Bifunctional Acid Proton Conductor Doping to Improve the Comprehensive Properties of a Cross-Linked Polybenzimidazole High-Temperature Proton Exchange Membrane

Improving the comprehensive properties of the high-temperature proton exchange membrane (HTPEM) under wide relative humidity (RH) is a crucial factor affecting the application. For this, a zirconium 4,4-[aminopropyl sulfonate (methyl phosphate)] diphenylamine sulfonic acid (Zr-PPSA), containing −SO3H suitable for proton transfer at high RH and -PO3H2 for conduction at low RH is prepared. The highly functionalized tri-glycidyl isocyanurate (TGIC) as a cross-linker of poly-m-polybenzimidazole (mPBI) is beneficial to improve the membrane-forming property, mechanical strength, and oxidative stability of the composite membranes under less addition. The mPBI–TGIC/ZrPPSA composite membranes are obtained by doping Zr-PPSA in the cross-linked mPBI–TGIC networks at a uniform and high level, which is expected to achieve efficient proton transport. The molecular dynamics simulation primarily proves the proton transfer mechanism. At 180 °C, the proton conductivity of mPBI–TGIC(5)/ZrPPSA(30) and mPBI–TGIC(10)/ZrPPSA(40) can reach 0.125 and 0.134 S/cm at 100% RH and 0.021 and 0.025 S/cm at 0% RH, respectively. After the washing test for 96 h, the decline of conductivity for mPBI–TGIC(10)/ZrPPSA(40) is 2.25%. The mPBI–TGIC(10)/ZrPPSA(40) membrane also exhibits low methanol permeability (8.33 × 10–8 cm2 s–1 at 90 °C). The mPBI–TGIC/ZrPPSA membranes with high proton conductivity, durability, and membrane selectivity are a good candidate for the application in HTPEM.