Microbial fuel cell (MFC) is a bioreactor for simultaneous electricity generation and wastewater treatment. Modified nanocomposite membranes based on sulfonated poly ether ether ketone (SPEEK) and sulfonated SiO2 (SiO2-SO3H) were fabricated and evaluated in a microbial fuel cell configuration. Proton conductivity, water uptake, ion exchange capacity (IEC), oxygen crossover, internal resistance and MFC performance of SPEEK membrane, SPEEK incorporated with silica (SPEEK-SiO2) composite membrane and SPEEK incorporated with various percentages of sulfonated silica composite membranes (S-2.5%, S-5%, S-7.5% and S-10%) were studied and compared. The results revealed that the incorporation of sulfonated SiO2 improved the proton conductivity of the SPEEK membrane effectively and exhibited the highest peak power density of 1008 mW m(-2) for S-7.5%, when compared to 680 mW m(-2) and 802 mW m(-2) obtained for SPEEK and SPEEK-SiO2 membranes respectively in a single chambered microbial fuel cell (SCMFC). In comparison to Nafion 115 (320 mW m(-2)) the composite membrane delivered more than 3-fold higher power density in the same MFC setup. The oxygen mass transfer coefficient (K-O) of the composite membranes decreased with the increase in the sulfonated SiO2 content of the membrane. The internal resistance for S-7.5% and SPEEK membranes were measured to be 46 Omega and 71 Omega respectively. The improved performance of the composite membranes was due to the higher proton conductivity of the introduced SiO2-SO3H that facilitated an effective proton transfer in the membrane. (C) 2015 Elsevier Ltd. All rights reserved.