Inorganic modification of proton conductive polymer membranes for direct methanol fuel cells

New organic-inorganic composite membranes based on sulfonated polyetherketone (SPEK) and sulfonated poly(ether ether ketone) (SPEEK) for application in the direct methanol fuel cell (DMFC) were synthesized. The membranes' water and methanol permeabilities were evaluated in pervaporation experiments and the conductivity determined by impedance spectroscopy. The permeabilities were decreased by inorganic modification. The first approach was the in situ generation of SiO₂, TiO₂ or ZrO₂. The modification with ZrO₂ led to a 60-fold reduction of the methanol flux. However, a 13-fold reduction of conductivity was also observed. Modification with organically modified silane led to a 40-fold decrease of the water permeability without a large decrease of proton conductivity. A good balance of high conductivity and low water and methanol permeability was possible with a mixture of ZrO₂ and zirconium phosphate. In this case, a 28-fold reduction of water flux was observed with only 10-30% reduction of proton conductivity.