Catalyst stability and expense remain serious obstacles to widespread adoption of hydrogen generation using proton-exchange membrane electrolysis. In a study published in Science, researchers led by Ryuhei Nakamura at the RIKEN Center for Sustainable Resource Science (CSRS) in Japan report a new method that reduces the amount of iridium needed for the reaction by 95%, without altering the rate of hydrogen production.

Li et al. devised a means of oxidizing iridium catalysts to the +6 oxidation state using manganese oxide as the oxidant. The resultant iridium(VI) oxide proved highly active and stable over several months of continuous PEM testing, consistent with prior modeling predictions.

The mass-specific activity (1.7 × 10⁵ amperes per gram of iridium) and turnover number (1.5 × 10⁸) exceeded those of benchmark iridium oxides, and in situ x-ray analysis during PEM operations manifested the durability of Ir^VI at current densities up to 2.3 amperes per square centimeter. The high activity and stability of Ir^VI-ado showcase its promise as an anode material for PEM electrolysis.

—Li et al.

The researchers found that when they spread out individual iridium atoms on a piece of manganese oxide so that they didn’t touch or clump with each other, hydrogen production in a proton exchange membrane (PEM) electrolyzer was sustained at the same rate as when using iridium alone, but with 95% less iridium.

With the new catalyst, continuous hydrogen production was possible for over 3000 hours (about 4 months) at 82% efficiency without degradation.

Nakamura believes that the level of hydrogen production achieved with the new catalyst has high potential for immediate usefulness. The team has begun collaborating with partners in industry, who have already been able to improve on the initial iridium-manganese catalyst.

Moving forward, the RIKEN CSRS researchers plan to continue investigating the specific chemical interaction between iridium and manganese oxide, with hopes of reducing the amount of necessary iridium even more. At the same time, they will continue collaborating with industrial partners, and plan on deploying and testing the new catalyst on an industrial scale in the near future.

Resources

• Ailong Li et al. (2024) “Atomically dispersed hexavalent iridium oxide from MnO2 reduction for oxygen evolution catalysis.” Science 384,666-670 doi: 10.1126/science.adg5193