Grain Boundary Defect Engineering in Rutile Iridium Oxide Boosts Efficient and Stable Acidic Water Oxidation

Proton exchange membrane water electrolysis (PEMWE) is considered a promising technology for coupling with renewable energy sources to achieve clean hydrogen production. However, constrained by the sluggish kinetics of the anodic oxygen evolution reaction (OER) and the acidic abominable environment render the grand challenges in developing the active and stable OER electrocatalyst, leading to low efficiency of PEMWE. Herein, we develop the rutile-type IrO₂ nanoparticles with abundant grain boundaries and the continuous nanostructure through the joule heating and sacrificial template method. The optimal candidate (350-IrO₂) demonstrates remarkable electrocatalytic activity and stability during the OER, presenting a promising advancement for efficient PEMWE. DFT calculations verified that grain boundaries can modulate the electronic structure of Ir sites and optimize the adsorption of oxygen intermediates, resulting in the accelerated kinetics. 350-IrO₂ affords a rapid OER process with 20 times higher mass activity (0.61 A mg_Ir ^-1) than the commercial IrO₂ at 1.50 V vs. RHE. Benefiting from the reduced overpotential and the preservation of the stable rutile structure, 350-IrO₂ exhibits the stability of 200 h test at 10 mA cm^-2 with only trace decay of 11.8 mV. Moreover, the assembled PEMWE with anode 350-IrO₂ catalyst outputs the current density up to 2 A cm^-2 with only 1.84 V applied voltage, long-term operation for 100 h without obvious performance degradation at 1 A cm^-2.