Kinetically Constrained Semicrystallization of IrO ₂ with Balanced Activity and Stability for Acidic Oxygen Evolution Reaction

The activity–stability trade-off for IrO 2 constrains the development of proton exchange membrane water electrolyzers (PEMWEs). Conventionally, high IrO 2 crystallinity ensures oxygen evolution reaction (OER) stability while compromising activity, while amorphous structure offers high OER activity while sacrificing durability. Herein, we develop a kinetically constrained amorphization strategy using high-temperature thermal shock to precisely tune IrO 2 crystallinity, capturing an ideal intermediate state: low-crystallinity IrO 2 (LC-IrO 2 ). LC-IrO 2 merges the high activity of amorphous IrO 2 derived from the short-range order and the robust stability of crystalline IrO 2 with structural rigidity. Consequently, the LC-IrO 2 catalyst simultaneously achieves excellent catalytic activity and stability for acidic OER. A PEMWE using a LC-IrO 2 anode requires only 1.69 V to reach 1 A cm –2 at 60 °C and maintains steady operation for 500 h with a negligible degradation rate. This study demonstrates kinetic crystallinity control as a new paradigm for electrocatalyst design.