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

Water electro-oxidation to form H 2 O 2 is an important way to produce H 2 O 2 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 H 2 O 2 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 3 2- via a C 2 O 6 2- intermediate. By quantifying the 18 O isotope in the product, we find that 93% of H 2 O 2 was formed via the CO 3 2- coupling route and 7% of H 2 O 2 is from OH (ads) -CO 3 •− 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 H 2 O 2 during oxygen reduction, we assemble a flow cell in which the cathode and anode simultaneously produce H 2 O 2 . It shows a Faradaic efficiency of 150% of H 2 O 2 at 1 A cm −2 with a cell voltage of 2.3 V.