An international team comprising scientists from Russia’s Southern Federal University, Kurchatov Institute, and Boreskov Institute of Catalysis of the Siberian Branch of the Russian Academy of Sciences, and their counterparts representing South Africa’s HySA program have proposed a way to reduce the cost of green hydrogen without giving up the key, but extremely expensive, material—iridium. Today, this metal has virtually no alternatives in terms of use for the oxygen evolution reaction in proton exchange membrane electrolyzers operating in aggressive acidic environments. Its high price, however, remains one of the main obstacles hindering the scaling of hydrogen technologies.
Instead of searching for a substitute for the rare metal, the scientists focused on how iridium, already in use, behaves under real-world operating conditions. One key element of the study was the catalyst activation stage, i.e. electrochemical preparation of the catalyst before testing. The study has demonstrated that an activation protocol largely determines the state of the iridium surface and, consequently, the catalyst’s efficiency. Depending on the activation mode, various combinations of metallic and oxidic forms occur on the surface, affecting the reaction rate, as well as the catalyst’s stability and service life, in different ways.
Previously, this factor was often overlooked, making it difficult to compare the results of various studies, and advanced materials did not always perform consistently when it was time to make transition from laboratory experiments to applied testing.
In order to accurately assess the contribution of each factor to the process, the researchers chose to work with monometallic iridium catalysts, eliminating possible influence of alloys and additives. This allowed them to establish a direct link between synthesis and activation conditions, on the one hand, and the material’s microstructure and its actual electrochemical efficiency, on the other.
The study’s findings were further tested not only in a standard laboratory three-electrode cell but also in a prototype electrolyzer, where the environment is closer to industrial conditions. These tests showed that even minor variations at the activation stage can significantly alter the catalyst’s performance under high loads and in long-term operation.
As a result of their research, the scientists were able to come up with clear-cut guidelines for the preparation and testing of iridium-containing catalysts, allowing for a more accurate assessment of their potential. For electrolyzer manufacturers, this method opens up an opportunity of cutting the cost of equipment without making radical changes in technology, and, for the industry at large, it offers a chance of reducing dependence on a scarce and expensive resource.
