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

Water electro-oxidation to form H₂O₂ is an important way to produce H₂O₂ which is widely applied in industry. However, its mechanism is under debate and HO_(ads), hydroxyl group adsorbed onto the surface of the electrode, is regarded as an important intermediate. Herein, we study the mechanism of water oxidation to H₂O₂ at Pt electrode using in-situ Raman spectroscopy and differential electrochemical mass spectroscopy and find peroxide bond mainly originated from the coupling of two CO₃^2- via a C₂O₆^2- intermediate. By quantifying the ¹⁸O isotope in the product, we find that 93% of H₂O₂ was formed via the CO₃^2- coupling route and 7% of H₂O₂ is from OH_(ads)-CO₃^•- route. The OH_(ads)-OH_(ads) coupling route has a negligible contribution. The comparison of various electrodes shows that the strong adsorption of CO_3(ads) at the electrode surface is essential. Combining with a commercial cathode catalyst to produce H₂O₂ during oxygen reduction, we assemble a flow cell in which the cathode and anode simultaneously produce H₂O₂. It shows a Faradaic efficiency of 150% of H₂O₂ at 1 A cm^-2 with a cell voltage of 2.3 V.