Microwave Irradiation For Preparation Of Eucommia Wood Derived Mesoporous Activated Carbon And The Electrochemical Properties

The development and utilization of clean renewable energy have become a research hot topic due to the increasing consumption of world’s energy and the negative impact of conventional energy supply on the environment.However,the disadvantage of new energy sources,such as intermittent and regionally,limit their development,and an advanced energy storage device need to be developed.The supercapacitor is an excellent energy storage device with unique advantages,including high power density,low maintenance cost,long cycle life,and fast charging and discharging.The preparation of supercapacitor electrode materials with high-performance porous activated carbon derived from biomass waste has attracted widespread attention because of its low cost and superior performance.However,the pore size structure of biomass-based activated carbon is limited by the characteristics of raw materials and pyrolysis methods,and the capacitive performance of the constructed activated carbon is difficult to significantly improve.To address this situation,annual Eucommia wood was used as the raw material to prepare activated carbon by microwave irradiation physical-chemical activation method.The composition of the wood was analyzed and the pyrolysis characteristics and the kinetics of pyrolysis of Eucommia wood were studied.The pyrolysis parameters were also optimized to obtain activated carbon materials with a reasonable pore size distribution and excellent electrochemical properties.The main research contents and results are as follows:（1）Pyrolysis properties and pyrolysis kinetics fitting of Eucommia wood.The effects of different particle sizes,heating rates and phosphoric acid impregnation concentrations on the pyrolysis properties of Eucommia wood were explored.The kinetic parameters of Eucommia wood pyrolysis were calculated by the Coats-Redfern（CR）method.Thermogravimetric analysis showed that the pyrolysis of Eucommia wood is divided into four stages:pre-pyrolysis of raw materials with water loss（<110℃）,depolymerization and"glass transition"of raw materials（110-210℃）,complex chemical and physical reactions of raw materials（210-400℃）and slow decomposition of char and ash generated by pyrolysis of raw materials（>400℃）.Kinetic fitting indicated that the activation energy of the main pyrolysis stage of Eucommia wood was 66.63-82.10 k J/mol,and the activation energy of the pyrolysis stage of Eucommia wood was reduced to 16.53-41.29 k J/mol after the addition of phosphoric acid impregnation pretreatment.（2）Preparation of Eucommia wood-based mesoporous carbon with microwave irradiation and analysis of electrochemical property.Eucommia wood was used as raw material in this section to the activated carbon materials with controlled pore structure and high specific surface area by using microwave irradiation heating method with phosphoric acid and water vapor as activators.The effect of pore structure on the electrochemical properties was investigated by electrochemical tests.The results demonstrated that the carbon material（AC-P-H-15）with developed pore structure could be prepared by ultrasonic impregnation of Eucommia wood in 40%phosphoric acid solution for 1.25 h,followed by heating at 900 W microwave power for 50 min and a further water vapor activation for 15 min was conducted.The final specific surface area reached 2570.06 m²/g,the total pore volume reached 1.77 cm³/g,and the average pore size was 2.68 nm.In the three-electrode system,the mass specific capacitance of AC-P-H-15 electrode reached 339 F/g at a current density of 1 A/g,and the capacitance retention rate was 95.6%after 5000 cycles.（3）Preparation of CoFe₂O₄/AC composite and electrochemical performance analysis:The mesoporous activated carbon loaded with Co Fe₂O₄ was prepared by hydrothermal method,and the physical composition and pore size distribution of the prepared composites were analyzed.The electrochemical properties of the composites were analyzed by systematic electrochemical tests.The results demonstrate that the composite material showed excellent multiplicative performance with a specific capacitance of 668.73 F/g in the three-electrode system.The power density and energy density of asymmetric supercapacitor assembled with AC and Co Fe₂O₄/AC were 750 W/kg and 40.01 Wh/kg at a current density of 1 A/g and a specific capacitance of 115.749 F/g,respectively.The capacitance retention rate could keep91.73%after 5000 cycles.