Synthesis and characterization of fluoro sulfonyl imide-based poly(benzoyl diphenyl benzene) membranes for proton exchange membrane fuel cells

This study aims to enhance proton exchange membrane fuel cell (PEMFC) performance by synthesizing and characterizing sulfonyl imide-based poly(benzoyl diphenyl benzene) (SI-PBDPB) membranes. The objective is to develop ether-free SI-PBDPB polymers with dibenzoyl functionalities, using Ni/Zn catalysts, to improve conductivity, flexibility, chemical and mechanical integrity. These membranes exhibit superior ion exchange capacity (IEC) ranging from 0.98 to 1.78 meq/g and water uptake between 8.11 % and 48.48 %. Notably, the SI-PBDPB-40 membrane achieves exceptional proton conductivity of 118.61 mS/cm and a maximum power density of 0.63 W/cm2, outperforming Nafion 211® benchmarks of 104.5 mS/cm and 0.59 W/cm2. The sulfonyl imide groups enhance chemical resistance and facilitate efficient proton transport through distinct hydrophilic-hydrophobic phase separation. The thermal, mechanical, and chemical integrity of the SI-PBDPB membranes is confirmed by thermogravimetric analysis (TGA), tensile test, and Fenton’s reagent test, respectively. Atomic force microscopy (AFM) reveals well-defined ionic channels that contribute to their elevated proton conduction. These findings position SI-PBDPB membranes as promising candidates for next-generation PEMFCs.