Lawrence Berkeley National Laboratory

Achieving a molecular-level understanding of interfacial (photo)electrochemical processes is essential in order to tailor novel and highly-performing catalytic systems. The corresponding recent development of in situ and operando tools has posed new challenges on experimental architectures. In this study, we use ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to probe the solid/liquid electrified interface of a polycrystalline Pt sample in contact with an alkaline electrolyte during hydrogen and oxygen evolution reactions. Using the “dip-and-pull” technique to probe the interface through a thin liquid layer generated on the sample surface, we observe that the electrolyte meniscus becomes unstable under sustained driving of an electrolyte-consuming reaction (such as water oxidation). The addition of an electrochemically inert supporting electrolyte mitigates this issue, maintaining a stable meniscus layer for prolonged reaction times. In contrast, for processes in which the electrolyte is replenished in the reaction pathway (i.e. water reduction in alkaline conditions), we find that the solid/liquid interface remains stable without addition of a secondary supporting electrolyte. The approach described in this work allows the extension of operando AP-XPS capabilities using the “dip-and-pull” method to a broader class of reactions consuming ionic species during complex interfacial faradaic processes.