Methylcellulose doped glycolic acid biopolymer electrolyte : preparation, conductivity, and ionic transport study

Abstract

Thin films of methylcellulose (MC) doped with various weight percentage (wt. %) of glycolic acid (GA) were produced through solution cast technique to obtain a solid polymer electrolyte (SPE) in a form of a biopolymer. The study determines the feasibility of producing a proton conducting biopolymer of MC doped with GA (MCGA) thin films, suitable for applications in batteries and fuel cells. The films obtained were transparent and mechanically strong. Electrochemical Impedance Spectroscopy (EIS) studies were conducted to analyse the conductivity and ionic transport properties of the MC-GA thin films. The samples were tested over a frequency range from 50 Hz to 1 MHz with the sample sandwiched between two stainless steel electrodes loaded with spring pressure. The highest conductivity, s, of MC-GA thin films obtained in room temperature was 7 .16 x 10- 10 S cm-1 • The Transference Number Measurement (TNM) studies were conducted to determine and correlate the ionic diffusion phenomena with the conductivity behaviour of the MC-GA thin film electrolytes. The calculated ionic transference number, tion, in the electrolytes were obtained from the current-normalised ionic transference number, lion, measured when the sample was subjected to a fixed direct current (DC) voltage of 1.5 V across the sample sandwiched between two stainless steel electrodes loaded with spring pressure. The s values were found to be directly proportional and controlled by the ionic mobility,μ, and ionic diffusion coefficient, D. The values of /1+ and D+ were higher than μ_ and D_ respectively, implying that the MC-GA thin film biopolymer electrolytes are proton conductors.