Preparation Of Fungus Bran-derived Carbon-based Composites And Study On Their Energy Storage Properties

Agricultural and forestry waste biomass is used as a carbon source to prepare high value-added carbon materials due to its abundant source,low cost,environmentally-friendly and renewable characteristics,and has been widely used in the field of energy storage.The preparation of biomass-based porous carbon not only solves the disposal problem of agricultural and forestry waste,but also makes the reuse of waste possible.As one of the common agricultural and forestry wastes,fungus bran is rich in hydroxyl groups and nitrogenous groups on its surface,which can be easily transformed into stable layered structure and has the potential to be used as a carbon-based carrier.However,the issues such as small specific surface area and limited porosity of fungus bran,and the utilization of fungus bran as an electrode material still needs further research.In this paper,fungus bran-derived carbon was prepared by the carbonization-activation method.Based on the stable layered structure and physicochemical properties of fungus bran-derived carbon,fungus bran-derived carbon-based composites were fabricated by introducing electric double layer capacitive and pseudocapacitive materials.To improve the utilization of fungus bran,fungus bran-derived carbon dots were further synthesized by hydrothermal method,and the structure and physicochemical properties of the pseudocapacitive materials were adjusted to enhance their electrochemical properties.The aim is to reveal the synthesis mechanism of fungus bran-derived carbon-based composites and to realize the practical application of them in the field of energy storage.It not only alleviates the environmental pollution caused by the disposal of agricultural and forestry waste biomass,but also achieves the purpose of turning waste into treasure.It provides a scientific method and broadens the research ideas for the high-value utilization of fungus bran.（1）Fungus bran was used as the raw material,and potassium permanganate was used as the template agent and activator to convert the bran into hierarchical porous carbon by adjusting the carbonization temperature under the premise of optimizing the carbonization time and activator concentration.The optimized FBC reached a specific surface area of 1623.9 m² g^-1 with a hierarchical porous structure while retaining its own heteroatoms.The optimal FBC sample was used to assemble a symmetric supercapacitor with a corresponding power density of 250 W kg^-1at an energy density of 6.1 Wh kg^-1.This study provides the basic theoretical support for the optimal preparation and micromorphology modulation of FBC.（2）In response to the problem of easy charge accumulation due to the smooth surface of carbon materials,a novel dual biomass porous carbon nanoparticles（MFCC）with rime-like scenery were prepared by using fungus bran-derived carbon as a layered carbon structure loaded with carboxymethyl cellulose（CMC）-derived carbon particles.MFCC activated by potassium permanganate has a unique structure and good electrical conductivity.MFCC also has a high microporosity ratio（0.77）and possesses the best conditions for the formation of a double layer in aqueous electrolytes.Profiting from the hierarchical structure of nanopores and nitrogen self-doping,the optimized MFCC electrode has a specific capacitance of 407 F g^-1 at a current density of 0.5 A g^-1 with good multiplicative characteristics and excellent cycling performance（the specific capacitance remains 96.9%of the initial capacitance after 5000 cycles）.The symmetric supercapacitor assembled from two MFCC electrodes has a relatively high energy density(11.4Wh kg^-1)and excellent electrochemical performance due to the interconnected network structure and multipath channels.This research realizes the utilization of biomass in carbon-based electrodes and lays the theoretical foundation for simultaneous utilization of multiple biomasses in energy storage devices.（3）The exclusive use of carbon material in the electrodes results in limited specific capacitance and suboptimal energy density,which may limit its application in practical energy storage applications.The nitrogen atom-doped carbon skeleton（FPC）was synthesized by using the abundant nitrogen in the fungus bran with KOH as the activator,with a view to loading zinc manganate as the backbone.FPC has a flake structure with a specific surface area of 1515 m²g^-1 and a suitable pore size distribution.The specific electric capacity of the FPC electrode was380 F g^-1 at a current density of 1 A g^-1.The composite materials（FPZM）loaded with different ratios of zinc-manganese oxides（ZMO）were fabricated by in-situ growth method using FPC as the carbon-based skeleton.When the mass ratio of FPC to ZMO was 1:3,the specific capacitance of the electrode material could reach 537 F g^-1 at 1 A g^-1 and favorable cycle performance（87.7%of the initial capacitance after 2000 cycles）.The energy density of the asymmetric supercapacitor with FPZM as the positive electrode and FPC as the negative electrode was 13.5 Wh kg^-1 at a power density of 700.3 W kg^-1.The synergistic effect between the bran-derived carbon and the pseudocapacitive oxide further improved the electrochemical performance of the composite electrode.（4）To tackle the issues of uneven distribution of ZMO on fungus bran-derived carbon and low capacitance,we further promote the robust anchoring of pseudocapacitive materials on fungus bran-derived carbon and improve the electrochemical performance.Nickel-cobalt layered double hydroxide（NCLDH）was grown in-situ on potassium permanganate-activated fungus bran-derived carbon（FBC）.The nitrogen-doped FBC has a layered porous structure,which facilitated the uniform growth of NCLDH and improved the ionic conductivity.The composite material（FBC/NCL）with a three-dimensional interconnected structure has a specific capacitance of 1938 F g^-1 at a current density of 1 A g^-1.The hybrid battery-supercapacitor device with FBC/NCL and FBC as positive and negative electrodes,respectively,provides good stability at an operating voltage window of 0-1.4 V.The capacitance was maintained at 76%of the initial capacitance after 3000 cycles at 5 A g^-1.The power density was 695.6 W kg^-1 at a high energy density of 37.3 Wh kg^-1.This study provides a new method to improve the electrical conductivity of metallic materials using FBC as a carbon matrix for growing LDH materials,aiming at the preparation of fungus bran-based supercapacitors with high performance.（5）In an attempt to improve the utilization of fungus bran and expand its application in the field of energy storage.2D nickel-cobalt layered double hydroxide（NCLDH）nanosheets were successfully modulated to form 3D flower-like spheres by utilizing negatively charged fungus bran-derived carbon dots（CDs）to adsorb metal cations and control crystal growth.The CDs/NCLDH samples have abundant accessible electroactive sites and good electrical conductivity,profiting from the strong interaction between CDs and NCLDH.The electrochemical performance of the optimized CDs/NCLDH electrode is significantly improved with ultra-high specific capacitance(2100 F g^-1 at a current density of 1 A g^-1)and better rate performance,which is twice that of the NCLDH electrode.The asymmetric supercapacitor assembled with CDs/NCLDH as the positive electrode and fungus bran-derived activated carbon（FBC）as the negative electrode obtained an energy density of 52.5 Wh kg^-1 at a power density of 750 W kg^-1.CDs enhance the electrical conductivity of the composites and accelerate the surface charge transfer,providing novel insights for developing LDH materials with better electrochemical performance.