Tuning the chlorine/oxygen terminal group ratio to modulate the adsorption strength of intermediates on MXene-supported single-atom catalysts toward high-performance electrochemical reduction of carbon dioxide.

In this study, we systematically investigate the electrocatalytic CO2 reduction reaction (ECO2RR) performance of OmCln (m + n = 6) single-atom catalysts (SACs) with varying ratios of Cl/O terminal groups using density functional theory. The results show that the mixed Cl/O terminal groups create an asymmetric coordination environment, which can significantly modulate the electronic structure of the Cu active center, thus enhancing both activity and selectivity toward formic acid (HCOOH) production. Among the studied structures, O1Cl5 exhibits the most promising performance with a theoretical limiting potential of -0.30 V vs. standard hydrogen electrode (SHE) for HCOOH generation, effectively superior to the competing CO pathway (-0.81 V) and hydrogen evolution (-0.47 V). Electronic structure analysis reveals that spin polarization and orbital hybridization between Cu 3d and *OCHO 2p play a crucial role in determining *OCHO adsorption, promoting CO2 activation and subsequent hydrogenation. This work highlights the importance of surface termination engineering in MXene-based SACs and provides a rational design strategy for developing high-performance ECO2RR catalysts.