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The usage of iridium as an oxygen-evolution-reaction (OER) electrocatalyst requires very high atom efficiencies paired with high activity and stability. Our efforts during the past 6 years in the Priority Program 1613 funded by the Deutsche Forschungsgemeinschaft (DFG) were focused to mitigate the molecular origin of kinetic overpotentials of Ir-based OER catalysts and to design new materials to achieve that Ir-based catalysts are more atom and energy efficient, as well as stable. Approaches involved are: (1) use of bimetallic mixed metal oxide materials where Ir is combined with cheaper transition metals as starting materials, (2) use of dealloying concepts of nanometer sized core-shell particle with a thin noble metal oxide shell combined with a hollow or cheap transition metal-rich alloy core, and (3) use of corrosion-resistant high-surface-area oxide support materials. In this mini review, we have highlighted selected advances in our understanding of Ir–Ni bimetallic oxide electrocatalysts for the OER in acidic environments.

Ir-based nanoparticles supported on conductive oxide supports show high water oxidation (oxygen evolution reaction, OER) activity and represent a promising alternative to state-of-art anode catalysts in water electrolyzers. Physicochemical interactions between the Ir-based catalytic nanoparticles and the oxide supports can critically affect the weight loading, surface area, activity, and stability of the Ir-based catalysts under electrochemical OER conditions. However, systematic insight on the influences of surface charge on deposition yield and dispersion of the nanoparticles on oxide supports and the influence of this interaction on the catalytic performance of supported Ir-based alloys is missing. In this work, the impact of electrostatic interactions between catalyst–support surface charges during catalyst synthesis on the structure and performance of Ir-based OER electrocatalysts is studied. Supported IrNi NPs were synthesized comparing a direct and a stepwise deposition technique onto selected doped tin oxide supports including antimony tin oxide (ATO), In-rich indium tin oxide (ITO), and fluorine tin oxide (FTO), with commercial ATO and unsupported particles as references. Data suggest that electrostatic attractions between particles and supports majorly impact the deposition yield of IrNi NPs. Photoemission spectra, XPS, of supports and supported catalysts show declines in the doping elements concomitant to the variation of the oxide oxidation state. We demonstrate how controlled pretreatments and alterations of repulsive forces between supports and nanoparticles resulted in great improvements in nanoparticle deposition and thus enhanced OER activity. Our findings can be transferred to other nanoparticles/support couples to help improve the distribution and adhesion of the nanoparticles and therefore improve their catalytic performances.

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