Kinetics and Mechanism of Heterogeneous Water Oxidation by α-Mn2O3 Sintered on an FTO Electrode

Kinetic studies of heterogeneous water oxidation by an alpha-Mn2O3/FTO electrocatalyst in nonaqueous (CH3CN/0.1 M n-Bu4NPF6 and DMF/0.1 M n-Bu4NPF6) and aqueous 0.1 M KPi (pH 7.0) solutions showed that the rate of water oxidation is first order in catalyst concentration and in H2O concentration. The square wave and cyclic voltammetry measurements reveal the stepwise proton-coupled electron transfer (PCET) oxidations of the active Mn-II-OH2 site to Mn-III-OH and then to Mn-IV=O and finally an electron transfer oxidation of Mn-IV=O to Mn-V=O species. The Mn-V=O species undergoes a rate-limiting O atom transfer to H2O to give a Mn-III-OOH2 species that, in turn, undergoes further oxidations to release O-2.