Engineered Spatial Confinement of Cu Single‐atoms with Diagonal N–Cu–N Motifs for High‐rate CO2 Methanation

The renewable‐electricity‐powered carbon dioxide reduction (eCO2R) to value‐added fuels and feedstocks like methane (CH4) holds the sustainable and economically viable carbon cycle at meaningful scales. However, this kinetically challenging eight‐electron multistep deep‐reduction encounters insufficient catalyst design principles to steer complex CO2 reduction pathways. Utilizing atomic copper (Cu) structures with unitary active site can boost eCO2R‐to‐CH4 selectivity due to the efficient suppression of unwanted C−C coupling. Herein, we report a sequential ion exchange strategy to fabricate periodic Cu single‐atom catalysts within a polymeric carbon nitride (PCN) matrix, where the uniformly dispersed, diagonally coordinated N–Cu–N configuration hosts low‐valent Cuδ+ centers. Leveraging the periodic N‐anchoring sites with delocalized π‐electron conjugation in PCN matrix, the isolated Cu sites are obtained with an interatomic distance of ~4.2 Å under high metal‐loading conditions. This engineered spatial configuration effectively inhibits C−C coupling to avoid subsequent multicarbon products formation. The optimized Cu1/PCN demonstrates exceptional eCO2R‐to‐CH4 performance, achieving 71.1% CH4 Faradaic efficiency with a high partial current density of 426.6 mA cm−2 at −1.50 V vs. reversible hydrogen electrode, outpacing the state‐of‐the‐art catalysts. This work delves into effective concepts for steering desirable reaction pathways via precisely modulating active site structures at the atomic level to create favorable microenvironments.