Ultrasonication‐Induced Iridium Single‐Atom Decoration on Anodized NiO Nanosponge Electrocatalyst for Enhanced Oxygen Evolution Reaction

ABSTRACT This study develops a facile strategy to engineer active and stable Ir single‐atom sites on nanostructured NiO to enhance the oxygen evolution reaction (OER). Electrochemical anodization is used to synthesize a NiO nanosponge, and sonochemical treatment is employed to simultaneously generate surface defects and decorate NiO with Ir single atoms. This method introduces active anchoring points and a favorable electronic environment to improve Ir stabilization and enhance electrocatalytic activity. Systematic characterizations, including high‐resolution transmission electron microscopy (HR‐TEM) and aberration‐corrected HAADF‐STEM, confirm the atomic dispersion of Ir for NiO decorated with 0.5 mM Ir (NiO‐0.5 Ir), and X‐ray photoelectron spectroscopy (XPS) demonstrates the formation of Ir 3+ and Ir 4+ chemical states. Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and principal component analysis (PCA) confirm the highest NiIr − fragment intensity and higher Ir‐Ni interaction values (NiIr − /Ir − ) for the NiO‐0.5 Ir electrode. Electrochemical measurements demonstrate enhanced OER activity for NiO‐0.5 Ir, exhibiting an overpotential of 290 mV at 10 mA cm −2 and a Tafel slope of 78 mV dec −1 , delivering 40 mA cm −2 at 1.6 V vs. RHE in 1.0 M KOH, which is twice the performance of IrO 2 /Ni. This approach facilitates the development of durable and highly active single‐atom catalysts for high‐performance OER.