Preparation And Characterization Of Three Dimensional Nanoarrays Electrode Based On Co-Ni Sulfides

Supercapacitor is one of the most promising environment-friendly and highly efficient energy storage systems, combining high power density of conventional capacitor and high energy density of battery. However, the poor electrical conductivity of metal oxides/hydroxides pseudocapacitive materials restricting fast electron and ions transport towards their theoretical capability. Therefore, we designed highly conductive three-dimensional(3D) nanostructured arrays scaffolds for loading the active materials. Highly conductive nanostructured arrays scaffold can facilitate electron transport and electrolyte diffusion, and thus enhance the electrochemical performance. In our work, we have reported that electrode materials are loaded on the 3D hollow carbon nanorod arrays and Ni Co2S4 tube arrays for high performance pseudocapacitors.Firstly, an advanced integrated electrode has been designed by growing the pseudocapacitive materials, including Cox Ni1-x(OH)2, Cox Ni1-x O, and(Cox Ni1-x)9S8, on a three-dimensional hollow carbon nanorod arrays(HCNA) scaffold prepared via a sacrificing template method. The HCNA scaffold not only can provide large surface area for increasing the mass loading of the pseudocapacitive materials, but also is with good electrical conductivity and hollow structure for facilitating fast electron and electrolyte ions transport, and thus improve the electrochemical performance. Among Cox Ni1-x(OH)2, Cox Ni1-x O, and(Cox Ni1-x)9S8,(Cox Ni1-x)9S8 nanosheets grown on the HCNA scaffold exhibited the best electrochemical performance. The discharge areal capacitance can be achieved to 1.32 F/ cm2 at 1 m A /cm2, ～1.5 times as that of the CoxNi1-x(OH)2 /HCNA electrode. The rate capability performance is also improved. 71.8% of the capacitance is retained with increasing the discharge current density from 1 to 10 m A /cm2, in contrast to ～59.9% for the CoxNi1-x(OH)2 /HCNA electrode. Remarkably, the cycling stability is significantly enhanced. ～111.2% of the initial capacitance is gained instead of decaying after the 3000 cycles at 8 m A/ cm2,while there is ～11.5% loss for the CoxNi1-x(OH)2 /HCNA electrode tested under the same condition. Such good electrochemical performance can be ascribed by the high electrochemical activity and electrical conductivity of(Cox Ni1-x)9S8,as well as the advantages of the 3D HCNA scaffold.Secondly, we have developed highly conductive Ni Co2S4 single crystalline nanotube arrays grown on a flexible carbon fiber paper(CFP), which can serve not only as a good pseudocapacitive material but also as a 3D conductive scaffold for loading additional electroactive materials. The resulting pseudocapacitive electrode is found to be superior to that based on the sibling Ni Co2O4 nanorod arrays, which are currently used in supercapacitor research due to the much higher electrical conductivity of Ni Co2S4. A series of electroactive metal oxide materials,including Cox Ni1-x(OH)2, Mn O2, and Fe OOH, were deposited on the Ni Co2S4 nanotube arrays through a facile electrodeposition method. Remarkably, the as-formed Cox Ni1-x(OH)2 / Ni Co2S4 nanotube array electrodes showed the highest discharge areal capacitance(2.86 F/ cm2 at 4 m A/ cm2), good rate capability(still 2.41 F /cm2 at 20 m A /cm2), and excellent cycling stability(～4% loss after the repetitive 2000 cycles at a charge-discharge current density of 10 m A /cm2).