Ni（OH）_2纳米材料的制备研究

综述了Ni（OH）2纳米材料的主要合成方法,介绍了各种制备方法的工艺条件及主要特点,指出氢氧化镍作为电池正极材料具有光明的前景,但对生产技术还需进一步研究。     

纳米片层状氢氧化钴/泡沫镍复合材料的超级电容性能研究

本文在2.3 V电压、30 mA电流、120 s沉积时间条件下,采用控电位电沉积方法在泡沫镍基体上沉积Co(OH)_2制备了复合电极材料并研究了其超电容性能。结果表明:所获得的复合电极材料表面为纳米片层状Co(OH)_2,且保留了泡沫镍的三维网状结构。这一结构促进了电极活性物质与电解液之间的充分接触以及离子在电极体相中的吸附与脱附,使复合材料具有优异的超电容特性,比电容值高达975.8 F/g(50 mV/s),内阻仅为0.74Ω。     

高容量高密度氢氧化亚镍的制备

研究了制备工艺参数对Ｎｉ（ＯＨ）２放电比容和堆积密度的影响并进行了理论分析，给出了最佳工艺条件范围，分析了氨的加入对Ｎｉ（ＯＨ）２堆积密度及形貌的影响采用ＸＲＤ、ＴＧ－ＤＴＡ等检测手段对样品进行分析，并与进口样品进行了比较     

Preparation and crystallization kinetics of micron-sized Mg(OH)2 in a mixed suspension mixed product removal crystallizer

Magnesium hydroxide is an important chemical, and is usually obtained from seawater or brine via precipitation process. The particle size distribution of magnesium hydroxide has great effects on the subsequent filtration and drying processes. In this paper, micron-sized magnesium hydroxide with high purity, large particle size and low water content in filter cake was synthesized via simple wet precipitation in a mixed suspension mixed product removal (MSMPR) crystallizer. The effects of reactant concentration, residence time and impurities on the properties of magnesium hydroxide were investigated by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Malvern laser particle size analyzer. The results show that NaOH concentration and residence time have great effects on the water content and particle size of Mg(OH)₂. The spherical Mg(OH)₂ with uniform diameter of about 30 μm was obtained with purity higher than 99% and water content less than 31%. Furthermore, the crystallization kinetics based on the population balance theory was studied to provide the theoretical data for industrial enlargement, and the simulation coefficients (R²) based on ASL model and C-R model are 0.9962 and 0.9972, respectively, indicating that the crystal growth rate of magnesium hydroxide can be well simulated by the size-dependent growth models.     

镍氢电池用高活性球形氢氧化亚镍生产的工程设计

球形氢氧化亚镍作为镍氢电池生产的核心原料，其质量的优劣决定了电池的许多性能。本文介绍了氢氧化亚镍的生产工艺。     

氢氧化镍纳米片的制备

以硝酸镍为镍源,采用水热法制备N i(OH)2纳米片,通过改变反应物浓度、反应时间、反应温度,研究不同实验条件对N i(OH)2纳米片的影响;通过X-射线衍射、扫描电子显微镜等手段对样品进行了表征。     

Effects of the coating characteristics of Y(OH)3 on the electrochemical performance of spherical Ni(OH)2 at elevated temperature

The effects of the coating characteristics of Y(OH)₃ on the high-temperature performance of spherical Ni(OH)₂ were studied. The coating was performed by chemical surface precipitation under different conditions, and the characterization of Y(OH)₃-coating layer was evaluated accordingly. The electrochemical properties of three as-prepared samples with different coating surface were characterized and compared at different temperature. The results reveal that the sample with dense and porous surface retains the excellent performance at elevated temperatures, and the necessary coating amount is only 0.55 at.%. The mechanism analysis suggests that the chemical nature and morphology of the coating layer plays an important role in oxygen evolution reaction (OER). The coating surface with dense and porous morphology, larger relative surface content and higher utilization ratio of yttrium is more effective on controlling OER and improving the high-temperature performance of Ni(OH)₂ electrode for nickel-metal hydride (Ni/MH) batteries.     

Electrochemically induced transformation of NiS nanoparticles into Ni(OH)2 in KOH aqueous solution toward electrochemical capacitors

Nickel sulfide nanoparticles (NPs) are first synthesized by virtue of a unique H₂O/CS₂ interface under mild hydrothermal treatment. Electrochemical data reveals that the as-synthesized NiS NPs themselves own poor supercapacitive behavior at initial cyclic voltammetry (CV) cycles in 2 M KOH solution, while a specific capacitance of 893 F g⁻¹ can be surprisingly obtained at a current density of 5 A g⁻¹ just after continuous 320 CV cycles. X-ray diffraction and Fourier transform infrared techniques demonstrate that what is really responsible for the good electrochemical capacitance in the KOH aqueous solution is the new electrochemically formed Ni(OH)₂ phase, rather than NiS NPs themselves. The Ni(OH)₂ is slowly formed during the continuous CV cycling process, in which the electrochemically induced phase transformation from NiS to Ni(OH)₂ phase takes place. Furthermore, the new Ni(OH)₂ phase demonstrates the great ability of delivering large specific capacitance at high rates.     

Enhanced room temperature ammonia response of 2D-Ti3C2Tx MXene decorated with Ni(OH)2 nanoparticles

Due to the expansion of human production activities, toxic ammonia (NH₃) is excessively released into the atmosphere, being a huge threat to human health and the natural environment. Therefore, it is of great significance to design an easy-synthesized gas-sensing material with both good room temperature sensitivity and selectivity for trace-level NH₃ detection. Herein, we fabricate a chemiresistive NH₃ gas sensor with enhanced performance based on Ni(OH)₂/Ti₃C₂T_x hybrid materials. The Ni(OH)₂/Ti₃C₂T_x hybrid materials are synthesized by an in-situ electrostatic self-assembly method. Attributed to the formation of interfacial heterojunctions and the modulation of carrier density, the Ni(OH)₂/Ti₃C₂T_x hybrid sensor exhibits high response, outstanding repeatability, good selectivity and stability in low concentrations of NH₃. Moreover, the Ni(OH)₂/Ti₃C₂T_x hybrid sensor has a higher response to 10 ppm NH₃ at the relative humidity of 40% and 60%, which makes it promising for applications in real complex environments with high humidity. Benefitting from the low power consumption and easy fabrication process, the Ni(OH)₂/Ti₃C₂T_x hybrid sensor possesses a broad application prospect in the internet of things (IoT) environmental monitoring.     

温度对电沉积氢氧化镍电化学性能的影响

在0.1mol/L的Ni(NO3)2溶液中,采用电化学沉积法制备出适用于锌镍微电池的氢氧化镍电极,研究了电沉积温度对Ni(OH)2电极的电化学循环伏安性能以及充放电性能的影响。测试结果表明,电沉积方法制备的Ni(OH)2电极适合于微电池的制作。30°C下电沉积制备的Ni(OH)2电极具有优异的电化学性能,其质子扩散系数为7.71×10-12cm2/s,放电比容量为1285μAh/cm2,利用率达91.4%。     

Nickel foam-supported porous Ni(OH)2/NiOOH composite film as advanced pseudocapacitor material

A porous net-like β-Ni(OH)₂/γ-NiOOH composite film is prepared by a chemical bath deposition. The as-prepared porous composite film shows a highly porous structure built up by many interconnected nanoflakes with a thickness of about 20 nm. The pseudocapacitive behavior of the porous composite film is investigated by cyclic voltammograms (CV) and galvanostatic charge–discharge tests in 1 M KOH. The porous β-Ni(OH)₂/γ-NiOOH composite film exhibits a noticeable pseudocapacitance with 1420 F g⁻¹ at 2 A g⁻¹ and 1098 F g⁻¹ at 40 A g⁻¹, respectively, much higher than those of the dense Ni(OH)₂ film (897 F g⁻¹ at 2 A g⁻¹ and 401 at 40 A g⁻¹). The porous architecture is responsible for the enhancement of the electrochemical properties, and it increases electrochemical reaction area, shortens ions diffusion paths and relaxes volume change caused by the electrochemical reactions.     

氢氧化镍纳米晶的水热合成和结构表征

用水热法在180℃合成了非球形的Ni(OH)2纳米晶,并用X射线衍射(XRD)、傅立叶变换红外光谱(FT-IR)、透射电镜(TEM)和高分辨透射电镜(HRTEM)等技术对其形貌和结构作了表征. 结果表明,Ni(OH)2纳米晶的生长习性和形貌都强烈依赖于前驱物溶液的pH值. 在较高的pH值(13.40)下,产物主要是六角片状粒子,而在近中性条件(7.80)下,产物主要是不规则形貌的粒子. 在pH值较高的条件下,除了通常的Ostwald ripening 晶体生长粗化机理外,合并生长机理对纳米晶生长过程也发挥了作用.     

Gas absorption into aqueous reactive slurries of calcium and magnesium hydroxide in a multiphase reactor

Investigation of absorption of SO₂ into aqueous slurries of fine and reactive hydroxide particle of calcium and magnesium was carried out in a stirred vessel at 298 K at realistically high mass transfer coefficients. Enhancement in the rate of gas absorption was measured at different solid loadings and speed of agitation. The absorption process is theoretically analyzed using two different models. For the SO₂–Ca(OH)₂ system, a single reaction plane model was used and for the SO₂–Mg(OH)₂ system, a two reaction plane model incorporating the solids dissolution promoted by the reactions with the absorbed SO₂ in the liquid film was employed. A correct procedure was adopted to estimate the contribution of the suspended particles in the enhancement of gas absorption. Theoretical enhancement factors thus obtained compared well with the experimental data. The extra enhancement observed for the SO₂–Mg(OH)₂ system could be explained from the reaction between SO₂ and the dissolved [SO₃]²⁻.     

Hydrodynamics of the flow transition from a bubble column to an airlift-loop reactor

The hydrodynamics of an airlift-loop reactor (ALR) and a bubble column (BC) were studied in the same reactor unit. When the liquid circulation in the ALR was impeded gradually in order to obtain a BC mode of operation, there was a transition flow regime inbetween that of the ALR-type flow and the BC-type flow. In the BC the heterogeneous flow was represented by an instationary circulatory flow pattern and characterized by a liquid circulation velocity. The liquid flow in the ALR was represented by a drift-flux model. In the transition flow regime, hydrodynamic calculations based on the plug-flow behavior of an ALR appeared to be valid up to a certain defined value of the total gas-liquid flow rate. To distinguish between BC and ALR flow characteristics, a simple criterion is proposed, qualifying that the distinction between both flow patterns is determined by the superficial liquid velocity and the liquid circulation velocity. If the latter velocity exceeds the superficial liquid velocity a hydrodynamic transition will occur from a uniform ALR type of flow to a heterogeneous BC type of flow. The criterion coincides with an empirical power law function in which the liquid velocity is given as a function of the gas velocity. The values of the power-law coefficients depended on the characteristics of the two-phase flow. The change in value cohered with the onset of a change in the flow pattern.     

Ni(OH)2 versus Ni/Al layered double hydroxides as matrices to immobilize glucose oxidase

Ni hydroxide and Ni/Al layered double hydroxide (LDH) were electrochemically deposited on Pt electrodes in the presence of glucose oxidase in the electrolytic solution, in order to verify if the performances of the two biosensors were dependent on the Ni content of the inorganic matrix used to entrap the enzyme. The comparative study was conducted by recording the current response due to the oxidation of H₂O₂, produced enzymatically after glucose additions, at +0.45 V versus SCE, pH 7.0 and T = 25 °C.A higher sensitivity and a narrower linearity range were observed for nickel hydroxide based biosensor (up to 5 mM against 15 mM exhibited when LDH was the immobilizing matrix). These results suggested that the amount of the enzyme entrapped on the electrode surface was higher when the matrix was Ni(OH)₂ and they were confirmed by EQCM measurements. On the contrary, the selectivity displayed by the two biosensors in the presence of interfering compounds, such as acetaminophen, citric, uric and ascorbic acids, was almost the same.     

Numerical simulations of the reactive mixing in a commercially operated stirred ethoxylation reactor

The computational fluid dynamics (CFD) technique was applied to describe the mixing and the chemical reactions in commercially operated stirred ethoxylation reactors. Two reactor sizes in the existing ethoxylation operations were studied in this work: a laboratory-scale autoclave with a single-Rushton turbine and an industrial-scale reactor with a dual-Rushton turbine. The ethoxylation reactor contents were described as an incompressible, turbulent single-phase liquid mixing regime with chemical species undergoing heat and mass transfer. Since the accurate experimental ethoxylation flow data could not be extracted from the industrial operations, the development of the CFD model for the ethoxylation process was undertaken in two stages. The first stage simulated a single-phase liquid agitation system based on the literature with experimental data on velocities, such as Wu and Patterson [1989. Laser-Doppler measurements of turbulent-flow parameters in a stirred mixer. Chemical Engineering Science 44, 2207–2221], for a Rushton stirred reactor of standard configuration. Once validated, the numerical model was applied to compute the flow field in ethoxylation reactors. The second stage integrated the ethoxylation kinetics into the numerical model and simulated the ethoxylation process. In the simulation of the mean flow field, the qualitative features of the literature data were well reproduced. The computed results of both the ethylene oxide consumption and the temperature calculation compared very well with the measurements in the laboratory-autoclave operations. Reasonably good agreement was also reached between the simulated and experimental data on the time-dependent changes of ethylene oxide mass fraction in the bulk liquid in the industrial ethoxylation operations. These demonstrate that the CFD process model was capable of predicting the reaction behaviour and would be useful for exploration of any opportunity for increasing the ethoxylation capacity in the industrial operations.     

Mass transfer of reactive crystallization in synthesizing calcite nanocrystal

An experimental study on the mass transfer and reactive crystallization of calcite nanocrystal was carried out in a Na₅P₃O₁₀-Ca(OH)₂-CO₂-H₂O multiphase system. According to the two-film theory and the two-steps crystal growth model, the kinetic characteristics in the system were investigated by the rate-comparison of the calcium hydroxyl dissolution, carbon dioxide absorption and calcium carbonate precipitation. The result indicated that the transfer resistance for the carbon dioxide absorption was negligible during the reactive crystallization, the rate-controlling step would shift from the crystallization of calcite to the dissolution of calcium hydroxyl at a turning time θ_c. When reaction time was less than θ_c, the calcite crystallization could be the rate-controlling step; while reaction time was larger than θ_c, the calcium hydroxyl dissolution became the rate-controlling step. The analysis of the relationship of Damköhler number Da with surface integration effective factor η showed the crystallization kinetics would be affected by sodium tripolyphosphate. When , the calcite crystal growth could be controlled by the growth unit transport from liquid bulk to the crystal boundary. With an increasing sodium tripolyphosphate concentration, the rate-controlling step could be shifted from the bulk diffusion to the surface-reaction of growth units.     

An experimental study of oscillatory states in a stirred reactor

Instabilities of the type which lead to sustained oscillations (limit cycles) were studied experimentally in a nonadiabatic, well-stirred, continuous-flow reactor. The study included: (1) the stabilization of unstable states by means of conventional feedback control, (2) the construction of phase-plane diagrams showing experimental limit cycles and other time-dependent behavior, and (3) comparisons of experimental results with theoretical predictions.The exothermic liquid-phase reaction between sodium thiosulfate and hydrogen peroxide was employed in all experiments. An empirical reaction rate expression for use in the describing equations was obtained from batch reactor experiments.Experiments were carried out with two reactors which differed only in wall thickness. The mass of the reactor with the thicker wall was sufficiently large to cause all oscillations to be damped, but for the other reactor, the mass of the wall did not seem to affect the reactor dynamics appreciably. The agreement between theoretical predictions and experimental observations was good, though there were some noticeable quantitative discrepancies in the time-dependent state.     

Modeling an electrochemical process to remove Cr(VI) from rinse‐water in a stirred reactor

Experimental studies were developed in a batch reactor (16 dm³), to obtain the kinetic model of Cr(VI) removal by means of an electrochemical process. An overall kinetic model was obtained and experimentally validated in a continuous stirred electrochemical reactor (16 dm³) with synthetic and industrial wastewater. To develop the mathematical model of the continuous reactor in relation to the Cr(VI) and Fe(II) concentration in the solution, a classical mass balance procedure was performed. The Cr(VI) concentration in the electrochemically‐treated waters was less than 0.5 mg dm^?3. In the electrochemical process the Cr(VI) reduction is caused by the Fe(II) released from the anode due to the electric current applied, by the Fe(II) released for the dissolution (corrosion) of the electrodes due to the acidic media, and by reduction at the cathode. During the process, reduction from Fe(III) to Fe(II) occurs. All of these different reactions cause a diminution in the quantity of sludge generated. Finally, it was found that due to the slow rate of reduction of Cr(VI) during the first part of the process it is necessary to develop a method of control to apply the process in a continuous industrial system. © 2003 Society of Chemical Industry