Anhydrous Polymeric Proton Conductors Based on Imidazole Functionalized Polysiloxane

Abstract

Intrinsically proton conducting polymers with imidazole as proton solvent tethered to a polysiloxane backbone via a flexible spacer have been synthesized. Apart from the standard characterization also their thermal properties and transport behavior have been investigated. The materials exhibit proton conductivity as a consequence of self‐dissociation of the imidazole moieties and “structure diffusion” of the resulting defects. In particular, no liquid phase such as water or monomeric imidazole is needed for the observed proton conductivities.To study the influence of the tether structure on the transport properties, cyclic oligomers and open chain polymers with different spacer lengths have been synthesized.The materials are thermally stable up to 200 °C and become soft around room temperature. The conductivity exhibits VTF and WLF behavior with maximum conductivities around σ = 1.5.10–3 S cm–1 at T = 160 °C. The activation volume of the conductivity as derived from pressure dependent measurements is found to be unusually high. The lowest activation volumes and the highest conductivities are observed for the materials with the highest segmental mobilities, i.e. the longest spacers.Proton self‐diffusion coefficients as obtained from PFG NMR diffusion measurements are significantly higher than expected from the proton conductivities obtained by dielectric spectroscopy. This corresponds to unusually high Haven ratios which have been interpreted by correlated proton transfers allowing for fast proton diffusion while minimizing the separation of ionic charge carriers.

Heterogeneous Doping of a Weak Covalent Electrolyte: Proton Conductivity Enhancement of Imidazole by Admixture of Oxide Particles

“…This is in agreement with the expectations from the literature. [10] The comparison of the conductivity results of the composites with those resulting from homogeneous doping of ImiH with sulfanilic acid [4] shows that the highest heterogeneous doping effect does not reach the overall enhancements that are possible by homogeneous doping, but exceeds them locally by far. Figure 4 shows the zeta potential measurements of asreceived oxide particles.…”

Immobilization of imidazole in polymer electrolyte membranes for elevated temperature anhydrous applications

“…The precursor was synthesized according to literature 12 by hydroxyformylation of 1-benzylimidazole (Alpha) and further nucleophilic substitution with allyl bromide (Aldrich) in anhydrous tetrahydrofuran using sodium hydride as catalyst. The raw product was further purified using column chromatography (Silicagel 60, Aldrich) using ethyl acetate/ acetone (1 : 1, v/v) as elution.…”

“…The thermomechanical property was enhanced by the complex formation of sulfonic acids group with imidazole. The introduction of simple hydrocarbon linkers facilitates the local mobility of imidazole compared with the reported immobilization of imidazole on a polymer backbone or on inorganic nanoparticles, [11][12][13][14] especially at elevated temperature.…”

“…To facilitate proton transfer inside membranes via structure diffusion, heterocyclic moieties is required to have certain local mobility. 10 For examples, the immobilization of heterocycles via flexible spacers onto inorganic particles, 11 inorganic polymers, 12,13 organic oligomers, or polymers 10,14 has been investigated. Because of the relatively low ionic conductivity or the difficulty of membranes formation of bulk materials, the synthesized materials are generally required to be associated with proton donors or polymer matrix for polymer electrolyte membrane applications.…”

Thermally Stable and Proton Conductive Ionogel Based on Brønsted Acidic Ionic Liquid with the Support of Silicate Network

“…Imidazole-based proton conductor shows good ionic conductivity at the temperature above 100 C, though the thermal and chemical stability are waiting to be improved. [10][11][12][13][14] Some ionic liquids are also expected as new proton conductors. [15][16][17] Ionic liquids generally show high thermal stability beyond 300 C, negligible vapor pressure, low glass transition temperature (T g ), and high ionic conductivity.…”