Construction And Capacitive Properties Of Sugar-derived Hierarchically Porous Carbon With Different Morphologies

With the increasing environmental pollution and the emergence of a variety of portable electronic products,new energy storage devices with high-power density and high-energy density appear and become the key issues.In particular,supercapacitors are gaining considerable attentions due to their advantages of low cost,environmental protection,commercial availability,etc.However,the performance of the supercapacitors still needs to be further improved.Carbon is always considered as an ideal electrode material because of its abundant resources,high chemical stability and large specific surface area.Nevertheless,most of carbon precursors such as the biomasses are insoluble and unevenly mixed with the active agents,resulting in unstable electrode performance.Fortunately,suger compounds,such as glucose,are non-toxic,harmless,cheap and hydrosoluble.As carbon precursors,suger compounds are not only hopeful to solve the problem of uneven mixture,but also convenient for using various strategies to prepare activated carbon materials with different structures.Meanwhile,the inherent oxygen-containing groups can improve the wettability of the electrolyte to the electrode surface,thereby accelerating the migration rate of electrons and improving the electrochemical performance when used as electrode materials for supercapacitors.In this thesis,the activated carbon materials with different morphologies and different porous structures were constructed by using glucose and chitosan as carbon precursors with various strategies,respectively.The resultant materials were characterized by various analytic techniques such as SEM,XRD,Raman,N₂adsorption-desorption and XPS.Furthermore,as the electrode materials,their electrochemical performance was investigated in both three-electrode and symmetrical two-electrode supercapacitor systems.The main contents are as follows:?1?A series of flake-like porous carbon materials?AGC-600-x?were prepared with an impregnation-calcination strategy by adjusting the mass ratio of the carbon precursor?glucose?to etching agent?Zn Cl₂?.In comparision with GC-600 prepared without using Zn Cl₂,AGC-600-x exhibited better capacitive performance and AGC-600-2 was the best one.Under the present conditions,the specific capacitance of AGC-600-2 was 176.75 F g^-1 at 1.0 A g^-1 in the three-electrode system.The energy density of AGC-600-2-based symmetrical supercapacitor was 17.99 Wh kg^-1 at the power density of 399.94 W kg^-1,and the initial specific capacitance was only 8.1%lost after 10000 charge-discharge cycles at 1.0 A g^-1.These outstanding electrochemical properties are presumably due to its high specific surface area(S_BET=1690 m² g^-1),the unique hierarchical porous structure,and the oxygen-containing groups.?2?Glucose was pre-carbonized into microspheres?GC?with a hydrothermal method.Then,a series of activated carbon microspheres?AGC-180-x?were prepared with an impregnation-calcination strategy by adjusting the mass ratio of GC to Zn Cl₂.In comparision with GC-180 prepared without using Zn Cl₂,the AGC-180-x possessed better capacitive performance and AGC-180-4 was the best one.Under the present 1.193 cm³ g^-1)had a specific capacitance of 237.35 F g^-1 at 1.0 A g^-1 in the three-electrode system.Meanwhile,AGC-180-4 exhibited superior recyclability and a high energy density of 24.65 Wh kg^-1 at 399.95 W kg^-1 in the two-electrode system.?3?The isolated carbon microspheres?SGC-x?were obtained with a hydrothermal pre-carbonization procedure by regulating the mass ratio of glucose to the dispersant?sodium lauryl sulfate?.Then,a series of microsphere fragment activated carbon?SAGC-x-4?were prepared with an impregnation-calcination strategy by using Zn Cl₂ with 4 times mass of SGC-x.To be noted,SAGC-1-4 owned a high specific surface of 2360 m² g^-1 and a large total pore volume of 1.241 cm³ g^-1.When used as electrode materials for supercapacitors,SAGC-1-4 exhbited a high specific capacitance of 303.02 F g^-1(1.0 A g^-1,three-electrode system),outstanding energy density(31.59 Wh kg^-1 at 400.00 W kg^-1,two-electrode system),as well as excellent rate capability and recyclability(only 11.2%initial capacitance loss after10000 charge-discharge cycles at 1.0 A g^-1,two-electrode system).?4?Using glucose as carbon precursor,ethyl silicate as silicon precursor and sodium lauryl sulfate as dispersant,Si O₂@SGC-x with glucose-based carbon as shell and Si O₂ as core were obtained with a hydrothermal pre-carbonization method by adjusting the dosage of glucose.Then,a series of hollow microspheres?SHGC-x?were successfully prepared by calcinating Si O₂@SGC-x under nitrogen atmosphere g^-1),which did not form the hollow structure,SHGC-5 possessed a more abundant the present conditions,SHGC-5 had a specific capacitance of 193.36 F g^-1 at 1.0 A g^-1in the three-electrode system.Meanwhile,SHGC-5 exhibited satisfactory recyclability and possessed an energy density of 20.32 Wh kg^-1 at 399.92 W kg^-1 in the two-electrode system.?5?Chitosan?M=1.0×10⁴?was pre-carbonized into CC with a hydrothermal method.Then,the hierarchical porous activated carbon?ACC-180-x?were prepared by an impregnation-calcination strategy by adjusting the mass ratio of CC to Zn Cl₂. Zn Cl₂,ACC-180-4 possesed a significantly increased specific surface area(S_BET= much better capacitive performance.Under the present conditions,ACC-180-4 had a specific capacitance of 287.94 F g^-1 at 1.0 A g^-1 in the three-electrode system.Meanwhile,ACC-180-4 exhibited good recyclability and deliverd an energy density of 28.74 Wh kg^-1 at 399.92 W kg^-1 in the two-electrode system.In summary,the resultant glycosyl carbon materials obtained from different precursors with different preparation methods owned different morphologies.Compared with the corresponding printine carbon,all the hierarchical porous carbon materials possessed superior capacitive performance when used as electrode materials.The results expand the scientific researches on carbon materials and supercapacitors.Also,the results lay a certain foundation for the possible commercialization.