Temperature-dependence of the electrical impedance properties of sodium hydroxide-contained polyethylene oxide as an ionic liquid

For designing materials for a thermometer, the fundamental electrical properties of its electrical components should be understood. The large Seebeck coefficient of sodium hydroxide-contained polyethylene oxide (PEO-NaOH), a thermoelectric ionic liquid, makes it a potential material for thermometers as well as power generators. In this study, the temperature- and thickness-dependence of the resistance and capacitance of this ionic liquid was investigated by electrical impedance spectroscopy. Although the temperature-dependence of the electrical properties of PEO-NaOH due to the electrical double layers (EDLs) has been studied extensively, the dependence of the thermodiffusion on temperature remains poorly understood. A PEO-NaOH solution as an ionic liquid was injected into a small chamber, and Nyquist plots were obtained at different chamber temperature differences and thicknesses. Further, changes in the resistance, capacitance, and noise amplitude arising from thermodiffusion and EDL were monitored. The resistance components of thermodiffusion and EDL decreased with increasing temperature difference and decreasing chamber thickness; conversely, the capacitance increased in both cases. The noise amplitude decreased as the temperature difference increased and the chamber thickness decreased. This paper reports the resistance, capacitance, and noise amplitude characteristics derived from not only EDLs but also thermodiffusion.