Two-electron oxidation of water to form hydrogen peroxide initiated by one-electron oxidation of Tin (IV)-porphyrins

Abstract 5, 10, 15, 20-tetra(N-methylpyridinium-4’-yl)porphyrinate tin(IV) (SnTMPyP) was found to exhibit two-electron water oxidation to form hydrogen peroxide as a primary product initiated by electrochemical one-electron oxidation. Dioxygen was also formed by the further two-electron oxidation of hydrogen peroxide on the anode. Isotope labelling experiment using H218O and enzyme catalase that converts H2O2 into O2 revealed an incorporation of 18O into the oxidation products, indicating the two-electron oxidation of water in the electrolysis catalysed by SnTMPyP. The overpotential of forming H2O2 under the practical condition is 370 mV. The Faradaic yield of the water oxidation was almost quantitative both under the basic (pH 10.9) and the nearly neutral conditions (pH 8.5), though the reactivity was much higher under the basic condition.