Synthesis, Structure, and Electrochemical Stability of Ir-Decorated RuO2 Nanoparticles and Pt Nanorods as Oxygen Catalysts

One major challenge of proton-exchange membrane fuel cells, water electrolyzers, and unitized regenerative fuel cells is to increase the oxygen catalysts stability by the systematic preparation of inhomogeneous catalyst surfaces via decoration with cocatalysts. Iridium (Ir) nanodots with a typical diameter of 2 nm were colloid chemically deposited on ruthenium oxide (RuO2) nanoparticles as oxygen evolution catalyst and on platinum (Pt) nanorods to yield bifunctional oxygen catalysts. The stepwise synthesis allows a higher control of the composite nanoparticles morphology and thus their activity and stability. The stability toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was studied with cyclic voltammetry. Structural characterization was carried out with X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) spectroscopy before and after the stability protocols. Ir nanodots as well as Ir-decorated RuO2 nanoparticles were found to be less stable toward the OER stability protocol than pure RuO2 nanoparticles. Bifunctional catalysts made of Ir deposited on Pt nanorods showed different behavior than the individual components. Concerning the OER, the stability decreased compared to unsupported Ir (monometallic OER catalyst), whereas improved stability was observed for the ORR in comparison to pure Pt nanorods (monometallic ORR catalyst).