Engineering Gradient Porosity and Wettability to Construct High-Efficiency Low-Iridium Anode for Proton Exchange Membrane Water Electrolysis

The efficiency of proton exchange membrane water electrolysis (PEMWE) is critical for green hydrogen production. However, transport limitations involving protons, electrons, and mass within the anode severely restrict catalyst utilization, typically necessitating high iridium (Ir) loadings. In this work, we design an anode featuring a dual-gradient (DG) design in both porosity and wettability to maximize three-phase interfaces and enhance mass transport. Compared to a single-diameter nanofiber network anode, the DG anode increases the electrochemically active surface area by a factor of 1.7 and reduces mass transport and ohmic overpotentials by 65% and 7%, respectively. Consequently, the membrane electrode assembly (MEA) with the DG anode achieves a high performance of 1.91 V at 4 A cm^-2 with a low Ir loading of 0.2 mg cm^-2 and demonstrates stable operation for over 500 h at 1.5 A cm^-2, which is significantly better than the conventional design with the same Ir loading. Pore-scale multiphysics provide visualized illustration of the gas-liquid two-phase transport behavior within different pore structures. This work provides a design strategy for high-performance, low-cost PEMWE devices.