Novel nanocomposite membranes were prepared by infiltration of a blend of sulfonated PEEK (SPEEK) with polyvinyl alcohol (PVA), using water as solvent, into electrospun nanolibers of SPEEK blended with polyvinyl butyral (PVB). The membranes were characterized for their application on Direct Methanol Fuel Cells (DMFCs) operating at moderate temperatures (>80 degrees C). An important role of the solvent on the crosslinking temperature for the SPEEK-PVA system was observed. A mat of hydrated SPEEK-30%PVB nanofibers revealed higher proton conductivity in comparison with a dense membrane of similar composition. Incorporation of the nanoliber mats to the SPEEK-35%PVA matrix provided mechanical stability, methanol barrier properties and certain proton conductivity up to a crosslinking temperature of 120 degrees C. Not remarkable effect of the nanofibers was found above that crosslinking temperature. The combined effect of the nanofibers and crosslinking temperature on the properties of the membranes is discussed. DIV1FC performance experiments concluded promising results for this new low-cost type of membranes, although further optimization steps are still required. (C) 2015 Elsevier B.V. All rights reserved.