Understanding the oxygen evolution reaction (OER) and Ir dissolution mechanisms in amorphous, hydrous iridium oxides (am-hydr-IrO_x) is hindered by the reliance on crystalline iridium oxide theoretical models to interpret its behaviour. This study presents a comprehensive investigation of hydrous iridium oxide thin films (HIROFs) as a model for am-hydr-IrO_x to elucidate electronic and structural transformations under OER conditions of proton exchange membrane water electrolyzers (PEM-WE). Employing in situ and operando Ir L₃-edge X-ray absorption spectroscopy supported by density functional theory calculations, we introduce a novel surface H-terminated nanosheet model that better characterizes the short-range structure of am-hydr-IrO_x compared to previous crystalline models, which exhibits elongated Ir–O bond lengths compared to rutile-IrO₂. This atomic model unveils the electronic and structural transformations of am-hydr-IrO_x, progressing from H-terminated nanosheets to structures with multiple Ir vacancies and shorter bond-lengths at OER potentials. Notably, Ir dissolution emerges as a spontaneous, thermodynamically driven process, initiated at potentials lower than OER activation, which requires a parallel mechanistic framework describing Ir dissolution by Ir defect formation. Moreover, our results provide mechanistic insights into the activity-stability relationship of am-hydr-IrO_x by systematically screening the DFT-calculated OER activity of diverse Ir and O chemical environments. This work challenges conventional perceptions of iridium dissolution and OER mechanisms in am-hydr-IrO_x, providing an alternative perspective within a dual-mechanistic framework.

中文翻译：

---

揭示高维非晶含水铱氧化物中析氧反应和 Ir 溶解的机理复杂性


由于依赖结晶氧化铱理论模型来解释其行为，因此无法理解非晶态含水铱氧化物 （am-hydr-IrO_x） 中的析氧反应 （OER） 和 Ir 溶解机制。本研究全面研究了含水氧化铱薄膜 （HIOF） 作为 am-hydr-IrO_x 的模型，以阐明质子交换膜水电解槽 （PEM-WE） 在 OER 条件下的电子和结构转变。采用由密度泛函理论计算支持的原位和原位 Ir L₃ 边缘 X 射线吸收光谱，我们引入了一种新的表面 H 封端纳米片模型，与以前的晶体模型相比，该模型更好地表征了 am-hydr-IrO_x 的短程结构，与金红石-IrO₂ 相比，该模型表现出拉长的 Ir-O 键长.该原子模型揭示了 am-hydr-IrO_x 的电子和结构转变，从 H 封端纳米片发展到在 OER 电位下具有多个 Ir 空位和更短键长的结构。值得注意的是，Ir 溶解是一个自发的热力学驱动过程，在低于 OER 激活的电位下启动，这需要一个平行的机理框架来描述 Ir 缺陷形成的溶解。此外，通过系统筛选不同 Ir 和 O 化学环境的 DFT 计算的 OER 活性，我们的结果为 am-hydr-IrO_x 的活性-稳定性关系提供了机制见解。 这项工作挑战了对 am-hydr-IrO_x 中铱溶解和 OER 机制的传统看法，在双重机制框架内提供了另一种视角。