A combined leaching and electrochemical activation approach to converting coal to capacitive carbon in molten carbonates

The impurities of coal plague its values not only for fuels but also for preparing functional carbon materials. Herein, we aim to develop a clean and one-step strategy to prepare activated carbon by molten salt leaching and electrolysis approach to converting anthracite/lignite to carbon for electrochemical supercapacitors. First, the major impurities such as silica and alumina were removed by a combined molten salt and water leaching process without using any toxic acid or alkaline solutions. Meanwhile, the carbonization and activation of coals take place together in the water- and oxygen-free molten salt medium. Moreover, the electrolysis can further increase the specific capacitance of the coal-derived carbon by the electrochemical regulation of carbon in molten salt using a low-cost and oxygen-evolution inert anode. The as-obtained carbon delivers a capacitance of 190 F g−1 at 5 A g−1 and shows nearly no capacitance loss after 10,000 cycles. This paper provides a clean molten salt approach to utilizing both high-rank and low-rank coals for the preparation of capacitive carbons. •Al2O3 and SiO2 in the coal can be removed by molten carbonate leaching.•The coal-derived carbon was regulated at the cathode in molten carbonate.•The coal-derived carbon delivered a specific capacitance of 190 F g−1 at 5 A g−1.•Both anthracite and lignite can be converted to capacitive carbon in molten salt.