Facile Ferric Nitrate Spray Fabrication and In Situ NAP-XPS Investigation of NiFeOxHy-Coated Nickel Foam Electrocatalysts for Alkaline Water Electrolysis

The development of efficient and scalable oxygen evolution reaction (OER) electrocatalysts is critical for advancing alkaline water electrolysis technologies. In this study, we present a facile spraying method for fabricating NiFeOxHy-coated nickel foam (NF) electrodes using aqueous Fe(NO3)3 solutions with varying concentrations and reaction times. Surface and chemical characterization via scanning electron microscopy (SEM) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) revealed that Fe(NO3)3 treatment etches the NF surface while promoting the formation of a NiFeOxHy layer. NAP-XPS further shows that this layer consists of mixed oxide and (oxy)hydroxide species, where increasing Fe content suppresses Ni oxidation while enabling the stabilization of high-valent Ni species at relatively higher anodic potentials through the electron-withdrawing effect of Fe sites. Electrochemical evaluation in a three-electrode setup demonstrated that higher Fe(NO3)3 concentrations reduce OER overpotentials by up to 42% compared to pristine NF. The results suggest that once a threshold Fe content is reached, further performance gains are primarily attributed to increased surface area. Single-cell testing under industrial conditions (30 wt % KOH, 90 °C) confirmed that performance improvements are governed by Fe(NO3)3 concentration rather than reaction time, with 1000 mM-treated electrodes achieving a ∼200 mV voltage reduction. Long-term testing over 800 h showed that initial degradation stabilizes, indicating robust electrode integrity. Additionally, this study underscores the importance of evaluating electrocatalysts under industrially relevant conditions to accurately assess their practical applicability.