An NMR study on the molecular dynamic and exchange effects in composite Nafion/sulfated titania membranes for PEMFCs Isabella Nicotera a,* , Vasiliki Kosma a , Cataldo Simari a , Giuseppe A. Ranieri a , Mirko Sgambetterra b , Stefania Panero b , Maria Assunta Navarra b a Department of Chemistry and Chemical Technologies, University of Calabria, via P. Bucci, 87036 Rende (CS), Italy b Department of Chemistry, Sapienza University of Rome, Piazzale A. Moro 5, 00185 Rome, Italy article info Article history: Received 13 March 2015 Received in revised form 24 June 2015 Accepted 25 June 2015 Available online xxx Keywords: Sulfated titania Nanocomposite PEMFC Self-diffusion NMR Water dynamics abstract Sulfated titania nanoparticles were evaluated as inorganic additives in composite Nafion- based membranes, to be considered as advanced electrolyte in proton exchange membrane (PEM) fuel cells (FCs). Three different filler loadings respect to the polymer were compar- atively investigated to elucidate the effect of the inorganic particles on membrane peculiar properties and finally establish the most effective electrolyte composition. Water dynamics were investigated by NMR spectroscopy, including pulsed-field-gradient diffusion and 1 H spectral analyses conducted as a function of temperature (20e130  C), and by water con- tent measurements, providing a general description of the water management inside the systems and of the effects of the fillers. Due to its strong acidity and hydrophilicity, sulfated titania was found to improve both the water retention and diffusion in the composite membranes in respect to plain recast Nafion, in the whole range of investigated temperatures, with a significant impact in the region of high temperatures and very low water content. In this work, self-diffusion coefficients data were interpreted in terms of a simple “two- sites” model involving exchange between relatively bound and mobile water sites to discuss the nature of water dynamics and the state(s) of the water (bound and free states) both inside composite and filler-free membranes, as well as its interaction with the hy- drophilic polymer sites and particles surface. A quantitative analysis was elaborated to estimate the number of water molecules involved in the hydration shell of the hydrophilic groups of both polymer and filler, as function of the membrane water content. Despite the simplicity of this “bound/free water exchange” model, we obtain consistent values corre- sponding to about thirteen water molecules per sulfonic group. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: þ39 0984 493379; fax: þ39 0984 492044. E-mail address: isabella.nicotera@unical.it (I. Nicotera). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (2015) 1 e10 http://dx.doi.org/10.1016/j.ijhydene.2015.06.137 0360-3199/Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Nicotera I, et al., An NMR study on the molecular dynamic and exchange effects in composite Nafion/ sulfated titania membranes for PEMFCs, International Journal of Hydrogen Energy (2015), http://dx.doi.org/10.1016/ j.ijhydene.2015.06.137