Ultralow Ash Semicoal Powder Obtained by Two-Step Acid Treatment and Its Supercapacitive Properties

The value-added utilization of byproducts of the coal chemical industry is very important for environmental conservation and sustainable development. In this article, we demonstrated the high value utilization of Shenfu semicoke powder as a supercapacitive electrode material. Different deashing processes and different weight ratios of carbon to alkali were used to prepare electrode material. The pore structure and electrochemical properties of the prepared activated carbon were studied systematically. The results reflect that the ultralow ash semicoke powder (0.53%) can be obtained by a two-step acid treatment. With the deep deashing process, the obtained activated carbon possesses a high specific surface area and high specific capacitance over the pristine sample. When the weight ratio of carbon to alkali is 1:2, the specific capacitance of the activated carbon is 193.3 F.g(-1) at a current density of 0.5 A.g(-1), even retaining a specific capacitance of 142.7 F.g(-1) at a current density of 5 A.g-1, while the capacitance retention rate reaches 73.8%. Also, the material shows a 97.8% initiated capacitance retention after 500 cycles of the charge-discharge process.