Acid-Doping Induced Phase Separation for Shaping Phase Morphology and Enhancing Performance of Polymer Electrolyte Membranes

The control of nanostructure and phase morphology within electrolytes is crucial in determining the performance of electrochemical devices, such as high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Random copolymers have been extensively utilized in this field due to their straightforward synthetic methods compared to block copolymers. However, achieving precise control over the nanostructure of these random copolymers is challenging, owing to the irregular distribution of hydrophilic and hydrophobic segments along their backbone. Herein, we introduce the acid doping-induced phase separation of random copolymers containing basic moieties driven by base–acid interaction with phosphoric acid (PA). Small-angle X-ray scattering analysis revealed that increased functionalization led to phase separation and inversion, indicative of dispersed PA distribution, impacting membrane morphology and phase dynamics. The phase morphology control improves proton conductivity and PA retention up to 130% and 260% increases, respectively, resulting in a significant enhancement in power density, a 20% boost to 200 mW/cm².