Effect of single atom loading on the CO2 reduction activity of pure and defective W2CO2 MXene

Two-dimensional (2D) transition metal carbides/nitrides (MXenes) have garnered considerable attentions for their potential in electrochemically reduction carbon dioxide (CO₂) to renewable fuels and chemical feedstocks. Despite significant advancements in employing MXenes as CO₂ reduction reaction (CO₂RR) catalysts have made, a deeper understanding and elucidation of the CO₂RR mechanism of MXenes are still lacked. In this work, the CO₂RR performance of W₂CO₂ and defective W₂CO₂ (W₂CO_2-x) loaded with various single transition metal (TM, TM= Ti, V, Fe, Ni, Cu, Mo, Pd, and Ag) atoms are systematically evaluated by first-principles calculations. The results indicate that W₂CO₂ and W₂CO_2-x are not suitable as catalysts for CO₂RR, while oxygen vacancy and TM loading can promote CO₂RR along P1 and P2 pathways. Especially, Ti@W₂CO₂ delivered relative highest selectivity in the production of formic acid (HCOOH), with the corresponding limiting potential of -0.11 V. Cu@W₂CO_2-x delivered relative higher selectivity for the production of carbon monoxide (CO), with the corresponding limiting potential of approximately -0.44 V. The improving CO₂RR activity for the generation of C1 products of studied single-atom catalysts (SACs) are attributed to the abundant electrons in the d-orbitals of the TM atoms, such as Ti and Cu, which can efficiently inject into the CO₂ molecule and intermediates, enhancing adsorption capacity for CO₂ and intermediates, reducing the energy barrier for hydrogenation reactions, and therefore promoting CO₂RR. The ab initio molecular dynamics (AIMD) simulations indicated that Ti@W₂CO₂ and Cu@W₂CO_2-x are dynamically stabilized at reaction temperature. This research not only provides new insights into the catalytic mechanisms of MXenes in CO₂RR but also paves the way for the development of efficient and selective MXene-based electrocatalysts for CO₂RR.