Barium-induced compressive strain engineering in low-iridium Co3O4 spinel for high-efficiency acidic oxygen evolution

Abstract

Iridium (Ir)-based materials are promising candidates for the acidic oxygen evolution reaction (OER) but face challenges such as high cost and aggregation. In this study, we synthesized a low-Ir-content Co₃O₄ spinel catalyst (IrBa-Co₃O₄ with 1.5 at. % Ir) via electrodeposition, where barium (Ba) doping introduces compressive strain to optimize Ir active sites while mitigating Ir aggregation into clusters or nanoparticles. Structural analyses, including X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and extended X-ray absorption fine structure (EXAFS), confirm atomic-level dispersion of Ir and Ba, lattice contraction, and shortened CoO bonds. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) reveal electron transfer from Ir to Co/Ba, elevating Ir’s oxidation state and enhancing OER activity. In 0.5 M H₂SO₄, the IrBa-Co₃O₄ catalyst achieves 10 mA cm⁻² at an overpotential of 249 mV and operates stable for 100 h, outperforming most reported spinel-type catalysts. In-situ electrochemical impedance spectroscopy (EIS), Raman spectroscopy, and XANES attribute the improved activity to compressive-strain-induced octahedral Co‑oxygen (Co_oct-O) bond shortening and optimized Ir-O-Ba/Co coordination. This work demonstrates a strategy for designing cost-effective, durable acidic OER catalysts through synergistic doping and strain engineering.