Design And Fabricate Of Co-based Nanocomposites For High-performance Supercapacitor

The development of supercapacitor has important scientific value,wide range of potential applications.Co-based materials attract more and more attention as a typical pseudocapacitance electrode material.With the higher theoretical capacity,simpler synthetic methods and greater element content,the cobalt-base materials have been extensively investigated.Nonetheless,several problems in cobalt-based electrode materials still need to be overcome,such as poor conductivity,short cyclic stability and narrow potential window,etc.These problems limit its development and application in the field of supercapacitors.In view of these problems,this dissertation designed and synthesized Co-pre nanosheet@NiCo-LDHs nanosheet core-shell array?Co-pre@NiCo-LDHs NNAs?,CoO nanosheet@MnO₂ nanosheet core-shell array?CoO@MnO₂ NNAs?,CoO nanowire@MnO₂ nanosheet core-shell array?CoO@MnO₂ NWAs?,Co₉S₈@N-doped graphene?Co₉S₈@NGR?respectively from the control aspects of material micro-nano structure.At the same time,due to the synergy between the multiple ingredients and build asymmetric capacitor,the capacitance properties are greatly improved,supercapacitor electrode materials with both high energy density and high power density were finally obtained.The details of our works are shown as follows:?1?A new core-shell nanostructure of Co-pre@NiCo-LDHs NNAs core-shell array was designed by a simple two step electro-deposition method,this core-shell nanostructure was directly grown on a 3D nickel foam.The results showed that Co-pre@NiCo-LDHs NNAs displayed specific capacitance of 1926 F g^-1 at a current density of 1 A g^-1,which was higher than 1416 F g^-11 of Co-pre nanosheet?Co-pre NAs?.The Co-pre@NiCo-LDHs NNAs was directly grown on a 3D nickel foam,this design provides a new way to improve the electrochemical properties of supercapacitor electrode materials.Co-pre@NiCo-LDHs NNAs//AC was fabricated by using of activated carbon?AC?as the negative electrode and Co-pre@NiCo-LDHs NNAs as positive electrode.The Co-pre@NiCo-LDHs NNAs//AC exhibited a density as high as62.33 Wh kg^-11 at power density of 0.85 kW kg^-1,and an excellent cycle stability with90.92%specific capacity retention at a current density of 10 A g^-11 after 10000 cycles.?2?Co?CO₃?_0.5?OH?0.11H₂O nanosheets arrays were successfully designed and directly grown on a 3D nickel foam substrate via a simple solution method in the first step.Then MnO₂ nanosheets were directly grow on the surface of Co?CO₃?_0.5?OH?0.11H₂O through the reduction of KMnO₄ due to the reducing ability of Co?CO₃?_0.5?OH?0.11H₂O forming a core-shell nanostructure in the second step.After being annealed in Ar,CoO@MnO₂ NNAs core-shell arrays were successfully synthesized.The BET surface area of CoO@MnO₂ NNAs was upto 125.3 m² g^-1.The CoO@MnO₂ NNAs displayed an excellent capacitance of 2.4 F cm^-2(about 1200 F g^-1)with a potential of 0.8 V at a current density of 2 mA cm^-2,which is better than the reported Co₃O₄ core-shell arrays.In addition,the asymmetric supercapacitor CoO@MnO₂ NNAs//AC was fabricated by using of activated carbon?AC?as the negative electrode and CoO@MnO₂ NNAs as positive electrode.CoO@MnO₂NNAs//AC exhibit a density as high as 1.4 mWh cm^-3,and an excellent cycle stability with 90.0%specific capacity retention at a current density of 20 mA cm^-22 after 10000cycles.?3?New 3D hierarchical hybrid electrodes CoO@MnO₂ NWAs core-shell arrays were designed and fabricated on a nickel foam by controlling the ratio of solution.The MnO₂ nanosheets was grown directly on the CoO precuor nanowires.The nickel foam with CoO@MnO₂ NWA was used as the negative electrode,the reaction of Co²⁺/Co³⁺,Co³⁺/Co⁴⁺,MnO₂/K⁺,Mn³⁺/Mn⁴⁺and OH^-occurred during the charge-discharge process.Potential achieved up to 0.8 V due to the synergy of MnO₂.The CoO@MnO₂NWAs delivered a highly enhanced specific capacitance of 3.03 F cm^-2(about 1515 F g^-1)with a wide potential window of 0.8 V at 2.0 mA cm^-2,which is superior to most reported Co₃O₄ based core-shell NNAs supercapacitive electrodes.An asymmetric supercapacitor devices based on CoO@MnO₂ NWAs//AC showed with a high-energy density of 2.08 mWh cm^-3,and excellent cycle stability with 93.58%specific capacity retention at a current density of 20 mA cm^-22 after 10000 cycles.?4?Co₉S₈@NGR hierarchical nanoarchitecture was obtained by using a facile one-pot solvothermal method.Co₉S₈ hierarchical nanoastructures was 50²00 nm.It was called island-like Co₉S₈ because they were made up of ultra-thin Co₉S₈ nanosheets with thickness¹0 nm.These island-like Co₉S₈ nanoastructures were successfully grown and evenly dispersed on the surface of two-dimensional N-doping graphene?NGR?.N-doping changed the electrochemical properties of graphene,ultra-thin nanosheets decreased charge transfer internal resistance and increased specific surface area.These changes are beneficial to the improvement the electrochemical properties of Co₉S₈@NGR.When used as a single electrode test for supercapacitor,the Co₉S₈@NGR nanocomposites delivered an ultra-high specific capacitance of 2992 F g^-1 at 1 A g^-1.Moreover,carbon?AC?as the negative electrode constructed by an asymmetric supercapacitor Co₉S₈@NGR//AC,which exhibit a density as high as 88.81 Wh kg^-1 at power density of 0.63 kW kg^-1,and an excellent cycle stability with 80.61%specific capacity retention at a current density of 10 A g^-11 after 10000 cycles.