Nickel Cobalt Sulfide Research Articles

Bi-Phase NiCo2S4-NiS2/CFP Nanocomposites as a Highly Active Catalyst for Oxygen Evolution Reaction

Pursuing oxygen evolution reaction (OER) catalysts with high activity and stability is attracting many researchers. Here, we first designed and synthesized a biphasic three-dimensional structured catalyst of nickel–cobalt sulfide NiCo2S4-NiS2/CFP, which is a nickel–cobalt sulfide composite decorated on carbon fiber paper (CFP) by a one-step hydrothermal method. It exhibited an overpotential of about 165 mV at a current density of 10 mA cm−2 and a small Tafel slope of 81.54 mV dec−1. Furthermore, the long-term stability of the NiCo2S4-NiS2/CFP nanocomposite was 90.0% of the initial current density even after 12 h. The excellent catalytic performance of the NiCo2S4-NiS2/CFP nanocomposite can be attributed to several aspects. Firstly, the petal-like morphology of the NiCo2S4-NiS2 nanocomposite exposes more active sites. Secondly, the stability of the composite catalyst is significantly enhanced by its firm anchoring on the CFP. Thirdly, the catalytic performance was significantly improved by the addition of mixed valence of Ni or Co on the {111} plane of spinel NiCo2S4. Finally, the three-dimensional CFP substrate provides an efficient pathway and a stable integrated structure for the transmission of electrons and ions. Our one-step hydrothermal synthesis method provides a simple and economical way to obtain high-performance and robust OER catalysts.

Achieving Self-Supported Hierarchical Cu(OH)2/Nickel-Cobalt Sulfide Electrode for Electrochemical Energy Storage.

Herein, nickel-cobalt sulfide (NCS) nanoflakes covering the surface of Cu(OH)2 nanorods were achieved by a facile two-step electrodeposition strategy. The effect of CH4N2S concentration on formation mechanism and electrochemical behavior is investigated and optimized. Thanks to the synergistic effect of the selected composite components, the Cu(OH)2/NCS composite electrode can deliver a high areal specific capacitance (Cs) of 7.80 F cm-2 at 2 mA cm-2 and sustain 5.74 F cm-2 at 40 mA cm-2. In addition, coulombic efficiency was up to 84.30% and cyclic stability remained 82.93% within 5000 cycles at 40 mA cm-2. This innovative work provides an effective strategy for the design and construction of hierarchical composite electrodes for the development of energy storage devices.

Bimetallic organic framework in situ fabrication nanoflower-like cobalt nickel sulfide and ultrathin layered double hydroxide arrays for high-efficient asymmetric hybrid supercapacitor

More and more attention has been attracted to regulate the morphology and structure of cobalt-nickel based compounds electrode materials through metal organic frameworks (MOFs) and explore the performance of the assembly them into asymmetric capacitors. In this study, NiCo-Metal organic framework derived carbon (NiCo-NC) is utilized as metal embedded template to in situ epitaxial fabricate nanoflower-like cobalt nickel sulfide (named NiCo2S4@NC) using alcohol heating in ethylene glycol sulfurization. Due to the dual electrochemical activity of NiCo2S4 and NiCo-NC, the NiCo2S4@NC multi-modal nanohybrid possesses a promising specific capacitance of 1021.6 F g−1 at 1 A g−1 in the voltage window of − 1 to 0 V. Besides, ultrathin cobalt nickel hydroxide nanosheets are in situ introduction on the surface of NC skeleton (NiCo-LDH@NC) with the help of absolute ethanol and L-ascorbic acid, which behave an excellent capacitance of 988.2 F g−1 (164.7 mA h g−1) at 1 A g−1, and exhibit an extraordinary charge-discharge stability. Due to the high conductivity of NC derived from NiCo-MOF, the appearance of more reaction sites after vulcanization and the specific hierarchical structure of cobalt nickel hydroxide, the assembled NiCo-LDH@NC//NiCo2S4@NC asymmetric supercapacitor device delivers a great energy density of 61.5 W h kg−1 (at 426.6 W kg−1) and pronounced cycle stability (retention of 92.7 % over 5000 cycles). This work provides a feasible strategy towards the practical application in supercapacitors using nickel cobalt multi-active centers with special morphology as high-efficiency and inexpensive electrode materials.

Hierarchical nickel cobalt sulfide nanoparticles encapsulated in rose-shaped carbon spheres as high-performance anode materials for lithium-ion batteries

A rose-shaped binary Ni/Co metal-organic framework (Ni/Co-MOF) precursor assembled from numerous cross-linked 2D nanosheets was prepared via a facile hydrothermal reaction. The hierarchical structure was inherited by a one-step carbonization and sulfurization of the precursor and derived nickel cobalt bimetal sulfide nanoparticles encapsulated in rose-shaped carbon spheres (NiS2/CoS2@RCSs) composite. As an anode material for lithium-ion batteries (LIBs), the final composite material could improve conductivity, facilitate electrolyte penetration, and alleviate volume change. Beneficial from the unique nano-architecture plus the bimetallic synergistic effect, the obtained anode electrode achieves an exceptional cycling stability (747.7 mA h g−1 at 1.0 A g−1 after 400 cycles) with a superior rate capability (500.9 mAh g−1 at 4.0 A g−1).

MOF-Derived Nickel–Cobalt Sulfide Nanoflakes Wrapped Carbon Nanotubes for Hybrid Supercapacitors

Transition metal sulfide has been regarded as an ideal electrode material for supercapacitors due to its high energy density. However, the poor cyclic stability caused by low electroconductivity seriously limits its practical application. Herein, carbon nanotubes and nickel–cobalt bimetallic organic framework composites were prepared by the in situ growth method and used as precursors to prepare carbon nanotubes/nickel–cobalt bimetallic sulfide (CNTs/Ni–Co–S-3) composites. Benefits from the synergy between the components, CNTs/Ni–Co–S-3, as a positive electrode material, presented an extremely high specific capacity of 734 C g–1 at 1 A g–1 and an improved rate capability. Furthermore, when CNTs/Ni–Co–S served as the positive electrode of the hybrid supercapacitor (CNTs/Ni–Co–S-3//AC HSC), the device provided a competitive energy density of 42.15 Wh kg–1 at the power density of 852 W kg–1 and long-term stability (88.46% of specific capacitance retention for 10000 cycles at 8 A g–1). This synthesis strategy provides a new pathway for further improving the energy density and cyclic stability of metallic sulfide group composite electrodes.

Coordination-derived nickel cobalt sulfide solid microspheres with surface defects for high-performance asymmetric supercapacitors

Bimetallic sulfides are effective cathode materials for asymmetric supercapacitors because of their excellent electrochemical properties. However, both the low utilization ratio of the electrode material and the low energy storage capacity have restricted further development. In this work, Ni and Co were reacted with terephthalic acid (H2BDC) and isonicotinic acid (Ina) under hydrothermal conditions, followed by hydrolysis in 1 M KOH and vulcanization in thiourea to yield nickel cobalt sulfide (CoNi2S4) solid microspheres (NiCoS) with surface defects consisting of bumps and holes. These structural and morphological features compensate for the shortcomings of bimetallic sulfide electrodes, enhance their energy storage capacity, and improve their capacitance performance. The specific capacitance of the asymmetric supercapacitor assembled with NiCoS and a self-made carbon electrode reached 168.0 and 101.6 F/g at specific currents of 1 and 20 A/g, respectively. An increase in the specific current by a factor of 20 corresponded to an increase in capacitance retention rate to 60.5%, improving the rate performance. When the specific power increased to 800 and 16 000 W/kg, the specific energy reached 59.7 and 36.2 Wh/kg, respectively. Following 5,000 charge/discharge cycles, the capacitance retention rate was 96.78%. Such excellent comprehensive electrochemical performance greatly increases the competitiveness of the NiCoS electrode in the field of electrochemical energy storage.

High performance hybrid supercapacitors assembled with multi-cavity nickel cobalt sulfide hollow microspheres as cathode and porous typha-derived carbon as anode

Unique hollow structures hold bright promise in the field of energy storage applications, but it is still challenging to synthesize bimetallic sulfide composites with complex hollow structures. In the present work, a NixCo1−xS2/NiCo2S4 composite with multi cavity hollow sphere structure is prepared by a simple liquid-phase reaction and solvothermal sulfurization and used as a supercapacitor positive electrode material. Benefiting from the well-designed unique structure and synergy between the nickel and cobalt elements, the composite exhibits excellent electrochemistry with a specific capacity of 797 C g−1 at 1 A g−1 and possesses good rate capability (78.8 % retention at 20 A g−1). In addition, Typha-derived carbon is prepared by calcination using discarded biomass Typha. And, a hybrid supercapacitor device is assembled by using NixCo1−xS2/NiCo2S4 and Typha-derived carbon as cathode and anode. The device exhibits a high energy density of 82.7 Wh kg−1 at 513.5 W kg−1 and possesses superior long-term cycling capacity (84.6 % after 10,000 cycles), indicating the great application potential of the composites in the field of supercapacitors. More importantly, the unique structural design and facile operation methods provide new ideas and broad prospects for the synthesis of complex metal sulfide materials in the energy storage field later.

Benchmarking the charge storage mechanism in nickel cobalt sulfide nanosheets anchored on carbon nanocoils/carbon nanotubes nano-hybrid for high performance supercapacitor electrode

To improve the capacity of electrodes for energy storage device, a promising architecture with enhanced electrochemical performance is extremely desired. Benefiting from the high conductivity and lower electronegativity of sulfur among chalcogens, transition metal sulfides are favorable contender of being used as an electrode material for supercapacitor device. Herein, three dimensional (3D) hybrid architecture composed of carbon nanocoils/nickel foam (CNCs/NF) substrate decorated with nickel cobalt sulfide (NiCoSx) nanosheets and carbon nanotubes (CNTs), has been fabricated via two step solvothermal reaction accompanied by vacuum filtration technique. CNTs act as conducting bridges between the porous nanosheets. The optimized CNTs/NiCoSx/CNCs/NF hybrid structure elucidates excellent specific capacitance of 3184 F g−1, outstanding capacitance retention (97.2 % after 3000 cycles) and significant capability rate (79 %). Furthermore, Density Functional Theory (DFT) calculations demonstrate that the significant capacitance enhancement in NiCoSx/CNCs originates from the enriched density of states near the Fermi level. The synergistic effect of NiCoSx anchored on CNCs/NF and CNTs is mainly responsible to significant electrochemical performance thereby achieves improved electron conductivity, increased ion diffusivity and efficacious redox reactions. Additionally, benefiting from the aforementioned properties, the CNTs/NiCoSx/CNCs/NF composite urges the researcher to use as a favorable contender for supercapacitor electrodes.

Sulfur Nanoparticle-Decorated Nickel Cobalt Sulfide Hetero-Nanostructures with Enhanced Energy Storage for High-Performance Supercapacitors.

Transition-metal sulfides exaggerate higher theoretical capacities and were considered a type of prospective nanomaterials for energy storage; their inherent weaker conductivities and lower electrochemical active sites limited the commercial applications of the electrodes. The sheet-like nickel cobalt sulfide nanoparticles with richer sulfur vacancies were fabricated by a two-step hydrothermal technique. The sheet-like nanoparticles self-combination by ultrathin nanoparticles brought active electrodes entirely contacted with the electrolytes, benefiting ion diffusion and charges/discharges. Nevertheless, defect engineers of sulfur vacancy at the atomic level raise the intrinsic conductivities and improve the active sites for energy storage functions. As a result, the gained sulfur-deficient NiCo2S4 nanosheets consist of good specific capacitances of 971 F g-1 at 2 A g-1 and an excellent cycle span, retaining 88.7% of the initial capacitance over 3500 cyclings. Moreover, the values of capacitance results exhibited that the fulfilling characteristic of the sample was a combination of the hydrothermal procedure and the surface capacitances behavior. This novel investigation proposes a new perspective to importantly improve the electrochemical performances of the electrode by the absolute engineering of defects and morphologies in the supercapacitor field.

Solvent-free synthesis of NiCo2S4 having the metallic nature.

Nickel-cobalt sulfide (NiCo2S4) is a prominent member of bimetallic transition metal sulfides. It is being widely used for a variety of applications such as electrode material, photocatalysis, and energy storage devices (like pseudo capacitors, supercapacitors, solar cells, and fuel cells) due to its better electronic conductivity, manageable morphology, and high capacitance. This work presents the one-step solventless synthesis of NiCo2S4 sheet-like nanostructures and then explores their metallic nature. Scanning electron microscopy (SEM) and transmission electron microscopic (TEM) analysis show the sheet-like grown morphology. Few nanorods are also seen. Except for a recent study (Xia et al. 2015) that shows metallic behavior, most of the reports show that NiCo2S4 is a semiconductor with claimed bandgap between 1.21 and 2.4eV. In this study, we observe from UV-Vis and diffuse reflectance spectroscopy (DRS) that NiCo2S4 has a specific band gap value between 2.02 and 2.17eV. However, IV characteristics in the temperature range of 300-400K show that NiCo2S4 is a metal with a positive temperature coefficient of resistance consistent with a recent report. Furthermore, we see the ohmic conduction mechanism. The Arrhenius plot is drawn, and the activation energy is calculated to be 3.45meV. The metallic nature is attributed to the coupling of two metal species (nickel and cobalt), which accounts for its superior conductivity and performance in a variety of essential applications.

Nanorod NiMoO4@NiCo2S4 as an advanced electrode material for high-performance supercapacitors

Nickel-cobalt sulfides exhibit good energy storage properties, but the poor stability affects the application of the material. In this work, we designed a simple route to synthesize NiMoO4 @NiCo2S4 composites by hydrothermal method combined with electrodeposition. The highly conductive NiCo2S4 nanorods and the highly reactive NiMoO4 showed good synergistic effects. NiMoO4 @NiCo2S4 exhibiting a high specific capacity of 1282.6 C g−1 (2565.2 F g−1) at 2 A g−1. The capacity retention of NiMoO4 @NiCo2S4 is increased from 75.93% to 84.7% after 5000 charge-discharge cycles compared with NiCo2S4 electrode. Further density functional theory (DFT) calculations show that the density of states (DOS) near the Fermi level of NiMoO4 @NiCo2S4 is significantly increased and the work function (WF) increases to 5.13 eV, which improves the electrochemical performance of the material. In addition, the NiMoO4 @NiCo2S4//Activated carbon asymmetric supercapacitor exhibits a high energy density of 75.3 Wh kg−1 at 800 W kg−1.

Metal-organic frameworks supported Ni–Co–S nanosheet arrays for advanced hybrid supercapacitors

Constructing self-supporting porous electrode material with abundant electrochemical active sites can effectively improve the energy storage capacity of supercapacitors. Herein, a novel electrode material (NCS@Co-ZIF/NF) is developed by depositing zeolitic imidazolate frameworks (Co-ZIF) on nickel foams (NF), which is adopted as a precursor (Co-ZIF/NF) to electrodeposit nickel-cobalt sulfides (NCS). The nanosheet arrays with cross-porous structures provide NCS@Co-ZIF/NF with excellent electrochemical characteristics, including a high specific capacity of 144.4 mAh g−1 at the current density of 1 mA cm−2, 60.5% capacity retention at 50 mA cm−2, and superb long-term cycle stability. Furthermore, NCS@Co-ZIF/NF//AC hybrid supercapacitor is fabricated by using NCS@Co-ZIF/NF as positive electrodes and activated carbon (AC) as negative electrodes, which exhibits a high energy density of 33.9 Wh kg−1 at a power density of 145 W kg−1.

In-situ assembly of 2D/3D porous nickel cobalt sulfide solid solution as superior pre-catalysts to boost multi-functional electrocatalytic oxidation

In this work, we fabricated an efficient pre-catalyst based on (Ni, Co)S2 solid solution with hierarchical architecture and high porosity to boost urea oxidation reaction and electrocatalytic oxidation of organic small molecules. The interaction between Ni and Co can optimize the electronic structure, resulting in the improved conductivity and accelerated charge transfer rate. The 2D/3D architecture can enrich more active species and endow the mass and electron transport to facilitate the surface oxidation and the following catalytic process. Post-structure and catalytic characterizations confirm the surface oxidation of (Ni, Co)S2 during the stability test, and the in-situ formed Co(Ni) based (oxy)hydroxides exhibit superior catalytic activity and facilitated charge transfer ability. As a result, the optimal (Ni, Co)S2 solid solution pre-catalyst displays facilitated catalytic behavior and good stability for multifunctional electrocatalytic oxidation, in which a high conversion of benzyl alcohol (97.50%), a good selectivity to benzoic acid (93.78%) and a satisfied faraday efficiency (91.86%) can be achieved.

One-step superficial electrodeposition of nickel-cobalt-sulfide for high-energy hybrid asymmetric supercapacitor

A cathodic electrodeposition (ED) technique is adopted to grow multi-component nickel–cobalt-sulfide (NCS) nanosheet arrays on highly conducting nickel foam substrate. The chronoamperometry (CA) deposited electrode has shown exceptional electrochemical activity in terms of specific capacity, rate capability and excellent redox reversibility than the cyclic voltammetry (CV) deposited electrode. Having the benefit of highly conductive nanosheet arrays and three-dimensional open framework of the nanostructure, the binary metal sulfide exhibits high specific capacity of 820 C g−1 at 2 A g−1. When the NCS electrodes were combined with boron-doped graphene oxide to form an asymmetric hybrid supercapacitor, it delivered a high energy density of 83 Wh g−1 and high-power density of 9619 W kg−1.

Polypyrrole-coated Boron-doped Nickel-Cobalt sulfide on electrospinning carbon nanofibers for high performance asymmetric supercapacitors

Although nickel–cobalt bimetallic sulfides have been widely studied for supercapacitor electrodes, how to obtain high specific capacity and cycle stability is still an important challenge. Here, an efficient chemical redox method is used to adjust the crystal and electronic structure of cobalt–nickel sulfide (NCS) via B doping, combined with electrospinning technology and conductive polymer polypyrrole (PPy) coating to facilitate faraday redox reactions and obtain high energy density electrode materials. The resulting composite with boron-doped nickel–cobalt sulfide on electrospinned carbon nanofibers with polypyrrole-coating (PPy@B-NCS/CNF) has a high specific capacity (751.61C/g at 1 A/g) and good cycle stability (82.49 % retention after 4000 cycles at 5 A/g). With PPy@B-NCS/CNF as the positive electrode and activated carbon as the negative electrode, an asymmetric supercapacitor (ASC) is prepared. It has excellent electrochemical properties with a power density of 65.58 Wh kg−1 and an energy density of 819.72 W kg−1. The low-temperature performance test shows high reversibility, which provides the possibility for the development of low-temperature electrolytes. Finally, density functional theory (DFT) explains that B-doped NCS has better electrochemical properties from the energy band and state density.

Bifunctional oxygen electrode cobalt–nickel sulfides catalysts originated from intercalated LDH precursors

Bimetallic cobalt–nickel sulfide nanoparticles anchored on S-, N-codoped holey carbon nanosheets (CoNi-S-T@NCFs) with a hydrangea-like morphology, were synthesized via a confinement synthesis route, in which an intercalated LDH precursor was subjected to the interlayer-confined carbonization and host-layer sulfurization. The phase transformation and structure evolution (e.g., atom site occupancy, crystallite size, and cell volume) of the CoNi-S-T@NCFs electrocatalysts, as a function of sulfurization temperatures, were confirmed by X-ray diffraction and Rietveld analyses. The sulfur vacancies effectively enhance the electrocatalytic activity, while the synergistic effect of (Co,Ni)7S8 alloy and S, N-codoped carbon matrix facilitates the electron transfer and accelerates reaction kinetics, making CoNi-S-900@NCFs an efficient and stable bifunctional electrocatalyst for oxygen reduction reaction (ORR). The rich high-valence Co (III) and Ni (III) of CoNi-S-900@NCFs facilitates the in-situ transformation of the metal (oxy)hydroxides intermediates with high catalytic activity for oxygen evolution reaction (OER). Thus, with a bifunctional parameter, ΔE, of 0.75 V (Ej=10, OER - E1/2, ORR), this electrocatalyst slightly outperforms the state-of-the-art commercial Pt/C + RuO2/C catalyst (ΔE = 0.76 V) in alkaline medium. This work demonstrates the influence that the sulfurization temperature has on the relationship between the structure and electrocatalytic performance of bimetallic sulfides prepared by the synthesis strategy using the intercalated LDH precursor. This strategy can be extended to prepare other chalcogenides with binary or ternary transition metals.

Direct decoration of carbon nanohorns with binary nickel-cobalt sulfide nanosheets towards non-enzymatic glucose sensing in human fluids

A highly controllable, green, and rapid strategy is demonstrated for fabricating of highly sensitive non-enzymatic glucose sensing platforms. Carbon nanohorns (CNHs) were decorated onto the screen-printed electrodes. Binary nickel-cobalt sulfide (NiCo-S) nanosheets (NSs) were then deposited on CNH-casted electrodes by a facile and scalable method. Following detailed structural characterization and the electrocatalytic activity of the fabricated NiCo-S/CNH electrodes towards electro-oxidation of glucose was examined in detail. The proposed electrodes operated within two distinct linear dynamic ranges of 0.001- 0.330 mM and 0.330 - 4.53 mM with sensitivities of 1842 µA.mM−1.cm−2 and 854 µA.mM−1.cm−2, respectively. Analytical sensitivity of 467 µA.mM−1.cm−2, within the linear dynamic range of 0.5 ∼ 6 mM, was obtained for the static chronoamperometric measurements. The proposed sensor showed outstanding selectivity against isostructures and co-existing interferences, long-term stability, fast response (1.7 s), excellent poisoning resistance against chloride ions, good repeatability, and high reproducibility. The structural and electrochemical properties of the NiCo-S/CNHs were also compared to its mono-metallic counterparts. Finally, to demonstrate the capability of the fabricated electrodes for glucose measurements in physiological specimens, the glucose level was successfully measured in human blood serum, urine, and saliva samples, without any sample pre-treatment.

Heterostructured bimetallic–sulfide@layered Ti3C2Tx–MXene as a synergistic electrode to realize high-energy-density aqueous hybrid-supercapacitor

Aqueous hybrid supercapacitors (AHSCs) exhibit promising electrochemical performance with long cyclic stability and high power density. However, the low-energy density restricted their development to commercialization. To improve the energy density, we proposed a heterostructured (HS) composite of nickel–cobalt–sulfide (NCS) nanoflowers embedded in exfoliated Ti3C2Tx−MXene layers (HS−NCS@MXene). The NCS nanoflowers were uniformly dispersed inside the MXene layers and formed a sandwich-like structure. The HS−NCS@MXene exhibited remarkable pseudocapacitive performance in a three-electrode system. The capacitance can reach 2637 F g−1 (1582 C g−1) at 2.5 A g−1 with stable cycling life over 10,000 cycles and retained 96% capacity of the initial value. Post−mortem investigations confirmed that the charge storage mechanism in HS−NCS@MXene composite is a combination of Faradic and electrochemical double-layer storage. An AHSC was assembled by coupling the HS−NCS@MXene as a positive electrode and activated carbon as a negative electrode (HS−NCS@MXene//AC–AHSC). The HS−NCS@MXene//AC–AHSC can operate in a potential range up to 1.6 V and deliver a high capacitance of 226 F g−1 at 1.5 A g−1 with stable cyclic life (92%) up to 20,000 cycles. Moreover, the HS−NCS@MXene//AC−AHSC also possessed a high energy density of 80 Wh kg−1 at a power density of 1196 W kg−1, which exceeds most recently published works. The synergistic effect of NCS and MXene enables the HS−NCS@MXene composite to deliver outstanding electrochemical performance for AHSCs.

Preparation of nanosheets of Ni5P2@Ni9S8/CoS1.097 heterostructure for aqueous asymmetric supercapacitors with high electrochemical performance

In recent years, transition metal sulfides, especially nickel-cobalt sulfide materials play a crucial role for supercapacitor applications. In this work, the Ni5P2@Ni9S8/CoS1.097 (Ni-P@NCS) core-shell material has been synthesized by simply phosphating the nickel mesh and subsequent electrodeposition of NCS to obtain a nanosheet heterostructure on nickel foam. The Ni-P@NCS composite material has a higher gravimetric capacitance of 2445.7 F g−1 than pure Ni-P of 1116.6 F g−1 and NCS materials of 1104.3 F g−1 at 1 A g−1. At the same time, Ni-P@NCS electrode yields excellent cycling stability (91.4% capacitance retention after 5000 charge–discharge cycles). An asymmetric supercapacitor (ASC) device assembled from Ni-P@NCS and activated carbon electrodes can deliver a highest energy/power density of 42.8 Wh kg−1/799.8 W kg−1, with 94.3% capacitance retention after 10,000 cycles at 5 A g−1. The improvement of electrochemical performance makes it possible to use it as an electrode material.

Copper Zinc Sulfide (CuZnS) Quantum Dot-Decorated (NiCo)-S/Conductive Carbon Matrix as the Cathode for Li-S Batteries.

Sulfur composites consisting of electrochemical reactive catalysts/conductive materials are investigated for use in lithium–sulfur (Li–S) batteries (LSBs). In this paper, we report the synthesis, physicochemical and electrochemical properties of CuZnS quantum dots (CZSQDs) decorated with nickel–cobalt–sulfide ((NiCo)–S)) mixed with reduced graphene oxide (rGO)/oxidized carbon nanotube (oxdCNT) (rGO/oxdCNT) ((NiCo)–S@rGO/oxdCNT) composites. These composites are for the purpose of being the sulfur host cathode in Li–S batteries. The as-prepared composites showed a porous structure with the CZSQDs being uniformly found on the surface of the rGO/oxdCNT, which had a specific surface area of 26.54 m2/g. Electrochemical studies indicated that the (NiCo)–S@rGO/oxdCNT cells forming the cathode exhibited a maximum capacity of 1154.96 mAhg−1 with the initial discharge at 0.1 C. The smaller size of the CZSQDs (~10 nm) had a positive effect on the CZSQDs@(NiCo)–S@rGO/oxdCNT composites in that they had a higher initial discharge capacity of 1344.18 mAhg−1 at 0.1 C with the Coulombic efficiency being maintained at almost 97.62% during cycling. This latter property is approximately 1.16 times more compared to the absence of the Cu–Zn–S QD loading. This study shows that the CuZnS quantum dots decorated with a (NiCo)–S@rGO/oxdCNT supporting matrix-based sulfur cathode have the potential to improve the performance of future lithium–sulfur batteries.