Carbonate-carbonate coupling on platinum surface promotes electrochemical water oxidation to hydrogen peroxide.

Water electro-oxidation to form HO is an important way to produce HO which is widely applied in industry. However, its mechanism is under debate and HO, hydroxyl group adsorbed onto the surface of the electrode, is regarded as an important intermediate. Herein, we study the mechanism of water oxidation to HO at Pt electrode using in-situ Raman spectroscopy and differential electrochemical mass spectroscopy and find peroxide bond mainly originated from the coupling of two CO via a CO intermediate. By quantifying the O isotope in the product, we find that 93% of HO was formed via the CO coupling route and 7% of HO is from OH-CO route. The OH-OH coupling route has a negligible contribution. The comparison of various electrodes shows that the strong adsorption of CO at the electrode surface is essential. Combining with a commercial cathode catalyst to produce HO during oxygen reduction, we assemble a flow cell in which the cathode and anode simultaneously produce HO. It shows a Faradaic efficiency of 150% of HO at 1 A cm with a cell voltage of 2.3 V.