Facile growth of homogeneous Ni(OH)<Subscript>2</Subscript> coating on carbon nanosheets for high-performance asymmetric supercapacitor applications

The growth of a Ni(OH)₂ coating on conductive carbon substrates is an efficient way to address issues related to their poor conductivity in electrochemical capacitor applications. However, the direct growth of nickel hydroxide coatings on a carbon substrate is challenging, because the surfaces of these systems are not compatible and a preoxidation treatment of the conductive carbon substrate is usually required. Herein, we present a facile preoxidation-free approach to fabricate a uniform Ni(OH)₂ coating on carbon nanosheets (CNs) by an ion-exchange reaction to achieve the in situ transformation of a MgO/C composite to a Ni(OH)₂/C one. The obtained Ni(OH)₂/CNs hybrids possess nanosheet morphology, a large surface area (278 m²/g), and homogeneous elemental distributions. When employed as supercapacitors in a three-electrode configuration, the Ni(OH)₂/CNs hybrid achieves a large capacitance of 2,218 F/g at a current density of 1.0 A/g. Moreover, asymmetric supercapacitors fabricated with the Ni(OH)₂/CNs hybrid exhibit superior supercapacitive performances, with a large capacity of 198 F/g, and high energy density of 56.7 Wh/kg at a power density of 4.0 kW/kg. They show excellent cycling stability with 93% capacity retention after 10,000 cycles, making the Ni(OH)₂/CNs hybrid a promising candidate for practical applications in supercapacitor devices.

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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 nanotube directed three-dimensional porous Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript> composite for lithium batteries

Lithium iron silicate (Li₂FeSiO₄) is capable of affording a much higher capacity than conventional cathodes, and thus, it shows great promise for high-energy battery applications. However, its capacity has often been adversely affected by poor reaction activity due to the extremely low electronic and ionic conductivity of silicates. Here, we for the first time report on a rational engineering strategy towards a highly active Li₂FeSiO₄ by designing a carbon nanotube (CNT) directed three-dimensional (3D) porous Li₂FeSiO₄ composite. As the CNT framework enables rapid electron transport, and the rich pores allow efficient electrolyte penetration, this unique 3D Li₂FeSiO₄-CNT composite exhibits a high capacity of 214 mAh·g^?1 and retains 96% of this value over 40 cycles, thus, outstripping many previously reported Li₂FeSiO₄-based materials. Kinetic analysis reveals a high Li⁺ diffusivity due to coupling of the migration of electrons and ions. This research highlights the potential for engineering 3D porous structure to construct highly efficient electrodes for battery applications.

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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.     

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.     

Synthesis,characterization, and electrochemical properties of Ni(OH)<Subscript>2</Subscript>/ultra-stable Y zeolite composite

A novel composite of Ni(OH)₂/ultra-stable Y zeolite materials was synthesized by an improved chemical precipitation method, which used the ultra-stable Y zeolite as the template. The Ni(OH)₂/ultra-stable Y zeolite composite and its microstructure were characterized by X-ray diffraction measurements and transmission electron microscopy. Electrochemical studies were carried out using cyclic voltammetry, chronopotentiometry technology and ac impedance spectroscopy, respectively. The result shows that the loose-packed whisker Ni(OH)₂ phase has profound impacts on electrode performance at very high power output. A maximum discharge capacity of 185.6 mA-h/g (1670 F/g), or 371 mA-h/g (3340 F/g) after correcting for weight percent of nickel hydroxide phase at the current density of 625 mA/g could be achieved in a half-cell setup configuration for the Ni(OH)₂/ultra-stable Y zeolite electrode, suggesting its potential application in electrode material for secondary batteries and electrochemical capacitors. Furthermore, the effect of NH₄Cl concentration on the electrochemical properties characteristics has also been systemically explored.     

Facile synthesis of porous carbon nitride spheres with hierarchical three-dimensional mesostructures for CO<Subscript>2</Subscript> capture

Porous carbon nitride (CN) spheres with partially crystalline frameworks have been successfully synthesized via a nanocasting approach by using spherical mesoporous cellular silica foams (MCFs) as a hard template, and ethylenediamine and carbon tetrachloride as precursors. The resulting spherical CN materials have uniform diameters of ca. 4 μm, hierarchical three-dimensional (3-D) mesostructures with small and large mesopores with pore diameters centered at ca. 4.0 and 43 nm, respectively, a relatively high BET surface area of ∼550 m²/g, and a pore volume of 0.90 cm³/g. High-resolution transmission electron microscope (HRTEM) images, wide-angle X-ray diffraction (XRD) patterns, and Raman spectra demonstrate that the porous CN material has a partly graphitized structure. In addition, elemental analyses, X-ray photoelectron spectra (XPS), Fourier transform infrared spectra (FT-IR), and CO₂ temperature-programmed desorption (CO₂-TPD) show that the material has a high nitrogen content (17.8 wt%) with nitrogen-containing groups and abundant basic sites. The hierarchical porous CN spheres have excellent CO₂ capture properties with a capacity of 2.90 mmol/g at 25 °C and 0.97 mmol/g at 75 °C, superior to those of the pure carbon materials with analogous mesostructures. This can be mainly attributed to the abundant nitrogen-containing basic groups, hierarchical mesostructure, relatively high BET surface area and stable framework. Furthermore, the presence of a large number of micropores and small mesopores also enhance the CO₂ capture performance, owing to the capillary condensation effect.     

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).     

SnO<Subscript>2</Subscript>-based thin films with excellent photocatalytic performance

SnO₂ semiconductor is a new-typed promising photocatalyst, but wide application of SnO₂-based photocatalytic technology has been restricted by low visible light utilization efficiency and rapid recombination of photogenerated electrons–holes. To overcome these drawbacks, we prepared B/Fe codoped SnO₂–ZnO thin films on glass substrates through a simple sol–gel method. The photocatalytic activities of the films were evaluated by degradation of organic pollutants including acid naphthol red (ANR) and formaldehyde. UV–Vis absorption spectroscopy and photoluminescence (PL) spectra results revealed that the B/Fe codoped SnO₂–ZnO film not only enhanced optical absorption properties but also improved lifetime of the charge carriers. X-ray diffraction (XRD) results indicated that the nanocrystalline SnO₂ was a single crystal type of rutile. Field emission scanning electron microscopy (FE-SEM) results showed that the B/Fe codoped SnO2–ZnO film without cracks was composed of smaller nanoparticles or aggregates compared to pure SnO2 film. Brunauer–Emmett–Teller (BET) surface area results showed that the specific surface area of the B/Fe codoped SnO₂–ZnO was 85.2 m² g^?1, while that of the pure SnO₂ was 20.7 m² g^?1. Experimental results exhibited that the B/Fe codoped SnO₂–ZnO film had the best photocatalytic activity compared to a pure SnO₂ or singly-modified SnO₂ film.     

A facile synthesis of ZnS nanocrystallites by pyrolysis of single molecule precursors,Zn (cinnamtscz)<Subscript>2</Subscript> and ZnCl<Subscript>2</Subscript> (cinnamtsczH)<Subscript>2</Subscript>

ZnS nanocrystallites were synthesised by pyrolysis method using Zn (cinnamtscz)₂ and ZnCl₂ (cinnamtsczH)₂ (cinnamtsczH = cinnamaldehyde thiosemicarbazone) as single source precursors. The prepared ZnS nanocrystallites were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, UV-Vis and fluorescence spectroscopy. The peak broadening in XRD and emission at shorter wavelength in fluorescence spectra showed the presence of nanocrystallites. The blue shift in UV-Vis absorption spectroscopy also proved the formation of nanocrystallites. TEM images show presence of plate-like and spherical ZnS nanoparticles obtained from Zn(cinnamtscz)₂ and ZnCl₂ (cinnamtsczH)₂ respectively.     

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

     

Investigation for the synthesis of hierarchical Co<Subscript>3</Subscript>O<Subscript>4</Subscript>@MnO<Subscript>2</Subscript> nanoarrays materials and their application for supercapacitor

We designed and fabricated hierarchical Co₃O₄@MnO₂ nanoarrays directly grown on nickel foam by hydrothermal and calcination methods. After the investigation of growth mechanism, we found that the deposition of MnO₂ was based on the self-decomposition of KMnO₄ and the reducibility of Co₃O₄ during the hydrothermal process. Thanks to the hierarchical structure, the obtained electrode exhibited excellent capacitive performance in supercapacitor. It delivered 21.72 F cm^?2 at a current density of 5 mA cm^?2 and retained ~94 % capacitance of initial value after 5000 cycles.     

Graphite intercalation in the graphite-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-R (R = H<Subscript>2</Subscript>O,C<Subscript>2</Subscript>H<Subscript>5</Subscript>OH,C<Subscript>2</Subscript>H<Subscript>5</Subscript>COOH) systems

The electrochemical behavior of graphite in polar solvent-H₂SO₄ electrolytes is studied in a wide range of H₂SO₄ concentrations. The results demonstrate that, with decreasing H₂SO₄ concentration, the charging curves become smoother and shift to higher potentials, the stage index increases, and intercalation compounds are more difficult to obtain. At H₂SO₄ concentrations of 50% and lower, graphite polarization is accompanied by a significant overoxidation, as evidenced by the anomalously small intercalate layer thicknesses: 7.75–7.85 Å. Anodic polarization of graphite in electrolytes consisting of H₂SO₄ and a polar solvent (H₂O and C₂H₅OH) follows the same mechanism as in the case of the formation of graphite bisulfate. In going from water to C₂H₅OH, a less polar solvent, the intercalation threshold increases from 30 to 70% H₂SO₄. It is shown using a set of characterization techniques that, in the graphite-H₂SO₄-R (R = H₂O, C₂H₅OH) systems, the solvent is not intercalated into graphite. Stage I–III ternary graphite intercalation compounds (TGICs) are synthesized for the first time in the graphite-H₂SO₄-C₂H₅COOH system: stage I TGICs at H₂SO₄ concentrations above 70%, stage II in the range 30–70% H₂SO₄, and stage III at H₂SO₄ concentrations down to 10%. The intercalate layer thickness in the TGICs is 7.94 Å. The mechanism of TGIC formation in this system is shown to differ from those in mixtures of H₂SO₄ and other organic acids. Thermal analysis in combination with spectroscopic analysis of gaseous products provides clear evidence for intercalation of propionic acid into the TGIC and indicates that the thermal stability of this compound is lower than that of graphite bisulfate.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 162–169.Original Russian Text Copyright © 2005 by Shornikova, Sorokina, Maksimova, Avdeev.     

A facile method to enhance electrochemical performance of high-nickel cathode material Li(Ni<Subscript>0.8</Subscript>Co<Subscript>0.1</Subscript>Mn<Subscript>0.1</Subscript>)O<Subscript>2</Subscript> via Ti doping

The cycle stability of Li(Ni_0.8Co_0.1Mn_0.1)O₂ is enhanced obviously by titanium doping via a facile solid-state method. The property of crystal structure is evaluated by XRD, which illustrates the samples possessed a layered α-NaFeO₂ structure with R-3m space group. According to the charge/discharge studies, the capacity retention of pristine sample is around 51% after 125 cycles at 5 C, and the sample with Ti dopant displays a good cyclic stability, after 125 cycles, the capacity retention increases to 75% under 5 C, suggesting it could be possibly applied in fast charge Lithium-ion battery area. The superb electrochemical performance might be attributed to the Ti⁴⁺ occupy the layer structure to broaden the Lithium-ion channel, which is benefit to lithium intercalation and deintercalation during cycling.     

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 structure of (NH<Subscript>4</Subscript>)<Subscript>3</Subscript>[UO<Subscript>2</Subscript>(CH<Subscript>3</Subscript>COO)<Subscript>3</Subscript>]<Subscript>2</Subscript>(NCS)

The compound (NH₄)₃[UO₂(CH₃COO)₃]₂(NCS) (I) was synthesized and examined by single crystal X-ray diffraction analysis. The compound crystallizes in the rhombic system with the unit cell parameters a = 11.5546(4), b = 18.5548(7), c = 6.7222(3) Å, V = 1441.19(10) ų, space group P2₁2₁2, Z = 2, R = 0.0345. The uranium-containing structural units of crystals of I are isolated mononuclear groups [UO₂(CH₃COO)₃]^? belonging to crystal-chemical group AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = CH₃COO^?) of uranyl complexes. The specific features of packing of the uranium-containing complexes in the crystal structure are considered.     

A facile synthesis of MInSe<Subscript>2</Subscript> (M = Cu,Ag) via low temperature pyrolysis of single source molecular precursors, [(R<Subscript>3</Subscript>P)<Subscript>2</Subscript>MIn(SeCOAr)<Subscript>4</Subscript>]

The reaction of KSeCOAr with InCl₃ and [MCl(PR₃)₂] in benzene afforded bimetallic complexes, [(R₃P)₂MIn(SeCOAr)₄] (PR₃ = PEt₃ or PPh₃; M = Cu or Ag; Ar = −C₆H₅ (phenyl) or 4-MeC₆H₄ (tolyl)). The triethylphosphine complexes decomposed rapidly when M = Ag while slowly when M = Cu. All these complexes were characterized by elemental analysis, IR, UV-VIS, NMR (¹H, ³¹P) spectral data. Pyrolysis in a furnace at 300°C gave tetragonal MInSe₂ (M = Cu, Ag) structure. Solvothermal decomposition of [(PPh₃)₂CuIn(SeCOAr)₄] in boiling ethylene glycol gave nanorods of CuInSe₂ which were characterized by XRD, EDAX, SEM and TEM.     

Self-assembly synthesis of LaPO<Subscript>4</Subscript> hierarchical hollow spheres with enhanced photocatalytic CO<Subscript>2</Subscript>-reduction performance

Urchin-like LaPO4 hollow spheres were successfully synthesized by a facile solution route using citric acid (CA) as a structure-directing agent.The size of the three-dimensional (3D) hollow spheres was tuned by changing the concentration of CA.The formation mechanism of the 3D LaPO4 hollow spheres was revealed by studying the time-dependent morphology evolution process.Importantly,compared with monodispersed one-dimensional (1D) LaPO4 nanorods,the 3D LaPO4 hollow spheres self-assembled from nanorods showed a 6.8-fold enhancement in photocatalytic activity for CO2 reduction,which is attributed to the synergistic effect of their hierarchical hollow structure,higher light-harvesting capacity,and faster electron transfer.Our findings provide not only a simple,facile method for the synthesis of hierarchical hollow micro/nanoarchitectures but also an efficient route for enhancing the photocatalytic performance.     

One-step strategy to graphene/Ni(OH)2 composite hydrogels as advanced three-dimensional supercapacitor electrode materials

Graphene-based three-dimensional (3D) macroscopic materials have recently attracted increasing interest by virtue of their exciting potential in electrochemical energy conversion and storage. Here we report a facile one-step strategy to prepare mechanically strong and electrically conductive graphene/Ni(OH)₂ composite hydrogels with an interconnected porous network. The composite hydrogels were directly used as 3D supercapacitor electrode materials without adding any other binder or conductive additives. An optimized composite hydrogel containing ～82 wt.% Ni(OH)₂ exhibited a specific capacitance of ～1,247 F/g at a scan rate of 5 mV/s and ～785 F/g at 40 mV/s (～63% capacitance retention) with excellent cycling stability. The capacity of the 3D hydrogels greatly surpasses that of a physical mixture of graphene sheets and Ni(OH)₂ nanoplates (～309 F/g at 40 mV/s). The same strategy was also applied to fabricate graphene-carbon nanotube/Ni(OH)₂ ternary composite hydrogels with further improved specific capacitances (～1,352 F/g at 5 mV/s) and rate capability (～66% capacitance retention at 40 mV/s). Both composite hydrogels obtained here can deliver high energy densities (～43 and ～47 Wh/kg, respectively) and power densities (～8 and ～9 kW/kg, respectively), making them attractive electrode materials for supercapacitor applications. This study opens a new pathway to the design and fabrication of functional 3D graphene composite materials, and can significantly impact broad areas including energy storage and beyond.