Synthesis and characterization of modified κ-carrageenan for enhanced proton conductivity as polymer electrolyte membrane

Polymer electrolyte membranes based on the natural polymer kappa-carrageenan were modified and characterized for application in electrochemical devices. In general, pure kappa-carrageenan membranes show a low ionic conductivity. New membranes were developed by chemically modifying kappa-carrageenan via phosphorylation to produce O-methylene phosphonic kappa-carrageenan (OMPC), which showed enhanced membrane conductivity. The membranes were prepared by a solution casting method. The chemical structure of OMPC samples were characterized using Fourier transform infrared spectroscopy (FTIR), H-1 nuclear magnetic resonance (H-1 NMR) spectroscopy and P-31 nuclear magnetic resonance (P-31 NMR) spectroscopy. The conductivity properties of the membranes were investigated by electrochemical impedance spectroscopy (EIS). The characterization demonstrated that the membranes had been successfully produced. The ionic conductivity of kappa-carrageenan and OMPC were 2.79 x 10(-6) S cm(-1) and 1.54 x 10(-5) S cm(-1), respectively. The hydrated membranes showed a two orders of magnitude higher ionic conductivity than the dried membranes.