Solvation of sulphonic acid groups in Nafion® membranes from accurate conductivity measurements

dcProton conductivity at low-frequency in Nafion conductivity spectrum probed by time-resolved SAXS measurements and impedance spectroscopy

“…However, strong divergence among different research groups concerning the interpretations of the electric spectrum of Nafion demonstrate that no consensus has been reached yet . Nyquist diagrams of Nafion membranes at T = 25 °C (RH = 100%) exhibit a frequency independent conductivity at high frequencies ( f ∼ 10 6 Hz), which was attributed to the transport of dissociated protonic charges occurring mainly via structural diffusion in the absorbed aqueous media . However, the low frequency tail observed for f < 10 6 Hz, representing a large increase of the capacitance, has received different interpretations such as electrode polarization or polarizations occurring within the polymer phase …”

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

“…Previous reports offered some insight into this phenomenon [23]. The authors have shown that during the conductivity measurements at high relative humidity, a maximum of four water molecules are solvating the protonic charges, indicating that the protons are not fully dissociated from sulfonic groups.…”

Synthesis and Solid‐State NMR Studies of Proton‐Conducting Mesoporous Niobium Oxide Polymer Composites with Nafion‐Like Thermal Durability

“…With Nafion 117, at 80 8Ct he conductivity has already decreased from that at room temperature (8.356 mS cm À1 ) [28,29] from dehydration and this trend continues over 24 ha t8 08Ca st he matrix furtherd ehydrates. By comparison, C 12 mNb 2 O 5 (SO 4 )-NSF begins with ac onductivity of 19.02 mS cm À1 ,w hich drops by more than half after one hour .A fter two hours the conductivity has further dropped to 5.96 mS cm À1 and then to 1.34, 0.22 and 0.03 mS cm À1 after 4, 8a nd 24 hr espectively.T hus, despite ah igh initial conductivity, after four hours the conductivity falls below that of the Nafion 117f ilm.…”

“…[28,29] However,t his composite shows graduall oss of conductivity at temperatures over 80 8Cd ue to leaching of the NSF out of the 20 p ores. With the goal of fabricating materials with similar proton conductivity,b ut improved thermals tability,f our new composites were synthesized using the new in situ polymerization technique outlined schematically in Figure 1B.T he first two composites (mNb 2 O 5 (SO 4 )-NSF and mNb 2 O 5 -NSF) weres ynthesized with and without sulfuric acidd oping prior to solution impregnation of naphthalene sulfonica cid (NSA) monomer and condensed using two molar equivalents of formaldehyde with respect to NSA in situ to drive polymerization within the pores.…”