The Construction Of CoMoO₄-based Coreshell Nanocomposites For Supercapacitor Applications

In recent years,the serious environmental pollution and energy shortage have brought many inconvenience for the human lives.Therefore,people try to develop and use the clean energy to meet the needs of daily life.The electric energy can be used in different occasions,and is convenient easy to get,high energy storage,no pollution.These advantages conform that the electric energy are applied to the needs of times.Supercapacitor with high power density,short charging and discharging time,long cycle life,convenient maintenance,clean and no pollution has become a hot topic of current research.This paper shows two metal oxide cobalt molybdate as electrode material of supercapacitors.Compared with the single metal oxide,cobalt molybdate have multiple oxidation reduced valences,better of conductivity,excellent rate capability and cycle stability.However,the previously reported show that the specific capacitance of cobalt molybdate is not satisfied.In this paper,we designed and synsized cobalt molybdate nanomaterials and further prepared the electrode materials with excellent performance by hydrothermal method.We prepared CoMoO₄@MnO₂,Co₃O₄@CoMoO₄,and CoMoO₄@NiMoO₄·x H₂O coreshell structures nanocomposite materials.The electrochemical properties of these core-shell structures showed the enhanced specific capacitance.The electrochemical performance of the devices were further researched by matching the as-prepared materials with the negative electroded materials.Flower-like CoMoO₄@MnO₂ heterostructure was prepared directly on Ni foam with outstanding pseudocapacitive performance by two steps hydrothermal method.The first step is directly growing CoMoO₄ nanoflowers on Ni foam.The second step is growing ultrathin MnO₂ nanosheets on the surface of CoMoO₄ nanoflowers and forming the CoMoO₄@MnO₂ core-shell heterostructure.Serving as a supercapacitor electrode,the specific area of CoMoO₄@MnO₂ is improved due to increasing the surface active sites and that the electrolyte can be fully contacted with the electrode material.The nanomaterials also shorten the diffusion path of ions and accelerate the conduction of ions and electrons.CoMoO₄@MnO₂ heterostructure electrode yields a high capacitance of 1800 F g-1 at a current density of 1 A g-1,high rate performance,and outstanding cycling stability with 98.6% retention after 10000 cycles?1 A g-1?and 96.3% retention after 30000 cycles?5 A g-1?of the initial specific capacitance.Furthermore,the as-fabricated asymmetric supercapacitor device based on CoMoO₄@MnO₂ positive electrode and activated carbon?AC?negative electrode can operated within a maximum voltage of 1.6 V,delivering both high energy density?54 Wh kg-1 at a power density of 800 W kg-1?and power density?8000 W kg-1 at 35.5 Wh kg-1?,which are better than that of the CoMoO₄//AC and MnO₂//AC asymmetric supercapacitors and the AC//AC symmetric supercapacitors.Furthermore,CoMoO₄@MnO₂//AC asymmetric supercapacitor device can retain 84% of its original capacitance after 10000 cycles at a current density of 3 A g-1.Co₃O₄@CoMoO₄ core-shell architectures directly grown on nickel foam have been prepared.Co₃O₄ nanocones grown vertically on the nickel foam as the core and CoMoO₄ nanosheets were further engineered on the surface of the nanocones as the shell.The electrode exhibits high specific capacitance of 1902 F g-1 at current density of 1A g-1,good rate capability,and cycling stability with 99% canpacitance retention after 5000 cycles.Solid-state asymmetric supercapacitor?Co₃O₄@CoMoO₄//CNTs?and symmetric supercapacitor?Co₃O₄@CoMoO₄//Co₃O₄@CoMoO₄?are fabricated.The asymmetric supercapacitor with a maximium voltage of 1.6 V delivers a high energy density of 50.1 W h kg-1 and outstanding cyclic stability.In this work,flexible CoMoO₄@NiMoO₄·x H₂O core-shell heterostructure and Fe₂O₃ nanorods electrodes directly grown on carbon cloth were fabricated via a facile hydrothermal procedure.The CoMoO₄@NiMoO₄·x H₂O yielded highcapacitance performance with a high specific capacitance of 1582 F g-1 at the current density of 1 A g-1,good cycling stability with 97.1 % capacitance retention after 3000 cycles and rate capability 66.4 % with the specific capacitance 1050 F g-1 at 15 A g-1.The electrode also shows excellent mechanical flexibility and little capacitance change after bending and twisting of three different forms over 3000 charge/discharge cycles at a current density of 3 A g-1.Fe₂O₃ nanorods exhibits better capacitive performance and wide negative potential window.A solid-state asymmetric supercapacitor device was successfully fabricated by using CoMoO₄@NiMoO₄·x H₂O and Fe₂O₃ as the positive and negative electrodes,respectively.The asymmetric supercapacitor with a maximum voltage of 1.8 V shows both high energy density?47.1 Wh kg-1 at 900 Wh kg-1?and power density?13500 W kg-1 at 28.3 Wh kg-1?.The cycle performance shows good stability with 89.3 % capacitance retention after 5000 cycles?3 A g-1?.These excellent electrochemical performances indicate the as prepared flexible electrodes could provide great potential for supercapacitor applications.