Unlocking asymmetric C-C coupling pathways on commercial Cu catalysts via Cu (100) grain boundaries for efficient and durable CO electroreduction

Copper (Cu)-based catalysts show significant potential for producing high value-added C 2+ products in electrocatalytic CO 2 /CO reduction reactions (CO (2) RR). However, the structural reconfiguration during operation poses substantial challenges in identifying the intrinsic catalytic active site, especially under similar mass transport conditions. Herein, three typical and commercial Cu-based catalysts (Cu, CuO, and Cu 2 O) are chosen as representatives to elucidate the structure-activity relationship of CORR in the membrane electrode assembly electrolyzer. Notably, only the Cu catalyst demonstrates the most suppression of hydrogen evolution reaction, thus achieving the highest FE of 86.7% for C 2+ products at a current density of 500 mA cm –2 and maintaining a stable electrolysis over 110 h at a current of 200 mA cm –2 . The influence of chemical valence state of Cu, electrochemical surface area, and local pH were firstly investigated and ruled out for the significant FE differences. Finally, based on the structure analysis from high resolution transmission electron microscope, OH – adsorption, in situ infrared spectroscopy and density functional theory calculations, it is suggested that the asymmetric C-C coupling ( via *CHO and *CO) is the most probable reaction pathway for forming C 2+ products, with Cu (100)-dominant grain boundaries (GBs) being the most favorable active sites. These findings provide deeper insights into the synergistic relationship between crystal facets and GBs in electrocatalytic systems.