Tuning Two-Electron Oxygen-Reduction Pathways for H2O2 Electrosynthesis via Engineering Atomically Dispersed Single Metal Site Catalysts

The hydrogen peroxide (H2O2) generation via the electrochemical oxygen reduction reaction (ORR) under ambient conditions is emerging as an alternative and green strategy to the traditional energy-intensive anthraquinone process and unsafe direct synthesis using H-2 and O-2. It enables on-site and decentralized H2O2 production using air and renewable electricity for various applications. Currently, atomically dispersed single metal site catalysts have emerged as the most promising platinum group metal (PGM)-free electrocatalysts for the ORR. Further tuning their central metal sites, coordination environments, and local structures can be highly active and selective for H2O2 production via the 2e(-) ORR. Herein, recent methodologies and achievements on developing single metal site catalysts for selective O-2 to H2O2 reduction are summarized. Combined with theoretical computation and advanced characterization, a structure-property correlation to guide rational catalyst design with a favorable 2e(-) ORR process is aimed to provide. Due to the oxidative nature of H2O2 and the derived free radicals, catalyst stability and effective solutions to improve catalyst tolerance to H2O2 are emphasized. Transferring intrinsic catalyst properties to electrode performance for viable applications always remains a grand challenge. The key performance metrics and knowledge during the electrolyzer development are, therefore, highlighted.