Structural and electronic effects of ultralow atomically dispersed Ir on TiO₂ nanowires

Iridium oxide is a promising catalyst for the oxygen evolution reaction (OER) under acidic conditions due to its excellent activity. However, the scarcity of iridium limits its large-scale industrial applications, prompting the need for strategies to reduce its use. Dispersing low quantities of Ir in oxide materials is a suitable approach for producing efficient electrodes. Nevertheless, the effects of low amounts of iridium on the morphology and electronic structure of oxide substrates remain unexplored. In this work, a hydrothermal approach is used to grow titanium dioxide (TiO₂) nanowires with ultralow concentrations of Ir, and a thorough electron microscopy characterization is conducted and correlated to the electrochemical activity of the materials. The results show that from a structural perspective, the Ir-doped TiO₂ nanowires maintain constant lattice spacings corresponding to the rutile structure regardless of the Ir concentration. Spatially resolved electron energy loss spectroscopy (EELS) demonstrates a local reduction in the oxidation state of the Ti atoms in the electronic structure of the Ir-doped TiO₂ when compared to pure TiO₂, proving the presence of Ir in substitutional sites on the TiO₂ nanowire. This work demonstrates that an ultralow loading of 0.1-0.2 at% Ir is sufficient to modify the electronic structure of TiO₂ and significantly enhance the OER performance of Ir-doped TiO₂.