An Efficient and Durable Low‐Iridium Catalyst Enabled by a Potential‐Triggered Dual‐Pathway Mechanism for Acidic Water Oxidation

ABSTRACT Addressing the activity‐durability trade‐off of low‐iridium anode catalysts remains a key challenge for acidic oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE). Herein, we develop a three‐dimensional ordered macroporous (3DOM) Cr─Ir solid solution oxide to regulate intersite oxygen intermediate reactivity for efficient and durable acidic water oxidation. Solid solution formation, together with the ordered macroporous architecture, creates electronically and geometrically coupled Cr─Ir dual sites that enable a potential‐triggered coupling between the conventional adsorption evolution mechanism (AEM) and the oxide pathway mechanism (OPM). Beyond the AEM pathway involving *OOH intermediates at Ir sites, anodic polarization activates surface Cr─OH species into Cr─O moieties that cooperate with adjacent Ir─O species to promote intersite O─O coupling, thereby preserving the structural robustness associated with AEM while harnessing the activity advantage of OPM. As a result, Cr 0.72 Ir 0.28 O x achieves an overpotential of 254 mV at 10 mA cm −2 in acidic electrolyte and sustains stable PEMWE operation for over 2000 h at current densities up to 3.0 A cm −2 at an Ir loading of 0.36 mg Ir cm −2 . This work establishes pathway coupling through architectural engineering as a viable design strategy for practical low‐iridium PEMWE catalysts, advancing sustainable hydrogen energy technologies.