Cellulose microfibers surface treated with imidazole as new proton conductors

Abstract

A newly synthesized polymeric proton-conductive composite (3.5CMF-Im), based on pure cellulose microfibers (CMF) functionalized with imidazole molecules (Im) on their surface, was comprehensively studied in terms of structural, thermal, and electrical properties. According to elemental analysis of 3.5CMF-Im composite contains on average one imidazole molecule per 3.5 glucose units. Fourier transform infrared spectroscopy (FTIR) was used to identify the crystalline structure and hydrogen bond network. Thermogravimetric analysis (TGA + DTG) and differential scanning calorimetry (DSC) tests were carried out to examine the stability and thermal decomposition of studied materials. In order to determine temperature dependences of electrical conductivity, the impedance spectroscopy was used. For the first time, evidence of imidazole dissociative mechanism in this type of material using FTIR was obtained. Imidazole may dissociate into an imidazolium cation and an imidazole anion, and this mechanism may contribute to the proton conductivity of cellulose-imidazole composites. The new material exhibits a maximum conductivity of 2.7 × 10−4 S m−1 at 150 °C, which is four orders of magnitude higher than that of pure cellulose microfibers. The composite is environmentally friendly solid polymer electrolyte operating in the temperature range above the water boiling point.