Mixed iridium-nickel oxides supported on antimony-doped tin oxide as highly efficient and stable acidic oxygen evolution catalysts

Proton exchange membrane (PEM) water electrolysis represents a promising technology for green hydrogen production, but its widespread deployment is greatly hindered by the indispensable usage of platinum group metal catalysts, especially iridium (Ir) based materials for the energy-demanding oxygen evolution reaction (OER). Herein, we report a new sequential precipitation approach to the synthesis of mixed Ir-nickel (Ni) oxy-hydroxide supported on antimony-doped tin oxide (ATO) nanoparticles (IrNi_yO_x/ATO, 20 wt.% (Ir + Ni), y = 0, 1, 2, and 3), aiming to reduce the utilisation of scarce and precious Ir while maintaining its good acidic OER performance. When tested in strongly acidic electrolyte (0.1 M HClO₄), the optimised IrNi₁O_x/ATO shows a mass activity of 1.0 mA g_Ir^-1 and a large turnover frequency of 123 s^-1 at an overpotential of 350 mV, as well as a comparatively small Tafel slope of 50 mV dec^-1, better than the IrO_x/ATO control, particularly with a markedly reduced Ir loading of only 19.7 g_Ir cm^-2. Importantly, IrNi₁O_x/ATO also exhibits substantially better catalytic stability than other reference catalysts, able to continuously catalyse acidic OER at 10 mA cm^-2 for 15 h without obvious degradation. Our in-situ synchrotron-based x-ray absorption spectroscopy confirmed that the Ir³⁺/Ir⁴⁺ species are the active sites for the acidic OER. Furthermore, the performance of IrNi₁O_x/ATO was also preliminarily evaluated in a membrane electrode assembly, which shows better activity and stability than other reference catalysts. The IrNi₁O_x/ATO reported in this work is a promising alternative to commercial IrO₂ based catalysts for PEM electrolysis.