The electrode-electrolyte interface of Cu via modulation excitation X-ray absorption spectroscopy

Accessing the electrode-electrolyte interface under operating conditions and capturing time-resolved kinetics remain challenging in electrochemical studies. Copper's interfacial oxidation dynamics remain unclear despite extensive research. Modulation excitation X-ray absorption spectroscopy (ME-XAS) was used to probe Cu in 100 mM KHCO₃ with sub-second sensitivity, revealing that hydroxide forms 30 ± 10 ms before the appearance of Cu₂O at positive potentials (0 to 0.5 V vs. RHE) near open-circuit conditions. From −0.4 to 0.8 V vs. RHE, hydroxide coverage reaches 49%, accompanied by a balanced presence of Cu(i) and Cu(ii) oxides. These insights into Cu interfacial redox behavior under intermittent renewable energy operation—relevant to CO₂ electrolyzer durability—enhance our fundamental understanding of electrochemical interfaces.