Design Principles of Single-Atom Catalysts for Electrocatalytic CO2 Reduction to High-Value Hydrocarbons.

The CO2 electrochemical reduction (CO2RR) is regarded as a promising approach to mitigate carbon emissions while producing valuable chemical feedstocks and fuels. Among the possible products, multi-carbon (C2+) compounds such as ethylene and ethanol are highly desirable due to their higher energy density and industrial relevance. Recently, single-atom catalysts (SACs) have emerged as a powerful class of electrocatalysts in CO2RR, offering high atomic efficiency and tunable active sites. However, challenges such as sluggish C─C coupling kinetics, dynamic evolution of the catalytic sites, limited understanding of reaction mechanism, and difficulties at controlling product selectivity hinder their further development for large-scale application. Hence, this review explores the underlying mechanisms for CO2 to C2+ product conversion, emphasizing catalyst design strategies to enhance C─C coupling efficiency and selectivity. Furthermore, recent advances in in situ characterization techniques that provide atomic-level insights into reaction intermediates and active site evolution are discussed. Finally, the potential of machine learning approaches in accelerating catalysts discovery by optimizing SACs structures, identifying key design parameters, and predicting catalytic performance is highlighted. Overall, this study aims to provide a comprehensive reference for the rational design of SACs for effective and selective CO2 conversion into C2 products.