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Free volume size Vf and proton conductivity σ of a novel polymer electrolyte membrane were investigated as a function of temperature and relative humidity up to 140 °C and 80%, respectively. The free volume size Vf for Nafion® HP JP reflect the α-transition temperature at about 98 °C. In addition the free volume size Vf for Nafion® HP JP is smaller than that for Nafion® NRE212 membrane which leads to lower methanol permeability of the former membrane. The proton conductivity σ for Nafion® HP JP decreases with increase of temperature up to transition temperature due to free and bound water loss, then it starts to increase due to dynamic segmental motion. It increases for Nafion® HP JP with the increase of the relative humidity. A good correlation between Vf and σ was successfully established for both membranes which indicates that σ is governed by the free volume. In conclusion, Nafion® HP JP is a suitable membrane for a proton exchange membrane fuel cell application. [ABSTRACT FROM AUTHOR]

The proton conductivity mechanism in per-fluorinated sulfonic acid/PTFE copolymer Fumapem® membranes for polymer electrolyte membranes has been investigated. Three samples of Fumapem® F-950, F-1050 and F-14100 membranes with different ion exchange capacity 1.05, 0.95, and 0.71 meq/g, respectively, were used in this study after drying. The o-Ps hole volume size (VFV,Ps) was quantified using the positron annihilation lifetime technique while the proton conductivities (σ) were measured using LCR Bridge as function of temperature. It was found that as the ion exchange capacity increases, the proton conductivity increases and the free volume expands. Temperature dependences of proton conductivity and the o-Ps hole volume size (VFV,Ps) reflect the glass transition temperature of the membrane. A good linear correlation between the reciprocal of the o-Ps hole volume size (1/VFV,Ps) and log(σ)+ΔEa/2.303kBT, (where ΔEa is the activation energy, T is the absolute temperature and kB is the Boltzmann constant) at different temperatures indicate that the ionic motion in dry Fumapem® is governed by the free volume. A linear relationship between the critical hole size γV*i and the ion exchange capacity was also achieved. [ABSTRACT FROM AUTHOR]