Probing Proton Mobility in Polyvinazene and its Sulfonated Derivatives Using ¹H Solid‐State NMR

Abstract

The proton dynamics of PV and its sulfonated derivatives have been studied using high‐resolution solid state 1H MAS NMR. Variable temperature experiments were used to determine the activation energy for transportation of hydrogen bonded protons, found to be 22 ± 1 kJ · mol−1 for PV and 13 ± 1 kJ · mol−1 for PV–B25. The proton exchange between sulfonic acid group and vinazene ring observed from both variable temperature experiments and 1H EXSY NMR experiments provides a good explanation for this difference. A rotor‐synchronized homonuclear double quantum filter sequence was used to distinguish protons of differing mobilities. A model is proposed to understand the distinct proton mobilities in these materials.magnified image

Backbone effects on the charge transport in poly-imidazole membranes: a theoretical study

“…The DFT analysis on small P2VI models shows that the PT reaction between adjacent imidazoles has a low activation energy and is not affected by adjacent cyano groups. These results are in clear disagreement with two common experimental beliefs: (1) withdrawing groups would increase proton conductivity by making the protons more labile (as a result of the increasing acidity of the imidazole) 27,40 and (2) proton transfer between neighboring imidazoles is the crucial step. 52,53 The subsequent analysis on larger models (3mer and 15mer) was focused on what can be dened as the true rate-limiting step of the hypothesized Grotthuss mechanism, the correlated reorientation of all the imidazoles.…”

“…20 In order to overcome this limit, considerable efforts have been devoted to incorporate these heterocyclic compounds into a polymeric matrix via covalent bonding. [21][22][23][24][25][26][27] Nevertheless, these materials are far from exhibiting acceptable performances. This is due in part to the incomplete understanding of how the proton conduction occurs.…”

Confinement Promotes Hydrogen Bond Network Formation and Grotthuss Proton Hopping in Ion-Conducting Block Copolymers

“…The resonance of N–H protons is known to shift dramatically depending on the nature of the hydrogen-bonding environment. ,,, Generally, a proton will become more deshielded and the resonance will shift downfield, as the hydrogen-bonding network becomes stronger. In the solid state, imidazole proton resonances appearing in the ∼9–12 ppm region are assigned to “mobile” protons in which the hydrogen-bonding network between N–H groups allows for rapid proton hopping. ,, Resonances in the region greater than ∼12 ppm are often assigned to “rigid” protons, where the hydrogen bonds between N–H groups are much stronger, and do now allow for fast proton dynamics. ,, In the spectra of the homopolymer (Figure a), two peaks from the imidazole N–H protons are indicative of a immobile, rigidly hydrogen-bonded population of protons at ∼14.0 ppm and a relatively weakly hydrogen-bonded or mobile population of protons at 11.4 ppm. As the temperature increases, the intensity of the 14.0 ppm peak (rigid, less mobile protons) decreases, while the intensity of the 11.4 ppm peak (mobile protons) increases (see Figure S4 for intensity plots).…”

“…The resonance of N−H protons is known to shift dramatically depending on the nature of the hydrogen-bonding environment. 47,48,57,58 Generally, a proton will become more deshielded and the resonance will shift downfield, as the hydrogen-bonding network becomes stronger. In the solid state, imidazole proton resonances appearing in the ∼9−12 ppm region are assigned to "mobile" protons in which the hydrogen-bonding network between N− H groups allows for rapid proton hopping.…”

Proton Mobilities in Phosphonic Acid-Based Proton Exchange Membranes Probed by 1H and 2H Solid-State NMR Spectroscopy

“…Though bulk ionic transport in PEMs is accessible via impedance spectroscopy, it does not provide insight into local proton mobilities. Rather, solid-state NMR under fast magic-angle spinning (MAS) is a powerful and locally selective tool for the characterization of functional materials such as PEMs. , …”