Zirconium hydrogen phosphate/disulfonated poly(arylene ether sulfone) copolymer composite membranes for proton exchange membrane fuel cells

A series of zirconium hydrogen phosphate/disulfonated poly(arylene ether sulfone) random copolymer composite membranes for proton exchange membrane fuel cell applications were prepared and characterized by optical clarity, water absorption, proton conductivity measurements, mechanical testing, direct methanol fuel cell (DMFC) performance, and methanol permeability. Composite membranes incorporating up to 40 wt.% of zirconium phosphate were prepared by an in situ precipitation method. In this method, the water-swollen acid form of directly prepared disulfonated copolymer films were immersed in aqueous solutions of zirconyl chloride (ZrOCl2) at 80 °C, followed by treatment in 1 M phosphoric acid (H3PO4) solution for 24 h. During this time the zirconium hydrogen phosphate (ZrP) nanoparticles precipitated in the swollen pores of the membrane. The content of ZrP in the composite membranes was controlled by the concentration of ZrOCl2 solution, and was determined by weight difference. Zirconium hydrogen phosphate concentration was also dependent upon the ion exchange capacity (IEC) of the polymer as well as the temperature at which the copolymers were acidified. The composite films had good thermal stability and excellent retention of zirconium hydrogen phosphate after water treatment at 120 °C for 100 h. Although the composite membranes exhibited lower proton conductivity than the pure copolymer membranes at room temperature, the presence of the inorganic particles led to an improvement in high-temperature conductivity. For example, fully hydrated membranes (40 mol% disulfonation) with 38 wt.% zirconium hydrogen phosphate had a conductivity of 0.06 S/cm at room temperature and linearly increased up to 0.13 S/cm in water vapor at 130 °C, whereas the pure copolymer which had 0.07 S/cm at room temperature only reached a conductivity of 0.09 S/cm at 130 °C.