Insight into the formation and transfer process of first intermediate of CO2 reduction over Ag‐decorated dendritic Cu

: It is still poorly understood how the first intermediates of CO2 reduction are formed and converted to multi-carbon products over Cu-based electrodes. Herein, Ag is used to decorate dendritic Cu and a high Faradaic efficiency (FE) for C2 H4 (25 %) is obtained on a CuAg electrode, which is about five times higher than dendritic Cu. The intermediates including *CO2- , OH groups, Cu-CO, C-O rotation, and CHx species are investigated by in situ Raman spectroscopy. This work provides spectroscopic evidence that the first intermediate of CO2 reduction on Ag-decorated Cu is carboxylate anion *CO2- bonded with the catalyst surface through the C and O atom. The formation and evolution process of the *CO2- intermediate over the applied potential are investigated in depth as well. This research contributes to a better understanding of the mechanism of CO2 reduction and multi-carbon product formation pathways over Ag-decorated Cu.