Irreversibility of proton conductivity of Nafion and Nafion-Titania composites at high relative humidity

Abstract

The temperature dependence of the proton conductivity of Nafion and Nafion-Titania composite in the hydrated state is investigated. The proton conductivity of Nafion-Titania measured in two successive heatings displays irreversibility, a behavior also observed in bare Nafion. The relationship between the proton transport and the dynamics of α-relaxation as proved by dielectric spectroscopy is discussed for Nafion and the composite electrolytes. The results indicate that in the first heating, the proton conductivities of Nafion and Nafion-Titania are modulated only by the glass transition of the ionomer, whereas in the second heating both the α-relaxation and the polymer glass transition are coupled to the charge transport. Such features are important for the development of high-performance electrolytes for high-temperature proton exchange membrane fuel cells.