Acid-Doping Induced\nPhase Separation for Shaping Phase\nMorphology and Enhancing Performance of Polymer Electrolyte Membranes

The control of nanostructure and phase morphology within\nelectrolytes\nis crucial in determining the performance of electrochemical devices,\nsuch as high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs).\nRandom copolymers have been extensively utilized in this field due\nto their straightforward synthetic methods compared to block copolymers.\nHowever, achieving precise control over the nanostructure of these\nrandom copolymers is challenging, owing to the irregular distribution\nof hydrophilic and hydrophobic segments along their backbone. Herein,\nwe introduce the acid doping-induced phase separation of random copolymers\ncontaining basic moieties driven by base–acid interaction with\nphosphoric acid (PA). Small-angle X-ray scattering analysis revealed\nthat increased functionalization led to phase separation and inversion,\nindicative of dispersed PA distribution, impacting membrane morphology\nand phase dynamics. The phase morphology control improves proton conductivity\nand PA retention up to 130% and 260% increases, respectively, resulting\nin a significant enhancement in power density, a 20% boost to 200\nmW/cm<sup>2</sup>.