| 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 ?<0.55 ?).The higher graphitization degree makes the conductivity stronger and the equivalent series resistance smaller(0.35 ?<0.47 ?).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 ?).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. |
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