Preparation Of Supercapacitor Electrode Based On In-situ Nitrogen-doped Porous Biochar Loaded With MnO₂

Supercapacitor is a new type of energy storage device with high power density and long cycle charge and discharge life.Biomass can prepare electrode active materials suitable for supercapacitors through effective activation methods.Therefore,the development of a technical route for preparing high-performance and low-cost electrode active materials for supercapacitors using biomass as raw materials has great research value and development prospects.Using bean pulp as raw material,in-situ nitrogen-doped porous activated carbon is prepared by CO₂ physical activation.The effect of carbonization temperature on the microscopic morphology,pore structure,crystallite composition,chemical properties and electrochemical properties of porous activated carbon is deeply explored.The physical and chemical properties of the prepared samples are best when the activation temperature is 800?.In the three-electrode system,the specific capacitance of BPC-800 at 0.25 A/g is 152.8 F/g,and it also has good rate performance and cycle performance.After 30,000 cycles of charge and discharge,the specific capacitance still maintains 96.7%of the initial value.The effect of CO₂ concentration on the physical and chemical properties of in-situ nitrogen-doped porous activated carbon was studied.The increase of CO₂ concentration will directly decrease the yield of porous carbon.The specific surface area and pore volume of BPC-100%reach the maximum,but the proportion of micropores(55%)of the sample with 50%CO₂ volume concentration is the highest.As the concentration of CO₂ increases,the specific surface area increases,which is not conducive to the formation of micropores,and reduces the relative content of pyridine N,which is beneficial to the formation of pyrrole N.BPC-50%exhibits a specific capacitance of 106 F/g at 0.25 A/g,and maintains 93%of the initial value after 20000 cycles.Based on BPC-800,BPC@MnO₂ was synthesized by hydrothermal method.The specific surface area and pore volume of BPC@MnO₂ are reduced by more than 50%,and there are more than 85%of micropores.It exhibits a specific capacity of 288.3 F/g at 0.25 A/g.The kinetic analysis shows that the increase of the voltage sweep rate leads to a decrease in the proportion of pseudocapacitance controlled by diffusion from 50.9%to 24.6%,which weakens the pseudocapacitance effect and reduces the specific capacity.After 30,000 continuous charge and discharge cycles,the composite material still has an initial capacitance value of 84.3%.