Substrate oxidation enhances the electrochemical production of hydrogen peroxide

Hydrogen peroxide (H2O2) is electrochemically produced via oxygen (O2) reduction on a carbon cathode surface. In order to enhance the production of H2O2, anodic loss pathways, which significantly reduce the overall H2O2 production rate, should be inhibited. In this study, we investigate the effects of organic electron donors (i.e., typical chemical contaminants) on the anodic loss pathways of H2O2 in a single-cell electrochemical reactor that employs an anode composed of TiO2 over-coated on a mixed-metal oxide ohmic contact catalyst, Ir0.7Ta0.3O2, deposited on a Ti-metal that is coupled with a graphite rod cathode in a sodium sulfate (Na2SO4) electrolyte that is saturated with oxygen (O2). Organic electron donors are shown to enhance the electrochemical production of H2O2, while simultaneously undergoing oxidative degradation. The observed positive effect of organic electron donors on the electrochemical production of H2O2 is due in part to a preferential adsorption of organic substrates on the TiO2 outer layer of the anode. The sorption of the organic electron donors inhibits the formation of surficial titanium hydroperoxo species (Ti-OOH) on the anode surface. The organic sorbates also act as scavengers of surface-bound hydroxyl radical Ti-OH. As a result, the decomposition of H2O2 on the anode surface is significantly reduced. The cathodic production rate of H2O2 at low pH is enhanced due to proton coupled electron transfer (PCET) to O2, while the anodic decomposition of H2O2 is inhibited due to electrostatic interactions between negatively-charged organic substrates and a positively-charged outer surface of the anode (TiO2 pHzpc = 5.8) at low pH.