Proton Exchange Membrane (PEM) water electrolysis technology can directly couple with fluctuating renewable energy sources for hydrogen production. This approach not only ensures grid safety but also enables the redistribution of renewable resources, making it a crucial technological foundation for achieving carbon neutrality. However, due to the acidic environment of PEM water electrolysis, the technology currently relies heavily on iridium, a precious metal that is stable under acidic conditions, as the anode catalyst. Iridium is one of the rarest resources on Earth, with an annual production of only 6-8 tons, and its scarcity poses a significant challenge to scaling up PEM-based hydrogen production.
In response to this, the research team led by Ryuhei Nakamura discovered and harnessed a special affinity between manganese (Mn) and iridium (Ir), developing a highly stable, atomically dispersed hexavalent iridium catalyst (IrVI-ado). This new catalyst maintains high activity and stability while reducing the iridium loading to below 0.1 mg/cm², more than 95% lower than the current iridium loading in PEM water electrolysis (2-4 mg/cm²). Compared to the commonly used Ir⁴⁺ catalysts, this novel catalyst has a higher valence state (Ir⁶⁺) and is atomically dispersed on the surface of γ-MnO₂. The Ir⁶⁺ state enhances the intrinsic activity and stability of iridium, while atomic-level dispersion allows for nearly 100% utilization of iridium. The team conducted a comprehensive analysis of the synthesis, structural characteristics, and PEM water electrolysis performance of the Ir catalyst, clarifying the interaction between Mn and Ir and demonstrating the superior performance of the catalyst with an iridium loading of less than 0.1 mg/cm² in PEM electrolyzers.
The research findings were published in Science under the title "Atomically Dispersed Hexavalent Iridium Oxide from MnO₂ Reduction for Oxygen Evolution Catalysis." The corresponding authors are Ailong Li and Ryuhei Nakamura, with Ailong Li and Shuang Kong as the first authors.
