Double filler reinforced ionomers: A new approach to the design of composite membranes for fuel cell applications

A novel approach to mechanically reinforce polymer electrolyte membranes for fuel cells was developed by using hydrophilic zirconium phosphate (ZP) and hydrophobic fluoroalkyl zirconium phosphate (ZF) as a two-component mixed filler of a short-side-chain perfluorosulfonic acid (PFSA) membrane. Composite membranes filled with 10 wt% ZF and 5 wt% ZP have a strongly enhanced elastic modulus (E) and yield stress (sigma(gamma)) with respect to the unmodified PFSA (Delta E/E similar to 300%, Delta sigma(gamma)/sigma(gamma) similar to 95% at 70 degrees C and 80% relative humidity (RH)) and to the single filler membranes with optimized ZP or ZF loadings. In the RH range 5095%, the in-plane conductivity of the mixed filler membrane is comparable with that of the unmodified PFSA, both at 80 and 110 degrees C, in spite of a lower water content. At 50% RH, the mixed filler membrane shows better fuel cell performance in H-2/air than the neat PFSA in terms of higher OCV, lower H-2 crossover and greater power density, with peaks of 0.82 W cm(-2) at 80 degrees C, and 0.70 W cm(-2) at 110 degrees C.