In situ growth of hierarchical mesoporous NiCo2S4@MnO2 arrays on nickel foam for high-performance supercapacitors

Oxygen vacancies enhancing hierarchical NiCo2S4@MnO2 electrode for flexible asymmetric supercapacitors

The limited energy density of supercapacitors hampers their widespread application in electronic devices. Metal oxides, employed as electrode materials, suffer from low conductivity and stability, prompting extensive research in recent years to enhance their electrochemical properties. Among these efforts, the construction of core-shell heterostructures and the utilization of oxygen vacancy (VO) engineering have emerged as pivotal strategies for improving material stability and ion diffusion rates. Herein, core-shell composites comprising NiCo2S4 nanospheres and MnO2 nanosheets are grown in situ on carbon cloth (CC), forming nanoflower clusters while introducing VO defects through a chemical reduction method. Density functional theory (DFT) results proves that the existence of VO effectively enhances electronic and structural properties of MnO2, thereby enhancing capacitive properties. The electrochemical test results show that NiCo2S4@MnO2-V3 exhibits excellent 1376 F g-1 mass capacitance and 2.06 F cm-2 area capacitance at 1 A g-1. Moreover, NiCo2S4@MnO2-V3//activated carbon (AC) asymmetric supercapacitor (ASC) can achieve an energy density of 39.7 Wh kg-1 at a power density of 775 W kg-1, and maintains 15.5 Wh kg-1 even at 7749.77 W kg-1. Capacitance retention is 73.1 % after 10,000 cycles at 5 A g-1, and coulombic efficiency reaches 100 %, demonstrating satisfactory cycle stability. In addition, the device's excellent flexibility offers broad application prospects in wearable electronic applications.

Chitosan-derived carbon and NiCo2O4 aerogel composite for high-performance supercapacitors

This work presents a multi-step strategy to fabricate chitosan-derived nitrogen-doped carbon (CCS) and CCS/NiCo2O4 (CNCO) aerogels for supercapacitor application. The various mass fractions of NiCo precursors and chitosan as well as different carbonization temperatures, were investigated. The best rationally designed aerogel carbonized at 300 °C (CNCO-2) had the highest specific surface area and nitrogen content. It exhibited a high capacitance of 1200 F g-1 at 1.0 A g-1 as an active electrode material for supercapacitors. In addition, the fully solid-state CCS//CNCO-2 device had a high capacitance of 172 F g-1 at 1.0 A g-1 and excellent cyclic stability (over 87 % capacitance retention after 10,000 cycles). This device displayed a maximum energy density of 53 Wh kg-1 at 750 W kg-1. Furthermore, two devices connected in series and parallel indicate typical voltage and capacitance expansion, highlighting practicable applications of chitosan-derived aerogel composites to meet different requirements in energy storage.

Designing Efficient Nitrate Reduction Electrocatalysts by Identifying and Optimizing Active Sites of Co-Based Spinels

Cobalt-based spinel oxides (i.e., Co3O4) are emerging as low-cost and selective electrocatalysts for the electrochemical nitrate reduction reaction (NO3-RR) to ammonia (NH3), although their activity is still unsatisfactory and the genuine active site is unclear. Here, we discover that the NO3-RR activity of Co3O4 is highly dependent on the geometric location of the Co site, and the NO3-RR prefers to occur at octahedral Co (CoOh) rather than tetrahedral Co (CoTd) sites. Moreover, CoOhO6 is electrochemically transformed to CoOhO5 along with the formation of O vacancies (Ov) during the process of NO3-RR. Both experimental and theoretic results reveal that in situ generated CoOhO5-Ov configuration is the genuine active site for the NO3-RR. To further enhance the activity of CoOh sites, we replace inert CoTd with different contents of Cu2+ cations, and a volcano-shape correlation between NO3-RR activity and electronic structures of CoOh is observed. Impressively, in 1.0 M KOH, (Cu0.6Co0.4)Co2O4 with optimized CoOh sites achieves a maximum NH3 Faradaic efficiency of 96.5% with an ultrahigh NH3 rate of 1.09 mmol h-1 cm-2 at -0.45 V vs reversible hydrogen electrode, outperforming most of other reported nonprecious metal-based electrocatalysts. Clearly, this work paves new pathways for boosting the NO3-RR activity of Co-based spinels by tuning local electronic structures of CoOh sites.

Recent progress, trends, and new challenges in the electrochemical production of green hydrogen coupled to selective electrooxidation of 5-hydroxymethylfurfural (HMF)

The production of clean electrical energy and the correct use of waste materials are two topics that currently concern humanity. In order to face both problems, extensive work has been done on the electrolytic production of green H2 coupled with the electrooxidative upgrading of biomass platform molecules. 5-Hydroxymethylfurfural (HMF) is obtained from forest waste biomass and can be selectively oxidized to 2,5-furandicarboxylic acid (FDCA) by electrochemical pathways. FDCA is an attractive precursor to polyethylene furanoate (PEF), with the potential to replace petroleum-based polyethylene terephthalate (PET). An integrated electrochemical system can simultaneously produce H2 and FDCA at a lower energy cost than that required for electrolytic water splitting. Here, the benefits of the electrochemical production of H2 and FDCA over other production methods are presented, as well as the innovative applications of each reaction product and the advantages of carrying out both reactions in a coupled system. The recently reported progress is disclosed, through an exploration of electrocatalyst materials used in simultaneous production, including the use of nickel foams (NF) as modification substrates, noble and non-noble metals, metal non-oxides, metal oxides, spinel oxides and the introduction of oxygen vacancies. Based on the latest trends, the next challenges associated with its large-scale production are proposed for its implementation in the industrial world. This work can offer a guideline for the detailed understanding of the electrooxidation of HMF towards FDCA with the production of H2, as well as the design of advanced electrocatalysts for the sustainable use of renewable resources.

NiCo2S4/MoS2 Nanocomposites for Long-Life High-Performance Hybrid Supercapacitors

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.

Long-Range Magnetic Order in Nickel Hydroxide-Functionalized Graphene Quantum Dots

In this work, we demonstrate the prospect of chemically synthesizing transition metal (Ni) doped magnetic graphene quantum dots (GQDs) with the sole aim of shedding light on their magnetic properties. Our results show that adsorption of nickel hydroxide on predominantly paramagnetic GQDs reveals antiferromagnetic ordering in the M-T profile around 10 K with change of the spin exchange coupling deviating from J = 1/2 to J = 1, mainly arising from the d-p mixing hybridization between the p orbital of carbon from the GQD and the d orbital of Ni. Furthermore, our results are well complemented by ab initio simulations showing asymmetry of the up and down spins around the Fermi level for nickel hydroxide-doped GQDs with long-range spin polarization. Furthermore, the magnitude of the net magnetic moment generated for doped GQDs on the carbon atoms is found to be site-dependent (surface or edge).

Ternary Nanohybrid of Ni3S2/CoMoS4/MnO2 on Nickel Foam for Aqueous and Solid-State High-Performance Supercapacitors

To overcome the issues related to supercapacitor (SC) electrodes, such as high cost, low specific capacitance (C_s), low energy density (ED), requirements for expensive binder, etc., binderless electrodes are highly desirable. Here, a new ternary nanohybrid is presented as a binder-free SC electrode based on Ni₃S₂, CoMoS₄, and MnO₂. A facile two-step hydrothermal route, followed by a short thermal annealing process, is developed to grow amorphous polyhedral structured CoMoS₄ and further wrap MnO₂ nanowires on Ni foam. This rationally designed binder-free electrode exhibited the highest C_s of 2021 F g⁻¹ (specific capacity of 883.8 C g⁻¹ or 245.5 mAh g⁻¹) at a current density of 1 A g⁻¹ in 1 M KOH electrolyte with a highly porous surface morphology. This electrode material exhibited excellent cycling stability (90% capacitance retention after 4000 cycles) due to the synergistic contribution of individual components and advanced surface properties. Furthermore, an aqueous binder-free asymmetric SC based on this ternary composite exhibited an ED of 20.7 Wh kg⁻¹, whereas a solid-state asymmetric SC achieved an ED of 13.8 Wh kg⁻¹. This nanohybrid can be considered a promising binder-free electrode for both aqueous and solid-state asymmetric SCs with these remarkable electrochemical properties.

Hollow C-LDH/Co9S8 nanocages derived from ZIF-67-C for high- performance asymmetric supercapacitors

The design of supercapacitor electrode materials greatly depends on the rational construction of nanostructures and the effective combination of different active materials. Due to the poor electrical conductivity and mechanical strength, nickel-cobalt double hydroxide (NiCo-LDH) cannot reach the theoretical high specific capacitance value, while Co₉S₈ shows many interesting features, such as excellent electrochemical properties, high conductivity, and greatly improved redox reactions. Therefore, we prepared ZIF-67-C derived hollow NiCo-LDH (C-LDH)/Co₉S₈ nanocages containing two components of Co₉S₈ and NiCo-LDH through a multistep transformation method. The prepared C-LDH/Co₉S₈ nanoparticles showed a hollow rhomboid dodecahedron structure, and many NiCo-LDH nanosheets were reasonably distributed on the surface. In the three-electrode test, it can be obtained that its specific capacitance is 1654 F·g^-1 when current density is 2 A·g^-1 and 82.5% capacitance retention after 5000 cycles. Moreover, asymmetric supercapacitors (ASCs) prepared with C-LDH/Co₉S₈ as cathode and AC as anode can achieve a large energy density of 47.3 Wh·kg^-1 under the condition of high power density of 1505 W·kg^-1. After 10,000 cycles, capacitance retention rate is 80.9%, exhibit excellent cycle performance, suggesting the great potential of hollow C-LDH/Co₉S₈ nanocages in the application of supercapacitors.

Facile Synthesis of Zn-Co-S Nanostrip Cluster Arrays on Ni Foam for High-Performance Hybrid Supercapacitors

Mixed metal sulfides exhibit outstanding electrochemical performance compared to single metal sulfides and mixed metal oxides because of their richer redox reactions and high electronic conductivity. In the present study, Zn-Co-S nanostrip cluster arrays were formed from ZnCo₂O₄ grown on Ni foam by an anion exchange reaction using a two-step hydrothermal process. Morphological characterization confirmed that the Zn-Co-S nanostrip cluster arrays had grown homogeneously on the skeleton of the 3D Ni foam. The length of the nanostrip was approximately 8 µm, and the width ranged from 600 to 800 nm. The Ni foam-supported Zn-Co-S nanostrip cluster arrays were assessed directly for electrochemical supercapacitor applications. Compared to ZnCo₂O₄, the Zn-Co-S electrode exhibited a three-fold higher specific capacity of 830 C g⁻¹ at a specific current of 2.0 A g⁻¹. The higher polarizability, lower electro-negativity, and larger size of the S²⁻ ion played an important role in substituting oxygen with sulfur, which enhanced the performance. The Zn-Co-S//AC hybrid device delivered a maximum specific energy of 19.0 Wh kg⁻¹ at a specific power of 514 W kg⁻¹. The remarkable performance of Zn-Co-S nanostrip cluster arrays highlights their potential as a positive electrode for hybrid supercapacitor applications.

Defect {(WVIO7)WVI4} and Full {(WVIO7)WVI5} Pentagonal Units as Synthons for the Generation of Nanosized Main Group V Heteropolyoxotungstates

We report on the synthesis and characterization of three new nanosized main group V heteropolyoxotungstates K_xNa_y[H₂(XW^VI₉O₃₃)(W^VI₅O₁₂)(X₂W^VI₂₉O₁₀₃)]·nH₂O {X₃W₄₃} (x = 11, y = 16, and n = 115.5 for X = Sb^III; x = 20, y = 7, and n = 68 for X = Bi^III) and K₈Na₁₅[H₁₆(Co^II(H₂O)₂)_0.9(Co^II(H₂O)₃)₂(W^VI_3.1O₁₄)(Sb^IIIW^VI₉O₃₃)(Sb^III₂W^VI₃₀O₁₀₆)(H₂O)]·53H₂O {Co₃Sb₃W₄₂}. On the basis of the key parameters for the one-pot synthesis strategy of {Bi₃W₄₃}, a rational step-by-step approach was developed using the known Krebs-type polyoxotungstate (POT) K₁₂[Sb^V₂W^VI₂₂O₇₄(OH)₂]·27H₂O {Sb₂W₂₂} as a nonlacunary precursor leading to the synthesis and characterization of {Sb₃W₄₃} and {Co₃Sb₃W₄₂}. Solid-state characterization of the three new representatives {Bi₃W₄₃}, {Sb₃W₄₃}, and {Co₃Sb₃W₄₂} by single-crystal and powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and elemental analysis, along with characterization in solution by UV/vis spectroscopy shows that {Bi₃W₄₃}, {Sb₃W₄₃}, and {Co₃Sb₃W₄₂} represent the first main group V heteropolyoxotungstates encapsulating a defect {(W^VIO₇)W^VI₄} ({X₃W₄₃}, X = Bi^III and Sb^III) or full {(W^VIO₇)W^VI₅} ({Co₃Sb₃W₄₂}) pentagonal unit. With 43 tungsten metal centers, {X₃W₄₃} (X = Bi^III and Sb^III) are the largest unsubstituted tungstoantimonate– and bismuthate clusters reported to date. By using time-dependent UV/vis spectroscopy, the isostructural representatives {Sb₃W₄₃} and {Bi₃W₄₃} were subjected to a comprehensive study on their catalytic properties as homogeneous electron-transfer catalysts for the reduction of K₃[Fe^III(CN)₆] as a model substrate revealing up to 5.8 times higher substrate conversions in the first 240 min (35% for {Sb₃W₄₃}, 29% for {Bi₃W₄₃}) as compared to the uncatalyzed reaction (<6% without catalyst after 240 min) under otherwise identical conditions.

We report on the synthesis and characterization of three new tungsten-based defect {(W^VIO₇)W^VI₄}K_xNa_y[H₂(XW^VI₉O₃₃)(W^VI₅O₁₂)(X₂W^VI₂₉O₁₀₃)]·nH₂O {X₃W₄₃} (x = 11, y = 16, and n = 115.5 for X = Sb^III; x = 20, y = 7, and n = 68 for Bi^III) or full pentagonal {(W^VIO₇)W^VI₅} unit K₈Na₁₅[H₁₆(Co^II(H₂O)₂)_0.9(Co^II(H₂O)₃)₂(W^VI_3.1O₁₄)(Sb^IIIW^VI₉O₃₃)(Sb^III₂W^VI₃₀O₁₀₆)(H₂O)]·53H₂O {Co₃Sb₃W₄₂} encapsulating main group V representatives. With 43 W centers, {Sb₃W₄₃} and {Bi₃W₄₃} exhibit the highest nuclearity among unsubstituted tungstoantimonates and bismuthates reported to date. The catalytic properties of {Sb₃W₄₃} and {Bi₃W₄₃} as homogeneous electron-transfer catalysts for the reduction of K₃[Fe^III(CN)₆] to K₄[Fe^II(CN)₆] was investigated.

Synthesis of Hierarchical Porous Ni1.5Co1.5S4/g-C3N4 Composite for Supercapacitor with Excellent Cycle Stability

In this work, the hierarchical porous Ni1.5Co1.5S4/g-C3N4 composite was prepared by growing Ni1.5Co1.5S4 nanoparticles on graphitic carbon nitride (g-C3N4) nanosheets via a hydrothermal route. Due to the self-assembly of larger size g-C3N4 nanosheets as a skeleton, the prepared nanocomposite possesses a unique hierarchical porous structure that can provide short ions diffusion and fast electron transport. As a result, the Ni1.5Co1.5S4/g-C3N4 composite exhibits a high specific capacitance of 1827 F g-1 at a current density of 1 A g-1, which is 1.53 times that of pure Ni1.5Co1.5S4 (1191 F g-1). In particular, the Ni1.5Co1.5S4/g-C3N4//activated carbon (AC) asymmetric supercapacitor delivers a high energy density of 49.0 Wh kg-1 at a power density of 799.0 W kg-1. Moreover, the assembled device shows outstanding cycle stability with 95.5% capacitance retention after 8000 cycles at a high current density of 10 A g-1. The attractive performance indicates that the easily synthesized and low-cost Ni1.5Co1.5S4/g-C3N4 composite would be a promising electrode material for supercapacitor application.

Electrochemical Fingerprint of CuS-Hexagonal Chemistry from (Bis(N-1,4-Phenyl-N-(4-Morpholinedithiocarbamato) Copper(II) Complexes) as Photon Absorber in Quantum-Dot/Dye-Sensitised Solar Cells

The main deficit of quantum dot/dye-sensitised solar cells (QDSSCs) remains the absence of a photosensitiser that can absorb the entire visible spectrum and increase electrocatalytic activity by enhancing the conversion efficiency of QDSSCs. This placed great emphasis on the synthesis route adopted for the preparation of the sensitiser. Herein, we report the fabrication of hexagonal copper monosulfide (CuS) nanocrystals, both hexadecylamine (HDA) capped and uncapped, through thermal decomposition by thermogravimetric analysis (TGA) and a single-source precursor route. Morphological, structural, and electrochemical instruments were used to assert the properties of both materials. The CuS/HDA photosensitiser demonstrated an appropriate lifetime and electron transfer, while the electron back reaction of CuS lowered the electron lifetime in the QDSSCs. The higher electrocatalytic activity and interfacial resistance observed from current density-voltage (I–V) results agreed with electrochemical impedance spectroscopy (EIS) results for CuS/HDA. The successful fabrication of hexagonal CuS nanostructures of interesting conversion output suggested that both HDA capped and uncapped nanocrystals could be adopted in photovoltaic cells.

NiCo2S4 nanosheet grafted SiO2@C core-shelled spheres as a novel electrode for high performance supercapacitors

A high-performance supercapacitor electrode NiCo₂S₄ (NCS) nanosheet on SiO₂@C core-shell nanospheres (SiO₂@C-NCS nanocomposite) is prepared via simple an effective solution-based method. Benefiting from compositional and structural advantages, the as-prepared SiO₂@C-NCS nanocomposite exhibits a high specific capacitance (625 F g^-1 at 1 mA cm^-2) and a stable cycling performance. An asymmetric supercapacitor (ASC) assembled with SiO₂@C-NCS nanocomposite as a positive electrode and carbon nanotube paper as a negative electrode in aqueous KOH solution demonstrated a high energy density of 16 Wh kg^-1 at an ultra-high specific power of 7200 W kg^-1. These promising results suggest the possible application of mixed transition metal sulfides-based composites as advanced electrode materials for high-performance ASCs.

General Synthesis of Mixed Semiconducting Metal Oxide Hollow Spheres with Tunable Compositions for Low-Temperature Chemiresistive Sensing

Metal oxide hollow spheres (MOHSs) with multicomponent metal elements exhibit intriguing properties due to the synergistic effects of different components. However, it remains a great challenge to develop a general method to synthesize multicomponent MOHSs due to the different hydrolysis and condensation rates of precursors for different metal oxides. Herein, we demonstrate a general strategy for the controllable synthesis of MOHSs with up to five metal elements by decomposition of metal-phenolic coordination polymers (MPCPs), which are prepared by chelation of tannic acid with various metal ions. After calcination to burn out the organic component and induce heterogeneous contraction of MPCPs, a series of MOHSs with multishell structure, high specific surface area (55-171 m²/g), and crystalline mesoporous framework are synthesized, including binary (Fe-Co, Ni-Zn, and Ni-Co oxides), ternary (Ni-Co-Mn and Ni-Co-Zn oxides), and quinary (Ni-Co-Fe-Cu-Zn oxides) MOHSs. The gas sensing nanodevices based on quinary MOHSs show much higher response (10.91) than those based on single component toward 50 ppm of ethanol at 80 °C with the response/recovery time of 85/160 s. The quinary oxides sensor also displays high selectivity toward ethanol against other interfering gases (e.g., methanol, formadehyde, toluene, methane, and hydrogen) and long-term stability (∼94.0% after 4 weeks), which are extremely favorable for practical applications.

In situ growth of MnO@Na2Ti6O13 heterojunction nanowires for high performance supercapacitors

One-dimensional tunnel and layer frame crystal structure materials are extremely attractive for energy storage in electrode materials. The energy storage properties of the electrode materials depend on their conductivity. Furthermore, the conductivity of electrode materials can be tailored through combination or doping with other materials, which transforms their properties from semiconductor to semimetallic or metallic and allow them to show unequaled performance for storage devices. In this work, heterostructures of manganese oxide (MnO) and modified sodium titanate (Na₂Ti₆O₁₃) (MnO@Na₂Ti₆O₁₃) nanowires are attained by the in situ thermal decomposition method. The heterojunction between MnO and Na₂Ti₆O₁₃ allows the semiconductor properties of pure Na₂Ti₆O₁₃ to show remarkable metallic behavior for improving the electrochemical performance. The capacitance of MnO@Na₂Ti₆O₁₃ heterojunction nanowires can reach 272.3 F g^-1, a power intensity of 250 W kg^-1 at the energy density of 37.83 Wh kg^-1 and retain 5000 W kg^-1 at 6.67 Wh kg^-1 as well. The energy storage mechanism of the MnO@Na₂Ti₆O₁₃ heterostructure is studied by density functional theory. All of the results show that the MnO@Na₂Ti₆O₁₃ heterostructure material has the potential to be an excellent supercapacitor material in the future.

A 3D self-supported coralline-like CuCo2S4@NiCo2S4 core-shell nanostructure composite for high-performance solid-state asymmetrical supercapacitors

Rational construction of three dimensional (3D) composite structure is an important method to flexible supercapacitor electrodes and has been extensively developed. In this work, a 3D self-supported CuCo₂S₄@NiCo₂S₄ core-shell nanostructure grown on Nickel (Ni) foam, constructed by a hydrothermal method, was used as a novel supercapacitor electrode material. The unique structure possesses a large, specific surface area, rapid diffusion of electrolyte ions by numerous channels and avoids the use of additives and adhesives. The high electrical conductivity of the CuCo₂S₄ nanoneedle arrays can speed up electronic transmission. At a current density of 1 A g^-1, the electrode material exhibits a high specific capacity of 539.2 C g^-1 and cycling stability with 100% capacity retention after 5000 cycles in 3 M KOH. Furthermore, when the obtained CuCo₂S₄@NiCo₂S₄ was used as the positive electrode and an activated carbon was used as the negative electrode, a solid-state asymmetric supercapacitor was assembled. More importantly, the obtained solid-state asymmetric supercapacitor demonstrated excellent electrochemical performance. When the power density was 400 W kg^-1, it delivered a high density of 23.4 W h kg^-1 with a high voltage window of 1.6 V, thus demonstrating that the material has the potential for use as an efficient electrode for electrochemical capacitors. Due to its comprehensive electrochemical performance, the CuCo₂S₄@NiCo₂S₄ solid-state asymmetric supercapacitor effectively operated a red LED.

Novel dealloying-fabricated NiCo2S4 nanoparticles with excellent cycling performance for supercapacitors

In this work, NiCo₂S₄ nanoparticles for supercapacitors are successfully synthesized with a top-down strategy, using a novel dealloying method with an ion exchange reaction. The surface morphology and x-ray diffraction investigations demonstrated that NiCo₂S₄ nanoparticles are interconnected by ligaments of the synthesized sample. The dealloyed NiCo₂S₄ shows an enhanced electrochemical performance of about 1132.5 F g^-1 at 0.5 A g^-1; kinetic analysis implies a surface-controlled contribution from NiCo₂S₄ (53.86% capacitive contributions). Notably, the NiCo₂S₄//AC (active carbon) device displays a comparatively high energy density (22.83 Wh kg^-1), maximum power density (1327.1 W kg^-1) and superior cycling performance (capacitance retention of 108% after 30 000 cycles).

A high-performance asymmetric supercapacitor based on Ni3S2-coated NiSe arrays as positive electrode

Cotton-like Ni₃S₂-coated NiSe rod composite electrode was synthesized by cyclic voltammetry electrodeposition with satisfactory electrochemical performance.

Facile one-pot synthesis of NiCo2Se4-rGO on Ni foam for high performance hybrid supercapacitors

A facile, innovative synthesis for the fabrication of NiCo₂Se₄-rGO on a Ni foam nanocomposite via a simple hydrothermal reaction is proposed. The as-prepared NiCo₂Se₄-rGO@Ni foam electrode was tested through pxrd, TEM, SEM, and EDS to characterize the morphology and the purity of the material. The bimetallic electrode exhibited outstanding electrochemical performance with a high specific capacitance of 2038.55 F g⁻¹ at 1 A g⁻¹. NiCo₂Se₄-rGO@Ni foam exhibits an extensive cycling stability after 1000 cycles by retaining 90% of its initial capacity. A superior energy density of 67.01 W h kg⁻¹ along with a high power density of 903.61 W kg⁻¹ further proved the high performance of this electrode towards hybrid supercapacitors. The excellent electrochemical performance of NiCo₂Se₄-rGO@Ni foam can be explained through the high electrocatalytic activity of NiCo₂Se₄ in combination with reduced graphene oxide which increases conductivity and surface area of the electrode. This study proved that NiCo₂Se₄-rGO@Ni foam can be utilized as a high energy density-high power density electrode in energy storage applications.

A hybrid supercapacitor comprising a NiCo₂Se₄-rGO composite has been fabricated on Ni foam and shows high energy and power density and superior flexibility.

pH-responsive chitosan-based flocculant for precise dye flocculation control and the recycling of textile dyeing effluents

In this work, we introduce a simple and effective method for the controlled release of dye from dye saturation flocs by a well-designed pH responsive chitosan-based flocculant. The dye flocculation capacities could be precisely controlled from 0.5 to 2 g g-1 by simply adjusting the pH of the desorption solution. A series of flocs with different dye flocculation capacities was prepared and used as nitrogen-rich precursors to prepare nitrogen-doped carbon materials through one-step carbonization. The results demonstrate that the specific surface areas, pore structures and supercapacitance performance of the resulting N-doped carbon materials could be readily controlled by varying the dye flocculation capacity. By using a dye sludge floc with an appropriate dye flocculation capacity (1.5 g g-1) as a precursor, the resulting N-doped material exhibited a high specific capacity and good cycling performance for a supercapacitor electrode. The unique pH-responsive properties of the chitosan-based flocculant facilitated easy tuning of the surface cationic degree and deprotonation behavior by varying pH. This work presents a new concept for balancing between environmental capacity and energy capacity using a smart pH-responsive carrier system based on modified chitosan, which is highly promising for the recycling of industrial wastewater to produce energy materials.

Facile synthesis and magnetic and electrical properties of layered chalcogenides K2CoCu3Q4 (Q for S and Se)

Layered transition-metal chalcogenides have attracted great interest due to their unique electronic and optical properties. Here, we represent two layered quaternary chalcogenides K2CoCu3S4 and K2CoCu3Se4 prepared by a convenient hydrothermal route. From powder XRD and TEM analyses, K2CoCu3Q4 possesses a tetragonal ThCr2Si2-type structure with a random arrangement of Co and Cu atoms. The phase purity of the samples was confirmed by ICP, SEM, and EDS analyses, and the oxidation states of Co and Cu atoms were determined to be +3 and +1 by XPS spectra. Both samples show a weak ferromagnetic behavior at low temperature induced by spin-canted antiferromagnetic ordering. The temperature dependent resistivity, ρ(T), reveals a metallic nature for stoichiometric K2CoCu3S4. The semiconducting behavior of K2CoCu3Se4 could be explained better by variable range hopping (VRH) rather than adiabatic small polaron hopping (SPH). This new series of layered chalcogenides may offer a promising candidate for potential electronic applications.

One-step synthesis of hollow C-NiCo2S4 nanostructures for high-performance supercapacitor electrodes

Carbon-containing NiCo2S4 hollow-nanoflake structures were fabricated by a one-step solvothermal method using CS2 as a single source for sulfidation and carbonization. The reaction mechanism for the hollow structure with carbon residues was explored based on the formation of a bis(dithiocarbamate)-metal complex and the Kirkendall effect during solvothermal synthesis. The NiCo2S4 nanoflake electrode exhibited a high specific capacitance of 1722 F g-1 (specific capacity 688.8 C g-1) at a current density of 1 A g-1 and an excellent cycling stability (capacity retention of 98.8% after 10 000 cycles). The as-fabricated asymmetric supercapacitor based on NiCo2S4 nanoflakes and activated carbon electrodes revealed a high energy density of 38.3 W h kg-1 and a high power density of 8.0 kW kg-1 with a capacitance retention of 91.5% and a coulombic efficiency of 95.6% after 5000 cycles, highlighting its great potential for practical supercapacitor applications.

Synthesis of nanostructured metal sulfides via a hydrothermal method and their use as an electrode material for supercapacitors

Metal sulfides have attracted considerable interest owing to their notable electrochemical properties and multiple application areas, such as solar cells and supercapacitors (SCs).

Improved Li-storage performance with PEDOT-decorated MnO2 nanoboxes

In this paper, MnO₂ nanoboxes coated with poly(3,4-ethylenedioxythiophene) film (denoted as MnO₂@PEDOT) are investigated as an anode material in lithium-ion batteries. The MnO₂ nanoboxes are developed through the surface chemical oxidation decomposition of MnCO₃ cubes and the subsequent removal of their remaining cores. PEDOT is coated on the surface of MnO₂ nanoboxes via in situ polymerization of 3,4-ethylenedioxythiophene. The charge-discharge tests demonstrate that this special configuration endows the resulting MnO₂@PEDOT with remarkable electrochemical performances, that is a reversible capacity of 628 mA h g^-1 after 850 cycles at a current density of 1000 mA g^-1 and a rate capacity of 367 mA h g^-1 at 3000 mA g^-1. The results indicate that the nanoboxes provide the paths for Li-ion diffusion, the reaction sites for Li-ion intercalation/deintercalation and the space to buffer the volume change during the charge-discharge process, while the conductive polymer ensures the structural stability and improves the electronic conductive property of MnO₂.

Fabrication and Synthesis of Highly Ordered Nickel Cobalt Sulfide Nanowire-Grown Woven Kevlar Fiber/Reduced Graphene Oxide/Polyester Composites

Well-aligned NiCo₂S₄ nanowires, synthesized hydrothermally on the surface of woven Kevlar fiber (WKF), were used to fabricate composites with reduced graphene oxide (rGO) dispersed in polyester resin (PES) by means of vacuum-assisted resin transfer molding. The NiCo₂S₄ nanowires were synthesized with three precursor concentrations. Nanowire growth was characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Hierarchical and high growth density of the nanowires led to exceptional mechanical properties of the composites. Compared with bare WKF/PES, the tensile strength and absorbed impact energy were enhanced by 96.2% and 92.3%, respectively, for WKF/NiCo₂S₄/rGO (1.5%)/PES. The synergistic effect of NiCo₂S₄ nanowires and rGO in the fabricated composites improved the electrical conductivity of insulating WKF/PES composites, reducing the resistance to ∼10³ Ω. Joule heating performance depended strongly on the precursor concentration of the nanowires and the presence of rGO in the composite. A maximum surface temperature of 163 °C was obtained under low-voltage (5 V) application. The Joule heating performance of the composites was demonstrated in a surface deicing experiment; we observed that 17 g of ice melted from the surface of the composite in 14 min under an applied voltage of 5 V at -28 °C. The excellent performance of WKF/NiCo₂S₄/rGO/PES composites shows great potential for aerospace structural applications requiring outstanding mechanical properties and Joule heating capability for deicing of surfaces.

Honeycomb-like NiCo2S4 nanosheets prepared by rapid electrodeposition as a counter electrode for dye-sensitized solar cells

Honeycomb-like nickel cobalt sulfide (NiCo₂S₄) nanosheets were directly deposited on fluorine-doped tin oxide substrate by a rapid voltammetric deposition method. The method was also controllable and feasible for preparing NiCo₂S₄ on flexible Ti foil without any heating processes. Compared with Pt, CoS and NiS, NiCo₂S₄ exhibited low charge-transfer resistances and excellent electrocatalytic activity for [Formula: see text] reduction, acting as a counter electrode for a dye-sensitized solar cell. The NiCo₂S₄-based solar cell showed higher power conversion efficiency (7.44%) than that of Pt-based solar cell (7.09%) under simulated illumination (AM 1.5 G, 100 mW cm^-2). The device based on the flexible NiCo₂S₄/Ti foil achieved a power conversion efficiency of 5.28% under the above illumination conditions. This work can be extended to flexible and wearable technologies due to its facile technique.

Graphene Dots Embedded Phosphide Nanosheet-Assembled Tubular Arrays for Efficient and Stable Overall Water Splitting

Bifunctional electrocatalysts are highly desired for overall water splitting. Herein, the design and fabrication of three-dimensional (3D) hierarchical earth-abundant transition bimetallic phosphide arrays constructed by one-dimensional tubular array that was derived from assembling two-dimensional nanosheet framework has been reported by tailoring the Co/Ni ratio and tunable morphologies, and zero-dimensional (0D) graphene dots were embedded on Co-Ni phosphide matrix to construct 0D/2D tubular array as a highly efficient electrode in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). On the basis of advanced merits, such as the high surface-active sites, well-dispersed graphene dots, and enhanced electron transfer capacity as well as the confinement effect of the graphene dots on the nanosheets, the integrated GDs/Co_0.8Ni_0.2P tubular arrays as anode and cathode exhibit excellent OER and HER performance. By use of GDs/Co_0.8Ni_0.2P arrays in the two-electrode setup of the device, a remarkable electrocatalytic performance for full water splitting has been achieved with a high current density of 10 mA cm^-2 at 1.54 V and outstanding long-term operation stability in an alkaline environment, indicating a promising system based on nonprecious-metal electrocatalysts toward potential practical devices of overall water splitting.

NiCo2 S4 Materials for Supercapacitor Applications

Cobalt-nickel sulfide (NiCo₂ S₄ ) shows extensive potential for innovative photoelectronic and energetic materials owing to distinctive physical and chemical properties. In this review, representative strategies for the fabrication and application of NiCo₂ S₄ and composite nanostructures are outlined for supercapacitors, with the aim of promoting the development of NiCo₂ S₄ and their composites in the supercapacitor field through an analysis and comparison of diverse nanostructures. A brief introduction into the structures, properties, and morphologies are presented. Further prospects and promising developments of the materials in the supercapacitor field are also proposed.

Layer-structured nanohybrid MoS2@rGO on 3D nickel foam for high performance energy storage applications

MoS₂@reduced graphene oxide on 3D nickel foam was synthesized using an inexpensive room-temperature two-step method composed of the layer-by-layer method and solution-based successive ionic layer adsorption and reaction.

Fabrication of an acetone sensor based on facile ternary MnO2/Gd2O3/SnO2 nanosheets for environmental safety

The facile hydrothermally synthesized (at low temperature, in alkaline medium of pH 10.5) nanosheets (NSs) of MnO₂/Gd₂O₃/SnO₂ are well crystalline-doped ternary metal oxides.