Calculation of the current density distribution of submicron copper electroplating based on uneven adsorption of poly(ethylene glycol)

Uneven adsorption of polyethylene glycol (PEG) along a submicron feature enabling the occurrence of void-free deposition has been identified and we have developed a simplified 1-D model to explain the phenomenon based on the distribution of hydrodynamic driving force along the trench depth. We also verified this new model based on the uneven PEG adsorption via an electrochemical quartz crystal microbalance study. The model shows that with only moderate PEG concentration, void-free deposition can be realized. Some parameters used in the modeling were developed from chronopotentiometry and rotating disc electrode experiments.     

Effect of concentration and temperature on electrochemical oscillations during sulfide oxidation on Ti/Ta2O5-IrO2 electrodes

The impact of current density, concentration, and temperature on the potential oscillations observed during the anodic oxidation of sulfide on Ti/Ta₂O₅-IrO₂ oxide electrodes is investigated. Electrochemical methods including: cyclic voltammetry, linear voltammetry, linear galvanic voltammetry, galvanostatic technique and electrochemical impedance spectroscopy are used in this study. The observed potential oscillations are caused by the periodic formation/removal of sulfur from the electrode surface. Increasing current density has the effect of increasing the frequency of oscillations as well as increasing the onset potential. Both increasing concentration and temperature gave rise to significant increases in current density prior to the onset of potential oscillations. The activation energy for electrochemical oxidation of sulfide was estimated from the temperature studies. Lifetime experiments were also conducted and demonstrated that potential oscillations have a detrimental impact on the electrode lifetime.     

The influence of suspended particles on the mass transfer at a rotating disc electrode. Non-conducting particles

The influence of suspended SiC particles on the mass transfer at an RDE (rotating-disc electrode) was investigated for the reduction of K₃Fe(CN)₆ and ZnO in alkaline electrolyte. A model for the increased mass transfer is developed, based on the decrease of the diffusion layer thickness by rotation of the particles in this layer. In experiments with different volume fractions of suspensions a critical value in the rotation speed and in volume fraction is found. The influences of hydrodynamic conditions, gravity, particle size and adhesion between particles and electrode were studied to investigate the origin of both critical values.     

Study on the treatment of waste metal cutting fluids using electrocoagulation

Electrocoagulation (EC) technique is applied for the treatment of waste metal cutting fluids (WMCFs) characterized by high COD and TOC concentration, discharged from metal manufacturing facilities including automotive engine, transmission, and stamping plants. The effects of initial pH, current density and operating time on the performance of EC are investigated by using sacrificial Al and Fe electrodes. Upon treatment by EC, the COD of WMCF is reduced by 93% and the TOC is reduced by 78% for Al electrode at pH 5.0, current density of 60 A/m² and operating time of 25 min. For Fe electrode, the reduction in COD is 92% and reduction in TOC is 82% at pH 7.0, current density of 60 A/m² and operating time of 25 min. Under optimal operating conditions, the operating costs are calculated as 0.497 $/m³ (0.023 $/kg removed COD or 0.144 $/kg removed TOC) for Fe electrode, and 0.768 $/m³ (0.036 $/kg removed COD or 0.228 $/kg removed TOC) for Al electrode. Fe electrode is found to be more efficient than Al electrode in terms of parameters such as COD and TOC removal efficiencies and operating costs.     

A Novel Membraneless Direct Hydrazine/Air Fuel Cell

In this paper multi‐walled carbon nanotubes (MWCNTs) supported binary AgNi nanoparticles are prepared by chemical reduction of Ag and Ni precursors with NaBH₄. Fe/PANI catalyst is obtained by direct pyrolysis of Fe‐doped polyaniline in N₂ atmosphere at high temperature. Results show that the Fe/PANI catalyst presents high electroactivity for oxygen reduction reaction (ORR) in alkaline media. The onset potential for ORR is 0.01 V(vs Hg/HgO) and the ORR current density is 3.4 mA cm⁻²@2000rpm at –0.4 V(vs HgO/Hg). A gas diffusion electrode is fabricated by using the Fe/PANI as the electrocatalyst of ORR. In alkaline media the AgNi/MWCNT catalyst displays efficient electroactivity for hydrazine oxidation. A lower onset potential of –0.5 V(vs Hg/HgO) and high current density for hydrazine oxidation are observed. A novel membrane‐less direct hydrazine/air fuel cell is designed by using the AgNi/MWCNT catalyst as the anode and the gas diffusion electrode as the cathode. The as‐fabricated fuel cell works properly and presents higher power density and current density.     

The effect of iron hydroxide on nickelous hydroxide electrodes with emphasis on the oxygen evolution reaction

The electrochemical response of mixed Ni(OH)₂ and Fe(OH)₂ electrodes prepared either by chemical coprecipitation or layer by layer precipitation in alkaline solutions at 25°C was studied. Ni(OH)₂ coprecipitated with Fe(OH)₂ forms a mixed hydrated oxide with specially high catalytic activity towards the oxygen evolution reaction (OER). In layer by layer precipitated electrodes, the catalytic activity for the OER depends on the sequence of precipitation of the hydroxides and there is a loss of efficiency when the inner layer is made of Fe(OH)₂ because of a poisoning of the electrode. Kinetic and mechanistic aspects are discussed. Some long term experiments at controlled potential were also carried out.     

Comparative study on surface behaviors of copper current collector in electrolyte for lithium-ion batteries

The chemical and electrochemical stability of Cu current collectors in electrolyte for lithium-ion batteries is investigated. During long-term storage, the surface section of Cu foil is oxidized to copper compounds along with the reduction reaction of electrolyte. A continuous surface film can be formed on the Cu current collector after the foil is immersed in electrolyte for lithium ion batteries at room temperature for 30 days. This surface film is composed of inorganic compounds located in the inner layer and organic/inorganic mixed components stayed outside. It comes from the spontaneous reaction at the interface between Cu foil and electrolyte for the existence of trace water in electrolyte. Different from SEI film spontaneous formation during storage, surface film generated on Cu foil during electrochemical process shows different characteristic and mechanism. By using metal lithium as counter electrode, SEI film on Cu foil in Cu foil/metal Li battery is formed from surface chemical species floating from lithium counter electrode and electrochemical oxidation/reduction process. In contrast, thinner SEI film can be generated merely from electrochemical electrolyte decomposition and precipitation. All the evidences reveal that the structure of SEI film from different conditions is similar, which shows inorganic fluorides located in the inner layer and organic/inorganic mixed lied in the outer layer.     

Potential and current oscillations during formaldehyde oxidation on platinum particles dispersed in three-dimensional pore networks of TiOx/Ti

Electrochemical oscillations during the anodic oxidation of formaldehyde (HCHO) were studied on a modified electrode of platinum particles highly dispersed in the three-dimensional pore networks of TiO_x/Ti (Pt-TiO_x/Ti). Under conditions of room temperature and stationary electrode, not only current oscillations under both cyclic voltammetric and potentiostatic conditions but also potential oscillations under galvanostatic conditions were obtained. The intensity of current oscillations strongly depends on the concentration of HCHO or H₂SO₄, upper potential limit (upl) of cyclic voltammetry, applied constant potential and duration of time (t_d) at constant potential. Potential oscillations exhibit various patterns such as periodic, quasi-periodic, mixed-mode oscillations and other different bifurcations, which are greatly effected by the applied constant current and the concentration of HCHO or H₂SO₄. Meanwhile, the oscillatory system has a bistable characteristic with stable states at both low and high potentials. The observed potential and current oscillations are caused by the cyclic formation/removal of intermediate poison CO from the electrode surface during HCHO oxidation. The highly dispersed Pt particles on the surface of Pt-TiO_x/Ti electrode improve the electrocatalytic activity of the electrode, which greatly facilitates the formation of CO by the oxidation of HCHO and the removal of CO by its reaction with hydroxyl radicals (OH). Furthermore, the three-dimensional pore networks of the electrode's TiO_x/Ti support are favorable to the adsorption/desorption of reactants or intermediate product and thus increase the rate of reactions giving rise to electrochemical oscillations.     

Transient mass transfer rate of Cu ion caused by copper electrodeposition with alternating electrolytic current

Copper electrolysis is carried out in a stagnant 0.05 M CuSO₄ aqueous electrolyte under alternating current (AC) condition. Transient mass transfer rate of Cu²⁺ ion caused by copper electrodeposition with AC is studied theoretically and experimentally with the holographic interferometer. The effect of buoyancy convection developing along the vertical plane electrodes on the transient concentration boundary layer (CBL) structure accompanying with AC is focused on. Two different electrode configurations, the horizontal cathode over anode and the vertical electrode settings, are employed for this purpose. The CBL thickness tends to increase over long duration time in the former configuration, while it converges to a steady-state value in the latter. Both calculated and measured concentration profiles in the vertical electrode configuration exhibit the characteristic transient behaviors composed of the pulsating CBL (PCBL) in the vicinity of the cathode surface and the stationary CBL (SCBL) outside the PCBL. The appearance of the SCBL is ascribed to mass transfer by advection, and the overall CBL thickness depends on the hydrodynamic conditions such as the magnitude of buoyancy convection.     

Photocurrent oscillations at the n-GaAs/electrolyte interface

Current-voltage characteristics of the illuminated n-type GaAs electrode in borax solutions were measured. The results indicate that, under certain conditions, a passivating oxide layer is formed on the electrode surface. In the region of negative differential resistance, sustained current oscillations could be observed. A mechanism accounting for these phenomena is proposed.     

Kinetics of the Internal Oxidation of (Mg, Fe)O Solid Solutions

Single crystals of Mg_{1- x} Fe _x O, x = 0.01, have been oxidized in air at temperatures between 1146 and 1389 K to determine the kinetics of the internal oxidation reaction. A two-phase region composed of MgFe₂O₄ precipitates in a (Mg, Fe)O matrix grows inward from the surface as the reaction progresses. The thickness of this layer as a function of time has been determined by optical microscopy; the growth kinetics are parabolic. In addition, an external oxide layer of (Mg, Fe)O grows outward from the original surface. The thickness of this external oxide layer as a function of time was determined by following the displacement of inert markers with Rutherford backscattering spectrometry; the kinetics of the growth of this external layer are also parabolic in time. The parabolic reaction rate constant determined for the growth of the external layer accurately predicts that for the growth of the internally oxidized region.     

纯Fe在酸性AlCl3-EMIC离子液体中的阳极行为

重点研究了纯铁（Fe）在2∶1酸性AlCl₃-氯化1-甲基-3-乙基咪唑（AlCl₃-EMIC）中的阳极行为。通过三电极体系测定了Fe在AlCl₃-EMIC中的阳极极化和不同电位下的电流-时间曲线,利用恒电位溶解计算了Fe溶解的价态,最后通过扫描电子显微镜（SEM）观察了不同电流密度下Fe的溶解形貌。结果表明：Fe表面的氧化膜会阻碍Fe的溶解,在去除氧化膜后,当电位达到-0.35 V时,Fe开始发生活性溶解,产物为Fe（Ⅱ）。Fe的阳极电流密度随电位的增加而增加,达到峰值后显著下降。小电流密度下（如2 mA·cm^-2）,Fe的溶解形貌随时间的延长,呈现先点状腐蚀再均匀腐蚀的特点;而大电流密度下（如15 mA·cm^-2）,Fe电极表面会生成一层固态物质,同时可见清晰的划痕,即不发生明显的腐蚀。     

Electrochemical generators of pulsating or alternating current

This paper concerns the design of three different electrochemical generators of nonsteady current: two generate a pulsating direct current, the third generates an irregular alternating current. The (Fe|NaBrO3(aq.)+H2SO4(aq.)|Pt) generator induces an alternating current in a secondary circuit connected to a transformer. The influence of electrode size and external resistance on current oscillation parameters and on power is shown. The shape of current oscillation in the generators (Fe|NaBrO3(aq.)+H2SO4(aq.)|Pt), (Zn/ZnSO4(aq.)||NaBrO3(aq.)+H2SO4(aq.)|Fe) and (Fe|NaBrO3(aq.) +H2SO4(aq.)|Fe) are also shown and the working of the three generators is explained.     

Modelling and calculation of the current density distribution evolution at vertical gas-evolving electrodes

During industrial electrolysis, for hydrogen, dichloride or aluminium production, there is bubbles creation at one or two electrodes which imply a great hydrodynamic acceleration but also a quite important electrical field disturbance. This disturbance can lead to the modification of the local current density and to anode effects for example. There is few works concerning the local modelling of coupled electro active species transport and electrochemical processes in a biphasic electrolyte. There are also few local experimental measurements in term of chemical composition, temperature or current density which would allow the numerical calculations validation. Nevertheless, effects like the anode effect, particularly expensive on the point of the process efficiency, should need a better understanding. Nowadays, the respective roles of the local temperature increases, the electro active specie composition or the transport properties modification due to bubbles are not known.The goal of the present work is the modelling and the numerical simulation of the vertical electrode configuration for a biphasic electrolysis process. Bubbles presence is supposed to modify the electrical properties, and then the electro active species diffusive transport and the current density. Bubbles are also motion sources for the electrolysis cell flow, and then hydrodynamic properties are strongly coupled with species transport and electrical field. The present work shows hydrodynamic and electrical properties in a laboratory scale electrolysis cell with a vertical electrode. The numerical algorithm used was the finite volume used in the computational fluid dynamic software Fluent^®.     

Reactions in Vapor-Phase Electrolytic Deposition for Preparing Yttria-Stabilized Zirconia Thin Films

The process of vapor-phase electrolytic deposition (VED) for the formation of yttria-stabilized zirconia (YSZ) films has been studied. This technology, which is similar to the electrochemical vapor deposition (EVD) process, is based on electrolytic deposition, using a glow-discharge plasma as the conductive medium. Radio-frequency (rf) glow-discharge plasma is generated in the vapor phase of a metal chloride (ZrCl₄ or YCl₃). A porous electrode layer, which is deposited on the stabilized zirconia layer, is connected to a dc power source. The grounded electrode, which is located in the plasma, is used as a counter electrode to complete the dc circuit. X-ray photoemission spectroscopy and electron probe microanalysis measurements identify the deposited layer to be YSZ that contains 8 mol% of Y₂O₃. This layer is free from pores and cracks, within the scale of scanning electron microscopy observation. The conductivities of the YSZ films that are prepared at different current densities via the VED process are almost equal, and the conductivity values of these thin films are very similar to that of the sintered YSZ pellet. The dependence of the current efficiency on the dc current density is investigated. The current efficiency decreases as the current density increases.     

中间层为聚吡咯的复合电极深度处理焦化废水

电催化技术深度处理焦化废水仍受极板导电性和催化活性制约而无法广泛应用。本文在以掺杂锑的二氧化锡的钛网（Ti/SnO₂-Sb）为底层、以掺杂铈的二氧化铅（PbO₂-Ce）为顶层的二维结构之间插入良好导电性的非离子型高聚化合物聚吡咯（PPy）,形成具有三维结构的Ti/SnO₂-Sb/PPy/PbO₂-Ce电极能够增加电流效率,提高催化活性。分别通过X射线衍射图谱、高分辨率透射电子显微镜、X射线光电子能谱和热重分析来表征电极的结构、元素的化学状态和热稳定性,通过线性扫描伏安法和循环伏安法测试电极的电化学表面行为。分析表明,铈的掺杂使极板羟基自由基（·OH）产生量有较大增幅;PPy中间层的插入增强了电极热稳定性,使电流效率提升至7.55%。电化学分析表明Ti/SnO₂-Sb/PPy/PbO₂-Ce电极具有较高的活性表面积和析氧电位。为使极板达到最佳应用条件,通过响应面法得到一组预测优化参数：电流密度161.18A/m²,电解质浓度5.90g/L,极板间距1.58cm,初始pH为9.05。在最优条件下,对焦化废水的降解效率达到90.47%,能耗为0.787kW·h/g,并据此对可能得催化氧化原理提供预测。     

Water electrolysis under microgravity: Part 1. Experimental technique

Water electrolysis was conducted in both alkaline (25 wt.% KOH, 2 wt.% KOH) and acid (0.1N H₂SO₄) solutions for 8 s under microgravity environment realized in a drop shaft. The gas bubble formation of hydrogen and oxygen on platinum electrodes was observed by CCD camera. In alkaline solutions, a bubble froth layer grew on the electrode surface. Hydrogen bubble size was smaller than that of oxygen. The current density at constant potential decreased continually with time. In spite of the growth of a bubble froth layer on the electrode, the electrolysis never stopped, apparently because fresh electrolyte is supplied to the electrode surface by microconvection induced by the gas bubble evolution. In acid solution, hydrogen gas bubbles frequently coalesced on the cathode surface, yielding a larger average bubble than that of oxygen. The current density did not vary at constant potentials from –0.4 to −0.8 V versus reversible hydrogen electrode (RHE), because the effective electrode surface area was significantly reduced by the larger bubble size compared to alkaline electrolyte. The present experiments indicate that, especially in a microgravity environment, the bubble evolution behavior and the resultant current–potential curves are significantly influenced by the wettability of the electrode in contact with the electrolyte.     

硝基苯在离子液体BPyBF4/H2O中的电化学行为

在离子液体1-丁基吡啶四氟硼酸盐(BPyBF₄)的水溶液中,采用循环伏安法(CV)、计时电流法(CA)、恒电位电解及原位红外光谱法(in-situ FTIRS)等研究了硝基苯在铂电极上的电化学还原行为。研究结果表明:硝基苯在离子液体BPyBF₄/H₂O体系中的还原过程是受扩散控制的,其还原产物主要是偶氮苯,经估算得到硝基苯在该体系中的扩散系数为3.1×10^-7 cm²·s^-1,提高温度和加入一定浓度的水均有利于硝基苯在该体系中的电化学还原。     

Application of conventional activated carbon loaded with dispersed Pt to PEFC catalyst layer

Improvement of the polymer electrolyte fuel cell (PEFC) requires development of highly active electrodes of low cost to facilitate its widespread use. In the present study, the possibility of applying conventional activated carbon particles loaded with Pt to the electrode catalyst layer was tested because the particles were promising in dispersion of Pt and preparation cost. The catalyst layer was formed from the particles and Nafion® and was supported as a thin film on a rotating glassy carbon disk electrode (GC RDE). Activity for oxygen reduction was evaluated by the hydrodynamic voltammetry in perchloric acid to give a current free of the influence of mass transfer in the solution. Compared with a conventional catalyst layer formed from carbon black loaded with Pt, the new catalyst layer exhibited a significant, approximately 6-fold increase in current in the high potential region corresponding to a 100 mV increase in electrode potential. Activity, however, was retarded in the low potential region. This disadvantage was overcome by mixing a conductive agent into the layer and covering it with another layer containing carbon black loaded with Pt. This double catalyst layer exhibited increased activity across all potential regions, indicating the availability of the activated carbon in the electrodes.