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

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 K₂Ti₈O₁₇ (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 IrO₂ 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 (H₂ 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.