New polymeric electrolyte membranes based on proton donorproton acceptor properties for direct methanol fuel cells

In order to reduce the high methanol permeability of membranes in a direct methanol fuel cell application new and better materials are still required. In this paper membranes made from polybenzimidazole/sulfonated polysulfone are given and compared with homopolymer membranes made from sulfonated polysulfone, blends of polyethersulfone with sulfonated polysulfone and Nafion N117. Various methods of characterization have been used such as swelling measurements, ion exchange capacity (I.E.C.), electrical resistance, permselectivity, sorption isotherms and methanol permeability which give information on the conductive properties and methanol permeability properties of the membranes. These methods were used as a first estimate to give information about what kind of material is better to be used in a direct methanol fuel cell application.

In this contribution proton donor-proton acceptor membranes based on PBI-SPSf have been prepared and characterized. Their properties were compared with homopolymer SPSf and blend PES/SPSf membranes. In order to select proper materials for DMFC applications critical parameters were used based on conductive properties and permeability properties. It is observed that the presence of PBI inside PBI/SPSf membrane decreases the swelling degree in methanol, water mixtures in comparison with the other obtained membranes and Nafion N117. Based on methanol permeability, PBI/SPSf has values of about one order of magnitude lower than for N117 and about two times lower than for the SPSf homopolymer membrane. The high amount of sulfonic acid groups in PBI/SPSf still dominates the properties.