Potential Dependence of Ir Dissolution Using Time-Resolved Measurements
Authors: Kariuki Nancy N. , Myers Deborah J. , Park Jae Hyung , Wang Xiaohua , Ahluwalia Rajesh 
Published: September 2023

Electrocatalysis efforts in low temperature, PEM-based electrolysis tend to focus on the oxygen evolution reaction (OER) since it is several orders of magnitude kinetically slower than its counterpart, the hydrogen evolution reaction (HER). 1 In comparison to other OER catalysts, Ir-based metal oxides (IrOx) 2-6 are regarded as the best PEM electrolyzer electrocatalysts as they are both active and are relatively stable.7, 8 However, even Ir-based electrocatalysts slowly undergo dissolution under the operating conditions of the electrolyzer anode. 9-10, 7 Considering the low Earth abundance and high-cost of Ir, understanding the kinetics and mechanism of its electrochemical dissolution is of vital importance to develop strategies targeting high activity, long-term stability, and limited metal dissolution in acidic media. Mechanistic studies of both OER and dissolution at the solid–liquid interface are more challenging, as they typically require detection of reaction intermediates with short lifetimes. An electrochemical cell coupled to a highly-sensitive analytical technique provides a platform for detection of dissolution products and may help to resolve the degradation pathway of Ir and its oxides and the correlation to the OER mechanism.

In this work, we aim to understand the structure-durability relation for different Ir oxides. An electrochemical flow cell system connected to an inductively-coupled plasma-mass spectrometer (ICP-MS) capable of detecting trace concentrations (<ppb) of dissolved elements in solution is used to investigate the dissolution processes of Ir from the oxides. The influence of various parameters such as potential, potentiodynamic profile parameters (e.g., scan rate, upper and lower potential limits) and catalyst type, on the dissolution processes in acidic electrolytes at room temperature will be investigated. Fundamental models have been developed to explain the mechanisms of the dissolution processes under various conditions. Moreover, the structural changes before and after catalyst testing will be studied. Further, the electrochemical data combined with the ICP-MS data will be correlated with X-ray absorption spectroscopy (XAS) and small angle X-ray scattering (SAXS) to obtain a comprehensive view of the oxide structure.

Acknowledgements

This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) under the H2NEW Consortium. This work was authored in part by Argonne National Laboratory, a U.S. Department of Energy (DOE) Office of Science laboratory operated for DOE by UChicago Argonne, LLC under contract no. DE-AC02-06CH11357.

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