Lattice-Doped Ir Cooperating with Surface-Anchored IrO_x for Acidic Oxygen Evolution Reaction with Ultralow Ir Loading

Reducing iridium (Ir) loading while maintaining efficiency and stability is crucial for the acidic oxygen evolution reaction (OER). In this study, we develop a synthetic method of sequential electrochemical deposition and high-temperature thermal shock to produce an IrO_x/Ir-WO₃ electrocatalyst with ∼1.75 nm IrO_x nanoparticles anchoring on Ir-doped WO₃ nanosheets. The IrO_x/Ir-WO₃ electrocatalyst with a low Ir loading of 0.035 mg cm^-2 demonstrates a low overpotential of 239 mV to achieve a current density of 10 mA cm^-2 and a mass activity of 6.6 × 10⁴ A g_Ir^-1 @1.75 V vs RHE in 0.5 M H₂SO₄. IrO_x/Ir-WO₃ on carbon paper as the anode and Pt/C as the cathode work stably for 40 h at 30 mA cm^-2 in a proton exchange membrane water electrolyzer. It is found that the cooperation of lattice-doped Ir and surface-anchored IrO_x enhances the activity and stability of IrO_x/Ir-WO₃ for acidic OER. Specifically, the doped Ir reduces the electron density of the anchored IrO_x, thus optimizing the adsorption energy of oxygen-containing intermediates and the kinetic barrier of H₂O dissociation, leading to an enhanced activity of IrO_x/Ir-WO₃. Also, the Ir-WO₃ support provides electrons to retard the overoxidation and dissolution of Ir atoms from the anchored IrO_x during acidic OER.