Design And Electrochemical Properties Of Metal Organic Frameworks(MOFs) Derived Transition-Metal Sulfides

Considerable efforts have already been made to develop high-performance stockpile equipment,such as batteries and supercapacitors,to tackle the increasingly serious energy crisis.Against this background,supercapacitors have attracted widely attention on account of ideal cycle stability,desirable power density and fast charge-discharge process.However,as the frequently-used electrode materials,carbon materials,conductive polymers and transition metal oxides are deficient in practical application.To search for environmental-friendly electrode materials with desirable electrochemical performances has significant meaning.Heren,due to the well-ordered structure,high porosity and diverse morphologies,MOF-derived electrode materials are supposed to be promising sacrificial precursors for the construction of supercapacitor electrodes.And bimetallic sulfides exhibit more abundant chemical reactions and higher electrochemical reactivity due to the addition of the second metal cations,which have attracted extensive attention to researchers.In this paper,we prepared bimetallic sulfides based on nickel foam by room-temperature coprecipitation reaction and hydrothermal synthesis.Meanwhile,we explored the influence of feed molar ratio and sulfide concentration on MOF-drived electrodes.The main research contents are as follows:(1)Using Co(NO3)2·6H2O,Cu(NO3)2·3H2O and 2-methyl imidazole as raw materials,zeolitic imidazolate frameworks(ZIFs,a class of MOF)derived bimetallic copper cobalt sulfide nanosheets grown on Ni foam were prepared through a cost-effective and expedient two-step method.The microstructure and composition of CuCo-S/NF could be regulated by tuning the feeding molar ratio of Cu/Co.The results showed that when the feeding molar ratio of Cu/Co in the precursor reaches 1/2,corresponding electrode(CulCo2-S/NF)existed desirable performance.The specific capacitance was 2313.6 F g-1 at 1 A g-1 and the capacitance retention reached 93.8%even after 6000 cycles.Moreover,Cu1Co2-S/NF and reduced graphene oxide(rGO)were chosen for fabricating an asymmetric supercapacitor(ASC),the Cu1Co2-S/NF//rGO device delivered desirable energy density of 37.6 Wh kg-1 at power density of 752.5 W kg-1,and outstanding cycling stability(90.4%retention after 8000 cycles).The co-existence of Cu and Co ions,suitable copper-cobalt ratios and increased specific surface area are the main reasons for its excellent electrochemical performance(2)Herein,coral-like cobalt-manganese sulfide nanoarrays directly grown on nickel foam were successfully designed and prepared by using zeolitic imidazolate frameworks as the self-sacrificing precursors.Synthesized by the convenient room-temperature coprecipitation and followed by a subsequent controlled sulfidation process,the additive-free Co-Mn-S-16/NF with well-designed structure exhibited desirable electrochemical performance.By tuning the concentration of S2-,the morphology,level of porosity and electrical conductivity were carefully controlled.The resultant Co-Mn-S treated with 16 mmol TAA(label as Co-Mn-S-16/NF)exhibited superior capacitance of 2015.3 F g-1 at 1 A g-1 and desirable rate performance(the capacitance retains 51.5%at 10 A g-1).Furthermore,Co-Mn-S-16/NF and rGO were chosen for fabricating an ASC,which demonstrated desirable energy density of 44.1 Wh kg-1 at 0.842 kW kg-1 and outstanding cycling stability.Benefiting from coral-like morphology,synergistic composition,as well as suitable porosity,the Co-Mn-S-16/NF electrode is very promising for supercpacitor.