CoNi2 S4 Electrode with High Mass-Loading for High-Energy-Density Supercapacitor: Role of S-Containing Anions Exchange.

Anion exchange is recognized as an effective method to regulate the composition, electronic conductivity, and electrochemical behavior of the transition metal-based compounds. In this work, anion exchange is adopted as a rational post-treatment route to facilitate the capacitive activity of CoNi2 S4 nanoparticle arrays grown on carbon cloth (CC) with high mass-loading. As soaked in saturated Na2 S solution, the CoNi2 S4 /CC electrode showed an increased capacity from 483 C g-1 to 841 C g-1 at 10 mA cm-2 with excellent rate performance and stable cycling performance, which was superior to the CoNi2 S4 /CC electrode activated by NaBH4 reduction. Anion exchange was beneficial for enhancing the crystallinity, retaining the adhesion of nanoarrays, and realizing low resistance nature in a mild route. The as-assembled CoNi2 S4 /CC//activated CC hybrid supercapacitor delivered a high areal capacitance of 1.28 F cm-2 at 5 mA cm-2 , and achieved an energy density of 0.58 mWh cm-2 at a power density of 4.5 mW cm-2 with excellent cycle stability with 90.6 % capacity retention after 10000 cycles.

Facile deposition of palladium oxide (PdO) nanoparticles on CoNi2S4microstructures towards enhanced oxygen evolution reaction.

Strong demand for renewable energy resources and clean environments have inspired scientists and researchers across the globe to carry out research activities on energy provision, conversion, and storage devices. In this context, development of outperform, stable, and durable electrocatalysts has been identified as one of the major objectives for oxygen evolution reaction (OER). Herein, we offer facile approach for the deposition of few palladium oxide (PdO) nanoparticles on the cobalt-nickel bi-metallic sulphide (CoNi2S4) microstructures represented as PdO@ CoNi2S4using ultraviolet light (UV) reduction method. The morphology, crystalline structure, and chemical composition of the as-prepared PdO@ CoNi2S4composite were probed through scanning electron microscopy, powder x-ray diffraction, high resolution transmission electron microscopy, energy dispersive spectroscopy and x-ray photoelectron spectroscopy techniques. The combined physical characterization results revealed that ultraviolet light (UV) light promoted the facile deposition of PdO nanoparticles of 10 nm size onto the CoNi2S4and the fabricated PdO@ CoNi2S4composite has a remarkable activity towards OER in alkaline media. Significantly, it exhibited a low onset potential of 1.41 V versus reversible hydrogen electrode (RHE) and a low overpotential of 230 mV at 10 mA cm-2. Additionally, the fabricated PdO@ CoNi2S4composite has a marked stability of 45 h. Electrochemical impedance spectroscopy has shown that the PdO@CoNi2S4composite has a low charge transfer resistance of 86.3 Ohms, which favours the OER kinetics. The PdO@ CoNi2S4composite provided the multiple number of active sites, which favoured the enhanced OER activity. Taken together, this new class of material could be utilized in energy conversion and storage as well as sensing applications.

Phosphorized CoNi2 S4 Yolk-Shell Spheres for Highly Efficient Hydrogen Production via Water and Urea Electrolysis.

Exploring earth-abundant electrocatalysts with excellent activity, robust stability, and multiple functions is crucial for electrolytic hydrogen generation. Porous phosphorized CoNi2 S4 yolk-shell spheres (P-CoNi2 S4 YSSs) were rationally designed and synthesized by a combined hydrothermal sulfidation and gas-phase phosphorization strategy. Benefiting from the strengthened Ni3+ /Ni2+ couple, enhanced electronic conductivity, and hollow structure, the P-CoNi2 S4 YSSs exhibit excellent activity and durability towards hydrogen/oxygen evolution and urea oxidation reactions in alkaline solution, affording low potentials of -0.135 V, 1.512 V, and 1.306 V (versus reversible hydrogen electrode) at 10 mA cm-2 , respectively. Remarkably, when used as the anode and cathode simultaneously, the P-CoNi2 S4 catalyst merely requires a cell voltage of 1.544 V in water splitting and 1.402 V in urea electrolysis to attain 10 mA cm-2 with excellent durability for 100 h, outperforming most of the reported nickel-based sulfides and even noble-metal-based electrocatalysts. This work promotes the application of sulfides in electrochemical hydrogen production and provides a feasible approach for urea-rich wastewater treatment.

CoNi2 S4 Nanoparticle/Carbon Nanotube Sponge Cathode with Ultrahigh Capacitance for Highly Compressible Asymmetric Supercapacitor.

Compared with other flexible energy-storage devices, the design and construction of the compressible energy-storage devices face more difficulty because they must accommodate large strain and shape deformations. In the present work, CoNi2 S4 nanoparticles/3D porous carbon nanotube (CNT) sponge cathode with highly compressible property and excellent capacitance is prepared by electrodepositing CoNi2 S4 on CNT sponge, in which CoNi2 S4 nanoparticles with size among 10-15 nm are uniformly anchored on CNT, causing the cathode to show a high compression property and gives high specific capacitance of 1530 F g-1 . Meanwhile, Fe2 O3 /CNT sponge anode with specific capacitance of 460 F g-1 in a prolonged voltage window is also prepared by electrodepositing Fe2 O3 nanosheets on CNT sponge. An asymmetric supercapacitor (CoNi2 S4 /CNT//Fe2 O3 /CNT) is assembled by using CoNi2 S4 /CNT sponge as positive electrode and Fe2 O3 /CNT sponge as negative electrode in 2 m KOH solution. It exhibits excellent energy density of up to 50 Wh kg-1 at a power density of 847 W kg-1 and excellent cycling stability at high compression. Even at a strain of 85%, about 75% of the initial capacitance is retained after 10 000 consecutive cycles. The CoNi2 S4 /CNT//Fe2 O3 /CNT device is a promising candidate for flexible energy devices due to its excellent compressibility and high energy density.

Morphology optimization strategy of flower-like CoNi2S4/Co9S8@MoS2 core@shell nanocomposites to achieve extraordinary microwave absorption performances.

Morphology optimization is an effective strategy to take full advantage of interface polarization for the improvement of electromagnetic wave attenuation capability. Herein, a general route was proposed to produce the flower-like core@shell structured MoS2-based nanocomposites through a simple hydrothermal process. Through the in-situ hydrothermal reaction between the Mo and S sources on the surface of CoNi nanoparticles, flower-like core@shell structured CoNi2S4/Co9S8@MoS2 nanocomposites could be successfully synthesized. By regulating the hydrothermal temperature, the flower-like geometrical morphology of samples could be effectively optimized, and the as-prepared sample (S2) synthesized at 200 °C displayed very excellent flower-like morphology compared to the samples (S1 and S3) obtained at 180 and 220 °C. Owing to the excellent interface polarization effect, the as-prepared S2 presented the evidently superior comprehensive microwave absorption properties in terms of strong aborption capability, wide absorption bandwidth and thin matching thicknesses compared to those of S1 and S3. The as-prepared core@shell structured CoNi2S4/Co9S8@MoS2 sample with very excellent flower-like morphology simultaneously displayed the minimal reflection loss of -50.61 dB with the matching thickness of 2.98 mm, and the effective absorption bandwidth of 8.40 GHz with the matching thickness of 2.36 mm. Therefore, we provided a general route for the production of flower-like core@shell structured MoS2-based nanocomposites, which could make the best of interface polarization to develop high-efficiency microwave absorbers.

Probing the Extent of Polysulfide Confinement Using a CoNi2S4 Additive Inside a Sulfur Cathode of a Na/Li-Sulfur Rechargeable Battery.

The extent of confinement of soluble metal polysulfides inside a sulfur cathode strongly determines the performance of metal-sulfur rechargeable batteries. This challenge has been largely tackled by loading sulfur inside various conducting porous scaffolds. However, this approach has not proven to be fully effective because of poor chemical interaction between the scaffold and polysulfides. Here, we demonstrate an excellent strategy of using a sulfide additive in the sulfur cathode, viz., cobalt nickel sulfide (CoNi2S4), to efficiently trap the soluble polysulfides inside the sulfur cathode. In situ Raman and ex situ UV-vis spectroscopies clearly reveal higher retention of polysulfides inside CoNi2S4/S compared to bare sulfur and carbon-sulfur mixture cathodes. Against sodium, the CoNi2S4/S assembly showed remarkable cyclability both as a function of current density (at room temperature) and temperature (at constant current density). The versatility of CoNi2S4 is further proven by the exemplary cyclability at various current densities at room temperature against lithium.

Well-designed cobalt-nickel sulfide microspheres with unique peapod-like structure for overall water splitting.

Achieving sustainable energy technology with outstanding performance and clean materials for overall water splitting, while fascinating, still include many challenges. Herein, the masterly CoNi2S4@CoS2/NF 3D microspheres assembled by peapod-like nanorods with a mass of CoS2 particles are successfully prepared on nickel foam. The well-preserved 3D porous materials with unique heterostructure have various merits including more electronic channels, small electrons transfer resistance and open interior space. Besides, the unique peapod-like structure endows the catalyst plentiful, dispersive and exposed reactive sites, which is vital important to significantly increase the electrochemical performance. Notably, the as-prepared CoNi2S4@CoS2/NF catalysts achieve optimized electrocatalytic activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) at low overpotentials of 259 mV and 173 mV while deliver 10 mA cm-2 current density, respectively. It can be anticipated that it is a potential alternative catalyst for rational utilization in electrolytic water splitting fields.

Fully Controllable Design and Fabrication of Three-Dimensional Lattice Supercapacitors.

Supercapacitors have been proven to be a superior candidate for energy storage systems. Yet, most of them are of an approximately two-dimensional structure, without taking full advantage of the spatial superiority to load more mass of active materials. Moreover, three-dimensional (3D) sponge electrodes may hinder ion transmission due to the significant variations in porous structures. In this work, fully controllable 3D lattice supercapacitors with the ordered porous structures were fabricated for the first time via using 3D printing technology. To increase the mass loading capacity, active materials, including metal films, carbon nanomaterials, and transition-metal sulfides, were hierarchically loaded onto the surface of the lattice substrate by using electroless plating, dip-coating, and electrodeposition methods. The as-fabricated CoNi2S4/Ni/octet-truss lattice (OTL) electrode demonstrates a high capacitance until up to 1216 F g-1 (KOH electrolyte). The lattice asymmetric all-solid-state supercapacitors, composed of CoNi2S4/Ni/OTL as anode and carbon materials/Ni/OTL as cathode, display the highest specific capacitance of 23.5 F g-1, a 10.6 Wh kg-1 energy density at the 2488.3 W kg-1 power density, and a robustness (77.3% capacitance retention after 1800 cycles). We expect that the design and fabrication method for the fully controllable 3D lattice supercapacitor with hierarchical activating materials can open a door to develop 3D supercapacitors.

Hierarchical Nanosheet-Built CoNi2S4 Nanotubes Coupled with Carbon-Encapsulated Carbon Nanotubes@Fe2O3 Composites toward High-Performance Aqueous Hybrid Supercapacitor Devices.

A hybrid supercapacitor system was designed with ternary Ni-Co sulfides (CoNi2S4) as cathode materials and Fe-based composites [carbon nanotubes (CNTs)@Fe2O3@C] as anode materials to achieve excellent overall electrochemical performance with high energy and power density as well as long lifespan. Here, hierarchical CoNi2S4 nanotubes were synthesized by a solvothermal route followed by sulfidation reaction for the first time, in which nanotubes were composed of interconnected ultrathin nanosheets. Consequently, such a unique nanosheet-built nanoarchitecture enables the CoNi2S4 cathode with multidimensional synergistic effect from one-dimensional nanotubes, two-dimensional nanosheets, and three-dimensional frameworks. Profiting from its structural merits, the as-prepared CoNi2S4 nanotubes deliver a high capacitance of 2552 F g-1 at 1 A g-1 with a high rate capacity of 81% at 25 A g-1. In addition, the CNTs@Fe2O3@C anode materials-incorporating carbon-encapsulated ultrafine Fe2O3 nanoparticles into CNT matrices-were achieved by atomic layer deposition and acetylene thermal decomposition, which realize excellent electrochemical properties (678 F g-1 at 1 A g-1 and capacity retention of 82% at 25 A g-1) that matched well with CoNi2S4 cathode materials. With the well-designed nanostructure and matching of materials and properties, the corresponding aqueous hybrid device exhibits a wide output voltage window of 0-1.75 V with a maximum energy density of 90.5 W h kg-1 at a power density of 1.84 kW kg-1. Meanwhile, a high energy density of 73.1 W h kg-1 can be retained at an ultrahigh power density of 26.9 kW kg-1. Moreover, the hybrid device has a stable cycling ability with 82.1% retention over 5000 cycles. This coordinative design strategy integrating the cathode and anode electrodes developed in this work provides a novel way to manufacture next-generation energy-storage device with high performance and safety.

CoNi(2)S(4) nanosheet arrays supported on nickel foams with ultrahigh capacitance for aqueous asymmetric supercapacitor applications.

We report that CoNi2S4 nanosheet arrays exhibit ultrahigh specific capacitance of 2906 F g(-1) and areal capacitance of 6.39 F cm(-2) at a current density of 5 mA cm(-2), as well as good rate capability and cycling stability, and superior electrochemical performances with an energy density of 33.9 Wh kg(-1) at a power density of 409 W kg(-1) have been achieved in an assembled aqueous asymmetric supercapacitor. The CoNi2S4 nanosheet arrays were in situ grown on nickel foams by a facile two-step hydrothermal method. The formation mechanism of the CoNi2S4 nanosheet arrays was based on an anion-exchange reaction involving the pseudo Kirkendall effect. The two aqueous asymmetric supercapacitors in series using the CoNi2S4 nanosheet arrays as the positive electrodes can power four 3-mm-diameter red-light-emitting diodes. The outstanding supercapacitive performance of CoNi2S4 nanosheet arrays can be attributed to ravine-like nanosheet architectures with good mechanical and electrical contact, low crystallinity and good wettability without an annealing process, rich redox reactions, as well as high conductivity and transport rate for both electrolyte ions and electrons. Our results demonstrate that CoNi2S4 nanosheet arrays are promising electrode materials for supercapacitor applications.