重稀土元素对氢氧化镍电极高温性能的影响

研究了在覆钴球镍中低量添加重稀土元素对镍电极性能的影响。结果表明,60℃时添加1%(原子分数)重稀土的镍电极的1C充放电效率比无添加剂的镍电极有所提高;重稀土氧化物的添加对镍电极的常温高倍率放电性能有一定的负面影响;在常温时,重稀土氧化物的加入增大镍电极氧化-还原反应的电位差,从而增大电极反应的不可逆性,其中添加氧化铥与氧化镥的电极最为明显;在60℃时,添加重稀土氧化物的镍电极的氧化峰与析氧峰区别明显,且镍电极的氧化峰电位与析氧电位普遍负移,还原峰电位普遍正移,显著提高镍电极在高温下的析氧过电位以及可逆性。     

Role of deposition parameters on microstructure and mechanical properties of chromium oxide coatings

Chromium oxide coatings were deposited by reactive magnetron sputtering on high speed steel (HSS) substrate under various oxygen flow rates and radio frequency (RF) powers. The effect of deposition conditions on the microstructure, hardness and critical load of chromium oxide coating failure was studied. The results indicated that a crystalline chromium oxide coating formed at a high oxygen flow rate and a low RF power exhibited a higher hardness and a lower critical load as compared to a chromium oxide coating with an amorphous microstructure.     

Pb-0.3%Ag/Pb-CeO2复合阳极材料电化学性能

采用双脉冲电沉积,在Pb-0.3%Ag(质量分数,下同)合金基体表面制备了Pb-0.3%Ag/Pb-CeO2复合阳极材料,研究了不同正向脉冲平均电流密度(2~5 A·dm-2)和镀液中CeO2颗粒浓度(0~20 g/L)下制备的复合阳极材料电化性能,在50 g·L-1 Zn2+,150 g·L-1 H2SO4,35℃溶液中测试了阳极极化曲线、循环伏安曲线和塔菲尔曲线,获得了析氧动力学参数、伏安电荷、腐蚀电位和腐蚀电流。结果表明:在正向脉冲平均电流密度为3 A/dm2和镀液中CeO2颗粒浓度为15 g/L下制备的Pb-0.3%Ag/Pb-CeO2复合阳极材料在[ZnSO4+H2SO4]溶液中具有较高的电催化活性,较低的析氧过电位,较好的电极反应可逆性和耐腐蚀性。在[ZnSO4+H2SO4]溶液中,复合阳极材料在测试电流密度500 A/m2下的析氧过电位为1.134V,比Pb-1%Ag合金降低37 mV;腐蚀电流为1.97×10-4 A,明显低于Pb-1%Ag合金,表现出了良好的耐腐蚀性能。     

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。     

Electrochemical oxidation of binary copper-nickel alloys in cryolite melts

Anodic oxidation of copper, nickel and two copper-nickel alloys was studied in cryolite melts at 1000 °C. In an oxide-free melt, anodic dissolution of each material was observed, and the dissolution potential increases with the content of copper. SEM characterization of a Cu55-Ni45 alloy showed that nickel is selectively dissolved according to a de-alloying process. In an alumina-containing melt, a partial passivation occurs at the copper-containing electrodes, at potentials below the oxygen evolution potential. A passive film forms on the copper electrode, while on the nickel electrode no dense oxide layer develops. Copper-nickel alloys were found to form a mixed oxide layer. At higher potentials, the formation of oxygen bubbles on the electrodes results in a degradation of the passive films and a strong corrosion.     

Active Ti/SnO2 anodes for pollutants oxidation prepared using chemical vapor deposition

The tin oxide films were successfully deposited on Ti substrates by chemical vapor deposition (CVD) using a gas phase mixture of SnCl₄ and H₂O as a precursor at 550 °C. The physicochemical and electrochemical properties as well as the electrocatalytic activity of the Ti/SnO₂ electrodes prepared were investigated. It was found that the new electrodes had compact microstructure, high overpotential for oxygen evolution, and superior activity for pollutants oxidation. Over 95% chemical oxygen demand (COD) removal was achieved for oxidation of both phenol and oxalic acid, with current efficiencies (CE) of 59% for phenol and 62% for oxalic acid obtained.     

溶胶凝胶法制备Ru-Ir-Sn-Ti阳极涂层及其电化学性能研究

采用溶胶凝胶法制备Ru-Ir-Sn-Ti阳极涂层,对涂层进行析氯电位、析氧电位、极化曲线、循环伏安曲线、电化学交流阻抗等电化学测试以及强化电解寿命测试,并与热分解法制备的阳极涂层进行对比。结果表明:与热分解法制备的阳极涂层相比,溶胶凝胶法制备的Ru-Ir-Sn-Ti阳极涂层具有较低的析氯电位、较高的析氧电位、良好的电催化活性和较长的强化电解寿命。     

Cyclic Oxidation and Hot Corrosion Behaviors of Gradient CoNiCrAlYSi Coatings Produced by HVOF and Diffusional Processes

The transient oxidation behaviour of a nickel-base superalloy in different oxygen partial pressures studied using electron and ion microscopy showed that at high pO₂, a triple-layered oxide developed: outer nickel oxide, then a complex aluminium-chromium oxide, and inner alumina layer. Lower pO₂ produced only alumina, as reduced oxygen activity suppressed nickel oxide formation. An aluminium-depleted region in the alloy with width proportional to pO₂ was observed.     

Vacuum plasma spraying of high-performance electrodes for alkaline water electrolysis

Electrode coatings for advanced alkaline water electrolysis were produced by applying the vacuum plasma spraying (VPS) process. The characteristics of the used VPS equipment that were essential for the development of effective electrocatalytic electrode layers are presented. Molybdenum-containing Raney nickel coatings were applied for cathodic hydrogen evolution, and Raney nickel/Co₃O₄ matrix composite layers were developed for the anodic oxygen evolution reaction. For the preparation of Raney nickel coatings, a precursor alloy such as Ni-Al was sprayed that had to be leached subsequently in caustic solution to remove the aluminum content, forming a porous, high-surface-area nickel layer. The spray powders and the resulting VPS layers were studied by metallography, x-ray diffraction (XRD), and scanning electron microscopy/energy dispersive analysis by x-ray (SEM/EDX). For spraying of thermally sensitive oxide electrocatalysts (e.g., Co₃O₄), special process conditions involving plasma-chemical effects (reactive plasma spraying) had to be developed. The electrocatalytic activity of the electrode coatings was investigated by performing polarization curves free of ohmic losses (IR-free) and long-term tests under conditions of continuous and intermittent operation, which showed excellent electrochemical properties.     

Passivity of Nickel electrodes in presence of the inhibitor PAB

The passivity of nickel electrodes is investigated at high potentials in absence and presence of the inhibitor 2-pentyl-aminobenzimidazole (PAB). At high potentials, the electrode is covered by a thick film of NiOOH. Various states of the 3-valent oxide film can be distinguished: Without inhibitor (3o), with an outer layer of inhibitor (3out), with an almost constant concentration profile in the total film (3tot) and a concentration gradient of inhibitor in the film caused by diffusion (3diff). Under steady state conditions, the films 3o, 3out and 3tot can be distinguished by the rate of anodic oxygen evolution, and the electrode capacity. Moreover, the reduction and reoxidation capacity of the electrode decreases from 3o to 3out and 3tot. If the film 3o is reduced and reoxidized in presence of PAB, the redox capacity decreases simultaneously with the electrode capacity due to the formation of 3diff. The role of the inhibitor is due to the formation of a thick polymer film on top of the oxide as well as to the formation of a nickel hydroxide/PAB complex. The outer polymer film has a good proton conductivity and presumably a good electron conductivity. It is concluded that the anodic oxygen evolution takes place at the inner boundary between the oxide and PAB film. The inhibition of local corrosion is probably due to formation of the outer polymer film. XPS measurements verify the expected concentration profiles of PAB in the oxide and on top of it. The PAB-film contains a lot of water, and within the passive film PAB causes a substitution of O^2? by OH^?.     

磷酸盐前驱体对泡沫镍上生长的镍/铁羟基氢氧化物形貌及析氧反应性能的影响（英文）

通过共沉积法和电化学激活法在泡沫镍网上生长制备镍/铁羟基氢氧化物纳米片。研究发现,不同磷酸盐前驱体(Na₃PO₄、Na₂HPO₄和NaH₂PO₄)对最终催化剂的形貌及析氧反应活性有不同的影响。使用Na₂HPO₄制备的镍/铁羟基氢氧氯化物纳米片在1 mol/L KOH溶液中电流密度达到50 mA/cm²时所需过电位为205 mV,Tafel斜率低至30 mV/dec,并可以在后续稳定性测试中保持稳定20 h。     

Solution combustion synthesis of high-entropy metal spinel oxide as oxygen evolution reaction catalyst

High-entropy metal spinel oxide(HEO) is proved to be a promising oxygen evolution reaction(OER) catalyst with high catalytic performance and stability.A short routine synthesis process based on solution combustion synthesis was proposed to prepare(Co_0.25Ni_0.25Mn_0.25Zn_0.25)Fe₂O₄ spinel HEO in this work.During the process,the products were rapidly synthesized and melted due to the high-temperature reaction,and then quickly crystalli...     

碳烟颗粒掺杂铅基复合阳极的制备及电化学性能研究

本文采用一种快速、低成本的方法制得纳米碳材料-碳烟颗粒(C_H),并通过粉末冶金和机械合金化技术制备出铅/碳烟颗粒(Pb/C_H)复合阳极材料,利用纳米碳材料高比表面积和高催化活性等优点,提高铅基阳极的析氧电催化性。使用场发射扫描电子显微镜(FE-SEM)、傅里叶红外光谱(FTIR)、循环伏安曲线(CV)和线性扫描伏安曲线(LSV)等测试进行表征。C_H呈疏松的球链状,具有丰富的羰基和羟基功能团,是良好的电子和质子传递载体。随着C_H含量增加, Pb/C_H复合阳极的析氧超电位降低。Pb/1.5 wt.% C_H复合阳极与纯Pb和传统Pb/0.75 wt.% Ag阳极相比,其表观交换电流密度分别提高3和2个数量级。在模拟锌电积条件下,其析氧电位低于铅银合金阳极20 mV,较纯铅阳极降低133 mV,具有优异的析氧电催化活性。     

不同酸处理对钛基体性能的影响

本研究在保持酸度和温度一致的条件下分别用草酸、硫酸及盐酸对TA2钛基体进行刻蚀处理,研究不同种类酸处理对钛基体及后续电极性能的影响。研究表明:钛基体在草酸和硫酸中的质量损失率要大于在盐酸中的损失率。金相及SEM观察表明:草酸对钛基体刻蚀效果最好,刻痕细致均匀。强化寿命测试结果显示:经草酸处理后的Sn-Sb氧化物涂层钛基电极强化寿命最长。循环伏安测试结果表明:3种酸刻蚀过后的Sn-Sb氧化物涂层电极的析氧电位基本相同,表明酸刻蚀对于该电极的析氧电位影响不大。     

离子液体[Emim]BF4改性二氧化铅电极的制备与表征

采用电沉积法制备了离子液体[Emim]BF₄改性PbO₂电极. 通过电化学氧化降解苯酚实验对电极催化性能进行了考察, 发现苯酚模拟废水的COD去除率符合一级反应动力学, [Emim]BF₄改性PbO₂电极的速率常数为0.00739 min_-1, 明显高于未改性PbO₂电极的速率常数0.00383 min_-1. 通过扫描电镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)对电极表面结构进行表征. 结果显示, 在加有离子液体[Emim]BF₄的电积溶液中沉积得到的钛基PbO₂涂层表面致密规整、结晶度高、晶格氧含量高. 通过莫特-肖特基(Mott-Schottky)曲线、稳态极化和线性扫描伏安法(LSV)考察了电极的电化学性质. 稳态极化实验表明改性电极的析氧过电位相比未改性电极有明显提高, 对莫特-肖特基曲线的分析表明, 改性电极表面氧空位含量相比未改性电极有很大降低. 通过与未改性电极结构和电化学性质的对比研究, 得出改性电极催化活性的提高主要是由于其氧空位含量较低, 从而降低了氧化物电极表面发生羟基自由基(?OH)向晶格氧(O_lat)转移的发生率.     

Depolarised gas anodes for aluminium electrowinning

Consumable carbon anodes are used in the electrowinning of aluminium by the Hall-Heroult process.Emissions of CO2 may be eliminated by introducing an inert oxygen evolving anode,which however will require a higher anode potential.An alternative approach is to use a natural gas or hydrogen gas anode to reduce the CO2 emissions and lower the anode potential.Preliminary laboratory experiments were carried out in an alternative molten salt electrolyte consisting of CaCl2-CaO-NaCl at 680 °C.Porous anodes of platinum and tin oxide were tested during electrolysis at constant current.The behaviour of inert anode candidate materials such as tin oxide and nickel ferrite were also studied.     

The contribution of different types of point defects to diffusion in CoO and NiO during oxidation of the metals

Starting from a general model for the defect structure of nickel and cobalt oxides, the concentrations and diffusion coefficients of the major defects in these oxides are determined as functions of temperature and oxygen pressure. At the higher oxygen pressures, the majority of cation defects are mononegative metal ion vacancies while at lower oxygen pressures appreciable concentrations of dinegative metal ion vacancies are present. It is shown that it is highly probable that the onion defects are dipositive oxygen vacancies. However, these are minority defects over the whole stability range of the oxides. It is not possible with the methods discussed here to determine their individual concentrations and diffusion coefficients. On the basis of this defect structure, a model for the oxidation of Co and Ni is proposed; the deductions from this model are compared with experimental results and good agreement is observed. It is shown that more than one type of defect contributes to the total transport through the oxide. For cobalt, these are mono- and dinegative metal ion vacancies; for nickel, dipositive oxygen vacancies also make a significant contribution.This work is part of a thesis submitted by G. J. Koel to the Twente University of Technology.     

The oxidation of chromium- and nickel-implanted nickel at high temperatures

The isothermal oxidation behaviour in oxygen of nickel, implanted with nickel and chromium ions, has been studied in the range 950–1150°C using kinetic and electronoptical techniques. Implantation with nickel ions has a significant and lasting effect on the oxidation kinetics and on the morphology and grain configuration of the NiO scale. The oxide grains are generally smaller, more facetted and more mismatched for the implanted surfaces and there is more extensive stress generation during oxide growth. After an initially slower rate, the oxide on the implanted surfaces develops at a faster rate than that on the unimplanted surfaces, particularly at the higher temperatures. Implantation with chromium ions inhibits the initial development of the NiO scale. However, subsequently, the oxidation rate is more rapid for the implanted surfaces and increases progressively with increasing chromium ion dose. The results can be accounted for in terms of doping of the NiO and the much decreased grain size of the oxide. It is concluded that short-circuit grain boundary diffusion processes, as well as bulk lattice diffusion of Ni²⁺ ions, are important in the oxidation of nickel at high temperatures.     

钛基镍钴合金电极的制备及析氢性能

目的降低电极的析氢过电位,提高析氢性能,从而降低电解水制氢的成本,促进氢储能技术的发展。方法通过异相共沉积法,制备了镍钴合金电极。利用场发射扫描电镜(SEM)、电化学交流阻抗(EIS)对纯镍电极及镍钴合金电极进行表征,采用阴极极化曲线(LSV)探究了电沉积液中Ni/Co元素的比例、电沉积电位及电沉积时间对镍钴合金电极析氢性能的影响。结果 SEM结果揭示了纯镍电极及镍钴合金电极表面分别是粒径约为100 nm左右的镍颗粒和镍钴颗粒。EIS结果说明了镍钴合金电极的导电性能优于纯镍电极。此外,纯镍电极、镍钴合金电极的阴极极化曲线测试表明在电流密度为30 mA/cm~2时,镍钴合金电极的析氢过电位比纯镍电极降低55 mV,降低了近20%。结论通过异相共沉积法制备镍钴合金电极,制备方法简单、方便、快速,其析氢性能优于纯镍电极。镍钴合金电极的最优制备工艺条件为:NiSO_4·6H_2O 27 g/L,CoSO_4·7H_2O_3 g/L,H_3BO_3 10 g/L,Na_2SO_4 10 g/L,柠檬酸10 g/L,十二烷基硫酸钠0.1 g/L,pH值4.0,电沉积电位-1.3 V,电沉积时间10 s。     

Early stage SCC initiation analysis of fcc Fe-Cr-Ni ternary alloy at 288 °C: A quantum chemical molecular dynamics approach

The initiation of stress corrosion cracking in fcc Fe-Cr-Ni ternary alloys was studied by means of quantum chemical molecular dynamics at 288 °C. This study showed that the iron and chromium atoms segregate faster than nickel atoms at the surfaces. The atomic model showed that nickel enrichment occurred at the inner oxide layer. The binding energy helps reduce the mobility of the nickel atoms. The surface morphology showed that Fe, Cr, and O accumulate on the very top surface while Fe, Cr, Ni, and O bonding takes place beneath this revealing the formation of an outer and inner oxide film. The diffusion of oxygen and hydrogen into the surface increases when it is under strain. The deeply diffused hydrogen becomes negatively charged by taking electron from metal atoms. Consequently, the process weakens the metallic bonds following with the result that oxygen can diffuse easily into the surface. It seems that hydrogen effectively functions as an oxygen carrier. This kind of reaction process can take place in the molecular domain of a crack tip and thus play a vital role in initiating the SCC process.