Feasibility study of electrochemical hydrodehalogenation of 2,4-dibromophenol in a paraffin oil

The feasibility of electrochemical hydrodehalogenation (HDH) of 2,4-dibromophenol (DBP) in paraffin oil has been evaluated for short or long operation periods of up to 170 h. HDH has been performed successfully using a solid polymer electrolyte reactor in a batch recycle mode with a dilute H₂SO₄ aqueous solution as the anode feed and source of protons. The work reported in this paper expands the application of electrochemical HDH from aqueous systems to non-conductive media. The effect of the operating conditions, including current density, reactant concentration and temperature, is evaluated. The results are compared with those achieved in the aqueous solutions.     

Reactor modelling for electrochemical processes

This paper presents a relatively straightforward approach to the modelling of electrochemical reactors operated in batch or continuous modes. The models are based on ideal flow assumptions of either well-mixed or plug flow and incorporate reaction rate models based on electrochemical kinetics and mass transport at one electrode. General characteristics of the reactor models are described, particularly with regard to the need for good mass transport in metal recovery applications. An example is given on the use of the model in the recovery of a heavy metal (Cd²⁺) from an acidified solution containing Cd(II) and Fe(III) ions. The reaction rate model is based on experimental data.     

Chemical and electrochemical ageing of carbon materials used in supercapacitor electrodes

Electrochemical double layer capacitors-supercapacitors-are usually based on highly porous activated carbon electrodes. The chemical and electrochemical inertness of carbon assures a very long lifetime. However, on the timescale of months the capacitors slowly lose some capacitance, and the equivalent series resistance rises. This “ageing” is faster when temperature and operation voltage are increased. To elucidate ageing processes in the electrodes, we analyzed aged samples of activated carbon, and also of carbon black, which is used as conductive additive. The experimental methods were infrared, Raman, and photoelectron spectroscopy, and nitrogen porosimetry. The electrodes are not completely inert, and their ageing is due to chemical and electrochemical reactions at the carbon. Moreover, the ageing procedures are much stronger at the positive pole. We found that oxygen, hydrogen, nitrogen, and fluorine, which originate from trace water and from the electrolyte, can covalently attach to the electrodes and form various chemical groups (e.g. OH, COOH, CONH, and F).     

Effect of leakage currents on the primary current distribution in bipolar electrochemical reactors

The primary current distribution in a bipolar electrochemical reactor with outside inlet and outlet electrolyte manifolds was investigated by numerical solution of the Laplace equation and by experimental measurement in simulated cells made from conductive paper and segmented electrodes. The geometric parameters determining the distribution were the interelectrode gap, electrode length, transverse section and length of the electrolyte manifold. The effect of the number of electrodes in the bipolar stack was also analysed. Values obtained numerically have been compared with those obtained experimentally and a good agreement is observed between them. These results are useful for estimating the performance of the bipolar stack.     

Influence of electrolytes of Li salts,EMIMBF4, and mixed phases on electrochemical and physical properties of Nafion membrane

Electrolyte‐soaked Nafion is commonly used as an ionic polymer in soft actuators. Here, a multitechnique investigation was applied to correlate the electrochemical behavior of Nafion membranes with their microstructures and nanostructures as a function of electrolyte type. The influence of electrolytes of Li salts with different counteranions on the Nafion membranes was investigated in terms of hydration level, structure (using X‐ray diffraction and small angle X‐ray scattering), stress–strain characteristics, and electrochemical behavior (by cyclic voltammetery and electrochemical impedance spectroscopy). The effects of using ionic liquid (IL), as the electrolyte, addition of different supporting solvent and the addition of Li⁺ ions to water‐free IL‐soaked membranes on the structural and electrochemical properties of Nafion were examined. The nano‐ and microstructure of the Nafion changed considerably as a function of the identity of the electrolyte solution. The electrochemical behavior of the IL‐soaked samples was compared with that of the water‐soaked Li⁺‐exchanged Nafion. It was seen that the ionic conductivity of the Nafion membranes was reduced significantly when water was replaced by pure IL. Using the supporting solvents increased the conductivity of IL‐soaked Nafion membranes dramatically. The presence of a small amount of Li⁺ ions together with the IL ions caused a significant decrease in charge transfer resistance and increases in double layer capacitance and in ionic conductivity over that of the water‐free sample and also over water‐soaked Li⁺‐exchanged Nafion. These findings can be useful to improve the knowledge on Nafion's microstructure and also to improve the electromechanical behavior of Nafion‐based ionic polymer–metal composites actuators. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45239.     

Copper-selective electrochemical filling of macropore arrays for through-silicon via applications

In this article, the physico-chemical and electrochemical conditions of through-silicon via formation were studied. First, macropore arrays were etched through a low doped n-type silicon wafer by anodization under illumination into a hydrofluoric acid-based electrolyte. After electrochemical etching, ‘almost’ through-silicon macropores were locally opened by a backside photolithographic process followed by anisotropic etching. The 450 × 450-μm² opened areas were then selectively filled with copper by a potentiostatic electrochemical deposition. Using this process, high density conductive via (4.5 × 10⁵ cm⁻²) was carried out. The conductive paths were then electrically characterized, and a resistance equal to 32 mΩ/copper-filled macropore was determined.     

SOFC内部重整反应与电化学反应耦合机理

以经过预重整反应的混合气为原料的固体氧化物燃料电池（SOFC）内部,甲烷蒸气重整反应与电化学反应同时发生在阳极多孔介质中,二者受到不同的操作与设计参数的影响,对电池总体性能起着决定性作用。编制了三维数值模拟程序,对由多孔阳极层、气体流动管道、固体支撑平板构成的单个复合管道进行了研究。结果显示：重整反应主要发生在多孔材料靠近流动管道的薄层内,只有靠近管道入口处才能在较深处进行;电化学反应发生在多孔层与电解质的交界面处;重整反应生成的H2、CO扩散到多孔材料底部参加电化学反应;电化学反应生成的热量供重整反应使用。说明研究范围内,SOFC阳极复合通道具有较好的传热、传质性能,化学/电化学反应存在较好的耦合关系。     

Vertically aligned ZnO nanorod core-polypyrrole conducting polymer sheath and nanotube arrays for electrochemical supercapacitor energy storage

Nanocomposite electrodes having three-dimensional (3-D) nanoscale architecture comprising of vertically aligned ZnO nanorod array core-polypyrrole (PPy) conducting polymer sheath and the vertical PPy nanotube arrays have been investigated for supercapacitor energy storage. The electrodes in the ZnO nanorod core-PPy sheath structure are formed by preferential nucleation and deposition of PPy layer over hydrothermally synthesized vertical ZnO nanorod array by controlled pulsed current electropolymerization of pyrrole monomer under surfactant action. The vertical PPy nanotube arrays of different tube diameter are created by selective etching of the ZnO nanorod core in ammonia solution for different periods. Cyclic voltammetry studies show high areal-specific capacitance approximately 240 mF.cm^-2 for open pore and approximately 180 mF.cm^-2 for narrow 30-to-36-nm diameter PPy nanotube arrays attributed to intensive faradic processes arising from enhanced access of electrolyte ions through nanotube interior and exterior. Impedance spectroscopy studies show that capacitive response extends over larger frequency domain in electrodes with PPy nanotube structure. Simulation of Nyquist plots by electrical equivalent circuit modeling establishes that 3-D nanostructure is better represented by constant phase element which accounts for the inhomogeneous electrochemical redox processes. Charge-discharge studies at different current densities establish that kinetics of the redox process in PPy nanotube electrode is due to the limitation on electron transport rather than the diffusive process of electrolyte ions. The PPy nanotube electrodes show deep discharge capability with high coulomb efficiency and long-term charge-discharge cyclic studies show nondegrading performance of the specific areal capacitance tested for 5,000 cycles.     

Effect of microstructure on the electrochemical behavior of Pt/YSZ electrodes

Two types of O₂,Pt/YSZ electrode preparation (Pt/YSZ cermet and sputtered platinum film) have been characterized by SEM and by cyclic voltammetry and chronoamperometry at 450 °C in 20 kPa oxygen. Cyclic voltammetry on the cermet and on the as-sputtered non-porous film electrode evidenced the characteristics of the PtO _x /Pt couple. The corresponding redox reaction occurs at the metal/electrolyte interface and it manifests itself by an anodic wave and one of more cathodic peaks in the voltammogram. Heat treatment of the sputtered electrode at 700 °C in oxygen atmosphere resulted in a porous structure by coalescence of the film. Cyclic voltammetry of the porous film electrode featured the characteristics of the O₂/O²⁻ couple, i.e. the redox reaction of gaseous oxygen occurring at the tpb. Chronoamperometry at anodic potentials showed similar features for both electrode preparations: an initial inhibition, a current peak and a slow activation, the latter being related to the phenomenon of electrochemical promotion of catalysis.     

Using electrochemical impedance spectroscopy to compensate for errors when measuring polarisation curves during three-electrode measurements of solid oxide fuel cell electrodes

The use of three-electrode techniques involving an independent reference electrode is invaluable in determining the overpotential losses at solid oxide fuel cell (SOFC) electrodes. However, there are numerous barriers to achieve the accurate measurement of such overpotentials in an SOFC. Furthermore electrochemical impedance spectroscopy (EIS) is commonly used to analyse the processes occurring on SOFC electrodes, and there has been considerable work in establishing viable three-electrode techniques for EIS experiments under open circuit conditions. However, the three-electrode techniques currently developed for EIS experiments are not well suited for conditions of high load, or changing gas compositions; either intentionally or under diffusion limiting conditions. This paper reports a solution for commonly used pellet cells, which mitigates these problems. The paper presents a method using EIS to correct for errors when measuring the working electrode overpotential during polarisation arising from a shift in the electrolyte current distribution from the primary to the secondary current distribution under load. This technique enables meaningful overpotentials to be calculated using experimentally simple cell geometries under conditions where they cannot normally be accurately measured.     

Uses of scanning electrochemical microscopy for the characterization of thin inhibitor films on reactive metals: The protection of copper surfaces by benzotriazole

Scanning electrochemical microscopy (SECM) was used to study the film formation of benzotriazole towards corrosion of copper. SECM was operated in the feedback mode by using ferrocene-methanol as redox mediator, and the sample was left unbiased at all times to freely attain its open circuit potential in the test environment. Following exposure to aggressive electrolytes the anticorrosion abilities of the layers were characterized by image analysis and by an electrochemical method derived from the experimental approach curves. Changes in the shape of the approach curves were clearly observed during the inhibitor film formation process. They showed the transition from an active conducting behaviour towards ferrocinium reoxidation typical of unprotected copper, to a surface exhibiting insulating characteristics when the metal was covered by a surface film containing the inhibitor. This supports that SECM is a practical technique in the investigation of corrosion inhibitor performance. However, a consistent tendency for the characterization of inhibitor film formation using SECM measurements in the positive feedback mode for the copper-benzotriazole system was only found if the experiments were conducted when the inhibitor molecule was not present in the test solution. That is, inhibitor molecules were found to interact not only with the copper surface during the monitoring process, but with the SECM tip as well, this effect being significantly enhanced when chloride ions were present in the electrolyte. Finally, a procedure to image the chemical activity of copper surfaces partially covered with the inhibitor film with SECM is proposed.     

The influence of electrolyte purity on electrochemical measurements using platinum electrodes

The influence of electrolyte purity on electrochemical processes at low-area platinum electrodes has been studied by a fast potential-step method and by cyclic voltammetry. Pre-purification of the electrolyte had no significant influence on the metal surface area available for H adsorption determined immediately after an electrochemical cleaning step. Maintaining the electrode potential within the ‘double-layer’ region of platinum (at 0.5 V vs rhe) for relatively long periods of time (1–30 min) results in the progressive suppression of H adsorption, owing to the adsorption of impurities blocking active Pt sites. All samples of electrolyte, irrespective of the degree of pre-purification, exhibited this effect. In the determination of current-time transients during the first few hundred milliseconds of the methanol electro-oxidation reaction, impurities in the untreated electrolyte contribute to the measured anodic currents at Pt electrodes working in the potential range of 0.4–0.6 V. The anomalous effects observed within this potential range can be largely eliminated by pre-electrolysis of the H₂SO₄ electrolyte for several days using Pt wire gauze electrodes at 2.1 V.     

Inherent emf relaxation of electrochemical cells with nanocrystalline Ag electrodes

The open circuit voltage of the electrochemical cell Ag (nano)|solid silver electrolyte|Ag (macro) is found to be inherently unstable. Even under conditions which support the morphological stability of the arrangement of nanocrystalline silver, the particles grow significantly as soon as they function as electrodes; i.e. when they are in contact with a silver electrolyte and connected electronically at the same time. The process is shown to be due to electrochemical Ostwald ripening with the interfacial transfer of Ag⁺ through the Ag/electrolyte interface being the rate limiting step. Its activation energy is 0.01 eV. The decay is in good agreement with modelling results.     

电化学增强催化的研究进展

综述了能够对固体催化剂活性可逆增强的电化学方法即催化活性的非法拉第电化学修饰。分别介绍了催化活性的非法拉第电化学修饰效应的概念、一般分析方法、催化活性的非法拉第电化学修饰效应的双电层作用机理以及基于不同固体离子电解质的电化学增强催化反应系统的结构、性能和研究现状。讨论了电化学增强催化的应用前景及当前存在的问题,期望对这种新型催化剂活性调控的方法加深认识和开展相关应用研究。     

Electrolysis in a closed electrochemical cell with a small inter-electrode distance. Metal dissolution/deposition in plain electrolytes

The present paper focuses on the specificity of electrolysis during metal dissolution/deposition in a closed electrochemical cell with a small inter-electrode distance. A mathematical model for the electrochemical process in such a cell has been developed. We give an analytical and a numerical solution to the system of mass transfer equations for such a cell, in binary solutions and solutions with supporting electrolyte. The dependence of metal deposition rate on the voltage applied to the cell and on the electrolysis time has been studied by numerical simulation. We also present the results of the experimental study of the rate of silver electrodeposition from an acid solution of AgClO₄ in a cell of size 1 mm × 1 mm. Metal deposition rate in a closed electrochemical cell with a small inter-electrode distance has been demonstrated to be at least three times higher than that at recessed electrodes. The results obtained may be used in the LIGA processes for accelerating the filling of photoresist cavities with metal.     

Selectively depositing Pt nanoparticles on pre-treated electrically conductive porous alumina and its electrochemical studies

To fabricate a composite modified with uniformly dispersed metallic particles, in this paper, electrical conductive porous alumina (CPA) was firstly pre-treated with mixed acids followed by deposition of Pt nanoparticles via reductive reaction. Crystal structure of uniformly deposited Pt nanoparticles was confirmed to face centered cubic (fcc). Based on characterization results, selective surface modification was achieved by surface pre-treatment, by which various functional groups were grafted onto three-dimensional conductive networks. The electrochemical behaviors of as-fabricated composites conducted in acidic electrolyte confirmed their improved activities, which merited from novel structure of designed electrode.     

Effects of charge redistribution on self-discharge of electrochemical capacitors

The effect of charge redistribution on the self-discharge profile of porous carbon (Spectracarb 2225) electrodes is examined. A model pore based on the de Levie transmission line circuit is used to show that self-discharge due purely to charge redistribution results in the same self-discharge profile as that expected for an activation-controlled self-discharge mechanism (the potential falls linearly with log t), thus the linear log time profile is not characteristic of an activation-controlled mechanism. The addition of a hold step reduces the amount of charge redistribution in porous carbon electrodes, although the hold time required to minimize the charge redistribution is much longer than expected, with electrodes which have undergone a 50 h hold time still evidencing charge redistribution effects. The time required for the charge redistribution through the porous electrode is also much greater than predicted, likely requiring tens of hours. This highlights the importance of the charge redistribution in self-discharge of systems using porous electrodes, such as electrochemical capacitors.     

Continuous electrochemical synthetic system using a multiphase electrolyte solution

A continuous electrochemical synthetic system has been developed using a cyclohexane-based multiphase electrolyte solution composed of lithium perchlorate and nitromethane. The upper cyclohexane phase functioned as both substrate supply and product assembly phases, whereas the electrochemical reactions took place in the lower electrolyte solution phase, achieving spatial separation of the electrolyte solution phase.     

Effects of porosity on the electrochemical oxidation performance of Ti4O7 electrode materials

Ti₄O₇ is a kind of conductive ceramic material with a high electrical conductivity and excellent electrochemical performance, rendering it a potential candidate for electrode applications. Here, for the first time, we report the successful preparation of Ti₄O₇ electrodes with different porosities by adding a pore-forming agent. The results showed that the as-prepared Ti₄O₇ electrodes contained both mesoporous and macroporous structures. In addition, with an increase in the porosity of the electrodes, the electrochemical oxidation degradation of high-concentration methyl orange (MO) solution first increased, until reaching a critical point, and then decreased. The Ti₄O₇ electrode with a porosity of 34.9% and an electrical conductivity of 336.1 S cm^-1 exhibited the highest electrochemical oxidation ability. The electrochemical oxidation rate constants for MO and chemical oxygen demand (COD) of the porous Ti₄O₇ electrode were 1.7 times those of the dense Ti₄O₇ electrode. Compared to commercial stainless steel, graphite, and Ti/RuO₂ electrodes, the Ti₄O₇ porous electrode showed superior electrochemical oxidation performance under the same experimental conditions. The result of this study provide new directions for the application of Ti₄O₇ electrode materials.     

多孔阳极氧化铝模板法合成纳米线阵列的研究及应用进展

综述了以多孔氧化铝为模板，采用电化学沉积技术合成金属、半导体、导电聚合物等纳米线材料的最新研究进展，阐述了多孔氧化铝模板在合成与组装纳米线材料方面的良好应用前景，以进一步拓展该领域的研究。