In recent years, the electrocatalytic carbon dioxide reduction reaction (CO2RR), driven by renewable energy and operated under mild conditions with controllable reaction pathways, has emerged as a promising route for carbon-neutral energy conversion. Two-dimensional supported catalysts have attracted particular interest owing to their tunable electronic structures and well-defined active sites. However, how the number and spatial configuration of active centers govern CO2RR activity and selectivity remains insufficiently understood, limiting the rational design of efficient catalysts. This review provides a comprehensive overview of recent experimental and theoretical advances in two-dimensional supported catalysts for the CO2RR, including single-atom (SACs), double-atom (DACs), and three-atom (TACs) catalysts, and metal clusters, with an emphasis on insights obtained from density functional theory (DFT). The fundamental reaction pathways of the CO2RR are first summarized, highlighting structure–activity relationships between active-site characteristics and catalytic performance. Subsequently, the advantages and limitations of different catalyst architectures are critically compared, and the mechanisms of CO2 reduction to C1 products such as CO, HCOOH, and CH4 are systematically analyzed. Particular attention is given to the role of DFT in elucidating reaction pathways, charge transfer, and adsorption energetics, thereby revealing key descriptors governing activity and selectivity. By integrating experimental observations with theoretical insights, this review aims to provide a mechanistic framework and design principles for the development of advanced two-dimensional supported catalysts for efficient CO2RRs.
