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Transition metal sulfides (TMSs) are attractive anode materials for lithium-ion batteries (LIBs) due to their cost effectiveness, impressive redox properties, and high specific capacity. Among them, NiCo 2 S 4 stands out with a substantial theoretical capacity of 703 mAh g−1 and a high electronic conductivity of 1.25 × 106 S m−1, making it a strong candidate for LIBs. However, NiCo 2 S 4 experiences volume changes and mechanical stress during long-term cycling, leading to structural degradation and rapid capacity decay, which hinders its application. To address these issues, we have developed dodecahedral NiCo 2 S 4 embedded within a nitrogen-doped porous carbon structure (NiCo 2 S 4 /NC). The optimal NiCo 2 S 4 /NC-300 material exhibits minimum charge transfer resistance, maximum pseudo-capacitive contribution, and exceptional lithium storage performance. At 0.1 A g−1, NiCo 2 S 4 /NC-300 exhibits an initial discharge/charge specific capacity of 1730.1/949.4 mAh g−1 and retains a discharge capacity of 454.4 mAh g−1 after 100 cycles. Even at 0.5 A g−1, it delivers an initial discharge/charge capacity of 1301.1/540.1 mAh g−1 with a capacity retention of 81.2 % after 500 cycles. This study presents significant potential for NiCo 2 S 4 /NC as a high-performance anode material for LIBs, providing new strategies and insights into the mechanisms for enhancing the performance of TMS-based bimetallic anode materials. [ABSTRACT FROM AUTHOR]

A NiCo2S4/N-CDs/RGO ternary composite hydrogel was prepared via a one-step hydrothermal method, utilizing lignin-based nitrogen-doped carbon dots as a bridge connecting NiCo2S4 and graphene. The specific capacitance of NiCo2S4/N-CDs/RGO significantly outperforms that of the GH and NiCo2S4/RGO electrodes, achieving 1050 F g−1. The 3D mesh porous hydrogel structure mitigates NiCo2S4 nanoparticle aggregation, providing a larger specific surface area for enhanced charge storage. The abundant functional groups of N-CDs interact with Ni (II) and Co (III) cations, favoring NiCo2S4 particle synthesis. Additionally, an assembled solid-state asymmetric supercapacitor employing NiCo2S4/N-CDs/RGO as the positive electrode exhibited excellent energy density (68.4 Wh kg−1) and cycle stability (82% capacitance retention after 10,000 constant current charge–discharge cycles). [ABSTRACT FROM AUTHOR]

Establishing Schottky barriers is a key tactic for enhancing the separation of photogenerated charge carriers and improving photocatalytic efficiency. Herein, a self‐assembled metal cocatalyst, NiCo2S4 nanorod, is loaded onto the flower‐like Zn3In2S6 microsphere via a hydrothermal method. Under visible light irradiation, the NiCo2S4/Zn3In2S6 composite material achieves a peak H2 production rate of 3436.72 μmol g−1 h−1 within 6 h, marking a 5.4 times greater increase compared to pristine Zn3In2S6. This outperforms the maximum H2 production rate of Pt/Zn3In2S6‐1% within the same 6‐hour timeframe, which is 3323.05 μmol g−1 h−1. Additionally, the apparent quantum efficiency reaches 7.86% at 420 nm. The outstanding photocatalytic activity stems from the synergistic effects between the visible‐light‐active Zn3In2S6 and the conductive cocatalyst NiCo2S4, facilitating spatial electrical promotion. In particular, the formation of a Schottky junction at the interface of NiCo2S4/Zn3In2S6 enables prompt electron transfer to NiCo2S4 nanorods, preventing backflow and thereby promoting the efficient separation of photogenerated charge carriers. Finally, a plausible reaction mechanism is proposed, drawing from the electrochemical characterization results. Thus, this research provides a new approach for designing metal‐semiconductor photocatalysts that are efficient in photocatalytic H2 production through water splitting. [ABSTRACT FROM AUTHOR]

Until now, crystalline NiCo2S4 and its composites have demonstrated improved performance in supercapacitor applications compared to their oxide analogues due to their relatively higher electrical conductivity and multifaceted redox reaction. However, amorphous phase materials have recently shown promise in electrochemical energy storage systems. This work reports on amorphous NiCo2S4 with the help of urea via the hydrothermal method. It was noted that urea not only aided the amorphous formation but also served as a nitrogen precursor. In comparison, amorphous NiCo2S4 demonstrated a higher nitrogen atom% of 5.9 compared to 4.49 for crystalline NiCo2S4. Furthermore, the amorphous NiCo2S4 electrode exhibited superior electrochemical performance, with a specific capacitance of ~3506 F g−1, which was higher than the cNCS electrode's specific capacitance of ~2185 F g−1 at 2 A g−1. Additionally, aNCS in a two-electrode asymmetric supercapacitor exhibited a specific capacitance and an energy density of ~196 F g−1 and 56 Wh kg−1, respectively. [ABSTRACT FROM AUTHOR]

In this study, a hierarchical heterostructure composed of NiCo 2 S 4 bound to a carbon substrate (NiCo 2 S 4 /CNs) was created. The heterostructure enhances OH− adsorption on Ni and Co active sites and boosts electronic conductivity. Ex-situ XRD reveals mutual transformations of sulfides and hydroxyl oxides during charging/discharging in alkaline solution. DFT confirms that the heterostructure facilitates faster, more efficient redox reactions by enhancing conductivity and OH− adsorption/desorption on active sites. This architectural approach stabilizes charge statuses at the interface, prevents electrode structure collapse, and leads to notable electrochemical performance. [Display omitted] • A hierarchical heterostructure of NiCo 2 S 4 anchored onto a carbon substrate is successfully fabricated. • The innovative design enhances the adsorption of OH− on independent active sites of Ni and Co. • Ex-situ XRD confirms the mutual transformation of sulfides, hydroxides, and hydroxyl oxides. • NiCo 2 S 4 /CNs electrode exhibits excellent specific capacity and high energy density. To improve the low energy density, low conductivity, and poor cycling stability of NiCo 2 S 4 in supercapacitors, a two-step hydrothermal method was used to prepare a composite material of NiCo 2 S 4 and carbon nanosheets (NiCo 2 S 4 /CNs). The electrochemical tests revealed a high specific capacitance of 1576 F g−1 at 1 A/g for the composite, and the NiCo 2 S 4 /CNs//AC asymmetric supercapacitor showed a energy density of 49.7 Wh kg−1 at 818 W kg−1. This study confirmed the phase transformation of NiCo 2 S 4 during charge/discharge in alkaline solution through ex-situ X-ray diffraction (ex-situ XRD) for the first time, and proposed a potential reaction pathway. Moreover, Density Functional Theory (DFT) confirmed that the NiCo 2 S 4 /CNs heterostructure enhances OH− adsorption/desorption on Ni and Co active sites and improves electronic conductivity. In conclusion, this study advances the application of transition metal sulfide in high-performance energy storage. [ABSTRACT FROM AUTHOR]

The rapid migration and separation of photoinduced carriers is a key factor influencing photocatalytic efficiency. Constructing an S-scheme heterojunction is a strategic technique to enhance the separation of photo-generated carriers and boost overall catalytic activity. Herein, a simple physical stirring technique was adopted to successfully fabricate a novel NiCo2S4/CoTiO3 S-scheme heterojunction photocatalyst. Upon exposure to light, the NiCo2S4/CoTiO3-10 specimen demonstrated an outstanding hydrogen evolution rate of 2037.76 µmol·g−1·h−1, exceeding twice the rate observed for the pristine NiCo2S4 (833.72 µmol·g−1·h−1). The experimental outcomes reveal that the incorporation of CoTiO3 significantly enhances the charge separation and transfer within the system. Concurrently, the formation of the S-scheme mechanism facilitates the separation of carriers while maintaining high redox capabilities. This work introduces an innovative approach to forming S-scheme heterojunctions based on bimetallic sulfides, thereby offering new prospects for the efficient utilization of solar energy. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of novel polythiophene (PTh)-based electrocatalysts incorporating NiCo-LDH and NiCo 2 S 4 additives for oxygen evolution reaction (OER) are investigated. NiCo-LDH and NiCo 2 S 4 are synthesized using standard precipitation techniques and characterized using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). PTh-based composite coatings are electrodeposited on steel substrates with varying concentrations of NiCo-LDH and NiCo 2 S 4. The electrochemical performance of the composite coatings is evaluated using linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and stability tests. Results reveal that the incorporation of NiCo-LDH and NiCo 2 S 4 enhances the catalytic activity of PTh-based electrocatalysts for OER, with PTh@NiCo 2 S 4 exhibiting superior performance. The synergistic effects of the additives improve charge transfer kinetics and interfacial conductivity, leading to efficient oxygen generation. The study demonstrates the potential of tailored composite materials for advancing sustainable energy conversion technologies. • Novel PTh-based electrocatalysts incorporating NiCo-LDH and NiCo 2 S 4 enhance OER catalysis. • Synergistic effects improve charge transfer kinetics and interfacial conductivity. • Structural disparities influence catalytic activity, with PTh@NiCo 2 S 4 exhibiting superior performance. • Unexpected findings challenge conventional beliefs on the correlation between C dl and catalytic activity. • Tailored composite materials offer promising avenues for advancing sustainable energy conversion technologies. [ABSTRACT FROM AUTHOR]

Supercapacitors require excellent cycling stability and rate capability for electrodes. The NiCo2S4 spinel structure has caught much attention for its high conductivity and high theoretical specific capacity. However, due to the lack of active sites, it has been restricted in supercapacitors. In this research, the NiCo2S4 nano-material with needle, sheet and porous network morphologies were prepared by the addition of different kinds of surfactants via a simple hydrothermal method. At 1 mA/cm2, capacitance of these NiCo2S4 nanomaterials is measured as 2.09 F/cm2, 3.22 F/cm2, and 4.42 F/cm2, respectively. It was found that the exposure ratio of (111) and (220) crystal facets also has an effect on electrochemical performance, and NiCo2S4 with I (1 1 1) /I (2 2 0) of 3:1 showed better performance. Furthermore, NiCo2S4-PN//AC asymmetrical supercapacitor was assembled with NiCo2S4-PN serving as positive electrode and activated carbon (AC) as negative electrode. At a power density of 7.284 mW/cm2, energy density achieved was 0.625 mWh/cm2. Additionally, capacitance retention rate remained at 79.6% of initial capacitance after 1500 cycles. These outcomes are of great significance for developing more efficient, stable and reliable transition metal sulfide-based supercapacitors. NiCo2S4 nanomaterials with needle, sheet, and porous network morphologies with different exposure ratios of (111)/(220) crystal facets were obtained using a simple two-step hydrothermal method. The type of surfactant plays a key role in the preparation of NiCo2S4 nanomaterials. The cyclic stability and rate capability of NiCo2S4 nanomaterials were improved by increasing the ratio of exposed (111)/(220) crystal facets. [ABSTRACT FROM AUTHOR]

Heterostructures comprising NiCoP and NiCo 2 S 4 (referred to as NCP/NCS) were created by incorporating P and S elements into NiCo 2 O 4 (NCO) micro-nanospheres through phosphorization and hydrothermal sulfurization processes. Selective construction of heterogeneous structures can balance the advantages and disadvantages of each single component and is desirable in HER applications. In alkaline media, the resulting product NCP/NCS had an overpotential of 195 mV at a current density of 10 mA cm−2, which is 337 mV higher than that of the original NCO and significantly better than the products of pure phosphide (NCP) and sulfide (NCS). Its Tafel slope was about 83 mV dec−1 and the HER performance did not decay significantly over 48 h. On the other hand, the formation of heterogeneous interfaces improves the intrinsic catalytic activity of the materials. Density functional theory (DFT) simulations show that the hydrogen adsorption capacity at the heterogeneous interface is optimized due to charge enrichment, which in turn enhances the intrinsic activity. • Micro-nanospheres heterostructures was prepared via gas-liquid diffusion method. • Morphology characterization displays the obvious interface and crystalline surface. • The heterostructures delivers a low overpotential than that of single component. • Density functional theory reveals the heterogeneous interface enhance hydrogen adsorption. [ABSTRACT FROM AUTHOR]

Supercapacitors have emerged as promising electrochemical storage, offering advantages such as rapid charge/discharge rates and environmental friendliness. Nevertheless, their practical applications have been limited due to their lower energy density, and selecting electrode materials with superior energy storage properties remains a critical factor. NiCo2S4 nanomaterials have gained significant attention due to their high theoretical specific capacitance, narrow band gap, and abundant redox reaction active sites, but challenges such as poor cyclic stability and volumetric effects associated with prolonged charging and discharging persist. This paper reviews the recent research progress on NiCo2S4 nanomaterials and comprehensively discusses various strategies to improve the electrochemical performance of NiCo2S4, including morphology control, design and development of NiCo2S4-based composite electrode nanomaterials, doping of different elements, utilization of defect engineering and phase engineering strategies, and exploration of theoretical studies. Finally, the prospects and challenges for the development of NiCo2S4 electrode nanomaterials in the field of supercapacitors are also suggested. [ABSTRACT FROM AUTHOR]

The free-binder NiCo2S4/nickel foam electrode was prepared using a two-step solvothermal method: double-layered hydroxide formation and sulfurization. The effects of cetyltrimethylammonium bromide (CTAB) on the structural, microstructural, and electrochemical properties throughout the sulfurization process were investigated using various characterization techniques. By adding the CTAB surfactant, the sheetlike morphology of NiCo2S4 material was transformed to a fine particular morphology. Using one mmol CTAB surfactant, the specific capacitance of NiCo2S4/nickel foam increased from 578 to 835 C g−1 due to the downsizing of particles, inducing the higher electroactive sites for redox reactions. An asymmetric capacitor of NiCo2S4 as positive and CuCo2S4 as negative electrodes demonstrated an energy density of 23.2 Wh kg−1 at a power density of 5040 W kg−1.

Until now, crystalline NiCo2S4 and its composites have demonstrated improved performance in supercapacitor applications compared to their oxide analogues due to their relatively higher electrical conductivity and multifaceted redox reaction. However, amorphous phase materials have recently shown promise in electrochemical energy storage systems. This work reports on amorphous NiCo2S4 with the help of urea via the hydrothermal method. It was noted that urea not only aided the amorphous formation but also served as a nitrogen precursor. In comparison, amorphous NiCo2S4 demonstrated a higher nitrogen atom% of 5.9 compared to 4.49 for crystalline NiCo2S4. Furthermore, the amorphous NiCo2S4 electrode exhibited superior electrochemical performance, with a specific capacitance of ~3506 F g−1, which was higher than the cNCS electrode’s specific capacitance of ~2185 F g−1 at 2 A g−1. Additionally, aNCS in a two-electrode asymmetric supercapacitor exhibited a specific capacitance and an energy density of ~196 F g−1 and 56 Wh kg−1, respectively.

One‐step colloidal synthetic route was adopted to in‐situ grow monodispersed NiCo2S4 nanoparticles (NPs) on nickel foam (NF) from metallic salts with benzyl disulfide in the media of oleylamine and octadecene. Owing to the favorable dispersion and considerable redox activity of NiCo2S4 along with tight and binder‐free connection with NF, the obtained battery‐type supercapacitor delivered a specific capacitance of 1790.8 F g−1 at 1 A g−1 via a three‐electrode system. Simultaneously, it just degraded 40 % at 20 A g−1 and maintained 86.8 % of initial specific capacitance (C0) after 2000 cyclic trials at 10 A g−1. When the NiCo2S4 NPs were assembled with active carbon (AC) forming an asymmetric capacitor device of NiCo2S4 NPs//AC, it delivered an energy density (E) of 48.7 W h kg−1 at a power density (P) of 161.1 W kg−1, and kept 21.9 W h kg−1 at a high P of 8.05 kW kg−1. Meanwhile, the capacitor manifested preeminent cycling life (C=94.5 % C0 after 5000 cyclic trials) at 5 A g−1. The in‐situ grown NiCo2S4 NPs on NF without any binder exhibited high performance in energy storage, providing a feasible way to improve the electrochemical performance of the electrode materials. [ABSTRACT FROM AUTHOR]

The Co-based organic skeleton was combined with graphene oxide (GO) as a precursor, Ni2+ hydrolysis etching was introduced, and finally, NiCo-LDH/GO was obtained. The final composite electrode material NiCo2S4/rGO was obtained by high-temperature vulcanization. The introduction of MOFs and rGO significantly increased the specific surface area of the material and made it have excellent electrochemical properties. The specific capacitance of the composite NiCo2S4/20rGO reaches an astonishing 272.5 mAh g−1 when the current density is 1 A g−1. In addition, at a large current of 10 A g−1, the specific capacitance of the material can also reach 139.5 mAh g−1, and after a long cycle of 5000 cycles at such a current density, the capacity remains at the original 73.2%. With NiCo2S4/20rGO electrode material as the positive electrode and activated carbon as the negative electrode, the hybrid supercapacitor is assembled. At an energy density of 56.9 Wh kg−1, its power density reaches an excellent 799 W kg−1, and it still has a capacity retention rate of 74% at a current density of 10 A g−1. The excellent properties of composites demonstrated in this work open up new possibilities for high-quality energy storage devices. [ABSTRACT FROM AUTHOR]

In the present study, a facile and simple hydrothermal technique was employed for the preparation of reduced graphene oxide (rGO) incorporated NiCo 2 S 4 and analyzed the hydrogen evolution reaction (HER) activity in alkaline media. The face centered cubic crystal structure is confirmed from the X-ray diffraction analysis and hexagonal cage like structure of NiCo 2 S 4 was visualized by FESEM analysis. With the increased number of facets in hexagonal cage structure, the electrochemical-active surface area (ECSA) gets increased, and the HER performance gets increased for bare NiCo 2 S 4. The additional ECSA is caused by the existence of rGO in the case of ternary nanocomposite (rGO-NiCo 2 S 4). The obtained small over potential (370 mV) and small Tafel slope (139 mV/dec) proves the excellent HER activity of rGO-NiCo 2 S 4 nanocomposite. The optimized rGO-NiCo 2 S 4 as excellent HER electrocatalyst provides a highly stable polarization curve up to 10 h and it can be more useful to replace the high-cost platinum noble electrocatalyst. [Display omitted] • A simple one step hydrothermal method was adopted to prepare pure and rGO incorporated NiCo 2 S 4. • A hexagonal cage like structure provides the large number of facet as well as high electrochemical-active surface area. • A small over potential of 370 mV and a small Tafel slope of 139 mV/dec was realized at 10 mA/cm2. [ABSTRACT FROM AUTHOR]

The excessive utilization of fossil fuels has resulted in an energy crisis. The implementation of a heterojunction for photocatalytic hydrogen evolution represents a promising solution to the current energy predicament. In this work, a 0D/2D S‐scheme graphdiyne/NiCo2S4 (GDY/NiCo2S4) heterojunction is constructed by semi‐crystalline NiCo2S4 nanoparticles (NPs) immobilized on the surface of GDY nanosheets through hydrothermal method. Atomic force microscopy (AFM) demonstrated the thickness of GDY nanosheets is 2.8 nm. The unique 2D laminar structure and porous structure of GDY ensures a tight bond with NiCo2S4 NPs. The maximum rate of photocatalytic hydrogen production is 6682.6 µmol h−1 g−1 over 15% GDY/NiCo2S4, which is much higher than GDY and NiCo2S4. The outstanding photocatalytic hydrogen production performance can be attributed to the S‐scheme GDY/NiCo2S4 heterostructure. The fluorescence results demonstrated that the incorporation of GDY significantly enhanced the efficiency of photoelectron‐hole transfer and prolonged the electron lifetime. The S‐scheme photogenerated charge transfer mechanism is verified through in situ irradiated X‐ray photoelectron spectroscopy. The present study introduces innovative concepts for the design of an S‐scheme heterojunction based on graphdiyne, aiming to enhance photocatalytic hydrogen production. [ABSTRACT FROM AUTHOR]

The construction of electrode materials with high rate and excellent cycling stability is the key to supercapacitors. Due to their remarkable high conductivity and great electrochemical activity, transition bimetallic sulfides are extremely appealing electrode materials for supercapacitors, but their synthesis is still challenging. In this study, a NiCo bimetallic sulfide (NiCo2S4) microspheres with porous structure were prepared via direct vulcanization of NiCo‐EG complexes followed by a thermal treatment, which were pre‐synthesized via coordination of ethylene glycol (EG) with transition metal ions (Ni2+, Co2+) under hydrothermal condition. Some experimental parameters were investigated, including the control of NiCo2S4 microspheres produced by the ratio of precursor NiCo‐EG to different masses of sulfur sources, which in turn affects the electrochemical properties. When applied as electrode for supercapacitor, the NiCo2S4 microspheres obtained under optimal condition delivered a high capacitance (1386 F g−1 at 1 A g−1), excellent rate capability (845 F g−1 at 10 A g−1) and stable cycling performance (80.05% after 5000 cycles at 10 A/g). Furthermore, for checking the practicality of the produced NiCo2S4 microspheres, an asymmetric supercapacitor device was built using activated carbon (AC) as the negative electrode and NiCo2S4 microspheres as the positive electrode. The assembled NiCo2S4//AC cell had a power density of 799.9 W kg−1 and an energy density of 30.5 Wh kg−1, confirming that the structurally optimized NiCo2S4 porous nanomicrospheres have excellent electrochemical properties and have a wide range of application prospects. [ABSTRACT FROM AUTHOR]

Binary transition metal sulfides have garnered widespread concentration result from their superior electrical conductivity and outstanding capacitance. However, their poor cycling stability hinders their applications in energy storage devices. The objective of this study is to devise and prepare graphene and NiCo2S4 composite (NiCo2S4@graphene) using a simple one-step hydrothermal modality. Graphene is used as a conductive substrate, and NiCo2S4 nanoparticles are formed in situ and homogeneously anchored on graphene nanosheets through C-S-C covalent bonds. For example, the NiCo2S4@graphene composite has a high specific capacitance of 918.0 C g−1 at a current density of 1 A g−1 and enhanced cycling stability (90.1% after 6000 cycles). In addition, the asymmetric supercapacitor was fabricated with NiCo2S4@graphene as the positive electrode and graphene (GR) as the negative electrode, and the device provided a maximum energy density of 49.8 Wh kg−1 at a power density of 845.3 Wh kg−1. Besides, the capacitance retention rate was as high as 92.0% after 1000 cycles. The superior electrochemical properties of the NiCo2S4@graphene material verified its huge potential for realistic applications. [ABSTRACT FROM AUTHOR]

Hexavalent chromium (Cr(VI)) compounds are considered to be occupational carcinogens, which can be transferred from the environment to the human body and pose a significant threat to human health. It is particularly urgent to explore a more efficient catalyst for removing Cr(VI) to comply with discharge standards. The addition of CNTs enables the separation and transfer of photogenerated charges. Thus, we synthesized a range of NiCo2S4 hybrid materials with different multi-walled carbon nanotube (MWCNTs) contents using a two-step hydrothermal method. The composites had significant advantages compared to pure NiCo2S4, such as an enhanced visible light absorption, increased specific surface area, high electron–hole pair separation, and fast electron transport. Thus, MWCNT addition enabled efficient photocatalytic performances in terms of reducing hexavalent chromium (Cr(VI)). Among all the composite samples, the MWCNT/NiCo2S4 with 0.050 g of MWCNTs achieved the highest efficiency in reducing Cr(VI) under light irradiation, which showed a removal rate close to 100% within 40 min. Such CNT-based composite photocatalysts could be used to reduce the highly toxic Cr(VI) in environmental applications. [ABSTRACT FROM AUTHOR]

It is an effective way to prepare multi‐dimensional and multicomponent electrode material to enhance the capacitance of supercapacitors. The multi‐dimensional micro CuCo2O4/nano NiCo2S4 structure was synthesized by wrapping NiCo2S4 nanosheets on urchin‐like CuCo2O4 microspheres on the surface of nickel foam by two‐step hydrothermal method, and then electrochemical deposition. Due to the synergistic effect of the one‐dimensional CuCo2O4 and the two‐dimensional NiCo2S4 composite and its especial three‐dimensional core‐shell structure, the composite electrode shows excellent supercapacitor performance. The CuCo2O4@NiCo2S4 with three electrodeposition cycles (CCO@NCS‐3) exhibits a high specific capacitance of 2283.3 F g−1 at 1 A g−1, good rate capability (79.9 % capacitance retention at 10 A g−1) and cycling stability of 84.0 % over 3000 cycles. All these results indicate that the concepts of multi‐dimensional and multi‐component integration provide a general approach for the development of high‐performance materials. [ABSTRACT FROM AUTHOR]

In this paper, NiCo2S4 nanoelectrode materials were prepared by a two-step hydrothermal method. Physical and morphological characterization and electrochemical testing revealed that the prepared NiCo2S4 has a sea urchin-like layered three-dimensional network structure, which can fully increase the contact area with the electrolyte, increase the active sites and improve the electrochemical performance. The specific capacitance of the prepared NiCo2S4 nanomaterials reached 717.32 F/g. The cyclic voltammetry test curve as well as galvanostatic charge-discharge (GCD) test curve have perfect symmetry, good material reversibility. Electrochemical impedance spectroscopy (EIS) indicates materials with low impedance. The specific capacitance remained 76.8% after 3000 cycles and the electrochemical stability was good. NiCo2S4 electrode material has excellent electrochemical properties and has a promising application in supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

Transition bimetallic sulfides exhibit high capacity and outstanding chemical performance in supercapacitors due to their abundant electrochemical active sites and conductivity. In this paper, NiCo2S4 with an obvious core–shell nanosphere structure was prepared by adjusting the amount of thiourea by a one-step hydrothermal method. This special core–shell structure of the NiCo2S4 material can provide more active sites to make it exhibit better electrochemical performance. The electrochemical performance test results show that the NiCo2S4 material prepared with 16 mmol thiourea can reach 1224.0 F g−1 at the current density of 1 A g−1, and maintain 88.74% capacitance even at 10 A g−1. In addition, with the NiCo2S4 as the positive electrode and activated carbon as the negative electrode, the supercapacitor (NiCoS3//AC) can achieve the specific capacitance of 121.9 F g−1 when the current density is 1 A g−1. At a power density of 614 W kg−1, the energy density reaches 38.1 Wh kg−1. The results show that the microstructure of the material is closely related to the amount of thiourea added, and that only appropriate degree of vulcanization is helpful for the formation of core–shell-like NiCo2S4 with excellent performance. NiCo2S4 material with its unique core–shell structure makes it exhibit a better energy storage performance. [ABSTRACT FROM AUTHOR]

The rational fabrication of composite structures made of mixed components has shown great potential for boosting the energy density of supercapacitors. Herein, an elaborate hierarchical MOF-derived NiCo2S4@Mo-doped Co-LDH arrays hybrid electrode was fabricated through a step-wise method. By leveraging the synergistic effects of a uniform array of NiCo2S4 nanowires as the core and an MOF-derived porous shell, the NiCo2S4@Mo-doped Co-LDH hybrid electrode demonstrates an exceptional specific capacitance of 3049.3 F g−1 at 1 A g−1. Even at a higher current density of 20 A g−1, the capacitance remains high at 2458.8 F g−1. Moreover, the electrode exhibits remarkable cycling stability, with 91% of the initial capacitance maintained after 10,000 cycles at 10 A g−1. Additionally, the as-fabricated asymmetric supercapacitor (ASC) based on the NiCo2S4@Mo-doped Co-LDH electrode achieves an impressive energy density of 97.5 Wh kg−1 at a power density of 835.6 W kg−1. These findings provide a promising approach for the development of hybrid-structured electrodes, enabling the realization of high-energy-density asymmetric supercapacitors. [ABSTRACT FROM AUTHOR]

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Converting biowaste into carbon-based supercapacitor materials provides a new solution for high-performance and environmentally friendly energy storage applications. Herein, the hierarchical PAC/NiCo2S4 composite structure was fabricated through the combination of activation and sulfuration treatments. The PAC/NiCo2S4 electrode garnered advantages from its hierarchical structure and hollow architecture, resulting in a notable specific capacitance (1217.2 F g−1 at 1.25 A g−1) and superior cycling stability. Moreover, a novel all-solid-state asymmetric supercapacitor (ASC) was successfully constructed, utilizing PAC/NiCo2S4 as the cathode and PAC as the anode. The resultant device exhibited exceptionally high energy (49.7 Wh kg−1) and power density (4785.5 W kg−1), indicating the potential of this biomass-derived, hierarchical PAC/NiCo2S4 composite structure for employment in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

In this study, hierarchical NiCo2S4 nanostructures have been successfully prepared on Ni foam support using a simple and economical two-step hydrothermal process. The hierarchical NiCo2S4 nanostructure comprises rod-like NiCo2S4 cores enveloped by a thin nanoribbon shell. When the NiCo2S4/Ni foam was employed as an electrode for methanol electrooxidation directly, a current density of 194 mA mg−1 was achieved at 0.60 V. The prepared NiCo2S4/Ni foam demonstrates high electrocatalytic activity and durability in alkaline environments for the methanol oxidation reaction. After 1000 cyclic voltammetry cycles in the alkaline electrolyte, the current density of the hierarchical NiCo2S4 decreased to 72.2% of its initial value, with the loss of catalytic activity during the cycling test attributed to their surface oxidation. These findings suggest the NiCo2S4 sample as a non-noble metal electrocatalyst holds great potential for direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

Great efforts have been made to increase the hydrogen evolution reaction (HER) of electrocatalysts by porous structure, dopants and heterostructure engineering. However, the HER catalytic properties have entered a bottleneck stage only depend on these methods. As a contact-free field to enhance the electrochemical reactions, magnetic field has attracted extensive attention recently. In this study, the Ni-MOF derived NiCo 2 S 4 nanostructures are prepared via a facile hydrothermal preparation. By applying an external magnetic field, the NiCo 2 S 4 delivers much better HER performance than in normal condition (without magnetic field). An overpotentials of 104 mV and a Tafel slope of 54 mV·dec−1 are attained at 10 mA cm−2 in 1 M KOH under a moderated magnetic field of 100 mT, showing that the external magnetic field taking a positive effect to enhance the kinetic process of the NiCo 2 S 4 nanostructure. The presented results can offer an alternative strategy for further improving the HER property of electrocatalysis by utilizing an external magnetic field. [ABSTRACT FROM AUTHOR]

Three different compositions of NiCo2S4 (NCS) materials were prepared using three solvents, named NCS HTDI (hydrothermal in DI water), NCS STEG (solvothermal in ethylene glycol), and a novel carbon‐encapsulated NCS STFA (solvothermal in formamide). The structural and morphological properties of the prepared NCS HTDI, NCS STEG, and NCS HTDI materials were analyzed using various physical characterization techniques. As prepared, NCS materials were tested as an electrode for supercapacitor (SC) application using a 3‐electrode system in a basic electrolyte (3 M KOH). NCS HTDI exhibits a specific capacitance of 2536 F g−1, NCS STEG shows 1355 F g−1, and NCS STFA shows 1178 F g−1 at an input current density of 1 A g−1. The SBN‐PSC material is utilized as a counter electrode in the NCS STFA || SBN‐PSC‐based asymmetric SC device. The device exhibits exceptionally superior electrochemical performance with a specific capacitance of 172 F g−1 at 10 A g−1 input current density and 97% capacity retention after 5000 cycles in a voltage window of 1.6 V. The results confirm the superiority of NCS STFA||SBN‐PSC deviceas an excellent high‐energy and high‐power SC. [ABSTRACT FROM AUTHOR]

Metal sulfides (MS) and mixed metal sulfides (MTMS) have been considered potential candidates over their metal oxide/mixed metal oxide counterparts in recent years. Herein, one MTMS, i.e., NiCo2S4, was combined with 2D MS MoS2 through a single-step solvothermal process with different morphologies (sheet-like and rod-like) for supercapacitor applications. The resulting electrode exhibited excellent coulombic efficiency, high specific capacitance, superior energy density, and, most importantly, ultra-high cycling stability. In particular, the electrode delivered a capacitance of 2594 F g−1 at 0.8 A g−1 after 45,000 charge/discharge cycles with a remarkable stability of 192%. Moreover, the corresponding hybrid supercapacitor device displayed an impressive coulombic efficiency of 123% after 20,000 cycles and 118% after 45,000 cycles. In addition, the device also exhibited a decent energy density of 31.9 Wh kg−1 and good cycling stability of 102% over 15,000 cycles. [ABSTRACT FROM AUTHOR]

The hydrothermal preparation of NiCo 2 S 4 /ZnIn 2 S 4 photocatalysts with different mass ratios is studied. Ni-cobalt bimetallic sulfide nanosheets are grown on zinc-indium bimetallic sulfide to form a compact heterojunction. First, both NiCo 2 S 4 and ZnIn 2 S 4 exhibit N-type semiconductor characteristics, a heterojunction formed by both can reduce the surface reaction energy barrier and use its synergy, strengthening the charge self-diffusion between the two semiconductors, it means the formation of a strong electric field. From the electron transfer path and band structure, NiCo 2 S 4 /ZnIn 2 S 4 has S-scheme heterojunction characteristics. NiCo 2 S 4 is a reducing photocatalyst (RP), and ZnIn 2 S 4 is an oxidative photocatalyst (OP). Under the action of built-in electric field (BIEF), strong photogenic electrons and holes exist in CB of RP (NiCo 2 S 4) and VB of OP (ZnIn 2 S 4). Thus, the overall redox capacity of the NiCo 2 S 4 /ZnIn 2 S 4 heterojunction is enhanced. Using visible light, the composite material can be used for photocatalytic hydrogen production. It is further shown that the composite material has a good effect in photocatalytic hydrogen production under the sensitizer eosin Y (EY) system. The optimal hydrogen production is about 221.75 μmol when the mass ratios of NiCo 2 S 4 /ZnIn 2 S 4 is 20%, and the photocatalytic activity of the composite is about 47 times that of ZnIn 2 S 4. Notably, the stability of the composites is the better. A reasonable photo-catalytic mechanism is proposed based on the band gap and photoelectrochemical properties of heterojunction. • Nanosheets NiCo 2 S 4 innovatively decorated on globular structure ZnIn 2 S 4 form S-scheme heterojunction. • The morphology of nanosheets NiCo 2 S 4 is innovative in the field of NiCo 2 S 4 /ZnIn 2 S 4 photocatalysis. • The heterojunction can short transfer route to promote electron efficient transport. • Dispersion of NiCo 2 S 4 on ZnIn 2 S 4 is important for the heterojunction HER activity and stability. [ABSTRACT FROM AUTHOR]

Throughout the evolution of supercapacitors, binary transition metal sulfides have been extensively researched for their potential as electrode materials. Here, NSAC-NiCo 2 S 4 composites are prepared by in-situ growing NiCo 2 S 4 nanosphere on N, S co-doped activated carbon (NSAC) using a simple solvothermal way. The optimized NSAC-NiCo 2 S 4 composite inherits the NSAC's huge specific surface area, hierarchical porous structure, and high electronic conductivity, along with the excellent capacitive performance of NiCo 2 S 4. This combination effectively reduces contact resistance and enhances the transfer rate. Calculations based on the density functional theory further indicate that synergistic interactions between NiCo 2 S 4 and NSAC in the composite lower the OH− adsorption energy and release more active electrons. This enhancement facilitates the electrochemical reaction kinetics in supercapacitors. The as-fabricated NSAC-NiCo 2 S 4 -2 electrode possesses a remarkable specific capacitance (762 F g−1) at 1 A g−1 and exhibits a minimal charge transfer resistance (0.28 Ω). Furthermore, an asymmetric supercapacitor (positive electrode: NSAC-NiCo 2 S 4 -2; negative electrode: NSAC), achieves an impressive energy density of 36.6 Wh kg−1 at a power density of 400.0 W kg−1. It also exhibits exceptional cycling stability, maintaining 86.2 % of its capacity after 10,000 cycles. These excellent results further highlight the great potential of the obtained NSAC-NiCo 2 S 4 composites for use in energy reserve systems. [Display omitted] • Spherical-like structure NiCo 2 S 4 in-situ growing on N, S co-doped activated carbon (NSAC). • NSAC-NiCo 2 S 4 -2 composites have fast electron transport and high specific capacitance performance. • NSAC-NiCo 2 S 4 -2//NSAC device exhibits high energy density and excellent cycling stability. [ABSTRACT FROM AUTHOR]

Electrode materials with outstanding stability and electrochemical activity are ideal for high-performance supercapacitors. Herein, we developed a simple two-step method for fabricating NiCo 2 S 4 /EG/Ti 3 C 2 T x nanocomposites with a sheet(2D)-rod(1D)-sheet(2D) structure. The NiCo 2 S 4 rods were embedded into the expanded graphite (EG) sheets via an in-situ hydrothermal method, then the Ti 3 C 2 T x sheets were assembled with NiCo 2 S 4 /EG by an electrostatic self-assembly method. The obtained NiCo 2 S 4 /EG/Ti 3 C 2 T x nanocomposites exhibited a synergistic effect among the components. The addition of EG inhibited the volumetric effect of NiCo 2 S 4 during charging and discharging processes, while the high conductivity of Ti 3 C 2 T x promoted charges transfer. The rod-like structure of NiCo 2 S 4 effectively inhibited the self-stacking of Ti 3 C 2 T x sheets. Consequently, the optimized composite exhibited an excellent specific capacitance of 1837.9 F·g−1 at a current density of 1 A·g−1. Additionally, the composite electrode exhibited a capacitance retention of 73.5 % during 10,000 charging-discharging cycles at a current density of 20 A·g−1. [ABSTRACT FROM AUTHOR]

• The simple preparation of ZnCo 2 S 4 with double hollow morphology by two-part hydrothermal method has excellent performance. • The synthesis of ZnCo 2 S 4 /Ti 3 C 2 T x and ZnCo 2 P 4 /Ti 3 C 2 T x via the electrostatic self-assembly method was successfully accomplished, and their subsequent assembly with AC led to the formation of LIC. • The specific capacitance of ZnCo 2 S 4 /Ti 3 C 2 T x is 1563 C·g−1, which exceeds that of ZnCo 2 P 4 /Ti 3 C 2 T x (936 C·g−1) and pure Ti 3 C 2 T x (289 C·g−1). • Lithium-ion capacitors based on ZnCo 2 S 4 /Ti 3 C 2 T x provide an energy density of 136.25 Wh kg−1 at a specific power of 337.10 W kg−1. Lithium-ion capacitors (LICs) represent a novel energy storage solution, merging the high energy storage capacity of lithium-ion batteries with the adequate power density of supercapacitors. However, the electrochemical performance of lithium-ion capacitors is notably constrained by the inherent imbalance between the charge storage mechanisms and electrochemical reaction dynamics of their anodes and cathodes. In this study, a dual-shell hollow structured ZnCo 2 S 4 was prepared via a two-step hydrothermal method and compared with spherical ZnCo 2 P 4 prepared by calcination. Subsequently, they were respectively anchored onto two-dimensional Ti 3 C 2 T x nanosheets, which possess abundant surface functional groups, through electrostatic adsorption, forming layered semi-encapsulated framework structures. The introduction of MXene significantly enhances the conductivity of the material, restricts the expansion of ZnCo 2 S 4 and ZnCo 2 P 4 during the Li+ insertion/extraction process, and inhibits their aggregation. Under a three-electrode configuration, ZnCo 2 S 4 /Ti 3 C 2 T x exhibits excellent rate performance (1004 C·g−1 at 10 A·g−1) and cycling stability (95 % capacity retention after 5000 cycles at 2 A·g−1). The discharge capacity of the ZnCo 2 S 4 /Ti 3 C 2 T x LIB is up to 1360 mAh·g−1 at 0.1 A·g−1, and the discharge capacity of the ZnCo 2 P 4 /Ti 3 C 2 T x LIB is 1121 mAh·g−1 at 0.1 A·g−1. As an anode material for LIC, ZnCo 2 S 4 /Ti 3 C 2 T x demonstrates excellent specific capacitance and rate performance (105 F·g−1 at 0.5 A·g−1). At a power density of 337.10 W·kg−1, ZnCo 2 S 4 /Ti 3 C 2 T x //AC LIC exhibits a significant energy density of 136.25 Wh·kg−1. At a current density of 2 A·g−1, ZnCo 2 S 4 /Ti 3 C 2 T x //AC LIC retains 89 % of its capacity after 5000 charge-discharge cycles, demonstrating excellent stability for practical applications. ZnCo 2 P 4 /Ti 3 C 2 T x //AC LIC exhibits an energy density of 45.20 Wh·kg−1 at a power density of 623.07 W·kg−1, and after 5000 cycles at 2 A·g−1, its capacity retention rate reaches 80 %. These findings suggest that ZnCo 2 S 4 /Ti 3 C 2 T x and ZnCo 2 P 4 /Ti 3 C 2 T x composites are promising anode materials for LICs. [ABSTRACT FROM AUTHOR]

Developing oxygen evolution reaction (OER) electrocatalysts with high efficiency, low cost and good stability for water splitting is significant to relieve the energy crisis and environmental pollution. Herein, NiCo alloy (NC) nanoparticles (NPs) embedded N-doped carbon fibers (NCF) were prepared by electrospinning and carbonization. The surfaces of the NC@NCF were anchored with nanocrystalline NiCo 2 S 4 (NCS) in a following solvothermal process to form NCS-NC@NCF composite. Synergistic effect of the alloy (NC) and the semiconductor (NCS) was successfully stimulated, i.e., rapid charge separation and transfer was achieved during the OER process. In addition, the carbon fibers substrate is beneficial for good dispersion of the NC and NCS NPs as well as the conductivity improvement of the as-prepared NCS-NC@NCF catalyst. The prepared NCS-NC@NCF catalyst electrode owns good OER performances of a low overpotential of 291 mV, 342 mV and 376 mV to respectively deliver current densities of 10 mA cm−2, 50 mA cm−2 and 100 mA cm−2, which are respectively 19 mV, 82 mV and 116 mV lower than those of the RuO 2 electrode (310 mV, 424 mV and 492 mV), indicating the great potential of the catalyst in water splitting. Moreover, good durability of current density retention of 90.7 % is observed after 60 h of continuous OER polarization for the catalyst. Additionally, a two-electrode system composed of commercial Pt/C and the NCS-NC@NCF electrodes only needs a driven voltage of 1.51 V to afford 10 mA cm−2 for water splitting, which is superior to that (1.69 V) of the Pt/C||RuO 2 system. [Display omitted] • Needle-liked NiCo 2 S 4 particles adhered on the NiCo alloy embedded N-doped 3D carbon fibers were prepared as OER catalyst. • The catalyst presents a smaller overpotential of 342 mV and 376 mV at 50 mA cm−2 and 100 mA cm−2 for OER than those of RuO 2. • The water splitting device assembled with the as-prepared catalyst exhibits a small voltage of 1.51 V to obtain 10 mA cm−2. [ABSTRACT FROM AUTHOR]

Effects of CTAB additions on the microstructural and electrochemical properties of NiCo 2 O 4 /nickel foam electrode. [Display omitted] • Free-binder NiCo 2 S 4 /NF electrode was prepared using various amounts of CTAB surfactant during sulfurization step. • The large sheet-like morphology was evolved to the fine particular one by adding CTAB surfactant. • A high specific capacitance of 835 Cg−1 was obtained using 1 mmol CTAB. • The asymmetric NiCo 2 S 4 //CuCo 2 S 4 capacitor showed a high energy density of 23.2 Whkg−1. The free-binder NiCo 2 S 4 /nickel foam electrode was prepared using a two-step solvothermal method: double-layered hydroxide formation and sulfurization. The effects of cetyltrimethylammonium bromide (CTAB) on the structural, microstructural, and electrochemical properties throughout the sulfurization process were investigated using various characterization techniques. By adding the CTAB surfactant, the sheetlike morphology of NiCo 2 S 4 material was transformed to a fine particular morphology. Using one mmol CTAB surfactant, the specific capacitance of NiCo 2 S 4 /nickel foam increased from 578 to 835 C g−1 due to the downsizing of particles, inducing the higher electroactive sites for redox reactions. An asymmetric capacitor of NiCo 2 S 4 as positive and CuCo 2 S 4 as negative electrodes demonstrated an energy density of 23.2 Wh kg−1 at a power density of 5040 W kg−1. [ABSTRACT FROM AUTHOR]

Developing battery-type electrode materials with diverse core-shell heterostructures is the most crucial aspect in fabricating hybrid supercapacitors with high energy density and cycling stability. Additionally, mixed-metal sulfides are highly regarded due to their favorable theoretical specific capacity and conductivity. Here, we have devised hierarchical CoGa 2 O 4 −S@NiCo 2 S 4 core−shell heterostructures, featuring urchin−like and hexagonal morphologies. The needle−like shell significantly promotes the contact area with the electrolyte, facilitating OH− penetration to the core structure. This elevation improves both the diffusion−controlled process and reaction kinetics, thereby enhancing electrode material utilization and redox capability. Therefore, the optimized CoGa 2 O 4 −S@NiCo 2 S 4 exhibits a specific capacity of 959.0 C·g−1 (capacitance of 2131.1 F·g−1) at 1 A·g−1. The assembled CoGa 2 O 4 −S@NiCo 2 S 4 //AC hybrid supercapacitor delivers an energy density of 41.17 Wh kg−1 at 850 W kg−1, with a capacity retention rate of 93.60 % after 10,000 cycles. This study provides a novel approach to enhance the electrochemical performance of supercapacitors by optimizing reaction kinetics. • Urchin-like and hexagonal core−shell heterostructures were successfully synthesized. • The needle-like NiCo 2 S 4 facilitates the permeation of OH− into the CGOS core layer. • The diffusion−controlled processes of the composite electrode have been enhanced. [ABSTRACT FROM AUTHOR]

An efficient approach is developed to fabricate hybrid nanomaterials by anchoring in situ NiCo 2 S 4 components on hollow double-layered carbon nanospheres (DCs). NiCo(CO 3)(OH) 2 is deposited on DCs and then reacted with S ions to create NiCo 2 S 4 phase. Because of the homogeneous distribution of nanoparticles and well-developed interface, samples reveal excellent electrochemical activity. The compositions of NiCo 2 S 4 /hollow DCs (denoted as DCs-x-y, x and y are the molar ratios of Ni and Co in precursors) are adjusted to test the growth kinetics and morphology evolution. Under optimized conditions, the capabilities of composite sample DCs-0.20–0.30 outperform DCs and NiCo 2 S 4 alone, which is ascribed to the high specific surface area and the existence of monodispersed hollow carbon spheres improving the distribution of NiCo 2 S 4 and the overall conductivity to increase active sites. Especially, the optimized sample DCs-0.20–0.30 exhibits high performances and stability for enhanced hydrogen evolution reaction (HER) in both acidic and alkaline conditions and oxidation evolution reaction (OER) in alkaline electrolyte. Furthermore, using DCs-0.20–0.30 sample as both the cathode and anode in the alkaline electrolyzer, the current density of 10 and 100 mA cm−2 at 1.736 and 2.171 V are obtained. The sample also displays excellent durability for 20 h at 10 mA cm−2. • NiCo 2 S 4 nanoparticles were anchored homogeneously on hollow double-layered carbon nanospheres (DCs). • The nanoparticles and well-developed interface make samples with excellentelectrochemical activity. • NiCo 2 S 4 /hollow DCs revealed enhanced HER in acidic and alkaline conditions as well as OER in alkaline electrolyte. [ABSTRACT FROM AUTHOR]

Manganese dioxide (MnO 2) and NiFe-layered double hydroxide (LDH) nanosheets were deposited on bimetallic metal sulfide (NiCo 2 S 4) by hydrothermal reaction method, and MnO 2 /NiFe-LDH@NiCo 2 S 4 was applied as cathode catalyst in microbial fuel cell (MFC). The combination of lamellar MnO 2 with NiFe-LDH coated on NiCo 2 S 4 achieved a typical core-double shell structure. The unique core-double shell structure created a rapid pathway for electron transport and reduced interfacial impedance. The MnO 2 /NiFe-LDH@NiCo 2 S 4 -MFC exhibited the maximum power density of 80 mW/m2, approximately 2.16 times that of the MnO 2 -MFC (37 mW/m2). Additionally, the maximum voltage was around 200 mV, with good stability maintained for approximately 10 d. The material exhibited excellent electrochemical properties and possessed great potential for application as cathode catalysts of MFC. [Display omitted] • MnO 2 /NiFe-LDH@NiCo 2 S 4 was prepared by simple hydrothermal method. • Maximum power density of MnO 2 /NiFe-LDH@NiCo 2 S 4 -MFC was 80 mW/m2. • Modification of MnO 2 , NiFe-LDH and NiCo 2 S 4 improved ORR ability. [ABSTRACT FROM AUTHOR]

Hexavalent chromium (Cr(VI)) compounds are considered to be occupational carcinogens, which can be transferred from the environment to the human body and pose a significant threat to human health. It is particularly urgent to explore a more efficient catalyst for removing Cr(VI) to comply with discharge standards. The addition of CNTs enables the separation and transfer of photogenerated charges. Thus, we synthesized a range of NiCo2S4 hybrid materials with different multi-walled carbon nanotube (MWCNTs) contents using a two-step hydrothermal method. The composites had significant advantages compared to pure NiCo2S4, such as an enhanced visible light absorption, increased specific surface area, high electron–hole pair separation, and fast electron transport. Thus, MWCNT addition enabled efficient photocatalytic performances in terms of reducing hexavalent chromium (Cr(VI)). Among all the composite samples, the MWCNT/NiCo2S4 with 0.050 g of MWCNTs achieved the highest efficiency in reducing Cr(VI) under light irradiation, which showed a removal rate close to 100% within 40 min. Such CNT-based composite photocatalysts could be used to reduce the highly toxic Cr(VI) in environmental applications.

Coaxial structure fiber supercapacitor has received extensive attention due to its good integrity and excellent electrochemical performance. However, the complicated preparation process, precise technical requirements and low yield restricted its development. A coaxial structure fiber supercapacitor with an operating voltage of 1.6 V was prepared by braiding a core yarn of AC@CNT (AC is activated carbon and CNT is carbon nanotubes) negtive electrode and a braided yarn of NiCo2S4@CNT positive electrode. This braiding strategy is simple and efficient, and the fabricated fiber supercapacitor has a high energy density (energy density of 35.1 mW·h/cm³ at power density of 233.2 mW/cm³) and outstanding flexibility (no obvious change after bending 1 000 cycles in cyclic voltammetry curve). The braided fiber supercapacitors show excellent integrability. The output voltage of 2-unit tandem fiber supercapacitors reaches 3.2 V, which can light up the "DHU 70" pattern composed of 65 LEDs. This work provides a new strategy for the preparation of coaxial structure fiber supercapacitors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Synthesize NiCo2S4 and its application to find out electrochemical performance of anionic reaction in nano chemistry. Because of binary transition metal sulfide NiCo2S4 are prepared by using a Chemical precipitation to find out anionic movement within the compound. But the electrochemical were used as a conductive network for the NiCo2S4 hexagonal nano plates. Hence hexagonal nano plates have an average crystalline size of the particles 38.34nm and 20.06nm. Nickel and cobalt sulfides with various stoichiometries have been synthesized from Ni(CH3COO)2.2H2O, CoCl2.6H2O with different sulfur precursors using as a direct method. The morphological composite were characterized by (scanning electron microscopy) SEM, XRD (X-ray diffraction), EDX, UV-visible, FTIR spectrum and optical band-gap energy were evaluated. Optical band-gap energies in the range 4.7 eV-5.1 eV were observed. [ABSTRACT FROM AUTHOR]

In this work, NiCo2S4–graphene hybrids (NCS@G) with high electrochemical performance were prepared using a hydrothermal method. The response surface methodology (RSM), along with a central composite design (CCD), was used to investigate the effect of independent variables (G/NCS, hydrothermal time, and S/Ni) on the specific capacitances of the NCS@G/Ni composite electrodes. RSM analysis revealed that the developed quadratic model with regression coefficient values of more than 0.95 could be well adapted to represent experimental results. Optimized preparation conditions for NCS@G were G/NCS = 6.0%, hydrothermal time = 10.0, and S/Ni = 6.0 of NCS@G (111) sample. The maximum specific capacitance of NCS@G (111)/Ni fabricated at the optimal condition is about 216% higher than the best result obtained using the conventional experimental method. The enhanced capacitive performance of the NCS@G (111) sample can be attributed to the synergistic effect between NCS nanoparticles and graphene, which has the meso/macropores conductive network and low diffusion resistance. Notably, the NCS@G (111) could not only provide numerous reaction sites but also prevent the restacking of graphene layers. Furthermore, a supercapattery cell was fabricated with an (G + AC)/Ni anode, a NCS@G (111)/Ni cathode, and a carboxymethyl cellulose–potassium hydroxide (CMC-KOH) gel electrolyte. The NCS@G (111)//(G + AC) demonstrates an outstanding energy density of 80 Wh kg−1 at a power density of 4 kW kg−1, and a good cycling performance of 75% after 5000 cycles at 2 A g−1. Applying the synthesis strategy of RSM endows remarkable capacitive performance of the hybrid materials, providing an economical pathway to design promising composite electrode material and fabricate high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

Sonication-supported hydrothermal process was used to synthesize nanoporous carbon composites of NiCo 2 S 4 @N−MWCNT and NiCo 2 S 4 @N−MWCNT/MOF67 for supercapacitor applications. The structural, morphological, and electrochemical properties of the synthesized composites were improved the use of the hydrothermal process. The composite electrodes were assembled via three-electrode configuration using 6 M KOH as electrolyte solution. The NiCo 2 S 4 @N−MWCNT and NiCo 2 S 4 @N−MWCNT/MOF-67 composites showed the specific capacitance of (254 and ∼455) F/g, respectively, at 1 A/g. Due to the incorporation of the metal organic framework nano porous structured composite, the increment of the specific capacitance was almost 1.78-fold. The electrode shows excellent capacitance retention of 98.43% and improved the cyclic stability in presence of 6 M KOH electrolyte. [ABSTRACT FROM AUTHOR]

To improve the electrochemical performance of the supercapacitor, three electrode nanocomposites, NiO, NiS and NiCo2S4, have been obtained by simple hydrothermal process and high temperature pyrolysis, and further, the impact of electrolytes of different concentrations on electrochemical performance of supercapacitor has been researched. During the research processing, synergistic effect of Ni, Co and S is considered to enhance the electrical conductivity, and promote electron transfer, ion diffusion and structural stability. The experiment results show that bimetallic sulfides display high electrical conductivity, shorter ion diffusion channels, and faster electron and ion transport rate with the feature of topping electrochemical properties of specific capacity, excellent cycling stability and high rate capability, and besides show that it can improve the electrochemical performance of the material by increasing the concentration of electrolyte. The transition-metal sulfides provide a new promising pathway for the expansion of high-performance electrode materials for supercapacitors. In this paper, the three-dimensional structure of NiCo2S4 nanomaterial is prepared by two-step hydrothermal method and applied to the electrode material of supercapacitor. First, the microstructure of the material is analyzed through physical characterization, and then its electrochemical performance was tested in the three-electrode system. [ABSTRACT FROM AUTHOR]