The activity key of s-block single-atom catalysts for superior CO2RR: sp2 hybridization of metal sites

Abstract

Single-atom catalysts (SACs), owing to their unique electronic structures, are widely applied in various catalytic reactions. Recent studies have indicated that SACs with s-block metals as active sites are potential catalysts for the CO₂ reduction reaction (CO₂RR). However, the origins of their activity and the underlying reaction mechanisms remain unclear. In this work, CO₂RR processes on a series of s-block SACs with different coordination environments are systematically investigated by constant potential simulations. Our research demonstrates that the coordination environment of s-block metal active sites can modulate their hybridization state and thus catalytic performance. Specifically, sp²-hybridized active sites exhibit superior CO₂RR activity due to optimal intermediate adsorption strength. Furthermore, we observe unique hybridization state transitions from inert sp to active sp² under working conditions. The weakened linear scaling relationship between *H and *CO₂ at sp²-hybridized active sites allows these sites to effectively suppress the hydrogen evolution reaction (HER). Finally, we predict that Ca-N₂-DV-1 with sp²-hybridized active sites is a highly active and selective catalyst for HCOOH production, with an ultra-low overpotential of 0.097 V vs. RHE. This work elucidates the activity origins of s-block metal SACs, highlights the significant role of orbital hybridization in intermediate adsorption, and provides valuable insights for the rational design of highly efficient SACs for various catalytic reactions.