Bifunctional ionic liquid in conductive biopolymer based on chitosan for electrochemical devices application

• We highlight the bifunctional role of [Bmim][OAc] - as charge carrier and plasticizer in the polymer host, chitosan.
• The highest conductivity until (2.44 ± 0.41) x 10- 3 S cm- 1 were achieved
• The mechanism of [Bmim][OAc] acts as charge carrier and plasticizer were proposed
• High electrochemical stability achieved up to 3.4 V.

Conductive polymer based on chitosan has been successfully prepared via solution casting technique with ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][OAc]). [Bmim][OAc] plays two important roles in the conduction of chitosan: i) charge carrier and ii) plasticizer in this system. Appearance of new peaks and shifting of several characteristic peaks in the FTIR spectra signify the strong interactions between chitosan and [Bmim][OAc]. XRD diffractograms showed an increase in the amorphous region as the weight percentage (wt.%) of [Bmim][OAc] increases. SEM observations have proven the smoother surface morphology of the plasticized chitosan. The enhancement in the ionic conductivity (σ), is observed as the wt.% of [Bmim][OAc] increases. The highest σ achieved is (2.44 ± 0.41) × 10− 3 S cm− 1 measured at ambient temperature (298 K) and the corresponding activation energy is 0.2961 eV. The temperature dependence of conductivity is Arrhenian in the studied temperature range and achieved σ of (7.60 ± 0.62) × 10− 3 S cm− 1 at 70 °C. The increase in the ionic conductivity is related to the decrease of glass transition temperature (Tg) as proven by the DSC analysis. High electrochemical stability of 3.4 V was achieved of the highest conducting electrolyte by means of linear sweep voltammetry (LSV). Transference number measurement confirms that ions predominate the conduction of electrolyte with 0.75 ion transference number.