Characterization of electrosprayed Nafion films

Nation has long served as a benchmark material when evaluating the performance of proton conducting membranes used in PEM fuel cells. Traditionally, the membranes are either extruded from dry polymer or cast from a liquid polymer solvent solution. Recently, a different technique for fabricating membranes has been developed. The new approach exploits electrostatic spraying, or electrospraying, to deposit PEM films, with the longer-term goal of fabricating membrane-electrode assemblies using this technique. The focus of this paper is to compare the proton transport and physical properties of electrosprayed membranes with those of extruded Nafion. Audio frequency complex impedance studies of the electrosprayed membranes were conducted at a variety of temperatures and pressures over a wide range of membrane water contents. The results are compared with similar data for Nation 117 and for membranes cast from the electrosprayed solutions. Water uptake, dimensional changes, and electrical conductivity measurements indicate that extruded, cast, and electrosprayed Nation films are similar, with the exception that the electrosprayed Nation absorbs as much Lis 15 wt.% water more than the other two membranes with only a slight increase in conductivity. The activation volumes for electrosprayed Nation are also consistent with those for Nation 117 and concur with proposed mechanisms for proton transport in Nafion membranes. As in Nation 117, a dielectric loss peak appeared in the electrosprayed Nation at low temperatures after heating in vacuum at 380 K, further demonstrating the similarity between the two materials. (C) 2003 Elsevier B.V. All rights reserved.