MOF-Derived Single-Atom and Nanocluster Electrocatalysts: Classification, Synthesis, and Active-Site Modulation

Single-atom–nanocluster (SA–NC) architectures combine atomically dispersed metal sites and nanoscale ensembles, leveraging high utilization, defined coordination, cooperative adsorption, and tunable electronics to generate synergy via spatial, electronic, and intermediate-transfer pathways. Metal–organic framework (MOF)-derived materials with ordered metal nodes and structural diversity enable regulating these active centers from atomic to nanometer scales. This review systematically summarizes recent advances in MOF-derived electrocatalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) from the perspectives of material classification, controllable synthesis, and active-site engineering. We highlight the coordination and electronic structure modulation of single-atom sites, the nuclearity control and interfacial effects of nanoclusters, and the synergistic mechanisms in SA–NC, which are categorized into adjacent, discrete, and core–shell configurations. We further discuss how spatial arrangement, electronic communication, and intermediate spillover collectively govern catalytic performance. Despite significant advances, a major challenge remains in correlating dynamically evolving active species under operating conditions with their intrinsic catalytic behavior. Future progress requires the integration of operando characterization and theoretical modeling to establish quantitative structure–activity relationships, thereby shifting catalyst design from composition-based optimization toward interaction engineering among multiscale active centers.