Preparation And Electrochemical Energy Storage Properties Of Heteroatom-doped Porous Carbon And Carbon-based Composites

In order to significantly reduce the dependence on traditional fossil energy,solve the problem of environmental pollution,maintain ecological balance and achieve green sustainable development,promoting the application of green energy is the top priority in future.For the purpose of solving these problems,the research and development of new electrode materials,especially porous carbon and carbon-based composite materials with high specific capacity,low cost,high cycle stability and versatile application,become the current research focus in this field.In this paper,the effects of different synthesis methods,microstructure control and heteroatom doping of porous carbon and carbon-based composite materials were studied for evaluating the the electrochemical energy storage performance.Meanwhile,the versatility of these materials in different electrochemical energy storage devices was also researched,and a series of related experiments and mechanism studies were carried out.The main research results are as follows:1.A new method was designed to treat pitaya peel with ethanol aqueous solution and KOH to obtain hierarchical porous carbon with ultra-high specific surface area.Firstly,the simple and time-saving synthesis without the autoclave reaction could be performed at low temperature and normal pressure which was different from the traditional hydrothermal method.Secondly,the raw material of pitaya peel from the agricultural waste were economical and eco-friendly.Thirdly,the ultrahigh specific surface area(3521 m²·g^-1)of the hierarchical porous carbon with massive O-doping could improve the wettability of the electrolyte to materials benefitting for electrochemical energy storage.Therefore,the electrochemical energy storage performance of the pitaya peel derived hierarchical porous carbon is very excellent,which can be used as an electrode material for solid-state flexible asymmetric capacitors,lithium ion batteries,and aqueous zinc ion battery hybrid capacitors with strong versatility for commercial application.2.Because diatomic doped porous carbon has more excellent electrochemical energy storage performance than monoatomic doped porous carbon.Thus,we first used KOH-triethanolamine solution as a solvent to conduct solvothermal treatment of rice straw at high temperature,and then directly calcined and activated it after drying.Then the obtained precursors were calcined and activated directly after drying without other treatments in the tubular furnace,producing the rice straw derived N/O co-doped biomass porous carbon（TJGD Carbon）finally.This new strategy owned the following characteristics:（1）At the high temperature,KOH is used to accelerate the glycosidic bond breaking of cellulose in rice straw,promoting the granulation of massive cellulose,and accelerating the peeling of cellulose layers.（2）The triethanolamine could not only provide a high-temperature reaction environment as the solvent,but also react with hydroxyl groups on cellulose at high temperature via hydroxyamination reaction to realize solvent self-doping effect,obtaining N/O co-doped hierarchical porous carbon.（3）The thermodynamic effect of high temperature made KOH easier to infiltrate into the interior of cellulose particles,which was conducive to the formation of hierarchical porous structure in the later activation process.（4）The designed synthesis process were easy to operate with low cost due to the prepared precursors could be calcined directly with out separation or washing procedure.Thus,this TJGD porous carbon possesses the advantages of high specific capacity,rapid charge and discharge,ultra-high energy density,and long cycle life.It is a versatile electrode material suitable for energy storage in supercapacitors,aqueous zinc ion hybrid supercapacitors,and lithium ion batteries.3.Recent research has confirmed that polyatomic doped porous carbon can provide richer active sites for energy storage and enhance the wettability between the electrolyte and the material,thereby improving the electrochemical energy storage performance of carbon materials.Here,we have designed a very simple solvent thermal synthesis method,which the citric acid,potassium citrate and thiourea were used as raw materials with the solvent of ethylene glycol via the facile solvothermal reaction at 175℃to prepare the carbon precursors.After that,the N/S/O ternary co-doped porous carbon（NSODCs）was obtained by calcining the carbon precursors directly without other treatments.In this preparation,citric acid,potassium citrate and thiourea not only acted as the basic raw materials to form the main structure of carbon materials,but also provided a large number of doped atoms,improving the energy storage active sites of carbon materials.In particular,thiourea was used as a dopant with two kinds of nitrogen and sulfur doping atoms simultaneously.The size and structure of the generated carbon precursor were controlled by the amidation and esterification polymerization reaction.Furthermore,the gasification of N and S atoms in the subsequent calcination process derived massive defects and micropores,which optimized the microstructure of carbon materials continuously.In addition,potassium citrate also played the role of structural agent,dopant and pore-forming agent in the reaction process,improving the specific surface area of the product further.To our knowledge,this novel synthesis method for the preparation of NSODCs has not been reported yet.Therefore,it has great application prospects in the field of electrode material preparation for multipurpose energy storage devices.4.Recently,the use of heteroatom doped porous carbon to composite modify two-dimensional metalloenes（MXenes）to obtain novel Mxenes/C composites has become a hot topic in the field of electrode materials research.According to a facile avenue by mixing the accordion-like Nb₂C MXenes and bio-derived porous carbon（PCarbons）directly via sonication and stirring simultaneously,the uniform-mixed MXenes and carbon composites（Nb₂C-PC carbons CPs）with excellent electrochemical energy storage performance were obtained.Compared with other methods for preparing Mxenes/C composite materials,the ultrasonic stirring mixing method is very suitable for large-scale industrial production due to its simple process,low cost,and short production cycle.The Nb₂C-PCarbons CPs possessed the following outstanding advantages:the excellent electronic conduction and pseudo-capacitance properties originating from Nb₂C MXenes,as well as the high specific surface area(about 2712 m²·g^-1)and rich hierarchical porous structure endowing by O-doped PCarbons,which improve the electrochemical energy storage performance of the composites greatly.Thus,this Nb₂C-PCarbons CPs had the advantages of high specific capacity,fast charge and discharge rate,ultra-high energy density,low resistivity and long cycle life,which were suitable for energy storage of supercapacitors and water-based zinc ion batteries as a dual-functional material.