X射线光电子能谱
透射电子显微镜
催化作用
降级(电信)
氧气
析氧
材料科学
X射线
光谱学
光化学
化学
X射线光谱学
纳米技术
化学工程
电化学
物理化学
物理
光学
计算机科学
电极
工程类
生物化学
有机化学
电信
量子力学
作者
Fabien Claudel,Laëtitia Dubau,G. Berthomé,Lluís Solà-Hernández,Christian Beauger,L. Piccolo,Frédéric Maillard
标识
DOI:10.1021/acscatal.9b00280
摘要
Determining the degradation mechanisms of oxygen evolution reaction (OER) catalysts is fundamental to design improved proton-exchange membrane water electrolyzer (PEMWE) devices but remains challenging under the demanding conditions of PEMWE anodes. To address this issue, we introduce a methodology combining identical-location transmission electron microscopy (IL-TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements, and apply it to iridium nanoparticles (NPs) covered by a thin oxide layer (IrOx) in OER conditions. The results show that, whatever the initial OER activity of the IrOx nanocatalysts, it gradually declines and reaches similar values after 30 000 potential cycles between 1.20 and 1.60 V versus the reversible hydrogen electrode (RHE). This drop in OER activity was ascribed to the progressive increase of the Ir oxidation state (fast change during electrochemical conditioning, milder change during accelerated stress testing) along with the increased concentrations of hydroxyl groups and water molecules. In contrast, no change in the mean oxidation state, no change in the hydroxyl/water coverage, and constant OER activity were noticed on the benchmark micrometer-sized IrO2 particles. In addition to chemical changes, Ir dissolution/redeposition and IrOx nanoparticle migration/agglomeration/detachment were made evident during the conditioning stage and in OER conditions, respectively. By combining the information derived from IL-TEM images and XPS measurements, we show that Ir(III) and Ir(V) are the best performing Ir valencies for the OER. These findings provide insights into the long-term OER activity of IrOx nanocatalysts as well as practical guidelines for the development of more active and more stable PEMWE anodes.
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