Polybenzimidazole (PBI)/ionic liquid (IL) functional Si-O-Si network composite membranes are prepared from PBI with 1-(3-trimethoxysilylpropyl)-3-methylimidazolium chloride. The IL can be hydrolyzed to form Si-O-Si network structure under acidic conditions. And such IL functional Si-O-Si network (NP) in the composite membranes could improve phosphoric acid doping levels and proton conductivities simultaneously. The ability of retaining more PA is also reflected in the high proton conductivity value of PBI/NP -15% membrane which shows almost three-fold increment compared to the pristine PBI. All the PBI/NP-X composite membranes display excellent chemical stability and improved mechanical strength. This is attributed to Si-O-Si network structure. Moreover, PBI/NP composite membranes have demonstrated high thermal stability up to 250 degrees C, which is attractive for high-temperature (>200 degrees C) proton exchange membrane fuel cells. (C) 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.