Metastable Hexagonal Ir Based Porous Transport Electrode for Durable and Efficient Oxygen Evolution Reaction in Acidic Media

The acidic oxygen evolution reaction remains a bottleneck in proton exchange membrane water electrolyzers due to sluggish kinetics and catalyst degradation. Here, we report a novel design strategy for one-dimensionally nanostructured, self-standing Ir-based porous transport electrodes featuring a metastable hexagonal Ir phase. This metastable structure is stabilized by dynamic rhenium (Re) dopants with multivalent oxidation states, which not only preserve phase stability but also balance catalytic activity and durability under acidic conditions. The catalyst has exceptional catalytic activity, with a minimal overpotential of 210 mV at a current density of 10 mA cm-2. Combined first-principles and in situ analyses reveal that Re incorporation facilitates dual oxygen evolution pathways via surface reconstruction to IrO₂, enabling synergistic enhancement of both activity and stability. The metastable Ir-based porous transport electrode achieves a high current density of 3.13 A cm-2 at 1.8 V and an exceptionally low degradation rate of 1.34 μV h-1 at 1 A cm-2, where the hierarchical pore networks and highly interconnected catalyst domains are responsible for the exceptional cell performance.