Covalent Functionalization Strategies for Tailoring the Outer-Sphere Microenvironments of Single-Atom Catalysts...

The design of single-atom catalysts (SACs) with high activity, selectivity, and stability relies on careful modulation of the active sites. The active-site structures of natural metalloenzymes provide blueprints for designing artificial catalysts. Spatially folded proteins surround the central atom, providing fascinating second spheres to optimize the microenvironments of metal sites and thereby influencing their catalytic properties. Inspired by the functions of metalloenzymes, this minireview focuses on optimizing the outer-sphere microenvironment of SACs on carbon materials via covalent functionalization strategies. The article begins by outlining the advantages and inherent challenges of SACs, then highlights the pivotal role of microenvironment engineering in natural metalloenzymes in enhancing catalytic performance. Then, the unique merits of SACs supported on carbon materials toward surface modulation are presented. Building on these insights, the covalent functionalization strategies for carbon-supported SACs are comprehensively elaborated. Furthermore, by leveraging recent examples of bioinspired photo- and electrocatalysts, the modulation mechanisms of the outer-sphere microenvironment in SACs are explored in depth. Finally, this work summarizes recent advances and remaining challenges in this field, critically discusses current limitations, and proposes perspectives to guide the development of advanced covalently modified SACs.