Contribution of Zeolitic Imidazolate Framework-8 in Improving the Performance of Polymer Electrolyte Membrane for Direct Methanol Fuel Cell

Proton conducting pathways in PES-cSMM were developed by introducing ZIF-8 within the PES-cSMM membranes. The PES-cSMM was fabricated using dry-wet phase inversion techniques and 3wt.% of cSMM was found to be the best combination. Compared to Nafion® 117, the selectivity is 38% higher and 95% greater in the methanol barrier but 30% lower in proton conductivity. This study highlights PES-cSMM/ZIF-8 as a potential candidate for DMFC applications comparable to or even better than Nafion® 117 in particular aspects. The imidazole -N-H linker forms a chain of hydrogen bonds in the terminal PES-cSMM/ZIF-8, which facilitates proton transport and the hydrophobic backbone acts as a filter for methanol. Despite the water uptake value of PES-cSMM/ZIF-8 being 13-fold higher than Nafion® 117, and the sieving performance towards methanol has increased by 99%, the proton conductivity remains unchanged at only about 20 mScm-1. The structural flexibility of ZIF-8 in PES-cSMM provides relatively good proton conduction, while the ZIF-8 cage provides an excellent barrier for methanol crossover. Computational findings suggest the PES-cSMM interaction has been identified to involve covalent bonding. The chemical interactions that involved in PES-cSMM/ZIF-8 were described via topology analysis using Atom in Molecules/ Non-covalent analysis (AIM/NCI) technique.