Comparative study of IrPt catalysts synthesized via a wet chemical technique: microstructure, composition, and electrochemical performance in oxygen evolution reaction

Proton exchange membrane water electrolyzers (PEMWEs) play a key role in green hydrogen production, but their large-scale adoption has been hampered by the high cost of iridium-based anodes. In this study, we report a wet-chemical synthesis of bimetallic IrPt nanoparticles using ethanol (IrPt-Et) and isopropanol (IrPt-IPA) as solvents, which reduced the Ir content by 50% while maintaining high oxygen evolution reaction (OER) activity. Comprehensive characterization of the samples revealed that IrPt-Et forms ultra-small nanoparticles (NPs) of about 2–3 nm with the presence of IrO x surface phases, while IrPt-IPA contains larger agglomerates of 2.5–4.8 nm with a less uniform distribution of Ir and Pt. Electrochemical testing in 0.1 M HClO 4 shows that IrPt-Et delivers a current density of 10.6 mA/cm 2 at 1.53 V, which is twice the activity of commercial Ir-black. The mass activity reaches 697 mA/mg Ir – 4 times higher than Ir-black - due to the optimal utilization of Ir. In contrast, the heterogeneous composition of IrPt-IPA and large NPs lead to worse performance in OER. XPS analysis of post-activation samples confirmed that both catalysts undergo surface oxidation under OER conditions, but the pre-oxidized surface of IrPt-Et facilitates the formation of a more active and stable interface. This study demonstrates that solvent choice in synthesis influences a combination of factors – including reduction kinetics, particle size, alloy homogeneity, and surface oxidation – to yield highly active bimetallic catalysts with reduced iridium content, which is critical for the larger-scale implementation of PEMWE technologies. • Facile wet-chemical synthesis allows to obtain highly active IrPt alloy nanoparticles • Solvent choice (ethanol vs. isopropanol) controls microstructure and composition • Ethanol enables ultra-small (2-3 nm) bimetallic IrPt nanoparticles • Optimized IrPt catalysts show high oxygen evolution reaction activity and stability