Synthesis and fuel cell performance of phosphonated hybrid membranes for PEMFC applications

The present work reports on the synthesis of novel organic–inorganic hybrid composites for proton exchange membranes. These original membranes are based on anionically synthesized phosphonic acid polymers, grafted to functionalized silica nanoparticles, and then dispersed in a matrix of poly(vinylidenefluoride-co-hexafluoropropylene), noted poly(VDF-co-HFP). In a first step, poly(vinylphosphonic acid) with different molecular weights (3.2 and 40 kg/mol) were synthesized from commercially available diethylvinylphosphonate and then grafted onto silica. In a second step, various amounts of phosphonic grafted silica nanoparticles, noted SiO2-g-PVPA, were dispersed in the poly(VDF-co-HFP) matrix to prepare membranes by solvent casting. Membranes with phosphonated silica particle loadings from 20 to 63 wt% exhibited proton conductivities from 23 to 54 mS/cm in immersed conditions at 80 °C. The highest values were obtained for the membrane with the highest silica content. Interestingly, the corresponding composite membrane, with a loading of 63 wt%, displayed a power density of 800 mW/cm2 (60 °C, 1.5 A/cm2) in single fuel cell tests.