Potential-Driven In Situ Formation of CuS@Cu2Se with Se-Vacancy-Rich for Steering the CO2 Electroreduction Path from HCOOH to C2H5OH

Copper chalcogenides are susceptible to electrochemical reconstruction, thus posing challenges to understand the precise structure-function relationships during CO2 electroreduction reaction (CO2RR). Here, we synthesize a hierarchical core-shell CuS@CuSe catalyst, exhibiting a controllable selectivity from 67.5% for HCOOH at −0.5 V vs. RHE to 54.7% for C2H5OH at −0.9 V vs. RHE. The overlap-labeled transmission electron microscopy and in-situ Raman spectroscopy dynamically monitor the potential-dependent structural evolution from the pristine CuS@CuSe to CuS@Cu2Se with Se vacancies (Cu2Se-VSe). Density functional theory (DFT) calculations reveal that the generated Se-vacancies stabilize Cu+ sites with shortened Cu−Cu spacing of 2.46 Å, which not only increases affinities to the adsorbed *COOH and *CO species but also promotes the easier dimerization of *CO to form *OCCO (ΔG ∼ −0.50 eV) while suppressing its direct desorption to CO (ΔG ∼ +1.63 eV) or hydrogenation to *CHO (ΔG ∼ +0.74 eV) and *COH (ΔG ∼ +1.15 eV), which is believed to determine the remarkable ethanol selectivity. And, the rapid dissociation of water over the synergistic CuS sites kinetically accelerates the proton-coupling process. Such potential-dependent imperative intermediates associated with the bifurcated pathway are directly distinguished by isotope labelling in-situ infrared spectroscopy. This work confers the prospect of designing electrochemical reconstructed copper chalcogenides catalyst for tuning C1/C2 products selectivity in CO2RR technology.