Lignite-derived high surface area mesoporous activated carbons for electrochemical capacitors

Mesoporous activated carbons (ACs) were successfully prepared from lignite using KOH as activation agent at the temperature above 700 °C. The pore structure and surface chemistry of the as-prepared ACs were characterized by means of nitrogen adsorption-desorption, X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy. The results show that such prepared mesoporous ACs have a high specific surface area (~ 3036 m²·g^{- 1}) with a hierarchical macro-meso-micro-pore structure and oxygen-enriched surface. The electrochemical performances of the ACs as electrode materials for electrochemical capacitors (ECs) were assessed by galvanostatic charge-discharge, cyclic voltammetry and cycling durability tests. It was demonstrated that the mesoporous ACs produced in this study possessed a maximum specific capacitance of 355 F·g^{- 1} and 196 F·g^{- 1} in 3 M KOH aqueous and 1 M (C₂H₅)₄NBF₄/PC organic electrolytes, respectively, at a current density of 50 mA·g^{- 1}, and exhibited a desirable energy and power density with a superior cycling performance. The excellent capacitive behavior of the prepared mesoporous ACs in aqueous system is attributed to their unique macro-meso-micro-hierarchical pore structure with high surface area and oxygen-containing surface. Their superb electrochemical performance in the organic electrolyte is attributed to their well-developed mesoporous structure.