(187c) A Low-Iridium Anode for Durable PEM Water Electrolysis

Proton exchange membrane (PEM) water electrolyzer is an emerging technology to produce green hydrogen of high purity at high current density. However, anode catalyst in industrial PEM electrolyzer heavily relies on iridium oxide (IrO₂), while the scarcity and high price of Ir can potentially impede rapid development of PEM water electrolyzer. Ruthenium oxide (RuO₂) is regarded as a promising alternative to IrO₂ due to its high oxygen evolution reaction activity, while it suffers from poor durability in the harsh environment in PEM electrolyzer anode. A few Ir-Ru bimetallic oxides have been reported quite robust under industrial level current density, while Ir remains the major metal component. On the other hand, some low-Ir OER catalysts succeeded in delivering high activity, while leaving the durability, especially at practical current density, under-investigated.

Herein, we synthesized a series of low-Ir doped RuO_x (Ir-RuO_x) with various Ir doping level, ranging from ~5 at% to ~15 at%. These catalysts have similar rutile structure and Ir atoms were found scattered homogeneously in RuO_x lattice. The OER durability progressively improves with increased Ir doping, and Ir_H-RuO_x successfully delivered outstanding stability of more than 1500 hours at industrial level current density without obvious degradation in a lab-scale PEM water electrolyzer. Metal dissolution rates exhibited a similar trend to the durability tests, validating the significantly suppressed Ru dissolution of Ir-RuO_x. X-ray absorption spectroscopy confirmed the strong interactions between Ir and Ru, which is in good consistent with density function theory study results that the superior durability of Ir_H-RuO_x originated from the stabilizing effects of Ir on adjacent Ru atoms. The Ir_H-RuO_x was also tested by a third party collaborator in a larger scale PEM water electrolyzer device at 60 ^oC for more than 1000 hours and it performed lower degradation rate than commercial IrB catalyst, suggesting potential in future commercialization.