Synergistic Acid–Base Interfaces in Phosphoric Acid-Doped Polymer Electrolytes for Efficient H2/O2 Fuel Cells

Developing high-temperature proton exchange membranes (HT-PEMs) with high performance is vital for advancing fuel cell technology. This research demonstrates the development and optimization of acid–base PEMs through the blending of a sulfonated poly(1,4 phenylene ether–ether sulfone) (SPEES) and a quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) doped with phosphoric acid (PA). In the PA-doped SPEES/QPPO polymer networks, the sulfonic acid (−SO₃H), quaternary ammonium (−NR₄⁺), and PA (−OH and −PO₄^3–) groups established acid–base interactions. The enhancement of thermomechanical stability, proton conduction, and durability of PEM fuel cells (PEMFCs) can be ascribed to the functional contributions of PA groups. Experimental findings reveal that the proton conductivity of SPEES-QPPO/PA reached 159.7 mS cm^–1 at 90 °C and 95% relative humidity (RH). The membrane exhibits a maximum power and current density of 0.770 W cm^–2 and 1.835 A cm^–2 at 70 °C in 95% RH, demonstrating excellent power performance and minimal degradation over 110 h of constant discharge at 0.4 A cm^–2. According to the findings, the PA-doped blended membranes achieved a 3.1-fold higher performance than pristine SPEES, making them well-suited for HT-PEMFC applications.