efficient catalysts for oxygen-oxygen bond formation. Here we report, through electrochemical methods and ex situ infrared spectroscopy, the identification of a Mn^VII = O intermediate during catalytic water oxidation by a c-disordered δ-MnO_x with an onset-potential-dependent reduction peak at 0.93 V and an infrared peak at 912 cm^-1. This intermediate is proved to be highly reactive and much more oxidative than permanganate ion. Therefore, we propose a new catalytic mechanism for water oxidation catalyzed by Mn oxides, with involvement of the Mn^VII = O intermediate in a resting state and the Mn^IV-O-Mn^VII = O as a real active species for oxygen-oxygen bond formation.