Preparation Of Biomass Carbon-based MnO₂ Composites And Study On Their Electrochemical Properties

Spercapacitor,a green energy storage device,has been used in many fields because of its high power density,long service life and fast charge and discharge speed.Especially in recent years,micro supercapacitors have become new research hotspots in portable electronic medical devices and smart wearable devices.As a key core component that determines the performance of supercapacitors,carbon electrode materials are subject to defects in precursors derived from traditional fossil fuels,such as non-renewable and high cost,cumbersome preparation process,and uncontrollable apertures,which greatly affects the performance of supercapacitors and the application of multi-scenario fields.Waste biomass carbon has the advantages of abundant and renewable raw material sources,and the formed hierarchical porous carbon has the advantages of developed pore structure,high specific surface area and abundant surface functional groups.Therefore,waste biomass carbon is an ideal electrode material,which shows great advantages in improving the performance of supercapacitors.In this paper,the deciduous leaves of terrestrial Populus alba L and aquatic fresh mature Laminaria japonica in Dalian were used as carbon precursors.First,the primary carbon material is obtained through a one-step high-temperature roasting process.Then,the electrochemical properties of biomass carbon-based electrode materials were further improved by activating the two strategies of manufacturing pores and recombining MnO₂with fake capacitance characteristics.So as to achieve the purpose of high value-added reuse of waste biomass as carbon energy storage materials.It provides theoretical support and experimental basis for the development of supercapacitors,a high-performance biomass-based carbon composite electrode material.The main research contents and achievements of the paper are as follows:1.Using the Populus alba L as the carbon source,porous activated carbon is prepared by cleaning,carbonization,activation and other processes.The effects of roasting temperature and activation conditions on the surface morphology,pore structure and electrochemical properties of activated carbon were studied,and the best preparation conditions were obtained to optimize its electrochemical properties.The results show that the carbonization temperature is 900°C,and the carbon material PALCH after mixing acid boiling and activating has a fibrous three-dimensional through porous structure with the best electrochemical properties.In the three-electrode system,and the specific capacitance was 110.2 F/g at a current density of 0.2 A/g,and at a current density of 5 A/g,the capacitance retention rate was 97.8%after 5000 charge and discharge cycles,and the material showed good electrochemical stability.2.Using PALCH activated carbon as the base,KMnO₄and Mn SO₄as Mn sources,to prepare MnO₂/PALCH composite materials by hydrothermal synthesis technology.The effects of Mn source type and concentration,hydrothermal reaction time,and hydrothermal reaction temperature on the microstructure and electrochemical properties of composites were studied.The results show that the MnO₂/PALCH composite carbon electrode material obtained by hydrothermal reaction of PALCH with 0.05 mol/L KMnO₄for 1 h at 160°C has the best micro/mesoporous structure and electrochemical properties.MnO₂/PALCH in the three-electrode test system,at a current density of 1 A/g,the specific capacitance can reach 468 F/g,and at a current density of 10 A/g,after 5000 cycles,the capacitance retention rate is 77.8%.Under the two-electrode test system,the energy density of the assembled asymmetric supercapacitors reaches 74.16 Wh/kg at a power density of 3.24 k W/kg.3.Using Laminaria japonica as a carbon source,porous activated carbon(LJC)is prepared by pretreatment,carbonization,activation and other methods.On this basis,MnO₂/LJCH composites were obtained by using hydrothermal synthesis technology with KMnO₄as the Mn source.The structure-activity relationship between its morphology,pore structure and electrochemical properties was studied.When the hydrothermal reaction temperature is 160°C,the reaction time is 12 h,and the KMnO₄concentration is 0.1 mol/L,the microstructure and electrochemical properties of MnO₂/LJCH composites are the best.With a specific surface area of 102.52 m²/g,it has a hierarchical porous structure and good hydrophilicity,which increases the effective contact area of the electrolyte with the material,resulting in excellent capacitive properties.MnO₂/LJCH-t12 in the three-electrode system,the specific capacitance reaches 600F/g at a current density of 1 A/g.At 5 A/g,the capacitance retention rate is 61.7%after 5000charge and discharge cycles.The asymmetric supercapacitor assembled under the two-electrode system has a specific capacitance of 37.06 F/g at a current density of 0.5 A/g.The energy density reaches 106.74 Wh/kg at a power density of 3.24 k W/kg.