High temperature composite membranes based on polybenzimidazole and dendrimer amine functionalized SBA-15 mesoporous silica for fuel cells

Abstract

In this study SBA-15, melamine-based dendrimer amine functionalized SBA-15 mesoporous silica (MDA-SBA-15), and the 1,3-di(3-methylimidazolium) propane dibromide dicationic ionic liquid (pr(mim)₂Br₂) were used in order to improve the proton conductivity, and thermal and mechanical stability of phosphoric acid (PA) doped polybenzimidazole (PBI)-based composite membranes for application in high-temperature proton exchange membrane (PEM) fuel cells. The effect of the porous structure of the mesoporous silica on the performance of the PA doped PBI-based membrane containing pr(mim)₂Br₂ was investigated under high temperature. The experimental results implied that MDA-SBA-15 containing the groups of NH₂, and melamine-based dendrimer amines (MDA) on the internal wall of its pores provides special sites for further interaction with pr(mim)₂Br₂, PBI, and PA in the composite membranes. The presence of NH₂ and MDA groups plays an important role in creating several pathways for proton exchange in the composite membranes. The PA-doped PBI-based composite membranes containing 4.5% w/w pr(mim)₂Br₂, and 1.5% w/w MDA-SBA-15 exhibit a high proton conductivity of 0.22 S cm⁻¹ at 180 °C under dry conditions. The current density of 1.18 A cm⁻², and power density of 0.60 W cm⁻² at 0.50 V and 180 °C confirm the enhanced potential of the PA doped PBI-based composite membranes for application in high-temperature PEM fuel cells.