Properties of phosphoric acid doped Poly(benzimidazole/sulfone/siloxane/amide)/Sulfonated Polystyrene/Silica nanoparticle-based proton exchange membranes for fuel cells

Abstract

New siloxane and sulfone containing poly(benzimidazole/sulfone/siloxane/amide) (PBSSA) has been prepared for the formation of hybrid membranes (PBSSA/PS-S/SiNPs) with sulfonated polystyrene (PS-S) and 0.1 wt%-2 wt% silica nanoparticles (SiNPs). Field emission scanning electron micrographs showed good dispersion of filler, formation of dense nanoporous honeycomb like structure and uniform ionic pathway in these hybrids. The porous membrane structure was responsible for the fine water retention capability and higher proton conductivity of the new hybrids. Increasing the amount of nanoparticles from 0.1 wt% to 2 wt% increased the tensile stress of acid doped PBSSA/PS-S/SiNPs nanocomposites from 65.7 MPa to 68.5 MPa. A relationship between nanofiller loading and thermal stability of the membranes was also experientially studied, as the glass transition temperature of phosphoric acid doped PBSSA/PS-S/SiNPs nanocomposites increased from 207 °C to 215 °C. The membranes also had higher ion exchange capacity (IEC) around 2.01 mmol/g to 3.01 mmol/g. The novel membranes with high IEC value achieved high proton conductivity of 1.10–2.34 S/cm in a wide range of humidity values at 80 °C which was higher than that of perfluorinated Nafion^®117 membrane (1.1 × 10⁻¹ S/cm) at 80 °C (94% RH). A H₂/O₂ fuel cell using the PBSSA/PS-S/SiNP 2 (IEC 3.01 mmol/g) showed better performance than that of Nafion^® 117 at 40 °C and 30% RH.