Synthesis and properties of the PVDF-based proton exchange membranes with incorporated cross-linked sulphonated polystyrene for fuel cells

• Thermal copolymerisation of styrene monomers inside a PVDF film was developed.
• New composite PEMs for FC have been obtained using this approach.
• The transport properties and performance of the PEMs in FC have been investigated.

New proton exchange membranes have been obtained by the thermal copolymerisation of styrene and divinylbenzene inside polyvinylidene fluoride (PVDF) films followed by sulphonation. The content of incorporated cross-linked polystyrene moieties and the ion exchange capacity (IEC) values of the membranes reach 50 wt.% and 2 mmol/g, correspondingly, under the proposed approach. It was found that the dependency of the membrane proton conductivity on the IEC values has a threshold character. This fact indicates that the cross-linked sulphonated polystyrene (CSPS) phase has a micro-heterogeneous distribution across the membrane section. The main feature of the obtained membranes is low methanol uptake. It was found that the membrane with IEC ~ 2 mmol/g sorbs approximately 45 wt.% of water and only 30 wt.% of methanol. The synthesised membranes were tested in both hydrogen and direct methanol fuel cells (DMFC). The highest power density of 130–155 mW/cm2 in the hydrogen fuel cell was found for the PVDF-CSPS membrane, which exceeds the corresponding value for a Nafion-115 cell (approximately 100 mW/cm2). The characteristics of DMFCs are similar to both the PVDF-CSPS and Nafion-115 membranes.