【作者】 李明；

【导师】 韩奎华；

【作者基本信息】 山东大学 ， 动力工程及工程热物理， 2021， 博士

【摘要】 近年来,以海藻酸盐或浒苔为原料制备多孔炭用作超级电容器电极材料的研究受到了关注。然而,它们的性能仍需进一步提高。基于前驱体中不同成分的作用提升多孔炭性能的策略极具潜力。本文在探究前驱体中Na、Ca元素对多孔炭微观结构影响的基础上,利用二者的协同作用构建三维互连层次的孔隙结构以提升海藻酸钠基多孔炭的超级电容性能;在探究前驱体中NH4+对海藻酸基多孔炭影响的基础上,以磷酸氢二铵、尿素和三聚氰胺为氮源,制备高性能的氮掺杂浒苔基多孔炭。利用SEM、氮气吸附脱附、HK、BJH、XRD、Raman、XPS等来表征多孔炭的性质。在二电极体系中,进行恒电流充放电、循环伏安、交流阻抗等测试表征多孔炭的超级电容性能。本文的主要工作如下:以海藻酸钠和海藻酸钙为前驱体制备多孔炭。通过对比所得炭材料的微观形貌、孔隙结构、表面化学性质等来探究前驱体中Na、Ca元素和KOH/C对多孔炭的影响,并分析多孔炭的微观结构与其超级电容性能之间的关系。发现Na能促进炭化样形成实心、片层状结构,而Ca能促进炭化样形成球形空腔结构。增大KOH/C不仅能促使多孔炭中较小孔径的微孔向较大孔径的微孔转变,使微孔孔径分布曲线在孔径较大的位置出现新的极值点,而且会促使孔径较大的中孔向孔径较小的中孔转变。随着KOH/C的增大,多孔炭有效比表面积的增大会使其比电容增大(1 Ag-1时最大为274.1 F g-1)。较多中孔使多孔炭的高倍率性能更好,相应电池的电荷迁移阻力更小(0.36 Ω<0.55Ω)。较高的石墨化程度使多孔炭的导电性更强,相应电池的等效串联电阻更小(0.35 Ω<0.47Ω)。以海藻酸钠为原料,乳酸钙为钙源,制备钙改性海藻酸钠基多孔炭。探究多孔炭的孔隙结构随前驱体中Ca含量的变化规律,揭示钠钙协同作用构建孔隙结构的机理,并探究钙改性海藻酸钠基多孔炭的超级电容性能。发现炭化过程中,SC1/4A的气态产物的释放同时受到Na的促进和Ca的抑制这两种相反的作用。Ca促使炭化样中形成球形空腔,而Na促使其形成平面结构,二者的协同作用使SC1/4A-C形成了规则的三维互连结构。与SA-PC-4相比,SC1/4A-PC-4的比表面积和总孔容大约分别增加了 25%和35%,达2776.6 m2 g-1和1.72 cm3 g-1。受益于三维互连层次多孔结构和良好的导电性,SC1/4A-PC-4的比电容更大(1 A g-1时为292.4 Fg-1),高倍率性能更好,相应电池的能量密度更大(功率密度为49.9Wkg-1时,相应电池的能量密度为11.7 Whkg-1),等效串联电阻和电荷迁移阻力更小,而且具有更好的循环性能。以海藻酸和海藻酸铵为前驱体制备多孔炭,探究前驱体中NH4+对海藻酸基多孔炭的影响,并分析多孔炭的微观结构与其超级电容性能之间的关系。基于多孔炭的孔隙结构特点和循环性能曲线的变化规律,构建循环过程中多孔炭基超级电容器的充放电机理,揭示电流密度和单次循环次数影响循环性能的机理。发现前驱体中的NH4+能够促进炭化样形成薄壁空腔结构,较厚的壁面会形成相应多孔炭的骨架结构支撑整个孔隙结构,而较薄的壁面被刻蚀破坏形成穿孔连通各个空腔。薄壁空腔的形成不仅取决于含N化合物的作用,而且受气态产物释放速率的影响。三维互连的孔隙结构使多孔炭具有更大的比电容(1 A g-1时为295.8 Fg-1)、更高的能量密度(在功率密度为49.9 Wkg-1时,相应电池的能量密度是11.5 Wh kg-1)、更强的电荷传输能力和更好的高倍率性能,更强的导电性使相应电池的等效串联电阻较低(0.37 Ω)。循环性能曲线的突变是由第三类表面导致的。循环性能曲线由阶段1转变到阶段2时,溶剂化的离子转变为去溶剂化的离子激活了第三类表面,使其提供电容而导致多孔炭的比电容突增。曲线由阶段2转变到阶段3时,比电容的突降是由第三类表面上储存有不被释放的离子使得放电过程中两极间的电压降减小而导致的。以浒苔为原料,磷酸氢二铵为铵态氮源,尿素为酰胺态氮源,三聚氰胺为氰胺态氮源,制备铵态氮/酰胺态氮/氰胺态氮掺杂浒苔基多孔炭。然后,探究所制备多孔炭的孔隙结构、表面化学性质及超级电容性能。发现氮掺杂浒苔基多孔炭的比表面积大于3400 m2 g-1,其孔隙主要分布在0.57～8 nm的范围内。三种氮掺杂都能促进多孔炭中2～6 nm范围内孔的发展,可以略微提高多孔炭的石墨化程度。它们都能提高多孔炭中C的含量而降低N、O的含量,而且几乎不改变C元素存在状态,会增加石墨化N的含量。与浒苔基多孔炭相比,受益于更发达的中孔结构,它们的比电容增加了约22%以上(1 A g-1时最大比电容为311.9 Fg-1),具有更好的高倍率性能、更大的能量密度(在功率密度为50.0 W kg-1时,相应电池的最大能量密度是12.7 Whkg-1),相应电池的等效串联电阻更小(最低为0.37Ω),而且都具有极好循环性能。更多还原

【Abstract】 In recent years,the preparation of porous carbons from alginate or Enteromorpha prolifera as electrode materials for supercapacitors has attracted much attention.However,their performance still needs to be further improved.Strategies to improve the performance of porous carbons based on the effects of different components in the precursor show great application potential.Based on the investigation of the effects of Na or Ca in the precursor on the microstructure of porous carbon,a three-dimensional interconnected hierarchical pore structure is constructed by the synergistic effect of Na and Ca to improve the supercapacitor performance of sodium alginate-based porous carbon.On the basis of exploring the effects of NH4+in the precursor on alginic acidbased porous carbon,high-performance nitrogen-doped Enteromorpha prolifera-based porous carbons are prepared with diammonium hydrogen phosphate,urea and melamine as nitrogen sources.SEM,nitrogen adsorption-desorption,HK,BJH,XRD,Raman and XPS are used to characterize the properties of these porous carbons.In a two-electrode system,the supercapacitor performance of porous carbons is characterized by galvanostatic charge-discharge,cyclic voltammetry and AC impedance.The primary work of this paper is as follows:Sodium alginate and calcium alginate are used as precursors to prepare porous carbons.By comparing the microstructure,pore structure and surface chemical properties of the obtained carbon materials,the effects of Na,Ca in the precursor and KOH/C on the porous carbon are investigated,and the relationship between the microstructure of the porous carbon and its supercapacitor performance is analyzed.It is found that Na could promote the formation of solid and lamellar structure of carbonized sample,while Ca could promote the formation of spherical cavity structure of carbonized sample.Increasing KOH/C can not only promote the transformation of micropores with smaller pore size to micropores with larger pore size in porous carbons,but also make the micropore size distribution curves appear new extreme points at the position of larger pore sizes,and promote the transformation of mesopores with larger pore size to mesopores with smaller pore size.With the increase of KOH/C,the specific capacitance increases with the increase of effective surface area(the maximum is 274.1 F g-1 at 1A g-1).More mesopores make the high-rate performance better and the charge transfer resistance smaller(0.36 Ω<0.55 Ω).The higher graphitization degree makes the conductivity stronger and the equivalent series resistance smaller(0.35 Ω<0.47 Ω).Calcium modified alginate-based porous carbon is prepared from sodium alginate and calcium lactate.The change rule of pore structure of porous carbons with Ca content in precursor is explored,the mechanism of pore structure constructed by sodium-calcium synergistic effect is revealed,and the supercapacitor performance of calcium-modified alginate-based porous carbon is investigated.It is found that the release of gaseous products of SC1/4A is promoted by Na and inhibited by Ca during carbonization.Ca promotes the formation of spherical cavity in carbonized sample,while Na promotes the formation of plane structure.The synergistic effect of the two makes SC1/4A-C form a regular three-dimensional interconnection structure.Compared with SA-PC-4,the specific surface area and total pore volume of SC1/4A-PC-4 increased by about 25%and 35%,respectively.Benefiting from the three-dimensional interconnection hierarchical porous structure and good conductivity,SC1/4A-PC-4 has larger specific capacitance(292.4 F g-1 at 1A g-1),better high-rate performance,larger energy density(when the power density is 49.9 W kg-1,the energy density of the corresponding battery is 11.7 Wh kg-1),smaller equivalent series resistance and charge transfer resistance,and better cycle performance.Alginic acid and ammonium alginate are used as precursors to prepare porous carbons.The effect of NH4+in the precursor on the microstructure of alginic acid-based porous carbon is investigated,and the relationship between the microstructure of porous carbon and its supercapacitor performance is analyzed.Based on the pore structure characteristics of porous carbon and the change rule of cycle performance curve,the charge and discharge mechanism of porous carbon-based supercapacitor during cycling is constructed,and the mechanism of current density and single cycle number affecting the cycle performance is revealed.It is found that NH4+in the precursor can promote the formation of thin-walled cavity structure of carbonized samples,and the thicker walls form a skeleton structure of porous carbon to support the whole pore structure,while the thinner walls are etched and destroyed to form perforations to connect cavities.The formation of thin-walled cavities depends not only on the effect of N-containing compounds,but also on the release rate of gaseous products.The three-dimensional interconnection pore structure makes porous carbon has larger specific capacitance(295.8 F g-1 at 1A g-1),higher energy density(when the power density is 49.9 W kg-1,the energy density of the corresponding battery is 11.5 Wh kg-1),stronger charge transfer ability and better high rate performance,and stronger conductivity makes the equivalent series resistance lower(0.37 Ω).The mutation of cycle performance curves is caused by the third type surface.When the cycle performance curve changes from stage 1 to stage 2,the transformation of solvated ions into desolvated ions activates the third type of surface,causing it to provide capacitance,resulting in a sudden increase in the specific capacitance of porous carbon.When the curve changes from phase 2 to phase 3,the sudden drop in specific capacitance is caused by the storage of unreleased ions on the surface of the third type,which reduces the voltage drop between the two electrodes during the discharge process.Using Enteromorpha prolifera as raw material,ammonium dihydrogen phosphate as ammonium nitrogen source,urea as amide nitrogen source,melamine as cyanamide nitrogen source,ammonium nitrogen/amide nitrogen/cyanamide nitrogen doped Enteromorpha prolifera-based porous carbons are prepared.Then,the pore structure,surface chemical properties and supercapacitor performance of the prepared porous carbon are investigated.It is found that the specific surface areas of these nitrogen doped Enteromorpha prolifera-based porous carbons are larger than 3400 m2 g-1,and the pores are mainly distributed in the range of 0.57～8 nm.Three nitrogen doping can promote the development of pores in the range of 2～6 nm in porous carbons,and slightly improve their graphitization degree.They can increase the content of C and reduce the content of N and O in porous carbons,and almost do not change the state of C element,increase the content of N graphitization.In addition,the pseudocapacitances of the three nitrogen-doped Enteromorpha-based porous carbons are negligible.Compared with the Enteromorpha-based porous carbon,their specific capacitance is increased by more than 22%due to the more developed mesopore structure(the maximum specific capacitance is 311.9 F g-1 at 1A g-1).They have better high-rate performance,higher energy density(when the power density is 50.0 W kg-1,the maximum energy density of the corresponding battery is 12.7 Wh kg-1),and smaller equivalent series resistance,as well as excellent cycle performance.更多还原