Toward a new type of proton conductor based on imidazole and aromatic acids

Abstract

The substitution pattern of the counterions affects electrical conductivity and thermal properties of the new proton conducting imidazolium salts.

Spectroscopic and Structural Study of a New Conducting Pyrazolium Salt

“…The formation of the amine salt results from the transfer phenomenon of a proton from the Lewis acid unit to the Lewis base. Bands at 1579 and 1380 cm −1 are due to the out-of-phase and in-phase COO − stretching vibrations of the carboxylate COO − group, respectively [ 14 , 15 ].…”

“…Besides TPT, a new class of imidazole-based organic proton conductors has been developed lately [ 12 , 13 ]. Many proton-conducting salts are based on heterocyclic bases and aromatic acids, such as imidazolium salts of benzoic, salicylic, orthophthalic, and terephthalic acids [ 14 , 15 ]. Nevertheless, the hydrogen bonds formed in such solids were weak and medium strength, and their mechanism of conductivity is based on the Grotthuss mechanism.…”

“…Nevertheless, the hydrogen bonds formed in such solids were weak and medium strength, and their mechanism of conductivity is based on the Grotthuss mechanism. On the other hand, the number and location of the carboxylic group influence the thermal stability and electrical conductivity of the proton conductors [ 15 ]. For example, imidazolium orthophthalate and terephthalate revealed high thermal stability with values of 464 and 422 K, respectively, and imidazolium orthophthalate also presented good electrical conductivity (10 −1 S⸱m −1 ) [ 14 ].…”

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

“…1−8 Imidazolium hydrogen dicarboxylates in anhydrous organic crystalline materials are attractive for elucidating the anhydrous proton conduction mechanism because their similar twodimensional (2D) hydrogen-bond (H-bond) network structures allow systematic investigations. 4,9,10 Among imidazolium hydrogen dicarboxylates, imidazolium hydrogen succinate (Im-Suc) has been studied in detail. 10−15 The X-ray crystal structure of Im-Suc reveals 2D H-bond network structures, in which imidazolium cations (ImH + ) and succinate anions form H-bonds.…”

“…Recently, anhydrous proton-conducting materials have been extensively developed as solid electrolytes for fuel cells because these conductors can operate at temperatures higher than 100 °C. In particular, the proton conductivities of imidazole (Im)-incorporated composite materials have been investigated both theoretically and experimentally. − Imidazolium hydrogen dicarboxylates in anhydrous organic crystalline materials are attractive for elucidating the anhydrous proton conduction mechanism because their similar two-dimensional (2D) hydrogen-bond (H-bond) network structures allow systematic investigations. ,, Among imidazolium hydrogen dicarboxylates, imidazolium hydrogen succinate (Im-Suc) has been studied in detail. − The X-ray crystal structure of Im-Suc reveals 2D H-bond network structures, in which imidazolium cations (ImH + ) and succinate anions form H-bonds. − , Notably, the proton conductivity is anisotropic, with the conductivities parallel to the 2D H-bond network ([100] and [149̅] directions) being almost two orders higher than those perpendicular to the H-bond network ([011] direction), indicating that efficient proton conduction in Im-Suc occurs within the 2D H-bond network (Figure S1). According to the X-ray crystal structure of Im-Suc, only H-bonds between succinic acid (Suc) and Im form along the [100] direction, whereas H-bonds between Suc and Im and between two Suc form along the [149̅] direction.…”