Polarization Curve of a Porous Hydrophobized Electrode for Electrosynthesis Involving a Side Electrochemical Reaction

A polarization curve, suggested for electrosynthesis in a porous hydrophobized electrode operating in an inner-kinetic mode at a current efficiency for the target product below 100%, depends on the balance between exchange currents and slopes of the side and target reactions and the difference between the equilibrium potential of the side reaction and the steady-state electrode potential. At different slopes of the side and the target reactions, the current efficiency depends on the polarization. Experimental and calculated data satisfactory agree.     

Polarization Dependence of a Hydrophobized Electrode for Electrosynthesis of a Soluble Product

An equation for a polarization curve of a hydrophobized electrode is proposed for electrosynthesis of a soluble electroactive product in an inner-kinetic mode. The equation contains the concentration of the target product (TP) in an explicit form. The shape of the curve depends on the biquadratic root of the TP concentration and the square root of the ratio between exchange currents of the side and target reactions.     

新型气体扩散电极体系高效产H2O2的研究

以自制新型石墨/聚四氟乙烯(PTFE)气体扩散电极在无隔膜体系中进行双氧水发生工艺的优化研究, 主要探讨了不同石墨和PTFE质量比、阴极电位、pH值和氧气流速对H2O2产率的影响. 结果表明, 以石墨和PTFE质量比为2:1的气体扩散电极为阴极, 在pH=3, Na2SO4浓度为0.1 mol•L−1, 氧气流速为0.4 L•min−1, 阴极电位为−0.55 V (vs SCE)时, 2 h后H2O2可以达到60 mg•L−1. 该新型体系有较高的H2O2产率和电流效率(可达60%以上), 且pH值适用范围较广, 可望应用于水中污染物的处理.     

高温质子交换膜燃料电池的复合催化层电极

高温质子交换膜燃料电池具有耐毒化,稳定性好的优势,是具有较强应用前景的一种能源转换装置。 本文制备了具有复合催化层结构的气体扩散电极,用于增强燃料电池阳极的催化性能。 在气体扩散电极中,将偏氟乙烯-六氟丙烯共聚物和聚苯基咪唑聚合物作为催化剂的粘结材料,调节了电极界面的浸润结构。 通过对电极表面形貌和润湿性的表征,发现该种结构的催化层孔隙率和粗糙度更高,双层结构的润湿性差别明显(接触角分别为149°和19°),这有利于形成稳定的三相反应界面。 测试结果表明,该种结构的催化层能够有效提高催化材料的利用效率,燃料电池对氢气燃料的峰值功率密度提高约22%。 与此同时,使用含一氧化碳质量浓度为10000和30000 mg/m³的氢气燃料,电池峰值功率密度能够分别保持82.1%和71.4%,证明该燃料电池对一氧化碳杂质保持了良好的耐毒性。     

锌空气电池中空气电极摆放方式的研究

从改变空气电极的摆放方式的角度研究了改善锌空气电池放电性能的方法.通过对比相同的空气电极在同样的锌空气电池系统中采用不同摆放方式后产生的不同的放电特性,分析了空气电极的摆放方式对电极性能的影响.提出采用立式的电极摆放方式,以改善电极和电池性能及效率.     

锡气体扩散电极上电化学还原二氧化碳制甲酸性能的稳定性

研究了Sn气体扩散电极(SGDE)上电化学还原CO₂制甲酸(ERCF)性能的稳定性。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能量色散谱(EDX)和活性表面积测试等技术手段 分别表征SGDE在电化学还原CO₂制甲酸过程前后的物相结构、表面形貌、元素组成和活性表面积。 采用生成甲酸的法拉第效率(f_HCOOH)评价SGDE上电化学还原CO₂制甲酸的性能。 结果显示,f_HCOOH随电解时间的延长急剧地降低,电解时间12 h的f_HCOOH((36.6±1.6)%)比电解时间0.5 h时的f_HCOOH((78.5±0.1)%)降低了53%。 SGDE在12 h电还原反应后,表面沉积了微量Fe,而且Sn含量(质量分数)减少了66%,活性表面积降低了41%。 进一步的研究发现,沉积的微量Fe对电化学还原CO₂制甲酸过程基本没有影响,Sn含量和活性表面积的降低可能是SGDE上电化学还原CO₂制甲酸性能降低的主要原因。     

Effect of the Electrode Potential on the Oxygen Reaction Rate in the Electrode System O2, Au/La0.88Sr0.12Ga0.82Mg0.18O2.85

The polarization dependences of a porous gold electrode in contact with a solid electrolyte of the composition La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 are studied at 600–800°C and oxygen pressures of 2 × 10⁻²-1 atm. It is shown that the rate of cathodic reduction of oxygen out of the gas phase depends on the preliminary treatment of the sample. The activation energy is equal to 110–135 kJ mol⁻¹ at a low polarization. After increasing the polarization, the activation energy for the cathodic reduction of oxygen equals 75–85 kJ mol⁻¹ and depends on the oxygen pressure as a power function with a power index of 1/4. The rate of the anodic evolution of oxygen is dependent neither on the preliminary treatment of the sample nor on the oxygen pressure in the gas phase and the polarization curve has a characteristic segment, which corresponds to a limiting overvoltage.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 954–962.Original Russian Text Copyright © 2005 by Shkerin, Sokolova, Beresnev.     

Location of Chemical Reaction of Indirect Electrochemical Synthesis in a Porous Hydrophobized Electrode

Location of chemical reaction of IES performed in a porous hydrophobized electrode is considered. Depending on the rate constant and order of the reaction, it can proceed in the electrode's porous space and in the electrolyte chamber.     

纳米碳管作为氧扩散电极催化层第二相碳载体的电极特性

A novel gas diffusion electrode using binary carbon supports (carbon nanotubes and active carbon) as the catalyst layer was prepared. The electrochemical properties for oxygen reduction reaction (ORR) in alkaline electrolyte were investigated by polarization curves and electrochemical impedance spectroscopy. The results show that the binary-support electrode exhibits higher electrocatalytic activity than the single-support electrode, and the best performance is obtained when the mass ratio of carbon nanotubes and activated carbon is 50 ∶50. The results from their electrode kinetic parameters indicate that the introduction of carbon nanotubes as a secondary support provides high accessible surface area, good electronic conductivity and fast ORR kinetics. The electrocatalytic activity of binary-support electrodes is obviously improved by the deposition of Pt nanoparticles on carbon nanotubes, even at very low Pt loading (45.7 μg/cm2). In addition, the EIS analysis results show that the process of ORR may be controlled by diffusion of oxygen in the thin film for binary-support electrodes with or without Pt catalyst.     

质子交换膜燃料电池梯度化膜电极

为实现质子交换膜燃料电池的高性能(高功率密度或大电流密度)、低成本(低铂载量)、长寿命发电,人们尝试在燃料电池的核心部件膜电极结构中引入梯度化设计的概念。梯度化膜电极包括膜电极中各组件的梯度化:气体扩散层的PTFE含量与孔隙率的梯度化,催化层的催化剂与Nafion用量的梯度化以及微孔层的疏水性与孔隙率的梯度化。梯度化膜电极中催化剂分布、孔隙率分布、亲/疏水性分布合理,具有良好的三相反应界面以及质子、电子、反应气体、水等多相物质高效传输通道,从而能满足在低铂载量、低加湿以及高电流密度条件下高性能稳定工作。本文整理了近几年来有关燃料电池梯度化膜电极研究的相关文献,梳理了梯度化膜电极研究发展脉络,归纳总结了各种梯度化膜电极的制备方法、性能以及构效关系,并展望了梯度化膜电极下一步研究方向,对高性能、低成本、长寿命的燃料电池开发具有指导意义。     

Mathematical model for the overlimiting state of an ion-exchange membrane system

A three-layered mathematical model is proposed for describing the overlimiting state in an ion-exchange membrane system. The model’s prominent feature is the allowance for the space-charge region; the water dissociation reaction, which is catalyzed by active ionogenic groups; and the coupled gravitational and electroosmotic convection, which leads to the emergence of dependence of the effective diffusion layer thickness on the electric current density. The model is used for calculating, on the basis of known initial current-voltage curves and dependences of effective transport numbers on the current density, such internal characteristics of the system as the diffusion layer thickness, distribution of concentration of ions, space charge, and electric-field strength at various current densities.     

Construction of a N-Acetyl-L-methionine Electrode and Determination of Acylase with an Ammonia Gas Sensor

Abstract

The N-acetyl-L-methionine electrode is based on a coupled enzymatic system consisting of acylase and L-amino acid oxidase with an ammonia gas sensor; conditions of imobilization are optimized. N-acetyl-L-methionine in the range 4×10^?5–2×10^?3M gives a linear potential vs. log(concentration) plot with a response time of 2–5 min over the range specified. This electrode combined with an L-methionine electrode, based only on L-amino acid oxidase and an ammonia gas sensor, can be used for the determination of both substrates in mixtures, thus extending the feasibility of the method. Acylase (0.1–2.00) is determined in aqueous solutions by adding N-acetyl-L-methionine to the sample, and measuring the ammonia evolved with the gas-sensing electrode.     

应用于锌-空气电池的新型碳载钴-聚噻吩复合催化剂

采用化学氧化聚合法合成了以碳为载体的钴-聚噻吩复合物(Co-PTh/C)作为气体扩散电极氧还原催化剂。 通过扫描电子显微镜-能量色散X射线能谱（SEM-EDX）、透射电子显微镜（TEM）等测试技术对催化剂进行表征。 结果表明,Co-PTh/C催化剂颗粒的粒径为10~30 nm,且分布均匀。 利用极化曲线、交流阻抗等电化学方法测试了其在碱性介质中(6 mol/L KOH)对氧还原的催化性能。 此催化剂在碱性介质中空气气氛条件下,电极电位在-0.20 V(vs.Hg/HgO)时电流密度达到0.152 A/cm2,催化性能高于质量分数5%Pt/C,显示出优越的氧还原电催化性能。 采取催化层/集流体/扩散层的排布方式,以纯锌为负极,6 mol/L的KOH为电解液,将气体扩散电极与锌负极组装成锌-空气电池。 电池以0.075 A/cm2进行恒流放电,放电电压为1.1 V且性能稳定。     

MH电极中氢扩散系数的测定及其应用

利用恒流放电法测定了金属氢化物(MH)电极中氢原子扩散系数的平均值. 通过恒电位法测定了MH电极中氢原子的扩散系数与其荷电态(SOC)的关系. 根据MH电极模型可知, 增大氢原子扩散系数或减小储氢合金粒径均能提高MH电极的快速充电性能, 并能计算出MH电极在不同的初始荷电态、不同充电倍率下, 表面氢原子浓度达到最大值所需的时间.     

锌电极有机复配缓蚀剂的性能研究

应用极化曲线、表面张力、放电实验和SEM等测试方法,研究了阴离子表面活性剂十二烷基苯磺酸钠(简称SDBS)和非离子表面活性剂吐温-20(简称Tween)之复配体系(简称ST)在碱性介质中对锌电极电化学性能的影响及其作用机理.实验表明,复配缓蚀剂ST具有比单一添加SDBS或Tween更高的缓蚀效率,并且二者具有明显的协同作用,Tween在复配体系中的作用是使活性物质于锌电极表面的临界胶团浓度显著降低,吸附分布更加均匀.从而可更有效的抑制锌电极腐蚀,改善锌电极的表观形貌,达到延迟钝化的效果,使活性物质利用率得到显著提高.     

Calculating a Characteristic Bulk Current Density in the Cathode of a Hydrogen-Oxygen Fuel Cell with a Solid Polymer Electrolyte

The magnitude of currents of electrodes in hydrogen-oxygen fuel cells of all types is shown to be fully determined by values of the effective coefficient of gas diffusion, the effective coefficient of ionic conduction, and the characteristic bulk current density. The characteristic bulk current density is estimated in two versions for cathodes with Nafion: the catalyst is distributed in the bulk of substrate grains or at their external surface. The currents commensurate with those observed in experiments are given only by the second version. Means of computer-aided simulation are used to imitate the formation of fractal films composed of the catalyst particles on the surface substrate grains. The simulation means made it possible to link the magnitude of the specific surface area of platinum particles with its weight content in substrate grains. Electrochemical characteristics of the cathode with Nafion-the potential dependence of the optimum magnitude of the overall current and the thicknesses of the active layer and the weight of platinum in it, as well as the magnitudes of the optimum current generated by a unit weight of platinum—are calculated. A notion of “ norm” is introduced for the characteristic bulk current density of the cathode. 1 × 10^?3 A cm^?3 is the electrochemical-process intensity, which the technology of preparation of active layers of cathodes can provide at this stage in the development of fuel cells with a solid polymer electrolyte.     

Optimizing Weights of Platinum in the Active Layer of the Cathode of a Hydrogen–Oxygen Fuel Cell with a Solid Polymer Electrolyte

The active layer of the cathode of a hydrogen–oxygen fuel cell with a solid polymer electrolyte is computer simulated. The active mass of the electrode consists of substrate grains (agglomerates of carbon particles with Pt particles embedded into them) and grains of a solid polymer electrolyte (Nafion). The substrate grains presumably contain hydrophobic pores, which facilitate the oxygen penetration into the active mass. A calculation of characteristics of such an electrode focuses on the optimization of platinum weights. The principal parameters of the system are concentration and size of grains of substrate and Nafion, Pt concentration in substrate grains, average diameter of hydrophobic pores in substrate grains, and the electrode polarization. The optimum, at a given electrode polarization, electrochemical activity of the active layer, its thickness, and the platinum weight are calculated. A link between these quantities and principal parameters of the active layer is revealed.     

Macrodistribution of Anodic Dissolution Rate at a Rotating Disk Electrode with Partially Insulated Surface

Macrodistribution of etching rates of a macroscopically nonuniform, partially dipped, rotating disk electrode of low-carbon steel in 1 M NaCl at pH 1 with photoresist insulation and the density of active rectangular holes being 1.6 holes/mm² is studied at dimensionless etching rates i ⁰ _avg /i _l = 0.2–1.1, where i ⁰ _avg is the average current density per active surface and i _l the limiting anodic current density determined by the ionic transport rate. The distribution of the average etching rates in the normal direction is determined by the primary current distribution and is insensitive towards the type of the dissolution rate distribution in a cavity.     

Physico-Mathematical Model of the Gas Flow in the Channel between the Separator Plate and the Anode of a Fuel Cell with Molten Carbonate Electrolyte

Some models for the gas mixture composition variation in the channel between the separator plate and anode of a molten carbonate fuel cell are considered. A two-dimensional model for the carbon dioxide diffusion in the channel is solved analytically and numerically. The anodic current density is estimated.     

标准气浓度对定量误差影响的探讨

In the trace gas analysis,experimental results show that the relative error can be kept in the range of±10% even in case where the difference in concentration between the standard mixture and sample gas is up to100 times.When the exponential dilution is used for calibration,the standard mixtures of higher concentra-tion with less period of time in the dilution procedure give quite accurate data.