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 (CO2) conversion into multi-carbon hydrocarbons. However, during the electrochemical reaction, Cu catalysts inevitably undergo surface reconstruction whose impact on CO2 conversion performance remains contentious. Here we report that polycrystalline Cu nanoparticles (denoted as Cu-s) with rich high-index facets, derived from Cu2-xS through desulphurization and surface reconstruction, offer an excellent platform for investigating the role of surface reconstruction in electrocatalytic CO2 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 CO2 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 C2H4 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 CO2 into the C2H4 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 CO2 conversion toward high-value multicarbon (C2+) chemicals, and highlight the significance of in situ characterizations in enhancing the understanding of the surface structure and its role in electrocatalysis.