Institute of Fundamental Technological Research

This paper describes an ionotronic-based sensor that can detect changes in temperature using a solid polymer electrolyte (SPE)-based transparent electrochemical capacitor (EC). The EC developed using flexible ITO as an active electrode and polyvinyl alcohol (PVA)- lithium chloride (LiCl) gel composite-based SPE. The electrochemical performances of the sensors are investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charging and discharging (GCD) analysis. The EC was fabricated using a freestanding SPE, which exhibits a specific capacitance of 4.19 μF. cm-² at a scan rate of 5 mV. s-1. The direct coating of the SPE on the electrode enhances the specific capacitance and is found to be 18.70 μF.cm-², which is 12 times higher than the EC fabricated using freestanding SPE. When a temperature was applied to the top of the EC with directly coated SPE, we observed a variation in the device’s capacitance due to the change in the mobility of ions of the SPE, which is directly related to the temperature change. The EC exhibits a sensitivity of 0.30 µF/ °C (R2= 0.9694) for the temperature range of -10 to 50 °C. Due to its ionic reaction, the EC demonstrates a high capacitance value in the range of µF in the low frequency range, which shows its potential application in ionotronic-based sensing and as an energy storage for the next generation of wearable devices.

Ionotronic sensor, Temperature monitoring, Transparent electronics, Electrochemical capacitor

The emergence of portable electronics in miniaturized and intelligent devices demands high-performance supercapacitors (SC) and batteries as power sources. For the fabrication of such energy storage devices, conducting polymers (CPs) have significant advantages due to their high theoretical capacitive performance and conductivity. In this work, we developed two CPs including polyaniline and polythiophene through a low-cost chemically synthesized approach and the film-by-spin coating method. The structural and morphological properties of the CPs are analyzed using Fourier-transform infrared spectroscopy (FTIR), contact angle measurement, and scanning electron microscopy (SEM). Based on these CPs, novel pristine polyaniline and polythiophene-based SCs (PASC and PTSC) are developed. The prepared CPs contribute to high electrochemical performances due to their high conductive nature of the electrode and conjugated polymer materials reaction. Hence both electrochemical double-layer formation and pseudocapacitance contributed to the energy-storing performances of the device. Electrochemical impedance spectroscopic analysis (0.1 Hz to 100 kHz) demonstrates faster ionic exchange and high capacitance of the PASC electrode as compared to PTSC in H3PO4 electrolyte. The PASC devices exhibit specific capacitance of 13.22 mF·cm−2 with energy and power densities of 1.175 μW·h·cm−2 and 4.99 μW·cm−2 at a current of 50 μA. Compared to PTSC (specific capacitance 3.30 mF·cm−2) the PASC shows four times higher specific capacitance due to its improved surface, structural and electrical properties. The electrochemical performance reveals the superior SC performance for this type of CP electrode.

Conductive polymers, Spin coating, Polyaniline, Polythiophene, Supercapacitor, Electrochemical performances