Synthesis of concentric multilayer fullerene nanostructures from mineral coal for applications in supercapacitors

Motivated by the need to find added value to Colombian mineral coal and explore its possible applications in energy storage systems, herein, carbon nano-onions (CNOs) structures were produced from mineral coal through thermal annealing under an inert atmosphere. Three coal samples were extracted from three distinct mines in Colombia, and thermal annealing was conducted on each sample at different times from 1 to 2 h, and temperatures between 1200 and 1600 °C. Through HR-TEM, it was possible to observe the formation of onion-like carbon structures with interlayer distances of 3.86 and 3.50 Å for annealing temperatures of 1600 and 1800 °C, respectively. On the other hand, cyclic voltammetry was carried out to evaluate the potential use of the materials in capacitive systems after undergoing heat treatment showing an increase of up to 5000 % in the specific capacitance of each sample concerning the original carbon. Additionally, the behavior of the charge storage process was analyzed by electrochemical impedance spectroscopy, where faradaic processes obtained the most significant contribution to the enhancement of the specific capacitance.