Structural investigation of solid biopolymer electrolytes: 2-hydroxyethyl cellulose doped ammonium formate as a promising proton conductor

Abstract

Fabrication of solid biopolymer electrolytes (SBEs) was mainly to cater the drawbacks of lithium-ion electrolytes in terms of leakage, high cost, and toxic material. In this present work, solid biopolymer electrolytes system comprises of 2-Hydroxyethyl Cellulose (2-HEC) as polymer host, and various weight percentage (wt.%) of Ammonium Formate (AF) as ionic doping salt are produced by using solution casting technique. The relation between structural and ionic conductivity of 2-HEC/AF was analyzed and investigated by using X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and Electrical Impedance Spectroscopy (EIS). Through the analysis of XRD, it can be observed that the amorphous region of SBEs increases as the concentration of AF salt increases. The amorphous region of SBEs can be confirmed due to the interaction of salt concentration and polymer. However, in this present work, the broadest peak in XRD of the sample does not necessarily correlate with the highest conductivity among the samples. The interaction between polymer-salt complexes is proved through FTIR spectrum at the range of 700 cm−1 to 1300 cm−1. The highest ionic conductivity of 2-HEC/AF achieved is 2.40 × 10−3 S/cm at room temperature for SBEs containing 40 wt.% of AF. The findings from this study made it clear that the concentration of Ammonium Formate salt affects the increase in ionic conductivity.