| To meet the explosive demand of mobile and portable energy devices,developing reliable energy storage and conversion devices has attracted widespread attention.Compared with traditional batteries,supercapacitors?SCs?have the advantages of high power density,fast charge and discharge speed,long cycle life and environmental friendly,but the relatively low energy density limits the practical application of supercapacitors.Electrode material is the key part of SCs,and it's important to design electrode materials with high redox activities and large specific capacitances.Recent years,transition metal phosphides?TMPs?are regarded as reliable supercapacitor electrode materials and have been extensively researched.Compared to hydroxides and oxides,phosphides have metalloid properties and higher electrical conductivity,which results in faster electron transport and more redox reactions.This paper mainly focuses on the application of nickel cobalt phosphates and hydroxides in SCs,and has successfully synthesized nickel cobalt phosphates and hydroxides with different morphologies and structures through different methods,and explores the influence of different factors on the morphology and electrochemical performance of the as-prepared products.Meanwhile,materials with different voltage window were assembled to further test the practical application of the electrode materials.The central research contents are as follows:1.NiCo-LDH is synthesized via electrodeposition techniques,followed by one-step phosphating to convert the hydroxide into a phosphide.The obtained NiCoP shows3D porous nanosheet stack structure,which provides a larger specific surface area and more active sites.The nickel cobalt bimetal hydroxide/phosphate combine the characteristics of high stability of Co-based and high specific capacitance of Ni-based,and electrochemical performances are obviously improved compared with than that of nickel cobalt monometallic hydroxide/phosphate.The as-fabricated NiCoP electrode exhibits good electrochemical performance with high specific capacitance(1142.84 F g-1 at 1 A g-1),good rate capabilities(62.07%of the initial specific capacitance at 10 A g-1)and outstanding cycle stability(maintains 74.5%of initial capacitances after 5000cycles at 10 A g-1).Owning to superior electrical conductivity and excellent redox activity of phosphide,its voltage window and cycle stability are significantly improved compared to NiCo-LDH.In addition,NiCoP is used as the positive electrode and rGO as the negative electrode to fabricate the NiCoP//rGO all-solid-state asymmetric supercapacitor,which delivers a voltage window of 1.5 V and a high energy density of14.7 Wh kg-1 at a power density of 753.6 W kg-1.2.The effects of different nickel cobalt ratios on the microstructure and electrochemical properties of NiCoP are investigated.At the Ni/Co=1:2,NiCoP nanowires with high length-diameter ratio are successfully synthesized.On the basic of previous work,a facile hydrothermal-electrodeposition-phosphating three-step way has been taken to synthesize NiCoP@NiCoP core-shell nanoarrays directly grown on carbon cloth,which is used as high-performance supercapacitor electrode.Compared with the NiCo-LDH precursor and NiCoP nanowire and NiCoP nanosheet,NiCoP@NiCoP core-shell composite shows higher electrochemical performance owing to the integration of the advantages of phosphides and core-shell structure.To be specific,the as-fabricated NiCoP C-S electrode exhibits great electrochemical performance with high specific capacitance(1492.5 F g-1 at 1 A g-1),good rate performance(68.82%of the initial specific capacitance at 15 A g-1)and outstanding cycling stability(maintains 80.9%of the initial capacitances after 5000 cycles at 10 A g-1).Moreover,the assembled NiCoP C-S//rGO asymmetric supercapacitor device delivers a high energy density of 48.13 Wh kg-1 at the power density of 1125 W kg-1and it still retains 20.94 Wh kg-1 at a high power density of 11250 W kg-1,indicating its great possibility of practical application.3.The NiCo-LDH-120 with nanoflower@nanosheet structure is obtained by hydrolyzing the pre-grown ZIF-67 on carbon cloth by solvothermal method at 120°C.Compared with the preparation of electrode with hydrothermal method and electrode made from the NiCo-LDH-120 powder,the self-supporting electrode synthesized by this method possesses better electrochemical performance.Meanwhile,the Prussian blue analogues?PBA?of FeCoNi is successfully synthesized on the surface of NiCo-LDH nanosheet by hydrothermal method.The composite structure of NiCo-LDH@PBA increases the specific surface area,provides more reactive sites for redox reaction,and enriches the redox reaction center.The as-fabricated NiCo-LDH@PBA composite structure exhibits good electrochemical performance with high specific capacitance(1527.7 F g-1 at 1 A g-1),good rate capabilities(85.4%of the initial specific capacitance at 20 A g-1)and outstanding cycle stability(maintains 88.2%of initial capacitances after 5000 cycles at 10 A g-1).The electrochemical test results show that NiCo-LDH@PBA has excellent electrochemical performance and PBA has a broad prospect in the application of supercapacitors. |
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