Spin-State Engineering for Multi-Electron Reactions: Active Sites and Reaction Mechanisms

Abstract Multi-electron-proton coupling reactions are fundamental in renewable energy conversion and environmental cleanup. However, achieving high catalytic efficiency and product selectivity remains a formidable challenge, primarily due to the complex transformations of intermediates, sluggish reaction kinetics, and intense competition from side reactions. In recent years, spin regulation has emerged as a crucial strategy to address these issues. By engineering spin states and controlling spin polarization, the electronic structure of catalysts can be effectively reconfigured, thereby optimizing the adsorption and desorption of intermediates and regulating charge transport and reaction pathways. This review comprehensively summarizes recent progress in spin-regulation strategies for key multi-electron reactions, including CO2RR, NRR/NO3RR, ORR, and water-splitting catalysis involving OER and HER, and further examines the roles of structural identity and reaction-dependent spin-electronic configurations in governing active-site function. We emphasize that different local spin configurations can each enhance catalytic performance under appropriate reaction conditions, whereas no single spin state can be regarded as universally superior. Accordingly, identification of the operative active site requires consideration of both its structural identity and its reaction-dependent spin-electronic state under working conditions. Within this framework, special attention is given to the roles of doping, defect engineering, coordination modulation, external fields, and multimetallic cooperation in regulating active-site identity, intermediate energetics, charge transfer, and product selectivity. Finally, we discuss current challenges and future directions for identifying operative active sites and establishing predictive design principles for efficient multi-electron catalysis. Overall, this review provides mechanistic insights and practical guidance for identifying operative spin-regulated active sites and rationally designing efficient and selective catalysts for multi-electron reactions.