Oxygen Evolution Reaction Activity in IrO x/SrIrO3 Catalysts: Correlations between Structural Parameters and the Catalytic Activity

The formation of unsaturated IrOx in SrIrO3 by cobalt-doping for acidic oxygen evolution reaction

Electrocatalytic water splitting is a promising route for sustainable hydrogen production. However, the high overpotential of the anodic oxygen evolution reaction poses significant challenge. SrIrO3-based perovskite-type catalysts have shown great potential for acidic oxygen evolution reaction, but the origins of their high activity are still unclear. Herein, we develop a Co-doped SrIrO3 system to enhance oxygen evolution reaction activity and elucidate the origin of catalytic activity. In situ experiments reveal Co activates surface lattice oxygen, rapidly exposing IrOx active sites, while bulk Co doping optimizes the adsorbate binding energy of IrOx. The Co-doped SrIrO3 demonstrates high oxygen evolution reaction electrocatalytic activity, markedly surpassing the commercial IrO2 catalysts in both conventional electrolyzer and proton exchange membrane water electrolyzer.

Modulating the oxygen evolution reaction activity of SrIrO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 catalysts using electric-field polarization

The physical properties of epitaxially grown SrIrO3 thin films are sensitive to external influences. This provides a rare opportunity to study their physical properties as regulated by electric-field polarization of their substrates, thus affecting their oxygen evolution reaction activity. In this work, SrIrO3 films were epitaxially grown on (001)-oriented Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMNPT) single-crystal substrates by pulsed laser deposition. After applying an electric field to the PMNPT along the [001] direction, a lattice strain is induced by rotation of its ferroelectric domains, and this lattice strain is transferred to the interior of the SrIrO3 film through the epitaxial interface. This changes the surface resistivity of the SrIrO3 film and affects its electrocatalytic activity. Our findings suggest that substrate polarization is a feasible method for regulating the electrocatalytic performance of SrIrO3 thin films, and this provides new inspiration for the structural design of other composite catalysts.

Supported Iridium-based Oxygen Evolution Reaction Electrocatalysts - Recent Developments

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.

Tuning Reconstruction Level of Precatalysts to Design Advanced Oxygen Evolution Electrocatalysts

Surface reconstruction engineering is an effective strategy to promote the catalytic activities of electrocatalysts, especially for water oxidation. Taking advantage of the physicochemical properties of precatalysts by manipulating their structural self-reconstruction levels provide a promising methodology for achieving suitable catalysts. In this review, we focus on recent advances in research related to the rational control of the process and level of surface transformation ultimately to design advanced oxygen evolution electrocatalysts. We start by discussing the original contributions to surface changes during electrochemical reactions and related factors that can influence the electrocatalytic properties of materials. We then present an overview of current developments and a summary of recently proposed strategies to boost electrochemical performance outcomes by the controlling structural self-reconstruction process. By conveying these insights, processes, general trends, and challenges, this review will further our understanding of surface reconstruction processes and facilitate the development of high-performance electrocatalysts beyond water oxidation.

Surface stability of perovskite oxides under OER operating conditions: a first principles approach

Understanding the surface stability of perovskite oxides under OER operating conditions is crucial for the atomistic design of electrocatalysts for electrochemical water-splitting.

Atomic-Level Manipulations in Oxides and Alloys for Electrocatalysis of Oxygen Evolution and Reduction

As chemical reactions and charge-transfer simultaneously occur on the catalyst surface during electrocatalysis, numerous studies have been carried out to attain an in-depth understanding on the correlation among the surface structure and composition, the electrical transport, and the overall catalytic activity. Compared with other catalysis reactions, a relatively larger activation barrier for oxygen evolution/reduction reactions (OER/ORR), where multiple electron transfers are involved, is noted. Many works over the past decade thus have been focused on the atomic-scale control of the surface structure and the precise identification of surface composition change in catalyst materials to achieve better conversion efficiency. In particular, recent advances in various analytical tools have enabled noteworthy findings of unexpected catalytic features at atomic resolution, providing significant insights toward reducing the activation barriers and subsequently improving the catalytic performance. In addition to summarizing important surface issues, including lattice defects, related to the OER and ORR in this Review, we present the current status and discuss future perspectives of oxide- and alloy-based catalysts in terms of atomic-scale observation and manipulation.

A Spin Coating Method To Deposit Iridium-Based Catalysts onto Silicon for Water Oxidation Photoanodes

Silicon has shown promise for use as a small band gap (1.1 eV) absorber material in photoelectrochemical (PEC) water splitting. However, the limited stability of silicon in acidic electrolyte requires the use of protection strategies coupled with catalysts. Herein, spin coating is used as a versatile method to directly coat silicon photoanodes with an IrO_x oxygen evolution reaction (OER) catalyst, reducing the processing complexity compared to conventional fabrication schemes. Biphasic strontium chloride/iridium oxide (SrCl₂:IrO_x) catalysts are also developed, and both catalysts form photoactive junctions with silicon and demonstrate high photoanode activity. The iridium oxide photoanode displays a photocurrent onset at 1.06 V vs reversible hydrogen electrode (RHE), while the SrCl₂:IrO_x photoanode onsets earlier at 0.96 V vs RHE. The differing potentials are consistent with the observed photovoltages of 0.43 and 0.53 V for the IrO_x and SrCl₂:IrO_x, respectively. By measuring the oxidation of a reversible redox couple, Fe(CN)₆^3-/4-, we compare the charge carrier extraction of the devices and show that the addition of SrCl₂ to the IrO_x catalyst improves the silicon-electrolyte interface compared to pure IrO_x. However, the durability of the strontium-containing photoanode remains a challenge, with its photocurrent density decreasing by 90% over 4 h. The IrO_x photoanode, on the other hand, maintained a stable photocurrent density over this timescale. Characterization of the as-prepared and post-tested material structure via Auger electron spectroscopy identifies catalyst film cracking and delamination as the primary failure modes. We propose that improvements to catalyst adhesion should further the viability of spin coating as a technique for photoanode preparation.