Homogeneous Photochemical Water Oxidation with Cobalt Chloride in Acidic Media

The precise mechanisms of four-electron-transfer water oxidation processes remain to be further understood. Oxide-based precipitation from molecular catalysts as a frequent observation during water oxidation has raised extensive debates on the differentiation between homogeneous and heterogeneous catalysis. Although soluble cobalt salts are known to be active in water oxidation, CoOx species formed in situ were generally considered to be the true catalyst. Here we report on the possibility homogeneous water oxidation with cobalt chloride in acidic conditions, which prevent CoOx precipitation. Interestingly, both the buffer media and counteranions were found to significantly influence the oxygen evolution activity, and their roles in the water oxidation process were analyzed with various techniques. This study sheds new light on Co2+ ions in key transformation processes of homogeneous water oxidation catalysts.