Ultrasonication-Induced Iridium Single-Atom Decoration on Anodized NiO Nanosponge Electrocatalyst for Enhanced Oxygen...

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 Ir³⁺ and Ir⁴⁺ 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 IrO₂/Ni. This approach facilitates the development of durable and highly active single-atom catalysts for high-performance OER.