Ordered Ba ₂ EuIrO ₆ Double Perovskite With Active Ir─O _bri ─Eu Unit for Enhanced Electrocatalytic Oxygen Evolution in PEMWE

ABSTRACT 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 Ba 2 EuIrO 6 double perovskite is demonstrated as a promising anode material for catalyzing oxygen evolution reaction (OER) in acid electrolyte. The Ba 2 EuIrO 6 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 BaIrO 3 and commercial IrO 2 catalysts. It is discovered that the oxygen bridged Ir─O bri ─Eu unit in Ba 2 EuIrO 6 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 Ba 2 EuIrO 6 ‐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.