Tannins for Sustainable Semi-solid-state Supercapacitors

Organic redox-active molecules extracted from natural sources (biosourced) are relevant for sustainable storage of renewable, yet intermittent, energy. When deposited on electrode surfaces, redox-active molecules bring about an increase of the energy density of the electrodes since the Faradaic storage mechanism adds to the electrostatic one. The engineering of the electrode surface and the interfaces between the electrode surface with the molecules and the electrolyte is key to optimization of storage. Here, we report on (i) electrodes prepared by depositing onto chemically modified surfaces of carbon paper solutions of the redox-active Catechin (Ctn) molecule, a member of the tannin family, and (ii) its use in symmetric electrochemical capacitors assembled by interfacing them to the polyvinyl alcohol (PVA)-based hydrogel electrolyte. Ctn-based supercapacitors reach capacitance values as high as 202 F g - 1 at 1 Ag −1 (based on the mass of Ctn). They feature 99.6% capacitance retention and 99.8% Coulombic efficiency, after 20,000 cycles. The devices exhibit an energy density of 55 W h kg - 1 and power density of 660 W kg - 1 (based on the mass of Ctn). Our work contributes to the development of eco-designed, low-cost, and potentially biodegradable electrochemical supercapacitors based on redox-active tannin materials. Graphical Abstract