Limited Surface Oxide Growth as a Prerequisite for Stabilizing Low-Loading Iridium Electrodes for PEM Water Electrolysis

As the demand for hydrogen production increases, the economic viability and stability of Ir-based catalysts are crucial in proton exchange membrane water electrolysis (PEMWE). In this study, stable low-loading Ir electrodes (0.2 mg$_{Ir}$ cm$^{–2}$) with nanometer-thick electrodeposited layers are prepared on Pt-deposited Ti felts. State-of-the-art techniques, such as operando quick extended X-ray absorption fine structure spectroscopy (QEXAFS) and identical-location transmission electron microscopy (IL-TEM) employing an ultramicroelectrode (UME), were used to demonstrate the structural transformation of surface Ir during oxygen evolution reaction (OER) and the pivotal role of catalyst film thickness control on the self-terminated growth of crystalline IrO$_2$, which enhances catalyst stability. A lack of a stabilizing IrO$_2$ sublayer in thin electrodeposited Ir layers (<10 nm) leads to a fully amorphous catalyst structure, directly impacting its durability. The obtained Ir/IrO$_2$/IrO$_x$ electrodes achieve catalytic activities of 1.8–12 A mg$^{–1}$ at 1.6 V$_{Cell}$ while maintaining a degradation rate of 8.7 μV h$^{–1}$ @ 2 A cm$^{–2}$ during accelerated stress tests (>1000 h) and 1.6 times greater stability (corresponding to a lifespan of 55,000 h) and 3.6 times higher mass activity compared to commercial Ir oxide electrodes.