Visualizing gas evolution on graphite and oxygen-evolving anodes

Recent progress in material science might soon allow the replacement of the consumable carbon anode by an inert material. This is likely to induce changes in the overall process, and particularly in the gas evolution. Video recordings of oxygen-evolving anodes (SnO₂, Cu, Cu-Ni) and carbon anodes were performed in laboratory electrolysis cells, using direct observation from above, a see-through cell, and radiography techniques. The gas behavior was very different between the two kinds of anodes, and probably linked to the wettability of the material by the electrolyte.     

Further Development on NiFe2O4-Based Cermet Inert Anodes for Aluminum Electrolysis

The new aluminum electrolysis technology based on inert electrodes has received much interest for several decades because of the environment and energy advantages. The key to realize this technique is the inert anode. This article presents China’s recent developments of NiFe₂O₄-based cermet inert anodes, which include the optimization of material performance, the joint between the cermet inert anode and metallic bar, as well as the results of 20 kA pilot testing for a large-size inert anode group. The problems NiFe₂O₄-based cermet inert anodes face are also discussed.     

Preparation and performance of 3D-Pb anodes for nonferrous metals electrowinning in H2SO4 aqueous solution

The effects of Pb²⁺ concentration, current density, deposition time and temperature on Pb deposit structure were investigated. In lower Pb²⁺ concentration (∼0.15 mol/L), carambola-like 3D-Pb structure was constructed, while in higher Pb²⁺ concentration (≥0.30 mol/L), Pb deposits exhibited pyramid-like structure. Furthermore, the oxide layer and anodic potential of carambola-shaped 3D-Pb (Cara-Pb) and pyramid-shaped 3D-Pb (Pyra-Pb) anodes were investigated and compared with those of fresh Pb anode. After 72 h galvanostatic electrolysis (50 mA/cm²) in 160 g/L H₂SO₄ solution, the oxide layer on Pyra-Pb was much thicker than that on Cara-Pb and Pb anodes, which remarkably relieved intercrystalline corrosion of the metallic substrate. Additionally, the oxide layer on Pyra-Pb anode presented a larger surface area and higher PbO₂ content. Hence, Pyra-Pb anode showed a 40 mV lower anodic potential compared to Cara-Pb and Pb anodes. In sum, Pyra-Pb anode had a potential to decrease energy consumption and prolong the life span of traditional Pb anode.     

Optimizing efficiency of polycrystalline p-Si anode organic light-emitting diode

Optimizing efficiencies of organic light-emitting diodes (OLEDs) with a structure of Al/glass/nanometer-thick polycrystalline p-Si (NPPS) anode/SiO₂/N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/tris (8-hydroxyquinoline) aluminum (Alq₃)/4,7-diphenyl-1,10-phenanthroline (BPhen):Cs₂CO₃/Sm/Au were studied. The NPPS anodes were fabricated by magnetron sputtering (MS) Si and Ni layers followed by Ni-induced crystallization of the amorphous Si layers. By adjusting the resistivity of the p-Si target adopted in MS, the electroluminescent efficiency of the OLED was optimized. When the resistivity of the p-Si target is 0.01 Ω·cm, the current and power efficiencies of the NPPS anode OLED reach maximum values of 6.7 cd·A^?1 and 4.64 lm·W^?1, respectively, which are 2.7 and 3.1 times those of the resistivity-optimized bulk p-Si anode counterpart and 2.9 and 3.7 times those of the indium tin oxide (ITO) anode counterpart, and then, the physical reasons were discussed.     

Laboratory-scale performance of a binary Cu-Al alloy as an anode for aluminium electrowinning

A binary Cu-Al alloy (9.4 wt.% Al) has been investigated as a potential inert anode for aluminium electrowinning. Anodes have been tested in a laboratory electrolysis cell both with and without preformed oxides. Electrolysis was conducted in cryolitic electrolytes with anode current densities of 0.5 A cm⁻². The anodes operated satisfactorily as measured by electrical parameters. However, substantial corrosion of the Cu-metal substrate was observed. The external oxide generated on pre-treated anodes was porous and allowed the electrolyte to penetrate through to the Cu-metal whereby corrosion was initiated. An untreated anode formed an in situ surface alumina film, but this did not prevent corrosion of the substrate.     

Variable temperature performance of intermetallic lithium-ion battery anode materials

Although a variety of cathode and electrolyte materials have been studied and commercialized over the past two decades, nearly all commercial cells have used a graphitic carbon anode. Several reasons exist for this choice—including cost, low insertion voltage, and ease of use in the cell manufacturing process. However as uses for lithium-ion batteries expand, alternative anodes that may offer better energy and power capability are being explored. For transportation-oriented purposes, anodes based on simple lithiated Zintl compounds, e.g. Li₁₇Sn₄, or intermetallic insertion anodes offer significant advantages in capacity (volumetric and gravimetric) and stability in the cell environment that make them attractive candidates for future cell chemistries. Within this context, little however is known about how these alternative anode materials perform as a function of temperature, which is important for applications where operation at temperatures as low as −30 °C can be expected. In this study we evaluated a series of intermetallic insertion anodes that operate by a simple metal displacement mechanism. We have found that for Cu₆Sn₅, Ag/Cu₆Sn₅, and Cu₂Sb, the drop-off in performance with temperature is in line with that observed for a commercial graphite-based anode and indicates that additional variables such as cation diffusion through the electrode passivation film or the electrochemical double layer may be playing an important role that is independent of the underlying anode material. We additionally characterized the NiAs-type mineral Sorosite (CuSn_0.9Sb_0.1), as various literature reports had indicated that substitution of antimony for tin eliminated the need for interstitial copper, however powder X-ray diffraction studies of samples made by annealing or high energy ball milling indicated mixed phase samples.     

Pb-Co阳极在含氯硫酸电解液中的电化学行为

采用粉末冶金法制备了不同Co含量(0.5%,1.0%,2.0%,质量分数)的Pb-Co阳极,并与传统的Pb-Ca-Sn阳极进行了对比试验。通过电化学测试研究了阳极在160 g/L H₂SO₄、500 mg/L Cl^-电解液中的电化学行为,研究了恒电流极化72 h后阳极氧化层的物相组成、表面形貌和元素分布。随着Co含量的增加,Pb-Co阳极的电位、电荷传递电阻和析氧过电位逐渐降低。恒电流极化72 h后,Pb-2%Co阳极的析氧过电位比Pb-Ca-Sn阳极低101 mV。此外,在Cl-的存在下,电荷传递得到改善,析氧反应受到抑制,阳极氧化层恶化。     

Stability and morphology of (Ti0·1Ru0·2Sn0·7)O2 coating on Ti in chloralkali medium

Abstract

Today's mixed metal oxide anodes are widely used in the chloralkali industry. Stability is one of the main properties of these anodes because of their high cost. Morphology of mixed metal oxide coating is a determining factor in electrochemical stability of mentioned anodes. In this article the effect of temperature and times of heat treatment on the morphology and electrochemical stability of Ti/(Ti_0·1Ru_0·2Sn_0·7)O₂ anode has been investigated. The anodes were prepared by brushing and thermal decomposition method. Mud cracked morphology appeared on the sample by this process. Increasing the temperature of calcination causes the density of cracks on the surface and electrochemical stability of coating to decrease. Increasing the time had different effects in the first and final calcination times. The anode which was prepared at 450°C, for 10 min in the first calcination time and 1 h in the final calcination time had the highest stability and optimum morphology.     

Fe-30Ni-5NiO alloy as inert anode for low-temperature aluminum electrolysis

Fe-30Ni-5NiO alloy anodes were prepared by a spark plasma sintering process for aluminum electrolysis. NiO nano-particles with the size of ∼20 nm were dispersed in the anodes. The oxidation behaviors of the anodes were investigated at 800°C and 850°C, respectively. The electrolysis corrosion behaviors were tested in a cryolite-alumina electrolyte at a low temperature of 800°C with anodic current densities of ∼0.5 A/cm². The results indicated that the oxidation kinetic of the anodes followed a parabolic law. A continuous Fe₂O₃ film selectively formed on the surface of the anode during the electrolysis process. A semi-continuous Al₂O₃ layer was observed at oxide film/alloy interface, probably caused by an in-situ chemical dissolution process.     

Cup-shaped functionally gradient NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>-based cermet inert anodes for aluminum reduction

Application of inert anode and wet-table cathode technology for aluminum reduction will result in significant energy and environmental benefits, so it has been a research focus for several decades. The candidate as inert anode concentrates on oxide ceramic, cermet, and alloy. This paper reviews briefly the research progress and presents the achievements of Central South University, Changsha, China, in developing an NiFe₂O₄-based cermet inert anode, which includes the preparation and optimization of material performance, the joint between the cermet anode and metallic bar, as well as the results of electrolysis testing for a large inert anode group. At the same time, the problems for NiFe₂O₄-based cermet inert anode faced are discussed.     

Vacuum Carbothermal Reduction for Treating Tin Anode Slime

In this work, a process of vacuum carbothermal reduction was proposed for treating tin anode slime containing antimony and lead. During vacuum carbothermal reduction, the antimony and lead were selectively removed simultaneously by reducing and decomposing the less volatile mixed oxide of lead and antimony into the more volatile Sb₂O₃ and PbO. Then the tin was enriched in the distilland and primarily present as SnO₂. Crude tin was obtained via vacuum reduction of the residual SnO₂. The results showed that 92.85% by weight of antimony and 99.58% by weight of lead could be removed at 850°C for 60 min with 4 wt.% of reductant and air flow rate at 400 mL/min corresponding to the residual gas pressure of 40 Pa–150 Pa. Under these conditions, an evaporation ratio of 52.7% was achieved. Crude tin with a tin content of 94.22 wt.% was obtained at temperature of 900°C, reduction time of 60 min, reductant dosage of 12.5 wt.%, and a residual gas pressure of 40 Pa–400 Pa. Correspondingly, the direct recovery of tin was 94.35%.     

提高KF-AlF3-Al2O3熔体中Cu-Al基阳极的耐腐蚀性

采用恒电流和动电位极化技术研究经预氧化的和未经预氧化的Cu-Al基阳极(Cu-10Al和Cu-9.8Al-2Mn)在KF-AlF₃-Al₂O₃熔体中的阳极行为。将合金在700℃下进行短时间(8 h)氧化,然后在800℃下施以0.4 A/cm²的电流密度进行1 h恒电流极化。测定扫描速率为0.01 V/s的动电位曲线。对在阳极表面冻结的熔体样品进行XRD分析,并在实验后对阳极进行SEM分析,以研究合金表面形成的氧化皮的物相。所有阳极材料的稳态电位都在2.30~2.50 V(vs Al/AlF₃)范围内。根据动电位极化获得的数据计算阳极的腐蚀速率。结果表明,经预氧化的阳极比未经预氧化的阳极具有更低的腐蚀速率。     

Simplified and cost-effective sintering processes for creep resistant Ni-10wt.%Cr MCFC anodes

Two sintering processes were designed for Ni-10wt.%Cr anodes. One included a full oxidation and reduction, referred to as FR hereafter, and the other included a reduction only, referred to as R hereafter. The processes were designed to replace the existing partial oxidation and reduction process, referred to as PR hereafter, which is known to be rather complicated and expensive. The morphologies and creep behaviors of the anodes were also investigated. The anode sintered through a FR process, with an oxidation time of 0.5 hr, showed almost as fine oxide dispersion and high creep resistance as that sintered through a PR process. The creep strain was 3.1% (porosity 60%) after a 100 hr creep test, with no micropores observed in the anode. Conversely, the anode sintered through an R process showed a morphology of coarse oxide dispersion with large Cr₂O₃ particles. Accordingly, the creep resistance of the anode was not as high as that of the anode sintered through the PR or FR processes.     

Progress in Metal-Supported Axial-Injection Plasma Sprayed Solid Oxide Fuel Cells Using Nanostructured NiO-Y0.15Zr0.85O1.925 Dry Powder Anode Feedstock

A composite NiO-Y_0.15Zr_0.85O_1.925 (YSZ) agglomerated feedstock having nanoscale NiO and YSZ primary particles was used to fabricate anodes having sub-micrometer structure. These anodes were incorporated into two different metal-supported SOFC architectures, which differ in the order of electrode deposition. The composition of the composite Ni-YSZ anodes is controllable by selection of the agglomerate size fraction and standoff distance, while the porosity is controllable by selection of agglomerate size fraction and addition of a sacrificial pore-forming material. A bi-layer anode was fabricated having a total porosity of 33% for the diffusion layer and 23% porosity for the functional layer. A power density of 630 mW/cm² was obtained at 750 °C in humidified H₂ with cells having the bi-layer anode deposited on the metal support. Cells having the cathode deposited on the metal support showed poor performance due to a significant number of vertical cracks through the electrolyte, allowing excessive gas cross-over between the anode and the cathode compartments.     

Anodische Korrosionsprozesse auf Stählen in inerten und in oxydierenden Atmosphären

Anodic corrosion processes on steels in inert and oxidising atmospheres The purpose of the investigation here described was to find out to what extent electrochemical techniques lend themselves to the examination of steel corrosion in the presence of molten sulphates and combustion gases. The measured equilibrium potentials of an inert metal electrode are intended to serve for the determination of the redox potential in the salt melt/combustion gases system. If no current is flowing, the stationary potential of a platinum electrode in a sulphate melt at 600° C can be expressed by the equation where E signifies the potential related to the silver/silver sulphate electrode, and p_SO2 p_O2 the partial pressures (in atmospheres) of the two gases in an inert gas (nitrogen + carbon dioxide). The formula permits the conclusion that the electrode reaction can be expressed by the equilibrium condition . The anode currents set up if the potential of a mild steel or pure iron electrode is kept at the above-mentioned temperature viz. ?0.3 V with N₂ + CO₂ + 5% O₂, or + 0.4 V with N₂ + CO₂ + 0.2% SO₂, show that under the test conditions, these metals would be greatly exposed to corrosion. Stainless steels become passive after a few hours although a residual corrosion current at + 0.4 V remains. These observations give rise to the expectation that electro-chemical examinations may well represent a useful means of examining corrosion phenomena caused by molten salts in the presence of combustion gases, so that they merit more detailed investigation.     

Electrooxidation of Cr<Superscript>3+</Superscript> ions in sulfuric acid solutions

The effects the material nature of an anode, the cation radius and the metal-oxygen bond strength in the oxide anode on the rates of Cr³⁺ ion electrooxidation and the anode corrosion. A correlation between the rates of Cr³⁺ cation electrooxidation and corrosion of the anodes made of different metals is revealed. It is shown that the electrocatalytic activity of oxide anodes in the Cr³⁺ electrooxidation is caused by crystallographic and energy factors. The highest electrocatalytic activity is demonstrated by the oxides whose metal cation radius exceeds that of dehydrated Cr³⁺ cation and the M-O bond energy is smaller than the bond energy in Cr₂O₃. The equation suggested takes simultaneously into account the effects of the oxide electrode cation radius and the mean energy of M-O bond on the relative rate of the Cr³⁺ ion electrooxidation.     

The Effect of Pre-oxidation Treatment on Corrosion Behavior of Ni–Cu–Fe–Al Anode in Molten CaCl<Subscript>2</Subscript> Salt

This article presents Ni–Cu–Fe–Al alloy as a novel inert anode used in FFC process (the Fray Farthing Chen) in molten calcium chloride salts for producing titanium. The alloy was prepared by vacuum induction melting; then utilized as anode material in molten CaCl₂ for 16 h at 900 °C. Morphology and the corrosion behavior of the samples were analyzed using scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The product on the cathode was analyzed using X-ray diffraction (XRD). After 16 h electrolysis of anodes, EDS and SEM analysis of the samples showed that the corrosion depth of the non-oxidized sample was shorter. Corrosion attacks more severe for the pre-oxidized sample than the non-oxidized sample, which indicated that the corrosion resistance of outer layer is higher on the non-oxidized sample. The XRD results show that the TiO₂ pellets were successfully reduced to the lower oxides using the Ni–Cu–Fe–Al inert anode.     

Reactions at the corroding nickel electrode in molten sodium carbonate under CO/CO2 atmosphere

Anodic reactions at the CO, CO₂|Ni electrode in molten sodium carbonate at 1000°C are examined in detail. Experimental polarization curves are fitted via a computer graphics procedure to a model employing five anodic reactions with activation, concentration and resistance polarization, and passivation. The resultant empirical parameters are interpreted in terms of absolute rate expressions describing possible anodic reactions. Three of the anodic reactions are found to be in accord with the findings at inert electrodes by previous investigators, i.e. oxidation of CO by two mechanisms and oxidation of carbonate, while the cathodic reaction is consistent with reduction of CO₂. The remaining two anodic reactions were associated with the oxidation of nickel to Ni²⁺ with formation of a NiO film above a passivation potential, and, at higher anodic overpotentials, oxidation of NiO to a higher oxide, e.g. Ni₂O₃. There is an indication of the formation of a third oxide at still higher anodic overpotentials.     

Thermodynamic and kinetic analysis for carbothermal reduction process of CoSb alloy powders used as anode for lithium ion batteries

Thermodynamic calculation and kinetic analysis were performed on the carbothermal reduction process of Co₃O₄-Sb₂O₃-C system to clarify the reaction mechanism and synthesize pure CoSb powder for the anode material of secondary lithium-ion batteries. The addition of carbon amount and thus the purity of CoSb powders were critical to the electrochemical property of CoSb anode. It was revealed that in an inert atmosphere, Co₃O₄ was preferentially reduced to CoO, followed by the reduction of Sb₂O₃ and CoO. CO₂ was the gas product for the reduction of Co₃O₄ and Sb₂O₃, while CO was the gas product for that of CoO. Based on the analysis result, pure CoSb powder without any oxides and residual carbon was synthesized, which showed a higher specific capacity and a lower initial irreversible capacity loss, compared to CoSb sample with residual carbon. This work can be a reference for other carbothermal reduction systems.     

Evaluation of nanometer-sized zirconium oxide incorporated Al—Mg—Ga—Sn alloy as anode for alkaline aluminum batteries

Zirconium oxide nanoparticles with 0.4 wt.% and 0.8 wt.% are incorporated into the Al—0.65Mg—0.05Ga— 0.15Sn (wt.%) alloy anode (base alloy) in order to improve the performance of the resulting anodes. Electrochemical characterization of the reinforced alloys was done by potentiodynamic polarization, electrochemical impedance spectroscopy and galvanostatic discharge and corrosion behavior was evaluated using self-corrosion rate and hydrogen evolution in 4 mol/L KOH solution. The surface morphology of the alloys was also studied using field emission scanning electron microscope (FESEM). The obtained results indicate that the base alloy shows high corrosion rate in 4 mol/L KOH solution by releasing 0.47 mL/(min·cm²) hydrogen gas, whereas the alloy containing 0.8 wt.% ZrO₂ provides the lowest hydrogen evolution rate by releasing 0.32 mL/(min·cm²) hydrogen gas. Furthermore, by increasing zirconium oxide nanoparticles, the corrosion current density of the aluminum anodes is decreased and their corrosion resistance increases significantly compared to the base alloy in alkaline solution. In addition, nanometer-sized zirconium oxide incorporated anodes exhibit the improved galvanic discharge efficiencies, so that 0.8 wt.% nano-zirconium oxide incorporated base alloy displays the highest power density and anodic utilization compared with the others in 4 mol/L KOH solution.