Tunnel-structured IrOx unlocks catalytic efficiency in proton exchange membrane water electrolyzers
2025-08-15
Proton exchange membrane water electrolyzers face challenges due to high iridium loading and sluggish oxygen evolution reaction kinetics when using conventional rutile-structured iridium oxide nanocatalysts. Here we find that iridium oxide catalysts with a specific tunnel-type crystal structure exhibit highly localized reactivity, where regions at tunnel mouths drive oxygen evolution far more efficiently than tunnel-wall regions. The intrinsic activity of tunnel mouths is 25-fold higher than that of tunnel walls, with shorter nanorods achieving a better balance between active site exposure and electron/mass transport efficiency. When implemented in proton exchange membrane water electrolyzers, this engineered catalyst achieves notable performance at low iridium loading (0.28 mg Ir cm −2 ), delivering over 2.0 A cm −2 at 1.8 V (80 °C) and operating stably for 1800 h—notably outperforming conventional catalysts. Our work identifies catalytic hotspots in tunnel-structured oxides and demonstrates their rational integration into high-performance, durable electrolyzer systems.