Anhydrous Purely Organic Solid-State Proton Conductors: Effects of Molecular Dynamics on the Proton Conductivity of Imidazolium Hydrogen Dicarboxylates

Proton Conduction Mechanism for Anhydrous Imidazolium Hydrogen Succinate Based on Local Structures and Molecular Dynamics

“…3,28 The proton conduction mechanism in Im-Suc has been recognized as a Grotthuss-type mechanism 10 involving proton transport through H-bond networks 13−15 and network rearrangement by molecular motion. 12,15 In agreement with such a mechanism, our PES displayed energetically reasonable PT between Im and Suc as well as Im and ImH + rotational motion during proton transport on the proton conduction pathway. The PES also showed that the formation energy of the orientationally disordered structure via rotational motion of ImH + is lower than the activation energy of PT.…”

“…In X-ray crystal structures above 80 °C, Im-Suc has two crystallographically independent layers (ordered and disordered). 15 The disordered layer contains orientationally disordered ImH + configurations in a five-membered ring plane, whereas the ordered layer maintains the ordered ImH + configuration. In addition, the librational motions of ImH + in Im-Suc have been observed using solid-state nuclear magnetic resonance measurements.…”

“…Using quantum chemical calculations and comparisons with experimental infrared (IR) absorption data, we discuss the proton conduction mechanism at the molecular level based on local structures and molecular motions. Given the two crystallographically independent layers observed for Im-Suc at temperatures above 80 °C, 15 we constructed two Im-centered modelsIm order (Im4Suc ord ) and Im disorder (Im4Suc disord )that included one Im and four Suc to investigate the local H-bond structures around ImH + (Figure 1a,b). In addition, we constructed two Succentered modelsIm order (3Suc4Im ord ) and Im disorder (3Suc4Im disord )that included four Im and three Suc to investigate the local H-bond structures around Suc (Figure 1c,d).…”

“…3 Figure 2 shows the experimental IR absorption spectra at 30 and 100 °C, which are below and above, respectively, the phase transition at 80 °C. 15 The intensities of some peaks observed at 30 °C decrease with the increase in temperature owing to the broadening of the thermal peak. The remarkable spectral change between 30 and 100 °C was a blue shift of the peak near 3100 cm −1 (dashed line in Figure 2).…”

“…These geometries are in good agreement with the X-ray structures. 15 RS led to an intermediate (IM1) by PT from the rotated ImH + to its neighboring Suc via the first transition state (TS1). The activation energy of the first PT between RS and TS1 was 1.23 eV.…”