An environmentally friendly hydrogel based on gelatin has been investigated as a gel polymer electrolyte in a symmetric carbon-based supercapacitor. To guarantee the complete sustainability of the devices, biomaterials from renewable resources (such as chitosan, casein and carboxymethyl cellulose) and activated carbon (from coconut shells) have been used as a binder and filler within the electrode, respectively. The electrochemical properties of the devices have been compared by using cyclic voltammetry, galvanostatic charge/discharge curves and impedance spectroscopy. Compared to the liquid electrolyte, the hydrogel supercapacitors show similar energy performance with an enhancement of stability up to 12,000 cycles (e.g., chitosan as a binder). The most performant device can deliver ca. 5.2 Wh/kg of energy at a high power density of 1256 W/kg. A correlation between the electrochemical performances and charge storage mechanisms (involving faradaic and non-faradaic processes) at the interface electrode/hydrogel has been discussed.
Keywords: carbon-based supercapacitor; charge storage mechanisms; cycle stability; gelatin; hydrogel electrolyte; pseudocapacitive material; sustainable binder; water processable.