The effect of stacking faults on the electrochemical performance of nickel hydroxide electrodes

The crystal structure of nickel hydroxide comprises of a repetitive stacking of charge neutral layers AbC AbC AbC. A and C denotes the hydroxyl ions which are hexagonally close packed, while b denotes the divalent nickel ions occupying octahedral interstitial sites. The random incorporation of other layers, such as AcB, BaC, CbA, etc., within AbC AbC AbC … stacking sequence can lead to the formation of stacking faults. DIFFaX simulations show that each kind of stacking fault produces a characteristic pattern of non-uniform broadening of the peaks corresponding to the (h 0 ?) reflections in the powder X-ray diffraction (PXRD) pattern of nickel hydroxide. The electrochemical property of each two types of stacking faulted nickel hydroxide is investigated. 2H₂ type of stacking faulted nickel hydroxide delivers better electrochemical activity compared to 3R₂ type stacking faulted nickel hydroxide.     

Effect of pH value on particle morphology and electrochemical properties of LiFePO4 by hydrothermal method

Lithium iron phosphate was prepared by hydrothermal synthesis using LiOH·H₂O, FeSO₄·7H₂O and H₃PO₄ as raw materials. The effects of pH value of reaction solution on particle morphology and electrochemical property were investigated. The pH value of the reaction solution was adjusted in the range of 2.5-8.8 by dilute sulfuric acid and ammonia water. The samples were characterized by field-emission scanning electronic microscope (FE-SEM), X-ray powder diffraction (XRD), constant-current charge/discharge cycling tests and chemical analysis. The results indicated that the particles exhibited acute angle diamond flake-like morphology at pH = 2.5, and as the pH value increased, the particle became hexagon flake-like, round flake-like and irregular flake-like morphology gradually. The optimal sample synthesized at pH = 6.4 exhibited discharge capacities of 151.8 mAh g⁻¹ at 0.2 C rate and 129.3 mAh g⁻¹ at 3 C rate. It was found that pH value affected the morphologies and properties of the product by means of different crystal growth rates.     

A simple method to synthesize layered double hydroxide nanoscrolls

Layered double hydroxide (LDH) is a promising drug carrier, ion exchanger, absorbent, and catalyst or even catalyst support due to its inimitable sandwich structure. If the LDH could be synthesized into the nanoscrolls, it will be promising ion channels for the biomolecule transfer, ion exchange, or catalysis. In this report, a simple technique has been developed to prepare layered double hydroxide nanoscrolls on a large scale. The composition of LDH nanoscrolls can be conveniently adjusted through experiment conditions. We proved the “rolling mechanism” to explain the formation of LDH nanoscrolls. Moreover, we unambiguously proposed the driving force for “rolling mechanism”, which is the change of the forces between the brucite-like sheets and the interanions and between the cations and cations in the brucite-like sheets.     

Magnetic properties of nano-clusters lanthanum chromite powders doped with samarium and strontium ions synthesized via a novel combustion method

A novel approach to synthesize a single-phase orthorhombic perovskite lanthanum chromite LaCrO₃ clusters doped with Sm³⁺ and Sr²⁺ ions via gel combustion route was reported. The producing materials were synthesized using metal nitrates as oxidizers and triethanol amine (TEA), N-butyl amine (NBA) or ethylene diamine (EDA) as a fuel. The effect of the annealing temperature, type of organic fuel and the variation of the samarium and/or strontium substitution and its impact on crystal structure, crystallite size, microstructure and magnetic properties of the LaCrO₃ powders formed was systematically studied. The results revealed that a well crystalline single phase of pure LaCrO₃ can be achieved at annealing temperature from 800 to 1000 °C for 2 h. Moreover, each organic carrier materials exhibited a different degree of effectiveness in the synthesis of the mixed oxide powders. The crystal structure was influenced by doped Sm³⁺ and/or Sr²⁺ ions. The crystallite size of the produced powders was increased with the increase the annealing temperature, increasing the Sm³⁺ ion and the decrease of Sr²⁺ ion substitution. The microstructures of the produced powders were found to be nanoclusters octahedra-like shaped. The saturation magnetization of the LaCrO₃ powders increased continuously with an increase in the Sm³⁺ ion concentration and it decreased with an increase in the Sr²⁺ ion up to 0.3 at annealing temperature of 1000 °C for 2 h. The maximum saturation magnetization (0.279 emu/g) was achieved at the Sm³⁺ ion molar ratio 0.3 and annealing temperature 1000 °C. Moreover, wide coercivities can be obtained at different synthesis conditions (49.25 to 522  Oe).     

High rate performances of the cathode material LiNi1/3Co1/3Mn1/3O2 synthesized using low temperature hydroxide precipitation

A low-temperature reaction route is introduced based on hydroxide precipitation method to synthesize the cathode material LiNi_1/3Co_1/3Mn_1/3O₂. The crystal structure and morphology of the prepared powder have been characterized by X-ray diffraction and Scan electron microscope, respectively. The charge–discharge tests were performed between 2.5 and 4.5 V. The discharge capacity of the material is strongly impacted by the reaction temperature. The powders sintered at 850 °C show the best electrochemical performance and the initial discharge capacity is about 160 mAh g⁻¹ at 5 C. Powder X-ray diffraction and Scan electron microscope results reveal that the excellent electrochemical performances should be ascribed to the lower precursor reaction temperature, the lower degree of cation mixing and analogous spherical small particles, which can improve the transfer of Li ions and electrons. All these results indicate that this material has potential application in lithium-ion batteries.     

The synthesis of composite Sn-SnSb films for lithium-ion batteries by electrochemical deposition

Composite Sn-SnSb nano-crystalline films were fabricated on Cu substrate by an electrochemical deposition process. X-ray diffraction, scanning electron microscopy, and galvanostatic cell cycling were used to characterize the structures and electrochemical properties of the films. The as-deposited films consist of only Sn/SnSb composite nanocrystals with a rather dense morphology. The Sn-SnSb composite electrode gives rise to a very small (6%) initial capacity loss and a rather high specific capacity of about 650 mAh/g, which is significantly higher than the values reported in the literature. The coulombic efficiency during charge-discharge cycles is close to 100%.     

Preparation and electrochemical properties of nickel oxide as a supercapacitor electrode material

Hydrothermal synthesis has been introduced to fabricate NiO precursor at different temperatures, then nanostructured NiO with a distinct flake-like morphology was obtained via heating at low temperature. The NiO nanoflakes are 50-80 nm in width and 20 nm in thickness. The electrochemical capacitive characterization of the as-prepared NiO was studied in 2 M KOH electrolyte solution. The as-prepared NiO exhibits excellent cycle performance and keeps 91.6% initial capacity over 1000 charge-discharge cycles. Electrochemical impedance spectroscopy study reveals that the NiO electrode is controlled by the mass transfer limitation, and its internal resistance is 0.2 Ω. A specific capacitance approximate to 137.7 F g⁻¹ could be achieved at the current density of 0.2 A g⁻¹ in the potential window of 0-0.46 V in 2 M KOH electrolyte solution, due to higher surface area of NiO nanoflakes, which facilitates transport of electrolyte ions during rapid charge/discharge process. Due to higher surface area of NiO nanoflakes, which facilitates transport of electrolyte ions during rapid charge/discharge process.     

Preparation and photoluminescence study of mesoporous indium hydroxide nanorods

Mesoporous indium hydroxide nanorods were successfully synthesized by a mild one-step one-pot method. The obtained samples were characterized by X-ray diffraction, transmission electron microscopy with selected area electron diffraction, N₂ adsorption, ultraviolet-visible absorption and photoluminescence, respectively. Transmission electron microscopy showed that there were some pores in the samples, which were mainly composed of rod-like shapes with length of 300 nm and diameter of 90 nm. N₂ adsorption/desorption measurements confirmed that the prepared powder was mesoporous with average pore diameter of 3.1 nm. The ultraviolet-visible absorption spectroscopy analysis indicated that the band gap energy of the samples was 5.15 eV. Photoluminescence spectrum showed that there were two strong emissions under ultraviolet light irradiation. The growth mechanism of indium hydroxide nanorods and the role of cetyltrimethyl ammonium bromide were also discussed.     

Nanostructured cobalt oxides (Co3O4 and CoO) and metallic Co powders synthesized by the solution combustion method

The combustion synthesis technique using glycine and urea as fuels and cobalt nitrate as an oxidizer is capable of producing well-crystallized Co₃O₄, CoO, as well as metallic Co powders. An interpretation based on the thermodynamic viewpoint and the measurement of the combustion temperatures during the reactions occurring for various fuel-to-oxidant ratios was proposed for a study of the nature of combustion and its correlation with the characteristics of as-synthesized powders. The largest measured specific surface area of the powders was 36 m²/g at a 0.14 glycine-to-nitrate ratio. The crystallites were nano-sized ranging from approximately 23 to 90 nm.     

Synthesis and electrochemical performances of spinel LiCr0.1Ni0.4Mn1.5O4 compound

The spinel compound LiCr_0.1Ni_0.4Mn_1.5O₄ was synthesized by a solid reaction method and a sol-gel method using citric acid as chelating agent. The pure phase LiCr_0.1Ni_0.4Mn_1.5O₄ was obtained by the wet method. The electrochemical performances of the pure phase sample were measured at different current rates. There were three voltage plateaus at about 4.9, 4.7 and 4.0 V in the charge-discharge curves, which were attributed to the oxidation/reduction of chromium, nickel and manganese respectively. In the range of 3.5-5.0 V, its first discharge capacity was 143, 118 and 111 mAh/g corresponding to current densities of 1.0, 4.0 and 5.0 mA/cm², respectively. After 50 cycles, the capacity retention remained well at the current densities of 1.0, 4.0 and 5.0 mA/cm². The electrochemical performances of pure phase LiCr_0.1Ni_0.4Mn_1.5O₄ at 55 °C was also measured, and the results were discussed.     

Microwave synthesis of nanocrystalline Sb2S3 and its electrochemical properties

Nanocrystalline antimony trisulfide (Sb₂S₃) was successfully synthesized via microwave irradiation by the reaction of antimony trichloride (SbCl₃) and thiourea (CS(NH₂)₂) with PVP as the surfactant. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). XRD results show that the as-prepared sample is orthorhombic-phase Sb₂S₃. TEM image of the as-prepared Sb₂S₃ shows the rod-like structure. HRTEM image indicates that rodbundles of Sb₂S₃ consists of a number nanorods with the diameter ranging from 30 nm to 50 nm. Detailed HRTEM image demonstrates the preferential direction growth of the Sb₂S₃ nanorods. The electrochemical properties of Sb₂S₃ were primarily investigated by constant current charge/discharge cycling tests in lithium hexafluorophosphate (LiPF₆) solution. The possible electrochemical reaction mechanism was explained. The results indicate that the nanocrystalline Sb₂S₃ shows potential application in the field of the electrode materials.     

Direct template synthesis of mesoporous carbon and its application to supercapacitor electrodes

A direct templating method which is facile, inexpensive and suitable for the large scale production of mesoporous carbon is reported herein. A meso-structure surfactant/silicate template was made in a solution phase and resorcinol-formaldehyde as a carbon precursor was incorporated into the template solution. After aging, carbonization and hydrofluoric acid (HF) etching, mesoporous carbon was obtained. Using X-ray diffraction, scanning and transmission electron microscopy and nitrogen sorption, the synthesis mechanism of the mesoporous carbon was elucidated. According to the small angle X-ray scattering measurements, the surface became smoother after the removal of the silica, indicating that the silica was mostly located at the pore surface of the carbon. Also, the calculation of the pore volume demonstrated that the silica was transferred into the pores of the carbon without structural collapse during HF etching. When the prepared mesoporous carbon was applied to a supercapacitor electrode, the rectangular shape of the cyclic voltammogram was less collapsed, even at a high scan rate, which is indicative of its high rate capability. This was due to the low resistance of the electrolyte in the pores (3.8 Ω cm²), which was smaller than that of conventional activated carbon electrodes and even comparable to that of ordered mesoporous carbon electrodes. This improved performance was probably due to the well developed mesoporosity and high pore connectivity of the prepared mesoporous carbon.     

Photochemical performance and electrochemical capacitance of titania nanocomplexes

Titania nanocomplexes, comprising the disordered nanoribbons or nanowires on the top surface and highly ordered nanotube array on the underlaying layer, has been fabricated by longitudinally splitting off nanotubes in a controlled anodization process. Anatase titania nanocomplexes show higher photovoltage and photocurrent responses and photocatalysis activity than titania nanotube array due to the enhanced light harvesting caused by nanoribbons and nanowires. Furthermore, titania nanowire-nanotube demonstrates a higher photoelectrical performance than nanoribbon-nanotube due to its thicker space charge layer caused by long nanotubes and more effective surface area contributed by nanowires. Cyclic charge-discharge measurements show that titania nanotube array exhibits a much higher electric double layer capacitance than titania nanocomplexes because the surface nanoribbons or nanowires inhibit the free diffusion and transportation of electrolyte ions into the underlaying nanotubes. Therefore, titania nanocomplexes can act as a photoactive material for photocatalysis applications and titania nanotube array can act as an electrode substrate for electrochemical supercapacitor applications.     

Intermittent microwave heating synthesized high performance spherical LiFePO4/C for Li-ion batteries

An intermittent microwave heating method was used to synthesize spherical LiFePO₄/C in the presence of glucose as reductive agent and carbon source without the use of the inert gas in the oven processes. The FePO₄ was used as iron precursor to reduce the cost and three lithium salts of Li₂CO₃, LiOH and CH₃COOLi were chosen for comparison of the resulting materials. The materials can be alternatively heated by this method at a temperature controllable mode for crystallization and phase transformation and to provide relaxation time for protecting particles growth. The X-ray diffraction and scanning electron microscope measurements confirmed that the LiFePO₄/C is olivine structured with the average particle size of 50-100 nm. The spherical LiFePO₄/C as cathode material showed better electrochemical performance in terms of the specific capacity and the cycling stability, which might be attributed to the highly crystallized phase, small particle distribution and improved conductivity by carbon connection.     

Preparation of activated carbon from sorghum pith and its structural and electrochemical properties

The cost effective activated carbon (AC) has been prepared from sorghum pith by NaOH activation at various temperatures, including 300 °C (AC1), 400 °C (AC2) and 500 °C (AC3) for the electrodes in electric double layer capacitor (EDLC) applications. The amorphous nature of the samples has been observed from X-ray diffraction and Raman spectral studies. Subsequently, the surface functional groups, surface morphology, pore diameter and specific surface area have been identified through FT-IR, SEM, histogram and N₂ adsorption/desorption isotherm methods. The electrochemical characterization of AC electrodes has been examined using cyclic voltammetry technique in the potential range of −0.1-1.2 V in 1.0 M H₂SO₄ electrolyte at different scan rates (10, 20, 30, 40, 50 and 100 mV/s). The maximum specific capacitances of 320.6 F/g at 10 mV/s and 222.1 F/g at 100 mV/s have been obtained for AC3 electrode when compared with AC1 and AC2 electrodes. Based on the characterization studies, it has been inferred that the activated carbon prepared from sorghum pith may be one of the innovative carbon electrode materials for EDLC applications.     

Synthesis, structure, and electrochemical characteristics of LiNi1/3Co1/3Mn1/3O2 prepared by thermal polymerization

A thermal polymerization route was adopted to synthesize layered LiNi_1/3Co_1/3Mn_1/3O₂ materials. After annealing the polymer gel containing metal salts at different temperatures from 850 to 1000 °C for different time between 6 and 25 h, powders of pure α-NaFeO₂ phase were obtained. The crystal structure, morphology and electrochemical properties of the products were investigated by XRD, SEM, electrochemical cell cycling and AC impedance spectroscopy. It is found that the powder annealed at 950 °C for 15 h shows the best electrochemical property with the first specific discharge capacity of 188 mAh/g at C/10 and 87% retention after 100 cycles. It exhibits good rate capability with the specific capacity of 169 mAh/g at 1 C and 110 mAh/g at 6 C. Adopting a slowly cooling procedure during the powder annealing can improve the electrochemical performance of the LiNi_1/3Co_1/3Mn_1/3O₂ powder.     

Synthesis of barium titanate nanoparticles via a novel electrochemical route

An electrochemical route from Ti metal plate in KOH and Ba(OH)₂ electrolyte at room temperature is first established for the synthesis of BaTiO₃ nanoparticles. Anodic sparks play a key role, and KOH concentration is one of the most significant factors which affect the appearance of anodic sparks in this method. XRD patterns show that the powder obtained in our study is a pure perovskite phase BaTiO₃ with a cubic structure, whose size and morphology are subsequently studied by TEM. The mean diameter of the particles is 13.8 nm and the standard deviation (S.D.) fitted is 6.26 nm. It is also found that the mean size of the obtained nanoparticles increase from 13.8 nm to 168.0 nm, when 60 vol.% absolute ethanol is replaced by distilled water as the solvent of the electrolyte.     

Structural properties and growth mechanism of flower-like ZnO structures obtained by simple solution method

Flower-shaped zinc oxide (ZnO) structures have been synthesized in the reaction of aqueous solution of zinc nitrate and NaOH at 90 °C. To examine the morphology of ZnO nanostructures, time-dependent experiments were carried out. Detailed structural observation showed that the flower-like structures consist of triangular-shaped leaves, having sharpened tips with wider bases. Photoluminescence spectrum measured at room temperature show a sharp UV emission at 381 nm and a strong and broad green emission at 480-750 nm attributed to structural defects. A possible growth mechanism for the formation of flower-shaped ZnO structures is discussed in detail.     

Synthesis of size-tunable mesoporous anatase titania spheres by a template-free method

A facile route was presented to fabricate mesoporous anatase titania spheres at low temperature; the titania precursor sphere was prepared through a template-free process and then treated by the boiling water. X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were adopted to characterize the morphology and crystal structure of the products. The adsorption properties and photocatalytic activities were also investigated. The results indicated that the porous structure and anatase nanocrystals were gradually formed from the surface to the interior of the titania precursor spheres with increasing treatment time. Moreover, there was little change in the size of the spheres during boiling water treatment, thus the size of the mesoporous anatase titania spheres could be easily tailored by controlling the diameter of precursor spheres. The as-prepared product showed excellent adsorption capacity and photocatalytic activity than the commercial P25 due to its high specific surface area.     

Synthesis of acid-base bifunctional mesoporous materials by oxidation and thermolysis

A novel and efficient method has been developed for the synthesis of acid-base bifunctional catalyst SO₃H-MCM-41-NH₂. This method was achieved by co-condensation of tetraethylorthosilicate (TEOS), 3-mercaptopropyltrimethoxysilane (MPTMS) and (3-triethoxysilylpropyl) carbamicacid-1-methylcyclohexylester (3TAME) in the presence of cetyltrimethylammonium bromide (CTAB), followed by oxidation and then thermolysis to generate acidic site and basic site. X-ray diffraction (XRD) and transmission electron micrographs (TEM) show that the resultant materials keep mesoporous structure. Thermogravimetric analysis (TGA), X-ray photoelectron spectra (XPS), back titration, solid-state ¹³C CP/MAS NMR and solid-state ²⁹Si MAS NMR confirm that the organosiloxanes were condensed as a part of the silica framework. The bifunctional sample (SO₃H-MCM-41-NH₂) containing amine and sulfonic acids exhibits excellent acid-basic properties, which make it possess high activity in aldol condensation reaction between acetone and various aldehydes.