Engineering a Hierarchical Pt/IrO ₂ Architecture with Tunable Hydrophilicity and High Conductivity for Ultralow‐Ir‐Loading PEM Water Electrolysis

Abstract The widespread adoption of proton exchange membrane water electrolysis (PEMWE) is hindered by inefficient catalyst utilization, primarily due to poor in‐plane conductivity and mass transport within the catalytic layer (CL). Here, a Pt/IrO 2 hierarchical nanostructured membrane electrode assembly (MEA) is presented that overcomes these limitations via structural and interfacial engineering: nanoimprint lithography constructs tapered arrays decorated with IrO 2 catalysts; ion‐sputtering creates an ultrathin Pt interlayer boosting in‐plane conductivity; and in situ growth of Pt nanoflowers confers tunable hydrophilicity. Such a hierarchical nanostructured MEA decreases charge transfer resistance and ohmic resistance by 30.6% and 21.7%, respectively, and lowers mass transport overpotential by 14.1%, in comparison with the conventional MEA. Multiphysics simulations reveal an accelerated transport of H 2 O, O 2 , and H + . PEMWE integrated with the hierarchical MEA delivers a cell voltage of 1.758 V at a current density of 2.0 A cm −2 and with over 300 h stability at an ultralow Ir loading of 0.096 mg cm −2 . This work establishes a scalable and highly efficient strategy for dramatically reducing Ir loading in PEMWE, offering a promising pathway toward cost‐effective hydrogen production.