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 degrees 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/cm(2) (60 degrees C, 1.5 A/cm(2)) in single fuel cell tests. (C) 2014 Elsevier B.V. All rights reserved.