Cu2−xS derived copper nanoparticles: A platform for unraveling the role of surface reconstruction in efficient electrocatalytic CO2-to-C2H4 conversion

Cu-based electrocatalysts have provoked much attention for their high activity and selectivity in carbon dioxide (CO 2 ) conversion into multi-carbon hydrocarbons. However, during the electrochemical reaction, Cu catalysts inevitably undergo surface reconstruction whose impact on CO 2 conversion performance remains contentious. Here we report that polycrystalline Cu nanoparticles (denoted as Cu- s ) with rich high-index facets, derived from Cu 2− x S through desulphurization and surface reconstruction, offer an excellent platform for investigating the role of surface reconstruction in electrocatalytic CO 2 conversion. During the formation of Cu- s catalyst, the two stages of desulphurization and surface reconstruction can be clearly resolved by in situ X-ray absorption spectroscopy and OH − adsorption characterizations, which are well correlated with the changes in electrocatalytic performance. It turns out that the high CO 2 conversion performance, achieved by the Cu-s catalyst (Faradic efficiency of 68.6% and partial current density of 40.8 mA/cm 2 in H-cell toward C 2 H 4 production), is attributed to the increased percentage of high-index facets in Cu- s during the surface reconstruction. Furthermore, the operando electrochemical Raman spectroscopy further reveals that the conversion of the CO 2 into the C 2 H 4 on Cu-s is intermediated by the production of *COCHO. Our findings manifest that the surface reconstruction is an effective method for tuning the reaction intermediate of the CO 2 conversion toward high-value multicarbon (C 2+ ) chemicals, and highlight the significance of in situ characterizations in enhancing the understanding of the surface structure and its role in electrocatalysis.