(511b) Solar Pyrolysis Production of Self-Activated Bio-Derived Carbons for Supercapacitors

Supercapacitors (SC), also known as ultracapacitor or electrochemical capacitors, are energy storage devices whose characteristics place them in the gap between high power density of traditional capacitors, and high energy density of rechargeable batteries. In particular devices that store energy mainly by ion adsorption at the electrode/electrolyte interface are called electric double layer capacitors (EDLC). Carbon materials with high surface area, adequate micro-meso pore size distribution, good electrical conductivity, and chemical stability, are the most common electrode materials used in EDLCs. In order to increase the sustainability of the production of these devices, bio-derived carbons (BDCs), sometimes called biochars can be used, in particular, those obtained from agricultural wastes that do not compete with food supply. The production of bio-derived carbons useful for supercapacitors by means of solar pyrolysis is reported in this work. Two abundant lignocellulosic wastes, agave angustifolia leaves, and pruned tomato plant, were transformed by solar pyrolysis to BDCs. The process was carried out in the IER-UNAM High flux solar furnace (HoSIER), by using a glass spherical reactor. We studied different solar pyrolysis temperatures ranging from 450°C to 1560°C to produce the BDCs and correlate their physicochemical properties with their ability to store energy. XRD was used to determine the effect of solar pyrolysis temperature on the obtained BDCs. Additional structural properties of BDCs were analyzed by SEM, Raman spectroscopy and physisorption. Elemental analysis and EDAX were used to determine the chemical composition of wastes, and their effect on BDCs. It was found that BDCs from tomato plant waste had higher surface areas with well-developed microporosity without any extra activation process, confirming a self-activation process during pyrolysis. Electrochemical properties of BDCs were analyzed by cyclic voltammetry in 3 electrode cells, and the ones showing better performance were tested in 2-electrode supercapacitor cells. These cells exhibit specific energies and power values similar to a commercial carbon designed for supercapacitors.