Dynamics of water confined in fuel cell Nafion membranes containing zirconium phosphatenanofiller

Abstract

A quasielastic neutron scattering investigation, to study the single particle dynamics of waterabsorbed in a Nafion/zirconium phosphate composite membrane hydrated at a saturationvalue, is herewith presented. The measurements were done on samples hydrated with bothH2O and D2O to properly select the spectral contribution of the confined water. Both the elasticincoherent structure factor (EISF) and the linewidth of the quasielastic component areevaluated as a function of the momentum transfer. Their trend suggests that themotion of the system hydrogen atoms can be schematized as a random jumpinginside a confining spherical region, which can be related to the boundaries of thecluster that water molecules form around the sulfonic and phosphate acid sites.The size of such a region, the characteristic time necessary to explore the regionand the number of mobile protons involved in this motion are similar to thoseestimated for water absorbed in a simple Nafion membrane at a saturation watercontent. Also the calculated jump diffusion coefficient resembles that of waterconfined in a simple Nafion membrane, and both are consistent with the value ofbulk water. The results indicate that the dynamical behaviour of water in Nafionmembranes is nearly unaffected by the presence of zirconium phosphate nanoparticles.