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Conversion of CO₂ to valuable chemicals driven by renewable electricity via electrocatalytic reduction processes is of great significance for achieving carbon neutrality. Copper-based materials distinguish themselves from other electrocatalysts for their unique capability to produce multicarbon compounds in CO₂ electroreduction. However, the intrinsic active composition and C–C coupling mechanism of copper-based catalysts are still ambiguous. This is largely due to the absence of appropriate in situ approaches to monitor the complicated processes of CO₂ electroreduction. Here, we adopted operando spectroscopy techniques, including Raman and infrared, to investigate the evolution of compositions and intermediates during gas-phase CO₂ electroreduction on Cu foam, Cu₂O nanowire and CuO nanowire catalysts. Although all the three copper-based catalysts possessed the activity of electroreducing gas-phase CO₂ to multicarbon oxygenates, Cu₂O nanowires showed the much superior performance with a 71.9% Faradaic efficiency of acetaldehyde. Operando Raman spectra manifested that the cuprous oxide remained stable during the whole gas-phase CO₂ electroreduction, and operando diffuse reflectance infrared Fourier transform spectroscopy (DRFITS) results provide direct evidences of key intermediates and their evolutions for producing multicarbon oxygenates, in consistence with the density functional theory calculations.