Facile synthesis of graphene@NiMoO<Subscript>4</Subscript> nanosheet arrays on Ni foam for a high-performance asymmetric supercapacitor

Honeycomb-like NiMoO₄ with nanosheet arrays is grown on reduced graphene oxide, which is supported on Ni foam having successfully fabricated by a simple hydrothermal treatment followed by a calcined process. In the as-synthesized Ni foam@reduced graphene oxide@NiMoO₄, Ni foam served as “skeleton” to support reduced graphene oxide and reduced graphene oxide directly grown on Ni foam served as the “skin” to provide high passway of electrons and ions, which simultaneously accommodated the volume change during the process of charge–discharge and NiMoO₄ acted as active substance to provide high areal capacitance. It shows a high areal capacitance of 2165.9 mF cm^?2 at a current density of 1 mA cm^?2 and long cycle stability with 93.8% capacitance retained over 1000 charge–discharge cycles. Moreover, an asymmetric supercapacitor has been constructed by using Ni foam@reduced graphene oxide and Ni foam@reduced graphene oxide@NiMoO₄ as negative and positive electrodes. The energy density of this asymmetric supercapacitor is 0.579 mWh cm^?2, and it retains 93.1% capacitance over charge–discharge 5000 cycles. Therefore, it reveals great promise for practical applications in energy storage devices.     

Controllable synthesis of triangular Ni(HCO<Subscript>3</Subscript>)<Subscript>2</Subscript> nanosheets for supercapacitor

Triangular Ni(HCO₃)₂ nanosheets were synthesized via a template-free solvothermal method. The phase transition and formation mechanism were explored systematically. Further investigation indicated that the reaction time and pH have significant effects on the morphology and size distribution of the triangular Ni(HCO₃)₂ nanosheets. More interestingly, the resulting product had an ultra-thin structure and high specific surface area, which can effectively accelerate the charge transport during charge–discharge processes. As a result, the triangular Ni(HCO₃)₂ nanosheets not only exhibited high specific capacitance (1,797 F·g^-1 at 5 A·g^-1 and 1,060 F·g^-1 at 50 A·g^-1), but also showed excellent cycling stability with a high current density (~80% capacitance retention after 5,000 cycles at the current density of 20 A·g^-1).

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Carbon quantum dot-induced self-assembly of ultrathin Ni(OH)<Subscript>2</Subscript> nanosheets: A facile method for fabricating three-dimensional porous hierarchical composite micro-nanostructures with excellent supercapacitor performance

Significant efforts have been directed towards the preparation and application of porous hierarchically structured materials owing to their large surface area, rich active sites, and enhanced mass transport and diffusion. In this study, a simple and cost-effective method for the carbon quantum dot (CQD)-induced assembly of two-dimensional ultrathin Ni(OH)₂ nanosheets into a three-dimensional (3D) porous hierarchical structure was developed. The electrostatic forces between the CQDs and cations drove the self-assembly of the 3D CQDs/Ni(OH)₂ hierarchical structures. As a new type of structure-directing agent, the CQDs played dual roles in tuning the morphology of the products and improving the supercapacitor performance. The multilevel CQDs/Ni(OH)₂ micro-nanostructures had a large specific surface area and rich porosity. Owing to their unique structures and the conductivity of the CQDs, an optimized asymmetric supercapacitor using the CQDs/Ni(OH)₂ exhibited a maximum specific capacity of 161.3 F·g^–1 and a high energy density of 57.4 Wh·kg^–1. This study introduces a potential method for the fabrication of many other 3D hierarchical structures with great potential for applications in various fields.

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Simulation of the adsorption of CaCl<Subscript>2 </Subscript>on Mg(OH)<Subscript>2</Subscript> planes

The adsorption behavior of Ca²⁺ and Cl⁻ on Mg(OH)₂ planes was simulated using Universal Force Field method. The energy, the capacity and the configuration involved in the adsorption process were estimated. The results showed that Ca²⁺ was easier to be adsorbed and incorporated on the (001) plane than other planes such as (100), (101) and (110) planes. The incorporation of Cl⁻ in Mg(OH)₂ was difficult since the radius for Cl⁻ is much bigger than that of OH⁻. The adsorption of Ca²⁺ on (001) plane at elevated temperature may inhibit the growth along [001] direction, leading to occurrence of the (001) plane, the shrinkage of the (101) and (110) planes and the formation of Mg(OH)₂ plates with bigger ratios of diameter to thickness. Project supported by the National Natural Science Foundation of China (No. 50574051).     

Facile synthesis and characterization of MnO<Subscript>2</Subscript> nanomaterials as supercapacitor electrode materials

MnO₂ nanomaterials are synthesized via calcinations in air at various temperatures. Amorphous MnO₂ masses appear between 100 and 300 °C and nanorods form above 400 °C. Transmission and scanning electron microscopy are used to observe the geometries of each material, with further structural analyses conducted using X-ray photoelectron spectroscopy, X-ray diffraction, and BET method. The electrochemical properties are investigated through galvanostatic charge/discharge cycling, electrochemical impedance spectra, and cyclic voltammetry within a three-electrode test cell filled with 1 mol L^?1 Na₂SO₄ solution. The slightly asymmetric galvanostatic cycling curves suggest that the reversibility of the Faradaic reactions are imperfect, requiring a larger time to charge than discharge. The specific capacitances of each sample are calculated and trends are identified, proving that the samples synthesized at higher temperatures exhibit poorer electrochemical behaviors. The highest calculated specific capacitance is 175 F g^?1 by the sample calcinated at 400 °C. However, the lower temperature samples exhibit more favorable geometric properties and higher overall average specific capacitances. For future research, it is suggested that surface modifications such as a carbon coating could be used in conjunction with the MnO₂ nanorods to reach the electrochemical properties required by contemporary industrial applications.     

Facile synthesis of Mg(OH)<Subscript>2</Subscript>/graphene oxide composite by high-gravity technology for removal of dyes

A facile high-gravity strategy is proposed for preparation of Mg(OH)₂/graphene oxide (MGO) composite using a rotating packed bed reactor at room temperature for 1 min. Lamellar Mg(OH)₂ nanocrystals of about 60 nm in diameter with a narrow size distribution are distributed homogeneously on the graphene oxide sheets without aggregation. The specific surface area of MGO with mesoporous structure reaches 590 m² g^?1, which is the highest among those reported in the literatures. The as-prepared MGO nanocomposite exhibits excellent adsorption capacity for methylene blue (MB). The removal rate of MB reaches 98% in 1 min. The preparation process of MGO nanocomposite is rapid, simple, and suitable for a large-scale production, and the product has great potential in the field of environmental protection as a promising absorbent.     

Surface nucleation and independent growth of Ce(OH)<Subscript>4</Subscript> within confinement space on modified carbon black surface to prepare nano-CeO<Subscript>2</Subscript> without agglomeration

Highly dispersed negative carboxyl groups can be formed on carbon black (CB) surface modified with strong nitric acid. Therefore positive cations can be uniformly absorbed by carboxyl groups and precipitated within a confinement space on modified CB surface to prepare highly dispersed nanomaterials. In this paper, the formation and dispersion status of surface negative carboxyl groups, adsorption status of Ce³⁺, surface confinement nucleation, crystallization and calcination process were studied by EDS, SEM, and laser particle size analysis. The results show that the carboxyl groups formed on modified CB surface are highly dispersed, and Ce³⁺ cations can be uniformly anchored by carboxyl groups. Therefore, highly dispersed Ce³⁺ can react with OH^? within a confinement surface region to form positive nano-Ce(OH)₄ nuclei which also can be adsorbed by electrostatic attraction. After independent growth of Ce(OH)₄ without agglomeration, highly dispersed CeO₂ nanoparticles without agglomeration can be prepared together with the help of effectively isolates by CO₂ released in the combustion of CB.     

TiO<Subscript>2</Subscript> nanosheets with exposed {001} facets for photocatalytic applications

TiO₂ nanosheets with highly reactive {001} facets ({001}-TiO₂) have attracted great attention in the fields of science and technology because of their unique properties. In recent years, many efforts have been made to synthesize {001}-TiO₂ and to explore their applications in photocatalysis. In this review, we summarize the recent progress in preparing {001}-TiO₂ using different techniques such as hydrothermal, solvothermal, alcohothermal, chemical vapor deposition (CVD), and sol gel-based techniques. Furthermore, the enhanced efficiency of {001}-TiO₂ by modification of carbon materials, surface deposition of transition metals, and non-metal doping is reviewed. Then, the applications of {001}-TiO₂-based photocatalysts in the degradation of organic dyes, hydrogen evolution, carbon dioxide (CO₂) reduction, bacterial disinfection, and dye-sensitized solar cells are summarized. We believe this entire review on TiO₂ nanosheets with {001} facets can further inspire researchers in associated fields.

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Cathodic electrosynthesis of CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/CuO composite nanostructures for high performance supercapacitor applications

In this work, CuFe₂O₄/CuO nanocomposites have been synthesized by galvanostatic cathodic electrodeposition. The obtained nanocomposites were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier Transform Infrared, and Brunauer–Emmett–Teller surface area analysis. The electrochemical properties of CuFe₂O₄/CuO nanocomposites were evaluated by cyclic voltammetry, galvanostatic charge–discharge cycling, and electrochemical impedance spectroscopy in 1.0 M KOH. The CuFe₂O₄/CuO nanocomposites have shown the high specific capacitance of 322.49 F g^?1 at the scan rate of 1 mV s^?1. After 5000 cycles, 92% of this specific capacitance was retained. Although the prepared nanocomposite has shown a mediocre specific capacitance compared to other metal oxide-based materials, the low cost of the starting materials and the ease of preparation make this nanocomposite a good candidate for supercapacitor applications.     

MoS<Subscript>2</Subscript>/CoS<Subscript>2</Subscript> composites composed of CoS<Subscript>2</Subscript> octahedrons and MoS<Subscript>2</Subscript> nano-flowers for supercapacitor electrode materials

In pursuing excellent supercapacitor electrodes, we designed a series of MoS₂/CoS₂ composites consisting of flower-liked MoS₂ and octahedron-shaped CoS₂ through a facile one-step hydrothermal method and investigated the electrochemical performance of the samples with various hydrothermal time. Due to the coupling of two metal species and a big amount of well-developed CoS₂ and MoS₂, the results indicated that the MoS₂/CoS₂ composites electrodes exhibited the best electrochemical performance with a large specific capacitance of 490 F/g at 2 mV/s or 400 F/g at 10 A/g among all samples as the hydrothermal time reached 48 h (MCS₄₈). Furthermore, the retention of MCS₄₈ is 93.1% after 10000 cycles at 10 A/g, which manifests the excellent cycling stability. The outstanding electrochemical performance of MCS₄₈ indicates that it could be a very promising and novel energy storage material for supercapacitors in the future.     

Enhanced adsorption performance of hierarchical S-doped Ni(OH)<Subscript>2</Subscript> hollow nanocomposites for the removal of Congo red

In this work, nonmetallic S was doped into hierarchical Ni(OH)₂ hollow microspheres by ethanol solvothermal method using thiourea as sulfur source. Although the morphology of precursor Ni(OH)₂ is maintained, the surface states and pore properties had greatly changed after S doping. Using the as-prepared S-doped Ni(OH)₂ as adsorbents for the removal of Congo red (CR), the S-doped Ni(OH)₂ exhibited much better adsorption capacity compared with undoped Ni(OH)₂. The adsorption behavior of both Ni(OH)₂ and S-doped Ni(OH)₂ followed the pseudo-second-order kinetic model and intraparticle diffusion model. The equilibrium data of Ni(OH)₂ could be better fitted by Langmuir model, while Freundlich model could be better used to describe the S-doped Ni(OH)₂ with a much larger adsorption capacity toward CR. The tuned microstructure and changed surface states of adsorbent after S doping may be responsible for the enhanced adsorption performance. Therefore, the doping of S species into hierarchical Ni(OH)₂ paves a new way to tune the microstructure and surface states of Ni-based materials.     

Polyol-mediated synthesis of nanoscale Mg(OH)<Subscript>2</Subscript> and MgO

Nanoscale Mg(OH₂) and MgO is prepared via a polyol-mediated synthesis. With concern to the experimental conditions, spherical particles, 20 and 100 nm in size are realized. Dynamic light scattering proves the presence of non-agglomerated and monodispersed Mg(OH)₂ in as-prepared suspensions of diethylene glycol. Based on the results of infrared spectroscopy, thermal analysis and X-ray powder diffraction, as-prepared Mg(OH)₂ can be dehydrated at a surprisingly low temperature (300 °C) to form MgO with almost similar particle size and shape.

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Graphical abstract Polyol-mediated Synthesis of Nanoscale Mg(OH) ₂ and MgO C. Feldmann*, S. Matschulo, S. Ahlert

     

Facile synthesis Mn/Co dual-doped Ni3S2 nanosheets for supercapacitor

Journal of Materials Science: Materials in Electronics - Ni3S2 nanosheets dual-doped with manganese, cobalt elements on conductive nickel foam (MC-Ni3S2) had been synthesized by two steps...     

Synthesis of In(OH)<Subscript>3</Subscript> and In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanomaterials incorporating Au

In(OH)₃ and In₂O₃ nanocrystals of rectangular shape and incorporating Au were synthesized with a hydrothermal process and thermal decomposition. Powder X-ray diffraction, electron microscopy (SEM, TEM), and energy-dispersive spectroscopy studies reveal that elemental Au nanoparticles are dispersed on the surface of In(OH)₃ rectangular nanocrystals and incorporated into In₂O₃ nanoporous particles. UV–vis spectral measurements reveal a surface-enchanced plasma band near λ ~532 nm for both Au-incorporating nanomaterials. The BET surface areas of Au-incorporating In(OH)₃ and In₂O₃ are 26.2 and 35.5 m²/g, respectively. The incorporation of elemental Au in In(OH)₃ and In₂O₃ nanomaterials is attractive for sensor, catalyst and solar-cell applications.     

Synthesis and crystal structure of [UO<Subscript>2</Subscript>(OH)(CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>)<Subscript>3</Subscript>]<Subscript>2</Subscript>(ClO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The complex [UO₂(OH)(CO(NH₂)₂)₃]₂(ClO₄)₂ (I) was synthesized. A single crystal X-ray diffraction study showed that compound I crystallizes in the triclinic system with the unit cell parameters a = 7.1410(2), b = 10.1097(2), c = 11.0240(4) Å, α = 104.648(1)°, β = 103.088(1)°, γ = 108.549(1)°, space group \(P\bar 1\), Z = 1, R = 0.0193. The uranium-containing structural units of the crystals are binuclear groups [UO₂(OH)· (CO(NH₂)₂)₃] ₂ ²⁺ belonging to crystal-chemical group AM²M ₃ ¹ [A = UO ₂ ²⁺ , M² = OH^?, M¹ = CO(NH₂)₂] of uranyl complexes. The crystal-chemical analysis of nonvalent interactions using the method of molecular Voronoi-Dirichlet polyhedra was performed, and the IR spectra of crystals of I were analyzed.     

Enhanced electrochemical performance of Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>F<Subscript>3</Subscript> for Na-ion batteries with nanostructure and carbon coating

Carbon-coating Na₃V₂(PO₄)₂F₃ nanoparticles (NVPF@C NP) were prepared by a hydrothermal assisted sol–gel method and applied as cathode materials for Na-ion batteries. The as-prepared nanocomposites were composed of Na₃V₂(PO₄)₂F₃ nanoparticles with a typical size of ~?100 nm and an amorphous carbon layer with the thickness of ~?5 nm. Cyclic voltammetry, rate and cycling, and electrochemical impedance spectroscopy tests were used to discuss the effect of carbon coating and nanostructure. Results display that the as-prepared NVPF@C NP demonstrates a higher rate capability and better long cycling performance compared with bare Na₃V₂(PO₄)₂F₃ bulk (72 mA h g^?1 at 10 C vs 39 mA h g^?1 at 10 and 1 C capacity retention of 95% vs 88% after 50 cycles). The remarking electrode performance was attributed to the combination of nanostructure and carbon coating, which can provide short Na-ion diffusion distance and rapid electron migration.     

Ultrathin Co(Ni)-doped MoS<Subscript>2</Subscript> nanosheets as catalytic promoters enabling efficient solar hydrogen production

The design of efficient artificial photosynthetic systems that harvest solar energy to drive the hydrogen evolution reaction via water reduction is of great importance from both the theoretical and practical viewpoints.Integrating appropriate co-catalyst promoters with strong light absorbing materials represents an ideal strategy to enhance the conversion efficiency of solar energy in hydrogen production.Herein,we report,for the first time,the synthesis of a class of unique hybrid structures consisting of ultrathin Co(Ni)-doped MoS2 nanosheets (co-catalyst promoter) intimately grown on semiconductor CdS nanorods (light absorber).The as-synthesized one-dimensional CdS@doped-MoS2 heterostructures exhibited very high photocatalytic activity (with a quantum yield of 17.3％) and stability towards H2 evolution from the photoreduction of water.Theoretical calculations revealed that Ni doping can increase the number of uncoordinated atoms at the edge sites of MoS2 nanosheets to promote electron transfer across the CdS/MoS2 interfaces as well as hydrogen reduction,leading to an efficient H2 evolution reaction.     

Effect of mechanical activation of Al(OH)<Subscript>3</Subscript> on its reaction with Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>

The effect of preliminary mechanical activation of Al(OH)₃ on its solid-state reaction with Li₂CO₃ at temperatures above 800°C has been studied by thermogravimetry, X-ray diffraction, in situ X-ray diffraction, electron microscopy, and specific surface area and particle size measurements. The results demonstrate that preliminary mechanical activation of Al(OH)₃ in an AGO-2 planetary mill at 40g for 1 min allows phase-pure γ-LiAlO₂ to be obtained. The composition of the lithium aluminates resulting from mechanical activation and heat treatment depends on the phase composition of the aluminum oxides resulting from the thermal decomposition of Al(OH)₃. The particle size and specific surface area of the forming γ-LiAlO₂ have been determined.     

Facile one-pot synthesis of NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> hollow spheres with controllable number of shells for high-performance supercapacitors

In this work,single-and double-shelled NiCo2O4 hollow spheres have been synthesized in situ by a one-pot solvothermal method assisted by xylose,followed by heat treatment.Employed as supercapacitor electrode materials,the double-shelled NiCo2O4 hollow spheres exhibit a remarkable specific capacitance (1,204.4 F·g-1 at a current density of 2.0 A·g-1) and excellent cycling stability (103.6％ retention after 10,000 cycles at a current density of 10 A·g-1).Such outstanding electrochemical performance can be attributed to their unique internal morphology,which provides a higher surface area with a larger number of active sites available to interact with the electrolyte.The versatility of this method was demonstrated by applying it to other binary metal oxide materials,such as ZnCo2O4,ZnMn2O4,and CoMn2O4.The present study thus illustrates a simple and general strategy for the preparation of binary transition metal oxide hollow spheres with a controllable number of shells.This approach shows great promise for the development of next-generation high-performance electrochemical materials.     

Vertically-aligned Mn(OH)<Subscript>2</Subscript> nanosheet films for flexible all-solid-state electrochemical supercapacitors

The arrangement of the electrode materials is a significant contributor for constructing high performance supercapacitor. Here, vertically-aligned Mn(OH)₂ nanosheet thin films were synthesized by cathodic electrodeposition technique on flexible Au coated polyethylene terephthalate substrates. Morphologies, microstructures, chemical compositions and valence state of the nanosheet films were characterized systematically. It shows that the nanosheets arranged vertically to the substrate, forming a porous nanowall structures and creating large open framework, which greatly facilitate the adsorption or diffusion of electrolyte ions for faradaic redox reaction. Electrochemical tests of the films show the specific capacitance as high as 240.2 F g^?1 at 1.0 A g^?1. The films were employed to assemble symmetric all-solid-state supercapacitors with LiCl/PVA gel severed as solid electrolyte. The solid devices exhibit high volumetric capacitance of 39.3 mF?cm^?3 at the current density 0.3 mA cm^?3 with robust cycling stability. The superior performance is attributed to the vertically-aligned configuration.