Beyond active sites: single-atom promoters for advanced electrocatalysis

Single-atom promoters (SAPs) represent an emerging class of atomic-scale modifiers in electrocatalysis, where isolated metal atoms are strategically designed to enhance the performance of host catalysts, rather than act as primary active sites as in single-atom catalysts (SACs). This distinct role addresses a key limitation of traditional catalyst optimization, which often improves catalytic performance at the expense of active site availability. SAPs enable precise performance tuning through electronic, structural, and relay effects while preserving the integrity of active centers. This review provides a comprehensive analysis of SAP-modified catalyst systems, beginning with a fundamental distinction from SACs, a detailed discussion of their promotion mechanisms, and a classification into all-in-one and combined types based on the spatial configuration. We further summarize key design principles, synthesis strategies, and advanced characterization techniques for developing SAP-modified catalysts, and highlight their power in important electrocatalytic reactions such as hydrogen evolution/oxidation, oxygen evolution/reduction, CO₂ reduction, and biomass conversion. Finally, we outline the challenges and future opportunities in the rational catalyst design, mechanism study under operating conditions, and scalable synthesis of SAP-based catalysts. This review aims to guide the development of high-performance electrocatalysts for efficient energy conversion technologies.