Electrochemical and spectroscopic investigation of the reduction of dimethylglyoxime at mercury electrodes in the presence of cobalt and nickel

Voltammograms (polarograms) obtained from solutions of cobalt and nickel containing dimethylglyoxime (dmgH(2)) are widely used for the trace determination of these metals. Detailed electrochemical and spectroscopic studies on the reduction process observed in the analytically important ammonia buffer media at mercury dropping, hanging, and pool electrodes are all consistent with an overall 10-electron reduction process, in which both the dmgH(2) ligand and cobalt ions are reduced in the adsorbed state: Co(II) + 2dmgH(2) ? (solution) [Co(II)(dmgH)(2)] + 2H(+); [Co(II)(dmgH)(2)] + Hg ? (electrode) [Co(II)(dmgH)(2)](ads)Hg; and [Co(II)(dmgH)(2)](ads)Hg + 10e(-) + 10H(+) → Co(Hg) + 2[2,3-bis(hydroxylamino)butane]. The limited solubility of the nickel complex in aqueous media restricts the range of studies that can be undertaken with this system, but an analogous mechanism is believed to occur. Low-temperature voltammetric studies in dichloromethane at a frozen hanging mercury drop electrode and in situ electron spin resonance electrochemical measurements on more soluble analogues of the dimethylglyoxime complexes are consistent with an initial one-electron reduction step being available in the absence of water. Deliberate addition of water to acetone solutions enables the influence of the aqueous environment on voltammograms and polarograms to be examined. The results of the present study are compared with the wide range of mechanisms proposed in other studies.     

Voltammetric reduction of nickel and cobalt dimethylglyoximate

The determination of cobalt and nickel in aqueous solutions by stripping voltammetry after adsorptive preconcentration is an established procedure. The method is highly sensitive, but there is some controversy concerning the reasons for the excellent sensitivity. Using a variety of voltammetric techniques, we have determined that the reduction of nickel dimethylglyoximate in an ammonia buffer is consistent with an overall process involving 16 or possibly 18 electrons. This hypothesis is confirmed by independently measuring the total quantity of metal adsorptively deposited on the mercury electrode and comparing the amount with the quantity of electricity required for its reduction.     

Carbothermic reduction of cobalt and nickel tungstates

Data are presented on the formation sequence of metallic, carbide, and intermediate oxide phases in the carbon reduction of CoWO₄ and NiWO₄. The surface reaction between CoWO₄ particles and solid carbon yields the mixed carbide Co₆W₆C, while the reaction with the CO originating from carbon vaporization yields the intermetallic phase Co₇W₆. The initial stage of the solid-state and gas-phase reduction of NiWO₄ yields a solid solution of tungsten in nickel (～10 at % W), Ni₄W, and, presumably, the NiWO₄-WO₃ eutectic. The solid solution reacts with carbon to form Ni₂W₄C and with CO to form filamentary tungsten crystals.     

Corrosion and electrochemical properties of binary cobalt and nickel alloys

The influence of pH of electrolyte on the tungsten content and current efficiency of a Co–W coating is determined. We determine the corrosion rates of Co–W and Ni–Pd alloys by the polarization resistance method and show that the coatings are classified as belonging to highly corrosion-resistant coatings. The catalytic reactivity of coatings in a model reaction of hydrogen release is assessed. Dependences of the corrosion resistance and catalytic reactivity of Co–W and Ni–Pd alloys on the contents of the components are obtained, and their character is justified. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 6, pp. 89–92, November–December, 2008.     

沉积钴镀层的球形Ni(OH)2的电性能研究

采用化学度的方法在球形Ni(OH)2表面包覆了金属钴,通过比较恒电流充放电实验和循环伏安实验结果,发现球形Ni(OH)2表面镀钴,可以明显提高电极的放电容量,活性物质利用率,增加电极反应的可逆性,用XRD法比较研究了包覆钴和掺钴球形Ni(OH)2正极在充放电过程中相的生成和变化,发现掺钴的球形Ni(OH)2可抑制γ－ＮiOOH的生成,这有利于提高Ni(OH)2电极的循环寿命。此外,本文还对镀钴层改进Ｎi(OH)2电极性能的机理进行了讨论。     

Carbothermic reduction of copper,nickel, and cobalt oxides and molybdates

The carbothermic reduction of NiO, CoO, CuO, MoO₃, and the MMoO₄ (M = Ni, Co, Cu) molybdates has been studied by thermogravimetry. The results demonstrate that the reactivity of the molybdates with solid carbon, the sequence of reduction reactions, and the composition of reaction intermediates are determined by the reactivity of the constituent oxides, which decreases in the order CuO > MoO₃ > NiO > CoO. The reaction intermediates in the reduction of CuMoO₄ are Cu₆Mo₅O₁₈ and Cu₂Mo₃O₁₀, and those in the reduction of CoMoO₄ are Co₂Mo₃O₈ and CoMoO₃. NiMoO₄ is reduced without oxide intermediates. The reactions of CuMoO₄ and NiMoO₄ with solid carbon lead to selective reduction of the molybdates to metals (Cu or Ni) and molybdenum oxides (MoO₂ and MoO_{3 ? x} ). In the reactions of NiMoO₄ and CoMoO₄ with CO gas, the metals are formed at comparable rates, which favors the formation of metal solid solutions, intermetallic phases, and mixed carbides.     

Structural and electrochemical properties of nanostructured nickel silicides by reduction and silicification of high-surface-area nickel oxide

Nanostructured nickel silicides have been prepared by reduction and silicification of high-surface-area nickel oxide (145 m² g^?1) produced via precipitation. The prepared materials were characterized by nitrogen adsorption, X-ray diffraction, thermal analysis, FT-IR spectroscopy, scanning electron microscopy, transmission electron microscopy, magnetic and electrochemical measurements. The nickel silicide formation involves the following sequence: NiO (cubic) → Ni (cubic) → Ni₂Si (orthorhombic) → NiSi (orthorhombic) → NiSi₂ (cubic), with particles growing from 13.7 to 21.3 nm. The nickel silicides are ferromagnetic at room temperature, and their saturation magnetization values change drastically with the increase of Si content. Nickel silicides have remarkably low electrical resistivity and noble metal-like properties because of a constriction of the Ni d band and an increase of the electronic density of states. The results suggest that such silicides are promising candidates as inexpensive yet functional materials for applications in electrochemistry as well as catalysis.     

Antimony film electrode for electrochemical stripping analysis

In this work, an antimony film electrode (SbFE) is reported for the first time as a possible alternative for electrochemical stripping analysis of trace heavy metals. The SbFE was prepared in situ on a glassy carbon substrate electrode and employed in combination with either anodic stripping voltammetry or stripping chronopotentiometry in nondeaerated solutions of 0.01 M hydrochloric acid (pH 2). Several key operational parameters influencing the electroanalytical response of SbFE were examined and optimized, such as deposition potential, deposition time, and composition of the measurement solution. The SbFE exhibited well-defined and separated stripping signals for both model metal ions, Cd(II) and Pb(II), surrounded with low background contribution and a relatively large negative potential range. The electrode revealed good linear behavior in the examined concentration range from 20 to 140 microg L-1 for both test metal ions, with a limit of detection (3sigma) of 0.7 microg L-1 for Cd(II) and 0.9 microg L-1 for Pb(II) obtained after a 120 s deposition step, and good reproducibility, with a relative standard deviation (RSD) of +/-3.6% for Cd(II) and +/-6.2% for Pb(II) (60 microg L-1, n = 12). When comparing the SbFE with the commonly used mercury film electrode and recently introduced bismuth film electrode, the newly proposed electrode offers a remarkable performance in more acidic solutions (pH < or = 2), which can be advantageous in electrochemical analysis of trace heavy metals, hence contributing to the wider applicability of electrochemical stripping techniques in connection with "mercury-free" electrodes.     

Effect of TiO2 support on immobilization of cobalt porphyrin for electrochemical CO2 reduction

Electrochemical reduction of CO2 is a promising strategy to manage the global carbon balance by trans-forming CO2 into chemicals.The efficiency of CO2 electroreduction is largely dependent on the design of hybrid electrode where both support and catalyst govern the performance of the electrolyzer.In this work,TiO2 calcined at different temperatures,was used as a support for immobilization of cobalt tetraphenyl porphyrin (CoTPP) and its effect on CO2 reduction was studied.It is demonstrated that the crystalline phase of TiO2 and doping of TiO2 apparently affecting CO2 electroreduction.It is found that anatase phase exhibits higher activity and selectivity compared to futile due to the enhanced conductivity which in turn enables faster electron transfer between the support and CoTPP.As for dopants,the carbon dop-ing in anatase TiO2 is proven to further enhance its conductivity,consequently resulting in the enhanced performance.This study implies that the rational design of supports is important for the performance of the hybrid electrode towards electrochemical CO2 reduction.     

Sintering diagrams for cobalt,nickel and iron

Sintering diagrams were calculated for cobalt, nickel and iron powders. Using parameters such as shrinkage, electrical conductivity or elastic modulus, it was possible to determine the activation energies and confirm the predominant sintering mechanisms predicted by the maps.     

Recovery of nickel and cobalt from organic acid complexes: adsorption mechanisms of metal-organic complexes onto aminophosphonate chelating resin

This study examined the recovery of nickel and cobalt from organic acid complexes using a chelating aminophosphonate Purolite S950 resin. These metal complexes are generated by bioleaching nickel laterite ores, a commercial nickel and cobalt mineral oxide, with heterotrophic organism and their metabolites or organic acid products. Equilibrium adsorption tests were conducted as a function of Ni and Co concentrations (15-2000 mg/L), solution pH (0.01 and 0.1 M acids) and three metabolic complexing agents (citrate, malate and lactate). It was shown that the adsorption of the various Ni- and Co-complexes on Purolite were quite low, 16-18 and 5.4-9 mg/g of resin, respectively, in comparison to the smaller nickel ions and nickel sulfate. This was attributed to the bulky organic ligands which promoted crowding effect or steric hindrance. The adsorption of these complexes was further hampered by the strong affinity of the resin to H+ ions under acidic conditions. Mechanisms of adsorption, as inferred from the fitted empirical Langmuir and Freundlich models, were correlated to the proposed steric hindrance and competitive adsorption effects. Nickel and cobalt elution from the resin were found be effective and were independent of the type of metal complexes and metal concentrations. This study demonstrated the relative challenges involved in recovering nickel and cobalt from bioleaching solutions.     

无钴镍基正极材料LiNi_(0.7)Mn_(0.3)O_2制备及性能研究

采用共沉淀-高温固相法合成正极材料LiNi0.7Mn0.3O2,利用X射线衍射分析(XRD)表征其结构、扫描电子显微镜(SEM)表征其形貌、X射线光电子能谱(XPS)表征其价态,最终确定了该材料最佳烧成温度为820℃。研究表明,该温度下合成的Li Ni0.7Mn0.3O2具有典型的α-NaFeO2型层状结构,颗粒形貌呈类球形且分布均匀;XPS数据表明,LiNi0.7Mn0.3O2中的Ni主要以+3价形态存在,Mn主要以+4价形态存在。室温条件下以0.2 C倍率在2.75~4.35 V的电压范围内充放电,首次放电比容量高达188.9 m Ah/g,70次循环后容量保持率为95.2%。     

纳米级氢氧化镍和钴对镍电极性能的影响

通过充放电曲线和交流阻抗谱的测定探讨了纳米级氢氧化镍和氢氧化镍表面包复CoOOH以及镍箔上电镀钴层对氢氧化镍粉末压制的镍电极性能的影响。结果表明．纳米级氢氧化镍有较快的活化能力，CoOOH包Ni(OH)2则有较高的放电容量，而比例适当的纳米复合镍电极才有更好的电化学性能。氢氧化镍表面包复CoOOH可改善镍电极的充放电性能；镍箔上镀钴可大大降低电极过程的电荷转移电阻；钴含量大于3％后．虽然活化速度有所下降，但是大电流充放电时，镍电极活性物的利用率更高，放电容量更大。纳米级Ni(OH)2含量大于30%后，镍电极的活化速度不仅未能加快，反而略有减慢，而且容量也降低。     

On the chemical transport of cobalt and nickel chromites

The chemical transport of CoCr₂O₄ and NiCr₂O₄ with chlorine as a transport agent has been investigated. On the basis of thermodynamic analysis of the transport reactions at 800–1500 K it has been established that the gas phase should contain Cl₂, CrO₂Cl₂ and CoCl₂ during transport of CoCr₂O₄, while Cl₂, CrO₂Cl₂ and NiCl₂ should be present when NiCr₂O₄ is transported. Within the same temperature range cobalt chromite should be transported without decomposition whereas nickel chromite would probably decompose at high temperatures and a low total pressure in the transport system. Octahedral single crystals of CoCr₂O₄ with a spinel structure have been obtained whereas NiCr₂O₄ formed octahedra and plates with a tetragonal structure. The reasons of the differences observed with the systems CoCr₂O₄  Cl₂ and NiCr₂O₄  Cl₂ have been discussed.     

反复浸渍法制备NiO及电化学性能研究

以NaOH为沉淀剂,NiCl2为前驱体采用反复浸渍法合成了Ni(OH)2,在300℃煅烧制备了NiO。X射线衍射(XRD)证明材料为立方晶相的NiO,扫描电子显微镜(SEM)显示了NiO呈现出波浪状的形貌。电化学性能测试:以10mA进行恒流充放电测试,起始容量为455F/g;随着循环次数的增加,比容量减小,200次后稳定于415F/g(为初始容量的91.2%)。     

掺铝α-氢氧化钴的制备及其电化学性能研究

以氯化钴和硝酸铝为原料、聚乙二醇为结构导向剂,采用化学共沉淀法制备成片状掺铝α-氢氧化钴.用X射线衍射(XRD)、场发射扫描电镜(SEM)对样品的结构和形貌进行了表征;用傅里叶变换红外光谱(FT-IR)对样品的成分进行了测定;用循环伏安、恒电流充放电等方法对其电化学性能进行了测试.测试结果表明,钴与铝的摩尔比时目标产物...     

Synthesis and electrochemical capacitance of sheet-like cobalt hydroxide

Cobalt hydroxide was synthesized via a new approach, in which the gel was prepared by the reaction of Co(NO₃)₂ solution with citric acid, and then the precursors were obtained after thermal treatment, finally the precursors reacted with KOH solution to produce the samples. The components of the precursors were measured by Fourier transforms infrared (FT-IR) spectroscopy. The morphology and structure of samples were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The results indicate that the as-prepared materials are β-Co(OH)₂ with sheet-like morphology. The effect of the treatment temperature for the precursor on sheet size was discussed in detail. Cyclic voltammetry and constant current charge/discharge measurements show that the prepared cobalt hydroxide exhibits excellent capacitance performance. The specific capacitance is up to 416.7 F g^?1 at a constant current charge/discharge test of 5 mA.     

Surfactant-dependant self organisation of nickel pyrophosphate for electrochemical supercapacitors

Journal of Materials Science: Materials in Electronics - In quest of potential electrode material with high redox sites, better wettability, rapid ionic channels and high rate capability here we...     

Synthesis and characterization of cobalt–nickel alloy nanowires

We report on the synthesis and magnetic characterization of ordered arrays of cobalt–nickel alloy nanowires. These alloy nanowires were electrodeposited into the pores of anodic alumina templates. The physical properties of the samples were investigated using scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and vibrating sample magnetometer. We found that for the alloy nanowires the field at which the magnetization saturates increases with increasing Co fraction and the saturation field in the normal direction is smaller than the parallel direction, indicating easy magnetization direction normal to wire axis. Nanowires with different compositional ratio of cobalt and nickel showed a nonlinear dependence of coercivity as a function of cobalt concentration. These findings will help tailor magnetic nanoalloys with controlled properties for various applications, such as high density magnetic storage or nanoelectrode arrays.