Oxidative energy storage behavior of a porous nanostructured TiO2–Ni(OH)2 bilayer photocatalysis system

TiO₂–Ni(OH)₂ bilayer electrodes were prepared by the cathodic electrodeposition of Ni(OH)₂ layer on a TiO₂/ITO substrate. The porous Ni(OH)₂ layers were obtained at relatively high current densities (≥1.0 mA cm⁻²), and the particle size increased with increasing the deposition current density. A porous nanostructured TiO₂–Ni(OH)₂ bilayer was obtained at a current density of 1.0 mA cm⁻². The effects of OH⁻ concentration in the electrolyte and surface structure in the Ni(OH)₂ layer on storage of the oxidative energy of TiO₂ were investigated. In our experimental conditions the oxidative energy storage of an UV-irradiated TiO₂ photocatalyst in Ni(OH)₂ was obviously enhanced in the electrolyte with 1.0 M OH⁻. The porous nanostructured TiO₂–Ni(OH)₂ bilayer electrode showed the notably improved oxidative energy storage performance, resulting from its porous structure and nanostructured Ni(OH)₂ particles. The TiO₂–Ni(OH)₂ bilayer electrode during UV irradiation exhibited much higher potentials and larger photocurrent than the TiO₂/ITO electrode. The transition from Ni(OH)₂ to NiOOH under UV irradiation proceeded in the potential range of −0.5 to −0.2 V, much more negative than the Ni(OH)₂/NiOOH redox potential. A possible mechanism on the oxidative energy storage of an UV-irradiated TiO₂ photocatalyst in Ni(OH)₂ was proposed, and the related experimental results were discussed in terms of the suggested model.     

Electrochemical characterization of amorphous LiFe(WO4)2 thin films as positive electrodes for rechargeable lithium batteries

Amorphous LiFe(WO₄)₂ thin films have been fabricated by radio-frequency (R.F.) sputtering deposition at room temperature. The as-deposited and electrochemically cycled thin films are, respectively, characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectra techniques. An initial discharge capacity of 198 mAh/g in Li/LiFe(WO₄)₂ cells is obtained, and the electrochemical behavior is mostly preserved in the following cycling. These results identified the electrochemical reactivity of two redox couples, Fe³⁺/Fe²⁺ and W⁶⁺/W^x+ (x = 4 or 5). The kinetic parameters and chemical diffusion coefficients of Li intercalation/deintercalation are estimated by cyclic voltammetry and alternate-current (AC) impedance measurements. All-solid-state thin film lithium batteries with Li/LiPON/LiFe(WO₄)₂ layers are fabricated and show high capacity of 104 μAh/cm² μm in the first discharge. As-deposited LiFe(WO₄)₂ thin film is expected to be a promising positive electrode material for future rechargeable thin film batteries due to its large volumetric rate capacity, low-temperature fabrication and good electrode/electrolyte interface.     

Light energy storage and photoelectrochemical behavior of the titanate nanotube array/Ni(OH)2 electrode

A new kind of TiO₂ nanotube array/Ni(OH)₂ (TiO₂/Ni(OH)₂) composite electrode with the storage ability of light energy was prepared by the deposition of Ni(OH)₂ on the TiO₂ nanotube array, which was synthesized by anodizing Ti foils in an HF aqueous solution. SEM and XRD results showed that Ni(OH)₂ particles were well distributed on high density, well-ordered and uniform TiO₂ nanotube arrays. The photoelectrochemical properties of the TiO₂/Ni(OH)₂ electrode were investigated in NaHCO₃/NaOH buffer solution (pH 10) by means of UV-vis absorption spectra, cyclic voltammogram (CV) and photocurrent measurements. It was found that the TiO₂/Ni(OH)₂ electrode was highly sensitive to light and exhibited excellent photoelectrochromic properties. Upon UV irradiation, the photogenerated holes by TiO₂ nanotube arrays can oxidize Ni(OH)₂ to NiOOH, and thus the TiO₂/Ni(OH)₂ electrode can be photo-charged by light.     

An unusual H2O2 electrochemical sensor based on Ni(OH)2 nanoplates grown on Cu substrate

In this work, Ni(OH)₂ nanoplates grown on the Cu substrate were synthesized and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Then a novel Cu-Ni(OH)₂ modified glass carbon electrode (Cu-Ni(OH)₂/GCE) was fabricated and evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and typical amperometric response (i-t) method. Exhilaratingly, the Cu-Ni(OH)₂/GCE shows significant electrocatalytic activity toward the reduction of H₂O₂. At an applied potential of −0.1 V, the sensor produces an ultrahigh sensitivity of 408.1 μA mM⁻¹ with a low detection limit of 1.5 μM (S/N = 3). The response time of the proposed electrode was less than 5 s. What's more, the proposed sensor displays excellent selectivity, good stability, and satisfying repeatability.     

花状Ni(OH)2的制备及其电化学性能研究

以NiCl₂·6H₂O和NH₃·H₂O为原料,采用简单的水热法,借助表面活性剂CTAB成功合成了β-Ni(OH)₂。研究表明,该材料具有以纳米片相互穿插构成的花状分层微米球结构,比表面积高达45 m²?g^-1。电化学测试表明材料具有良好的电化学性能,在3 A?g^-1的充放电电流密度下,Ni(OH)₂的比容量达到505 C?g^-1,在超级电容器领域具有良好的应用前景。     

Ni(OH)2修饰对a-Fe2O3薄膜光电化学性能的增强效应

利用一种简便的电沉积方法制备氧化铁薄膜,并在过程中引入Ni(OH)₂进行修饰,对具体电沉积实验参数进行优化,从而建立最佳制备条件。利用场发射扫描电子显微镜、X射线粉末衍射对Fe₂O₃/Ni(OH)₂光电极膜的结构进行表征。利用循环伏安和计时电流测量析氧过电位和光电流密度。结果表明,Ni(OH)₂修饰的α-Fe₂O₃薄膜可提高光生电子与空穴的分离效率,从而显著提高光电催化活性。     

Study of the effects of nanometer β-Ni(OH)2 in nickel hydroxide electrodes

Nanometer β-Ni(OH)₂, showed by XRD, was prepared by our supersonic coordination-precipitation method, with an average grain size of about 50 nm by TEM. Proton diffusion coefficient of nanometer Ni(OH)₂ and spherical Ni(OH)₂ were 1.93 × 10⁻¹¹, and 5.50 × 10⁻¹³ cm²/s, respectively, with combination of chronocoulometry and cyclic voltammetry. Charge-discharge test of simulated batteries at 0.2 °C showed that addition of 8 mass% of our prepared nanometer Ni(OH)₂ in nickel hydroxide electrodes led to increases in cathode discharge specific capacity (CDSC) by nearly 10% and the chargeability of the electrode by about 50 mAh/g, and a decrease in polarization. Cycle life test of AA-type MH-Ni batteries discovered that effect of nanometer Ni(OH)₂ in increasing CDSC was more apparent for the first 100 cycles and not much difference was found after 350 cycles. XAS demonstrated a higher oxidation state of Ni in fully charged nanometer Ni(OH)₂ composite electrode (Nano-E) and a lower one in discharged Nano-E, compared with micrometer Ni(OH)₂ spherical electrodes (Micro-E). A larger structure distortion was found in Nano-E, offering more vacancies for proton diffusion. Thus conversion between Ni²⁺ and Ni³⁺ was promoted during the charge-discharge process, which was assumed to be one explanation of increasing CDSC with the addition of nanometer Ni(OH)₂.     

Facile synthesis and flame retardant performance of NaAl(OH)2CO3 whiskers

The regular and well-dispersed NaAl(OH)₂CO₃ whiskers were successfully synthesized via facile hydrothermal route using aluminium isopropoxide and NaHCO₃. The effects of reactants and reaction temperature on the structure and morphology of NaAl(OH)₂CO₃ whiskers have been investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermo-gravimetric analysis (TGA) were employed to characterize the synthesized samples. Most NaAl(OH)₂CO₃ whiskers possess an average diameter of about 500 nm and lengths ranging from 10 to 30 μm. NaAl(OH)₂CO₃ whiskers exhibit excellent flame retardant performance and mechanical strength in poly(ethylene-co-vinyl acetate) matrix (EVA).     

Synthesis of carbon nanotubes by pyrolysis of solid Ni(dmg)2

We describe the high yield synthesis of multi-walled carbon nanotubes (MWCNTs) and the determination of the optimum production conditions. The method involves the catalytic pyrolysis of solid Ni(dmg)₂ under an Ar atmosphere. The obtained materials were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and thermogravimetry analysis (TGA). The data revealed the formation of MWCNTs surrounded by a varying quantity of byproducts such as amorphous carbon and metallic particles, depending mainly on the reaction temperature. Pyrolysis of Ni(dmg)₂ at 900 °C results in the production of nanotube material with the highest degree of crystallinity.     

Preparation of surface modified nano-Mg(OH)2 via precipitation method

Nano-magnesium hydroxide was prepared via wet precipitation by using the mixture of sodium dodecyl sulfate (SDS) and monoalcohol ether phosphate (MAP) as surface modifiers. The yield of the surface modified nano-Mg(OH)₂ was about 98%. The usage and dosage of surface modifiers were optimized by means of the measurements of suspension volume of the nano-particles in liquid paraffin. As the mass ratio of SDS to MAP was 2:1 and the total of 0.2 wt.% of Mg(OH)₂ theoretical weight (4.35 g) was used, the nano-Mg(OH)₂ with optimized dispersibility was obtained. The volume percent of the surface modified nano-particles suspension in liquid paraffin could reach 96% after 11 h while that of the nano-Mg(OH)₂ without modification would be 62%. The as-prepared samples were characterized through N₂ adsorption, X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry-differential scanning calorimetry (TGA-DSC). The results show that hexagonal crystal nano-particles with both SDS and MAP molecules on the surfaces were obtained. The LOI value of PP composites is 35.0 at 150 phr (50% by weight) of surface modified nano-Mg(OH)₂.     

脲酶诱发合成纳米Ni(OH)2及其电化学性能

采用脲酶催化尿素水解,诱发均匀沉淀制备了纳米Ni(OH)2,经XRD测试为-βNi(OH)2。TEM测试显示,向反应体系中加入表面活性剂可将Ni(OH)2的粒径由50 nm降为10 nm。恒流充放电和循环伏安实验表明,纳米Ni(OH)2比微米级Ni(OH)2具有更优的电化学性能,放电容量提高11%左右。其原因在于脲酶的高效催化性使均匀沉淀在很短时间内即被诱发,生成的纳米Ni(OH)2晶体内部缺陷多,有更大的扩散系数(约是微米级Ni(OH)2的3倍),降低了电极的反应内阻,从而有效地改善了质子的传递和扩散。     

Electrochemical assembling of aligned porous Nd(OH)3 nanobelts with high performance in water treatment

In this study, aligned Nd(OH)₃ nanobelts with abundant mesopores are successfully assembled by a facile, and template-free electrochemical method. The well-defined porous structure in Nd(OH)₃ nanobelts leads to its superior adsorption and the remove rate of Congo red contained in wastewater reach to 99.1% in 30 min.     

A rate equation for Ca(OH)2 and CO2 reaction in a spouted bed reactor at low gas concentrations

In the present study, the carbonation reaction of hydrated lime in semi-dry condition is investigated experimentally in a laboratory-scale spouted bed reactor. Results show that for operating conditions where the concentration of CO₂ is low, the capture efficiency is raised by increasing the inlet CO₂ concentration. Additionally, because of the inconsistency between the experimental reaction rate and the calculated values based on the previous proposed equations, a new rate equation is introduced that considers the dependency of CO₂ concentration too. To validate the proposed equation, its predictions were compared with another set of experimental data.     

Synthesis and H2 uptake of Cu2(OH)3Cl, Cu(OH)2 and CuO nanocrystal aggregate

Monodispersed Cu₂(OH)₃Cl nanoplatelets, Cu(OH)₂ nanowires, CuO nanoparticles and nanoribbons with a spherical morphology were synthesized using hydrothermal and heat-treatment reactions, and their H₂ storage characteristics were examined. The Cu₂(OH)₃Cl nanoplatelets particles formed immediately after mixing the reactant, which subsequently formed larger uniform spherical particles in the submicron range. This procedure highlights a practical strategy for producing spherical Cu(OH)₂ and CuO materials consisting of monodispersed nanocrystals. The spherical aggregates of Cu₂(OH)₃Cl nanoplatelets heat-treated at 473 K could reversibly store up to 2.35 wt.% H₂ at 38 bar and 293 K.     

The preparation of Mg3Si2O5(OH)4 nanotubes under solvothermal conditions

With magnesium carbonate hydroxide and nanoporous silica as the starting materials, chrysotile (Mg₃Si₂O₅(OH)₄) nanotubes were prepared by using a solvothermal method at 400^∘C within four hours. This new method needs no strong alkali medium and the reaction time is very short. EDX analysis showed a molar ratio of 3Mg:2Si:9O of the product. Selected Area Electron Diffraction (SAED) pattern indicated that the tube axis is along [100] direction. HRTEM image showed the nanotubes were multi-walled and the distance between the two close layers was about 0.75 nm, which is very near to the distance of {001} planes. Thus, combining the results of SAED and HRTEM, we can conclude that the {001} planes of serpentine roll up along the [100] direction to form the tubular structure. The effects of various reaction conditions and the formation mechanism were also discussed.     

Predicting Ca(OH)2 content and chemical shrinkage of hydrating cement pastes using analytical approach

A semiempirical model is proposed to predict the evolution of chemical shrinkage and Ca(OH)₂ content of cement paste at early age of hydration. The model is based on chemical equations and cement compound hydration rates. Chemical shrinkage and Ca(OH)₂ amount are computed using the stoichiometric results of the hydration reactions considered in the model and the density of hydration products and reactants. The model validation is conducted by comparison between computed and experimental results achieved on ordinary cement pastes with different water-to-cement (w/c) ratios (0.25, 0.30, 0.35 and 0.40) cured at 10, 20, 30, 40 and 50 °C, respectively. Hydration degree and Ca(OH)₂ content are determined using the thermogravimetric analysis (TGA) and chemical shrinkage evolution using a gravimetric method.The comparison reveals a good consistency between modelled and experimental data at early age of hydration.     

Controllable synthesis of CaTi2O4(OH)2 nanoflakes by a facile template-free process and its properties

Serrated leaf-like CaTi₂O₄(OH)₂ nanoflake crystals were synthesized via a template-free and surfactant-free hydrothermal process. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The growth process for CaTi₂O₄(OH)₂ nanoflakes was dominated by a crystallization–dissolution–recrystallization growth mechanism. BET analysis showed that CaTi₂O₄(OH)₂ nanoflakes had mesoporous structure with an average pore size of 8.7 nm, and a large surface area of 88.4 m² g⁻¹. Cyclic voltammetry and galvanostatic charge–discharge tests revealed that the electrode synthesized from CaTi₂O₄(OH)₂ nanoflakes reached specific capacitances of 162 F g⁻¹ at the discharge current of 2 mA cm⁻², and also exhibited excellent electrochemical stability.     

Indirect electrooxidation of crotyl and cinnamyl alcohol using a Ni(OH)2 electrode

The heterogeneous catalytic redox behaviour of the nickel oxyhydroxide electrode surface was investigated with and without crotyl and cinnamyl alcohols using cyclic voltammetry. A comparison of the cyclic voltammograms recorded in the absence and presence of these alcohols confirmed the catalytic oxidation of the alcohols by the surface Ni³⁺/Ni²⁺ redox system at the electrode surface. Preparative scale experiments were also carried out using Ni(OH)₂ electrodes of large surface area and the redox behaviour of the electrode was confirmed by the isolation of crotonic and cinnamic acids with high yield efficiency. The influence of molecular size on the catalytic oxidation process is examined.     

A novel method to synthesize whisker-like Co(OH)2 and its electrochemical properties as an electrochemical capacitor electrode

A loose whisker-like Co(OH)₂ was synthesized by means of polyethylene glycol 4000 as soft template under ultrasonic condition, and investigated as an active electrode material for electrochemical capacitors. The composition and microstructure of the as-prepared Co(OH)₂ were investigated by X-ray diffraction spectroscopy and transmission electron microscopy. The formation mechanism of the whisker-like Co(OH)₂ was attentively proposed based on Fourier transform infrared spectroscopy analysis. Electrochemical studies revealed that the whisker-like Co(OH)₂ delivered a specific capacitance of 325 F/g at a current density of 20 mA/cm² (ca. 1.3 A/g) and even 279 F/g at 80 mA/cm² (ca. 5.3 A/g) due to its special nanostructure, indicating its fast electrochemical response property. A capacitance attenuation of ca. 7% over 1000 cycles meant the good cyclic stability of the whisker-like Co(OH)₂ for electrochemical capacitors application.