Layered double hydroxides (LDH) were incorporated into Nafion polymer for the development of innovative hybrid nanocomposites exploitable in the high temperature PEM fuel cells. Mg2+/Al3+ LDHs (at two metal ratios, 2:1 and 3:1) with different countervailing anions in the interlayer space (CO32-, CIO4-, NO3-) were synthesized, while fully exfoliated composite membranes were prepared by solution intercalation method. NMR technique (diffusion and relaxation) was used to investigate the transport properties of water confined in membranes. The protons dynamics appears to be influenced from the Mg2+/Al3+ metal ratios of the nanoadditives, while the type of anion affects the electrochemical measurements. Compared to filler-free Nafion, both water absorption and diffusion in the hybrid membranes are increased with a noteworthy behavior at high temperature, proving the exceptional water retention property of these materials together with superior mechanical properties. The proton conductivity reaches 2.7 x 10(-2) S cm(-1) at 100 degrees C and 50% RH, as the best value for the composite based on Naf-LDH-Mg2+/Al3+(2/1)-NO3-. (C) 2015 Elsevier B.V. All rights reserved.