Regulating nonmetallic species beyond the first coordination shell of single-atom catalysts for high-performance electrocatalysis

The local microenvironment of single-atom electrocatalysts (SACs) governs their activity and selectivity. While previous studies have focused on the first coordination shell (FCS) of metal centers, functional species beyond FCS (e.g., non-coordination heteroatom dopants, functional groups, intrinsic defects, and ligand vacancies) could affect or even dictate the electrocatalytic performance of SACs via long-range interaction with the metal atoms/adsorbates. This article aims to provide an overview of the latest advances in regulating nonmetallic species beyond FCS (NSBF) of SACs. The article begins by defining NSBF based on their distance from the metal atom. It then discusses various strategies for constructing NSBF in carbon, metal-organic frameworks, covalent organic frameworks, and immobilized molecular catalyst-based SACs. A characterization protocol was further built. The article goes on to analyze the promotional effect of NSBF in terms of a remote electronic induction effect, serving as an active site, steric effect, synergistic adsorption effect, conductivity enhancement, and stability improvement. The following section highlights the structure-activity correlation for oxygen reduction/evolution, carbon dioxide reduction, and other electrocatalytic reactions. In situ characterization for NSBF involving dynamic evolution is summarized. Finally, perspectives on precise synthesis, direct characterization, model construction, dynamic variation studies, and broader applications of NSBF are provided.