Ion effects in water oxidation to hydrogen peroxide

Abstract

We investigate the effect of pH, potential and electrolyte ions in the electrochemical oxidation of water to produce hydrogen peroxide. This process has the potential to provide a low energy-cost route to the generation of hydrogen peroxide, either for in situ use as a “green” oxidant or as part of a water splitting process for the generation of oxygen and hydrogen. Electrodeposited manganese oxide films were used as the working electrode along with aqueous solutions of various ammonium-based cations as the electrolyte. Oxidation of water was carried out at potentials as low as 0.6 V vs. Ag/AgCl at pH 10. Hydrogen peroxide production was found to be highly sensitive to pH, only occurring above pH 9.5, in solutions where the pH had been adjusted by the addition of excess amine. Highly efficient, approaching 100% Faradaic efficiency, production of hydrogen peroxide was observed the range pH 10–10.5. Faradaic efficiency of hydrogen peroxide formation decreased at applied potentials higher than 1 V vs. Ag/AgCl where direct, or further, oxidation to oxygen begins to dominate. Investigation of a number of alkylammonium cations and alkyl sulphate anions of different alkyl chain length indicated that the optimum system is butylammonium sulphate at concentrations around 1 M.