Thermal Charging Supercapacitors Based on Graphene Films.

Utilizing supercapacitors to convert low-grade heat into electrical energy for storage is an efficient waste heat recovery technology. In this study, the graphene films with a hierarchical porous structure are prepared, and a thermal charging supercapacitor is designed using RGO films as the electrode material. Under the influence of varying temperature fields, a different potential is induced on the working electrode and reference electrode surface of the supercapacitor, resulting in a potential difference U out between them. The balanced voltage U s of the supercapacitor increases linearly with the increase of the temperature difference ΔT and grows with the rise in solution concentration. The thermoelectric coefficient of the supercapacitor with 0.1 M KCl solution can reach 1.46 mV/°C. The thermoelectric coefficient increases with the height of the RGO film, the area of the RGO film, and the concentration of KCl solution. Discharge tests reveal that the capacitance of the supercapacitor is less affected by temperature difference, but significantly influenced by components constituting the supercapacitor (such as the concentration of the electrolyte solution). Furthermore, increasing the temperature and the concentration of the solution can effectively reduce the internal resistance of the supercapacitor.