Ordered Ba₂EuIrO₆ Double Perovskite With Active Ir─O_bri─Eu Unit for Enhanced Electrocatalytic Oxygen Evolution in...

The design of a low-Ir-loading anode catalyst with high activity and stability is crucial for the proton exchange membrane water electrolysis (PEMWE), yet it remains a formidable challenge. Herein, an ordered Ba₂EuIrO₆ double perovskite is demonstrated as a promising anode material for catalyzing oxygen evolution reaction (OER) in acid electrolyte. The Ba₂EuIrO₆ achieves a low overpotential of 250 mV at 10 mA cm^-2 and high mass activity with 1.39 A mg^-1 toward OER, outperforming BaIrO₃ and commercial IrO₂ catalysts. It is discovered that the oxygen bridged Ir─O_bri─Eu unit in Ba₂EuIrO₆ plays a critical role as the catalytically active center. In situ spectroscopic studies, isotope labeling measurements and theoretical calculations reveal that the Ir─O_bri─Eu units possess strong proton affinity for proton capture from OOH* and OH*, triggering the bridging oxygen-mediated deprotonation mechanism to break traditional scaling relationships during the OER. Furthermore, the incorporation of Eu modulates the Ir d_z2 orbital to increase the spin density of adsorbed oxygen, accelerating ─OH attack and reducing the energy barrier for OOH* formation. The Ba₂EuIrO₆-loading PEMWE delivers over 1.0 A cm^-2 at only 1.67 V and operates stably for 350 h at 1.0 A cm^-2, demonstrating its good potential for practical applications.