A novel polymeric electrolyte membrane for direct alcohol fuel cells(DAFCs) and direct formic acid fuel cells (DFAFCs) was developed using a pore-filling method. This composite consisted of a porous polytetrafluoroethylene (PTFE) microporous substrate filled with silane-crosslinked sulfonated poly (styrene-ethylene/butylene-styrene) (sSEBS). This composite membrane was characterized using field emission scanning electron microscopy, Fourier-transform infrared spectrometry, thermal gravimetric analysis, and differential scanning calorimetry. The thermal and mechanical stabilities of this composite membrane were good. The methanol and ethanol permeabilities of this composite membrane were lower than Nafion 117, and these two membranes had comparable ionic conductivities. The power densities in direct methanol fuel cells with this composite electrolyte were higher than with the Nafion electrolyte. A peak power density of 91.4mW cm(-2) was achieved at 70 degrees C when the cell was fed with 0.5 M methanol. A direct ethanol fuel cell using this composite exhibited a peak power density of 16.5 mW cm(-2) at 60 degrees C. In a DFAFC, a peak power density of 81.4 mW cm(-2) was achieved with this composite and 3 M fuel at 60 degrees C. Long-term cell performance was sustained during a 180-h continuous operation using this pore-filled PTFE/sSEBS composite electrolyte. This PTFE/sSEBS composite membrane has potential for use in proton-exchange DAFC and DFAFC applications. (C) 2014 Elsevier B. V. All rights reserved.