Dissolution of hydrogen and the ratio of the dissolved hydrogen content to the produced hydrogen in electrolyzed water using SPE water electrolyzer

Concentration of dissolved hydrogen in electrolyzed water using a solid polymer electrolyte (SPE) water electrolyzer was investigated using a DH-meter. A ratio of the dissolved hydrogen content to an amount of hydrogen concentration calculated from charge passed during electrolysis was estimated. The ratio increased from 10 to 20% with a decrease in current density from 3.0 to 0.3 A dm⁻². The effect of the linear velocity of water on the ratio of dissolved hydrogen was studied. The cross-sectional area of the water channel was changed to change the linear velocity of water. The ratio of dissolved hydrogen increased with increasing the velocity. Due to the fast mass transport by high velocity, the small hydrogen bubbles are fast transferred by the diffusion into the bulk water and dissolved. The population density of the small hydrogen bubbles is found to have an effect on the ratio of the dissolving hydrogen.     

Role of mass transfer on hydrogen evolution in aqueous media

The process of hydrogen evolution during alkaline electrolysis of aqueous solutions is governed by mass transfer, growth of hydrogen bubbles and removal of hydrogen from the cathode. Two mechanisms are decisive for hydrogen removal: (i) hydrogen dissolved in the solution is carried off from the cathode surface by diffusion and convection, and (ii) gas bubbles are transported by a two- phase flow. The paper describes experiments to determine the local concentration of dissolved hydrogen and the void fraction of hydrogen bubbles in aqueous solutions. Measurements were performed in a flow channel by varying the height of the cathode (40–400mm), the current density (up to 6250Am–2) and the mean velocity of the electrolyte (up to 0.95 m s–1). Two operating regimes of the electrolyser are found. At high current densities a back flow is observed leading to an increase in the electrolyte resistance. Traces of dissolved oxygen are detected at high current densities. At low current densities the two-phase flow is confined to a thin layer along the cathode surface, the concentration of dissolved hydrogen being small.     

Hydrogen concentration in water from an Alkali–Ion–Water electrolyzer having a platinum-electroplated titanium electrode

The supersaturated concentration of hydrogen in electrolyzed water obtained from a flow-type electrolytic cell was studied under various electrolysis conditions. The degree of supersaturation was found to decrease as the solution supply rate to the cell increased. The ratio of observed hydrogen concentration to the theoretical hydrogen concentration obtained from the electrochemical equivalent, as calculated from the transfer of charge in the cell, was found to increase with the solution supply rate. The concentration of hydrogen in solution has a maximum at a current density of approximately 0.3 A dm^–2. This maximum was found to be independent of the flow rate, indicating that the hydrogen concentration is related to both the diffusion of dissolved hydrogen from the electrode surface to the bulk solution and hydrogen bubble growth.     

Role of mass transfer on hydrogen evolution in aqueous media

The process of hydrogen evolution during alkaline electrolysis of aqueous solutions is governed by mass transfer, growth of hydrogen bubbles and removal of hydrogen from the cathode. Two mechanisms are decisive for hydrogen removal: (i) hydrogen dissolved in the solution is carried off from the cathode surface by diffusion and convection, and (ii) gas bubbles are transported by a two- phase flow. The paper describes experiments to determine the local concentration of dissolved hydrogen and the void fraction of hydrogen bubbles in aqueous solutions. Measurements were performed in a flow channel by varying the height of the cathode (40–400mm), the current density (up to 6250Am?2) and the mean velocity of the electrolyte (up to 0.95 m s?1). Two operating regimes of the electrolyser are found. At high current densities a back flow is observed leading to an increase in the electrolyte resistance. Traces of dissolved oxygen are detected at high current densities. At low current densities the two-phase flow is confined to a thin layer along the cathode surface, the concentration of dissolved hydrogen being small.     

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...     

电流密度对氯碱工业离子膜电解槽传递特性影响

为考察电流密度对氯碱工业中离子膜电解槽内流体传递特性的影响,利用流体力学计算软件,对不同电流密度下电解槽阳极室进行了数值模拟,得到了阳极室单个格栅内流体的速度、温度和浓度分布。以液体循环量、膜附近处速度的最大值、膜表面温度和浓度为指标,考察了不同电流密度下电解槽的运行情况。结果表明:随着电流密度的增加,电解槽内液体循环量增大,膜表面温度升高,盐水浓度降低;在电流密度为4.5 kA·m^-2的典型工况下,电解槽内平均温度为86.39℃,膜表面平均温度为87.40℃;当电流密度提高时,可以通过降低进口溶液温度,获得与典型工况相近的电解槽内平均温度和膜表面平均温度。     

Investigation of 30-cell solid oxide electrolyzer stack modules for hydrogen production

The 30-cell nickel-yttria stabilized zirconia (Ni-YSZ) hydrogen electrode-supported planar solid oxide electrolyzer (SOE) stack modules were manufactured and tested at 800 °C in steam electrolysis mode for hydrogen production. The electrolysis efficiency of the stack modules was higher than 100% at a total steam and hydrogen flow of 2.1 sccm cm⁻², a H₂O/H₂ ratio of 80/20, and a current density of <0.2 A cm⁻². The electrolysis efficiency, current efficiency, and actual hydrogen production rate of the stack modules increased with increasing H₂O/H₂ ratio at a constant current density. However, the electrolysis and current efficiencies decreased steadily at high current densities. During hydrogen production, the stack modules were operated at 800 °C and a constant current density of 0.15 A cm⁻² for up to 1100 h. A steam conversion rate of 62% and current efficiency of 87.4% were obtained; the actual hydrogen production rate reached as high as 103.6 N L h⁻¹. Post-mortem analysis showed that delamination of the LSM–YSZ oxygen electrode mainly occurred in the steam and air inlet area of the 10×10 cm² cells.     

Hydrogen peroxide production by water electrolysis: Application to disinfection

Hydrogen peroxide was produced by direct current electrolysis using only two electrodes, a carbon felt cathode and a RuO₂ coated titanium anode. The required oxygen was supplied by oxidation of water and by transfer from the atmosphere or by pure oxygen injection. The current was maintained below a maximum value to avoid peroxide reduction. A high peroxide production rate was reached and a 15 mg l^–1 concentration was maintained. The electrolysis removed turbidity and dissolved organic carbonaceous compounds from municipal sewage plant effluents. Real effluents were significantly disinfected owing to the direct effect of electric current and the indirect effect of peroxide. A residual effect was also observed.     

Experimental study on the effect of reactant flow arrangements on the current distribution in proton exchange membrane fuel cells

Current distribution in a proton exchange membrane fuel cell (PEMFC) is significantly influenced by reactant flow configurations. In this study, the current distribution has been measured experimentally using a segmented flow-field plate and printed circuit board (PCB). Local current distributions for a PEMFC with serpentine flow field and three different flow arrangements including co-flow, cross-flow, and counter-flow arrangements for the anode and cathode streams are investigated along with the effect of flow channel orientation. It is shown that the counter-flow arrangement yields most uniform distribution for the current density, whereas the co-flow arrangement results in a considerable variation in the current density from the reactant gas stream inlet to exit. Flow channel orientation can also impact the cell performance and the current distribution appreciably. The limiting hydrogen concentration at the anode side due to the low stoichiometry condition can have a predominant effect on the current distribution and cell performance.     

湿法净化铝电解含氟烟气的工艺研究

采用湿法净化工艺,利用硫酸钙溶液吸收铝电解过程中产生的含氟烟气,对净化过程的主要影响因素如：含氟烟气流量、气液比、吸收剂浓度等进行了研究。实验结果表明：当含氟烟气流量为800 L/h,气液比为5：1,吸收剂浓度为1.53 g/L时,含氟烟气中氟化氢的吸收率可以达到99.22％,符合国家大气污染物综合排放标准。     

超重力-电催化耦合法降解含酚废水

将自制的超重力多级同心圆筒电解装置应用于电催化降解含酚废水的过程中, 解决电化学法处理废水存在"气泡效应"和"传质受限"导致的废水处理效率降低的难题。考察了超重力因子、电流密度、电解时间、电解质浓度、液体循环流量、苯酚初始浓度对废水降解效果的影响, 确定了超重力-电催化耦合法处理含酚废水的最佳工艺条件。结果表明:超重力因子为30、电流密度为200A/m²、电解质浓度为3g/L、液体循环流量为80L/h、电解时间为7h时, 处理初始浓度100mg/L的含酚废水, 苯酚去除率可达99.1%, COD去除率可达24.7%。超重力电催化法强化了离子传质过程, 实现了废水中苯酚的高效去除, 为含酚废水的处理研究探索了一种新途径。     

活性黑5染料模拟废水电解脱色探究

为明确活性黑5染料在电化学体系中的脱色过程,以石墨为阴极,Ti/PbO_2为阳极,考察了电流大小、初始pH值、电解质种类及浓度、电解时间、温度、染料初始浓度对染料脱色过程的影响。结果表明:电流大小、氯化钠浓度对活性黑5脱色率影响较大,一定条件下染料脱色率可达99%;初始pH对染料脱色率几乎无影响,随着初始pH在4~10范围内变化,脱色率始终稳定在99%以上;染料的脱色率随着电解时间的增加而增大,当电解时间达到60 min时,染料脱色率达到99%。     

Mass transfer and current distribution on a metallic wire

The current and copper deposit distribution on a metallic fibre (stainless steel, diameter of 2 mm) was studied numerically and experimentally. The experimental copper deposit was measured with an optical microscope and the current distribution was deduced. The influence of electrolysis time on copper deposit distribution was also studied. A typical current tertiary distribution was observed. The experiment with a longer electrolysis time exhibited a larger current variation around the wire. A numerical study of this problem was also carried out. The simulation involved a laminar and turbulent flow solver together with a numerical model for the mass transfer of ionic species due to diffusion, migration and convection. A good correlation was found between simulated and experimental results for experiments with a short electrolysis time. This numerical model was then used to study the influence of the flow velocity and the diffusion coefficient on the current density and on the average mass transfer around a wire a few microns in diameter. The general relation: for 0.02 < Re_p < 14.22 and 1000 < Sc < 12,000 was obtained. Comparison with data available in the literature demonstrates good agreement between our model and previous results.     

电解法处理含镍废水的研究

含镍废水不仅造成镍金属的浪费,并且带来环境污染。通过配制硫酸镍溶液模拟含镍废水,采用电解法确定最佳阳极材料为钌涂层钛板,并研究了电解时间、电流强度和Ni~(2+)浓度等因素对Ni~(2+)的回收率的影响。实验结果表明:在电解时间240min,电流强度15A,Ni~(2+)质量浓度20g/L,电解温度50℃,p H值6,搅拌速率300r/min的条件下,Ni~(2+)的回收率为85.42%,电流效率为52.16%。     

OXIDATION OF C.I. ACID ORANGE 7 WITH OZONE AND HYDROGEN PEROXIDE IN A HOLLOW FIBER MEMBRANE REACTOR

The degradation of C.I. Acid Orange 7 by ozone combined with hydrogen peroxide was carried out in a hollow fiber membrane reactor, and batch recirculation mode of aqueous phase was employed. The effect of initial pH, hydroxyl radical scavenger, hydrogen peroxide concentration, liquid recirculation rate, gas flow rate, and gaseous ozone concentration on the decolorization of C.I. Acid Orange 7 was investigated. The results showed that the decolorization of C.I. Acid Orange 7 fits the pseudo-half-order kinetic model. The rate constant increased with the increase of initial pH, hydrogen peroxide concentration, liquid recirculation rate, gas flow rate, and gaseous ozone concentration. The presence of hydroxyl radical scavenger inhibited the decolorization rate by over 50%. The combination of ozone with hydrogen peroxide achieved a higher COD removal efficiency than ozone alone in the membrane reactor.     

Galvanostatic Pb(II) removal from a simulated wastewater by using a stainless-steel wool cathode in a flow-through cell: a factorial-design study

The response surface methodology was used to find the optimal condition for electrolytic Pb(II) removal by using, as the experimental design, a central composite rotatable design for two variables (current and flow rate) at five levels. The surfaces generated with the second-order-equation fitted data showed the positive influence of increasing the current variable on the removal efficiency, leading to 93% removal after 30-min electrolysis. However, high current values lowered the current efficiency due to parasitic reactions. On the other hand, the flow rate variable did not substantially affect either the removal or the current efficiency. Electrolysis carried out at the optimised condition (250 L h⁻¹ and −0.25 A), after 90-min electrolysis, lowered the Pb(II) concentration from 50 ppm to 0.5 ppm, corresponding to 99% removal.     

The effect of corrugated membranes on salt splitting

An investigation of the electrohydrolysis of sodium sulfate using a corrugated Nafion^® 117 membrane is reported. A comparison of the performance of a flat and corrugated Nafion^® 117 in a two-compartment membrane electrolysis cell is made. Corrugating the membrane increased the active membrane area by 57% compared to the projected area. The effect of flow rate, current density and salt concentration on current efficiencies, transport properties and achievable product concentrations are presented. The results show a large improvement on transport properties, current efficiencies and product formation using corrugated membranes. Corrugated membranes gave an improvement of up to 77% on achievable base concentration and an increase of approximately 22% in current efficiency.     

Hydrogenation of chalcones using hydrogen permeating through a Pd and palladized Pd electrodes

The hydrogenation of benzalacetone and benzalacetophenone was carried out using atomic hydrogen permeating through a palladium membrane. A two-compartment cell separated by a Pd sheet or a palladized Pd (Pd/Pd black) sheet electrode was employed. The reduction products were identified by (GC) gas chromatography, UV-vis absorption spectroscopy and NMR spectroscopy. The carbon-carbon double bond was hydrogenated and the benzylacetone and benzylacetophenone were obtained as products using palladium catalyst. The current efficiency for hydrogenation reaction increases when the current density for water electrolysis decreases and depends on the initial chalcone concentration. It is over 90% at the concentration of 10 mmol L⁻¹. The hydrogen absorption and diffusion into and through a palladium membrane electrode has been studied by using an electrochemical impedance spectroscopy method. The impedance results would indicate that the hydrogen permeated through the membrane is consumed by the chalcone during the hydrogenation process keeping as the permeable boundary condition in the outer side of the Pd membrane the hydrogen activity almost zero. The hydrogen entering the metal through an adsorbed state and the rate of hydrogen absorption is diffusion-controlled.     

The effect of liquid flow distribution on the behaviour of a trickle bed reactor

A mathematical model has been formulated of the effect of flow distribution of the liquid phase carrying a dissolved reactant on the progress of an nth order, irreversible, catalytic reaction with heat effects in an adiabatic trickle bed reactor. The model has been stated in terms of the density of irrigation, temperature and concentration of the reactant in the liquid, all treated as spatially distributed variables. Provisions have been made to account for the existence of the flow down the surface of the wall, which has no catalytic effect.Local concentration and temperature have been proven to be coupled by the invariant T + Uγc = γU. The same invariant governs also local concentration and temperature of the wall flow. Mathematically, the model is represented by a coupled set of nonlinear parabolic partial differential equations enabling concentration and temperature fields to be obtained for an arbitrary type of liquid distribution and intensity of the wall flow.Numerical solutions have been obtained by the finite-difference method simulating reactors irrigated by liquid distributors as central discs of different radii, or a central annulus, and strongly exothermic reactions with the reaction order ranging between 0.1 and 2. Numerical results have shown the effect of liquid distribution on the overall reaction conversion to be very complex. Optimum initial distribution varies depending on the reaction order as well as the required degree of conversion. In general, however, the entrance region flow pattern may play a significant role in affecting especially reactions exhibiting kinetics close to zero order (hydrogenations). The effect of the wall flow has been found unambigously adverse to reaching high conversions and of increasing importance for low order reactions.