Increasing the Oxygen-Evolution Reaction Performance of Nanotubular Titanium Oxynitride-Supported Ir Nanoparticles by a Strong Metal-Support Interaction

This study targets one of the grand challenges of electrochemical hydrogen production: a durable and cost-effective oxygen-evolution catalyst. We present a thin-film composite electrode with a unique morphology and an ultralow loading of iridium that has extraordinary electrocatalytic properties. This is accomplished by the electrochemical growth of a defined, high-surface-area titanium oxide nanotubular film, followed by the nitridation and effective immobilization of iridium nanoparticles. The applicative relevance of this production process is justified by a high oxygen-evolution reaction (OER) activity and high stability. Enhanced OER performance is due to the strong metal-support interaction (SMSI). The high durability is achieved by self-passivation of the titanium oxynitride (TiON) surface layer with TiO2, which in addition also effectively embeds the Ir nanoparticles while still keeping them electrically wired. An additional contribution to the enhanced durability comes from the nitrogen atoms, which according to our density functional theory (DFT) calculations reduce the tendency of the Ir nanoparticles to grow. Materials are analyzed by advanced electrochemical characterization techniques. Namely, the entire process of the TiON-Ir electrode's preparation and the electrochemical evaluation can be tracked with scanning electron microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) at identical locations. In general, the experimental approach allows for the unique morphological, structural, and compositional insights into the preparation and electrocatalytic performance of thin films, making it useful also outside electrocatalysis applications.