Influence of the anion on diffusivity and mobility of ionic liquids composite polybenzimidazol membranes

The study of proton conductivity processes has received increasing attention in the past decades due to their potential applications in fields such as electrochemical devices and fuel cells. Despite the high number of composite membranes which have been described for this purpose, fundamental studie...

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Bibliographic Details
Published in:Electrochimica acta 2020-09, Vol.354, p.136666, Article 136666
Main Authors: Compañ, Vicente, Escorihuela, Jorge, Olvera, Jessica, García-Bernabé, Abel, Andrio, Andreu
Format: Article
Language:English
Subjects:
Activation energy
Anions
Carrier density
Charge density
Conductivity
Current carriers
Dependence
Diffusion coefficient
Diffusivity
Electrochemical impedance spectroscopy
Electrode polarization
Fuel cells
Ion currents
Ion pairs
Ionic liquids
Ionic transport
Ions
Membranes
Mobility
Permittivity
Polybenzimidazole
Polybenzimidazoles
Polymer electrolytes
Stabilization
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Summary:The study of proton conductivity processes has received increasing attention in the past decades due to their potential applications in fields such as electrochemical devices and fuel cells. Despite the high number of composite membranes which have been described for this purpose, fundamental studies of the conduction phenomena in polymeric membranes are scarce. In this article, we study on the effect of the anion on ionic conductivity of ionic liquid composite polybenzimidazole (PBI) membranes. These membranes, which contain 1-butyl-3-methylimidazolium (BMIM) with different counterions ([Cl]–, [NCS]–, [NTf2]– and [BF4]–) were analyzed by electrochemical impedance spectroscopy (EIS) in order to study the influence of the anion on the ionic conductivity, but also mobility and charge carrier density at different temperatures. The methodology for this analysis is based on the Coelho model of electrode polarization (EP), where the dependence of the complex dielectric permittivity on frequency is represented in terms of a Cole-Cole function, contrarily to the generally used simple Debye relaxation. The calculated activation energies associated to the conductivity showed a dependence on the anion and is around 65–84 kJ mol−1, which suggests that the ionic conductivity mainly occurs through the vehicle-type mechanism. The calculated diffusivity values followed the trend D NTf2 > D Cl > D BF4> D SCN, with an associated activation energy (in kJ·mol−1) following the trend Eact(NTf2) = 10.9 
ISSN:0013-4686
1873-3859
DOI:10.1016/j.electacta.2020.136666