Toward Biosourced Materials for Electrochemical Energy Storage: The Case of Tannins

Sustainable electrochemical energy storage solutions are needed to efficiently exploit renewable intermittent energy sources. In principle, redox active biosourced (natural) molecules deposited on the surface of carbon materials allow for an increase in the energy density of corresponding electrochemical capacitors, since faradaic processes add to electrostatic ones. Herein, we report on tannins as possible redox active molecules for sustainable electrochemical capacitors operating in aqueous electrolytes. A key element determining our choice to study tannins is that they can be extracted from forest residues or agricultural biomass waste, a clear advantage in terms of sustainability. In our work, we considered two different molecules belonging to the tannin family (tannic acid and (+)-catechin), deposited on an electrochemically activated carbon paper substrate. The morphology and elemental composition of the electrodes were observed with scanning electron microscopy and X-ray photoelectron spectroscopy. Electrochemical characteristics of the material were determined by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. Our results contribute to pave the way for the use of tannins, and more in general biosourced molecular materials, as redox active molecules for electrochemical energy storage.