Characterization of solid biopolymer electrolytes based on kappa-carrageenan with Magnesium nitrate hexahydrate and its application to electrochemical devices

Abstract

ABSTRACT Biopolymers have been widely investigated due to their environmental friendly nature. Kappa carrageenan is one of a biopolymer with strong stability, good film-forming tendency, and soluble in hot water. In this work, solid Magnesium biopolymer electrolytes has been developed using Kappa carrageenan with various molecular weight percentage (Mwt%) of Magnesium nitrate as salt, by solution casting technique using distilled water as a solvent. Structural, thermal, electrical, and electrochemical behavior of developed membrane are investigated using various techniques such as XRD, DSC, AC impedance, LSV, and transference number measurement. XRD confirms the amorphous nature of the polymer electrolyte. The biopolymer electrolyte of 1g Kappa carrageenan: 0.5 Mwt% of Magnesium nitrate Mg(NO3)2.6H2O has got maximum magnesium ion conductivity of 7.05 × 10−4 S cm−1.This membrane has got highest amorphous nature. The ionic connectivity has been improved to one order of magnitude due to the inclusion of 0.5 Mwt% of Ethylene carbonate plasticizer with the highest connecting biopolymer electrolyte 1 g K-Carrageenan: 0.5 Mwt% of Mg(No3)2.6H2O.Glass transition temperature of the prepared membrane has been measured by DSC technique. LSV technique is used to measure the electrochemical stability of the highest conducting biopolymer electrolytes. Primary magnesium battery is fabricated using maximum ionic conductivity biopolymer electrolyte (1 g K-Carrageenan: 0.5 Mwt% of Mg(NO3)2.6H2O and 1 g K-Carrageenan: 0.5 Mwt% of Mg(NO3)2.6H2O:0.5Mwt% of EC). The fabricated primary magnesium battery exhibits open circuit voltage of 1.8 V and 1.97 V have been observed for the 1 g K-C:0.5 mwt% of Mg(No3)2.6H2O and 1 g K-C:0.5 Mwt% of Mg(No3)2.6H2O:EC, respectively, and its performance is studied.