Low methanol permeable and highly selective membranes composed of pure and/or partially sulfonated PVdF-co-HFP and polyaniline

Blend membranes fabricated from partially sulfonated poly(vinylidene fluoride-co-hexafluoro propylene) and partially sulfonated polyaniline (SPVdF-co-HFP/SPAni) have shown inspiring results in terms of methanol permeability, membrane selectivity and ion-exchange capacity toward their targeted application as a low cost polymeric membrane in direct methanol fuel cell. It is widely known that compared to conventional blending, layered membrane coating results in superior membrane properties. Therefore, in this work, we demonstrate fabrication of tri-layered sandwich PAni/PVdF-co-HFP/PAni, PAni/SPVdF-co-HFP/PAni and SPAni/SPVdF-co-HFP/SPAni membranes and the resulting enhancements of transport properties of these coated membranes in comparison to that of pristine PVdF-co-HFP, pristine SPVdF-co-HFP, pristine Nafion, PVdF-co-HFP/PAni blend, SPVdF-co-HFP/PAni blend and SPVdF-co-HFP/SPAni blend membranes. The tri-layered coated sandwich membranes exhibited higher proton conductivities, ion-exchange capacities, membrane selectivities and open-circuit potentials, and lower methanol permeabilities at all methanol concentrations, compared to their blend counterparts. In addition, the coated membranes exhibited superiority over pristine Nafion in terms of methanol permeability and membrane selectivity at high methanol concentrations. Furthermore, the DMFC performance obtained with the SPAni/SPVdF-co-HFP/SPAni tri-layered coated membrane was found to be superior to that of pristine Nafion, pristine SPVdF-co-HFP and SPVdF-co-HFP/SPAni blend membranes at high methanol feed concentration (i.e. 6 M).