Isotropic Anhydrous Superprotonic Conductivity Cooperated with Installed Imidazolium Molecular Motions in a 3D Hydrogen‐Bonded Phosphate Network

Abstract

Utilizing molecular motion is essential for the use of anhydrous superprotonic molecular proton conductors (σ beyond 10 À 4 S cm À 1 ) as electrolytes in hydrogen fuel cells. However, molecular motion contributing to the improvement of intrinsic proton conduction has been limited and little clarified in relation to the proton conduction mechanism, limiting the development of material design guidelines. Here, a salt with a threedimensional (3D) hydrogen-bonded (H-bonded) phosphate network with imidazolium cations installed inside was studied, whose components are known to exhibit molecular motions that contribute to proton conduction. Despite its anisotropic H-bonded network, the salt exhibits isotropic anhydrous superprotonic conductivity exceeding 10 À 3 S cm À 1 at � 351 K, which is the first example for organic molecular crystal. Variabletemperature X-ray structural analysis and solid-state 2 H NMR measurements revealed significant 3D molecular motion of imidazolium cations, which accelerate proton conduction via the 3D H-bonded phosphate network.

Recent Progress of Crystalline Porous Frameworks for Intermediate-Temperature Proton Conduction

“…Crystalline porous materials, especially for metal–organic frameworks (MOFs) and covalent organic frameworks (COFs), have emerged as promising candidates for proton conductors in the past decades. − The former is constructed through coordination bonds between metal nodes and organic ligands, while the latter is built by strong covalent bonds. − The well-defined and well-tunable porous structures enable MOFs and COFs to be a platform to construct proton transport channels for high proton conductivity. − They are promising candidates as proton exchange membranes for application in fuel cells, shown in Scheme . The crystalline porous structure endowed MOFs and COFs with several advantages over polymer proton conductors.…”

Design of Novel Solid-State Electrolytes Based on Plastic Crystals of Quinuclidinolium Methanesulfonate for Proton Conduction

“…The gradual phase transition behavior of enantiopure R-[QH]MS was also observed at the HSM (see Figure a). The highest conductivity of 1.03 × 10 –3 S cm –1 was reached at 145 °C which is considered a high value under anhydrous conditions at this temperature range as a pure material. ,,, The Arrhenius plots of three heating and cooling cycles of R-[QH]MS (see Figure S12) compared with those of [QHrac]MS, and [QHco]MS (see Figure S13) are drawn not only to show reproducibility but also to calculate the activation energies before and after the phase transition regions by using the Arrhenius equation: σ ( T ) = σ 0 T exp ( − E a k b · T ) where σ 0 is a preexponential constant and E a is the activation energy, k b is the Boltzmann constant, and T is the temperature. The E a values of [QHrac]MS, [QHco]MS, and ordered phase of R-[QH]MS are found to be 151, 143, and 146 kJ mol –1 , respectively.…”

“…The highest conductivity of 1.03 × 10 −3 S cm −1 was reached at 145 °C which is considered a high value under anhydrous conditions at this temperature range as a pure material. 17,20,85,86 The Arrhenius plots of three heating and cooling cycles of R-[QH]MS (see Figure S12) compared with those of [QHrac]-MS, and [QHco]MS (see Figure S13) are drawn not only to show reproducibility but also to calculate the activation energies before and after the phase transition regions by using the Arrhenius equation: of R-[QH]MS are found to be 151, 143, and 146 kJ mol −1 , respectively. As a typical behavior of OIPCs, after the plastic phase transition, the E a is decreased to 92 kJ mol −1 , indicating point defect-mediated conduction through bulk plastic phase in the case of enantiopure R-[QH]MS. 60,61,87 ■ CONCLUSIONS…”

“…The highest conductivity of 1.03 × 10 −3 S cm −1 was reached at 145 °C which is considered a high value under anhydrous conditions at this temperature range as a pure material. 17,20,85,86 The Arrhenius plots of three heating and cooling cycles of R-[QH]MS (see Figure S12) compared with those of [QHrac]-MS, and [QHco]MS (see Figure S13) are drawn not only to show reproducibility but also to calculate the activation energies before and after the phase transition regions by using the Arrhenius equation: Interestingly, only the enantiopure salt R-[QH]MS exhibited plastic phase behavior with temperature, which was confirmed by XRD, thermal, and micro-Raman spectroscopy measurements, whereas [QHco]MS and [QHrac]MS underwent melting as the temperature was increased; the R-[QH]MS salt was also found to be an excellent proton-conducting material at high temperature with ionic conductivity passing from 10 −11 S cm −1 (RT) to 1.57 × 10 −8 S cm −1 (109 °C) and increasing nonlinearly to 1.03 × 10 −3 S cm −1 at around 145 °C which is attributed to a marked acceleration of motion associated with temperature variations and the plastic phase transition.…”

A stable Mn(ii) coordination polymer demonstrating proton conductivity and quantitative sensing of oxytetracycline in aquaculture

“…52 The activation energy ( E a ) for the proton conduction was fitted using the Arrhenius equation: σT = σ 0 exp(– E a / k B T ), where σ , σ 0 , E a , k B , and T is the proton conductivity (S cm −1 ), pre-exponential factor, proton transport activation energy (eV), Boltzmann constant and the test absolute temperature (K), respectively. 53…”