Proton Conductor Confinement Strategy for Polymer Electrolyte Membrane Assists Fuel Cell Operation in Wide‐Range Temperature

Abstract Acid loss and plasticization of phosphoric acid (PA)‐doped polymer electrolyte membranes are critical hampers for its actual application especially during startup/shutdown stages due to the produced water and thermal stress. To conquer these barriers, a proton conductor confinement strategy is introduced, which may trap PA molecules in the side‐chain acidophilic microphase and weaken plasticizing effect caused by PA toward the polymer backbone to remain membrane tensile stress. The grafted polyphenylene oxide (PPO) is synthesized as model polymers, both molecular electrostatic potential and molecular dynamics reveal the retention mechanism between PA and side‐chain of PPO as well as the aggregation state of PA. Through precisely regulating polymer side‐chain structure and defined plasticization quantitative indicator, significant refinements in membrane's conductivity, durability, and single‐cell performance are achieved successfully. The designed PPO membranes exhibit ultra‐fast and stable proton conducting even at low proton carrier concentrations and under wide‐range working temperature between 80 ^oC–180 °C as well as satisfied resistance to harsh accelerated aging test. These insights will shed light on holistic understanding of PA interactions and retention from molecular level, and provide radical approaches toward high‐performance PA/PEMs design.