Preparation And Supercapacitor Property Characterization Of Cobalt Phosphide-based MOFs Derivatives

In recent years,along with the massive consumption of fossil energy,the development and utilization of new green energy sources has become increasingly urgent,and as an important part of energy utilization,the development of energy storage facilities has also received close attention from researchers.As a member of the family of energy storage facilities,supercapacitors are favored by more practitioners because of their long service life,high safety and short charging time.As an important part of supercapacitor,electrode material plays a pivotal role in capacitance performance and energy density.In this paper,we try to prepare electrode materials with high capacitive performance,long cycle life,and adaptable to high current density operation.In this paper,a series of phosphorylated cobalt-based and transition metal composite electrode materials were designed and prepared by MOF as a template.Subsequently,the surface interface morphology of the synthesized samples was analyzed by a series of characterizations such as XRD,SEM,TEM and XPS,and the electrochemical properties of the electrode materials were evaluated by an electrochemical workstation to elaborate the performance and constitutive relationships.The main research process and the results obtained are as follows:（1）The bimetallic organic framework Co-MnPBA was prepared and Co-Mn bimetallic oxide was obtained by high-temperature calcination under air atmosphere.To further enhance its capacitive properties,Co-Mn-O@CoP composites with core-shell structure were obtained by surface phosphorylation of the bimetallic oxide using a simple vapor deposition method.Due to the unique structure of the organometallic framework Co-MnPBA and the synergy between the cobalt-manganese bimetallic oxide and cobalt phosphide nanosheets,the Co-Mn-O@CoP composite exhibits a specific capacitance of 1144.2 F g^-1at 1 A g^-1,which is higher than that of Co-MnPBA(708.9 F g^-1)and Co-Mn-O-C(962.0 F g^-1).Moreover,it exhibits excellent multiplicative characteristics in the charge/discharge test at 10 A g^-1,and maintains 79.14%capacitance retention after 5000charge/discharge tests.In addition,the assembled Co-Mn-O@CoP//AC asymmetric supercapacitor has an energy density of 29.0 W h kg^-1at 800 W kg^-1and a capacitance retention of 93.91%after 5000 charge/discharge cycles at 10 A g^-1.（2）The bimetallic organic framework Co-FePBA was prepared and nitrogen-doped carbon nanotubes（CoFe@NCNTs）grown on the Co-FePBA framework structure were successfully fabricated by introducing dicyandiamine under a nitrogen atmosphere with high-temperature calcination.Subsequently,the composites of cobalt phosphide nanosheets interwoven with carbon nanotubes（denoted as CoP-CoFe@NCNTs）were successfully prepared by hydrothermal method combined with vapor deposition.The synergistic effect of the hollow porous structure of CoP-CoFe@NCNTs combined with interspersed CoP nanosheets is not only beneficial to increase the sites of energy storage and accelerate the rate of charge transfer,but also facilitates the rapid infiltration of electrolyte,thus reducing the impedance and improving the capacitive performance.The specific capacitance of the synthesized CoP-CoFe@NCNTs in 6 M KOH electrolyte reached 1474.3 F g^-1(1 A g^-1),and the capacitance retention was 76.2%when the current density was increased from 1 A g^-1to 10 A g^-1,and the capacitance retention was still 86.3%after 5000charge/discharge tests at 10 A g^-1.Meanwhile,when CoP-CoFe@NCNTs were assembled as asymmetric supercapacitors with CoP-CoFe@NCNTs as the positive electrode and AC as the negative electrode,the energy density reached 44.6 W h kg^-1at a power density of 808.7 W kg^-1.（3）A new MOF-loaded cobalt-molybdenum phosphide nanoribbon composite（denoted as Co-Mo-P/MOF）with a three-dimensional cross-linked network structure using Co-MOF as the substrate was successfully prepared by hydrothermal method combined with vapor deposition.Scanning transmission images show that the cobalt-molybdenum phosphide nanoribbons form a three-dimensional cross-linked network structure in space with MOF particles as connecting nodes and form a large number of pore structures,which is conducive to exposing the active area of the composites and accelerating the contact between the active sites and the electrolyte,thus improving the capacitive performance and multiplicative performance of the materials.Electrochemical experiments showed that the specific capacitance of Co-Mo-P/MOF composites was as high as 2496.8 F g^-1at a current density of 1 A g^-1,which was much higher than that of the prepared Co-MOF(769.4 F g^-1),Co-Mo-P(1056.1 F g^-1),and CoP(605.2 F g^-1).When assembled with AC to form an asymmetric supercapacitor,it has a high energy density(52.2 W h kg^-1)at a power density of 775 W kg^-1and a high cycle stability of 93.24%after 5000 cycles at a current density of 10 A g^-1.