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 (PGM) 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 (IrNiyOx/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 IrNi1Ox/ATO shows a mass activity of 1.0 mA µgIr-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 IrOx/ATO control, particularly with a markedly reduced Ir loading of only 19.7 µgIr cm-2. Importantly, IrNi1Ox/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 IrNi1Ox/ATO was also preliminarily evaluated in a membrane electrode assembly, which shows better activity and stability than other reference catalysts. The IrNi1Ox/ATO reported in this work is a promising alternative to commercial IrO2 based catalysts for PEM electrolysis.