Preparation Of Heteroatom-doped Biomass-derived Carbon And Their Performance In Supercapacitor

As a new type of energy storage equipment,supercapacitors with the advantages of high power density,long cycle life,rapid charge-discharge capability,have a broad application prospect in the field of renewable energy storage and conversion.Carbon materials have been widely used as supercapacitor electrodes due to the features of high conductivity,large specific surface area and low cost.However,the lower energy density and poor rate performance limit the carbon-based supercapacitor further development and application.Heteroatom doping into carbon skeletons not only can significantly improve the wettability of carbon materials toward electrolyte and promote the ion transfer rate,but also provide more electrochemical active sites,thus effectively improving the energy density and rate performance of supercapacitors.The traditional production processes of porous carbon materials are often accompanied with complicated synthetic conditions,serious environmental pollution and energy consumption.Using biomass to prepare high value-added derived carbon materials can effectively solve the problems mentioned above.The key challenge for promoting the commercialization of supercapacitors is the exploitation of a green and low energy consumption process to manufacture the biomass-derived carbon materials.In this thesis,heteroatom-doped biomass-derived carbon materials were successfully fabricated by using biomass as carbon source,selecting eco-friendly inducer and activator,assisting with the alkali-free synthesis route.Based on the as-made biomass-derived carbon,supercapacitors with high energy density and excellent rate performance can be assembled with appropriate electrolyte.The specific research contents are as follows:Using glucose and phytic acid as carbon sources and zinc nitrate as activation agent,a three-dimensional crosslinking network structure was constructed by hydrogen bonding.The N,P-doped biomass-derived porous carbon was successfully prepared after carbonization and acid treatment.The effects of the ratio of zinc nitrate to carbon source on the morphology,pore structure and heteroatom amount of porous carbon were investigated.Also the key factors affecting the electrochemical performance of porous carbon were studied.The results show that the prepared biomass-derived carbon possesses the 3D porous structure.And the specific surface area and mesoporous proportion of porous carbon increase with the increase of the proportion of zinc nitrate,which can effectively improve the ion and electron transport properties of electrodes.The N,P-doped biomass-derived porous carbon was used as the electrode material of supercapacitor,which exhibits the high specific capacity(231 F g^-1@1 A g^-1)and excellent rate performance(80%@100 A g^-1).Symmetric capacitor was assembled by using ionic liquid EMIMBF₄ as electrolyte and deliver the high energy density up to 97 W h kg^-1@1 k W kg^-1.Using sweet potato leaves as carbon source and boric acid as boron source,N,B-doped biomass-derived superhydrophilic carbon was prepared by alkali-free activation process.The activator recycling process can be realized due to the mutually reversible transformation between boric acid and boron oxide.The effects of the mass ratio of boric acid to sweet potato leaves on the morphology,pore size distribution,surface chemical properties and electrochemical properties of superhydrophilic carbon were investigated.The results show that boric acid not only can induce the formation of 2D planar structure of carbon,but also can change the mesoporous proportion and hydrophilicity of biomass carbon.The in-situ doping feature has a significant effect on improving the electrochemical properties.Electrochemical test results show that the N,B-doped biomass superhydrophilic carbon exhibits excellent mass specific capacitance(296 F g^-1@1 A g^-1)and well rate performance(76%@50 A g^-1).The symmetric supercapacitor assembled based on this material with 10mol kg^-1 Na OTF electrolyte delivers high energy density up to 14 W h kg^-1@1.2 k W kg^-1.