RESUMO
Aiming at speeding up the discovery and understanding of promising electrocatalysts, a novel experimental platform, i.e., the Nano Lab, is introduced. It is based on state-of-the-art physicochemical characterization and atomic-scale tracking of individual synthesis steps as well as subsequent electrochemical treatments targeting nanostructured composites. This is provided by having the entire experimental setup on a transmission electron microscopy (TEM) grid. Herein, the oxygen evolution reaction nanocomposite electrocatalyst, i.e., iridium nanoparticles dispersed on a high-surface-area TiOxNy support prepared on the Ti TEM grid, is investigated. By combining electrochemical concepts such as anodic oxidation of TEM grids, floating electrode-based electrochemical characterization, and identical location TEM analysis, relevant information from the entire composite's cycle, i.e., from the initial synthesis step to electrochemical operation, can be studied. We reveal that Ir nanoparticles as well as the TiOxNy support undergo dynamic changes during all steps. The most interesting findings made possible by the Nano Lab concept are the formation of Ir single atoms and only a small decrease in the N/O ratio of the TiOxNy-Ir catalyst during the electrochemical treatment. In this way, we show that the precise influence of the nanoscale structure, composition, morphology, and electrocatalyst's locally resolved surface sites can be deciphered on the atomic level. Furthermore, the Nano Lab's experimental setup is compatible with ex situ characterization and other analytical methods, such as Raman spectroscopy, X-ray photoelectron spectroscopy, and identical location scanning electron microscopy, hence providing a comprehensive understanding of structural changes and their effects. Overall, an experimental toolbox for the systematic development of supported electrocatalysts is now at hand.
RESUMO
A versatile approach to the production of cluster- and single atom-based thin-film electrode composites is presented. The developed TiO x N y -Ir catalyst was prepared from sputtered Ti-Ir alloy constituted of 0.8 ± 0.2 at % Ir in α-Ti solid solution. The Ti-Ir solid solution on the Ti metal foil substrate was anodically oxidized to form amorphous TiO2-Ir and later subjected to heat treatment in air and in ammonia to prepare the final catalyst. Detailed morphological, structural, compositional, and electrochemical characterization revealed a nanoporous film with Ir single atoms and clusters that are present throughout the entire film thickness and concentrated at the Ti/TiO x N y -Ir interface as a result of the anodic oxidation mechanism. The developed TiO x N y -Ir catalyst exhibits very high oxygen evolution reaction activity in 0.1 M HClO4, reaching 1460 A g-1 Ir at 1.6 V vs reference hydrogen electrode. The new preparation concept of single atom- and cluster-based thin-film catalysts has wide potential applications in electrocatalysis and beyond. In the present paper, a detailed description of the new and unique method and a high-performance thin film catalyst are provided along with directions for the future development of high-performance cluster and single-atom catalysts prepared from solid solutions.
RESUMO
Decreasing iridium loading in the electrocatalyst presents a crucial challenge in the implementation of proton exchange membrane (PEM) electrolyzers. In this respect, fine dispersion of Ir on electrically conductive ceramic supports is a promising strategy. However, the supporting material needs to meet the demanding requirements such as structural stability and electrical conductivity under harsh oxygen evolution reaction (OER) conditions. Herein, nanotubular titanium oxynitride (TiON) is studied as a support for iridium nanoparticles. Atomically resolved structural and compositional transformations of TiON during OER were followed using a task-specific advanced characterization platform. This combined the electrochemical treatment under floating electrode configuration and identical location transmission electron microscopy (IL-TEM) analysis of an in-house-prepared Ir-TiON TEM grid. Exhaustive characterization, supported by density functional theory (DFT) calculations, demonstrates and confirms that both the Ir nanoparticles and single atoms induce a stabilizing effect on the ceramic support via marked suppression of the oxidation tendency of TiON under OER conditions.
RESUMO
The commercialization of acidic proton exchange membrane water electrolyzers (PEMWE) is heavily hindered by the price and scarcity of oxygen evolution reaction (OER) catalyst, i. e. iridium and its oxides. One of the solutions to enhance the utilization of this precious metal is to use a support to distribute well dispersed Ir nanoparticles. In addition, adequately chosen support can also impact the activity and stability of the catalyst. However, not many materials can sustain the oxidative and acidic conditions of OER in PEMWE. Hereby, we critically and extensively review the different materials proposed as possible supports for OER in acidic media and the effect they have on iridium performances.
RESUMO
The widespread utilization of proton exchange membrane (PEM) electrolyzers currently remains uncertain, as they rely on the use of highly scarce iridium as the only viable catalyst for the oxygen evolution reaction (OER), which is known to present the major energy losses of the process. Understanding the mechanistic origin of the different activities and stabilities of Ir-based catalysts is, therefore, crucial for a scale-up of green hydrogen production. It is known that structure influences the dissolution, which is the main degradation mechanism and shares common intermediates with the OER. In this Minireview, the state-of-the-art understanding of dissolution and its relationship with the structure of different iridium catalysts is gathered and correlated to different mechanisms of the OER. A perspective on future directions of investigation is also given.
RESUMO
The production of hydrogen via a proton-exchange membrane water electrolyzer (PEM-WE) is directly dependent on the rational design of electrocatalysts for the anodic oxygen evolution reaction (OER), which is the bottleneck of the process. Here, we present a smart design strategy for enhancing Ir utilization and stabilization. We showcase it on a catalyst, where Ir nanoparticles are efficiently anchored on a conductive support titanium oxynitride (TiON x ) dispersed over carbon-based Ketjen Black and covered by a thin layer of copper (Ir/CuTiON x /C), which gets removed in the preconditioning step. Electrochemical OER activity, stability, and structural changes were compared to the Ir-based catalyst, where Ir nanoparticles without Cu are deposited on the same support (Ir/TiON x /C). To study the effect of the sacrificial less-noble metal layer on the catalytic performance of the synthesized material, characterization methods, namely X-ray powder diffraction, X-ray photoemission spectroscopy, and identical location transmission electron microscopy were employed and complemented with scanning flow cell coupled to an inductively coupled plasma mass spectrometer, which allowed studying the online dissolution during the catalytic reaction. Utilization of these advanced methods revealed that the sacrificial Cu layer positively affects both Ir OER mass activity and its durability, which was assessed via S-number, a recently reported stability metric. Improved activity of Cu analogue was ascribed to the higher surface area of smaller Ir nanoparticles, which are better stabilized through a strong metal-support interaction (SMSI) effect.
