Effect of IrO₆ Octahedron Distortion on the OER Activity at (100) IrO₂ Thin Film

Abstract

The (100) crystallographic plane is the most active facet of iridium dioxide (IrO 2 ) for the oxygen evolution reaction (OER). Pulsed laser deposition was used to grow (100) IrO 2 on a (100) SrTiO 3 substrate at deposition temperature ranging from room temperature to 600 °C. Detailed structural and morphological characterization was performed using AFM, XRD, and X-ray reciprocal space mapping (RSM) to unravel the geometrical arrangement of [IrO 6 ] octahedra in the (100) IrO 2 thin films. It is shown that the symmetry mismatch between the substrate and the epitaxial thin film imposed an orthorhombic distortion of the tetragonal structure of IrO 2 and, as a consequence, the [IrO 6 ] geometry is distorted. These data were correlated to the OER characteristics established from electrochemical measurements. DFT modeling was employed to relate differences in surface relaxation of IrO 2 films prepared at different temperatures with changes in OER activity. Vacancy formation leads to higher surface stability at temperatures around 500 °C, which corresponds to the deposition temperature at which the electrocatalytic activity of (100) epitaxial IrO 2 film is maximal.

Influence of the MnO2 Phase on Oxygen Evolution Reaction Performance for Low‐Loading Iridium Electrocatalysts

“…Meanwhile, the increase of iridium valence may also lead to the distortion of IrO 6 octahedron. These would be beneficial for OER performance [26b,28] . Moreover, the Mn valence was lower than 4+ while the iridium valence was higher than 4+, revealing the electron transfer from IrO 2 to MnO 2 .…”

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

“…As catalytic reactions are in most part shape dependent this could result in a less active surface for the OER. [6,[74][75][76] Second, Ir on Ir/middle-TiON x /rGONRs has the smallest average nanoparticle size (2.5 ± 0.3 nm) of the Ti-containing catalysts, so it has the highest available active surface area per mass of Ir. Both Ir/low-TiON x /rGONRs and Ir/high-TiON x /rGONRs have larger Ir particles with a size of 3.4 ± 0.5 and 2.9 ± 0.2 nm, respectively.…”

Advanced Transition Metal‐Based OER Electrocatalysts: Current Status, Opportunities, and Challenges

“…The symmetry mismatch between substrate and epitaxial thin film can also impose an orthorhombic distortion of the tetragonal structure of IrO 2 , which produces the distorted [IrO 6 ] geometry and tensile strain in the direction perpendicular to the substrate. [ 77 ] A surface relaxation by the formation of oxygen vacancy appears at the same time, which becomes an active site and contributes to the increase in the activity of strained IrO 2 film. Doping heteroatom is another effective method to regulate the electronic structure of active sites.…”