Surface-initiated atom transfer radical polymerization has been performed on poly(vinylidene fluoride) electrospun nanofibers (PVDFNF) to incorporate poly(styrenesulfonic acid) (PSSA) chains tethered on PVDFNF surfaces. The obtained PSSA-g-PVDFNF nanofibers are used as reinforcement for Nafion to prepare Nafion/PSSA-g-PVDFNF composite membrane (Nafion/NF-CM). The PSSA chains tethered on the nanofiber surfaces improve the interfacial compatibility between the nanofiber reinforcement and the Nafion matrix, and might provide a proton-conducting pathway along the nanofibers. As a result, the proton conductivity of Nafion/NF-CM membrane is 2.5-fold of the value recorded with the nanofiber-free recasting Nafion membrane. The H-2/O-2 single cell employing Nafion/NF-CM membrane shows a maximum power density of 770 mW cm(-2) which is 1.5-fold of the value recorded with the commercial Nafion 212 membrane and a current density at 0.6 V of 940 mA cm(-2) which is about 2.7-fold of the value recorded with Nafion 212. The Nafion/NF-CM membrane is also suitable for direct methanol fuel cell, in which it could be operated at a 5 M methanol solution to show a cell performance of 91.2 mW cm(-2) for maximum power density and 464 mA cm(-2) for current density at 0.2 V, which are about 1.5-fold of the values recorded with the commercial Nafion 117 membrane at 2 M methanol solution. (C) 2014 Elsevier B.V. All rights reserved.