Electronic and\nStructural Property Comparison of Iridium-Based\nOER Nanocatalysts Enabled by <i>Operando</i> Ir L<sub>3</sub>‑Edge X‑ray Absorption Spectroscopy

In this study, we investigate the electronic and structural\nbehavior\nof a newly developed and of a commercially available Ir-based oxygen\nevolution reaction (OER) catalyst under relevant conditions employing\nan <i>operando</i> Ir L<sub>3</sub>-edge X-ray absorption\nnear-edge structure and extended X-ray absorption fine structure approach.\nThe newly developed Kopernikus P2X amorphous IrO<sub><i>x</i></sub>/TiO<sub>2</sub> catalyst is compared to the current commercial\nbenchmark catalyst: crystalline IrO<sub>2</sub>/TiO<sub>2</sub>, Umicore\nElyst. Analysis of the redox behavior of the catalysts shows distinct\nelectronic differences between the amorphous and crystalline oxides,\nwith the former exhibiting significant reversible electronic transformations.\nEmploying an equivalent charge transfer approach following Faraday’s\nlaw of electrolysis, we study the behavior of the catalysts under\nequivalent OER conditions (chronopotentiometric steps), as opposed\nto the conventional chronoamperometric approach. This enables the\nderivation of property–structure relationships under equivalent\nOER conditions for materials exhibiting distinctly different activities.\nThe P2X IrO<sub><i>x</i></sub>/TiO<sub>2</sub> catalyst\nundergoes substantial electronic structure changes, with larger reduction\nin the Ir–O bond lengths compared to that of the commercial\nbenchmark catalyst. The correlation between electronic states and\nlocal geometric information highlights diverse OER pathways, suggesting\nthat the newly developed P2X IrO<sub><i>x</i></sub>/TiO<sub>2</sub> catalyst and the benchmark IrO<sub>2</sub>/TiO<sub>2</sub> commercial catalyst follow mechanisms akin to those of amorphous\niridium oxide (am-IrO<sub><i>x</i></sub>) and rutile-IrO<sub>2</sub>, respectively. These results shed light on the intrinsic\nactivities of different iridium oxide-based catalysts and provide\ncrucial insights for enhancing their performances in proton exchange\nmembrane water electrolyzers.