One of the main limiting factors in the production of “green” hydrogen via electrochemical water splitting is the relatively slow rate of the oxygen evolution reaction (OER) and the use of very expensive noble metals like iridium to catalyze the reaction. Now, a team of scientists from University of Bayreuth in Germany (www.uni-bayreuth.de) and Shenzhen University in China (en.szu.edu.cn), led by professor Francesco Ciucci, have demonstrated a novel atomic geometry to catalyze the reaction, significantly improving OER activity while also reducing the volume of noble metals used. Their method disperses individual iridium atoms — in a much smaller amount than typically required for OER — coupled with dimethylimidazole (MI) and cobalt-iron (CoFe) hydroxide supports, in an out-of-plane orientation.
Another benefit of this method is the ultra-low overpotential (the additional energy required to speed up the reaction) for this catalyst geometry when compared with traditional OER catalysts. Scientists have been studying single-atom catalysis with out-of-plane coordination to improve different electrochemical processes, but this was the first work to report on noble-metal single atoms on metal hydroxides in the context of OER.
The team’s work indicated the unique coordination between the single iridium atoms and MI, which they believe redistributes charge around the Ir site and reduces the reaction energy barrier. According to the team, the catalyst synthesis takes place in a simple, two-step process at ambient temperatures and pressures. They also used this method to synthesize additional types of atomically dispersed single-atom geometries supported by porous hydroxide materials, showing that this preparation platform can be used for a wide range of catalytic reactions, including those requiring platinum, palladium and ruthenium.
The researchers have tested the iridium-CoFe-OH-MI catalyst in a two-electrode water-splitting cell in the laboratory, as well as in an anion-exchange membrane (AEM) electrolyzer. In the AEM demonstration, the electrolyzer exhibited stable operation for over 150 h with little degradation at a voltage of 500 mA cm–2. This work was first described in the October 2024 issue of Nature Nanotechnology.