In situ and operando thermal characterization in aqueous electric double layer capacitors using the 3[formula omitted] hot-wire method

Abstract

The thermal properties of aqueous electric double layer capacitors (EDLCs) with KOH electrolytes were measured using the in situ and operando 3ω hot-wire method. The reversible entropy and free energy changes in the EDLCs caused dynamic changes in the effective heat capacity of the electrodes, which were monitored real-time during charge and discharge operations. In an EDLC with a 6 M KOH electrolyte, the effective heat capacities of the positive and negative electrodes with a varying voltage from 0 to 1 V were estimated to decrease by approximately 9.14% and 3.91%, respectively. This polarization dependence may be attributed to the capacitance capability, which is determined by the size of the adsorbed hydrated ions. Regarding the effect of KOH concentration, the maximal capacitance and change in effective heat capacity were observed in the vicinity of 8 M concentration, and attributed to changes in the thermodynamic state by the capacitance effect.