NiCo₂S₄ Nanosheets Grown on Nitrogen‐Doped Carbon Foams as an Advanced Electrode for Supercapacitors

Abstract

mers usually suffer from poor cyclic stability in long term charge-discharge processes. [ 15 ] The low electron conductivity of transition metal oxides leads to inferior rate capability. [ 16 ] In the search for high performance electrode materials, transition-metal sulfi des have been extensively studied as new class of pseudocapacitive materials for supercapacitors. [17][18][19][20] In particular, NiCo 2 S 4 possess higher electrochemical activity and higher capacity than mono-metal sulphides based on richer redox reactions. [ 21,22 ] More signifi cantly, NiCo 2 S 4 exhibited an excellent electrical conductivity, at least two orders of magnitude higher than that of NiCo 2 O 4 . [ 23 ] The development of novel nanostructured materials will effectively improve the utilization of active materials because of their high surface area, and short electron-and ion-transport pathways. Several different types of NiCo 2 S 4 nanostructures, including nanoplates, [ 24 ] nanoprisms, [ 25 ] nanotubes, [ 26,27 ] microspheres, [ 28 ] have been recently synthesized and their electrochemical performance was investigated. For example, Lou et al. [ 25 ] reported the fabrication of Ni x Co 3-x S 4 hollow nanoprisms through a simple sacrifi cial template method and a high reversible capacity (895 F g −1 under 1 A g −1 ) can be achieved. However, it should be noted that the introduction of a conductive agent and a polymer binder during the thin fi lm electrode preparation not only increase extra contact resistance but also inevitably compromises the overall energy storage capacity that still seriously limit their performance. [ 29,30 ] Three dimensional (3D) electrode architectures have emerged as a new direction because it can provide 3D interconnected network of both electron and ion pathways, allowing for effi cient charge and mass exchange during faradic redox reactions. Greatly enhanced performance has kindled the interest of researchers in the fi eld of 3D electrode architectures designs, such as copper pillar array, [ 31 ] nickel network, [ 32,33 ] stainless steel mesh, [ 34 ] carbonaceous interpenetrating structures. [ 35 ] The rigid electrode with metals as current collectors lead to the devices less fl exible, and they also have a low energy density. Carbon nanotubes sponge and graphene foams have been recently fabricated using chemical vapor deposition and used as electrode architectures for supercapacitors. [36][37][38] However, it is diffi cult to produce carbonaceous foams in large-scale because of their relatively high-cost and complex preparation processes. Additionally, due to the potential incompatibility issue between To push the energy density limit of supercapacitors, a new class of electrode materials with favorable architectures is strongly needed. Binary metal sulfi des hold great promise as an electrode material for high-performance energy storage devices because they offer higher electrochemical activity and higher capacity than mono-metal sulfi des. Here, the rational design and fabrication of NiCo 2 S 4 nan...

Is NiCo2S4 Really a Semiconductor?

“…[1][2][3][4][5] Essentially, all reports on this material have presumed it to be semiconducting, like many of the chalcogenides, with a reported band-gap in the range of 1.2-1.7 eV. 6,7 In this report, we have conducted detailed experimental and theoretical studies, most of which done for the first time, which overwhelmingly show that NiCo 2 S 4 is in fact a metal.…”

Role of anions on structure and pseudocapacitive performance of metal double hydroxides decorated with nitrogen-doped graphene

“…In Ni2p spectrum (Figs 3b and d) of both hybrids two shakeup satellite peaks (sat.) along with two spin orbit doublets can be assigned to Ni2p 1/2 (874 eV) and Ni2p 3/2 (856 eV) signals of Ni 2+ [23,35]. Similarly, in Co2p spectrum of NiCoDH@NG hybrid spin orbit splitting energy value is almost 15.9 eV (Co2p 1/2 : 797.4 eV and Co2p 3/2 : 781.5 eV) and sat.…”

One-step synthesis of architectural Ni3S2 nanosheet-on-nanorods array for use as high-performance electrodes for supercapacitors

“…Chen et al and Pu et al 25,26 prepared NiCo 2 S 4 nanotubes on nickel foam using a multistep hydrothermal method that converted the corresponding nickel cobalt carbonate hydroxide precursors via S 2 − ion exchange. Shen et al 18 reported a similar multistep route to growth of NiCo 2 S 4 nanotube arrays on nitrogen-doped carbon foams. The NiCo 2 S 4 electrode exhibited a capacitance of 877 F g − 1 at 20 A g − 1 .…”

“…4, [8][9][10] Transition metal oxides, hydroxides and sulfides have been demonstrated as alternative electrode materials with significantly enhanced capacity via surface-bound capacitor-like (that is, pseudo-capacitives) faradaic reactions. [11][12][13][14][15][16][17][18][19][20][21] Ni-or/and Co-based oxides/hydroxides/sulfide usually exhibit a main capacitive behavior, especially at high current density, but the bulk materials still exhibit battery-type behavior. Therefore, these materials are considered as 'extrinsic pseudocapacitors.'…”