Study On The Synthesis Of Metal Oxide And The Performance Of Their Composites With Multiwall Carbon Nanotubes As Pseudacapacitor Supercapacitors

In this paper,we pay attention to the synthesis of cobalt,zinc and iron metal oxides.The combination of MWCNTs and metal oxides,their electrochemical behaviors and applications in supercapacitors were also studied.The detailed content of the study and the results obtained are as shown as below:1)ZnCo₂O₄/ZnO@multiwall carbon nanotubes?Zn1Co2@MWCNTs?hybrid in situ grown on Ni foam was designed via two-step methods,including a hydrothermal reaction to synthesis of ZnCo₂O₄/ZnO?Zn1Co2?on Ni foam and then a dipping-drying process to cover MWCNTs on Zn1Co2 at room temperature.The sandwich structure of Zn1Co2@MWCNTs with jungle flake inside was directly used as electrode material displaying a high specific capacitance of 2069 F g^-1at 1 A g^-1which is higher than those of ZnCo₂O₄-based electrode materials in most of the previous reports,and a great cycling stability of 80.2%retention after 3000 cycles.2)An all-solid-state asymmetric supercapacitor?ASC?is assembled,utilizing Zn1Co2@MWCNTs as positive electrode and activated carbon?AC?as negative electrode.The ASC device could get a high specific capacitance of 111.8 F g^-1(at 1 A g^-1),a high energy density of 48.1 W h kg^-1(at 900 W kg^-1).Two serial connected Zn1Co2@MWCNTs//AC ASCs are utilized to light four parallel connected light-emitting diode?LED?bulbs?5 mm,red color?,which keep bright for 23 minutes.If three serial connected Zn1Co2@MWCNTs//AC ASCs are utilized to light one LED bulb?5 mm,yellow color?,the LED bulb can keep bright for 55 minutes.The excellent electrochemical performances make the all-solid-state Zn1Co2@MWCNTs//AC ASCs have higher practical application in the energy storage field.3)The Fe₃O₄ based complex of high specific capacitance was prepared by optimizing synthesis method,and the experiment scheme that could combine Fe₃O₄with MWCNTs more effectively was obtained.We used two strategies to fabricate unique Fe₃O₄/Fe-multiwalled carbon nanotubes?Fe₃O₄/Fe-MWCNTs?nanocomposites and Fe₃O₄/MWCNTs@MnO₂ composites by facile chemical synthesis method.In the Fe₃O₄/Fe-MWCNTs ternary complex,MWCNTs were linked and coated by catenulate Fe₃O₄/Fe particles and were able to form conductive networks,which could reduce interfacial resistance between the electrode and electrolyte,improving the ions diffusion.Compared with single Fe₃O₄,discharge times of Fe₃O₄/Fe-CNTs nanocomposites were improved.We explain the mechanism of its synthesis,including how iron ions attach to the functional groups on the surface of the carbon nanotubes and how to evolve into the final Fe₃O₄/Fe particles.Secondly,we synthesized the Fe₃O₄/MWCNTs complex by hydrothermal method.The synthetic method is relatively simple.The Fe₃O₄ in the synthesized sample has a very uniform spherical morphology and the particle size is basically maintained at 30 nm.Fe₃O₄ is closely associated with MWCNTs forming a wide range of conductive networks.The capacitance performance improved a lot.The specific capacitance can reach 489.2 F g^-1under the current density of 1A g^-1,and the capacitance is increased by 30%compared with the previous Fe₃O₄ based capacitors.We continue to grow a layer of MnO₂ on Fe₃O₄/MWCNTs to effectively improve the cyclic stability of the samples.Thin slice MnO₂ overlay on Fe₃O₄@MWCNTs to make Fe₃O₄ and MWCNTs closer.At the same time,we synthesized the Fe₃O₄ pellets as the control group.The electrochemical properties Fe₃O₄/MnO₂@MWCNTs is comparable to that of activated carbon,so it has a promising future.