Nanotubular Titanium Oxynitride with an Ultra-Low Iridium Loading as a High-Performance Oxygen-Evolution-Reaction Thin-Film Electrode

Abstract

The present 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 ultra-low 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 remarkable oxygen-evolution reaction (OER) activity and high stability. Due to the confinement inside the pores and the strong metal-support interaction (SMSI) effects, the OER exhibited a higher turnover. The high durability is achieved by self-passivation of the titanium oxynitride (TiON) surface layer with TiO<sub>2</sub>, 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 DFT calculations reduce the tendency of the Ir nanoparticles to grow. We also introduce an advanced electrochemical characterization platform for the in-depth study of thin-film electrodes. 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 novel 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.

Titanium nitride (TiN) as a promising alternative to plasmonic metals: a comprehensive review of synthesis and applications

“…In another work, Bele et al developed an inexpensive, oxygen-evolution catalyst by synthesising a thin-film composite electrode with a unique morphology, ultralow iridium loading, and high stability. 206 The composite electrode, consisting of a TiO 2 nanotubular film subjected to nitridation and efficient immobilization of iridium nanoparticles, exhibits high OER activity and remarkable stability. The electrode's exceptional durability can be attributed to the self-passivation phenomenon occurring on the titanium oxynitride (TiON) surface, which forms a protective layer of TiO 2 .…”

Depth profiling characterization of the titanium chemical state on electrode surfaces for technological applications

“…In this case, self-passivation of titanium oxynitride (TiON) is achieved by a surface layer of TiO 2 obtaining high stability and durability. 12 Semiconductor TiO 2 thin films are used in the production of solar cells. Recently a combination of 3D printing and liquid deposition modeling (LDM) was used for controlling the pattern of TiO 2 electrodes.…”