This work reports the successful fabrication of Pd nanostructured proton conducting-fluid blocking barriers on standard perfluorosulfonic acid membranes, able to reduce considerably methanol crossover in Direct Methanol Fuel Cells. The barrier nanostructure and grafting to the underlying membrane was optimized by fine-tuning the deposition conditions. A reduction in methanol crossover up to 50% was achieved, increasing significantly the fuel cell efficiency, admitting a slight power density reduction with respect to a reference cell. The developed barriers hindered methanol transport through the membrane as well as water transport, therefore membrane dehydration can be observed at low current density, if operating conditions are not suitably modified. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.