Atomic Samarium Doping Reinforces Ir/IrO 2 Heterointerface for Efficient Acidic Overall Water Splitting

ABSTRACT Proton exchange membrane water electrolysis (PEMWE) is constrained by the sluggish oxygen evolution reaction (OER) kinetics and the intrinsic activity‐stability trade‐off of Ir‐based anodes. In this work, an atomically Sm‐doped Ir/IrO 2 heterointerface catalyst is fabricated via a facile ligand‐assisted foaming strategy. The optimized catalyst achieves overpotentials of 246 mV for OER and 19 mV for HER at 10 mA cm −2 in an acidic electrolyte, with a remarkable mass activity of 835.91 A g Ir −1 at 1.53 V and long‐term stability for 500 h. In PEM electrolyzer, the catalyst delivers 1 A cm −2 at 1.70 V and maintains stability for 325 h, demonstrating great promise for practical acidic water splitting. Combining in‐situ spectroscopy and DFT calculations reveals that Sm, with its unique 4f electronic configuration, serves as an electron donor to downshift the d‐band center of Ir and strengthen the Ir–O covalent bond. Such electronic modulation tends to the AEM pathway and optimizes the adsorption energetics of oxygenated intermediates. The rate‐determining step shifts from *OOH formation to *OH dehydrogenation, thereby reducing the reaction free‐energy and mitigating irreversible Ir overoxidation. This work establishes lanthanide doping at heterointerfaces as a powerful strategy to break the activity‐stability trade‐off in acidic water splitting.