多孔气体扩散型氧阴极用于氯酸盐电化生产

简述了采用氧阴极代替铁阴极,以空气作退极化剂的电化生产氯酸盐平板压滤机式复极电解槽的结构与性能.当电极工作电流密度为100mA/cm~2时,电解槽的平均单池电压在2.000～2.200V之间;电解液中无需添加Na_2Cr_2O_7,电流效率可达90±2%,生产每吨NaClO_3的直流电耗为3700±100kw·h.电解槽运行稳定,单池电压分布均匀.     

氧阴极用于氯酸盐电化生产

前言用气体扩散型氧阴极替换氯酸盐电化生产过程的铁阴极,其电化反应由NaCl 3H_2O(?)NaClO_3 3H_2↑改为NaCl 3/2O_2(?)NaClO_3消除副产物氢的小试工作在八一年六月通过科学院鉴定。鉴定结果指出,该法具有独创性,可节省直流电耗25～30％,并可根除原法中为提高电流效率而向电解液中投放的1.5～2.0g/l Na_2Cr_2O_7所造成的六     

氧阴极用于氯酸盐电化生产的电流效率(Ⅰ)电解系统中各种因素对电流效率的影响

用直接测量电解系统析氧量的方法,确定了氯酸盐电化生产过程的电流效率,并考察了溶液的组成(Cl~-、ClO_3~-、HClO及ClO~-)、操作参数(电流密度、电解槽和反应器温度、溶液的酸碱度及电极表面的液流速率)、添加盐及电极性能对电流效率的影响.     

氧阴极用于氯酸盐电化生产的电流效率(Ⅰ)电解系统中各种因素对电流效率的影响

用直接测量电解系统析氧量的方法,确定了氯酸盐电化生产过程的电流效率,并考察了溶液的组成(Cl~-、ClO_3~-、HClO及ClO~-)、操作参数(电流密度、电解槽和反应器温度、溶液的酸碱度及电极表面的液流速率)、添加盐及电极性能对电流效率的影响.     

氧阴极用于氯酸盐电化生产的电流效率

本文分析了在氯酸盐电化生产过程中引起电流效率损失的各种原因,在此基础上导出了物料平衡方程并与实验结果进行了对比。     

空气阴极用于氯酸盐电槽结构的研究

在电解工业中节能,防止环境污染和防止爆炸是引人瞩目的问题,目前国内外电解法生产氯酸盐是以析氢的阴极及析氯的阳极组成电解槽。电解时电解液中加入2g/1的重铬酸钠以防止ClO~-的阴极还原,为了强化化学反应进程,进一步提高电流效率,广州珠江电化厂进行了复极式电解槽研究,电流效率提高到93%左右,但其电极反应机理没有改变,槽压仍达3.35V之高。根据这种反应机理生产每吨氯酸钾电耗高达5300度(系属国内先进指标)。而且进行氢阴极电解,不能避免重铬酸盐的污染,槽中产生氢也混有     

加酸对电解槽性能的影响

介绍电解槽发生的反应和副反应。分析副反应对电解槽性能的影响。向电解槽加酸,可以降低氯中含氧量,减少氯酸盐含量,保护阳极涂层和电解槽垫片,降低游离氯含量。但是加酸过多也会引起盐水结晶。对氯酸盐分解加酸量进行计算,通过加酸量和阳极出口酸度计算电流效率。     

金属阳极和氢阴极：它们对放氧反应和氯酸根还原反应作用的活性

本文介绍一个在两个活性控制的反应正在同时出现时的有关电流效率与电流密度依赖关系的理论基础。讨论了在钌阳极上放 Cl_2时影响 O_2放电的动力学因素以及在钢阴极上放 H_2时影响氯酸盐还原反应的动力学因素,还讨论了抑制这些副反应的方法。     

膜法电解碱金属氯化物时氯酸盐和氧的生成

工业化膜法电解装置运转数年间，一直存在着与主产物电流效率相关的阳极气体中副产氧和阴极液中氯酸盐生成问题。已发现副产物的电流效率随主产物氯和烧碱电流效率下降而直线上升。当使用两种阳极时，其中一种比另一种生产的氧要多得多。高氧阳极比低氧阳极显然与氯酸盐生成的减少有关。已报导了两种阳极氧含量和氯酸盐生成速度加快与碱电流效率下降的关系。如果用盐酸消除氯酸盐，添加的酸量必需相当于碱电流效率的下降。两种阳极所     

新型的阳极促进剂

<正> 本文报导多孔石墨空气(氧)电极作阴极,应用于电解法生产H_2O_2,考虑到工厂应用的原促进剂对NH_4CNS对多孔电极的毒化作用,试验新的阳极促进剂——尿素和亚铁氰化钾的用量、温度等因素对H_2O_2生产阳极电流效率的影响。一、前言传统电解法生产H_2O_2用铅阴极,铂阳极来电解     

A NEW METHOD FOR MEASURING THE LOSS OF CURRENT EFFICIENCY OWING TO CATHODIC SIDE REACTION IN CHLORATES PRODUCTION

A double cathode composed of a Ni screen cathode and a porous gas diffusion oxygen cathode with a porous diaphragm in between was constructed for the purpose of measuring the loss of current efficiency in an electrolytic cell for chlorate production. With this device the cathodic side reactions, i. e. reduction of ClO~-, HClO, etc., have been investigated, revealing the dependence of the loss of efficiency on the concentration of NaClO_3, the pH of the electrolytic solution and the presence of Na_2Cr_2O_7. The suggested method can also be applied to studying the side reactions and the loss of efficiency for the alkalichlorine cell and the electrolytic production of BrO_3~-, IO_3~-, ClO_4~-, etc.     

Electrochemical extraction of oxygen from air via hydroperoxide ion

A novel electrochemical method for the extraction of pure oxygen from air is described. The system consists of an undivided cell with a nickel anode, a carbon–polytetrafluoroethylene (CP) air-fed cathode and a KOH+HO2- solution as electrolyte. In such a Ni–CP cell, oxygen from the air is reduced in the cathode to form HO2- via a two-electron process, whereas anodic generation of oxygen gas can take place by the two-electron oxidation of HO2- and/or the four-electron oxidation of OH- of the medium. Gas chromatography confirmed that the oxygen produced from cells operating up to 190mAcm-2 does not contain hydrogen, as expected if cathodic reduction of H2O does not take place. The presence of HO2- causes a decrease in energy consumption of the cell, since it is easier to oxidize than OH-. Ni–CP cells containing solutions with concentrations of OH- to 2.4moldm-3 and HO2- from 0.1 to 0.5moldm-3 are stable at 25°C for voltages to about 1.0V. These cells work in a steady state in which the same number of moles of HO2- ions electrogenerated at the cathode are also anodically decomposed at the anode, without OH- oxidation. In this state, the oxygen consumed in the cathode is anodically generated and extraction of oxygen from air occurs by a two-electron process. Energy consumptions between 1.710kWhkg-1 O2 and 1.224kWhkg-1 O2 are obtained for bielectronic stable cells operating at 100mAcm-2 and at temperatures between 25°C and 45°C, which are significantly lower than those reported for previous electrochemical oxygen generators based on the anodic decomposition of OH-.     

The electroreduction of oxygen to hydrogen peroxide on fluidized cathodes

The cathodic reduction of oxygen to hydrogen peroxide on fluidized beds of graphite has been studied. The cathodes were fluidized by an oxygen saturated solution of 0.1M NaOH, or by the simultaneous introduction of oxygen gas and hydroxide solution. With increasing current density, the current efficiency always decreased while the product peroxide concentration went through a maximum. In the two-phase system the maximum peroxide concentration increased with bed height. Both current efficiency and the rate of peroxide production generally decreased with catholyte flowrate. For the three-phase fluidized cathode the rate of peroxide production and the current efficiency increased with both catholyte and oxygen flowrate. Possible rate controlling steps are discussed. Current densities for both two phase and three phase fluidized beds were too low to be of commercial use.     

The electroreduction of oxygen to hydrogen peroxide on fluidized cathodes

The cathodic reduction of oxygen to hydrogen peroxide on fluidized beds of graphite has been studied. The cathodes were fluidized by an oxygen saturated solution of 0.1M NaOH, or by the simultaneous introduction of oxygen gas and hydroxide solution. With increasing current density, the current efficiency always decreased while the product peroxide concentration went through a maximum. In the two-phase system the maximum peroxide concentration increased with bed height. Both current efficiency and the rate of peroxide production generally decreased with catholyte flowrate. For the three-phase fluidized cathode the rate of peroxide production and the current efficiency increased with both catholyte and oxygen flowrate. Possible rate controlling steps are discussed. Current densities for both two phase and three phase fluidized beds were too low to be of commercial use.     

X-ray Photoemission Spectroscopy (XPS) and Thermally Stimulated Current (TSC) Studies on the Resistance Degradation of Iron-Doped Titania Ceramics

An anomalous increase of current with time has been found in iron-doped titania ceramics that have been subjected to a constant field. The result of thermally stimulated current analysis shows a peak at a temperature of 170°–180°C, which increases because of the depolarization of oxygen vacancies. X-ray photoemission spectroscopy indicates that an electrical stress results in an electrochemical reduction inside the specimen, particularly on the cathodic side. These results reinforce the viewpoint that the space charge that is responsible for the anomalous current results from a blockage of the O₂( g )/O²⁻( s ) ion transfer at the cathode.     

Multi-cathode cell with flow-through electrodes for the production of iron(ii)-triethanolamine complexes

Nonregenerable reducing agents used in dye houses for the application of indigo, vat dyes and sulfur dyes can be substituted by indirect cathodic reduction techniques. An electrochemical cell for the indirect cathodic reduction of dispersed indigo dyestuff using an alkaline solution of the Fe(iii/ii)-triethanolamine complex as redox mediator was constructed and tested. The cell is built up as divided cell (cathode area 5–10m2, catholyte volume 12L, anolyte volume 1.5L) with several three dimensional cathode units (up to 10) in the same cathode compartment. The cathodes were connected to a common anode and to separately adjustable power supplies. The catholyte was circulated through the porous cathode units parallel to the current direction. Two different electrode materials (copper and stainless steel) and cathode constructions were tested, resulting in an optimized cell construction. The electrochemical cell was characterized by a series of batch electrolysis experiments. Results are given dealing with the cell voltage drop in the cathode, the product yield and the current efficiency at different current densities and cell current. After an optimization step the current efficiency reaches 70–80% at 2 A m–2 current density and 7.8×10–3moldm–3 Fe(ii)-complex. The cell current is 10A.     

The electrochemical reduction of nitrate in acidic nitrate solutions

Cathodic regeneration of nitrous acid by electrochemical reduction of nitrates could yield a catholyte which is useful in the processing of manganiferous ores. The purpose of the present investigations was to study the cathodic reaction in an electrolytic cell with an acidic nitrate electrolyte. Electrochemical reduction of nitrate has been investigated in the ranges 0.45–2.70m H+, 0.0–0.1m HNO2, 0.5–2.0m NO3– and 20–80°C at several cathode materials. Potentiodynamic scanning experiments with a platinized titanium cathode showed limiting current densities of 0–300Am–2 at cathode potentials of +950–+700mV vs SHE. At cathode potentials less than +700mV vs SHE, cathodic reduction of nitrous acid to nitric oxide took place. A linear relation between the nitrous acid concentration and the limiting current density was found in this experimental range. Nitrous acid can be produced by cathodic reduction of nitric acid in a membrane cell. However, the maximum concentration of nitrous acid that can be produced is limited by two reactions; decay of nitrous acid to nitric acid and nitric oxide and cathodic reduction of nitrous acid to nitric oxide.     

锌酸盐镀锌阴极电流效率的研究

对碱性锌酸盐镀锌阴极电流效率的影响因素进行系统的研究。通过控制镀液组成及工艺条件可以在一定程度上提高阴极电流效率。增加镀液中锌离子质量浓度、适当控制阴极电流密度，升高镀液温度均可提高阴极电流效率；铁离子配合剂ZFC及添加剂ZFA的加入，使阴极电流效率降低。碱性锌酸盐镀锌阴极电流效率低的原因是配合离子Zn(OH)4^2-电沉积的阴极电势很负引起阴极大量析氢。合金镀层中引入铁明显降低了电沉积的阴极电流效率。     

Correlation of film structure and molecular oxygen reduction at nitrogen doped amorphous carbon thin film electrochemical electrodes

Nitrogen doped amorphous carbon (a-C:N) thin film electrodes with a range of film structures have been deposited using a filtered cathodic vacuum arc system. The correlation between film structure and electro-reduction of molecular oxygen in aqueous media at the electrodes has been explored. In aqueous 0.1 M NaOH, dioxygen reduction is inhibited at all the a-C:N electrodes compared with that at glassy carbon electrodes. The potential of the dioxygen reduction current peak shifts negatively at a-C:N electrodes as the sp³ C fraction in the a-C:N materials increases, while the current peak height decreases simultaneously. The a-C:N electrodes possess high sensitivity for investigating the mechanism of dioxygen reduction. It was found that the catalytic H₂O₂ reduction to H₂O on carbon materials is attributed to oxygen species at sp² C sites.     

Carbon‐supported perovskite oxides as oxygen reduction reaction catalyst in single chambered microbial fuel cells

BACKGROUND: Pt‐free cathodic catalyst is needed for microbial fuel cells (MFCs). Perovskite‐type oxide could be a substitute for Pt because it has been proved to be a highly active and low‐cost oxygen reduction catalyst in chemical fuel cells. RESULTS: A nano‐sized La_0.4Ca_0.6Co_0.9Fe_0.1O₃ perovskite‐type oxide on a carbon support (LCCF/C) was prepared and tested for its performance and stability (15 cycles) in MFCs. An exchange current density of 7.030 × 10^?5 (A cm^?2) was obtained with fresh LCCF/C cathode and is increased to 7.438 × 10^?5 (A cm^?2) after 15 cycles operating in MFCs. A power density of 405 mW m^?2 was achieved with the LCCF/C cathode at the 2nd cycle which was between those of Pt/C (560 mW m^?2) and C (339 mW m^?2) cathodes. At the end of the 15th cycle, the lowest decay (due to biofouling) rate on the open circuit voltage (2%) and the maximum power density (15%) were observed with LCCF/C cathode compared with those of Pt/C (4%, 17%) and C (22%, 69%) cathodes, respectively. CONCLUSIONS: This study demonstrated that perovskite‐type oxide on carbon support catalysts could be a potential substitute for Pt for cathodic oxygen reduction reaction (ORR) in air‐cathode MFCs. © 2012 Society of Chemical Industry