Phase composition of electrodeposited silver-indium alloys

The phase composition of electrochemically obtained Ag-In alloy coatings electrodeposited at different conditions was determined. With the increase in the current density, both indium content and heterogeneity of the deposited layers increase. The amount of the indium-richer phase increase as well. Before the thermal treatment, the phases Ag, Ag₃In, and In₄Ag₉ are observed in coatings with spatio-temporal structures. As a result of heating the new phase Ag₄In appears at temperatures above 500 °C and indium is oxidized up to In₂O₃ from the oxygen in the heating chamber. Up to 500 °C, the spatio-temporal structures are still visible. Probably they consist of both Ag-rich α-phase and one of the phases of the alloy system with small indium content, such as Ag₄In or Ag₃In.     

Electrocatalytic behavior of electroless Ni-P alloys for the oxygen evolution reaction

The structural and morphological characteristics of electroless nickel phosphorous films (P content from 4.0 to 13.8 at %) are described. Different treatments such as heat (400°C, 1 h) or electrochemical (anodizing at 0.5 V vs. SCE followed by multi-cycle polarization) are employed and their effect on the alloys properties is analyzed using x-ray diffraction and atomic force microscopy. Information on the performance of the as-deposited and treated electroless Ni-P coatings as anodes for oxygen evolution reaction, in alkaline media, is taken from the steady state polarization curves and the correspondent Tafel slopes. The data shows the importance of the deposit crystalline nature and of the electrochemical treatment on the formation of β-Ni(OH)₂ and subsequently β-Ni(OOH), crucial for obtaining Ni-P films with good electrocatalytic properties. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 12, pp. 1427–1434. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes.” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Nonstoichiometric Ti-Zr-Ni-V-Mn alloys: the effect of composition on hydrogen sorption and electrochemical characteristics

The effect of the stoichiometric factor on the electrochemical and gas-phase behavior of hydride-forming intermetallic alloys of the Ti_0.45Zr_0.55Ni_yV_0.45Mn_x general composition is studied. The structure and the phase composition of the alloys were investigated by means of X-ray diffraction, electron microscopy, and electron probe microanalysis. An introduction of hydrogen does not change the structure type and hydriding is accompanied by an isotropic increase in the cell volume by about 20%. The alloys studied demonstrate maximum values of hydrogen sorption capacity, discharge capacity, and good rate capability throughout a wide range of compositions, rather than in a narrow region in the vicinity of the stoichiometric composition.Dedicated to Professor W. Vielstich on his 80th birthday as an acknowledgement of the contribution he made to the development of electrochemistry.     

Towards the object-oriented design of active hydrogen evolution catalysts on single-atom alloys

Given a desired property, locating relevant materials is always highly desired but very challenging in a range of areas, including heterogeneous catalysis. Obviously, object-oriented design/screening is an ideal solution to this problem. Herein, we develop an inverse catalyst design workflow in Python (CATIDPy) that utilizes a genetic-algorithm-based global optimization method to guide on-the-fly density functional theory calculations, successfully realizing the highly accelerated location of active single-atom alloy (SAA) catalysts for the hydrogen evolution reaction (HER). 70 binary and 752 ternary SAA candidate catalysts are identified for the HER. Furthermore, via considering the segregation stability and cost of materials, we extracted 6 binary and 142 ternary SAA candidate catalysts that are recommended for experimental synthesis. Remarkably, guided by these theoretical identifications, homogeneously dispersed Ni-based bimetallic catalysts (e.g., NiMo, NiAl, Ni₃Al, NiGa, and NiIn) were synthesized experimentally to test the reliability of the CATIDPy workflow, and they showed superior HER performance to bare Ni foam, indicating huge potential for use in real-world water electrolysis techniques. Perhaps more importantly, these results demonstrate the capacity of such a proposed approach for investigating unexplored chemical spaces to efficiently design promising catalysts without knowledge from the expert domain, which has far-reaching implications.

An inverse catalyst design workflow in Python (CATIDPy) for discovering unexplored chemical spaces successfully realized the highly accelerated location of active single-atom alloy (SAA) catalysts for the hydrogen evolution reaction (HER).     

Studies of the hydrogen evolution reaction on smooth Co and electrodeposited Ni–Co ultramicroelectrodes

The hydrogen evolution reaction (HER) was studied on smooth Co and on electrodeposited Ni–Co ultramicroelectrodes (UMEs) in alkaline solutions at several temperatures by steady-state polarisation curves. The real electrochemical area was previously estimated by cyclic voltammetry to account for the large difference in roughness factor of the two surfaces. The values obtained for the Tafel slopes were very close to 2.303RT/βnF while the ‘apparent’ energies of activation were 59 and 41 kJ mol⁻¹ for Co and Ni–Co, respectively. A common Volmer–Heyrovsky mechanism with Heyrovsky as the rate-determining step (RDS) was initially proposed. This was confirmed when the experimental results were mathematically treated by a non-linear fitting procedure using the kinetic equations derived for that mechanism. The calculations revealed that Ni–Co is a more efficient catalyst for the HER then pure Co, with a rate constant value of 0.16×10⁻¹⁰ mol s⁻¹ cm⁻² at 25°C for the slow step. Although this value is more than one order of magnitude smaller than that already reported for deposited Ni, it is considerably larger than the one measured here (0.02×10⁻¹⁰ mol s⁻¹ cm⁻²) for pure Co at 25°C.     

Effects of ultrasonic field on structure evolution of Ni film electrodeposited by bubble template method for hydrogen evolution electrocatalysis

Journal of Solid State Electrochemistry - Self-supporting porous Ni film with uniform honeycomb-like micropores and a thickness of up to 66 μm is electrodeposited by dynamic hydrogen...     

The effect of bubbles on the measured electrochemical parameters during hydrogen evolution on nickel

The hydrogen evoluton reaction has been investigated at nickel rotating and vertical stationary electrodes in 1 M HC1. Steady state current—potential, impedance—potential and potential step—current—time transients results are reported. The impedance is analysed by equivalent circuit to produce double layr capacity—potential, ohrnic resistance—potential (and charge transfer resistance—potential) curves. Some deductions are made about the bubble layer and its effect on the electron transfer mechanism for the reaction.     

The effect of hydrogen on amorphization of iron-tungsten alloys produced by electrochemical synthesis

It is shown that the transition from common crystal form (iron-based solid solutions) to the nanocrystalline form occurs at a hydrogen content exceeding 2–3 cube centimeters (at standard conditions) per 1 g of alloy. Therewith, the current density and potential of deposition can vary and depend on the solution composition and other conditions. It is proposed that the transition occurs as an explosive process: in a thin juvenile alloy layer containing a certain limiting amount of hydrogen, high stresses arise; as a result, the concentration of defects increases accelerating hydrogen incorporation. The relevant calculations are performed and the dimensionless constant of hydrogen codeposition is determined (within the framework of the model developed). An alternative supposition is that iron hydroxide precipitating in the near-electrode layer, which also enters into the alloy composition, plays an important role in these processes.     

电沉积非晶态镍磷合金的研究

本文用电化学方法, X射线衍射及电子能谱方法研究了阴极恒电位沉积非晶态镍磷合金镀层,实验结果表明,影响镍磷合金非晶结构的主要因素是镀层中的磷含量,当磷含量大于9%时,镀层具有良好的非晶结构,镀层中镍和磷主要以元素态形式存在,磷的析出具有诱导共析特点。     

Hydrogen electrosorption properties of electrodeposited Pd-Ir alloys

Journal of Solid State Electrochemistry - The study of the hydrogen sorption process in metals/alloys of different forms is crucial for developing the fields of catalysis and energy storage. The...     

Correlations between hydrogen electrosorption properties and composition of Pd-noble metal alloys

Hydrogen adsorption on and absorption into Pd alloys with other noble metals was studied in acidic solutions (0.5 M H₂SO₄) using cyclic voltammetry. Correlations were found between the potentials of adsorbed/absorbed hydrogen oxidation peaks and surface/bulk compositions of Pd–Rh alloys. The potential of the α–β-phase transition depends linearly on Pd bulk content in Pd–Au, Pd–Rh, Pd–Pt and Pd–Pt–Rh alloys. The obtained relationships can be utilized for the determination of the composition of homogeneous Pd-noble alloys from hydrogen electrosorption experiments.     

Effect of sodium dodecyl sulfate on the rate of hydrogen evolution at a cathode

The effect of H(2) evolution on the mass-transfer coefficient of cathode reduction of potassium ferricyanide at a mercury cathode was studied with the aim of (i) comparing the mass transfer behavior at a Hg cathode with that at solid electrodes under gas-evolving conditions and (ii) testing the effect of anionic surface-active agent on the mass transfer behavior of an H(2)-evolving Hg cathode. It is found that the mass transfer coefficient at the Hg cathode was much higher than the value at a solid cathode. The mass transfer coefficient at H(2)-evolving Hg was found to decrease in the presence of sodium dodecyl sulfate (SDS) surfactant by an amount ranging from 58.8 to 76%, depending on the H(2) discharge rate and the SDS concentrations.     

Occlusion of hydrogen in electrodeposited platinum layers

Occlusion of hydrogen in platinized platinum electrodes has been studied in 1 mol/dm³ H₂SO₄ electrolyte. It has been found that the amount of hydrogen dissolved in the platinum layer depends on the structure of the Pt deposit, which is determined by the parameters of electrodeposition. Composition of the platinizing solution as well as the potential of Pt deposition are decisive parameters. On the basis of experimental results it is assumed that occlusion of hydrogen takes place in special structural elements of the platinum layer which are formed in the course of Pt deposition. Hydrogen dissolution versus H-deposition potential, H-deposition time and Pt layer thickness relationships are also presented. Received: 2 March 1999 / Accepted: 25 May 1999     

The effect of cooling rate on the solidification and microstructure evolution in duplex stainless steel

The effects of the cooling rate on the solidification and microstructure evolution in the duplex stainless steel SAF 2205 was studied using DSC and light microscopy. A ferritoscope was used to measure the ferrite content. It was revealed that the cooling rate has an influence on the ??-ferrite nucleation temperature and the width of the solidification interval. Moreover, with an increase in cooling rate, the content of ??-ferrite increases, while the quantity of austenite in the ferrite matrix decreases and its morphology changes to acicular. A two-cycle DSC experiment made possible a more accurate interpretation of the collected data.     

Effect of benzaldehyde derivatives on the rate of hydrogen evolution in a sealed lead-acid battery

The influence exerted by a number of benzaldehyde derivatives on the rate of hydrogen evolution from a lead-acid battery was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1467–1471.Original Russian Text Copyright © 2004 by Kamenev, Kiselevich, Ostapenko, Varypaev.     

Surface composition of alloys

The practical importance of alloy surfaces in catalysis, corrosion andother aspects of materials performance is widely recognized. What is needed now is sufficient knowledge of the relationship between externally controllable factors — alloy composition, temperature, environment — and surface properties — composition, structure, chemical activity — to control materials performance in these applications. Our purpose here is to review progress in determining and predicting the relationship between one surface property, composition, and certain externally controllable variables: overall composition, temperature, environment and physical form.We find that theoretical treatments of metal alloy surface composition now include essentially all significant physical effects and can predict values for most parameters of interest. Though improvements are still possible, the accuracy of predictions is more often limited by uncertainties or absence of the basic data for the calculations (e.g., thermochemical values) than by the models themselves.Alloy surface composition can now be measured well. The first monolayercomposition of large alloy slabs can be determined quantitatively over a wide temperature range in ultra-high vacuum. Difficulties with specimens of practical interest still challenge experimentalists. Among these are supported catalysts, surfaces under chemisorbed layers and composition of layers below the first. Significant progress is being made and we expect the next few years will see success.     

Characterization of the passive films on electrodeposited Fe-Ni-Cr alloys in borate solution at pH 8.4

The corrosion properties of the passive layers formed on iron-nickel-chromium electrodeposits of Fe₂₉Ni₅₁Cr₂₀ were investigated in 0.3 M borate solution at a‘ pH of 8.4. On the basis of measurements by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy, a low passive dissolution/corrosion rate was identified for the electrodeposited Fe-Ni-Cr alloys due to the nature of the established corrosion layer. The stability of this passive layer was further enhanced after corrosion under oxidizing conditions. Mössbauer spectroscopic measurements confirmed the existence of a thin passive layer on the amorphous electrodeposits.