Improved proton conductive membranes from poly(phenylenebenzophenone)s with pendant sulfonyl imide acid groups for fuel cells

Abstract

Super gas-phase acidity of the sulfonyl imide groups have become the attractive materials for polymer electrolyte membranes. Therefore, sulfonyl imide functionalized proton exchange membranes (SI-PPBP) have been prepared from poly(phenylene)s by carbon-carbon coupling polymerization. Initially, fully aromatic poly(phenylenebenzophenone)s backbones (PPBP) have been synthesized from newly synthesized symmetrical 1,4-dichloro-2,5-diphenylene methoxy benzophenone (PMBP) and 1,4-dichloro-2,5-dibenzoyl benzene (PBP) monomers using Ni (0) catalyst. Afterward, the incorporation of the sulfonyl imide groups onto the PPBP polymer backbones has been carried by post-modification process. The synthesized sulfonyl imide based PPBP polymers (SI-PPBP) membranes exhibit a rational ion exchange capacity from 1.00 to 1.76 meq/g., water uptake from 28.7 to 62.7% and proton conductivity from 74.9 to 142.85 mS/cm. Noticeably, SI-PBP- 40 shows higher conductivity (142.85 mS/cm) compare to Nafion 117® (84.73 mS/cm). The thermogravimetric analysis (TGA), tensile strength and Fenton test have been used to evaluate the thermal, mechanical and chemical stability of the synthesized SI-PPBP membranes, respectively. The hydrophilic/hydrophobic phase separation of the polymer membranes have been investigated by the atomic force microscopic (AFM). All the results support the potential features of the synthesized SI-PPBP membranes to be used an alternative material to Nafions for fuel cells.