Electrical studies on chitosan based proton conductors and application in capacitors

Ionic conductivity of four chitosan based electrolyte systems viz., chitosan-H(3)PO4, chitosan-H3PO4-Al2SiO5, chitosan-H3PO4-NH4NO3 and chitosan-H3PO4-NH4NO3-Al2SiO5 were studied by impedance spectroscopy in the frequency range from 50Hz to 1 MHz and varying temperatures from 293 K to 373 K. The sample 0.62 chitosan - 0.38 H3PO4 has the highest room temperature conductivity of (5.36 +/- 1.32) x 10(-5) S cm(-1). The sample 0.615 chitosan-0.377 H3PO4-0.008 Al2SiO5 exhibits the highest ambient conductivity of (1.12 +/- 0.18) x 10(-4) S cm(-1) in the ternary system with filler. In the ternary system with salt but without filler, 0.56 chitosan-0.34 H3PO4-0.10 NH4NO3 has the highest ambient conductivity of (1.16 +/- 0.35) x 10(-4) S cm(-1). The quarternary sample 0.5572 chitosan-0.3383 H3PO4-0.0995 NH4NO3-0.0005 Al2SiO5 has the highest conductivity of (1.82 +/- 0.10) x 10(-4) S cm(-1). All compositions are in weight fraction. The conductivity-temperature relationship is Arrhenian. Results were analyzed using the Rice and Roth model, Joncher's universal power law, sigma = sigma(DC) + A omega(s) and models based on polarons. The frequency dependence conductivity plot shows a frequency independent plateau at low frequency and a high frequency dispersive region, which is dominant at lower temperatures. From the plot of s versus T, it has been shown that the conductivity for Al2SiO5 containing chitosan-based electrolyte occurs by way of the overlapping large polaron tunneling model (OLPT) and for the binary chitosan-phosphoric acid system, conduction mechanism may be explained by the quantum mechanical tunneling (QMT) model. The best conducting sample in each system was used as electrolyte in an electric double layer capacitor. From the charge-discharge profile, a small ohmic voltage drop was observed for each 1 mA constant current discharge curve. The specific discharge capacitance of the best EDLC was found to be similar to 220 mF g(-1) for 100 cycles.