Construction Of Nano-arrays Based On Metal Oxide And Sulfide And Their Electrochemical Performance

With the increasing demands for portable electronics and hybrid electrical vehicles,new-fashioned energy storage devices are playing an important role in the daily life of human beings.Among all of the next-generation power devices,supercapacitors,which combine the advantages of traditional capacitors and rechargeable batteries have attracted tremendous attention owing to their excellent electrical properties of fast charging and discharging,high power density and long cycling life.Transition metal oxides and sulfides,pseudocapacitive materials,have been extensively studied as promising alternative electrode materials for supercapacitors,which are substantially larger by at least one order of magnitude than that of carbon materials.To maximize the electrochemical performance of a pseudocapacitor,one needs to engineer the electrodes with large amount of electroactive sites and high transport rates for both electrolyte ions and electrons that simultaneously take part in the Faradaic reactions.However,electrodes of supercapacitors are commonly binder-enriched made by the traditional slurry-coating technique for electrochemical evalution,where a large portion of the electroactive materials surface is "dead surface" and blocked from the contact with the electrolyte to participate in the Faradaic reactions for energy storage.Moreover,the binder involved will greatly decreases the electrical conductivity of the electrode materials,hindering their potential application in high-performance supercapacitors.In order to achieve supercapacitors with both high capacity and high rate performance,we employed a series of synthetic methods to obtain well-aligned nanomaterials on the surface(i.e.nanoarrays)and investigated the relationship between structures and the energy storage performance.(1)A simple hydrothermal method combined with a post annealing treatment is successfully developed to grow mesoporous NiCo2O4 NWAs on carbon cloth with robust adhesion.After annealing at high temperature in H2 atmasphere,the as-otained NiCo2O4 NWAs turns to NiCoO2 NWAs with no much structure variation.Both two hybrid structures are then directly used as an electrode for electrochemical evaluation in a three-electrode system at room temperature.The as-obtained mesoporous NiCo2O4 NWAs supported on carbon cloth is able to deliver high areal capacitance of 1.4 and 0.95 F cm-2 at current densities of 2 and 24 mA cm-2,respectively,with excellent cycling stability.NiCoO2 NWAs also shows excellent electrochemical performance after annealing treatment.(2)We present a facile and novel one-step method of growing Ni-Co LDH hybrid film with ultrathin nanosheet and porous nanostructure on the surface of nickel foam.Owing to the highly oriented layered single crystal structure and ultrathin nature of hybrid nanosheets,the electrodes based on the as-obtained Ni-Co LDH hybrid films showed ultrahigh specific capacitance,good rate performance and excellent cycling stability.(3)We demonstrated a facile and scalable strategy to obtain carbon coating ZnO nanorods array derived from zeolitic imidazolate framework-8(ZIF-8).After that,NiCo2O4 nanosheets were synthesized to form core shell hybrids via electrodeposition for further improve the performance of supercapacitors on flexible carbon cloth.Benefiting from advanced core-shell nanoarrays heterostructures and effective protection of carbon layer,the composite exhibited a high specific capacitance of 3.18 F cm-2 at the current density of 6 mA cm-2,excellent rate capability and showed good cycle stability(76%of the initial capacitance after 4000 cycles).Due to the excellent performance,we believe that the ZnO@C@NiCo2O4 nanorod sheet arrays is a potential promising electrode material for the application of energy storage or conversion with fine electrochemical performance and deserved to be further investigated.(4)Hierarchical Fe3O4@Ni-Mn LDH arrays on carbon cloth have been successfully fabricated by a facile self-sacrificing template route combined with hydrothermal reaction.The hierarchical nanostructure which exhibited high surface areas and short ion/electron transport paths endow the Fe3O4@Ni-Mn LDH arrays with high charge storage performances.The electrodes of the hierarchical Fe3O4@Ni-Mn LDH arrays deliver a high areal capacitance of 1.63 F cm-2 at a current density of 2 mH cm-2,and superior long-term cycle stability retaining 91%of the initial capacitance after 1000 cycles.(5)We designed and fabricated 3D core-shell hierarchical nanoarrays with CoS nanowires as the conducting scaffold to support ultrathin NiCo2S4 nanosheets as the shell to achieve the highest possible capacitance.The CoS@NiCo2S4 nanowire sheet arrays(NWSAs)were synthesized through sulfide ion exchange using CoO@NiCo2O4 nanowire sheet arrays(NWSAs)as precursor.Benefiting from advanced core-shell nanoarrays heterostructures and S ion exchange reaction,the composite exhibited a high specific capacitance of 5.52 F cm-2 even at a high current density of 30 mA cm-2,and showed excellent cycle stability(71.7%of the initial capacitance after 3000 cycles).Due to the excellent performance,we believe that the CoS@NiCo2S4 NWSAs is a potential promising electrode material for the application of energy storage or conversion with fine electrochemical performance and deserved to be further investigated.