The Preparation Of Biochar From Several Agricultural Residues And Its Application In Supercapacitors

China is an agricultural country with rich agricultural resources.However,the environmental pollution and waste resources caused by the unreasonable treatment of agricultural residues have seriously obstructed the sustainable development of the society.At the eighth National Ecological Environment Protection Conference,it was proposed to uphold the harmonious coexistence of human and nature,to solve the ecological and environmental problems,and to advance the ecological civilization construction.Furthermore,the sustainable development with high-quality,high-efficiency traits will promote the construction of ecological civilization to a new level.So,it is a pressing need to propose a smart strategy to convert the agricultural residues into high value-added materials,which aims to revitalize rural China in all aspects,including the ecology and the environment.Biochar presents many application prospects in the agriculture(soil amendment,soil remediation,nitrogen fixation,etc.),the environment(organic pollutant adsorbent,heavy metal adsorbent,pollutant water purification,air purification,etc.),and energy storage devices(supercapacitor,alkali-metal ion battery,alkali metal-sulfur battery,etc.)due to their unique physical and chemical properties,natural microstructures,high specific surface area,and rich surface functional groups.It is very important that agricultural residues can be transformed into biochar with high added-value.Moreover,the conversion of agricultural residues into biochar is a significant step to realize the comprehensive utilization of agricultural residues.However,the application of biochar derived from agricultural residues in many fields still faces a great challenge.This paper mainly focuses on the research about the efficient utilization of agricultural residues and simple preparation procedures to obtain biochar from agricultural residues.The supercapacitor made by the resulting biochar showed excellent electrochemical performance.The following presents the brief research contents:1.The nitrogen-doped biochar with high specific surface area(>2800 m2 g-1)and three-dimensional structure,was prepared from agricultural residues via pre-carbonization and activation in proper temperature,which derived from agricultural residues(Pleurotus ostreatus residue and silkworm excrement).When obtained biochar was applied to the supercapacitor as an electrode material,it realized great electrochemical performance.According to this research,an unsophisticated method to prepare biochar materials was systematically developed.2.The biochar with ultrahigh specific surface area and three-dimensional structure derived from the Pleurotus ostreatus residue was prepared after fungi-assisted treatment,the pre-carbonization,and KOH activation procedures.The concept of a novel pore formation mechanism in root-colonizing fungi and anticipations of a valuable function for fungi in developing the useful biochar were put forward.When the carbonized Pleurotus ostreatus residue was mixed thoroughly with KOH(the mass ratio of KOH/biochar was 4),the specific surface area of biochar at 800 °C reached 3439 m2 g-1.The concept of lithiumion hybrid electrochemical capacitors(Li-HEC)based on the resulting biochar cathode coupled with the Si/C anode is proposed.The Li-HEC displayed a superb energy density of 263.9 Wh kg-1 at the power density of 0.7 k W kg-1.3.The nitrogen-doped biochar with high specific surface area and three-dimensional structure was prepared from silkworm excrement via pre-carbonization and KOH activation(the mass ratio of KOH/biochar was 4)procedures.The specific surface area of biochar reached 2826 m2 g-1 at 700 °C.The symmetric supercapacitor composed of the nitrogendoped biochar provided an energy density of 138.4 Wh kg-1 at the power density of 495.9 W kg-1 in 1-ethyl-3-methylimidazolium tetrafluoroborate(EMIMBF4)electrolyte.It was found that the operating potential of the supercapacitor reached up to 4 V in EMIMBF4 electrolyte,while the operating potential of the supercapacitor in sulfuric acid electrolytes only exhibited 1 V.The obtained nitrogen-doped biochar and Si/C composites were respectively chosen as the cathode and the anode to construct Li-HEC.The as-designed LiHEC presented a superb energy density of 242.2 Wh kg-1 at the power density of 325.3 W kg-1.