Recent advances in the rational design of single-atom catalysts for electrochemical CO₂ reduction

Electrochemical CO₂ reduction (CO₂R) represents a sustainable way to store intermittent renewable energies and produce carbon-neutral fuels, yet the energy efficiency remains a huge bottleneck owning to its sluggish kinetics and complex reaction pathways. Highly active, selective, and robust electrocatalysts are strongly demanded to accelerate CO₂ conversion and deploy this technology to practical applications. In this review, we focus on single-atom catalysts (SACs), a unique category of electrocatalysts with atomically dispersed metal active sites, which have shown distinctive performances in CO₂R and offer an ideal platform for in-depth mechanistic studies at the atomic level. Despite various SACs with attractive CO₂R performances have been reported, the relationship between electronic/geometric structure of SACs and the corresponding electrocatalytic performance still needs to be discussed with caution. Here we take a broad overview on the recent progress in understanding the structure–function correlation of SACs in CO₂R, with the purpose of providing deep insights and guiding the future rational design of SACs. First, we provide the fundamental understandings of CO₂R on SACs, following different reaction pathways. Then, we describe the progresses in the development of well-defined SACs and the mechanistic studies on the influences from particular structural parameters, such as first-shell and second-sphere coordination, conductive supports and interface with a secondary catalyst. Finally, some perspectives are highlighted on the path towards efficient CO₂R on SACs.