Galvanostatic oxidation of formaldehyde-methanol solutions on Ti/Ru0.3Ti0.7O2 electrodes using a filter-press cell

The galvanostatic oxidation of methanol-containing formaldehyde solutions, under conditions of simultaneous oxygen evolution, in 0.5 M H₂SO₄ acid was studied using a Ti/Ru_0.3Ti_0.7O₂ dimensionally stable anode (DSA^®), in a filter-press cell. The reaction products detected were HCOOH, CO₂ and CO₃ ^2–. The CO₃ ^2– species is formed from the oxidation of HCOOH and subsequently decomposes in solution to CO₂. Conversely CO₂ is also formed electrochemically from the electrooxidation of formaldehyde and methanol. A mechanism, which considers the active and non-active nature of the electrode, is suggested. First-order kinetics, with respect to the variation of formaldehyde and methanol, are displayed and two linear regions observed. This is interpreted as being due to the presence of the reaction products of oxidation inhibiting the oxidation of formaldehyde at the electrode surface. Further, a mechanism is proposed considering the species present in solution.     

The motion of electrolytic gas bubbles near electrodes

Several reports in the literature mention oscillatory bubble motions close to, or in contact with electrodes. Such behaviour is obviously related to a time-variable force, but it was not apparent what the origin of this variable force was. Recent advances in understanding of the surfactant behaviour of gases, and in particular the gases liberated during electrolysis, have cast a new light on the underlying mechanism of these oscillations. Other unexpected, but not necessarily oscillatory bubble behaviour is discussed, and the role of electrolytic gas acting as a surfactant illuminates these non-oscillatory motions as well. Finally, the paradox of bubbles remaining attached to electrodes with zero contact angle is resolved.     

几何结构对滤压式电解槽内部传质的影响

Effect of configuration （structure of electrode, interelectrode gap, positions of inlet and outlet, volume of the cell and additional nets） on mass transfer characteristic of a filter-press type electrochemical cell has been studied. The mass transfer coefficients on the electrodes were obtained by using the well-known technique based on the determination of limiting diffusion current. It is found that mass transfer coefficients with mesh electrode are greater than that of with plate electrode. Mass transfer coefficient is decreased with interelectrode gap. While interelectrode gap achieved a certain value （7 ram）, mass transfer coefficient is steady, no more declining. Mass transfer characteristic for different positions of inlet and outlet are different and dimensionless number groups correlated equations are obtained by experiment. Mass transfer characteristic is the best when inlet located on the top and outlet on the bottom of the cell respectively. While magnified the volume of the cell to eight times, mass transfer characteristic changes little. Mass transfer characteristic without nets is lower than that of with additional nets in the exit region, but higher than that of with additional nets in the entry region.     

具扩张阳极及活性阴极的隔膜电解槽

介绍具有扩张阳极、活性阴极的隔膜电解槽的结构,并与普通铁丝网电解槽槽电压进行对比,说明采用该类电解槽是节电的最好途径。     

Performance of an electrocoagulation cell with horizontally oriented electrodes in oil separation compared to a cell with vertical electrodes

Demulsification of oily wastewater by electrocoagulation in a batch cell with horizontally oriented electrodes was studied. The anode of the cell was an array of separated horizontal cylinders made of aluminium, the cathode was a rectangular aluminium plate placed on the cell bottom below the anode. The effect of pH, temperature, current density, and sodium chloride concentration on separation efficiency was studied. The suggested cell design was found to be more efficient than the traditional vertical parallel plate cell. The horizontal electrode cell could reduce oil concentration in wastewater from 500 to 6 ppm within 30 min (i.e. below the maximum permissible value which is 10 ppm) with a separation efficiency of 99.8%. The use of an anode made of horizontal tubes offers the advantage of using the inner side of these tubes as heat exchanger to control cell temperature if necessary.     

Direct methanol fuel cell with non-equipotential electrodes

Our model of a direct methanol fuel cell with straight channels is extended to take into account finite conductivity of current collector plates and local contact resistances. Co-flow conditions are assumed and the two cases are considered: (i) when load resistor is connected at the inlet of the feed channels and (ii) when it is connected at the outlet. In both cases voltage loss in the plates induces growth of current production close to the point of load connection. The increase in local current j is accompanied by the growth of local polarization voltages η^a and η^c of the anode and the cathode sides, respectively. Moving the point of load connection one can change the distribution of j,η^a and η^c along the channel. Local “spot” of contact resistance decreases local current and polarization voltages; in the rest part of the cell these values increase.     

Optimization of an electrolytic cell with use of a GRG algorithm

Recent technological improvements and changing economic factors indicate the need to apply more sophisticated and efficient optimization techniques to today's increasingly complex electrochemical processes. In this study a reduced gradient optimization scheme is applied to a model of a chloralkali cell to determine maximum profit for a single cell and to investigate the sensitivity of the optimal solution to changes in selected design variables. The model consists of 39 constraints, 37 equalities and 2 inequalities, including mass, voltage and heat balance relationships, in 40 variables. A methodology is developed that allows state-of-the-art optimization techniques to be easily applied to electrochemical cells and processes for which algebraic models can be formulated. Electrochemical systems represent a new area of application for nonlinear programming algorithms.     

Approximate evaluation of cell resistance with resistive electrodes

The resistance of a cell composed of a resistive anode and a conductive cathode has been theoretically calculated by solving the two-dimensional Laplace equation for the solution phase where the anode has an overpotential of a linear type. Conditions were evaluated under which the cell resistance could be obtained on the assumption that the direction of the current flowing in solution was perpendicular to the electrode. These were not strongly dependent on the ratio of the interelectrode distance to the height of the electrodes. The main parameters which determine the conditions were the Wagner number and the ratio of the electrode resistance to the solution resistance.     

CFD evaluation of internal manifold effects on mass transport distribution in a laboratory filter-press flow cell

The internal manifold geometry strongly influences the flow distribution inside an electrochemical reactor. The mass transport coefficient is a function of the flow pattern and is a key parameter in successful electrochemical reactor design and scale-up. In this work, a commercial computational flow dynamics (CFD) package was used to describe the flow pattern in the FM01-LC reactor at controlled volumetric flow rates (corresponding to mean linear flow velocities past the electrode surface between 0.024 and 0.11 m s^?1). Numerical Re numbers were obtained for each local flow velocity at different positions in the reactor channel. From a known mass transport correlation (based on dimensionless groups, i.e. Sh, Re, Sc), numerical k _m values were obtained (in the range 200 < Re < 1,000) at different positions in the reactor channel. Computed k _m numbers are compared against experimental values. This computational approach could be useful in reactor design or selection since it facilitates a fast, preliminary reactor flow and mass transport characterisation without experimental electrochemical measurements.     

A study of electrolyte-phobic molten carbonate fuel cell electrodes

The incorporation of electrolyte-phobic material into gas diffusion electrodes enhances their performance. The principles governing the choice of electrolyte-phobic materials in molten carbonate electrolyte are discussed. Contact angle measurements of molten NaLiCO₃ on materials which have hexagonal layer-like structures confirmed that provided _{LV SV}, the contact angle will be greater than 90°. Of the materials tested (C, BN, BaO.6.Fe₂O₃, PbO.6Fe₂O₃), only C possessed adequate corrosion resistance. Electrolyte-phobic anodes, prepared by incorporation of graphite fibres into the electrocatalyst mixture, significantly reduced concentration polarization and paste electrolyte cells using such electrodes gave 160 mA/cm² at 0.6 V on 80% H₂/20% CO₂ fuel at 600°C, as opposed to 80 mA/cm² for conventional cells.     

Evaluation of the wetting time of porous electrodes in electrolytic solutions containing ionic liquid

The wetting time of porous electrodes with electrolytes based on organic solvents and ionic liquids, respectively, was investigated with two different techniques: with a tensiometer and by impedance spectroscopy. The results of this study showed that the wetting time of a porous electrode with ionic liquid-based electrolytes is up to 20 times longer than that with electrolytes comprising organic solvents. A significant reduction in the wetting time with ionic liquid-based electrolytes could be achieved by adding organic solvents. This effect can be explained by the interplay of reduced viscosity, increased surface tension and change in contact angle caused by the addition of the organic solvent, with the lower viscosity being the main driver of improved wetting kinetics.     

使用钛涂钌电极作为阳极电解法制备次磷酸的研究

研究了以钛涂钌电极作为阳极,不锈钢作为阴极,采用四室电渗析槽电解法制备次磷酸的最佳工艺条件(如电解电流、电解时间、原料室次磷酸钠浓度等)。测量了电解过程中钛涂钌电极的阳极电位。结果显示钛涂钌电极在硫酸介质中,具有高的电催化活性和低的析氧电位,是非常省电的阳极材料,在最佳条件下制得的产品纯度高,各项指标都达到了分析纯的标准。该方法没有废物产生,不污染环境,符合清洁生产。     

A simplified approach to the thermal behaviour of electrolytic Dewar cell calorimeters

A simplified approach, based on the concept of an overall heat loss coefficient, is described for the estimation of time-variant temperature profiles. The computation of the loss coefficient from experimental temperature maxima under programmed power input is also discussed.     

影响离子膜电解槽槽电压的因素

阐述了离子膜电解槽操作温度、电流密度、电解液流量、阴极液质量分数、阳极液质量分数、阳极液ｐＨ值、阳极液中金属离子以及阴极材料等九方面对电解槽电压的影响。     

A uniform renewal theorem

It is shown that the Renewal Theorem holds uniformly with respect to the step distribution F when the latter is restricted

a weakly closed class K of non-arithmetic distribution functions for which |x| is uniformly integrable with respect to F and the means pF are bounded away from 0. The proof uses a coupling argument of which a uniform version of-the Recurrence Theorem is an interesting byproduct. An application to asymptotic local minimaxity in sequential estimation is described.     

隔离式电解槽电解制备高铁酸钠研究

采用隔离式电解槽电解制备高铁酸钠,考察了不同电解液浓度、电解时间、电流、温度及加入不同种类微量电解质等因素对高铁酸钠浓度的影响,并通过正交试验得出了此方法制备高铁酸钠的最佳工艺参数。研究表明,在电解液中加入0.020～0.030 mol/L的碘酸根离子时,制备高铁酸钠的稳定性最佳;高铁酸钠最佳的合成条件为:温度为45℃、电解液浓度为14 mol/L、碘酸根离子的投加量为0.020 mol/L、电流为2.0 A、电解时间为3.0 h,制备得到的高铁酸钠的浓度为60.44 mmol/L。     

A practical photoelectrochemical cell using non precious metal electrodes

In this study a Photoelectrochemical Cell (PEC) constructed with inexpensive materials photodegraded selected organic compounds present in model waste waters, with the concomitant production of electrical current. Organic substrates dissolved in salt water included formic acid, 2-propanol, 1,2-dihydroxybenzene and ascorbic acid. Significant degradation of ascorbic acid was achieved when the cell was illuminated with a household 60 W tungsten light bulb, although better results were achieved with UV sources. Degradation of all the compounds was found to occur by zero order kinetics, and the PEC was shown not to work appreciably in dark conditions. Using a conventional light bulb, a formic acid PEC produced a power density of 19.1 ± 2 mW m⁻². When exposed to natural daylight, a power density of 31.5 ± 2 mW m⁻² was achieved. There is considerable scope for scale up of this device for exterior use.     

Electrooxidation of benzyl alcohol and benzaldehyde on a nickel oxy-hydroxide electrode in a filter-press type cell

The electrooxidation of benzyl alcohol and benzaldehyde in alkaline medium was carried out in a filter-press type cell on a nickel oxy-hydroxide electrode under different experimental conditions. An overpotential occurs in the presence of organic molecules in the solution shifting oxygen evolution towards higher potentials. The results obtained were conclusive that benzyl alcohol and benzaldehyde electrooxidation on NiOOH layers yielded benzoic acid as the main final reaction product. Chromatographic analysis of the bulk solution showed that the electrocatalytic oxidation of harmful molecules was carried out until the formation of acid compounds (benzoic acid) as an ultimate stage, suggesting that a Ni anode can be used successfully for waste remediation.