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

Abstract

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.

Enhancing Iridium Nanoparticles’ Oxygen Evolution Reaction Activity and Stability by Adjusting the Coverage of Titanium Oxynitride Flakes on Reduced Graphene Oxide Nanoribbons’ Support

“…We note that TiO 2 signal comes from the surface which is in accordance with what was already observed in our previous studies. [58,65,67] It is, however, not straightforward to distinguish between the different Ticontaining phases due to the partial overlapping of their respective peaks. Nevertheless, the presence of all phases was confirmed.…”

“…A third possible contribution is the presence of strong metal-support interaction (SMSI) between TiON x and Ir. [65] The interaction of the support with Ir via the heterojunction can affect the growth of the less active Ir-oxide, the so-called "inner" oxide, which is thus expected to affect OER activity [58] and also stabilize Ir nanoparticles. [65] We note that not only its nature but also the morphology of the support was shown to affect Ir OER performance.…”

“…[58,65,67] In addition, TiON x material was chosen as it provides beneficial SMSI on the Ir OER performance. [58,65,67] Current study explores how adjusting the composition of nanocomposite support influences the OER activity and stability of Ir nanoparticles. Three samples with a varying TiON x /rGONRs ratio and thus interfacial contact areas between the three phases have been synthesized and investigated in detail with classical and advanced electrochemical techniques, as well as structural characterization.…”

Effect of the Morphology of the High-Surface-Area Support on the Performance of the Oxygen-Evolution Reaction for Iridium Nanoparticles

“…The final step of the OER catalyst’s preparation, i.e., the deposition of Ir in the form of finely dispersed, ultrasmall nanoparticles, was already demonstrated by our group. 30 − 32 In this investigation, we developed a new, anodic, oxidation-based synthesis process for the cost-effective fabrication of high-performance OER TiON x -Ir nanopowder electrocatalysts. The influence of the anodization time on the catalyst’s support morphology, structure, and composition was studied in detail using various state-of-the-art characterization methods, such as X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS).…”

Low-Temperature Synthesis of Titanium Oxynitride Nanoparticles

“…Transition metal oxynitrides, for example titanium oxynitride (TiON) nanoparticles, represent powerful active sites when added to photocatalytic devices, or to electrodes for capacitors, batteries, and fuel cells [ 1 , 2 , 3 ]. Typically, TiON nanoparticles are prepared via a solvothermal route, which involves annealing the respective oxide with ammonia at temperatures between 600 °C and 850 °C [ 2 , 4 , 5 , 6 , 7 , 8 , 9 ]. Alternative routes require high pressures or complex reaction conditions, such as sol–gel preparation, laser pyrolysis, and plasma-supported atomic layer deposition [ 2 , 3 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ].…”