Depression of proton conductivity in recast Nafion® film measured on flat substrate

The proton conductivity of recast Nafion® thin films in the lateral direction (parallel to the interface) was measured in humidified atmospheres. The conductivity decreased with a decrease in the thickness of the film: e.g., the conductivity of a film with a thickness of about 100 nm was about an order of magnitude less than that of the bulk material. The dependence of the conductivity on temperature was also measured, and a thinner film showed a higher apparent activation energy for conduction. Since both the conductivity and the apparent activation energy for conduction were affected by the thickness, these phenomena may be due to an intrinsic change in the material. Based on the fact that the apparent activation energy for conduction in the bulk membrane under dry conditions is high, the high apparent activation energy for conduction in thin films may be due to the hindrance of water adsorption.