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

TL;DR

This study combines first-principles simulations with operando XANES to understand iridium oxide catalysts in water-splitting, revealing surface oxygen species and oxidation processes relevant to the oxygen evolution reaction.

Contribution

It introduces a novel computational approach integrating first-principles and continuum models to predict XANES spectra and surface chemistry of IrO₂ under realistic electrochemical conditions.

Findings

Electron-deficient surface oxygen species form during OER.

Surface hydroxyl groups are stable up to ~1 V and oxidize at higher potentials.

Predicted XANES spectra qualitatively match experimental data.

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 \emph{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 $\sim$1 V are suggested to be progressively oxidized at larger potentials, giving rise to a shift in the Ir L$_3$-edge cross-section that qualitatively agrees with measurements.