The Regulation And Capacitor Performance Of MoO₂ And NiO Micro/nanomaterials

In recent years,semiconductor micro-nanomaterials have attracted much more research interests because of the surface and interface effect,small size effect,quantum size effect and macroscopic quantum tunneling effect,and have been widely used in the area of the supercapacitors.Among these materials,transition metal oxides?TMOs?have been widely concerned in the application of supercapacitors because of their high storage,low cost and light quality,especially their multiple charge valences can benefit to improve energy density and specific capacity during the redox reaction process.Molybdenum dioxide?MoO₂?as one of TMOs materials has become an interesting supercapacitor material for the metallic electrical resistivity,high chemical stability and theoretical energy densities.Furthermore,nickel oxide?NiO?materials also have a commercial advantage over the binary transition-metaloxides because of their low cost and ease of preparation.In this paper,we successfully synthesized MoO₂ nanoparticles and porous tremella-like NiO structures,and assembled them with graphene oxide?GO?to construct MoO₂/GO and NiO/GO to increase the specific surface area,and Ag particles were deposited on the surfaces to construct MoO₂/GO/Ag and NiO/GO/Ag composite structures.In addition,mesoporous MoO₂ nanoparticles were also directly grown on carbon cloth as electrodes for electrochemical capacitors.A three-electrode experimental cell was used for measuring all the electrochemical properties of the working electrodes.The main contents of this paper are as follows:1.The MoO₂,MoO₂/GO and MoO₂/GO/Ag heterostructures were successfully fabricated as high-performance supercapacitors electrode materials by using a hydrothermal process and a photoreduction process.The electrochemical properties of MoO₂,MoO₂/GO and MoO₂/GO/Ag nanomaterials were tested in a three-electrode experimental cell system.Compared to MoO₂/GO and MoO₂ nanoparticles,MoO₂/GO/Ag composite electrode exhibited optimal electrochemical performance,showing a higher specific capacitance of 323.7 F g-1 at a current density of 1 A g-1 and an excellent cyclic performance with 90 % capacity retention after 1000 cycles at a scanrate of 20 mV s-1.2.Mesoporous MoO₂ nanoparticles were successfully synthesized on a flexible carbon cloth by a facile hydrothermal method,and then annealed at 500 °C in argon flow.The intensity of diffraction peaks are strengthened for the annealed sample compared with that of the unannealed ones,suggesting the improved crystallinity during annealing process.The experimental results showed that unannealed Mo O₂ exhibited higher specific capacitance of 310 F g-1 than that of annealed MoO₂?93 F g-1?.3.Hierarchical Ni O/GO and NiO/GO/Ag heterostructures were successfully synthesized as high-performance supercapacitors electrode materials by using a hydrothermal process and a photoreduction process.The tremella-like Ni O hierarchical structures were composed of large amounts of two-dimensional?2D?porous ultrathin NiO nanoflakes,after the addition of the conductive support GO,the ultra-thin NiO nanosheets agglomeration disappeared and the NiO nanosheets were branching uniformly on the individual GO surfaces.Then Ag particles with high conductivity were deposited on the NiO/GO surface to construct NiO/GO/Ag heterostructures.The research results showed that NiO/GO/Ag electrode exhibited higher electrochemical performance,and the heterostructures showed specific capacitance of 229 F g-1 at a current density of 1 A g-1 and cyclic performance with 76 % capacity retention after 2000 cycles at a scanrate of 20 mV s-1,which were higher than those of NiO/GO and bare NiO nanosheets.