Scalable Hydrogen Peroxide Electrosynthesis and Electro-Fenton Pollutant Degradation Using Indium Single-Atom Catalysts

Abstract Electrochemical synthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e– ORR) offers a safer, decentralized alternative to the centralized anthraquinone process. However, achieving high current efficiency at industrially relevant current densities (>100 mA cm–2) remains a major challenge for practical deployment. While rotating ring-disk electrode (RRDE) measurements provide valuable information on intrinsic ORR characteristics and H2O2 selectivity under well-defined hydrodynamic conditions, bulk electrosynthesis measurements provide complementary information on the realized electrochemical response and H2O2 production under coupled catalyst–electrode–electrolyte and mass-transport conditions. Herein, we report the development of a robust indium-based single-atom catalyst supported on oxidized carbon black (In-CB(O) SAC) that exhibits high electrocatalytic activity in both batch and flow electrolyzers. The catalyst shows a high onset potential (∼0.83 V vs RHE) and a low Tafel slope, hallmarks of efficient 2e– ORR kinetics, underscoring strong promise for scalable H2O2 production. The optimal In-CB(O) SAC achieves H2O2 production rates of 4.97 mol gcat–1 h–1 at 100 mA cm–2 (67% current efficiency) in batch and 13.8 mol gcat–1 h–1 at 200 mA cm–2 (>90% current efficiency) in flow mode, demonstrating competitive performance among reported 2e– ORR catalysts. Sustained high performance for 50 h at 125 mA cm–2 demonstrates the catalyst’s excellent durability, overcoming common stability challenges in H2O2 electrosynthesis. Furthermore, the in situ generated H2O2 enables ∼94% degradation of the recalcitrant organic pollutant methylene blue within 15 min via an electro-Fenton process, with a 51% reduction in TOC further confirming substantial mineralization, demonstrating its dual utility in both sustainable chemical synthesis and environmental remediation.