Sustainable production of self-activated bio-derived carbons through solar pyrolysis for their use in supercapacitors

摘要

This work aims to propose a sustainable green process to obtain bio-derived carbons (BDCs) for utilization in supercapacitors. The process consists in carrying out solar pyrolysis to produce BDCs from abundant lignocellulosic wastes, Agave Angustifolia leaves and pruned tomato plant. Concentrated solar radiation from a high flux solar furnace was utilized to reach sample temperatures between 450 and 1564 degrees C in a spherical reactor. Before pyrolysis, both wastes were characterized by thermogravimetric analysis to semi-quantify cellulose and hemi-cellulose as well as ash content. XRD was used to determine the ash composition in both wastes, and 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 the effect of this on BDCs. Electrochemical properties of BDCs were analyzed by cyclic voltammetry in half cells, and those showing better performance were also tested in supercapacitor cells. Results show that BDCs from tomato plant waste have higher surface areas, with well-developed microporosity, without needing an additional activation process. This is attributed to self-activation during pyrolysis, produced by the high K and Ca content of the tomato plant pruning. Ragone plots indicate that the assembled supercapacitor cells employing the best BDCs from solar pyrolysis have specific energies and power values similar to a commercial carbon designed for supercapacitors. These results indicate that the proposed green procedure is suitable for obtaining BDCs with properties suitable for supercapacitors.