Study On The Electrochemical Activation Approach To Converting Coal To Capacitor Activated Carbon Electrode Material And Its Properties

Because of the high specific surface area,controllable pore size,high conductivity,high chemical stability and thermal stability,activated carbon is widely used in various fields,such as water and flue gas treatment,catalytic and supported catalysts,supercapacitors and lithium battery materials,clinical medicine and hydrogen storage.In recent years,the demand for activated carbon in China is increasing,but there are some problems in the traditional physical and chemical activation methods.The expensive price of the wood raw material has limited the large-scale use,but the coal with rich resources and high carbon content is a high-quality raw material with a very promising development prospect.At present the difficulty of preparing coal-based activated carbon materials lies in the effective removal of impurities,which not only produce a large number of harmful gases during combustion,but also limit the properties of the prepared active carbon.In order to meet the requirements of environmental protection,we aim to develop a clean and one-step impurity removal,carbonization and activation strategy to prepare activated carbon by the approaches of molten salt leaching and electrolysis to converting anthracite/lignite for electrochemical supercapacitors.In this experiment,the mixed carbonate(Na2CO3-K2CO3)is the reaction medium,the inert metal rod is an anode,and the coal is placed on the cathode by the method of soaking or constant voltage electrolysis.The effects of different preparation methods(soaking or electrolysis),applied voltage and KNO3 additive on the properties of activated carbon are studied.The materials were characterized by means of XRD,SEM,EDS and Roman.The electrochemical performances were analyzed by the methods of CV,EIS and GCD.The results show that:(1)Coal has been successfully converted into activated carbon by molten salt method.(2)The capacity of anthracite-derived carbon prepared by molten salt electrolysis increases with the increase of voltage.The specific capacitance of AC-3.0V-5h electrode material obtained by electrolysis at 3.0V for 5h is 239F·g-1 at 0.1A·g-1 and 173F·g-1 at 5A·g-1,the capacitance retention rate is 72.4%.The capacitance has almost no loss after 10000 cycles in the three-electrode system.After adding KNO3,the capacity of activated carbon increased to 190F·g-1 at 5A·g-1,the capacity retention rate decreased.(3)The capacity of lignite-derived carbon prepared by molten salt electrolysis also increased with the increase of voltage.The specific capacitance of HAC-2.3V-5h electrode material obtained by electrolysis at 2.3V for 5h can reach 292F·g-1 at the current density of 0.1A·g-1,but 153F·g-1 at 5A·g-1.This experimental method has two advantages as follows:First,the major impurities(silica and alumina)were removed by a combined molten salt and water leaching process without using any toxic acid or alkaline solutions in the reaction process.Meanwhile,a low-cost and oxygen-evolution inert alloy anode was used to produce no harmful gas.The environment pollution can be reduced in two ways.Besides,the electrolysis can further increase the specific capacitance of the coal-derived carbon by the electrochemical regulation of carbon in molten salt.It provides a new idea for the treatment of other carbon-containing wastes and minerals.