A facile preparation and electrochemical properties of nickel based compound-graphene sheet composites for supercapacitors

Composites of a nickel based compound incorporated with graphene sheets(NiBC-GS) are prepared by a simple flocculation,using hydrazine hydrate as flocculant and reductant,from a homogeneous intermixture of nickel dichloride and graphene oxide dispersed in N,N-dimethylformamide.Morphology,microstructure and thermal stability of the obtained products were characterized by field-emission scanning electron microscopy,X-ray diffraction and thermal gravimetric analysis.Furthermore,the electrochemical properties of NiBC-GS,as electrode materials for supercapacitors,were studied by cyclic voUammetry and galvanostatic charge/discharge in 2 mol L~(-1) KOH solution.It was determined that for NiBC-GS annealed at 250 ℃.a high specific capacitance of 2394 Fg~(-1) was achieved at a current density of 1 Ag~(-1),with 78%of the value(i.e.,1864 Fg~(-1)) retained after 5000 times of repeated galvanostatic charge/discharge cycling.The high specific capacitance and available charge/discharge stability indicate the synthesized NiBC-GS250 composite is a good candidate as a novel electrode material for supercapacitors.     

Enriching redox active sites by interconnected nanowalls-like nickel cobalt phospho-sulfide nanosheets for high performance supercapacitors

Although transition metal phospho-sulfides deliver outstanding electrochemical performance, complex preparation methods hindered their further development. Herein, we report a facile one-step electrodeposition approach to deposit interconnected nanowalls-like nickel cobalt phospho-sulfide (Ni-Co-P-S) nanosheets onto the surface of carbon cloth. The thin Ni-Co-P-S nanosheets with multi-components and synergetic effects delivered rich active sites, further enhancing reversible capacitance. Therefore, the as-prepared Ni-Co-P-S electrode materials exhibit excellent electrochemical performance in a three-electrode system, showcasing a high specific capacitance of 2744 F/g at 4 A/g. The full supercapacitors based on Ni-Co-P-S as positive electrode and active carbon as negative electrode showcase a high specific capacitance of 110.9 F/g at 1 A/g, impressive energy density of 39.4 Wh/kg at a power density of 797.5 W/kg in terms of excellent cycling stability (91.87% retention after 10,000 cycles). This simple electrode position strategy for synthesizing Ni-Co-P-S can be extended to prepare electrode materials for various sustainable electrochemical energy storage/conversion technologies.     

Epitaxial electrodeposition of cadmium selenide thin films on indium phosphide single crystal

Epitaxial CdSe layers were electrodeposited from a standard aqueous electrolyte onto a (111) InP single crystal. By using various characterization techniques (RHEED, XRD, HREM,...) it was demonstrated that a good epitaxy can be achieved by monitoring the experimental parameters very carefully, in particular the selenium concentration in the electrolyte and the deposition potential. For optimum conditions, the composition of the semiconducting layer is close to stoichiometry and the carrier density is around 1 × 10¹⁷ cm⁻³. Received: 23 January 1992 / Accepted: 3 March 1997     

Semiconducting thin films of zinc selenide quantum dots

A novel chemical route for deposition of zinc selenide quantum dots in thin film form is developed. The deposited films are characterized with very high purity in crystallographic sense, and behave as typical intrinsic semiconductors. Evolution of the average crystal size, lattice constant, lattice strain and the optical properties of the films upon thermal treatment is followed and discussed. The band gap energy of as-deposited ZnSe films is blue-shifted by ≈0.50 eV with respect to the bulk value, while upon annealing treatment it converges to 2.58 eV. Two discrete electronic states which originate from the bulk valence band are observed in the UV-VIS spectra of ZnSe 3D quantum dots deposited in thin film form via allowed electronic transitions to the 1S electronic state arising from the bulk conduction band—appearing at 3.10 and 3.50 eV. The splitting between these two states is approximately equal to the spin-orbit splitting in the case of bulk ZnSe. The electronic transitions in the case of non-quantized annealed films are discussed in terms of the direct allowed band-to-band transitions with the spin-orbit splitting of the valence band of 0.40 eV. The effective mass approximation model (i.e., the Brus model) with the static relative dielectric constant of bulk ZnSe fails to predict correctly the size dependence of the band gap energy, while only a slight improvement is obtained when the hyperbolic band model is applied. However, when substantially smaller value for ε_r (2.0 instead of 8.1) is used in the Brus model, an excellent agreement with the experimental data is obtained, which supports some earlier indications that the quantum dots ε_r value could be significantly smaller than the bulk material value. The ionization energy of a deep donor impurity level calculated on the basis of the temperature dependence of the film resistivity is 0.82 eV at 0 K.     

Recent advances in metal oxide/hydroxide on three-dimensional nickel foam substrate for high performance pseudocapacitive electrodes

The high demand for long-lasting and portable energy storage devices with enhanced energy and power densities has attracted researcher's interest globally. The three-dimensional (3D) nickel foam is a promising electrode material for storing energy in various devices because they possess large surface area, are very conductive and enjoy a continuous permeable 3D system. This article provides a review and detailed information on the uses of 3D nickel foam-based electrodes with metal oxides/hydroxides of different morphologies for high-performance pseudocapacitors. We assess the limitations and future prospects of 3D nickel foam-based electrodes with metal oxides/hydroxides for industrial application towards enhancing pseudocapacitors' energy storage capability.     

Impact of polypyrrole incorporation on nickel oxide@multi walled carbon nanotube composite for application in supercapacitors

In this article we report the synthesis of polypyrrole incorporated nickel oxide multi walled carbon nanotube (NiO@NMWCNT/PPy) composites by thermal reduction protocol for supercapacitor applications. The structural and morphological properties of the composites were confirmed by the aid of X-ray diffraction (XRD), Field-emission scanning electron microscope (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and Field-emission transmission electron microscopy (FE-TEM) analysis indicating the hexagonal crystal structure of NiO decorated on NMWCNT/Ppy. The electrochemical characteristics of the NiO@MWCNT/PPy composite were analyzed in the presence of 2 M KOH as an electrolyte. The NiO@NMWCNT/PPy nanostructured composite produced a plenty of active sites for ion migration reactions that facilitate the energy storage mechanism. As a proof of concept demonstration, the NiO@NMWCNT/PPy composite was explored as an electrode materials in supercapacitor and exhibited specific capacitance of 395 F g⁻¹ and cyclic stability up to 5000 cycles at 0.5 A g⁻¹. Enhanced performance of composite is attributed to the incorporation of polypyrrole in NiO@NMWCNT. The improved capacitance and cyclic stability demonstrated by the composite indicates the NiO@NMWCNT/PPy to be a promising candidate for supercapacitor applications.     

CeO2 quantum dots doped Ni-Co hydroxide nanosheets for ultrahigh energy density asymmetric supercapacitors

By integrating the merits of lanthanide elements and quantum dots, we firstly design CeO₂ quantum dots doped Ni-Co hydroxide nanosheet via a controllable synthetic strategy, which exhibits a large specific capacitance (1370.7 F/g at 1.0 A/g) and a good cyclic stability (90.6% retention after 4000 cycles). Moreover, we assemble an aqueous asymmetric supercapacitor with the obtained material, which has an extremely high energy density (108.9 Wh/kg at 378 W/kg) and outstanding cycle stability (retaining 88.1% capacitance at 2.0 A/g after 4000 cycles).     

Recent progress of composite solid polymer electrolytes for all-solid-state lithium metal batteries

In comparison with lithium-ion batteries (LIBs) with liquid electrolytes, all-solid-state lithium batteries (ASSLBs) have been considered as promising systems for future energy storage due to their safety and high energy density. As the pivotal component used in ASSLBs, composite solid polymer electrolytes (CSPEs), derived from the incorporation of inorganic fillers into solid polymer electrolytes (SPEs), exhibit higher ionic conductivity, better mechanical strength, and superior thermal/electrochemical stability compared to the single-component SPEs, which can significantly promote the electrochemical performance of ASSLBs. Herein, the recent advances of CSPEs applied in ASSLBs are presented. The effects of the category, morphology and concentration of inorganic fillers on the ionic conductivity, mechanical strength, electrochemical window, interfacial stability and possible Li⁺ transfer mechanism of CSPEs will be systematically discussed. Finally, the challenges and perspectives are proposed for the future development of high-performance CSPEs and ASSLBs.     

Highly N/O co-doped ultramicroporous carbons derived from nonporous metal-organic framework for high performance supercapacitors

A new nonporous Zn-based metal-organic framework (NPMOF) synthesized from a high nitrogen-containing rigid ligand was converted into porous carbon materials by direct carbonization without adding additional carbon sources. A series of NPMOF-derived porous carbons with very high N/O contents (24.1% for NPMOF-700, 20.2% for NPMOF-800, 15.1% for NPMOF-900) were prepared by adjusting the pyrolysis temperatures. The NPMOF-800 fabricated electrode exhibits a high capacitance of 220 F/g and extremely large surface area normalized capacitance of 57.7 μF/cm² compared to other reported MOF-derived porous carbon electrodes, which could be attributed to the abundant ultramicroporosity and high N/O co-doping. More importantly, symmetric supercapacitor assembled with the MOF-derived carbon manifests prominent stability, i.e., 99.1% capacitance retention after 10,000 cycles at 1.0 A/g. This simple preparation of MOF-derived porous carbon materials not only finds an application direction for a variety of porous or even nonporous MOFs, but also opens a way for the production of porous carbon materials for superior energy storage.     

The electrochemical performance of ordered mesoporous carbon/nickel compounds composite material for supercapacitor

A series of high performance ordered mesoporous carbon/nickel compounds composites have been synthesized by a combination of incipient wetness impregnation and hydrothermal method for the first time. X-ray diffraction (XRD), N₂ adsorption/desorption isotherms and transmission electron microscopy (TEM) are used to characterize the composites derived at the hydrothermal temperature of 125, 150, 175, 200, 250, 275 and 300 °C. The formation of nanosized nickel compounds, fully inside the mesopore system, was confirmed with XRD and TEM. An N₂ adsorption/desorption isotherms measurements still revealed mesoporosity for the host/guest compounds. It is noteworthy that an OMC/nickel nitrate hydroxide hydrate composite (OMCN-150) exhibits more excellent performance. Based on the various hydrothermal temperatures of the composite, the capacitance of an OMCN-150 delivering the best electrochemical performance is about 2.4 (5 mV s⁻¹) and 1.5 (50 mV s⁻¹) times of the pristine OMC. The capacitance retention of an OMCN-150 is 96.1%, which indicates that the electrochemical performance of the supercapacitor is improved greatly, and represents novel research and significant advances in the field of electrode composite materials for supercapacitor.     

Atomic force microscopy investigation of asymmetric diblock copolymer morphologies in thin films

Microphase separation and the resulting morphology of asymmetric diblock copolymers of poly(ε-caprolactone) (PCL) in thin films have been investigated by atomic force microscopy. Copolymers consisted of a short block of PCL (M_n∼2500-4500 g/mole) and a longer second block of poly(methyl methacrylate) (PMMA), poly(styrene) (PS) or poly(cyclohexene oxide) (PCHO). Tendency for microphase separation above the glass transition temperature of the second block (PMMA, PS or PCHO) resulted in a pitted morphology on the surface of the thin films. This tendency was strongest for PMMA and weakest for PCHO. The presence of up to 54% PMMA homopolymer in PCL-PMMA block copolymer did not prevent the formation of such pitted morphology on the surface. The effect of the chemical structure of the second block and the possible orientations of the block copolymer molecules in thin films are discussed.     

Synthesis of porous biocarbon supported Ni3S4/CeO2 nanocomposite as high-efficient electrode materials for asymmetric supercapacitors

Biocarbon-supported polymetallic composites (CAS@Ni₃S₄/CeO₂) were fabricated by a facile hydrothermal process. The as-prepared CAS@Ni₃S₄/CeO₂ materials integrated the advantages of transition metal sulfides (good conductivity), rare-earth metal oxides (excellent stability), as well as porous carbon with high surface area, thus exhibiting promising electrochemical performance in supercapacitor applications. Indeed, the optimal CAS@Ni₃S₄/CeO₂-150 composite displayed a high specific capacitance of 1364 F g^?1 and impressive cycle performance with capacitance retention of 93.81 % after 10,000 cycles. The calculation of capacitance contribution showed that the satisfying behavior of the electrode was a combination of the diffusion process and the surface capacitance characteristics. Furthermore, the assembled asymmetric supercapacitor (CAS@Ni₃S₄/CeO₂-150//CAS) delivered an ultrahigh energy density of 102.76 Wh kg^?1, which was better than that of the commercial activated carbon-based ASC device. This novel strategy might provide a new perspective for transition metal sulfide/rare earth metal oxide composite in the electrochemical energy storage field.     

Interaction between organic molecules and electrogenerated nickel fluoride films: the choice of organic reactants for electrochemical perfluorination

The interactions of organic molecules such as acetonitrile, propylene carbonate, and sulfolane on the electrogenerated nickel fluoride films were investigated using cyclic voltammetry and scanning electron microscopy. The effect of water, alkali metal fluorides, fluoride content, and acidity are also reported. Based on these studies, the potential effect of these factors on electrochemical perfluorination processes are projected. Water and alkali metal fluorides would enhance the dissolution of nickel fluoride film. Organic molecules like acetonitrile dissolve nickel fluoride film, while propylene carbonate forms thick polymeric layers on nickel surface. Higher acidity and fluoride ion content enhance the stability of a thin, catalytically active nickel fluoride film. Organic reactants like sulfolane form a composite film with nickel fluoride and, thus, enhance the long-term stability and electrocatalytic activity.     

Synthesis of dandelion-like three-dimensional nickel nanostructures via solvothermal route

The objectives of the present research are synthesizing three-dimensional （3D） nickel nanostructures and investigating their magnetic properties. Thus a template-free method was used to prepare 3D dandelion-like nickel nanostructures via reducing of nickel chloride with hydrazine hydrate in ethylene glycol solution at 100 ℃. The resulting Ni nanostructures were characterized by means of powder X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and selected-area electron diffraction （SAED）. And the magnetic properties of the 3D Ni nanostructures were measured as well. Results indicated that solvothermal process could be successfully used to prepare 3D dandelion-like nanostructures of Ni at a relatively mild temperature of 100℃. And the conclusions were made as follows： as-prepared Ni samples had obvious shape anisotropy and were composed of fine nanocrystallites, while they had significantly enhanced ferromagnetic properties than bulk Ni and Ni nanoparticles.     

Facile synthesis of nickel cobalt sulfide nano flowers for high performance supercapacitor applications

A facile synthesis of nickel cobalt sulfide (NCS) nanoflowers have been deposited successfully onto binder free 3D nickel foam electrodes using simple successive ionic layer adsorption and reaction (SILAR) method for supercapacitor applications. The obtained NCS nanoflowers manifest ultrahigh specific capacitance of 1899 F g^?1 at a scan rate of 5 mV s^?1. The NCS nanoflowers exhibit a prominent energy density of 55.16 Wh kg^?1 at power density of 495 W kg^?1 and superior cyclic stability of 94% after 10000 cycles. In addition, the asymmetric supercapacitor (ASC) device is fabricated using NCS nanoflower as positive and reduced graphene oxide (rGO) as negative electrodes, respectively. The ASC (NCS//rGO) delivered good capacity with excellent energy and power densities within 1.6 V wider potential window. Hence, NCS nanoflowers are an outstanding material for energy storage applications in near future.     

Nanoporous asymmetric polyaniline films for filtration of organic solvents

A new family of functional materials is reported for organic solvent nanofiltration, with excellent chemical stability and high retention of solute molecules. Integrally skinned asymmetric polyaniline (PANI) membranes were fabricated from concentrated solutions of doped PANI by phase inversion. Doped PANI solutions were prepared by adding organic acids directly to PANI dissolved in a mixture of NMP and 4-methyl piperidine before casting. Among the organic acids investigated, maleic acid, phthalic acid, sulfosalicylic acid and camphorsulfonic acid were able to dope PANI without causing gelation. These acids acted as soft templates, creating nanoporosity in the thin skin layer of the asymmetric PANI film. Their removal by alkaline extraction created membranes through which small solvent molecules can pass. After extracting the organic acids, the membranes were thermally crosslinked which conferred excellent solvent stability. These membranes had a molecular weight cut-off (MWCO) in the range of 150–250 g mol⁻¹ in methanol, making them the tightest OSN membranes reported to date. It was found that an increase in crosslinking temperature or time led to a decrease in solvent flux. PANI membranes were found to be resistant to a variety of organic solvents such as ethyl acetate, acetonitrile and acetone. These remarkable membranes have the potential to be used in OSN operations at high temperatures (up to 150 °C), and gave increasing fluxes with increasing temperature while maintaining a high solute rejection.     

In-situ growth of vertically aligned nickel cobalt sulfide nanowires on carbon nanotube fibers for high capacitance all-solid-state asymmetric fiber-supercapacitors

Fiber-supercapacitors(FSCs)are promising power sources for miniature portable and wearable electronic devices.However,the development and practical application of these FSCs have been severely hindered by their low volumetric capacitance and narrow operating voltage.In this work,vertically aligned nickel cobalt sulfide(Ni Co_2S_4)nanowires grown on carbon nanotube(CNT)fibers were achieved through an in-situ two-step hydrothermal reaction method.The as-prepared Ni Co_2S_4@CNT fiber electrode exhibits a high volumetric capacitance of 2332 F cm~(-3),benefiting from its superior electric conductivity,large surface area,and rich Faradic redox reaction sites.Furthermore,a Ni Co_2S_4@CNT//VN@CNT(vanadium nitride nanosheets grown on CNT fibers)asymmetric fiber-supercapacitor(AFSC)was successfully fabricated.The device exhibits an operating voltage up to 1.6 V and a high volumetric energy density of 30.64m Wh cm~(-3).The device also possesses outstanding flexibility as evidenced by no obvious performance degradation under various bending angles and maintaining high capacitance after 5000 bending cycles.This work promotes the practical application of flexible wearable energy-storage devices.     

Synthesis, characterization, and electrochemical properties of ordered mesoporous carbons containing nickel oxide nanoparticles using sucrose and nickel acetate in a silica template

New ordered mesoporous carbons containing nickel oxide nanoparticles have been successfully synthesized by carbonization of sucrose in the presence of nickel acetate inside SBA-15 mesoporous silica template. The obtained samples were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, and transmission electron microscopy (TEM). The NiO nanoparticles were embedded inside the mesoporous carbon framework due to the simultaneous pyrolysis of nickel acetate during carbonization. The electrochemical testing of the as-made nanocomposites showed a large specific capacitance of 230 F g⁻¹ using 2 M KOH as the electrolyte at room temperature. This is attributed to the nanometer-sized NiO formed inside mesoporous carbons and the high surface area of the mesopores in which the NiO nanoparticles are formed. Furthermore, the synthetic process is proposed as a simple and general method for the preparation of new functionalized mesoporous carbon materials, for various applications in catalysis, sensor or advanced electrode material.     

One-step synthesis of biomass derived O,N-codoped hierarchical porous carbon with high surface area for supercapacitors

We report a convenient method to synthesize O, N-codoped hierarchical porous carbon by one-step carbonization of the mixture of KHCO₃, urea and alginic acid. Benefiting from KHCO₃ and urea synergistic effect, the obtained O, N-codoped hierarchical porous carbon (NPC-700) material has a well-developed interconnected porous framework with ultrahigh specific surface area (2846 m²/g) and massive heteroatoms functional groups. Consequence, such porous carbon displays high specific capacitance (324 F/g at 1 A/g), excellent rate performance (212 F/g at 30 A/g) and good electrochemical stabilization in 6 mol/L KOH solution. More importantly, the assembled NPC-700//NPC-700 symmetrical supercapacitor can achieve a high energy density of 18.8 Wh/kg and good electrochemical stabilization in 1 mol/L Na₂SO₄ solution. This process opens up a new way to design heteroatoms-doped hierarchical porous carbon derived from biomass materials for supercapacitors.     

Structural,morphological, optical and sensing properties of SnSe and SnSe2 thin films as a gas sensing material

In this work, orthorhombic tin selenide thin films were grown onto three different substrates using an organophosphorus precursor (Ph₃PSe) via chemical vapor deposition. Structural, microstructural and morphological properties of the as-grown films were systematically investigated using XRD, ESEM and AFM respectively. Grain size, microstrain and dislocation were calculated and correlated with different factors. The effects of selenization temperature and substrate type on different film properties and gas sensing response of films deposited onto alumina substrates were investigated. XRD analysis reveals the appearance of a mixed phase as a function of temperature. Furthermore, substrate type plays a key role in the rate of appearance of each phase. EDAX analysis confirms the existence of the desired elements and detect the evaporation of selenium and the appearance of oxygen at higher temperatures. Atomic force microscopy (AFM) was used to investigate the surface topography of the grown thin films.Optical properties of the films grown onto glass and silicon substrates were studied. From the recorded optical data, a direct optical band gap in the range of 0.9–1.3 eV was obtained with an absorption coefficient α > 10⁴ cm⁻¹ throughout large spectral regions. Optical studies were remarkably affected by the obtained phase as well as the selenization temperature. Gas sensing properties of the samples deposited onto alumina substrates were examined as a new sensing material for detection of methane gas at different concentrations. SnSe sensors show high sensitivity, are reversible and exhibit fast response and recovery times compared to SnSe₂ sensors.