Positron annihilation characteristics, water uptake and proton conductivity of composite Nafion membranes

Abstract

The free volumes and proton conductivities of Nafion membranes were investigated at different humidities by positron annihilation lifetime spectroscopy (PALS) and using an electrochemical workstation, respectively. The results showed that the variation in o-Ps lifetime τ was closely associated with the microstructure evolution and the development of hydrophilic ion clusters in Nafion membranes as a function of water uptake, regardless of metal oxide additives. In particular, with increasing relative humidity, the maximum value of τ in the Nafion membranes corresponded to the formation of numerous water channels for proton transportation. Numerous well-connected water channels in Nafion-TiO hybrid membranes could be formed at a much lower relative humidity (∼40% RH) than in the pristine one (∼75% RH), due to the better water retention ability of the Nafion-TiO membranes. Further, a percolation behavior of proton conductivity at high water uptake in Nafion membranes was observed, which showed that the percolation of ionic-water clusters occurred at the water uptake of ∼4.5 wt%, and ∼6 wt% was basically enough for the formation of a well-connected water channel network.

Morphology and ion diffusion in PEDOT:Tos. A coarse grained molecular dynamics simulation

“…21 Ionic conductivity enhancement with increased humidity level and the ionic Seebeck effect were recently reported for Na + ions in PEDOT:PSS. 5 Previously the effect of hydration level was mainly studied experimentally 22,23 and theoretically 24,25 in proton transport through hydrated Nafion for application in fuel cells.…”

Effect of Elevated Temperature Annealing on Nafion/SiO2 Composite Membranes for the All-Vanadium Redox Flow Battery

“…PALS was then used to study the free volume of these membranes, with the o-Ps annihilation lifetime τ3 value providing a measure of their free volume element sizes and number densities [35]. Figure 4b shows the results obtained from the positron annihilation experiments of the pure Nafion, 5%@Nafion/SiO 2 @240°C, 5%@Nafion/SiO 2 @270°C, and 5%@Nafion/SiO 2 @300°C membranes.…”

Insightful understanding of the correlations of the microstructure and catalytic performances of Pd@chitosan membrane catalysts studied by positron annihilation spectroscopy

“…As determined by positron annihilation spectroscopy, our initial study 41 showed that the mean diameter of the free volume holes of swollen Pd@CS membrane catalyst ranged from 0.5 to 1.2 nm, which is close to the size of the reactants as applied in Heck reaction. Moreover, previous studies [45][46][47][48][49][50] have demonstrated the free volume properties of the polymer membrane was the governing factor controlling the transport performances of gas (CO 2 ), water, solutes, and so on. Therefore, it is believed that the free volume holes of the polymer membrane could be the diffusion channels for the reactants.…”