Chitosan Solid Polymer Electrolytes Doped with Cyano-Based Ionic Liquids

Abstract

The aim of this work was to synthesize and characterize Solid Polymer Electrolytes (SPEs) based on chitosan and the cyano-based ionic liquids (ILs): 1-ethyl-3-methylimidazolium dicyanamide ([C2mim][DCA]), 1-ethyl-3-methylimidazolium thiocyanate ([C2mim][SCN]), 1-butyl-3-methylimidazolium thiocyanate ([C4mim][SCN]) and 1-ethyl-3-methylimidazolium tricyanomethanide ([C2mim][TCM]). SPEs attract a lot of attention due to their enormous potential, mostly because of the wide range of possible applications in the energy storage field. The synthesis of a SPE is quite straightforward: it implies the dissolution of an ionic salt in a high molecular weight polymer, provided that the latter contains cation-coordinating species [1-3]. Because of its extraordinary solvating ability toward salts, poly(oxyethylene) (PEO) has been the most widely employed macromolecule to produce SPEs, but in the last few years attention has been drawn to natural polymers like cellulose, chitosan, starch, gelation, agar or DNA, because of their biodegrability, low production cost, good physical and chemical properties and good performance as SPEs [4-8]. Chitosan is obtained by deacetylation of its parent polymer chitin, a polysaccharide widely distributed in nature (e.g. crustaceans, insects and certain fungi) [9]. Along with the natural polymers, ILs gained momentum as well. Since ILs are composed only of ions they show very high ionic conductivity, non-volatility and non-flammability [10], which are valuable proprieties to the envisaged applications. The solvent-free electrolyte samples prepared in this work were characterized by means of thermal analysis (DSC and TGA), ionic conductivity, cyclic voltammetry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Acknowledgements This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/QUI/UI0686/2013 and PEST-OE/EQB/LA0004/2011, projects PTDC/CTM-NAN/121274/2010 and PTDC/QUI-QUI/117340/2010, POPH/FSE for a grant SRFH/BD/90366/2012 (R.L.) and FCT Investigator Programme (J.M.S.S.E.). M. M. Silva acknowledges CNPq, for the mobility grant provided by this institution.