Anisotropic conductivity over in-plane and thickness directions in Nafion-117

Proton conductivity of Nafion-117 membranes in the direction of thickness was measured in 30 degrees C, 30-90% relative humidity, by means of 2- and 4-probe methods in thickness direction developed in this group. Heavy conductivity anisotropy of sigma(in-plane)/sigma(thickness) = 2.5-5 was found over the in-plane and thickness directions for membranes pretreated by hot-pressing at high temperature of 150 degrees C and pressures of 1200 and 600 kgf/cm(2), respectively. On the other hand, no conductivity fade was found for membrane pretreated at 0 kgf/cm(2) in the thickness direction compared to that in the plane direction. Small angle X-ray scattering measurements revealed ion domains flattened along the in-plane direction and ordered along the thickness direction. The origin of the persistent conductivity anisotropy is believed to come from the maximized potential energy barrier for ion transport in interaggregate along the thinned thickness direction. (c) 2006 The Electrochemical Society.