Design of CO<sub>2</sub> Reduction Electrocatalysts Based on Metal Active Center Structures: From Single-atom Sites to Nanomaterials

The catalytic activities and product selectivities of the electrochemical CO2 reduction reaction (CO2RR) are strongly influenced by the atomic-scale structure of the metal active centers in the catalysts. This review discusses recent progress in CO2RR catalysts, from atomically dispersed single-atom catalysts to inorganic nanomaterials. These materials are categorized into three classes: (i) single-atom catalysts featuring high atomic utilization and unique adsorption properties of the reaction intermediates, (ii) Cu-based nanomaterials exhibiting specific catalytic activity and product selectivity, and (iii) intermetallic compounds with ordered crystal structures that result in specific surface atomic arrangements and electronic structures distinct from conventional alloys. For each category, the correlations between structural characteristics and catalytic activities are examined. In addition, representative synthesis and design strategies are discussed, as well as the influence of coordination environments on electronic structures, stability of reaction intermediates, and overall catalytic activity and selectivity. This review provides insights into the rational design of future CO2RR catalysts through precise control over the structure of the metal active centers.