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Three different compositions of NiCo 2 S 4 (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., (© 2023 Wiley-VCH GmbH.)

Porous NiCo2S4 networks have been successfully synthesized by a facile one-pot solvothermal method without the use of any surfactant or template. Crystal structure, morphology, composition and surface area of the as-synthesized samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy and Brunauer-Emmet-Teller techniques. Owing to their porous nature and small crystalline size, the as-prepared NiCo2S4 networks based supercapacitor electrodes showed a high specific capacitance of 1250Fg at 1Ag, and excellent cycling stability with the retention capacity of 70.3% after 5000 cycles in the KOH aqueous solution electrolyte. Porous NiCo2S4 networks have been successfully synthesized by a facile one-pot solvothermal method, without the use of any surfactant or template. Owing to their porous nature and small crystalline size, the as-prepared NiCo2S4 networks-based supercapacitor electrodes showed a high specific capacitance of 1250Fg at 1Ag, and excellent cycling stability with the retention capacity of 70.3% after 5000 cycles in the KOH aqueous solution electrolyte. [ABSTRACT FROM AUTHOR]

A recent approach for solar-to-hydrogen generation has been water electrolysis using efficient, stable, and inexpensive bifunctional electrocatalysts within strong electrolytes. Herein, the direct growth of 1D NiCo2S4 nanowire (NW) arrays on a 3D Ni foam (NF) is described. This NiCo2S4 NW/NF array functions as an efficient bifunctional electrocatalyst for overall water splitting with excellent activity and stability. The 3D-Ni foam facilitates the directional growth, exposing more active sites of the catalyst for electrochemical reactions at the electrode-electrolyte interface. The binder-free, self-made NiCo2S4 NW/NF electrode delivers a hydrogen production current density of 10 mA cm-2 at an overpotential of 260 mV for the oxygen evolution reaction and at 210 mV (versus a reversible hydrogen electrode) for the hydrogen evolution reaction in 1 m KOH. This highly active and stable bifunctional electrocatalyst enables the preparation of an alkaline water electrolyzer that could deliver 10 mA cm-2 under a cell voltage of 1.63 V. Because the nonprecious-metal NiCo2S4 NW/NF foam-based electrodes afford the vigorous and continuous evolution of both H2 and O2 at 1.68 V, generated using a solar panel, they appear to be promising water splitting devices for large-scale solar-to-hydrogen generation. [ABSTRACT FROM AUTHOR]

A novel hierarchical NiCo 2 S 4 nanoflower assembled by nanotubes containing S-vacancy was successfully synthesized. S-vacancy, serving as electron trap, can restrain recombination of photoinduced e−-h+, accelerate active electrons transfer and gather electrons into NI-Co active sites. And S-vacancy can capture more photons, improving the utilization rate of light. The above advantages collectively achieved higher C 2 H 4 yields of 13.4 μmol g−1 h−1 and selectivity of (57.1%). [Display omitted] • A novel hierarchical S-vacancy NiCo 2 S 4 -NF assembled by nanotubes were synthesized. • Vs-NiCo 2 S 4 -NF exhibited 57.1% selectivity and 13.4 μmol g−1 h−1 yields for C 2 H 4. • S-vacancy accelerated electron transfer and concentrated electron near active site. • S defects and special nanotubes collectively improved photocatalytic CO 2 to C 2 H 4. Photocatalytc CO 2 reduction, which is used to produce high-efficiency and selective olefiant (C 2 H 4), involves significant challenges. In this study, an S-defect dual-site NiCo 2 S 4 nanoflower assembled by using hollow tubes is synthesized. Under simulated sunlight in a gas–solid reaction system, the prepared material exhibits excellent selectivity and efficiency of photocatalytic C 2 H 4 production. The C 2 H 4 yields reach 80.5 μmol g−1 within 6 h and the corresponding selectivity achieves 57.1%, which are 2.5 and 2.0 times higher than those of NiCo 2 S 4 without defects, respectively. By Carefully analyzing the structure and photoelectric property, we discover that the construction of S-defects into NiCo 2 S 4 lattice serve as an electron trap, restricting carrier recombination and accelerating the transfer of more active electrons to CO 2 molecular. The S-defects further enhance the CO 2 adsorption capacity, contributing to CO 2 molecular activation. This study presents a simple route for synthesizing high-performance photocatalysts for high-value C 2 H 4 production. [ABSTRACT FROM AUTHOR]

A composite material (NiCo 2 S 4 @CeO 2) containing NiCo 2 S 4 and CeO 2 was synthesized by a two-step hydrothermal method, and the material was physically mixed with carbon black (CB) to fabricate a nitrite sensor based on CB/NiCo 2 S 4 @CeO 2 composites. [Display omitted] • NiCo 2 S 4 successfully grown on the surface of CeO 2 sphere through a hydrothermal method. • Carbon black as a conductive agent to fabricate CB/NiCo 2 S 4 @CeO 2 based nitrite sensors. • The abundant surface ionic valence and the multi-component synergy promote the rapid catalytic oxidation of nitrite. • The sensor exhibited remarkable catalytic performance in detecting nitrite. A composite material (NiCo 2 S 4 @CeO 2) containing NiCo 2 S 4 and CeO 2 was synthesized, and the material was physically mixed with carbon black (CB) to fabricate a nitrite sensor based on CB/NiCo 2 S 4 @CeO 2 nanocomposites. The composition and morphology of the composite material were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray electron spectroscopy (XPS). The evidence revealed that the material is spherical and consists of a composite of two compounds, NiCo 2 S 4 and CeO 2 , with NiCo 2 S 4 successfully grown on the CeO 2 surface. The results of cyclic voltammetric electrochemical experiments showed that CB/NiCo 2 S 4 @CeO 2 /GCE (E p = 0.78 V, I p = 145.6 μA) showed significant electrocatalytic performance against nitrite compared with GCE (E p = 0.96 V, I p = 66.7 μA). The analytical performance of the sensor proposed in this paper was investigated using the amperometric method, and the results were that the proposed nitrite sensor has a linear range of 0.2–7400 μM, and a sensitivity of 470 μA mM-1cm−2, and a detection limit of 0.003 μM. Compared with the similar type of nitrite sensors previously reported, the linear range of the sensors is broadened to 5 orders of magnitude. In addition, the sensor maintained 90.38% of its initial response after 30 days of storage in air at room temperature. The sensor was used in the recovery experiments of actual samples of tap water and mineral water, and good results were obtained. Therefore, CB/NiCo 2 S 4 @CeO 2 would be a promising electrode material for nitrite detection. [ABSTRACT FROM AUTHOR]

A one-step in situ tailoring of NiCo2S4 nanostructures is demonstrated on fluorine-doped tin oxide (FTO) as Pt-free counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) with performance surpassing that of a conventional Pt-sputtered CE. An interconnected NiCo2S4 nanosheet network is successfully constructed on the FTO glass via a hydrothermal method, attributed to the synergistic effect of structure-directing hexamethylenetetramine and L-cysteine. A growth mechanism is proposed, and the effects of nanostructures and sulfur atomic percentages on the electrocatalytic performance are discussed in depth. A DSSC with the optimized interconnected NiCo2S4 nanosheet CE exhibits higher power conversion efficiency (7.22%) compared to that with a conventional Pt-sputtered CE (6.87%) due to excellent charge transport properties and enhanced electrocatalytic activity of the NiCo2S4 nanostructures. This work showcases the strong potential of nanostructured ternary chalcogenides, which are composed of earth-abundant elements and prepared through a single-step hydrothermal process without tedious posttreatments, to reduce the dependence of platinum in DSSCs and other electrochemical devices. [ABSTRACT FROM AUTHOR]

• Hollow micro-sized spheres formed from NiCo 2 S 4 and CuCo 2 S 4 were successfully synthesized through facile solvothermal method. • Polypyrrole improved electrochemical performance of both as-prepared NiCo 2 S 4 and CuCo 2 S 4 materials. • Prepared symmetric supercapacitors from NiCo 2 S 4 /Polypyrrole and CuCo 2 S 4 / Polypyrrole were able to light up a 3.2 V white LED for 14.2 min and 10.1 min, respectively. NiCo 2 S 4 and CuCo 2 S 4 have been proven to be effective electrode materials in energy storage applications. In this study we investigate the influence of polypyrrole on the electrochemical behavior of these two potential materials. At first, high surface area micro-sized hollow spheres of NiCo 2 S 4 and CuCo 2 S 4 were successfully synthesized through facile solvothermal method and then pyrrole was polymerized through oxidative polymerization on the surface of as-prepared spheres. Resuls demonstrate improved electrochemical performance of both NiCo 2 S 4 and CuCo 2 S 4 after composing with polypyrrole. At current density of 1 A g–1, the specific capacitance of NiCo 2 S 4 /Polypyrrole and CuCo 2 S 4 /Polypyrrole was calculated to be 1412 F g–1 and 1005 F g–1, respectively. A symmetric supercapacitor assembled by NiCo 2 S 4 /Polypyrrole as both cathode and anode was able to light up a 3.2 V white LED for 14.2 min and an assembled supercapacitor from CuCo 2 S 4 /Polypyrrole as both cathode and anode lit up the same LED for 10.1 min. [ABSTRACT FROM AUTHOR]

• Control of microscopic morphology by modulation of the water-to-alcohol ratio. • The high capacitance of NCS-3 (857C/g) and the capacitance retention rate is 80% (20 A g−1). • Asymmetric supercapacitor shows high energy density 48.7 Wh kg−1 at a power density of 801 W kg−1. Because of high electrical conductivity, theoretical capacity, and numerous redox pairs, NiCo 2 S 4 has sparked a lot of interest in energy storage. In the paper, with citric acid as inductive agent, NiCo 2 S 4 mesoporous microspheres have been successfully prepared via solvothermal approach by regulating the solvent ratio (water/ethanol ratio = 1/3). It reveals that citric acid dominate in the nucleation and orientated growth of NiCo 2 S 4 and the morphology of NiCo 2 S 4 with different submicron structures can be tuned by the ratio of water/ethanol. The morphology, structure, and electrochemical properties of all NiCo 2 S 4 samples have been investigated. Among these samples, NiCo 2 S 4 mesoporous microspheres display the best electrochemical properties due to their unique mesoporous structure and high specific area. It has a high discharge capacity of 857C/g at a current density of 1 A/g, and exhibit exceptional rate capability (80 % retention even at 20 A/g). Additionally, when employed as positive of an asymmetric NiCo 2 S 4 //active carbon (AC) supercapacitor, it yields an energy density of 48.7 Wh kg−1 at 801 W kg−1 and 81 % capacity retention after 10,000 cycles at a current density of 5 A/g. The work describes a quick and easy way to increase the performance of NiCo 2 S 4 electrode materials and demonstrates its potential in practical application. [ABSTRACT FROM AUTHOR]

Crystal facet engineering is considered to be a powerful method to maximize the inherent catalytic properties of electrocatalysts. In this research, polyvinylpyrrolidone (PVP) served as a surfactant to realize the controllable synthesis of sub-microspheres NiCo 2 S 4 with a highly exposed (400) crystal facet. The sub-microspheres NiCo 2 S 4 (P-0.2) shows excellent catalytic activities as a cathode toward hydrogen evolution reaction (HER) with a lower overpotential of 235 mV at 10 mA·cm−2 in alkaline electrolyte. Moreover, the sub-microspheres NiCo 2 S 4 presents satisfactory durability in the alkaline solution for 24 h. Such remarkable HER performance of electrocatalyst is benefited from the unique sub-microspheres structure, which could highly expose specific crystal facets to provide abundant active sites, and thus enhance the mass/electron transfer efficiency. Furthermore, the increased exposure of (400) facet of NiCo 2 S 4 crystal will offer more S2- during HER, it can effectively stabilize the reaction intermediates. [Display omitted] • Sub-microspheres NiCo 2 S 4 with highly exposed (400) crystal facet has been prepared. • The exposure of (400) facet of NiCo 2 S 4 could offer more S2-. • P-0.2 displays remarkable electroactivity towards hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C 3 N 4) with high nitrogen contents and excellent thermal/chemical stability is widely applied as active material of supercapacitors (SC). Small surface area and electrical conductivity of g-C 3 N 4 lead to poor electrochemical performance, which can be improved by heteroatom doping and metal compound incorporation. In this work, it is the first time to fabricate NiCo 2 S 4 /S-doped g-C 3 N 4 (NCS-C) composite using thermal polymerization and hydrothermal reaction as active material of SC. The S-g-C 3 N 4 electrode shows a higher specific capacitance (C sp) of 72.4 mF/g at 20 mV/s than that of 49.5 mF/g of g-C 3 N 4 electrode. Using sulfur as doping source and anion in metal compound favors for improving compatibility of composites. NCS-C composite shows favorable S-g-C 3 N 4 nanosheets-covered NCS flower-like structures. The NCS-C electrode presents a higher C sp value of 351.0 F/g at 1 A/g (886.2 F/g at 20 mV/s) than that of 348.9 F/g at 1 A/g (794.2 F/g at 20 mV/s) of NCS electrode, due to sulfur and nitrogen-rich carbon of S-g-C 3 N 4 and abundant redox reactions of NCS. The symmetric SC with NCS/C electrodes delivers potential window of 1.0 V, maximum energy density of 9.7 Wh/kg at 0.65 kW/kg, and C sp retention of 97.6% and Coulombic efficiency of 90% after 10,000 charge/discharge cycles. [Display omitted] • NiCo 2 S 4 /S-g-C 3 N 4 (NCS/C) is firstly got as active material for supercapacitor(SC). • Optimal NCS/C electrode shows specific capacitance (C sp) of 886.2 F/g at 20 mV/s. • The pristine g-C 3 N 4 electrode only shows a C sp value of 49.5 mF/g at 20 mV/s. • Sulfur as dopant and anion in metal compound favors for composite compatibility. • SC shows C sp retention of 98.4% and Coulombic efficiency of 90% after 10,000 cycle. [ABSTRACT FROM AUTHOR]

As a metallic cocatalyst, the photothermal effect of NiCo 2 S 4 in the process of photocatalytic hydrogen evolution has not been deeply discussed elsewhere. It has been well known that how to intrinsically speed the photogenerated electrons transfer and active absorbed Water (*H 2 O) to release more hydrogen proton (*H) are extremely meaningful to photocatalytic hydrogen evolution improvement. Herein, a convenient and mild two-step solvothermal strategy was developed to meticulously design the intimate contact structure between a noble-metal-free cocatalyst NiCo 2 S 4 and semiconductor ZnIn 2 S 4 nanoflower, which facilitates the charge rearrangement at the interface to boost the separation of photogenerated carriers. Importantly, photothermal effect induced by NiCo 2 S 4 was demonstrated to ameliorate slow kinetics of water spilling with the apparent activation energy reduction form 50.5 kJ·mol−1 to 38.8 kJ·mol−1, which was responsible for improving photocatalytic hydrogen evolution rate of 6834.6 μmol·g−1·h−1 accompanied by apparent quantum efficiency of 13.0% at 400 nm. The electron transfer was accelerated due to localized electric field enhancement determined by Finite difference time domain (FDTD) simulations. The decline of Gibbs free energy barrier of adsorbed water from 2.94 eV on ZIS to 1.62 eV on NCS/ZIS resulted in H-OH bond activating was demonstrated using density functional theory (DFT). This work will provide an effective pathway to design semiconductor-metal-based photothermal assisted photocatalytic system and expand the application of metallic NiCo 2 S 4 in solar-to-fuel conversion. [Display omitted] • The mechanism of NiCo 2 S 4 -induced photothermal effect was investigated systematically for the first time. • The kinetic studies were carried out to pursuit the contribution of photothermal effect for H-OH bond activation. • NiCo 2 S 4 was responsible for accelerating the electron transfer due to localized electric field enhancement. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a transparent NiCo2S4 thin film as an effective counter electrode (CE) was incorporated into a Pt-free dye-sensitized solar cell (DSC) for the first time. NiCo2S4 was synthesized via a facile solvothermal method and then subjected to electrophoresis onto a fluorinated tin oxide (FTO) glass substrate. X-ray diffraction, energy dispersive spectrum, and field-emission scanning electron microscope confirmed that the NiCo2S4 nanoparticles were successfully synthesized and deposited onto the FTO substrate, while the electrochemical analyses showed its superior electrocatalytic activity for the I3 − reduction compared to the conventional Pt CE. Additionally, the NiCo2S4 CE demonstrated a high transmittance (>75%) at visible wavelengths. Thus, the DSC assembled with the transparent NiCo2S4 CE achieved a promising photovoltaic conversion efficiency of 6.14% in comparison with that using the Pt CE (6.29%). [Copyright &y& Elsevier]

Spinel nickel-cobalt sulfide (NiCo 2 S 4) supported on reduced graphene oxide (rGO) was fabricated through a facile one-step hydrothermal method for energy storage applications. The distribution of the NiCo 2 S 4 nanoparticles on the rGO surface was found to improve the supercapacitive performance of the assembled device. The NiCo 2 S 4 /rGO nanocomposite exhibits outstanding electrochemical behavior with a capacity (C)/specific capacitance (C s) of 536 C g−1/1072 F g−1 at a current density of 1 A g−1. To further investigate the electrochemical behavior of the NiCo 2 S 4 /rGO nanocomposite, a hybrid supercapacitor (HSC) was constructed utilizing a NiCo 2 S 4 /rGO positive electrode and an activated carbon (AC) negative electrode. The assembled NiCo 2 S 4 /rGO//AC HSC results in outstanding specific energy (E s) of 41.52 Wh kg−1 at a specific power (P s) of 1067 W kg−1 relative to previously reported NiCo 2 S 4 -based supercapacitors (SCs). The HSC had an E s of 36.51 Wh kg−1 at a P s of 2065 W kg−1. Additionally, excellent cycling stability of 82% capacitance retention after 3000 repeated charge/discharge cycles was accomplished. These realized results confirm that the NiCo 2 S 4 /rGO nanocomposite is a suitable electrode material for SCs. [Display omitted] • NiCo 2 S 4 /rGO nanocomposite was prepared using a one-step hydrothermal method as an electrode for a hybrid supercapacitor. • NiCo 2 S 4 nanoparticles are homogeneously distributed and tightly anchored to the surface of the wrinkled rGO. • NiCo 2 S 4 /rGO nanocomposite exhibited a specific capacitance of 1072 F g−1 at a current density of 1 A g−1. • NiCo 2 S 4 /rGO//AC hybrid supercapacitor showed specific energy of 41.52 W h kg−1 at a specific power of 1067 W kg−1. [ABSTRACT FROM AUTHOR]

• N, S co-doped graphene could effectively improve the structural stability of NCS. • NCS-G 3 electrode exhibits a specific capacitance of 1145 F g−1. • The asymmetric supercapacitor device demonstrates the high energy density of 33.8 Wh kg−1. • The asymmetric supercapacitor exhibits good cycling performance. With high electrochemical activity and good energy storage performance, bimetallic pseudocapacitive materials of Ni-Co sulfides have been extensively and deeply researched. However, the low electrical conductivity, irreversible reduction reaction and structural instability significantly limit the practical application of bimetallic NiCo 2 S 4. In this work, NiCo 2 S 4 @N, S co-doped graphene (NCS-G) composite material with high electrochemical performance is prepared by an efficient chemical precipitation assisted hydrothermal method. As the ideal skeleton and excellent conductive network, N, S co-doped graphene could effectively improve the structural stability of the as-prepared NCS-G, thus increasing the utilization and efficient electron transfer of NCS. Notably, the NiCo 2 S 4 could not only provide numerous reaction sites, but also avoid the re-stacking of graphene sheets. Owing to the above merits, the NCS-G 3 electrode exhibits a maximum specific capacitance of 1145 F g−1 (at 0.5 A g−1). The rate performance of the electrode retains 91.7% at the current density of 10 A g−1 compared with that of 0.5 A g−1. Furthermore, consisting of the graphene anode and the NCS-G 3 cathode, the asymmetric SC device demonstrates the outstanding energy density of 33.8 Wh kg−1 at the power density of 799.8 W kg−1 and good cycling performance of 74.5% after 5000 cycles at 2 A g−1. The synthesis strategy exploited in this work endows the electrode with marvelous rate performance, providing a new pathway to engineer the promising electrode material and manufacture high-performance energy storage devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• NiCo 2 S 4 NWs/GF and CoNi 2 S 4 NAs/GF were successfully synthesized. • NiCo 2 S 4 NWs/GF anode was tested in DEGDME electrolyte at 0.3–3.0 V. • The NiCo 2 S 4 NWs/GF showed better electrochemical performance than CoNi 2 S 4 NAs/GF. • NiCo 2 S 4 NWs/GF anode with more Co content shortens diffusion length of Na+ and e-. [Display omitted] Bimetallic Ni x Co 3−x S 4 (x = 1 or 2) with synergistic effect is a promising candidate material for sodium-ion battery (SIB) anodes because of its higher electrical conductivity than monometallic sulfides owing to its lower bandgap. In this study, samples of bimetallic sulfide Ni x Co 3−x S 4 with tunable chemical Ni/Co components are successfully grown on graphene foam (GF), forming free-standing Chinese knot-like nanowires (NiCo 2 S 4 NWs/GF) and Chinese lantern-like nanoarrays (CoNi 2 S 4 NAs/GF). When evaluate as anodes for SIBs at 0.3–3.0 V in ether-based electrolytes, the NiCo 2 S 4 NWs/GF electrodes offer superior rate performance and cycling stability than the CoNi 2 S 4 NAs/GF electrodes. More specifically, the NiCo 2 S 4 NWs/GF electrode has a high capacity of 650–556 mAh g−1 at 0.1–2.0 A g−1 and 457 mAh g−1 after 200 cycles at 0.5 A g−1 with a high initial coulombic efficiency (ICE) of 95.6%. And its rate performance outperforms most existing electrodes those contain NiS x , CoS x , or NiCo 2 S 4. The excellent electrochemical performance of the NiCo 2 S 4 NWs/GF electrode is attributed to its unique composition, smaller size, and porous nanowires that can reduce the diffusion length of e- and Na+, and enhance reaction kinetics. [ABSTRACT FROM AUTHOR]

All-solid-state asymmetric supercapacitor based on hierarchical hybrid structure decorated with conductive NiCo 2 S 4 on NiCoAl-LDH has good energy density and power density. [Display omitted] • NCA-LDH@NCS@CC is synthesized by a simple and low-cost hydrothermal method. • Hierarchical hybrid structure NCA-LDH@NCS is formed on carbon cloth. • NiCo 2 S 4 boosts overall electrical conductivity and hinders agglomeration of LDH. • NCA-LDH@NCS@CC//AC@CC is assembled with high energy density and cycle stability. Rational construction of microstructure and successful incorporation of multiple components offer a scalable strategy for applying electrode materials in asymmetric supercapacitors. Herein, a hierarchical hybrid structure of NiCoAl-layered double hydroxide (NCA-LDH) and ternary spinel NiCo 2 S 4 (NCS) on carbon cloth (CC) without binders is obtained through three-step hydrothermal reaction. The NCA-LDH@NCS@CC electrode exhibits outstanding electrochemical performance with 1775F g−1 at 1 A g−1. Its capacitance retention is 79.6% when cycles reach 10 000 under 10 A g−1, benefiting from the hierarchical hybrid structure and improved overall conductivity. A flexible solid-state asymmetric supercapacitor (FSASC) is assembled using NCA-LDH@NCS@CC and activated carbon coated on carbon cloth (AC@CC) for positive and negative electrodes, respectively. It possesses 33.13 Wh kg−1 under 750 W kg−1, and also maintains a better cycling performance of 71.4% at 1 A g−1 after 10 000 cycles. Hierarchical hybrid NCA-LDH@NCS@CC electrode provides a favorable and scalable candidate for the development of FSASC device with superior performance. [ABSTRACT FROM AUTHOR]

The detection of cholesterol is very crucial in clinical diagnosis for rapid and accurate monitoring of multiple disease-biomarkers. There is a great need for construction of a highly reliable and stable electrocatalyst for the efficient detection of cholesterol. In this work, mesoporous NiCo 2 S 4 nanoflakes of enhanced electrochemical properties are prepared through a facile hydrothermal approach. The developed nanoflakes modified nickel foam electrode exhibits outstanding electrocatalytic properties for the detection of cholesterol with high selectivity. The electrode displays excellent sensitivity of 8623.6 μ A mM -1 cm -2 , in the wide linear range from 0.01 to 0.25 mM with a low detection limit of 0.01 μ M. In addition, NiCo 2 S 4 structure reveals good thermal stability and reproducibility over a period of 8 weeks. Moreover, the nanoflakes show good response for detection of cholesterol in real samples. Our results demonstrate the potential use of NiCo 2 S 4 as a catalyst for the development of cost-effective electrochemical sensors for medical and industrial applications., (© 2022 IOP Publishing Ltd.)

• A shell-strengthened hollow structure of NiCo 2 S 4 is built by a hydrothermal method. • The hollowing process follows an in-situ reaction Ostwald Ripening mechanism. • Rich pores, hollow structure and cobalt ions lead to excellent high-rate performance. • The mechanically strengthened shell of NiCo 2 S 4 prolongs its cycling life. For Faraday supercapacitors, some battery-type electrode materials such as nickel-based materials attract intensive attention by virtue of their high theoretical capacity. However, it is quite difficult for these materials to achieve the satisfied high-rate performance and cycling life concurrently due to the contradiction of their individual requirements to the microscopic structure of materials. In this work, we build a hollow architecture of NiCo 2 S 4 at hydrothermal condition following an in-situ reaction Ostwald Ripening mechanism. The as-prepared NiCo 2 S 4 presents a shell-strengthened hollow structure, satisfying the as-mentioned two requirements: (1) the rich pores in shell and hollow structure plus structural cobalt ions lead to the excellent high-rate performance of NiCo 2 S 4 ; (2) the dense particulate layer in shell with additional mechanical strength prolongs the cycling life of NiCo 2 S 4. Consequently, the asymmetrical supercapacitors assembled with NiCo 2 S 4 as positive electrode material show both high energy and power densities, and excellent cycling stability. [ABSTRACT FROM AUTHOR]

[Display omitted] One-dimensional (1D) electrospun carbon nanofibers functionalized with NiCo 2 S 4 nanoparticles have been synthesized and exhibits excellent performance as a low-cost, lightweight, flexible and binder-free cathode for aqueous Ni-Zn batteries. • Electrospun carbon nanofibers functionalized with NiCo 2 S 4 nanoparticles are synthesized. • The CNF@NiCo 2 S 4 electrode is lightweight, flexible and binder-free. • The CNF@NiCo 2 S 4 exhibits excellent performance for aqueous Ni-Zn batteries. • The quasi-solid-state CNF@NiCo 2 S 4 //Zn battery is also fabricated with polymer electrolyte. Aqueous nickel-zinc (Ni-Zn) batteries hold great promise for large-scale energy storage systems. However, traditional Ni-based cathode electrodes are generally consist of none capacity contribution additives and heavy current collectors, resulting in a low percentage of the active materials. In this regard, developing lightweight, flexible and binder-free cathode electrodes for aqueous Ni-Zn batteries is highly desirable. Herein, for the first time, we develop a simple electrospinning technique to synthesize the one-dimensional (1D) electrospun carbon nanofibers functionalized with ternary NiCo 2 S 4 nanoparticles (denoted as CNF@NiCo 2 S 4) as a lightweight, flexible and binder-free electrode for aqueous Ni-Zn batteries. Based on the self-standing CNF@NiCo 2 S 4 film as cathode, the as-fabricated aqueous CNF@NiCo 2 S 4 //Zn battery exhibits a high capacity of 0.32 mAh cm−2 and 35.9 mAh cm−3 at a current density of 2 mA cm−2, and good rate performance (0.21 mAh cm−2 at 20 mA cm−2) and long-term cycling stability (83% capacity retention at 10 mA cm−2 after 2000 cycles). More importantly, a quasi-solid-state CNF@NiCo 2 S 4 //Zn battery is also fabricated, which also displays an impressive energy density of 362.3 Wh kg−1, indicating the potential towards practical applications. Impressively, the volumetric energy density of CNF@NiCo 2 S 4 //Zn battery are 58.2 mWh cm−3 (liquid) and 45.4 mWh cm−3 (quasi-solid-state), which are much larger than the values of other reported Ni-Zn batteries. Theses results indicate the self-standing CNF@NiCo 2 S 4 film is promising for for next generation electronic applications. [ABSTRACT FROM AUTHOR]

Herein, we report a comparison of the electrochemical performance of two kinds of NiCo2S4-based electrodes for solid-state hybrid supercapacitors (HSCs). For the binder-free electrode, NiCo2S4 was grown on Ni foam by the chemical bath deposition (CBD) method. For the binder-using electrode, NiCo2S4 powder was synthesized by the hydrothermal method. FESEM images depicted the hierarchical nanostructure of NiCo2S4 synthesized by the hydrothermal method and uniform distribution of nanostructured NiCo2S4 grown on Ni foam by the CBD method. Half-cell studies of both NiCo2S4 electrodes showed them exhibiting battery-type charge storage behavior. To assemble HSCs, NiCo2S4 and activated carbon were used as a positive and negative electrode, respectively. Electrochemical studies of the HSCs showed that the accessible potential window was wide, up to 2.6 V, through cyclic voltammetry (CV) analysis. Chronopotentiometry (CP) studies revealed that the energy and power densities of binder-using HSC were 51.24 Wh/kg and 13 kW/kg at 1 Ag−1, respectively, which were relatively higher than those of the binder-free HSC. The binder-free HSC showed 52% cyclic stability, relatively higher than that of the binder-using HSC. Both HSCs, with unique benefits and burdens on energy storage performance, are discussed in this work. [ABSTRACT FROM AUTHOR]

In this report, NiCo 2 S 4 nanoparticles (NPs) are successfully synthesized by a simple cost effective one step hydrothermal method using dissimilar sulfur sources (thiourea- NTU, thioacetamide- NTA) separately. The influence of sulfur source on structure, morphological, surface area and electrochemical performance are examined carefully. The X-Ray Diffraction Pattern of both samples displays the cubic phase of spinel NiCo 2 S 4 crystal structures. TEM studies reveal Uniform Spherical (19–21 nm) and spheroidal (22–23 nm) shaped NPs. XPS spectra of both sample conforms the coexistence of Ni3+ and Ni2+ valence states of spinel cubic NiCo 2 S 4. The surface area of NTA- NiCo 2 S 4 found superior (91.23 m2 g−1) than NTU- NiCo 2 S 4 (43.12 m2 g−1). The Electrochemical performance of NTA based NiCo 2 S 4 /Ni foam electrode results in showing high specific capacity values of 1051.49 C g−1 (292 m A h g−1) compare with NTU- NiCo 2 S 4 (690 C g−1/191 m A h g−1) at a current density of 2 A g−1 moreover, NTA- NiCo 2 S 4 holds exceptional Capacity retention of 98 % after 10,000 GCD cycles at current density of 6 A g−1 with excellent energy density of 88.377 W h Kg−1 with power density of 2179.15 W kg−1. The admirable electrochemical performance of NTA- NiCo 2 S 4 brings out potential anticipation in supercapacitor applications. • NiCo 2 S 4 nanoarchitectures have been prepared using two diverse sulfur sources thiourea (NTU) and thioacetamide (NTA). • Both electrodes (NTU/NTA) displays battery type energy storage mechanism. • NTA electrode is capable of delivering high specific capacity of 1051.49 C g−1 (292 m A h g−1) compare to NTU (690 C g−1/191 m A h g−1) with ultra high capacity retention of 98 % after 10,000 successive GCD cycles. • NTA offer a high energy density of high energy density of 88.37 W h Kg−1 with a suitable power density of 2179.15 W kg−1 at a cur rent density of 2 A g−1 [ABSTRACT FROM AUTHOR]

• Spreading GO nanosheets-coated NF framework (NF@sGO) is fabricated. • NF@sGO provides more supporting surfaces and abundant oxygen-containing groups. • The superiority of NF@sGO is clarified by loading NiCo 2 O 4 and NiCo 2 S 4. • NF@sGO/NiCo 2 O 4 composite delivers a capacity of 1135 C g−1 at 1 A g−1. • NF@sGO/NiCo 2 O 4 /NiCo 2 S 4 electrode has a capacity of 1341 C g−1 at 1 A g−1. Porous nickel foam (NF) is often wrapped by reduced graphene oxide (rGO) for loading active nanomaterials. To clarify the influence of the dispersion of graphene nanosheets in NF framework on the electrochemical performance, herein, spreading GO nanosheets-coated NF (NF@sGO) is developed via negative pressure immersion method, in which, GO sheets spreading on the macropores adjust the pore structure and enlarge the supporting surface of NF framework. Compared to the NF@rGO prepared by hydrothermal method, NF@sGO scaffold exhibits a high capacitance for the pseudocapacitance contributed by GO. Acting as a porous scaffold for growing NiCo 2 O 4 nanoneedles, the NF@sGO/NiCo 2 O 4 composite delivers a specific capacitance of 2522 F g−1 (1135 C g−1) at 1 A g−1, much higher than that of the control sample NF@rGO/NiCo 2 O 4. To further improve the electrochemical performance of NF@sGO/NiCo 2 O 4 , thin NiCo 2 S 4 nanosheets are decorated on NiCo 2 O 4 nanoneedles. Optimized NF@sGO/NiCo 2 O 4 /NiCo 2 S 4 -0.02 sample delivers a maximum specific capacitance of 2980 F g−1 (1341 C g−1) at 1 A g−1 and a superior long-term cycling stability. The performances of NF@sGO/NiCo 2 O 4 and NF@sGO/NiCo 2 O 4 /NiCo 2 S 4 -0.02 are both higher than existing composites. The superior electrochemical performance is attributed to the combination of novel NF@sGO scaffold and NiCo 2 O 4 nanoneedles or optimized NiCo 2 O 4 /NiCo 2 S 4 hybrid nanostructures. In view of the easy preparation and superior performance, NF@sGO scaffold has a promising prospect for preparing high-performance integrated electrodes. Spreading GO nanosheets-coated NF framework (NF@sGO) is fabricated with an enlarged supporting surface and abundant oxygen-containing groups. Serving as a porous scaffold, the superiority of NF@sGO is testified for loading NiCo 2 O 4 and NiCo 2 S 4 nanostructures as integrated electrode. [Display omitted] [ABSTRACT FROM AUTHOR]

Taking advantage of both Faradaic and carbonaceous materials is an efficient way to synthesize composite electrodes with enhanced performance for supercapacitors. In this study, NiCo 2 S 4 nanoflakes were grown on the surface of nitrogen-doped hollow carbon nanospheres (NHCSs), forming a NiCo 2 S 4 /NHCS composite with a core-shell structure. This three-dimensionally confined growth of NiCo 2 S 4 can effectively inhibit its aggregation and facilitate mass transport and charge transfer. Accordingly, the NiCo 2 S 4 /NHCS composite exhibited high cycling stability with only 9.2% capacitance fading after 10 000 cycles, outstanding specific capacitance of 902 F g -1 at 1 A g -1 , and it retained 90.6% of the capacitance at 20 A g -1 . Moreover, an asymmetric supercapacitor composed of NiCo 2 S 4 /NHCS and activated carbon electrodes delivered remarkable energy density (31.25 Wh kg -1 at 750 W kg -1 ), excellent power density (15003 W kg -1 at 21.88 Wh kg -1 ), and satisfactory cycling stability (13.4% capacitance fading after 5000 cycles). The outstanding overall performance is attributed to the synergistic effect of the NiCo 2 S 4 shell and NHSC core, which endows the composite with a stable structure, high electrical conductivity, abundant active reaction sites, and short ion-transport pathways. The synthesized NiCo 2 S 4 /NHCS composite is a competitive candidate for the electrodes of high-performance supercapacitors., (© 2021 IOP Publishing Ltd.)

Development of alternate counter electrode for the dye-sensitized solar cell (DSSC) using simple and single method are the major focus of the research to resolve problems related to the platinum (Pt)-based counter electrode. In the present work, NiCo 2 S 4 based counter electrode has been directly developed on the fluorine-doped tin oxide coated glass substrate (FTO) using one step and simple hydrothermal method. The prepared NiCo 2 S 4 @FTO electrode was characterized by the range of spectroscopic and microscopic techniques as well as further assembled in the DSSC device in order to evaluate the electrode performance. The NiCo 2 S 4 counter electrode exhibited the 6.53% photovoltaic performance in the assembled DSSC which is almost similar to the benchmark Pt based counter electrode (6.88%) under similar experimental conditions. The excellent performance of the elected NiCo 2 S 4 @FTO electrode could be due to the high electrocatalytic activity towards the reduction of the I 3 − to I− and smaller size of the nanoparticle which provide high surface area and catalytic sites. We adapted a theoretical model based on electrical considerations to study the impact of physical parameter of DSSC cell on the – characteristic, performance and photovoltaic efficiency, using the experimental parameters. The model is reproducing perfectly the I–V curve and related DSSC characteristics. [Display omitted] • NiCo2S4 counter electrode directly deposited on the fluorine-doped tin oxide. • NiCo2S4 counter electrode exhibited superior PEC of 6.53% than Pt. • High electrocatalytic activity of NiCo2S4@FTO towards reduction of I3- to I-. • Pt free counter electrode for dye-sensitized solar cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A well-designed Ti 3 C 2 T x /NiCo 2 S 4 @CC flexible electrode was fabricated. • Ultrathin MXene nanosheets are injected in electrode by spray coating technique. • The MXene material improved the conductivity of the electrode. Although MXenes with outstanding electrical conductivity possess great potential as energy-storage materials for flexible supercapacitors (SCs), the electrochemical performance of the pure MXene-based SCs are often restricted by inherent limitations such as inferior energy densities and serious aggregation. Alternatively, it will be an effective strategy to develop rationally designed composite electrodes that can simultaneously provide both high electrical conductivity and large surface area via complementary functions of each constituent. Here, hierarchically layered MXene nanosheets on nickel cobalt sulfide/carbon cloth (Ti 3 C 2 T x /NiCo 2 S 4 @CC, herein TNSC) was prepared through spray injection of MXene on nickel cobalt sulfide, which not only achieved an excellent specific capacitance at high current densities but also possess improved cycling stability. The optimized TNSC electrode shows maximum specific capacities of 2326F g−1 at a current density of 1 A g−1, and excellent cycling stability of 93.8% at 10 A g−1. We show that these outstanding electrochemical performances can be achieved by a proper loading amount of surface-coated Ti 3 C 2 T x , which can simultaneously enhance electrical conductivity and permeate ions to nickel cobalt sulfide. Furthermore, a quasi-solid‐state flexible SC (QFSC) based on TNSC presents a high energy density of 57.5 W h kg−1 at a power density of 800 W kg−1 in a wide potential window of 1.6 V. Therefore, the excellent electrochemical performances of the TNSC electrode makes it as a prominent candidate for high-performance and flexible energy storage devices. [ABSTRACT FROM AUTHOR]

The structural stability of electrode materials is the crux of significantly improve the electrochemical performance of pseudocapacitor electrodes. Herein, we demonstrate the preparation of NiCo 2 S 4 with core-shell and micro-porous structure on nickel foam as an efficient anode material for asymmetric supercapacitor (ASC) via hydrothermal and co-sulfurization processes. The NiCo 2 S 4 electrode shows a remarkable specific capacitance of 850.2 C g−1 at 1 A g−1, and retains 93.6 % original capacitance after 5000 cycles. Furthermore, the NiCo 2 S 4 electrode also have excellent electrochemical performance when used as an anode of asymmetric NiCo 2 S 4 //Active Carbon (AC) supercapacitor, which generates an energy density as 38.1Wh Kg−1 at 700 W kg−1 and 84.3% capacity retention after 5000 cycles. This work provide an efficiently method to suppress volume expansion during sulfuration reaction by core-shell structure, which potential application in transition metal sulfides electrode materials in electrochemical energy storage and conversion devices. [ABSTRACT FROM AUTHOR]

• Novel sulfide-rich NCS@MX were designed and synthesized via a hydrothermal method. • NCS@MX was used for the enhanced degradation of RhB under visible light irradiation. • NCS@MX exhibited excellent photo-stability over five adsorption-desorption cycles. • Possible photocatalytic mechanisms and oxidative pathways of RhB were proposed. Herein, a two-step hydrothermal treatment was used to synthesize a novel hybrid photocatalyst with sulfide-rich layered double hydroxides intercalated MXene for the degradation of rhodamine B (RhB). The fabricated NiCo 2 S 4 on MXene (denoted as NCS@MX) photocatalyst showed higher catalytic activity and degraded RhB to approximately ≈100% within 20 min under visible light irradiation. The optical response and recombination rate used increased the separation efficiency of photoinduced e− and h+ by NCS@MX, thus enhancing the photocatalytic degradation of RhB. The OH and O 2 − radicals were non-toxic by-products of the NCS@MX system for the mineralization of organic pollutants. Furthermore, NCS@MX exhibited great photo-stability in five repetitive runs for the degradation of RhB with a minimal drop on catalytic activity. Possible oxidative pathways of RhB and the reaction intermediates were observed by liquid chromatography-mass spectrometry (LC-MS). The pollutant was primarily oxidized into non-toxic products such as H 2 O, CO 2 , and few inorganic species. Therefore, NCS@MX is expected to have prospects for applications in wastewater management considering its environmental friendliness, low-cost, and non-toxic by-products production. [ABSTRACT FROM AUTHOR]

To enhance the electrochemical performance of Li–S battery, a composite sulfur cathode was designed by doping sulfur onto N-doped carbon nanotubes with metal sulfide particles attached to their surface. This designing approach allowed performing high sulfur loading in the cathode, while maintaining prominent stability and good charge/discharge capacity. The results showed that at a sulfur loading of 2.1 mg cm−2, the cell with S/NiCo 2 S 4 /N-CNT cathode delivered an average discharge capacity of 998 mA h g−1 at 0.1C, and preserved an excellent discharge capacity of 713 mA h g−1 at a high current density of 1 C. At the same time, the cell demonstrated high stability and reversibility delivering a capacity of 950 mA h g-l when current density reduced back again to 0.1C. Furthermore, the S/NiCo 2 S 4 /N-CNT cathode showed a steady capacity of 915 mA h g−1 at 0.2C over 100 cycles. Image 1 • NiCo 2 S 4 nanoparticles are embedded in nitrogen-doped CNT for Li–S batteries. • NiCo 2 S 4 /N-CNT shows a strong ability to restrict the volume expansion of sulfur. • NiCo 2 S 4 /N-CNT demonstrates obvious polysulfides adsorption effect. • S/NiCo 2 S 4 /N-CNT cathode displays excellent performance under high sulfur loading. [ABSTRACT FROM AUTHOR]

The development of low-cost cocatalysts is desirable for photocatalytic H 2 generation. Here, we are the first to demonstrate the in situ hydrothermal growth of NiCo 2 S 4 nanosheets on g-C 3 N 4 surfaces to construct a "sheet-on-sheet" heterostructure. The as-prepared NiCo 2 S 4 /CN heterostructured nanohybrid exhibits remarkably enhanced rates of visible-light-driven photocatalytic H 2 evolution without using a noble metal cocatalyst, such as Pt. Notably, the optimum loading of NiCo 2 S 4 nanosheets is 10 wt%, providing the best H 2 performance rate of 293.4 μmolh−1g−1, which is approximately 7 times higher than that of the single-component bulk CN. This result suggested that the improved photocatalytic activity can be primarily ascribed to the efficient interfacial transfer of the photogenerated charge pairs from CN to the NiCo 2 S 4 nanosheets. These nanosheets serve as temporary electron reservoirs, resulting in a reduced charge recombination rate on the CN surfaces and increasing the amount of photogenerated charge pairs in the NiCo 2 S 4 nanosheets. Furthermore, the increased potential of reactive surface sites, together with the extended light absorption range after the introduction of NiCo 2 S 4 nanosheets on the CN substrate, may also play a certain role in improving the photocatalytic performance. This study reveals a promising and efficient route for using CN-based photocatalysts incorporated with a ternary transition metal sulfide cocatalyst, which have been prepared by the nanoarchitecture engineering of noble metal-free heterostructured interfaces for use in renewable energy production. Novel sheet on sheet NiCo 2 S 4 /CN heterostructure catalyst for efficient solar hydrogen production based on photogenerated interfacial charge transfer. Image 1 • NiCo 2 S 4 /CN sheet on sheet heterostructure was fabricated by facile in-situ hydrothermal method. • 2D NiCo 2 S 4 /CN heterostructure efficiently promoted the electron-hole pair separation. • NiCo 2 S 4 nanosheets as low-cost synergist significantly accelerated the hydrogen reduction process. • The origin of superior H 2 evolution rate by 2D NiCo 2 S 4 /CN heterostructure was proposed. [ABSTRACT FROM AUTHOR]

• MWCNTs/NiCo 2 S 4 composite was prepared by a simple hydrothermal method. • MWCNTs increases the specific surface area and electrical conductivity of the material. • The composite showed a high specific capacitance of 2210 F/g. • Both electrode and device demonstrated high energy, power density and stability. In this study, in-situ decoration of a binder-free pseudocapacitive NiCo 2 S 4 and NiCo 2 S 4 /MWCNTs hybrid electrode has been synthesized via a wet chemical synthesis route on Ni foam. The hybrid electrodes of bimetallic metal sulfides were investigated using the X-ray diffraction technique and scanning electron microscopy. The electrochemical technique was used to investigate the electrochemical properties of the synthesized bimetallic metal sulfide materials. The good galvanostatic discharge time of 1077 s, the areal capacitance of 5.38 F/cm2, and specific capacitance of 2210 F/g were observed for NiCo 2 S 4 /MWCNTs hybrid electrode materials, respectively at 3 mA/cm2. The results show that the addition of highly conductive, MWCNTs, and the synergic effects of bimetallic sulfides (Ni, Co) greatly contribute to the excellent electrochemical properties, making the NiCo 2 S 4 /MWCNTs hybrid electrode as a potential material for supercapacitor applications. [ABSTRACT FROM AUTHOR]

Several transition metal sulfides have been studied as electrode materials for supercapacitor. With high electrical conductivity and theoretical capacity, NiCo 2 S 4 have gained much attention in this field where several methods are employed to enhance its performance. In this work, the effects of Mn doping on electrochemical performances of NiCo 2 S 4 /Ni 3 S 2 electrodes are investigated. The electrodes were prepared by a facile hydrothermal method with an addition of MnCl 2 , which not only gives Mn ion but also influences pH of the solution and the electrodes' morphology. With small amount of Mn, capacity of the doped electrode is enhanced by a maximum of 160% resulting in a capacity of 145 mAh/g (or 1350 Fg−1 in capacitance). At the same time, the nanosheet feature, good cycle stability, and rate capability of the electrode are preserved. Experiments and computations suggest that the increased capacity is caused by the increased electrical conductivity and the improved interaction between Co metal center on the electrode surface and OH– ion in the electrolyte. Thus, it is shown that doping metallic ions into NiCo 2 S 4 lattice could be an effective strategy to enhance the electrochemical performance of the material. [ABSTRACT FROM AUTHOR]

• Report a mass production paper-making method for flexible electrodes. • The HWF supported paper electrodes show high volumetric capacitance of 246.4 f cm−3 and good flexibility. • The HWF supported ASCs achieve a high energy density of 10.1 mWh cm−3 with power density of 93.9 mW cm−3. In this study, paper supported flexible electrodes for supercapacitors are prepared by paper-making process with the hardwood fiber (HWF), multi-walled carbon nanotube (MWCNT) and NiCo 2 S 4 powder. Compared with previous reported cellulose nanofiber (CNF), nickel foam and carbon cloth supported electrodes, the HWF supported paper electrodes demonstrate its advantages of low-cost, mass production, low-thickness and superior flexibility. It can achieve a high specific capacitance of 1725 F g−1 at 1 A g−1, a remarkable rate retention of 79.3 % from 1 A g−1 to 10 A g−1, an ultrahigh volumetric specific capacitance of 246.4 F cm−3 at 1 mA cm−2 and an excellent cycling stability at 20 A g−1 after 5000 cycles. The as-fabricated HWF supported flexible asymmetric supercapacitors (ASCs) have achieved excellent volumetric specific capacitance of 10.25 F cm−3 and energy density of 10.1 mWh cm−3 with power density of 93.9 mW cm−3. All results suggest that the paper-making method and the HWF supported paper electrodes provide great opportunity for developing high-performance flexible energy-storage electrodes with the feasibility of mass production. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• NiCo 2 S 4 /CF composite was obtained by one-step hydrothermal sulfidation. • The NiCo 2 S 4 /CF shows high specific capacity and excellent rate capability. • The asymmetric supercapacitor exhibits an energy density of 28.8 Wh kg−1. The intertwined fiber structure is advantageous as a structure of supercapacitor electrode material. In this paper, the NiCo 2 S 4 embedded in carbon fiber (NiCo 2 S 4 /CF) has been prepared through hydrothermal vulcanization of electrospun NiCo 2 O 4 /carbon nanofibers precursor. It is a simple way to integrate the pseudocapacitive material with carbon, rendering high capacitance (1169 F g−1 at 1 A g−1), excellent rate capability (81.3% at 20 A g−1) and superior cycle stability (87.2% capacitance retention after 10,000 cycles). Afterwards, an all-solid-state asymmetric supercapacitor device (ASC) has been prepared with the NiCo 2 S 4 /CF positive electrode and porous carbon nanofiber negative electrode. When the power density of ASC is 878.3 W kg−1, the energy density can reach 28.8 Wh kg−1 with excellent cycle stability. [ABSTRACT FROM AUTHOR]

Bimetallic transition metal sulfides (TMSs) hold great promise as electrode materials for supercapacitive energy storage devices compared with their monometallic counterparts. However, it is still necessary to develop efficient synthetic protocols for favorable electrode architecture in order to further improve the electrochemical performance. This study presents a facile and controllable method to construct NiCo 2 S 4 heterostructure based on electrochemically exfoliated graphene with good adhesion, which involves the growth of bimetallic MOF precursor and in-situ conversion into NiCo 2 S 4 nanoparticles. This integrated architecture was found to be efficient for supercapacitive energy storage, as evident by the improved utilization of NiCo 2 S 4 and excellent electrochemical performance including high capacity of 1802.5 F g−1 at 1 A g−1 and good rate capability (86.1% capacity retention at 10 A g−1). Additionally, N-doped mesoporous carbon spheres (NMCS) were synthesized by sacrificial template method and used as anode for practical application. Benefiting from good charge balance and compatibility, the assembled EEG@NiCo 2 S 4 //NMCS hybrid supercapacitor (HSC) exhibited outstanding energy density (30.4 Wh kg−1 at 800.0 W kg−1) and excellent cycling stability (80.1% capacitance retention after 9000 cycles). • Advanced NiCo 2 S 4 /graphene heterostructure is created by conversion of MOF based on electrochemically exfoliated graphene. • The heterostructure is of importance to promote electrochemical performance compared with NiCo 2 S 4 and Ni 3 S 4 /NiS counterparts. • The N-doped mesoporous carbon anode with multidimensional transport pathways allows for efficient electrical/ionic transfer. [ABSTRACT FROM AUTHOR]

High conductivity NiCo 2 S 4 (NCS) nanosheets in situ grown in porous nitrogen-doped reduced graphene oxide (PN-rGO) materials were successfully prepared via a simple hydrothermal method. A synergistic effect between the NCS and PN-rGO matrix is observed on the electrochemical performance of the composites. PN-rGO/NCS exhibits an equivalent ultralow diffusion resistance and charge transfer resistance (0.16 Ω), ultrahigh specific capacitance (1,687 F g−1 at a current density of 0.5 A g−1), and an excellent rate capability (1,478 F g−1 at a current density of 10 A g−1). The asymmetric supercapacitor (ASC) is designed with PN-rGO/NCS as the positive electrode and active carbon as the negative electrode. The ASC device exhibits a high capacitance (355.5 F g−1 at a current density of 1 A g−1). Density functional theory calculations show PN-rGO/NCS to increase the electrical conductivity of the material, and concomitantly the electrochemical performance. The data suggest that the PN-rGO/NCS hybrid structure can be considered as a future supercapacitor electrode material. Image, graphical abstract [ABSTRACT FROM AUTHOR]

With the extensive use of pesticides, the problem of pesticide residues has become people's concern. In this work, NiCo 2 S 4 nanoneedle arrays grown on an electrospun graphitized carbon nanofiber film (NiCo 2 S 4 /GCNF) is successfully prepared by a simple two-step hydrothermal method, and further applied to detection of fungicide pyrimethanil (PMT). NiCo 2 S 4 arrays exhibit a unique core-shell structure with rough surface, providing abundant electrochemically active sites exposed to the electrolyte. The NiCo 2 S 4 /GCNF modified electrode displays excellent electrocatalytic activity, and the electrode surface is controlled both by diffusion and adsorption processes. When applied to PMT determination, NiCo 2 S 4 /GCNF sensor displays wide linear range from 0.06 to 800 μM with low detection limit (20 nM). Furthermore, the as-proposed sensor also displays other outstanding advantages, including simple preparation, low cost, perfect reproducibility and good application in practical samples. Such attracting analytical properties could be attributed to high electrocatalytic activity of NiCo 2 S 4 and superior electrical conductivity of GCNF frameworks. In addition, the detailed oxidation mechanism of PMT at NiCo 2 S 4 /GCNF electrode was also studied. The results indicate that NiCo 2 S 4 /GCNF is a promising platform for PMT sensors. NiCo 2 S 4 /GCNF is fabricated by hydrothermal process in steps that were produced NiCo 2 O 4 /GCNF and NiCo 2 S 4/ GCNF for the determination of pyrimethanil with wide linear range (0.06–800 μM) and low detection limit (20 nM). Image 1 • NiCo 2 S 4 nanoneedles growed on graphitic nanofiber film (NiCo 2 S 4 /GCNF) was prepared. • NiCo 2 S 4 arrays provide abundant active sites exposed to the electrolyte. • NiCo 2 S 4 /GCNF sensor showed good sensing properties toward pyrimethanil detection. [ABSTRACT FROM AUTHOR]

• 3D NiCo 2 S 4 /C hybrid composites were successfully constructed for the first time. • The optimal RL of NiCo 2 S 4 /C reaches −64.74 dB with the maximum EAB of 5.26 GHz. • The enhancement is attributed to the matched impedance and improved loss ability. • The attenuation mechanism was discussed according to the characterization results. Advanced electromagnetic wave (EMW) absorbing materials with low-cost, lightweight, high absorption efficiency and wide absorption frequency are extremely desirable for solving electromagnetic radiation. Herein, an excellent microwave absorber composed of NiCo 2 S 4 nanosheets decorated three-dimensional (3D) hierarchically porous carbon derived from biomass was successfully designed and constructed via a facile strategy for the first time. The results shown that the morphology and EMW absorption ability of 3D NiCo 2 S 4 /C hybrid composites could be synchronously tailored just by controlling the initial content of cetyltrimethyl ammonium bromide (CTAB) as a surfactant, and a substantial enhancement of microwave absorption performance could be achieved after the introduction of NiCo 2 S 4 nanosheets, resulting from the matched impedance and the enhanced attenuation constant. The optimized NiCo 2 S 4 /C composites exhibit strong EMW absorption abilities, whose minimum reflection loss (RL min) value reaches −64.74 dB with an ultra-thin thickness of 1.91 mm, and the effective absorption bandwidth (EAB, RL ≤ − 10 dB) is up to 5.26 GHz ranging from 9.22 to 14.48 GHz, which could also cover the entire X-band within 2.23–2.31 mm thickness. This work provides a new sight to design and prepare next-generation microwave absorbers with high absorption efficiency and wide absorption frequency through a low-cost, sustainable and effective method. [ABSTRACT FROM AUTHOR]

Incorporation of electroactive Fe 2 O 3 and NiCo 2 S 4 (NCS) into graphene aeorgel (GA) is presented in this work. The efficient adsorption of precursor ions on the graphene oxides sheets and subsequent hydrothermal gelation yield the GA-Fe 2 O 3 and GA-NCS composites that can be used as negative and positive electrode, respectively, for constructing a high-energy asymmetric supercapacitor (ASC). Influences of mass contents of Fe 2 O 3 and NCS on capacitive performances of GA-Fe 2 O 3 and GA-NCS electrodes are systematically investigated in KOH aqueous electrolyte. The uniform distribution of Fe 2 O 3 on the graphene sheets (GS) and the NCS nanoparticles wrapped by GS provide sufficient electroactive sites for Faradaic redox reactions, while the GA interconnected with macropores offers favorable channels for electrolyte transport. Thereby, the specific capacitance of 200 F g−1 (178 C g−1) and 386 F g−1 (170 C g−1) are achieved for GA-Fe 2 O 3 (20 wt% Fe 2 O 3) and GA-NCS (77 wt% NCS), respectively. A coin-type capacitor built with GA-Fe 2 O 3 as negative electrode and GA-NCS as positive electrode delivers a specific capacitance of 93 F g−1 (128 C g−1) at 0.1 A g−1, corresponding to a maximum energy density of 25 Wh kg−1 at a power density of 54 W kg−1. Meanwhile, the ASC also exhibits a good rate capability and a satisfying cycling stability with 72.3 % capacitance retention after cycling at 2 A g−1 for 5000 cycles. These results show great potentials of GA-Fe 2 O 3 and GA-NCS electrodes in electrochemical energy storage. [ABSTRACT FROM AUTHOR]

• Key strategies for improving electrochemical properties of NiCo 2 S 4 -based electrodes are proposed. • This work provides one specific perspective for the development of NiCo 2 S 4 -based composites used in energy storage devices. • This work is helpful to researchers around the world who are working on the synthesis and application of nanostructure TMSs. NiCo 2 S 4 has received wide attention as a promising electrode material for supercapacitors (SCs), Li-ion batteries (LIBs), and Na-ion batteries (SIBs) in the past few years because of its excellent mechanical property, low cost, and rich redox chemistry. In addition, NiCo 2 S 4 has higher electronic conductivity than the corresponding nickel cobaltite oxide (NiCo 2 O 4) and higher redox ability than the corresponding single-phase sulfide. Nevertheless, the actual applications of pristine NiCo 2 S 4 without unique morphology have been restrained on account of the small specific surface area, agglomeration, and big volume change during cycling, resulting in low reversible specific capacity (capacitance) and poor cycle stability at high rates. Constructing NiCo 2 S 4 with novel nanostructures and heterogeneous core-shell structures have been considered as one of the most promising strategy to solve these problems. In the present review, the recent research developments in the electrochemical reaction mechanisms, preparation methods, morphology control, and electrochemical property of NiCo 2 S 4 -based composites as electrode materials for SCs and secondary batteries are summarized. The main focus is to discuss the dominant factors affecting the electrochemical properties of NiCo 2 S 4 -based materials, and then highlight hopeful strategies to improve specific capacitances/capacities and cycling stability, especially at high current densities. Finally, several insights into the future developments, challenges, and prospects of NiCo 2 S 4 -based composites for SCs, LIBs, and SIBs are proposed. [ABSTRACT FROM AUTHOR]

Although potassium ion batteries (KIBs) have been invested in development as an emerging low-cost, high-content energy storage system at present. However, the large ionic radius of K+-ion lead to poor rate performance and low cycle life. Therefore, it is extremely necessary to develop a new type of potassium storage material. Here, we report a novel three-dimensional (3D) structural self-supported anode composite material for KIBs, which consists of tapered rod-shaped nanomaterial NiCo 2 S 4 and nitrogen-doped hollow carbon nanofibers (NiCo 2 S 4 @N-HCNFs). Then, the composite material was obtained by high temperature carbonization and hydrothermal reaction process. The prepared electrode materials were used to assemble K half-cells for electrochemical performance measurement, achieved the capacity of 263.7 mAh g−1 after 200 cycles at a current density of 100 mA g−1 and an outstanding stability of retaining 134.3 mAh g−1 at 3200 mA g−1 after 600 cycles. It has superior performance and convenient synthesis process over other reported metal sulfides self-supported anode materials for KIBs so far. The novel structure not only shorten the ion transmission distance, but also increase the contact area with the electrolyte. It can improve electrochemical performance effectively. Image 1 • 3D composite NiCo 2 S 4 @N-HCNFs self-supported anode was successfully fabricated. • The synthetic sample exhibits excellent potassium-storage performance. • The excellent performance thanks to the special structure of NiCo 2 S 4 @N-HCNFs. [ABSTRACT FROM AUTHOR]

Asymmetric supercapacitor as a promising energy storage system utilizes both redox-type and electric double-layer type electrodes in one single device, but it is urgent to design sustainable electrodes with low-cost and high-performance. Herein, hybrid NiCo 2 S 4 /carbon and porous carbon electrodes are prepared by using carboxylated cellulose nanofibers as the carbon source due to the carbon-rich backbone and abundant hydroxyl groups on the surface. The NiCo 2 S 4 /carbon electrode displays a large specific capacity/capacitance of 783C g−1/1569 F g−1 at 0.5 A g−1 with the capacity retention ratio of 78% after 5000 cycles. The specific capacitance of porous carbon material is 376 F g−1 at 1 A g−1. With the utilization of the different electrochemical potential windows, an asymmetric device is fabricated by using the NiCo 2 S 4 /carbon hybrid and porous carbon as the positive and negative electrodes, showing a high energy density of 53.7 W h kg−1 at 184.4 W kg−1. The asymmetric device maintains an excellent capacity retention rate of 97% after 10,000 cycles. These promising properties are related with the synergistic effect from the high-performance positive and negative electrodes. Considering the advantage in terms of sustainability, this work paves the way for the design of advanced electrodes for high-efficiency energy storage equipment. Image 1 • Carbon coated metal sulfide and porous carbon were obtained using cellulose nanofibers. • Asymmetric supercapacitor with high energy was fabricated. • This work opens a new avenue to design sustainable electrodes for energy storage. [ABSTRACT FROM AUTHOR]