The efficient electrochemical conversion of CO2 provides a route to fuels and feedstocks. Cu catalysts are well-known to be selective to multicarbon products although the role played by the surface architecture and the presence of oxides is not fully understood. Here, we report improved efficiency towards ethanol by tuning the morphology and oxidation state of the Cu catalysts via pulsed CO2 electrolysis. We establish a correlation between the enhanced production of C2+ products (76 % ethylene, ethanol and n-propanol at -1.0 V vs RHE) and the presence of (100) terraces, Cu2O, and defects on Cu(100). We monitored the evolution of the catalyst morphology by analysis of cyclic voltammetry curves and ex situ atomic force microscopy data, while the chemical state of the surface was examined via quasi in situ X-ray photoelectron spectroscopy. We show that the continuous (re-)generation of defects and Cu(I) species synergistically favors the C-C coupling pathways.