Preparation Of Biomass-based Carbon Functional Materials And Its Application In Supercapacitors

To meet the challenge of global resource shortage and prevent excessive consumption of fossil fuels,the development of clean energy storage and energy conversion equipment based on sustainable resources is regarded as an effective strategy.Lithium-ion batteries as energy storage have been used in many fields.With the continuous maturity and improvement of technology,many defects of lithium batteries are gradually being exposed,such as high production requirements,high cost,and poor high-power discharge.With the upgrade of the contradiction between demand and insufficient performance,it is urgent to focus on new energy storage devices with lower cost and more outstanding performance.Supercapacitors are considered to be a promising energy storage device due to their advantages of fast charging and discharging,long-term stability,low cost,and low maintenance requirements.Electrode materials are the key factors affecting the energy storage performance of supercapacitors.In recent years,carbon materials represented by activated carbon,graphene,and carbon nanotubes are the preferred materials for supercapacitor electrode materials.However,due to the complex characteristics and high cost of these carbon materials,their road to industrialization is still very distant.From a socio-economic and sustainable perspective,biomass materials that can be obtained from nature have been explored as alternative materials for supercapacitors because of their low cost,non-toxic and harmless.At present,there are many reports on the development of porous carbon materials with high pore structure,but the process is cumbersome and generates a variety of by-products,and still suffers from low specific capacitance and energy density.Therefore,it is still a challenge to develop functional electrode materials with simple synthesis steps,green activation processes,high specific capacitance and energy density,and universal preparation methods.Based on that,many biomass materials were selected to prepare biomass-based porous carbon by doping and activation in this paper.At the same time,composite materials were prepared by introducing transition metal oxides to the porous carbon.（1）Boron/sulfur co-doped porous carbon（B/S-SC_S-1）was prepared by using the Zn Cl₂ activation process using boric acid and thiourea as B and S sources and sedum stem as raw materials for the electrode material of the supercapacitor.Due to the synergistic effect between the activation treatment of Zn Cl₂ and the doping of B and S,the as-prepared B/S-SC_S-1 as-electrode material displayed a great capacitance of290.7 F g^-1 at 0.5 A g^-1 as well as a brilliant rate performance.In addition,the supercapacitor established with B/S-SC_S-1 produced maximal specific energy of16.65 Wh g^-1 in the 1 M Na₂SO₄ electrolyte,and it showed high stability with 97.09%of the initial capacitance retention posterior to 10000 cycles.（2）The surface of biomass waste-derived carbon was modified by transition metal oxide Fe₂O₃,and the synergistic effect of the two was used to obtain higher specific capacitance and stability.The prepared composite existed a certain pore structure,and Fe₂O₃ nanoparticles were anchored on the carbon surface.The optimal electrochemical performance was obtained as the ratio of Fe₂O₃ and biomass-derived carbon was 1:1.The composite provided 430.8 F g^-1 at a current density of 1.0 A g^-1when 3 M KOH was utilized as the three-electrode electrolyte.The asymmetric supercapacitor constructed by using it as the negative electrode had a high voltage window（0-1.6 V）and achieved a high energy density of 39.1 Wh kg^-1.