Passivity characteristics on Ni(Cr)(Fe)SiB glassy alloys in phosphate solution

Passivity characteristics of three nickel-metalloids glassy alloys (Ni_92.3Si_4.5B₃₂, Ni_82.3Cr₇Fe₃Si_4.5B_3.2 and Ni_75.5Cr₁₃Fe_4.2Si_4.5B_2.8) and the immersion time effect on the corrosion resistance were carried out by AC and DC electrochemical methods and SEM and XPS analyses. The study also focused on the effect of H₃PO₄ concentration and its role on the corrosion rate, passivation ability of nickel base glassy alloys surface. The present investigation revealed (i) corrosion resistance of Cr-free alloy shows pseudo passivity at all examined H₃PO₄ concentrations, (ii) high corrosion resistance of Cr contains alloys due to the formation of protective layer of chromium oxyhydroxide on the surface which acts as a diffusion barrier against alloy dissolution, (iii) the negative resistance observed in the case Ni_75.5Cr₁₃Fe_4.2Si_4.5B_2.8 alloy revealed the sudden transition of metal/solution interface from a state of active dissolution to the passive state.     

混合稀土对A_2B_7型储氢合金结构和电化学性能的影响

采用感应熔炼方法制备了A2B7型La0.83-0.5x(Pr0.1Nd0.1Sm0.1Gd0.2)xMg0.17Ni3.1Co0.3Al0.1(x=0~1.66)储氢合金,并在He+Ar气氛和1 173 K下进行退火处理。通过X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学方法,研究了混合稀土(Pr,Nd,Sm,Gd)替代La元素对合金物相结构和电化学性能的影响。合金相结构分析表明,混合稀土含量对合金组成和相结构有重要的影响,随混合稀土含量x的增加,合金中主相A2B7型(2H-Ce2Ni7型+3R-Gd2Co7型)相丰度逐渐增多,其中2H-Ce2Ni7型相丰度先增多后减少,3RGd2Co7型相丰度则逐渐增加,主相晶胞参数随x增加而减小。电化学结果表明,随混合稀土含量增加,放氢平台压逐渐升高,合金电极的最大放电容量和循环稳定性均呈先增大后减小的规律,其中x=0.4合金电极具有最高的电化学放电容量(389.8 mAh·g-1)和最佳的循环寿命(S100=91.30%);合金电极的高倍率放电性能(HRD)则随x的增加获得显著提高。适量的混合稀土替代量可显著改善合金电极的综合电化学性能。     

混合稀土对A2B7型储氢合金结构和电化学性能的影响

采用感应熔炼方法制备了A₂B₇型La_0.83-0.5x（Pr_0.1Nd_0.1Sm_0.1Gd_0.2）_xMg_0.17Ni_3.1Co_0.3Al_0.1（x=0~1.66）储氢合金,并在He+Ar气氛和 1 173 K下进行退火处理。通过X射线衍射（XRD）、扫描电子显微镜（SEM）和电化学方法,研究了混合稀土（Pr,Nd,Sm,Gd）替代La元素对合金物相结构和电化学性能的影响。合金相结构分析表明,混合稀土含量对合金组成和相结构有重要的影响,随混合稀土含量x的增加,合金中主相A₂B₇型（2H-Ce₂Ni₇型+3R-Gd₂Co₇型）相丰度逐渐增多,其中2H-Ce₂Ni₇型相丰度先增多后减少,3R-Gd₂Co₇型相丰度则逐渐增加,主相晶胞参数随x增加而减小。电化学结果表明,随混合稀土含量增加,放氢平台压逐渐升高,合金电极的最大放电容量和循环稳定性均呈先增大后减小的规律,其中x=0.4合金电极具有最高的电化学放电容量（389.8 mAh·g^-1）和最佳的循环寿命（S₁₀₀=91.30%）;合金电极的高倍率放电性能（HRD）则随x的增加获得显著提高。适量的混合稀土替代量可显著改善合金电极的综合电化学性能。     

X-ray photoelectron spectroscopic and electrochemical impedance spectroscopic analysis of RuO2-Ta2O5 thick film pH sensors

The paper reports on investigation of the pH sensing mechanism of thick film RuO₂-Ta₂O₅ sensors by using X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Interdigitated conductimetric pH sensors were screen printed on alumina substrates. The microstructure and elemental composition of the films were examined by scanning electron microscopy and energy dispersive spectroscopy. The XPS studies revealed the presence of Ru ions at different oxidation states and the surface hydroxylation of the sensing layer increasing with increasing pH. The EIS analysis carried out in the frequency range 10 Hz–2 MHz showed that the electrical parameters of the sensitive electrodes in the low frequency range were distinctly dependent on pH. The charge transfer and ionic exchange occurring at metal oxide-solution interface were indicated as processes responsible for the sensing mechanism of thick film RuO₂-Ta₂O₅ pH sensors.     

Structural and electrochemical properties of high-capacity Ml-Mg-Ni-based hydrogen storage alloys

The Ml-Mg-Ni-based (Ml = La-rich mixed lanthanide) hydrogen storage alloy Ml_0.88Mg_0.12Ni_3.0-Mn_0.10Co_0.55Al_0.10 was prepared by inductive melting. The micro-structure was analyzed by XRD and SEM. The alloy consists mainly of CaCu₅-type phase, Ce₂Ni₇-type phase and Pr₅Co₁₉-type phase. The electrochemical measurements show that the maximum discharge capacity is 386 mAh/g, 16.3% higher than that of the commercial AB₅-type alloy (332 mAh/g). At discharge current density of 1 100 mA/g, high rate dischargeability is 62%, while that of the AB5-type alloy is only 45%. The discharge capacity decreases to 315 mAh/g after 300 charge/ discharge cycles, 81.5% of the maximum discharge capacity. __________ Translated from Journal of Xi’an Jiao Tong University, 2008, 42(3) (in Chinese)     

Electrochemical study of spinel oxide systems with nominal compositions Ni1− x Cu x Co2O4 and NiCo2− y Cu y O4

Studies on the electrochemical behaviour of Ni_{1− x} Cu _x Co₂O₄ (x ≤ 0.75) and NiCo_{2− y} Cu _y O₄ (y ≤ 0.30) electrodes in 5 mol dm⁻³ KOH aqueous solutions are presented. The oxide layers have been prepared by thermal decomposition of aqueous nitrate solutions on nickel supports at 623 K. Powder samples were also prepared by thermal decomposition under the same conditions. The powder samples and the oxide layers were characterised by X-ray powder diffraction. The influence of the copper content on the voltammetric response of the electrodes and activity towards oxygen evolution reaction is analysed and correlated with the surface composition of the electrodes by means of X-ray photoelectron spectroscopy data. The analysis of the results reveals that the presence of Cu affects the electrode behaviour and its influence depends on which cation has been replaced. Received: 22 February 1999 / Accepted: 26 October 1999     

层状锰酸锂衍生物的阳离子价态与锂电池的电化学性能研究

采用溶胶-凝胶法, 通过锂盐、镍盐、钴盐与锰盐生成锂镍钴锰氧化合物的前驱体, 随后采用高温固相法合成了Li(Mn_1/3Co_1/3Ni_1/3)O₂. 借助于X射线光电子能谱(XPS)、X射线衍射(XRD)、循环伏安(CV)及充放电测试等现代测试手段研究了材料的晶型结构、离子价态及电化学性能. 前驱体经950 ℃煅烧可获得晶体结构完整、晶胞参数为a＝0.2864 nm, c＝1.4235 nm的六方层状Li(Mn_1/3Co_1/3Ni_1/3)O₂化合物; XPS结果表明Li(Mn_1/3Co_1/3Ni_1/3)O₂化合物表面上的Mn, Ni和Co分别以Mn^4＋, Ni^2＋和Co^3＋存在; 材料的高温放电比容量比室温要高, 在55 ℃下, 在2.5～4.6 V电压范围内, 电流密度为28 mA/g时材料首次放电容量195 mAh/g, 循环10次后容量保持在170 mAh/g; 循环伏安曲线上3.7 V和4.4 V的氧化还原过程对应于Ni^2＋/4＋和Co^3＋/4＋氧化还原电对的反应.     

The effect of Nb and Ni addition on crystallization behavior of amorphous–nanocrystalline Fe–Cr–B–Si alloys

The crystallization behavior of amorphous Fe–Cr–B–Si alloys in the presence of Ni and Nb elements was the goal of this study. In this regard, four different amorphous–nanocrystalline Fe₄₀Cr₂₀Si₁₅B₁₅M₁₀ (M=Fe, Nb, Ni, Ni_0.5Nb_0.5) alloys were prepared using mechanical alloying technique up to 20 h. Based on the achieved results, in contrast to Fe₅₀Cr₂₀Si₁₅B₁₅ alloy, the amorphous phase can be successfully prepared in the presence of Ni and Nb in composition. Although the crystallization mechanism of prepared amorphous phase in different alloys was the same, the Fe₄₀Cr₂₀Si₁₅B₁₅Nb₁₀ alloy showed higher thermal stability in comparison with other samples. The crystallization activation energy of this amorphous alloy was estimated about 410 kJ mol^?1 which was much higher than Fe₄₀Cr₂₀Si₁₅B₁₅Ni₁₀ (195.5 kJ mol^?1) and Fe₄₀Cr₂₀Si₁₅B₁₅Ni₅Nb₅ (360 kJ mol^?1) samples. The calculated values of Avrami exponent (1.5 < n < 2.2) indicated that the crystallization process in different alloying systems is the same and to be governed by a three-dimensional diffusion-controlled growth.     

Investigation on Electronic Property of Passive Film on Nickel in Bicarbonate/Carbonate Buffer Solution

The electronic properties of passive film formed on nickel in bicarbonate/carbonate buffer solution were studied by electrochemical impedance spectra (EIS) and Mott‐Schottky plot. The film composition was analyzed by X‐ray photoelectron spectroscopy (XPS). The results showed that passive film exhibited p‐type semi‐conductive character, and the acceptor density (N_A) decreased with increasing potential, prolonging time, decreasing temperature, increasing pH value and decreasing chloride/sulfur ions concentration. The transfer resistance and film resistance increased with the above factors changing. XPS results showed that passive film was composed of NiO and a little amount of Ni₂O₃.     

Ni-Mn共掺杂高电压钴酸锂锂离子电池正极材料

以金属硫酸盐为原料,NaOH和NH₃·H₂O为沉淀剂,用共沉淀法合成了Co_0.9Ni_0.05Mn_0.05(OH)前驱体,再进行配锂并通过高温固相法合成了Ni-Mn共掺杂高电压钴酸锂锂离子电池正极材料Li(Co_0.9Ni_0.05Mn_0.05)O₂。用X射线衍射(XRD)、扫描电镜(SEM)、 循环伏安(C-V)、交流阻抗(EIS)和充放电测试研究样品的晶体结构、形貌和电化学性能。结果表明Ni-Mn共掺杂正极材料Li(Co_0.9Ni_0.05Mn_0.05)O₂有优秀的电化学性能:在3.0~4.4 V和3.0~4.5 V区间,0.5C倍率下首次放电比容量分别为162 mAh·g^-1和187 mAh·g^-1,循环100次后容量保持率分别为94%和94%。     

Ni-Mn共掺杂高电压钴酸锂锂离子电池正极材料

以金属硫酸盐为原料,Na OH和NH3·H2O为沉淀剂,用共沉淀法合成了Co0.9Ni0.05Mn0.05(OH)前驱体,再进行配锂并通过高温固相法合成了Ni-Mn共掺杂高电压钴酸锂锂离子电池正极材料Li(Co0.9Ni0.05Mn0.05)O2。用X射线衍射(XRD)、扫描电镜(SEM)、循环伏安(C-V)、交流阻抗(EIS)和充放电测试研究样品的晶体结构、形貌和电化学性能。结果表明Ni-Mn共掺杂正极材料Li(Co0.9Ni0.05Mn0.05)O2有优秀的电化学性能:在3.0~4.4 V和3.0~4.5 V区间,0.5C倍率下首次放电比容量分别为162.5 m Ah·g-1和185 m Ah·g-1,循环100次后容量保持率分别为94.4%和93.7%。     

Bimetallic Co–Ni/TiO<Subscript>2</Subscript> catalysts for selective hydrogenation of cinnamaldehyde

Bimetallic Co–Ni catalysts in the composition range Co_(1?x)Ni_x with x?=?0.0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8 and 1.0, with total metal loading of 15% w/w and supported on TiO₂-P25, have been prepared by chemical reduction of the metal acetates by glucose in aqueous alkaline medium and characterized by XRD, TEM, TPR, XPS and H₂-TPD techniques. Selective hydrogenation of cinnamaldhyde (CAL) to hydrocinnamaldehyde (HCAL), cinnamyl alcohol (COL) and hydrocinnamyl alcohol (HCOL) has been investigated at 20 bar pressure, in the temperature range 120–140 °C. Co/Ni crystallite sizes in the range 6.0?±?1 nm are observed by TEM. TPR and XPS results indicate the formation of nanoscale Co–Ni alloys, which tend to weaken M–H bond strength, as revealed by H₂-TPD measurements. Ni/TiO₂ displays very high conversion of CAL (86.9%) with high selectivity (78.7%) towards HCAL formation at 140 °C. Co/TiO₂, on the other hand, exhibits relatively lower CAL conversion (55%) and higher selectivity (61.3%) for COL formation at the same temperature. However, bi-metallic Co–Ni catalysts in the composition range x?=?0.3–0.6 display very high conversion (>?98%) due to alloy formation and weakening of M–H bonds. Bimetallic Co_0.7Ni_0.3 catalyst displays high conversion of CAL (98.1%) and high selectivity (82.9%) towards HCOL. Overall CAL hydrogenation activity at 140 °C, when expressed as TOF, displays a maximum value at the composition Co_0.5Ni_0.5. Activity and selectivity patterns have been rationalized based on the reaction pathways observed on the catalysts and the influence of Co–Ni alloy formation and M–H bond strength. Thus, a synergetic effect, originating from an appropriate composition of base metal catalysts and reaction conditions, could result in hydrogenation activity comparable with noble metal based catalysts.     

A more general method for ranking the enrichment of alloying elements in passivation films

The corrosion of alloys is often characterized by an enrichment of one or other of the alloying elements within the surface oxide or even within the underlying metallic phase. For some three decades the measurement of such surface enrichment has been one of the most important contributions made by XPS to corrosion science. X‐ray photoelectron spectroscopy permits the composition of the oxide film to be distinguished from that of the metallic surface underlying the oxide so that both can be determined independently. In the mid‐1970s these measurements were crucial in showing that the selective enrichment of chromium in the electrochemical passivation of stainless steel occurred by selective dissolution of iron, and not by selective oxidation of chromium. Measurements of this type are important also in active corrosion, where there is no stable oxide film, as in studies of dealloying phenomena. The literature now contains numerous cases, many published by one of us (K.A.) based on studies of novel alloys produced in the Institute for Materials Research at Sendai. Typically, measurements are made for a series of binary compositions A_xB_y ranging from A‐rich to B‐rich alloys, in media that reflect the intended use of the alloy. The results are normally produced in the form of plots of cation composition Aⁿ⁺/(Aⁿ⁺ + B^m+) against bulk composition A/(A + B) or, in the case of dealloying, as A_surface/(A_surface + B_surface) against the bulk composition. Although graphical representation is useful in giving the full picture of the alloy's behaviour, it is not so useful in cataloguing or indexing performance. In this paper we suggest a means to give a rank or performance index as a single number that will characterize the behaviour of the alloy over a wide range of composition for a given medium or exposure condition. The rank number does not imply that any particular mechanism of enrichment is in operation; in various cases of corrosion it might occur by selective precipitation (FeOOH on steels, CuO on cupronickels), by selective dissolution (dezincification of brass) or by preferential incorporation of ions in a passivating oxide or oxyhydroxide (Cr³⁺ on stainless steels). Although the rank has no mechanistic implications, it is useful within a known class of mechanistic behaviour for indicating the magnitude of the effect and thus for enabling an XPS measurement to be indicative of wanted, or unwanted, behaviour. For example, the rank number could be useful in indicating, perhaps from a single alloy composition, whether a degree of passivation is likely to be achieved for that mix of metallic elements. Copyright © 2004 John Wiley & Sons, Ltd.     

Improvement of high-voltage cycling behavior of Li(Ni1/3Co1/3Mn1/3)O2 cathodes by Mg, Cr, and Al substitution

To improve the electrochemical properties of Li[Ni_1/3Co_1/3Mn_1/3]O₂ at high charge end voltage (4.6 V), a series of the mixed transition metal compounds, Li(Ni_1/3Co_{1/3 − x} Mn_1/3M _x )O₂ (M = Mg, Cr, Al; x = 0.05), were synthesized via hydroxide coprecipitation method. The effects of doping Mg, Cr, and Al on the structure and the electrochemical performances of Li[Ni_1/3Co_1/3Mn_1/3]O₂ were compared by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge–discharge tests, and electrochemical impedance spectroscopy. The XRD results show that all the samples keep layered structures with R3m space group as the Li[Ni_1/3Co_1/3Mn_1/3]O₂. SEM images show that all the compounds have spherical shapes and the Cr-doped sample has the largest particle size. Furthermore, galvanostatic charge–discharge tests confirm that the Cr-doped electrode shows improved cycling performance than the undoped material. The capacity retention of Li(Ni_1/3Co_{1/3 − 0.05}Mn_1/3Cr_0.05)O₂ is 97% during 50 cycles at 2.8∼4.6 V. The improved cycling performance at high voltage can be attributed to the larger particle size and the prevention of charge transfer resistance (R _ct) increase during cycling.     

High-capacity Li(Ni0.5Co0.2Mn0.3)O2 lithium-ion battery cathode synthesized using a green chelating agent

Quasi-spherical (Ni_0.5Co_0.2Mn_0.3)(OH)₂ precursor is prepared via a continuous hydroxide co-precipitation method using sodium lactate as the green chelating agent. A layered structure Li(Ni_0.5Co_0.2Mn_0.3)O₂ is synthesized by calcining the mixture of as-prepared precursor and Li₂CO₃ in air. X-ray photoelectron spectroscopy (XPS) indicates that Ni, Co, and Mn exist in the oxidation states of +2/+3, +3 and +4, respectively. The influence of calcination temperature on the structural, morphological, electrochemical properties of Li(Ni_0.5Co_0.2Mn_0.3)O₂ oxides are investigated in detail. As a result, the sample calcined at 850 °C shows excellent electrochemical performance, which could be ascribed to its good crystal structure, low cation disorder, appropriate crystallinity. This sample delivers an initial discharge capacity of 192.6 mA h g^?1 with a coulombic efficiency of 89.5 % at a current density of 20 mA g^?1, and exhibits good rate capability and stable cyclability. Finally, the electrochemical performance of the sodium lactate-derived sample is briefly compared with those of the oxalic acid-derived and ammonia-derived oxide.     

Pulse plating effect on microstructure and corrosion properties of Zn–Ni alloy coatings

The influence of pulse plating parameters on the surface morphology, grain size, lattice imperfection and corrosion properties of Zn–Ni alloy has been studied. The coatings were electrodeposited in an alkaline cyanide-free solution. AFM was applied for surface morphology examination, XRD measurements were carried out for phase composition and texture analysis, electron probe microanalysis was used for alloy chemical composition studies, while electrochemical techniques were applied for corrosion performance evaluation. The pulse plated Zn–Ni coatings appeared to consist of the γ-Zn₂₁Ni₅ phase and the composition of the alloy depended on the plating parameters. The grain size, lattice imperfection and homogeneity of grain distribution were established to be the main factors determining corrosion behaviour of the coating. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005     

Effect of TiO2-coating on structure and electrochemical performance of LiCo0.2Ni0.4Mn0.4O2

LiCo_0.2Ni_0.4Mn_0.4O₂, as the cathode material for lithium ion batteries, was modified by TiO₂-coating. The effect of TiO₂-coating on the structure and electrochemical performance of LiCo_0.2Ni_0.4Mn_0.4O₂ was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and galvanostatic charge-discharge tests. The results suggest that a small amount of TiO₂-coating does not change the crystalline structure, but considerably improves the electrochemical performance of LiCo_0.2Ni_0.4Mn_0.4O₂ in terms of capacity delivery and cyclability. XPS measurements confirm that the improved electrochemical performance is most possibly attributed to a decrease in interaction between the layered material and non-aqueous electrolyte during the charge-discharge processes. __________ Translated from Chinese Journal of Inorganic Chemistry, 2007, 23(5): 753–758 [译自: 无机化学学报]     

Preparation of Ni3B2O6 nanosheet-based flowerlike architecture by a precursor method and its electrochemical properties in lithium-ion battery

A novel flower-like nickel borate of Ni₃B₂O₆ nanostructure was prepared through a hydrothermal treatment and sequential thermal decomposition of precursor without employing any template or surfactant. All the samples were characterized by XRD, IR, XPS, TG–DTA, nitrogen adsorption, SEM and TEM. The flower-like Ni₃B₂O₆ nanostructure was self-assembled by nanosheets with the thickness of about 40 nm. The electrochemical properties in lithium-ion battery of flower-like Ni₃B₂O₆ nanostructure were studied by the cyclic voltammetry, galvanostatic cycling test, and electrochemical impedance spectroscopy, which showed it had a high initial discharge capacity and a good reversibility.     

Mm0.78Mg0.22Ni2.48Mn0.09Al0.23Co0.47储氢合金的表面改性

为了提高AB3型合金Mm_(0.78)Mg_(0.22)Ni_(2.48)Mn_(0.09)Al_(0.23)Co_(0.47)(Mm由82.3%La和17.7%Nd组成)的电化学性能,将石墨烯添加到合金中。通过XRD和SEM可以看出,石墨烯并没有改变合金的相结构,仅是简单地附在合金表面。当加入质量分数为2%的石墨烯时,合金电极的最大放电容量Cmax达到364.9 m Ah·g-1。石墨烯的添加加速了合金表面的电化学反应。     

Preparation and characterization of Co80Nb20-xBx amorphous metallic ribbons

Co₈₀Nb₁₄B₆, Co₈₀Nb₁₂B₈ and Co₈₀Nb₁₀B₁₀ amorphous alloys were obtained through the melt-spinning process. The ribbons structure was investigated by X-ray diffractometry and the crystallization process and the thermal stability were studied by means of differential thermal analysis and thermomechanical technique. It was observed that the crystallization temperature depends on the alloy composition and occurs in a temperature range between 420 and 730°C. The coercive field of all alloys was determined by magnetic susceptibility measurements, the values of which range from 2.78 to 5.95 A m^-1. This revised version was published online in August 2006 with corrections to the Cover Date.