Unlocking the mystery of pulse-enhanced CO₂ electroreduction on copper in carbonate media

Pulsed electrolysis for CO₂ reduction reaction has emerged as an effective method to enhance catalyst efficiency and optimize product selectivity. However, challenges remain in understanding the mechanisms of surface transformation under pulsed conditions. In this study, using in-situ time-resolved surface-enhanced Raman spectroscopy and differential electrochemical mass spectroscopy, we found local pH at the surface and Cu–O–C species that was generated during the anodic pulse played a key role in pulsed electrolysis. During the pulsed oxidation, an oxidation layer first formed, depleting OH^– and lowering the local pH. When the pH was below 8.4, HCO₃^– transformed the oxidation layer to a nanometer-thick Cu–O–C species, which is a highly reactive catalyst. In the reduction pulse, about 7.4% of the surface Cu–O–C was transformed into CO and CuO_x species, enhancing CO₂ reduction activity. Even in Ar-saturated 0.1 M KHCO₃, through a Cu–O–C intermediate, a Faradaic efficiency of 0.17% for bicarbonate reduction to CO was observed. Our findings highlight the crucial role of the anodic pulse process in improving CO₂ reduction activity.