Abstract
Proton exchange membrane water electrolyzers (PEMWEs) have emerged as one of the most promising technologies for the large-scale production of clean hydrogen. Gigawatt scale deployment of PEMWEs requires substantial reduction in the loading of iridium (Ir), which is one of the most expensive and rarest elements. Substantial reduction in Ir loading calls for the development of innovative Ir-based anodes, which requires a clear understanding of how iridium oxides accelerate the sluggish oxygen evolution reaction (OER) in acidic media. Herein, we studied the structure and OER electrocatalysis of three representative iridium oxides ─ hydrous, amorphous, and rutile ─ by employing a combination of physicochemical and electrochemical characterization. We found that the hydrous iridium oxide had a different local structure of IrO6 octahedra and a superior OER intrinsic activity compared with the other two, and that the OER activities of all three types decreased with decreasing pH of acidic solution. We proposed that the OER process of these iridium oxides is limited by water nucleophilic attack on the OER intermediate oxygenated adsorbates. Based on this mechanism, we attributed the superior OER activity of hydrous iridium oxides to their longer Ir-O bonds and the pH-dependent OER activity of iridium oxides to the pH-dependent oxidation of Ir.
| Original language | English |
|---|---|
| Pages (from-to) | 8414-8425 |
| Number of pages | 12 |
| Journal | ACS Catalysis |
| DOIs | |
| State | Accepted/In press - 2025 |
Funding
Part of this research is supported by the US Army Contract: W911NF2320017, Clean Hydrogen by Electrochemical Methods (CHEM). This research used beamline 7-BM (QAS) of the National Synchrotron Light Source II, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract DE-SC0012704. Beamline operations were supported in part by the Synchrotron Catalysis Consortium Grant DE-SC0012335. A portion of this work was conducted as part of the Hydrogen from Next-generation Electrolyzers of Water (H2NEW) consortium, funded by the U.S. DOE Office of Energy Efficiency and Renewable Energy (EERE) Hydrogen and Fuel Cell Technologies Office (HFTO). Electron microscopy research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. We also would like to thank Dr. Cortney Mittelsteadt for his insightful discussions on the experiments and results.
Keywords
- cyclic voltammogram
- iridium oxides
- MEAs
- OER mechanisms
- tafel slopes
- water electrolysis