Water Oxidation to Hydrogen Peroxide on Carbonaceous Materials

Hydrogen peroxide (H 2 O 2 ) is one of the most important chemicals used in the chemical industry. It has been widely utilized in pulp and paper manufacturing, chemical synthesis, wastewater management, and disinfection. 1 The primary industrial approach to producing H 2 O 2 is via the fossil-based anthraquinone process - an energy-demanding multi-step process requiring high-cost catalysts and generating substantial volumes of waste. Another route to the classic anthraquinone process is the electrochemical production of H 2 O 2 from oxygen (O 2 ) and water (H 2 O). This electrochemical route based on renewable energy is an appealing “green” alternative. Our research group has been extensively working on the electrochemical production of H 2 O 2 through anodic water oxidation using various electrode materials, including metal oxides, commercial carbon materials, and boron-doped diamond (BDD). Besides the electrode material, a suitable electrolyte is equally essential to achieve high H 2 O 2 concentrations and production rates. The role of carbonate ions (HCO 3 - and CO 3 2- ) for producing H 2 O 2 has been investigated using commercial carbon fiber paper (CFP). The electrolyte pH was correlated with the activity of CO 3 2- ions in enhancing H 2 O 2 production. Thereby, a cyclic mechanism of H 2 O 2 generation involving the oxidation of CO 3 2- ions to peroxodicarbonate (C 2 O 6 2- ) species has been proposed. 2 The role of the CO 3 2- ions in enhancing the anodic H 2 O 2 production was further studied in a continuous flow reactor using BDD anodes. The flow rate and setup configuration for 2e - water oxidation to H 2 O 2 have been optimized at current densities up to 700 mA cm -2 , with an impressive H 2 O 2 production rate and faradaic efficiency. Additionally, the role of a chemical stabilizer in avoiding the H 2 O 2 decomposition in the flow system has been addressed. The importance of electrolyte composition, pH, operating parameters, and cell setup to enhance the production of H 2 O 2 at the anode was shown. Finally, outstanding H 2 O 2 yields were obtained in continuous flow for at least 30 hours. References Perry, S. C.; Pangotra, D.; Vieira, L.; Csepei, L.-I.; Sieber, V.; Wang, L.; Ponce de León, C.; Walsh, F. C., Electrochemical synthesis of hydrogen peroxide from water and oxygen. Nat. Rev. Chem. 2019, 3 (7), 442-458. Pangotra, D.; Csepei, L.-I.; Roth, A.; Ponce de León, C.; Sieber, V.; Vieira, L., Anodic production of hydrogen peroxide using commercial carbon materials. Appl. Catal. B Environ. 2022, 303 , 120848.