Fabrication Of Nickel/Cobalt-based Nanocomposite Arrays With Hierarchical Structure And High Mass Loading On Carbon Cloth And Their Capacitive Properties

Compared with batteries,supercapacitors(SCs)have higher power density(>10k W kg^-1),faster charge and discharge processes(only several seconds),longer service life(>100,000 cycles),and more safety and lower maintenance cost,and have been regarded as a promising energy storage system.However,the wide application of supercapacitors is suppressed because of their low energy density.Increasing the specific capacity of the electrode material is key to increase the energy density of supercapacitors.Herein,nickel/cobalt-based nanocomposite arrays withhierarchical structure and high mass loading was fabricated in situ on carbon cloth.The structure,morphology and phase of the nanocomposite arrays were systematically analyzed by a series of modern instrument characterization techniques.In addition,the electrochemical test method was used to study their capacitance properties.Moreover,the relationship between microstructure and properties of materials was discussed.The main contents are as follows:Low-crystallinity Ni/Co oxyhydroxide composite nanoarrays with hierachical structure and high mass loding were synthesized in situ on carbon cloth by electrochemical reconstruction method and their capacitance properties were studied.A series of characterization results showed that the Ni/Co oxyhydroxide nanoarrays were consisted of(Co_0.25Ni_0.75)O(OH)oxyhydroxide nanosheets and Ni-doped Co O(OH)nanoneedles.Electrochemical test results showed that the prepared Ni/Co oxyhydroxide nanoarrays delievered excellent capacitance performance.The area specific capacitance of the Ni/Co oxyhydroxide nanoarrays with high mass loading(9.0 mg cm^-2)reached 8.87 F cm^-2 under a current density of 5 mA cm^-2 in 6 M KOH.When the current density was increased to 50 mA cm^-2,the area specific capacitance retained at 6.15 F cm^-2,and the corresponding capacitance retention was69.33%.It indicated that the nanorrays had high capacitance and good rate performance.Furthermore,after 2000 cycles of a galvanostatic charge/discharge measrment under a current density of 20 mA cm^-2,he nanoarrays still had excellent cycle stability(91.6%retention of the initial capacitance).Carbon dots(CDs)modified Ni/Co hydroxycarbonate nanocomposite arrays with hierachical structure and high mass loading were synthesized in situ on carbon cloth by a two-steps method and their capacitance properties were analyzed.A series of characterization results showed that the carbon dot-modified Ni/Co hydroxycarbonate nanoarrays were consisted of nanoneedles and nanoflakes,and the carbon dots were uniformly modified on the surface of the nanoneedles and nanosheets;In addition,the carbon dots significantly influenced the crystallinity and morphology of the Ni/Co hydroxycarbonate nanoarrays,resulting in the increase of defectsin the nanoarrays.Electrochemical measurement results showed that carbon dots(CDs)modified Ni/Co hydroxycarbonate nanoarrays had excellent capacitance performance,which can delivered a high area specific capacitance up to 14.37 F cm^-2 with a high mass loading of 7.2 mg cm^-2 at a current density of 5 mA cm^-2 in 6 M KOH.When the current density was increased to 50 mA cm^-2,the area specific capacitance was still as high as9.79 F cm^-2 with a high capacity retention of 68.13%.Moreover,afte 3000galvanostatic charge/discharge cycles under a current density of 20 mA cm^-2,the area specific capacitance of the nanoarrays still maintained 75.1%of the initial specific capacitance,indicating the good cycle stability.