Electrochemical behavior of Pd–Rh alloys

Pd–Rh alloys were prepared by electrochemical codeposition. Bulk compositions of the alloys were determined by the energy dispersive X-ray analysis method, while surface compositions were determined from the potential of the surface oxide reduction peak. Cyclic voltammograms, recorded in 0.5 M H₂SO₄ for Pd–Rh alloys of different bulk and surface compositions, are intermediate between curves characteristic of Pd and Rh. The influence of potential cycling on electrochemical properties and surface morphologies of the alloys was studied. Due to electrochemical dissolution of metals, both alloy surface and bulk become enriched with Pd. Carbon oxides were adsorbed at a constant potential from the range of hydrogen adsorption. The presence of adsorbed CO₂ causes remarkable diminution of hydrogen adsorption but it does not significantly influence hydrogen insertion into the alloy bulk. On the other hand, in the presence of adsorbed CO, both hydrogen absorption and adsorption are strongly suppressed. Oxidative removal of the adsorbates results in a characteristic voltammetric peak, whose potential increases with the decrease in Rh surface content. Electron per site (eps) values calculated for the oxidation of the adsorbates change with alloy surface composition, more for CO₂ than CO adsorption, indicating the variation of the structure and composition of CO₂ and CO adsorption products. The course of the dependence of eps values on surface composition suggests that the products of CO₂ and CO adsorption on Pd–Rh alloys are similar but not totally identical.     

Selected electrochemical properties of Pd–Au alloys: hydrogen absorption and surface oxidation

Hydrogen absorption into and surface oxidation of Pd–Au alloys in acidic solutions were studied by cyclic voltammetry (CV) and chronoamperometry (CA) coupled with the electrochemical quartz crystal microbalance (EQCM). The influence of alloy bulk and surface composition on the process of oxidation of absorbed hydrogen was examined. The stresses induced by hydrogen insertion in Pd–Au alloys were compared with the case of pure Pd. The potential corresponding to the formation of a monolayer of surface oxide was determined for Pd–Au alloys of different surface states. Electrochemical dissolution of Pd–Au alloys was investigated.     

Microstructural and in-depth electrochemical characterization of Zn diffusion layers on aluminum 3xxx alloy

AA 3XXX alloys are widely used in heating, ventilation, and air conditioning (HVAC) field. Diffusion joining using a filler metal together with flux is employed in some applications as for heat exchangers. In this work, the effect of diffusion of a Zn-based flux on both microstructure and electrochemical behavior has been investigated. In particular, an AA3xxx was coated with a Zn-rich flux and subjected to controlled atmosphere brazing (CAB). Glow discharge optical emission spectroscopy (GDOES) composition profiles were acquired in order to determine the Zn distribution in the diffusion layer. The GDOES was also employed to produce a controlled erosion of the surface in order to obtain craters with defined depths in the Zn diffusion layer, in which electrochemical analyses could be performed. The Volta potential maps at different depths in the Zn diffusion layer were obtained by scanning Kelvin probe force microscope (SKPFM). The Zn diffusion layer was also investigated by means of Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM-EDXS) and the chemical composition of the phases present in the regions was investigated by SKPFM. Finally, the electrochemical microcell was used in the produced craters in order to determine the electrochemical behavior along the Zn diffusion profile. SKPFM and microcell results showed a correlation between the Zn content and the electrochemical properties. In particular, a higher Zn content in the diffusion layer leads to an increase of the Volta potential difference between the intermetallic particles and the matrix. The electrochemical measurements also showed that the Zn diffusion layer provides galvanic protection to the underlaying aluminum alloy.     

LY12铝合金表面电化学沉积制备DTMS硅烷膜及其耐蚀性研究

采用电化学技术在LY12铝合金表面沉积制备了十二烷基三甲氧基硅烷(DTMS)膜. 反射吸收红外光谱表明, DTMS硅烷试剂与铝合金基体表面发生了化学键合作用, 生成—SiOAl键实现成膜. 通过对膜覆盖电极在质量分数为3.5%的NaCl溶液中的电化学阻抗谱(EIS)测试结果表明, 与开路电位下相比, 采用阴极电位沉积方法得到硅烷膜的耐蚀性能有明显提高, 且存在一个最佳“临界电位”, 在此电位下沉积得到的硅烷膜具有最高的耐蚀性. 扫描电镜观察结果表明, 在“临界电位”下制备得到的硅烷膜的结构最致密. 给出了硅烷膜覆盖电极的阻抗模型及相关参数的拟合结果.     

Unique activity of Pd monomers: hydrogen evolution at AuPd(111) surface alloys

Well-defined Au/Pd(111) alloy films have been prepared on a Ru(0001) substrate by electrochemical metal deposition and subsequent heating up to 700 degrees C. The electrochemical behaviour of the 20 monolayers thick epitaxially-grown films is in excellent agreement with both equilibrium surface composition and distribution for Au/Pd alloys on Mo(110) as previously reported (D. W. Goodman et al., J. Phys. Chem., 2005, B109, 18535). The electrocatalytic activity of the AuPd(111) surface alloys was studied for the hydrogen evolution in 0.1 M H(2)SO(4) as a function of surface composition. Maximum activities were found for Pd fractions of 0.2 +/- 0.1, where the population of Pd atoms surrounded by Au has its maximum. These Pd monomers are found to be about 20 times more active than Pd atoms in the Pd overlayer.     

Synthesis of Co–Pd alloys by co-electroreduction of aquachloro-cobalt(II) and palladium(II) complexes

The work presents results of the studies on the synthesis of Co–Pd alloys from acid electrolytes containing chloride ions. The main aim of the tests was to identify reactions responsible for alloy formation and to determine an influence of the electrolysis parameters, i.e. working electrode potential, electrolyte composition and temperature on the composition of the resulted alloy coatings. Electrochemical investigations were performed by applying cyclic voltammetry (CV) combined with electrochemical quartz crystal microbalance (EQCM). The electrolyte composition was selected based on a thermodynamic analysis and spectrophotometric tests which were described in our previous papers [1, 2]. They allowed determination of equilibrium distribution of the metals complex forms and a stability analysis of the electrolyte. The alloys were synthesized within the potential range from ?0.7 to ?1.1 V. The tests indicate a possibility of alloys synthesis already at the potential range 相似文献   

Spontaneous near-substrate composition modulation in electrodeposited Fe–Co–Ni alloys

Conventional and reverse depth profile analysis of electrodeposited Fe–Co–Ni alloys was performed by secondary neutral mass spectrometry (SNMS). It was found that the reverse sputtering method gave a much better depth resolution at the vicinity of the substrate. The reverse SNMS spectra showed that the deposition of Fe–Co–Ni alloys starts with the formation of an Fe-rich zone followed by an increase in Co concentration, then the nickel content increases and a steady-state alloy composition is achieved. At high current density, the initial depth pattern reproduces itself twice before the composition becomes stable. It was concluded that the varying depth profile is a consequence of the anomalous nature of the codeposition of the alloy components, the depletion of the electrolyte with respect to the metal salts, and the dependence of the intensity of the hydrogen evolution on the deposit surface composition.     

Analysis of the surface of PtxNi1?x alloys

Summary The surface composition of three polycrystalline Pt_xNi_1–x alloys (metal foils) was determined by ion scattering spectroscopy (ISS) with He ions of an energy of 1 keV. The targets have been pretreated by bombarding with rare-gas ions (He, Ar and Xe), by annealing at 500°C and by exposing them to increasing amounts of oxygen (up to 20 Langmuir). The results obtained from the polycrystalline alloys are compared to results from a Pt₁₀Ni₉₀ silica supported catalyst. The surface composition was also measured by ISS. The catalyst was pretreated by bombarding with He ions and by exposing it to 10 L oxygen.     

Thermodynamics of oxygen in dilute liquid silver–tellurium alloys

Abstract  

The activity coefficient of oxygen in liquid Ag and binary Ag–Te dilute alloys were determined between 1,285 and 1,485 K by coulometric titration using the electrochemical cell (Ir, [O] in liquid metal or alloy | yttria stabilized zirconia | air, Pt). The experimental and evaluation procedures described in the literature were adopted. The oxygen activity coefficient was determined in pure liquid silver to be . Next, the oxygen activity coefficient in dilute Ag–(Te)–O alloys for variable X _Te content (from 0.01 to 0.06) was measured. From the obtained results, Wagner’s interaction parameter as a function of temperature was derived in the form . The electrochemical coulometric titration method seems to be very useful to study the thermodynamics of oxygen interaction in liquid silver and its alloys.     

Electrocatalysis on binary alloys: II. Oxidation of molecular hydrogen on supported Pt+Ru alloys

The electrocatalytic properties of Pt+Ru alloys supported on graphitized carbon have been studied using oxide-free metal alloys that have been well characterized for phase identification, specific metal surface area, and surface composition. The CO tolerance of the Pt+Ru alloys for the oxidation of CO contaminated hydrogen in hot concentrated H₃PO₄ increases monotonically with Ru content of the surface and is a direct result of a decreasing coverage of the alloy by adsorbed CO. Furthermore, the strength of bonding of adsorbed CO with the metal surface decreases dramatically with increasing Ru content in the surface. The absolute activity of Pt+Ru alloys for the oxidation of CO contaminated hydrogen is a complex function of temperature and electrode potential. At 160°C, pure Pt is the most active catalyst at all potentials, but at temperatures lower than 120°C the reaction-limiting current for pure Ru exceeds that of pure Pt. At any temperature from 110–160°C or any electrode potential from 0–0.3V (HE), the variation of electrocatalytic activity with alloy composition indicates only dilution of the activity of the more active component.     

KCl-MgCl2-K2ZrF6-ZrO2熔盐体系中Mg-Zr合金的制备

在1023 K条件下,开展了Zr（IV）在KCl-MgCl₂-K₂ZrF₆和KCl-MgCl₂-K₂ZrF₆-ZrO₂熔盐中Mo电极上的电化学实验,并获得如下结果：Zr（IV）还原为Zr（0）是通过两步反应,即Zr（IV）+ 2e^- → Zr（II）和Zr（II）+2e^- → Zr（0）。两个反应是准可逆的。KCl-MgCl₂-K₂ZrF₆-ZrO₂熔盐中的电极反应表明在预沉积的Zr上欠电位沉积Mg可以用来制备Mg-Zr合金。感应耦合离体子体-原子发射光谱（ICP-AES）分析结果表明,在1023 K和KCl-MgCl₂-K₂ZrF₆-ZrO₂熔盐中K₂ZrF₆含量在9.2%（w）条件下,恒电流电解获得的Mg-Zr合金中Zr含量可以达到7.2%（w）。并采用X射线衍射（XRD）和扫描电镜-能谱仪（SEM-EPS）对合金进行表征。利用KCl、MgCl₂、K₂ZrF₆、KF和ZrO₂为原料,直接恒电流电解制备Mg-Zr合金是可行的,且在确定反应条件下实现合金中Zr含量可控;揭示了KCl-MgCl₂熔盐体系可以实现Mg和Zr的共电沉积,并且验证了直接电解ZrO₂获得Mg-Zr合金的可行性。     

Calculating the thermodynamic parameters of the surface layer of the binary sodium-potassium system

The composition and number of surface monoatomic potassium layers in Na-K alloys are calculated on the basis of theory of the thermodynamic stability of surface layers of metal alloys with respect to their thickness. The surface layer of Na-K alloys is shown to be thermodynamically stable at surface layer thickness of two monoatomic potassium layers in the range of compositions with K in Na content of ∼13–15 at %. Good agreement is obtained using the surface activities of the components in binary metal melts as criteria.     

Structural and electrochemical characterization of sputter-deposited nitrided NiCr alloys

Nickel-based coatings are potential candidates for the protection of electrochemical dissolution of steel surfaces. Such coatings, elaborated by magnetron sputtering in a nitrogen atmosphere, offer good corrosion protection, good adherence as well as stability for metallic structures. NiCr alloys with almost constant composition have been deposited with different nitrogen contents on stainless steel and carbon steel surfaces. The coating uniformity, homogeneity, composition and crystallinity have been studied by scanning electron microscopy, energy-dispersive X-ray spectrometry, atomic force microscopy and X-ray diffraction techniques. The corrosion degradation behavior of all the samples was tested in NaCl and NaCl and CO₂ mixture exposures using electrochemical impedance spectroscopy measurements. Nitrided NiCr alloys on a stainless steel substrate resulted with better adhesion than carbon steel, by delaying the corrosion mechanism when exposed to NaCl and CO₂ solution. A comparison of the corrosion resistive behavior of the substrates (stainless steel, carbon steel) and the coatings is made by using the electrical capacitance concept from a double-layer model for the coating–metal interface.     

The electrodeposition of Zn-Ti alloys from ZnCl2-urea deep eutectic solvent

The electrochemical behavior of Ti(IV) and the electrodeposition of Zn-Ti alloys were investigated in a ZnCl₂-urea (1:3 molar ratio) deep eutectic solvent containing 0.27 mol L^?1 TiCl₄. The electrochemical reduction of Ti(IV) to Ti was complicated by the formation of intermediate oxidation states of Ti(III) and Ti(II), as well as the precipitation of TiCl₃. It was possible to prepare Zn-Ti alloys containing 5.8–16.7 at.% Ti. The composition and surface morphology of Zn-Ti alloys depended on deposition potential and temperature. The deposits could be indexed to a disordered hexagonal close-packed structure similar to pure Zn and were completely chloride-free. The current efficiency for the deposition of Zn-Ti alloys varied from 38.4 to 67.9 %.     

贮氢合金表面处理改善Ni/MH电池1C充放电性能

研究了贮氨合金两种表面化学处理方法对MH电极活化性能及Ni／MH电池IC充放电性能的影响：第一种处理方法是贮氢合金在6th。l·L－’KOH溶液中80T处理sh，第二种处理方法是在含有0．04mol·L－‘KBH4的6mol·L’‘KOH溶液中80t处理sh．通过MH电极的放电容量、充放电过程中电极极化和电化学阻抗谱测试评价了上述化学处理对电极活化性能的影响．电子探针表面分析表明化学处理后贮氢合金表面由于铝元素的优先溶解形成一层具有较高电催化活性的富镍表面层，它是改善电极活化性能的主要原因·以处理的贮氨合金为负极材料的Ni／MH电池具有较高IC充放电循环寿命和1．ZV以上放电容量．     

铂基Pb-Sb表面合金电催化剂的制备与结构表征

通过电化学方法,在玻碳载体表面制备以Pt、Pb、Sb为主要成分的铂基Pb Sb表面合金电催化剂.运用电化学循环伏安、石英晶体微天平（EQCM）和扫描隧道显微镜（STM）技术对催化剂电极进行表征.结果表明：酸性溶液中在所制备的表面合金电极上,析氢起始电位负移至－0.45 V,表面合金的起始氧化电位为0.15 V,其稳定性明显高于电催化还原中常用的铅、锑等金属电极.通过EQCM研究表面合金电极的形成过程,结合STM观察和XPS深度剖析,确定电催化剂表面是由粒度均匀的纳米颗粒构成的表面合金层.     

Electrochemical separation of uranium and cerium in molten LiCl–KCl

The electrochemical separation of uranium from cerium in LiCl–KCl eutectic and the electrochemical behavior of Ce(III) were studied. According to the cyclic voltammogram of Ce(III) and the former result of U(III), electrodeposition potential was determined at ?1.65 V (vs Ag/AgCl). The uranium metal was successfully deposited and separated from cerium. The morphology of deposit and cross section of electrode were investigated by SEM, firstly uranium deposit alloys with stainless steel and forms a thin transition layer, and secondly the uranium metal layer grows from the transition layer. The separation factors of uranium/cerium on different recovery ratios were determined through a series of steps. It was found that the content of cerium in the deposit and separation factors declined with increasing the initial concentration of U³⁺ in molten salts; the separation factors remained stable at around 20 in different uranium recovery ratios.     

Kinetic and thermodynamic studies of hydrogen storage alloys as negative electrode materials for Ni/MH batteries: a review

This paper reviews the present performances of intermetallic compound families as materials for negative electrodes of rechargeable Ni/MH batteries. The performance of the metal-hydride electrode is determined by both the kinetics of the processes occurring at the metal/solution interface and the rate of hydrogen diffusion within the bulk of the alloy. Thermodynamic and electrochemical properties for each hydride compound family will be reported. The steps of hydrogen absorption/desorption such as charge-transfer and hydrogen diffusion for evaluating the electrochemical properties of hydrogen storage alloys are discussed. Exchange current density (I ₀) and hydrogen diffusion coefficient (D _H) are the two most important parameters for evaluating the electrochemical properties of metal hydride electrode. The values of the two parameters for a number of hydrogen storage alloys are compared. The relationship between alloy composition and electrochemical properties is noted and evaluated.     

高指数晶面纳米催化剂的电化学制备及应用

催化剂的性能与其表面结构及组成密切相关,高指数晶面纳米晶的表面含有高密度的台阶原子等活性位点而表现出较高的催化活性. 本文综述了电化学方波电位方法用于Pt、Pd、Rh等贵金属高指数晶面结构纳米晶催化剂的制备、形成机理及其电催化性能的研究. 针对贵金属利用率问题,还着重介绍了具有较高质量活性的小粒径Pt二十四面体的制备. 在此基础上,还介绍了电化学方波电位方法用于低共熔溶剂中制备高指数晶面纳米晶,以及高指数晶面纳米催化剂的表面修饰及应用;最后对高指数晶面纳米催化剂的发展做出了展望.     

Corrosion-stable nickel- and cobalt-based alloys for dental applications

In a comparative study the in vitro corrosion behavior of a selection of nickel- and cobalt-based alloys for application in dentistry containing no noble metals was studied with slow scan cyclic voltammetry. The obtained breakthrough potentials, the repassivation behavior and further typical features of the cyclic voltamograms are correlated with the chemical composition as measured with electron beam microanalysis. Surface inhomogenities detected with the latter method are discussed with respect to the electrochemical behavior. For all alloys stabilities in terms of breakthrough potential superior to previously reported data for nickel-base alloys are found.