Tuning binding strength between single metal atoms and supports enhances electrochemical CO₂ methanation

Single-atom catalysts (SACs) with tunable site density and activity are promising for catalytic processes. However, the relationship between interacting sites and the catalytic mechanism, as well as the effect of the support on this relationship, remains incompletely understood. Here we report a support geometry engineering strategy to control the inter-site distance (d_site) of Cu-N-C (CuNC) SACs via strong interactions between CuNC and a secondary support (ss). This process allows tuning of the binding strength (that is Cu-N bond length) between individual Cu atoms and the N-doped primary supports, concomitantly suppressing defect formation and Cu atom detachment in the CuNC framework. The continuous optimization of the electronic and coordination structure of individual active Cu sites, achieved by reducing the d_site to approximately 0.7 nm, enhances their inherent CO₂-to-methane selectivity and activity. As a result, the ss-engineered CuNC with a moderate d_site of 0.68 nm exhibits enhanced methane selectivity of 70% and a partial current density of 303.9 mA cm^-2, over 1.5 times higher than that of unmodified CuNC.