Structural Modulation of TiO2 Supports by Cr Doping to Tune Ir Electronic Structure and Accelerate Acidic OER

Abstract

The oxygen evolution reaction (OER) in acidic media is a critical bottleneck for proton-exchange membrane water electrolysis (PEMWE) due to sluggish kinetics and the high cost of noble-metal catalysts. To address these challenges, we report a lowloading Ir catalyst supported on Cr-doped TiO₂ (Ir/TiCrO_x) synthesized via a molten-salt method. This catalyst exhibits excellent acidic OER activity, delivering an overpotential of 219 mV at 10 mA cm^-2 and a Tafel slope of 76 mV dec^-1. When integrated into a membrane electrode assembly under simulated industrial PEMWE conditions, Ir/TiCrO_x achieves a cell voltage of 1.73 V at 2.0 A cm -2 and sustains stable operation for 380 h with a low degradation rate of ~10 µV h^-1 . Structural characterization shows that Cr doping promotes the anatase-to-rutile phase transformation of TiO₂, inducing lattice expansion and generating abundant oxygen vacancies in the supported IrO₂. These structural distortions and vacancy-rich environments modulate the electronic structure of Ir sites and reduce the oxidation energy barrier of Ir species. Mechanistic studies indicate that the modified support facilitates oxidation of Ir⁴⁺ to highly active Ir⁶⁺, and the presence of Ir⁶⁺ accelerates the proton-transfer step during the *OH → *O conversion, thereby improving OER kinetics. Overall, this work demonstrates a practical structural-modulation strategy to enhance the activity and durability of low-loading Ir-based catalysts for industrial PEMWE applications.