Chronoamperometry at channel electrodes: analytical theory of transient behaviour at double electrodes

An analytical theory is presented which permits the calculation of transient effects at widely-separated double channel electrodes. In particular the current response of a downstream (detector) electrode to a potential leap at an upstream (generator) electrode is established and theoretical predictions are found to be in excellent agreement with experiments carried out using the oxidation ofN,N,N,N-tetramethyl-phenylenediamine in aqueous solution at a platinum double channel electrode.     

Visual observation of bubbles at horizontal electrodes and resistance measurements on vertical electrodes

A comparison was made of the bubbles formed on a horizontal bottom-facing electrode in a physical analogue model with those formed electrolytically. Bubbles formed in a physical analogue model by forcing air through a porous plate are larger, with wetted clear areas between bubbles. In contrast, electrolytically generated gas bubbles are smaller and the electrode surface is covered with a foamy layer of tiny bubbles. To measure the bubble resistance on horizontal electrodes, a method was developed for vertical electrodes so that the measurements may be validated by comparison with published data. Voltage fluctuations were measured and analysed using fast Fourier transform (FFT). The magnitude of the bubble impedance was obtained at a superimposed a.c. frequency f0. The phase angle caused by the effects of the double layer capacitance and the faradaic impedance on bubble resistance were determined. The effects of the faradaic impedance and the double layer capacitance were shown to be negligibly small under experimental conditions.     

Double-channel electrodes: Homogeneous kinetics and collection efficiency measurements

The theory of collection-efficiency measurements (under steady-state conditions) at double-channel electrodes has been extended to include the effects of homogeneous kinetics. In particular first- and second-order decompositions of the species electrogenerated at the upstream electrode have been examined. These problems have been treated numerically using the backwards implicit finite difference method. This theory is readily generalized to allow for more complicated homogeneous chemical reactions.     

Electrochemical deposition of fine Pt particles on n-Si electrodes for efficient photoelectrochemical solar cells

Fine platinum (Pt) particles were deposited electrochemically on n-type silicon (n-Si) electrodes from an aqueous hexachloroplatinic acid(IV) solution by the single potential step (SPS) and double potential step (DPS) methods. The distribution density of the Pt particles on n-Si was 10⁸ cm⁻² for the SPS method, whereas it increased from 10⁹ to 10¹⁰ cm⁻² by a shift of the pulse potential at the initial step of the DPS method from −1.0 to −4.0 V versus SCE and remained nearly constant at more negative potentials. The size of the Pt particles enlarged with the charge density passing across the electrode surface at a potential of −0.70 V versus SCE, which was applied throughout for the SPS method and at the second step for the DPS method. Photoelectrochemical (PEC) solar cells equipped with Pt-electrodeposited n-Si electrodes generated open-circuit photovoltages (V_OC) of 0.51–0.61 V, much higher than those for n-Si electrodes coated with continuous Pt layers (ca. 0.2–0.3 V). Solar cell characteristics changed with the pulsed potential and charge density passing across the electrode surface which changed the size and distribution density of the Pt particles. The characteristics were explained well by our previous theory on metal-dot coated n-Si electrodes.     

Investigation of Hydrophobic porous electrodes. I. Differential capacitance by a low frequency a.c. impedance technique

A simple a.c. technique has been developed for measuring the double layer capacitances of porous electrodes. A small alternating potential (±15 mV at 1 Hz) is applied potentiostatically to the test electrode and the phase and amplitude of the alternating current are monitored on an oscilloscope by the method of Lissajous figures. The value of the double layer capacitance for carbon and gold, together with the potential dependence for the gold capacitance,agree with published data for smooth electrodes. The technique can follow changes in the interfacial surface area between a porous electrode and the electrolyte as well as providing information about surface processes on finely divided materials.     

Electrochemical performance of polymer-derived SiOC and SiTiOC ceramic electrodes for artificial cardiac pacemaker applications

In an implantable electrode, such as a pacemaker electrode, fibrotic tissue formation due to a foreign body reaction is an important challenge affecting the efficiency to transmit the electrical signal of the device. The chemical inertness, biocompatibility, and electrical conductivity of polymer-derived ceramics (PDCs) are promising features in terms of overcoming this challenge. Here, the electrochemical behavior of polymer-derived silicon oxycarbide (SiOC) and titanium-doped SiOC (SiTiOC) ceramic electrodes for use as pacemaker electrodes is investigated by measuring impedance spectroscopy and cyclic voltammetry. In addition, typical stimulation electrodes such as iridium oxide, titanium nitride, platinum, and glassy carbon were prepared and loaded simultaneously into a custom-made electrochemical testing platform for comparison with SiOC and SiTiOC electrodes under identical conditions. The SiOC and SiTiOC electrodes shows a wide electrochemical stability window in the range of ?0.9 to 1.2 V with a double layer capacitance as the charge injection mechanism at the electrode/phosphate-buffered saline interface. Also, analyzing the voltage transient shows that the maximum charge injection of the SiTiOC electrode was about 28 μC/cm². The results of the electrochemical evaluation and comparison of SiOC and SiTiOC stimulating electrodes will be helpful to understand fundamental characteristics for the potential of this material as candidate for next-generation pacemaker electrodes.     

Removal of sulfuric acid aerosol in a wet electrostatic precipitator with single terylene or polypropylene collection electrodes

Wet electrostatic precipitators (ESPs) are good options for effective control of sulfuric acid aerosol emission. However, various problems caused by materials and non-uniform distribution of water film limited the applicability of typical wet ESPs. Research on ESP technology has tried to find more suitable and anti-corrosive methods to solve these imperfections. This research was inspired by the requirement to replace rigid collection electrode by single terylene or polypropylene fabrics. A patented system was designed, and the capillary difference between terylene and polypropylene fabrics was illustrated. Contrastive V–I curves of different collection electrodes were investigated under same conditions. The effects of several important parameters on the removal of sulfuric acid aerosol were analyzed. The results demonstrated that the variations of absorbed mass were significantly influenced by physical properties of the liquids and the structure of fabrics. The behavior of the new ESP was consistent with the typical ESP using a thimbleful of water penetrating terylene or polypropylene collection electrode via capillary flow. The collection efficiencies by terylene and polypropylene fabrics were higher than those by fiberglass reinforced plastics (FRP) under certain conditions. The collection efficiency had linear relationship with specific surface area (SCA) and mass concentration. The collection efficiency increased with increasing electric field strength, average diameter of particles and with decreasing gas temperature. As long as there was any water on the collector surface, any particle would exhibit similar collection efficiencies, whether of high resistivity or not. Experimental and theoretical investigations indicated that single terylene or polypropylene collection electrode had significant advancement which could improve wet ESP applications, such as superior performance and continuous operation ability compared with typical materials.     

采用垂直电场电泳分离脱盐技术模拟海水淡化的探索

由于受环境污染的影响,淡水资源的供给问题日趋严峻,供给方式的新技术探索是有效解决问题的重要途径,尤其是海水淡化的相关技术。利用实验室自制的垂直电场电泳装置,研究模拟海水的脱盐效果(以氯离子为研究对象)。考察了氯离子初始浓度、停留时间和电压3个因素分别对脱盐率、能量效率(单位电功能量的正极区迁移的氯离子质量)和分布比率的影响。出水分为4个区域,正极区、负极区、中间区和两极邻近区,其中中间区代表模拟海水淡化的目标收集区。结果表明,随着入水口处的氯离子初始浓度的增加,电泳装置出水口的中间区的脱盐率降低,能量效率逐渐升高,中间区、负极区和两极邻近区的分布比率增大,而正极区的分布比率减小。随着停留时间的增加,中间区脱盐率明显升高,高达69.5%,能量效率逐渐降低,中间区和负极区的分布比率减小,而正极区和两极邻近区的分布比率增加。随着电压升高,中间区的脱盐率逐渐升高,最高达13.9%,能量效率逐渐降低,正极区的分布比率逐渐增大,而负极区和两极邻近区的分布比率逐渐减小,中间区分布比率呈先上升后降低趋势。     

Surface activation of manganese oxide electrode for oxygen evolution from seawater

Utilizing the fact that the equilibrium potential of oxygen evolution is lower than that of chlorine evolution, oxygen evolution in seawater electrolysis was enhanced by decreasing the polarization potential under galvanostatic conditions through increasing the effective surface area of manganese oxide electrodes. Electrodes were prepared by a thermal decomposition method. IrO2-coated titanium (IrO2/Ti electrode) was used as the substrate on which manganese oxide was coated (MnOX/IrO2/Ti electrode). Subsequently, oxide mixtures of manganese and zinc were coated (MnOX–ZnO/MnOX/IrO2/Ti electrode). The effective surface area of the MnOX–ZnO/MnOX/IrO2/Ti electrodes was increased by selective dissolution of zinc (leaching) into hot 6M KOH. The oxygen evolution efficiency of the MnOX/IrO2/Ti electrode was 68–70%. Leaching of zinc from the MnOX–ZnO/MnOX/IrO2/Ti electrodes with 25mol% or less zinc led to a significant increase in the oxygen evolution efficiency. The maximum efficiency attained was 86% after leaching of zinc from the MnOX–25mol%ZnO/MnOX/IrO2/Ti electrode. However, large amounts of zinc addition, such as 40mol% or more are detrimental because of a decrease in the oxygen evolution efficiency. This is due to the formation of a double oxide, ZnMnO3, which is hardly dissolved in hot 6M KOH.     

Modelling the 3D microstructure and performance of solid oxide fuel cell electrodes: Computational parameters

In this paper, the computational parameters for a 3D model for solid oxide fuel cell (SOFC) electrodes developed to link the microstructure of the electrode to its performance are investigated. The 3D microstructure model, which is based on Monte Carlo packing of spherical particles of different types, can be used to handle different particle sizes and generate a heterogeneous network of the composite materials. Once formed, the synthetic electrodes are discretized into voxels (small cubes) of equal sizes from which a range of microstructural properties can be calculated, including phase volume fraction, percolation and three-phase boundary (TPB) length. Transport phenomena and electrochemical reactions taking place within the electrode are modelled so that the performance of the synthetic electrode can be predicted. The degree of microstructure discretization required to obtain reliable microstructural analysis is found to be related to the particle sizes used for generating the structure; the particle diameter should be at least 20–40 times greater than the edge length of a voxel. The structure should also contain at least 25³ discrete volumes which are called volume-of-fluid (VOF) units for the purpose of transport and electrochemical modelling. To adequately represent the electrode microstructure, the characterized volume of the electrode should be equivalent to a cube having a minimum length of 7.5 times the particle diameter. Using the modelling approach, the impacts of microstructural parameters on the electrochemical performance of the electrodes are illustrated on synthetic electrodes.     

Design and development of a self-contained personal electrostatic bioaerosol sampler (PEBS) with a wire-to-wire charger

Here, we present a concept of a personal electrostatic bioaerosol sampler (PEBS), which is an open channel collector consisting of a novel wire-to-wire particle charger and a collection section housing a double-sided and removable metal collection plate and two quarter-cylinder ground electrodes. The charger consists of a tungsten wire (25.4 mm long and 0.076 mm in diameter) connected to high voltage and positioned in the center of the charging section (a cylinder 50.8 mm long and 25.4 mm in diameter); a ring of stainless steel wire 0.381 mm in diameter surrounds the hot electrode at its midpoint and is grounded. The newly designed wire-to-wire charger produces lower ozone concentrations compared to traditional wire-to-plate or wire-to-cylinder charger designs. The particles captured on the collection plate are easily eluted using water or other fluids. The sampler was iteratively optimized for optimum charging and collection voltages, and collection electrode geometry. When tested with polystyrene latex particles ranging from 0.026 µm to 3.1 µm in diameter and 10 L/min collection flow rate, the sampler's collection efficiency was approximately 70%–80% at charging and collection voltages of +5.5 kV and ?7 kV, respectively. The PEBS showed this collection efficiency at sampling times ranging from 10 min to 4 h. Preliminary tests with Bacillus atrophaeus bacterial cells and fungal spores of Penicillium chrysogenum showed similar collection efficiency. The use of a unique wire-to-wire charger resulted in ozone production below 10 ppb. Due to low ozone emissions, this sampler will allow maintaining desirable physiological characteristics of the collected bioaerosols, leading to a more accurate sample analysis.

© 2017 American Association for Aerosol Research     

二茂铁的电合成

以双环戊二烯为原料,铁板和镍板分别为阳极和阴极,饱和甘汞电极为参比电极,无水乙醇作溶剂,溴化钠作导电盐,在无水无氧的条件下,利用恒电流电解合成法制备了二茂铁。首先,将双环戊二烯解聚为环戊二烯,通过气相色谱测得环戊二烯纯度达91.9%。其次,考察反应阳极的极化曲线,确定最佳电流密度为7.73 mA/cm2。再次,通过紫外光谱的吸收峰与时间的变化关系,确定最佳反应时间为4~8 h。最后,在最佳实验条件下电解合成的二茂铁,产率达到50.33%,电流效率51.9%。     

电絮凝法去除新农村微污染水体中磷的研究

文章采用光伏电池为电源,采用电絮凝工艺来治理新农村微污染水体中的磷,并从电解时间、电极材料、电极板间距和起始pH等影响因素进行了研究。研究结果表明:电解时间越长,总磷的去除率越高,45 min时,达95%以上;电导率在5 min内,有一个快速升高过程,此后逐渐下降;铝板电极和铁板电极总磷的去除速率和去除效率均比不锈钢板电极高,铝极板为最佳的电极材料;最佳间距为25 mm,此时总磷的去除效率和去除速度较高;最适宜的pH范围为4～5.5该工艺可行。     

The rate of gas evolution of electrodes—I. An estimate of the efficiency of gas evolution from the supersaturation of electrolyte adjacent to a gas-evolving electrode

The rate of gas evolution immediately at the electrode has a great effect on heat and mass transfer (of any substance) at gas-evolving electrodes. The question of how much of the gas generated in dissolved form is transformed into the gaseous phase of bubbles adhering to the electrode is studied on the basis of calculations of mass transfer of dissolved gas. Contrary to the established view of the matter it is found that only a fraction of the dissolved gas is transformed into bubbles at the electrode. This fraction, expressed as the efficiency of gas evolution, increases as the current density increases but is far smaller than unity in usual industrial current density values and remains different from unity in the whole range of nucleate gas evolution.     

Diffusion model for charge transfer from a photosynthetic reaction center to an electrode in a photovoltaic device

In spite of a high quantum efficiency in the bacterial photosynthetic reaction center (RC) the overall efficiency in a RC-based photovoltaic device is very poor partly because of an inefficient collection of charges by electrodes. To explain charge transport between the RC and an electrode a diffusion model is proposed. The numerical solution of the diffusion process describes the measured photocurrent well. An approximation of the initial condition is also made to obtain analytical expressions for the photocurrent. The model suggests that the slow transient response of the photocurrent is due to the diffusion in a biological photovoltaic device.     

Curvature effects on electric-double-layer capacitance

Understanding the microscopic structure and thermodynamic properties of electrode/electrolyte interfaces is central to the rational design of electric-double-layer capacitors (EDLCs). Whereas practical applications often entail electrodes with complicated pore structures, theoretical studies are mostly restricted to EDLCs of simple geometry such as planar or slit pores ignoring the curvature effects of the electrode surface. Significant gaps exist regarding the EDLC performance and the interfacial structure. Herein the classical density functional theory (CDFT) is used to study the capacitance and interfacial behavior of spherical electric double layers within a coarse-grained model. The capacitive performance is associated with electrode curvature, surface potential, and electrolyte concentration and can be correlated with a regression-tree (RT) model. The combination of CDFT with machine-learning methods provides a promising quantitative framework useful for the computational screening of porous electrodes and novel electrolytes.     

A comparison of the aging of electrochemical double layer capacitors with acetonitrile and propylene carbonate-based electrolytes at elevated voltages

The aging behavior of electrochemical double layer capacitors (EDLCs) based on activated carbon electrodes bound with poly(tetrafluoroethylene) (PTFE) was tested in electrolyte solutions based on acetonitrile (AN) and propylene carbonate (PC) at a constant elevated cell voltage of 3.5 V. The aging was quantified in terms of capacitance loss and resistance increase for the full cell and the individual electrodes. It is shown that the enhanced aging rate of symmetric EDLCs in either solvent at elevated voltages is dominated by the aging of a single electrode, and that the polarity of this limiting electrode depends directly on the solvent. In AN, the positive electrode ages much more rapidly than the negative, while in PC the negative electrode exhibits faster aging than the positive. After aging, the electrodes were investigated by nitrogen adsorption and X-ray photoelectron spectroscopy, revealing significant modifications of the electrode surface and providing clear evidence for the deposition of electrolyte degradation products on the electrodes.     

Enhanced electron collection efficiency of nanostructured dye‐sensitized solar cells by incorporating TiO2 cubes

Herein, enhancement of dye‐sensitized solar cell (DSC) performance is reported by combining the merits of the dye loading of TiO₂ nanoparticles and light scattering, straight carrier transport path, and efficient electron collection efficiency of TiO₂ cubes. We fabricate DSC devices with various arrangement styles and compositions of the electrodes in the forms of monolayer and double layer films. For this purpose, the solvothermal synthesized TiO₂ cubic particles (100‐600 nm) are employed as the scattering layer, whereas TiO₂ nanoparticles (15‐30 nm) synthesized via a combination of solvothermal and sol‐gel routes are used as the active layer of devices. We improve the photovoltaic characteristics of DSCs by two mechanisms. First, the light harvesting of DSC devices made of nanoparticles is improved by controlling the thickness of monolayer films, reaching the highest efficiency of 7.0%. Second, the light scattering and electron collection efficiency are enhanced by controlling the composition of double layer films composed of mixtures of TiO₂ nanoparticles and cubes, obtaining the maximum efficiency of 8.21%. The enhancements are attributed to balance between charge transfer resistance and charge recombination of photo‐generated electrons as well as dye loading and light scattering.     

几种多孔电极材料镓电沉积性能的研究

在工业上,稀散金属镓通常是从碱性溶液中电解提取得到的。在镓电解过程中,由于析氢副反应和传质速率低的原因导致镓电沉积的电流效率很低。本工作采用三维多孔电极电沉积镓,利用三维多孔电极发达的表面积促进镓电沉积过程,研究了不同电极材料(泡沫金属和多孔碳)的析氢特性,结合不同电解温度和电流密度下各材料的镓电沉积行为,揭示三维多孔电极上镓电沉积的特性规律。结果表明,泡沫铜和石墨毡(GF)具有较低的析氢活性,但两种电极的镓电沉积性能差别很大。其中泡沫铜表现出最佳的镓电沉积性能,在温度为40℃、电流密度为0.1 A/cm²条件下镓电沉积的电流效率(QE)达到22.5%,远高于铜片电极(10.7%);而相同条件下,GF电极的QE值仅为9.6%,低于铜片,这与电极表面的疏水性有关。具有较高析氢活性的泡沫铁、泡沫镍和网状玻璃碳(RVC)电极的镓电沉积过程受电解温度和电流密度的影响较大。在高电流密度下,泡沫铁电极表现出仅次于泡沫铜的QE值,在低电流密度下难以发生镓的电沉积;泡沫镍和RVC电极仅在低于镓熔点(20℃)的条件下发生镓的电沉积,在高于镓熔点(40℃)的条件下,由于电沉积的液态镓...     

Filtration Characteristics of a Miniature Electrostatic Precipitator

This study investigates the filtration characteristics of a miniature dual saw-like electrodes electrostatic precipitator (ESP). Parameters such as particle size, rate of airflow through the ESP, voltage of charge electrode, and discharge polarity were considered to study their influence on aerosol penetration through the ESP. Polydisperse and monodisperse particles with sizes ranging from 30 nm to 10 w m were used as the challenge aerosols. Experimental results indicated that the aerosol penetration through the ESP decreased (from 96% to 15% for 0.3 w m) as the voltage of the discharge electrode increased (from + 4 kV to +8 kV) at a flow rate of 30 L/min. At a fixed electrode voltage (+8 kV), aerosol penetration increased from 15% to 69% for 0.3 w m particles as the flow rate increased from 30 to 120 L/min. The most penetrating particle size was in the range of 0.25 w m to 0.5 w m depending on the discharge voltage and the flow rate. In general, the most penetrating particle size of the ESP decreased with decreasing discharge voltage or with increasing flow rate. At the same voltage level but opposite polarity, the aerosol penetration through the ESP with negative corona was lower than that with positive corona. The difference in aerosol penetration was a factor of about 2 between the negative and positive coronas for 0.3 w m particles, and this difference was found to be independent of discharge voltage. Regarding energy conservation, use of a negative-polarity ESP was more economical if the same efficiency was required. However, the ozone generated by the ESP with negative polarity was about five times greater than that generated with positive polarity. Therefore when using an ESP as an indoor air cleaner, the search for an optimum balance between ozone production and aerosol collection efficiency should be considered.