Operando XANES from first-principles and its application to iridium oxide

Abstract

Efficient electro-catalytic water-splitting technologies require suitable catalysts for the oxygen evolution reaction (OER). The development of novel catalysts could benefit from the achievement of a complete understanding of the reaction mechanism on iridium oxide (IrO 2 ), an active catalyst material that is, however, too scarce for large-scale applications. Considerable insight has already been provided by operando X-ray absorption near-edge structure (XANES) experiments, which paved the way towards an atomistic description of the catalyst's evolution in a working environment. We combine here first-principles simulations augmented with a continuum description of the solvent and electrolyte to investigate the electrochemical stability of various IrO 2 interfaces and to predict the XANES cross-section for selected terminations under realistic conditions of applied potential. The comparison of computed O K-edge XANES spectra to corresponding experiments supports the formation of electron-deficient surface oxygen species in the OER-relevant voltage regime. Furthermore, surface hydroxyl groups that are found to be stable up to ∼1 V are suggested to be progressively oxidized at larger potentials, giving rise to a shift in the Ir L 3 -edge cross-section that qualitatively agrees with measurements.

Increased Ir–Ir Interaction in Iridium Oxide during the Oxygen Evolution Reaction at High Potentials Probed by Operando Spectroscopy

“…This redox change at higher potentials is important to note since mostly an increase of the Ir oxidation state at applied OER potentials was observed, which are also highly oxidizing conditions. [30][31][32][33]49 However, the applied potentials used here are also higher than in these previous studies.…”

Epitaxial Stabilization and Oxygen Evolution Reaction Activity of Metastable Columbite Iridium Oxide

“…We first observe R-IrO 2 (110) to be more stable than R-IrO 2 (100) under both synthesis and OER conditions, in agreement with previous studies. 59,60 For α-IrO 2 , the (101) facet is less stable than the (100) facet for all chemical potentials less oxidative than the OER conditions, although this effect is less pronounced when considering surface energies normalized per surface area instead of surface units (Figure S3). This result is consistent with the larger number of Ir-O bonds broken (4 vs. 3 per surface unit) at the surface for the (101) facet compared to that for the (100) facet (Figure S14 and Table S5).…”

Discovery of Acid-Stable Oxygen Evolution Catalysts: High-Throughput Computational Screening of Equimolar Bimetallic Oxides

“…Four low-index facets ([001], [100], [101], [110]) were considered, the most stable coverages at the reaction condition were determined, and catalytic activities of all unique active sites were evaluated . Although not all facets are equivalently stable because of different surface energies and the relative stability of facets could be affected by the electrode potential, it is much more informative to consider various possible facets instead of focusing only on the most stable one. For example, it was found that an exhaustive search of active sites by modeling multiple facets could rationalize the experimental observations of interesting catalytic properties of Ni–Ga catalysts for CO 2 reduction .…”