Operando Characterization of Porous Nickel Foam Water Splitting Electrodes Using Near-Ambient Pressure X-ray Photoelectron Spectroscopy

This study presents a practical approach for characterizing industrial water-splitting nickel foam electrodes under both cathodic and anodic conditions by employing synchrotron radiation near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). The in situ studies reveal quantitatively reduced and oxidized Ni species on the electrode surface by recording the Ni 2p_3/2 signals after cycling the potential in cathodic and anodic regions, respectively. Operando studies demonstrate that a stable electrolyte film forms, allowing the probing of the solid/liquid interface under applied potentials. We attribute this stability to capillary forces within the porous structure of the foam, which enables the monitoring of surface deprotonation under anodic potentials and surface protonation under cathodic potentials. Given that the most common industrial alkaline water electrolyzer electrodes are based on nickel foams similar to the samples measured in this study, the demonstrated method offers a valuable approach for fundamental NAP-XPS examination directly on industrially employed electrodes.