Synthesis Of MMoO₄?M=Ni,Co?@Ni₃S₂ Composite Materials In Situ Grown On Ni Foam And The Investigation Of Their Electrochemical Performance

Supercapacitors?SCs?,also called electrochemical capacitors,have attracted worldwide attention because of their high power density,fast charge/discharge rate,long lifespan,low maintenance cost and safety.Based on the charge storage mechanism,SCs are generally classfied into two categories: electric double layer capacitors?EDLCs?and pseudocapacitors.Pseudocapacitors,especially,transition metal oxides can provide higher capacitance and energy density than electric double-layer capacitors?EDLCs?based on carbonaceous materials.Therefore,transition metal oxides have been widely investigated as promising candidates for applications in supercapacitors because of their multiple oxidation states for redox charge transfer.However,it is still a major challenge to further improve the electrochemical performance realize the advantage of active materials at nanometer scale for practical applications.Currently,tremendous efforts have been devoted to combining the unique properties of individual constituents to further improve their electrochemical performance.Meanwhile,to boost the electrochemical utilization and specific capacitance of pseudocapacitive materials,an emerging attractive concept is to directly grow smart electrode nanoarchitectures on conduct substrates as binder-free electrodes for supercapacitors.This thesis devoted to synthesis of MMo O4?M=Ni,Co?@Ni₃S₂ composite materials in situ grown on Ni foam and the investigation of their electrochemical performance,mainly including two sections as following:In the second chapter of this thesis,we successfully synthesized the unique NiMoO₄@Ni₃S₂ core/shell nanostructure through a facile two-step hydrothermal method.The unique NiMoO₄@Ni₃S₂ core/shell nanostructure achieved excellent electrochemical performance by utilizing the synergic effects of multicomponents.The firstly grown NiMoO₄ arrays provide a scaffold for the later growth of ultrathin Ni₃S₂ sheets.Ultrathin nanosheet-like Ni₃S₂ can increase the contact area with the electrolyte,enable fast redox reaction,and protect the inner structure of NiMoO₄ as a result of improving the structural integrity.Benefiting from these advantages,the unique NiMoO₄@Ni₃S₂ core/shell hybrid electrodes exhibit remarkable electrochemical performance and hold great potential applications in supercapacitors.In the third chapter of this thesis,the hierarchical CoMoO₄@Ni₃S₂ core/shell nanosheet arrays have been synthesized,which are grown directly on Ni foam as an integrated electrode for supercapacitors.Nanosheet arrays of CoMoO₄ are synthesized first by a mild hydrothermal reaction with a successive annealing and used as the “core”.After the second facile hydrothermal process,connected Ni₃S₂ sheets were used as the “shell” and formed the CoMoO₄@Ni₃S₂ core/shell nanostructure.This core/shell heter-structure exhibits desirable electrochemical properties.It shows a high specific capacitance of 1801 F g^-1 at 2 A g^-1and high cycle stability with 84.1% retention of its initial specific capacitance at 10 A g^-1 after 2000 cycles in 2 M KOH solution.In conclusion,the CoMoO₄@Ni₃S₂ composites could be used as promising electrode materials for electrochemical energy storage due to their remarkable electrochemical properties.