Temperature-dependent performance of sustainable supercapacitors with hydrogel electrolyte

The temperature-dependent electrical behavior of an environmentally friendly, symmetric carbon-based supercapacitor with a gelatin-based hydrogel electrolyte containing acetate salt has been investigated. In addition to the electrolyte, the electrodes have been fabricated using sustainable components, including chitosan as a binder and activated carbon derived from coconut shells. To assess the impact of temperature on the electrochemical properties of the fabricated devices and overall performance, experimental measurements have been conducted over a temperature range of 277 K (4 °C) to 313 K (40 °C). These included cyclic voltammetry, galvanostatic charge/discharge, and impedance spectroscopy. The findings indicate that higher temperatures markedly augment the charge storage capacity and diminish the series resistance of the device. Within the tested temperature range, the supercapacitor exhibits a positive temperature coefficient of capacitance, ranging from 0.6% K^−1 at 10 mV s^−1 to 1.3% K^−1 at 500 mV s^−1. The charge storage mechanism of the supercapacitor involves both faradaic and double-layer contributions, with pseudocapacitance becoming more dominant at higher temperatures. At 305 K, near the gelation point of the hydrogel, ionic conductivity increases, leading to enhanced overall performance. Specifically, the specific energy density increases by approximately 50%, while the specific power density rises by about 7%. Furthermore, the series resistance decreases from 2.8 Ω to 0.3 Ω, representing a 90% reduction compared to its initial value.