Construction And Electrochemical Performance Of Carbon Material/Transition Metal Compounds Composite

Supercapacitors as a kind of energy storage devices have been widely concerned due to its high power density,rapid charging/discharging rate,long life cycle and environmental friendly.The electrochemical performances of supercapacitors depend on electrode materials,mainly including carbon materials,metal oxides,transition metal oxides/hydroxides and conductive polymers.Among numerous electrode materials,nickel and cobalt oxide?NiCo₂O₄?has caused great attention due to its simple synthesis,rich resources,environmental friendly,especially high theoretical specific capacitance.However,the stability and conductive performances of the NiCo₂O₄ are poor,so the combination of the transition metal oxides with carbon-based materials to improve its performance is becoming a hot spot of current researches.Besides,the suitable base also plays a vital role.Such as Ni foam,as a result of high porosity,large specific surface area and unique three-dimensional network structure,has been widely used in storage devices.In this paper,the uniform C/NiCo₂O₄ mesoporous nanoneedles arrays grown on Ni foam?NF?as a composite electrode material are synthesized by a facile one-step hydrothermal and annealing processes.Using X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,Scanning electron microscope?SEM?,High-resolution transmission electron microscopy?HRTEM?,Specific surface area and porosity analyzer?BET?to characterize the structure and morphology of the NF/NiCo₂O₄ and NF/C/NiCo₂O₄.Cyclic voltammetry?CV?tests,galvanostatic charge-discharge?GCD?tests and electrochemical impedance spectroscopy?EIS?tests are recorded sequentially from-0.1-0.8 V at various scan rates,2 to 10 mA cm^-2 and100 kHz to 0.01 Hz to test electrochemical performance.The results of the studies are as follows:?1?The structure of NiCo₂O₄ and C/NiCo₂O₄ both are nanoneedles arrays.It is worth noting that the nanoneedles arrays of the C/NiCo₂O₄ are more homogeneous and uniform than the NiCo₂O₄.The nanoneedles arrays of the C/NiCo₂O₄ are smaller in diameter than the NiCo₂O₄ on NF.In addition,the elemental mappings of the composite are obtained to represent the distribution of elements.It is obvious that Ni,Co,C and O are distributed uniformly in the composite.?2?The BET dispalys that the C/NiCo₂O₄ nanoneedles arrays are mesoporous structure,but NiCo₂O₄ nanoneedles arrays are mesoporous and microporous structure.?3?The C/NiCo₂O₄ shows excellent electrochemical properties,including a high areal capacitance(4.974 F cm^-2 at 2 mA cm^-2),remarkable rate capability(2.928 F cm^-2at 10 mA cm^-2).In contrast,NiCo₂O₄ areal capacitance is 2.355 F cm^-22 at 2 mA cm^-2.And the specific capacitance retains 1.808 F cm^-2 at 10 mA cm^-2.Importantly,the 81%of the initial areal capacitance of the C/NiCo₂O₄ electrode is retained which is higher than the NiCo₂O₄ with 70%retention,demonstrating its remarkable cycle stability.?4?Electrochemical tests show that C and NiCo₂O₄ have a synergistic effect.And the synthesized composite has higher specific capacitance and better cycle stability.In order to further study the interaction between carbon materials and transition metal compounds,the NF/RGO/Ni-Mn LDH composite were synthesized by water bath and one-step hydrothermal method.Among them,graphene oxide was directly reduced by foam nickel to synthesize NF/RGO.The structure and morphology of NF/RGO/Ni-Mn LDH composite are characterized by XRD,XPS and SEM.And the electrochemical properties of NF/Ni-Mn LDH and NF/RGO/Ni-Mn LDH composite in alkaline electrolyte are investigated by CV and GCD.The results of the study are as follows:?1?SEM shows that Ni-Mn LDH fabricared on the surface of NF/RGO in the form of nanosheets.?2?The specific capacitance of NF/RGO/Ni-Mn LDH at a current density of 1 A g^-1is 2250 F g^-1.At a current density of 10 A g^-1,capacitance is still 1440 F g^-1,indicating that NF/RGO/Ni-Mn LDH has a high rate performance compared to Ni-Mn LDH/NF(1A g^-1,1068 F g^-1;10 A g¹,440 F g^-1).?3?Electrochemical tests show that RGO and Ni-Mn LDH have a synergistic effect.Composite has higher specific capacitance,better conductivity and cycle stability.