Researchers have developed a nickel-stabilized, ruthenium dioxide (Ni-RuO2) anode catalyst for proton exchange membrane (PEM) water electrolysis. The ruthenium—a more abundant precious metal—serves as a promising alternative to the more rare and expensive iridium—currently the practical anode catalyst for electrolysis.
The Ni-RuO2 catalyst shows high activity and durability in acidic OER for PEM water electrolysis. Although pristine RuO2 shows poor acidic OER stability and degradesd within a short period of continuous operation, the incorporation of Ni greatly stabilizes the RuO2 lattice and extends its durability by more than one order of magnitude.
A schematic shows the experimental water electrolyzer developed at Rice to use a nickel-doped ruthenium catalyst. Illustration by Zhen-Yu Wu
A paper on the work by the lab of chemical and biomolecular engineer Haotian Wang at Rice’s George R. Brown School of Engineering and colleagues at the University of Pittsburgh and the University of Virginia is published in Nature Materials.
When applied to the anode of a PEM water electrolyser, our Ni-RuO2 catalyst demonstrated >1,000 h stability under a water-splitting current of 200 mA cm−2, suggesting potential for practical applications. Density functional theory studies, coupled with operando differential electrochemical mass spectroscopy analysis, confirmed the adsorbate-evolving mechanism on Ni-RuO2, as well as the critical role of Ni dopants in stabilization of surface Ru and subsurface oxygen for improved OER durability.—Wu et al.
Iridium costs roughly eight times more than ruthenium, Wang said, and it could account for 20% to 40% of the expense in commercial device manufacturing, especially in future large-scale deployments.
Water splitting involves the oxygen and hydrogen evolution reactions by which polarized catalysts rearrange water molecules to release oxygen and hydrogen.
The cathode is very stable and not a big problem, but the anode is more prone to corrosion when using an acidic electrolyte. Commonly used transition metals like manganese, iron, nickel and cobalt get oxidized and dissolve into the electrolyte. That’s why the only practical material used in commercial proton exchange membrane water electrolyzers is iridium. It’s stable for tens of thousands of hours, but it’s very expensive.—Feng-Yang Chen
The lab is working to improve its ruthenium catalyst to slot into current industrial processes.
Now that we’ve reached this stability milestone, our challenge is to increase the current density by at least five to 10 times while still maintaining this kind of stability. This is very challenging, but still possible.
The annual production of iridium won’t help us to produce the amount of hydrogen we need today. Even using all the iridium globally produced will simply not generate the amount of hydrogen we will need if we want it to be produced via water electrolysis. That means we can’t fully rely on iridium. We have to develop new catalysts to either reduce its use or eliminate it from the process entirely.—Haotian Wang
Boyang Li of the University of Pittsburgh is co-lead author of the paper. Co-authors are Rice graduate student Peng Zhu; graduate student Shen-Wei Yu at Virginia; physicist Zou Finfrock at Argonne National Laboratory; scientist Debora Motta Meira of Argonne and Canadian Light Source; Virginia alumnus Zhouyang Yin; and Qiang-Qiang Yan, Ming-Xi Chen, Tian-Wei Song and Hai-Wei Liang of the University of Science and Technology of China, Hefei. Co-corresponding authors are Sen Zhang, an associate professor of chemistry at Virginia, and Guofeng Wang, a professor of mechanical and materials science at Pittsburgh. Haotian Wang is the William Marsh Trustee Chair at Rice and an assistant professor of chemical and biomolecular engineering.
The research was supported by the Welch Foundation (C-2051-20200401), the David and Lucile Packard Foundation (2020–71371), a Roy E. Campbell Faculty Development Award, the National Science Foundation (1905572, 2004808), the University of Pittsburgh Center for Research Computing and the Advanced Photon Source of Argonne National Laboratory.
Wu, ZY., Chen, FY., Li, B. et al. (2022) “Non-iridium-based electrocatalyst for durable acidic oxygen evolution reaction in proton exchange membrane water electrolysis.” Nat. Mater. doi: 10.1038/s41563-022-01380-5