Quaternised Polymeric Ionic Liquid/Polybenzimidazole Membranes with Improved Acid Retention for Fuel Cells

Abstract

Phosphoric acid (PA)-doped polybenzimidazole (PBI) is an ideal choice of membrane materials for high temperature proton exchange membrane fuel cells (HT-PEMFCs) as efficient clean energy devices. PA-doped PBI (PBI/PA) membranes exhibit favorable proton conductivity. However, extended usage results in the leaching of PA and the deterioration of mechanical qualities. Here, we prepared quaternised linear polymeric ionic liquid (PIL)/quaternary ammonium (QA)-type methyl polybenzimidazole (QMPBI) containing silane cross-linker composite membranes through a series of treatments. This design improves both proton conductivity and PA retention through the QA group, the conserved NH site and the high attraction of PIL to PA. Meanwhile, the introduced silane cross-linked structure ensures the mechanical properties and chemical stability of the membranes. Among them, the QMPBI-P-O10-T90 (P: PIL, O: TOPEA, T: TEA) membrane achieves a proton conductivity of 135.5 mS cm-1 at 180 °C and an acid retention of 85.3% at 160 °C/0% RH. In addition, at 160 °C without humidity, the peak power density of QMPBI-P-O10-T90 membrane can reach 523.2 mW cm-2. This synthesis strategy offers a promising new approach to fabricate polymeric ionic liquid-based crosslinked membranes for various applications.

Keywords: quaternary ammonium, polymeric ionic liquid, polybenzimidazole, silane cross-linker, high proton conductivity.