Defective K ₂ Ti ₈ O ₁₇ Nanorod Supports Enable Stable High‐Current‐Density Acidic Water Electrolysis via Confinement‐Engineered IrO _x

Abstract This study tackles the dual challenges of sluggish oxygen evolution reaction (OER) kinetics and excessive iridium loading in proton exchange membrane water electrolysis (PEMWE) via rational catalyst design. Through a rapid synthesis strategy, it is anchored ultrafine IrO _x nanoparticles (<3 nm) on K ₂ Ti ₈ O ₁₇ (KTO), achieving exceptional acidic OER activity with ultra‐low Ir content (10.89 wt.%). The IrO _x /KTO‐1 catalyst exhibits 4.4× higher mass activity than IrO ₂ in acidic OER. In PEMWE cells, it delivers 3 A cm ⁻² at 1.79 V (44.0 kWh kg ⁻¹ ) and sustains >550 h at 1000 mA cm ⁻² (H ₂ cost: $0.88 kg ⁻¹ , 56% below US‐DOE 2026 target). Crucially, it maintains stability for 500 h at 3000 mA cm ⁻² and strong operational reliability under volatile renewable energy inputs, showcasing its potential for industrial‐scale implementation. In situ Raman spectroscopy, X‐ray analyses, and DFT calculations reveal that interfacial charge redistribution between KTO and sub‐nano IrO _x dynamically activates Ir sites during OER, accelerates charge transfer, and reduces the OER reaction barrier. The synergy of size‐controlled active sites and defect‐mediated electronic modulation enables simultaneous high activity, stability, and industrial current density tolerance. This work establishes a paradigm for designing confinement‐stabilized nanocatalysts toward practical green hydrogen production.