| The growing problem of environmental pollution caused by the burning of fossil fuels has led to new demands for the development of new,green and sustainable energy storage devices.Supercapacitors have been widely studied due to their advantages such as wide operating temperature range and fast charging and discharging.The performance of supercapacitors is influenced by a number of factors,of which the choice of electrode material is particularly important.Transition metal nitrides,a class of interstitial compounds,are used as electrode materials for supercapacitors due to their high electrical conductivity and unique electronic structure.In this paper,Ni3N/NF self-supported electrodes were synthesized in situ on the surface of nickel foam(NF)by a simple preparation method.Based on this,Co2N-Ni3N/NF heterostructure and NiCo-LDH@Ni3N/NF core-shell structure electrode materials were prepared using two different strategies,and the electrochemical performance test results showed that the electrochemical performance of the Ni3N/NF self-supported electrode was effectively improved.The main elements are as follows:(1)Self-supported Ni3N electrode materials with nanosheet morphology were synthesized in situ on the surface of nickel foam by hydrothermal and nitriding treatments.This selfsupporting structure can overcome the agglomeration of traditional powder electrodes during the electrode preparation process.The nanosheets are composed of numerous nanoparticles,and there are a large number of gaps between the particles,which greatly increases the contact area with the electrolyte,thereby improving the electrochemical performance of the Ni3N selfsupporting electrode material.The Ni3N/NF electrode exhibits an areal capacitance of 1.35 F·cm-2 at a current density of 1 mA·cm-2 when the hydrothermal reaction conditions is 120℃、6 h.In a two-electrode system with Ni3N/NF as the positive electrode and activated carbon as the negative electrode,an energy density of 83.63 μWh·cm-2 can be provided at a power density of 0.75 mW·cm-2.(2)Co2N-Ni3N/NF heterostructure electrode materials with nanosheet-nanowire morphology were prepared on the surface of nickel foam by hydrothermal method and nitriding treatment,and the effect of introducing a second metal element on the electrochemical performances of the electrode materials was investigated.By introducing cobalt elements to form a heterogeneous structure,the synergistic effect between the two metal nitrides is exploited,thereby enhancing the electrochemical properties.The electrochemical test results show that the Co2N-Ni3N/NF heterostructure has an areal capacitance of 2.17 F·cm-2 at a current density of 1 cA·cm-2,and when the current density is increased to 20 mA·cm-2,the capacitance can still be maintained at 1.35 F·cm-2,with a rate performance of 62.2%.In the two-electrode test,the maximum energy density was 145.65 μWh·cm-2 at a power density of 0.75 mW·cm-2,and the original capacitance was still maintained at 85.90%after 5000 cycles.(3)The NiCo-LDH@Ni3N/NF core-shell structure electrode material was designed and synthesized by depositing a layer of NiCo-LDH nanosheets on the surface of Ni3N nanosheets by electrochemical deposition.The NiCo-LDH sheet layer introduced on the outside of the core-shell structure electrode can effectively protect the inner Ni3N nanosheets from electrolyte erosion during the electrochemical reaction,thus improving the electrochemical stability.In addition,the cross-linked nanosheets can provide enough space for electrolyte storage and conversion.In addition,when controlling the electrochemical deposition time at 180 s,the electrochemically tested composite electrode exhibited a maximum areal capacitance of 3.22 F·cm-2 at 1mA·cm-2 and a rate performance of 72.66%at a high current density of 20 mA·cm2.In the two-electrode system test,the maximum energy density was 33.13 Wh·kg-1 at a power density of 400 W·kg-1.Moreover,the capacity was maintained at 87.16%after 10,000 cycles,showing an excellent cycle stability. |
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