Single-Atom Metal-Based Electrocatalysts (Fe, Ni, and Co) for CO2-to-CO Conversion: A Comprehensive Review

The electrocatalytic carbon dioxide reduction reaction (eCO2RR) presents a promising route for sustainable carbon conversion, enabling the production of valuable chemical feedstocks while mitigating CO2 emissions. Among various electrocatalysts, single-atom catalysts (SACs) have emerged as highly efficient candidates for CO2-to-CO conversion due to their well-defined active sites, high atom utilization, and remarkable selectivity. However, the practical implementation of the eCO2RR remains hindered by several challenges, including low selectivity, insufficient current densities, and the high cost of catalytic materials. The reaction kinetics are primarily limited by the proton-coupled electron transfer (PCET) process, which involves multiple electron–proton transfers (ranging from 2 to 12 PCET steps) to generate a variety of valuable products. Notably, the two-electron proton transfer pathway yielding CO is of particular interest for syngas production, a key intermediate in industrial chemical synthesis. In this perspective, we provide a comprehensive overview of SACs for eCO2RR to CO, covering their synthesis methods, advanced characterization techniques, electrochemical setups, and catalytic performance. By systematically compiling and analyzing reported SACs for CO2-to-CO conversion, this study aims to offer valuable insights into the structure–activity relationships governing their catalytic behavior, thereby guiding future research toward the development of highly efficient and scalable electrocatalytic systems. Furthermore, we provide forward-looking perspectives on emerging strategies, including dynamic coordination environments, dual-atom synergy, machine-learning-guided catalyst design, and in situ/operando techniques to accelerate innovation in CO2 electroreduction.