The Preparation And Performances Of Transition Metal Compound And Carbon Based Capacitive Materials

Charge storage capacity and energy density are the main indicators of a supercapacitor.The design and preparation of faradic electrodes with high specific capacitance?C_s?and the construction of capacitive system with high energy density(E_cell)are the main focus in fundimental investigation fields of supercapacitors.Transitional metallic oxides,double hydrides and N doped carbonaceous materials are significant candidates as electrode mateials with high C_ss by vitue of their high faradic activities.Furthermore,the construction of Hybrid supercapacitors?HSCs?and redox electrolyte mediated capacitive system based on these electrode materials are feasible approaches to effectively enhance the E_cells.In this thesis,faradic metallic oxides,double hydrides and N doped carbonaceous materials with different morphologies were designed and prepared,which were further used to assemble HSCs and redox electrolyte mediated supercapacitors,so as to improve the E_cells from different approaches.The main content of this thesis can be summarized as follows:1.ZnCo₂O₄-rGO composite with interconnected primary sheets were constructed directly onto Ni foam substrate.The as-prepared ZnCo₂O₄-rGO demonstrates high specific surface area and efficient ions diffusion channels,therefore ensures the sufficient faradic reaction of ZnCo₂O₄ component.The electrode based on this ZnCo₂O₄-rGO composite can offer a C_s of 3222 Fg^-1 at 1 Ag^-1,and maintains to be 860 Fg^-1 at20 Ag^-1.The resultant ZnCo₂O₄-rGO//AC HSC delivers a device specific capacitance of 139 Fg^-1 at 0.5 A g^-1,which therefore contributed to an E_cell of 49.1 Whkg^-1 at power density(P_cell)of 400 Wkg^-1.Upon increases the P_cell to 7625 Wkg^-1,the E_cell retains to 18.8 Whkg^-1.Additionally,only 6%capacitance is lost after 5000 GCD cycles.The balanced E_cell,P_cell and good cycleability manifest the potential of ZnCo₂O₄-rGO composite based electrode in efficient and long lifetime energy storage devices.2.Layered CoNi double hydride?CoNiLDH?architecture was contructed onto Ni foam substrate by hydrothermal reaction in alkali medium.The CoNiLDH can be tightly anchored onto Ni foam substrate,which can effectively reduce the in-series resistance and charge transfer resistance of the electrode.By further manipulating the hydrothermal reaction time and temperature,the morphologies and the capacitance of the CoNiLDH were further optimized.The fabricated CoNiLDH electrode can offer a a C_s of 1882 Fg^-1at 1 Ag^-1 in 2 M KOH electrolyte,and considerable rate capability and cycleability can also be ensured,showing the good capacitive performance of transitional metal double hydrides.3.N doped carbon-graphene composite was synthesized by hydrothermal reaction and the fullowed activation treatment,the as-prepared carbonaceous material owns high specific surface area,and the N,O heteroelementals also exhibit high faradic capacitive activity,therefore possesses high C_s.The carbonaceous composite offers a C_s of 242 Fg^-1 at 1 A g^-1 in 2 M KOH electrolyte,good rate capability and cycleability.Meanwhile,the heteroelements doped carbonaceous composite is capable of promoting the faradic reaction of redox mediator in electrolyte,which can further augment the C_s of the redox electrolyte mediated capacitive system by two folds,which is beneficial for enhancing the E_cell of the redox electrolyte mediated supercapacitor.