Recent advances in electrochemical water oxidation to produce hydrogen peroxide: A mechanistic perspective

Electrochemical production of hydrogen peroxide (H2O2) has recently gained traction as a green alternative to the unsustainable anthraquinone auto-oxidation process and the high-risk direct synthesis route. While the two-electron oxygen reduction reaction (2e- ORR) toward H2O2 has been covered extensively in the literature, the unorthodox two-electron water oxidation reaction (2e- WOR) remains far less popular, due to the thermodynamic unfavorability of the pathway. Nonetheless, the 2e- WOR constitutes a coveted procedure as it enables the electro-generation of H2O2 solely from water. A thorough understanding of the reaction mechanism, including all intermediates and competing reaction routes, is essential for the fabrication of electrocatalysts, and assembly of electrochemical reactors, capable of greater H2O2 production rates with an optimal efficiency. This review focuses exclusively on the 2e- WOR to electrochemically produce H2O2. A summary of all prevailing water oxidation mechanisms is presented, supported with computational and experimental data, and key challenges and limitations that require attention are addressed.