Rational Design of MXene-Supported Single-Atom Catalysts for Electrochemical CO _<b>2</b> Reduction with Tunable Activity and Product Selectivity

The electrochemical CO2 reduction reaction (CO2RR) represents a promising pathway for the sustainable conversion of CO2 into energy-dense fuels and commodity chemicals, thereby contributing to carbon neutrality. Nevertheless, achieving simultaneously high catalytic activity and product selectivity remains a formidable challenge. Herein, a comprehensive first-principles investigation integrating density functional theory (DFT) and ab initio molecular dynamics (AIMD) was conducted to elucidate the structure–stability–reactivity correlations of transition metal (TM)-doped Mo2TiC2 single-atom catalysts (SACs) in the context of CO2RR. The results demonstrate that the efficient activation of CO2 originates from the strong orbital hybridization between TM d-states and the CO2 antibonding orbitals, accompanied by pronounced charge redistribution at the catalytic centers. The TM–Mo2TiC2 catalysts exhibit intrinsic selectivity toward CH3OH formation, among which Ni–, Cu–, Os–, and Pt–Mo2TiC2 display remarkably low limiting potentials of −0.39, −0.52, −0.37, and −0.49 V, respectively, outperforming the benchmark Mo3C2O2 catalyst (−0.54 V). These findings unveil the fundamental origin of product selectivity and provide atomistic design guidelines for the development of next-generation CO2RR electrocatalysts featuring enhanced CH3OH selectivity and superior activity.