Synergistic Catalysis of Metal Single Atoms and Clusters: Structural-Electronic Modulation of Catalytic Mechanisms and Applications.

Metal single-atom/cluster synergistic catalysts integrate the well-defined coordination of isolated atoms with the ensemble effects and electronic delocalization of clusters, creating a versatile platform for complex catalytic transformations. This perspective establishes a coupled structural-electronic framework linking atom-cluster interactions to catalytic behavior. Structural regulation of atom-cluster proximity, coordination environment, cluster nuclearity, and active-site density determines the spatial organization and local bonding of active species. Electronic regulation through charge redistribution, orbital hybridization, spin-state modulation, and hydrogen-bond-network reorganization further governs intermediate adsorption, molecular activation, proton-transfer kinetics, and reaction pathways. Application of this framework to oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), nitrogen reduction reaction (NRR), electrocatalytic hydrodechlorination (EHDC), hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and related systems clarifies reaction-specific links among atom-cluster structures, electronic responses, key intermediates, and catalytic pathways. We further argue that major challenges lie in resolving catalytically relevant atom-cluster structures under operating conditions and quantitatively establishing synergy rather than inferring it from performance enhancement alone. Future progress therefore requires operando characterization of working-state structures, quantitative descriptors of synergy, and precise control over cluster nuclearity, atom-cluster proximity, and interfacial bonding for rational catalyst design.