Formation of powdered copper deposits by constant and pulsating overpotential electrolysis

The possibility of electrodepositing copper powder by pulsating overpotential is shown. These powders are compared to the powders obtained by constant overpotential electrodeposition. It is also shown that the grain size and the morphology of deposited powder is a function of overpotential, and of amplitude and frequency of pulsation in constant and pulsating overpotential deposition respectively.     

Formation of powdered copper deposits by square-wave pulsating overpotential

Copper powder deposits were obtained by square-wave pulsating overpotential electrolysis and by constant overpotential electrolysis. It is shown that the particle grain size and the morphology of deposited powders are functions of amplitude overpotential, frequency of pulsation and pulse to pause ratio in pulsating potential deposition, and of overpotential in constant overpotential deposition.     

The comparison of galvanostatic and potentiostatic copper powder deposition on platinum and aluminium electrodes

Experiments have been carried out on copper powder electrodeposition by constant overpotential and constant current on aluminium, graphite, platinum and copper electrodes. It is shown that for one and the same quantity of electricity, electrode material, electrode surface area, electrolyte, temperature and time of deposition, different particle size distribution curves, current efficiency and specific energy consumption are obtained in galvanostatic and potentiostatic deposition.     

Performance of Ni-added Pd-Ag/Al2O3 catalysts in the selective hydrogenation of acetylene

Effects of Ni addition on the performance of Pd-Ag/Al₂O₃ catalysts in the selective hydrogenation of acetylene were investigated. Ni-added Pd-Ag catalysts showed higher conversions than Ni-free Pd-Ag catalyst under hydrogen-deficient reaction conditions, hydrogen/acetylene <2.0, due to the spillover of hydrogen from reduced Ni to Pd and the suppression of hydrogen penetration into the Pd bulk phase, which enriched the Pd surface with hydrogen. Ethylene selectivity was also increased by Ni addition because the amounts of surface hydrogen originating from the Pd bulk phase, which was responsible for the full hydrogenation of ethylene to ethane, were decreased due to the presence of Ni at the sub-surface of Pd-Ag particles. Added Ni also modified the geometric nature of the Pd surface by blocking large ensembles of Pd into isolated ones, which eventually improved ethylene selectivity.     

Single pulse deposition of Pd-Ag alloy nanowires on highly oriented pyrolytic graphite: A mechanistic assessment

Single pulse electrodeposition, which differs from the method of multi-pulse electrodeposition, is a process of fabricating nanowires by synchronous nucleation and growth. This report discusses the mechanistic aspect of the effect of overpotentials on the formation of Pd-Ag alloy nanowires on Highly Oriented Pyrolytic Graphite (HOPG) in the process of single pulse electrodeposition. The experiment results show that the deposition of Pd-Ag alloy nanowires at the overpotential of 100-150 mV can be described as an instantaneous nucleation mechanism on active sites of HOPG and a diffusion-controlled 3-D growth. However, when the overpotentials are below 100 mV or over 150 mV, the diffusion-controlled growth is not obeyed in the process of electrodeposition of Pd-Ag alloy. The Pd-Ag alloy nanowires with diameters ranging from 60 to 150 nm and lengths up to 300 μm have been obtained on HOPG by single pulse electrodeposition at the overpotential of 120-150 mV. The alloy nanowire arrays thus deposited are continuous, parallel, and ordered. The Ag content of the alloy nanowires is found to be in the range of 16-25%. These results are discussed to assess some of the mechanistic aspects of the electrodeposition process.     

Polarization curves in the ohmic controlled electrodeposition of metals

The conditions under which ohmic controlled metal electrodeposition occurs are discussed using a simple mathematical model. It is shown that ohmic controlled electrodeposition can be operative if the value of the exchange current density for the electrodeposition process is more than 10 times larger than the corresponding value of the limiting diffusion current density. In this case, a linear dependence of the current density on overpotential up to the value of the limiting diffusion current density can be observed. On the other hand, the initiation of dendrite growth under these circumstances is possible, even at very low values of overpotential, at the moment when the limiting diffusion current density is attained in potentiostatic electrodeposition. In this way, instead of a limiting diffusion current density plateau, an inflection point on the polarization curve can be observed, since dendritic growth is followed by an increase in the deposition current density. At the same time, it is shown that the ensemble of tips of dendrites can behave as an ensemble of microelectrodes working independently under mixed or activation control due to the absence of a common diffusion layer. This was confirmed by deposition of copper on a copper dendritic electrode and by silver electrodeposition from a silver nitrate solution onto a graphite substrate.     

Preparation of palladium-silver alloy composite membranes for hydrogen permeation

Pd-Ag/α-alumina composite membranes were fabricated by electroless plating technique. Permeability measurements were performed with hydrogen and nitrogen at temperatures ranging from 423 to 616 K and pressures ranging from 80 to 250 kPa. The results confirmed that the skin layers of prepared membranes were not defect-free. The ideal separation factor of H 2 /N 2 through Pd 0.9 -Ag 0.1 composite membrane ranged from 30 to 178 under the present experimental conditions. Furthermore, a resistance model was used to account for the simultaneous transport of hydrogen through the defects as well as the bulk Pd-Ag alloy film in Pd 0.9 -Ag 0.1 composite membrane. It revealed that the transport mechanism for hydrogen in this membrane was a combination of solution-diffusion and Knudsen diffusion with minimal contribution of viscous flow.     

Electrodeposition of palladium-indium from 1-ethyl-3-methylimidazolium chloride tetrafluoroborate ionic liquid

Voltammetry at a glassy carbon electrode was used to study the electrochemical co-deposition of Pd-In from a chloride-rich 1-ethyl-3-methylimidazolium chloride/tetrafluoroborate air-stable room temperature ionic liquid at 120 °C. Deposition of Pd alone occurs prior to the overpotential deposition (OPD) of bulk In. However, underpotential deposition (UPD) of In on the deposited Pd was observed at the potential same as the deposition of Pd. The UPD of In on Pd was, however, limited by a slow charge transfer rate. Samples of Pd-In alloy coatings were prepared on nickel substrates and characterized by energy dispersive spectroscope (EDS), scanning electron microscope (SEM) and X-ray powder diffraction (XRD). The electrodeposited alloy composition was relatively independent on the deposition potential within the In UPD range. At more negative potentials where the OPD of Pd-In has reached mass-transport limited region, the alloy composition corresponds to the Pd(II)/In(III) composition in the plating bath. The Pd-In alloy coatings obtained by direct deposition of Pd and UPD of In on the deposited Pd appeared to be superior to the Pd-In alloys that were obtained via the co-deposition of Pd and bulk In at OPD potentials.     

The effect of pulsating overpotential on the morphology of electrodeposited silver powder particles

The effects of overpotential amplitude, frequency and pulse-to-pause ratio in silver deposition by squarewave pulsating overpotential on the morphology of powdered particles were investigated. These results were compared with those obtained in constant overpotential electrolysis. The possibility of obtaining powder particles, with different properties, depending on conditions of electrolysis was demonstrated.     

Synthesis and electrochemical study of nanoporous Pd-Ag alloys for hydrogen sorption

We report on the synthesis of novel nanoporous Pd-Ag electrocatalysts using a facile hydrothermal method where the portion of Ag was varied from 0 to 40%. Scanning electron microscopy (SEM) was used to examine the morphologies of the prepared nanoporous materials. Energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) were used to directly and indirectly characterize the composition of the formed Pd-Ag nanostructures. X-ray diffraction (XRD) analysis confirmed that the formed Pd-Ag nanomaterials were alloys with a face-centered cubic structure. Electrochemical methods were used to study the capacity and kinetics of hydrogen sorption into the nanoporous Pd and Pd-Ag alloys. The nanoporous Pd-Ag alloy with 20% silver possesses the highest capacity for the α phase hydrogen sorption, which is over 4 times higher than the pure nanoporous Pd. The combination of the enhanced α phase hydrogen sorption capacity and diminishing of the α- and β-phase transition makes the nanoporous Pd-Ag alloys promising for hydrogen selective membranes and hydrogen dissociation catalysts.     

工艺条件对钯系催化剂乙炔选择性加氢性能的影响

为了研究工艺条件对钯系催化剂选择性加氢性能的影响,制备Pd/Al_2O_3、Pd-Ag/Al_2O_3和Pd-Ag/Al_2O_3-KOH催化剂,并在微型催化剂评价装置上进行乙炔选择性加氢反应,考察了工艺条件(压力、空速)对催化剂性能的影响。结果表明,随着压力的升高,催化剂活性提高,乙烯选择性会下降;随着空速的提高,催化剂乙炔转化率先升高后降低,MAPD转化率迅速下降,乙烯选择性提高。     

Synthesis of Cu–Pd alloy thin films by co-electrodeposition

This paper presents results on the synthesis of Cu–Pd alloy thin films on Ti substrates by co-electrodeposition of Pd and Cu from nitrate-base electrolytic baths. The deposition rates of Cu and Pd were determined by Electrochemical Quartz Crystal Microbalance as a function of the electrode potential and Cu⁺² and Pd⁺² concentrations. It is shown that electrodeposition of copper and palladium occurs simultaneously at −0.50 V vs. SCE and that Cu–Pd thin films over the entire composition range were obtained by changing the composition of the solution. X-ray diffraction analyses indicated that these films have a nanocrystalline single-phase face-centered cubic structure and scanning electron microscopy analyses showed that potentiostatically deposited films are rough and porous, which is appropriate for electrocatalysis applications. In an attempt to get denser deposits as required for H₂ purification applications, pulsed potential co-electrodeposition was performed and the effect of the deposition conditions on the roughness of the films was assessed by double layer capacitance measurements. It was shown that smooth Cu–Pd films (with R_f value as low as 8, as opposed to more than 120 for films prepared in the potentiostatic mode) could be obtained with a proper choice on the deposition conditions.     

化学湿法生产电子元件用超细球形钯银合金粉的研究

介绍了化学湿法生产电子元件用高纯超细球形钯银合金粉的工业生产工艺，形貌控制方法及其生产设备特点，探讨了影响钯银合金粉形貌的各个因素。     

Hydrogen absorption by palladium electrode polarized in sulfuric acid solution containing surface active substances—II. The anodic region

The hydrogen pressure equivalent to hydrogen overpotential on Pd electrode was determined under anodic polarization by combining the data of the electric resistance of a Pd foil electrode observed at various overpotentials with the electric resistance vs hydrogen pressure relationship which was obtained in a separate, gas phase experiment. The equivalent hydrogen pressure under anodic polarization was less diminished as compared with the value calculated by the Nernst equation from the total overpotential. Results are consistent with the conclusion reported previously for the cathodic region (Part I) that the Tafel—Volmer route is followed on the Pd hydrogen electrode with comparable value of the constituent step rates. Effect of addition to the solution of tetrabutylammonium hydroxide was also examined. Hydrogen content in Pd at the equilibrium hydrogen electrode potential under 1 atm hydrogen pressure was evaluated electrochemically to be H/Pd = 0.691. Hydrogen content in Pd under anodic polarization was evaluated.     

Nucleation and growth of copper under combined charge transfer and diffusion limitations: Part I

The nucleation and growth of copper crystals on a glassy carbon electrode are studied under potentiostatic conditions. Current transients are recorded at different overpotentials and are interpreted in terms of the theory of progressive nucleation and growth under combined charged transfer and diffusion limitations. Data are obtained on the overpotential dependence of the stationary nucleation rate and on the size of the critical copper nuclei. The influence of ion transfer and electron transfer electrochemical reactions taking place prior to and simultaneously with the process of nucleus formation is discussed and their contribution to the total current is accounted for.     

Correlation of Subsolidus Phase Relations in the Ag─Pd─O System to Oxidation Reduction Kinetics and Dilametric Behavior

The relationship between the equilibrium subsolidus phase diagram of the Ag─Pd─O₂ system, and the oxidation/reduction kinetics and microstructure development of 70Ag/30Pd coprecipitated and alloyed powders is presented. For the same Ag/Pd ratio and similar powder characteristics, the onset temperatures of Pd oxidation and PdO reduction for coprecipitated powders are lower than those of alloyed powders. For Ag/Pd alloyed powders, complete oxidation of Pd does not occur, because of kinetic limitations and the equilibrium phases present at high temperatures. Significant differences in microstructural evolution were observed and correlated to the oxidation processes and densification kinetics. The impact of these results on the use of the Ag/Pd system as conductors is discussed.     

碱液中添加酒石酸钾对锌电极性能的影响

利用循环伏安、恒电位阴极极化和动电位线性扫描等测试手段,研究了向 6mol/LKOH(ZnO饱和 )水溶液中加入酒石酸钾对锌电极电化学性能的影响。结果表明,添加酒石酸钾后,不仅可以增大锌电极的析氢过电位,减小腐蚀电流密度,而且可有效抑制锌枝晶的形成,其中以w(酒石酸钾) =2%为最优,恒电位阴极极化电流由未加时的 927. 7mA降为 72. 2mA。     

Effects of different nano-agglomerated powders on the microstructures of PS-PVD YSZ coatings

Plasma spray physical vapor deposition (PS-PVD) is a technology that combines the advantages of traditional atmospheric plasma spraying (APS) and electron beam physical vapor deposition (EB-PVD). As the feedstock of the PS-PVD, nano-agglomerated powder is critical on determining the microstructure of the obtained coating. In this study, a method to characterize the cohesion of nano-agglomerated powders was investigated. The nano-agglomerated powders fractured into smaller particles under ultrasonic waves. Their particle size distributions were measured to quantitatively compare their cohesiveness. The change rate in the percentage of powders with particle size less than 5 μm was selected as the value for the cohesion comparison. A high change rate corresponded to a faster fracture and lower powder cohesion. Furthermore, the fracture behavior and heat and mass transfer process of nano-agglomerated powders in the plasma torch were studied by combining 3-D simulation and observation of the microstructures of PS-PVD coatings sprayed with different powders. To obtain a quasi-columnar coating, the nano-agglomerated powder required high cohesion. Finally, a suitable powder was selected and quasi-columnar structure coatings were obtained by optimizing the PS-PVD parameters.     

Nucleation and growth of Pd nanoparticles during electrocrystallization on pencil graphite

The aim of present study was to investigate the mechanism of palladium electrodeposition on a pencil graphite surface from an aqueous solution containing 1 mM PdCl₂ and 500 mM H₂SO₄. Cyclic voltammetry revealed that the electrodeposition process proceeds via an initial underpotential deposition (UPD) and subsequently, it follows by the overpotential deposition (OPD) under diffusion control. Current transients showed a complex deposition trend, i.e. the electrodeposition of Pd includes at least three stages: adsorption on the surface, and two types of nucleation courses; two-dimensional (2D) and three-dimensional (3D) which limited by the lattice incorporation of Pd adatoms and the diffusion of Pd ions, respectively. Therefore the electrocrystallization of Pd on pencil graphite conforms to the Stranski–Krastanov growth mechanism. Furthermore, theoretical models were applied to evaluate each of above mentioned stages for different electrode potentials and to estimate the electrochemical parameters of Pd electrodeposition. The micrographs of electrodeposited Pd at relatively high frequency of the nucleation rate, illustrated a well dispersed Pd nanoparticles with a relatively narrow size distribution.     

Large specific surface area nanocrystalline Ti–Ru–Fe cathode materials for sodium chlorate

Ball-milled nanocrystalline Ti3RuFe powders were mixed with 1, 2, 4, 10 and 20 equivalents of Al and the mixtures were milled again for 20 h. The amount of Al atoms dissolved into the B2 structure of Ti3RuFe does not exceed 8–9 at %, the remaining being present as elemental Al into the powder mixture. During a subsequent treatment of the composite powder in alkaline solutions, the elemental Al is leached out, while Al solutes in the B2 structure are not affected. An examination of the surface by scanning electron microscopy reveals that the leached powder has a highly porous surface structure. Surface area measurements performed by BET measurements show that there is a tenfold increase in the effective surface area. Activated electrodes made from these porous materials show a significant decrease of the cathodic overpotential for hydrogen evolution in typical chlorate electrolysis conditions of about 80 mV.