Wet-chemical Synthesis of Tin Oxide and Titania Supported Iridium Oxide Nanoparticles with Ultralow Iridium Density as Novel Catalysts for PEM Electrolysis

The proton exchange membrane (PEM) is a promising and intensively researched technology for large-scale production of hydrogen from sustainable sources. However, the economic viability of the PEM process remains limited by the high capital cost of the individual components, particularly the rare and valuable iridium used as a catalyst for the oxygen evolution reaction (OER). An established approach to reduce Ir loading in PEM is to disperse the catalytically active material on corrosion-stable supports with formation of a catalyst with low volumetric Ir density, which increases the noble metal mass-based activity. The material and morphology of the support, as well as the coating process, have a strong influence on catalyst performance and are investigated here to optimize catalyst performance and further reduce iridium content<br/>Here, a novel and scalable catalyst synthesis is presented in which corrosion-resistant crystalline SnO₂ and TiO₂ nanoparticles are coated with an ultrathin layer of amorphous iridium hydroxide using a simple low-temperature wet chemical synthesis. In a further step, the amorphous IrO(OH)_x layer is oxidized in a molten salt-assisted process. This process enables controllable phase transformation and crystallization to form a layer of interconnected, partially crystalline IrO_x nanoparticles with a size of ≈1.5 - 2 nm on the surface of the supporting nanoparticles, which form a percolation pathway. To elucidate the impact of different core-shell designs, transmission electron microscopy (TEM) imaging with a strong focus on iridium coating and crystallinity was performed. The final compounds contain highly active iridium oxide with overall very low Ir weight fractions of only 16% compared to a modern reference catalyst with 75 wt% Ir. Measurements on a rotating disk electrode (RDE) showed that SnO₂-supported IrO_x exhibits higher electrochemical activity and stability than TiO₂-supported IrO₂ at low loading. Further investigation of the membrane electrode assembly (MEA) in a single-cell electrolyzer indicates the possibility of future large-scale application in PEM at industrially relevant current densities.