Abstract: The electrochemical reduction of carbon monoxide (COER) to high-value multicarbon (C₂₊) products is an emerging strategy for artificial carbon fixation and renewable energy storage. However, the slow kinetics of the C-C coupling reaction remains a significant obstacle in achieving both high activity and selectivity for C₂₊ production. In this study, we demonstrated the use of defect engineering to promote COER towards C₂₊ products by introducing single chlorine vacancy (SV_Cl) into two-dimensional (2D) non-noble transition metal dichlorides (TMCl₂). Density functional theory (DFT) calculations revealed that SV_Cl in TMCl₂ exhibits low formation energies and high stability, ensuring its feasibility for synthesis and application in electrocatalysis. The introduction of three-coordinated, unsaturated metal sites substantially enhances the catalytic activity of TMCl₂, facilitating effective CO activation. Notably, SV_Cl-engineered CoCl₂ and NiCl₂ nanosheets exhibit superior performance in COER, with SV_Cl@CoCl₂ showing catalytic activity for ethanol and propanol production, and SV_Cl@NiCl₂ favoring ethanol production due to a lower limiting potential and smaller kinetic barrier for C-C coupling. Consequently, defective 2D TMCl₂ nanosheets represent a highly promising platform for converting CO into value-added C₂₊ products, warranting further experimental investigation into defect engineering for CO conversion.

Key words: Co electroreduction, Multicarbon products, 2D metal dichlorides, Cl vacancy, DFT computations