Unveiling the mechanism of CO2 electroreduction to C1 and C2 products of ordered double transition metal MXenes†

Abstract

Design of highly active and durable electrocatalysts for CO₂ utilization and conversion into value-added chemicals in a green manner is central to addressing the global concerns of energy crisis and climate change for a sustainable future. Herein, we used rigorous first principles simulations to comprehensively screen and explore the CO₂ reduction activity of twelve different two-dimensional ordered double transition metal MXenes. Our results indicate that all twelve MXenes show metallic characteristics and can significantly activate CO₂ with strong binding energy (−1.60 to −2.40 eV). The van der Waals and solvation effects in general have little impact on the CO₂ binding energy; however, Hubbard correction is found to significantly influence the CO₂ binding on these catalysts. Electronic structure analysis reveals that charge redistribution from MXene catalysts to antibonding states of CO₂ results in strong hybridization between CO₂ orbitals and surface metal orbitals. The strong CO₂ binding is further confirmed by enhanced charge transfer (−1.17 to −1.65 |e⁻|) from MXenes to the adsorbed CO₂ molecule. Simulations based on free energy pathways show that Mo₂TaC₂ and Mo₂TiC₂ possess superior catalytic activity for conversion of CO₂ into methanol and methane with very low limiting potential values of −0.35 and −0.39 V, respectively, whereas Mo₂TaC₂ and Mo₂VC₂ were found to display excellent performance for ethanol formation with record low limiting potentials of −0.32 V and −0.42 V, respectively. Further, the MXene-based catalysts Mo₂TiC₂ and Mo₂VC₂ were found to be highly selective for CO₂ reduction to methane and ethanol respectively. Extensive analysis based on linear scaling relations between the adsorption free energy of different reaction intermediates and limiting potential values highlights that the adsorption free energy for *CO₂ and *OCHO intermediates plays a critical role in deciding the overall activity of the MXene catalysts. We believe that the above findings can be highly important for the design of MXene-based catalysts for CO₂ conversion.