Multilayer Zn Research Articles

Multilayer Zn nanosheets promote electrochemical CO2 reduction to CO in KCl electrolyte

Electrochemical conversion of Carbon dioxide (CO2) into fuel is an effective strategy to alleviate the energy crisis and reduce carbon emissions. As the metal in lower cost, Zinc has good catalytic performance in CO2 electrochemical reduction reaction (CO2RR). Here, we report a multilayer Zn nanosheets electrode (MZN) made by electrochemical reduction in KCl electrolyte. The Zn atoms on the MZN surface and the chloride ions in the electrolyte formed a layer of Zn-Cl adsorption bond on the MZN surface, which promoted the electron transfer of CO2RR. The MZN catalyst has a maximal CO Faraday efficiency of about 86.6% at − 1.65 V vs. Ag/AgCl. And the MZN shows good stability during long-time electrolysis work. Electrochemical characteristic analysis indicates that the increased selectivity and activity of CO2RR were attributed to the formation of Zn-Cl adsorption bonds.

Microstructural evolution, damping and tensile mechanical properties of multilayer Zn–22Al alloy fabricated by accumulative roll bonding (ARB)

Multilayer Zn–Al eutectoid alloy (ZA22) was fabricated via accumulative roll bonding (ARB) for the first time, and the microstructural evolution, damping and tensile mechanical properties of the resultant specimens were studied. In the early stage of ARB, Zn–Al alloy layers were firstly formed between Zn and Al layers. With increasing the cycles of ARB, the volume fraction of the alloy layers increased gradually. After 9 cycles of ARB, the ZA22 alloy with uniform composition was obtained. Property tests showed that after 6 cycles of ARB, the damping in a wide temperature range from room temperature to around 275 °C, the tensile strength and the elongation to failure began to be higher than those of the cast ZA22 alloy. In particular, the elongation to failure of the ARB-7 specimen was 10.7 times that of the cast ZA22 alloy. Solution treatment could further significantly improve the damping and the elongation to failure. The microstructural origins of the improved properties were discussed in detail.

Hybrid effect of an in situ multilayer Zn–ZnO–Cr2O3 electrodeposited nanocomposite coatings for extended application

ABSTRACTMultifunctional composite coatings of Zn−ZnO−Cr2O3 were deposited electrolytically on prepared carbon mild steel (CS) from Zn electrolyte, having Zn2+ ions and uniformly dispersed nano ZnO−Cr2O3 particulates. The corrosion resistance characteristics of the deposited coatings were evaluated using the linear polarization measurement method in 3.65% NaCl. The microstructural properties of the produced multilayered coatings were evaluated by scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), x-ray diffraction (XRD), and atomic force microscope (AFM). Thermal deformations were observed after 4 h at 250°C and the mechanical response of the coated samples was investigated using a diamond-based Dura Scan microhardness tester and a MTR-300dry abrasive wear tester. From the results, a significant improvement in the corrosion performance of coatings was observed with bath containing less than 2 g/L. The microhardness, thermal stability, and anti-wear properties of Zn−ZnO−Cr2O3 shows improved performance against Zn−ZnO coating matrixes, which was attributed to dispersive strengthening effect and grain induced effect of the ZnO/Cr2O3 particulate.

Mechanism of power consumption inhibitive multi-layer Zn:SiO2/SiO2 structure resistance random access memory

In this paper, multi-layer Zn:SiO2/SiO2 structure is introduced to reduce the operation power consumption of resistive random access memory (RRAM) device by modifying the filament formation process. And the configuration of multi-layer Zn:SiO2/SiO2 structure is confirmed and demonstrated by auger electron spectrum. Material analysis together with conduction current fitting is applied to qualitatively evaluate the carrier conduction mechanism on both low resistance state and high resistance state. Finally, single layer and multilayer conduction models are proposed, respectively, to clarify the corresponding conduction characteristics of two types of RRAM devices.

Photocurrent Enhancement by Multilayered Porphyrin Sensitizers in a Photoelectrochemical Cell

Multilayer Zn(II) tetraphenylporphyrin chromophores, assembled using copper-catalyzed azide-alkyne cycloaddition (CuAAC), provide a new sensitization scheme that could be useful in dye-sensitized solar cells (DSSCs). We report on the photoelectrochemical responses of multilayer films of Zn(II) 5,10,15,20-tetra(4-ethynylphenyl)porphyrin (1) assembled on planar ITO substrates operating as a p-type DSSC using three different redox mediators. The traditional I(-)/I3(-) redox couple results in the greatest short circuit current densities (JSC) but very low open circuit potentials (VOC). The use of cobalt sepulchrate ([Co(sep)](2+/3+)) and cobalt tris-bipyridine ([Co(bpy)3](2+/3+)) as redox mediators generates higher VOC values, but at the expense of lower photocurrents. These results highlight the inherent differences in the interactions between the redox mediator and Zn(II) tetraphenylporphyrin multilayer films. Increasing the porphyrin content through multilayer growth proved to be effective in increasing the performance of photoelectrochemical cells with all three redox mediators. Cells using I(-)/I3(-) reached maximum performance (power output) at five porphyrin layers, [Co(bpy)3](2+/3+) at five layers, and [Co(sep)](2+/3+) at three layers. For all mediators, JSC increases with the addition of porphyrin layers beyond a monolayer. However, JSC reaches a maximum value at a point greater than one layer after which it decreases, presumably due to exciton diffusion limitations and the insulating effects of the multilayer film. Similarly, all cells also reach a maximum VOC beyond one porphyrin layer. We show that porphyrin arrays assembled using newly developed CuAAC layer-by-layer growth may be useful as a multilayer sensitization scheme for use in photoelectrochemical cells.

Formation of compositionally modulated Zn–Ni alloy coatings on steel

The results of experiments involving the compositionally modulated multilayer Zn–Ni alloy coatings obtained by electrochemical method are presented. The determination of morphology, corrosion resistance and surface roughness of obtained coatings and their hardness by Vickers method were described. It was found that coatings consisting of the highest number of sublayers (50) were characterised as having the best anti-corrosion properties, which arise from the alternating (anodic/cathodic) mechanism of the corrosion process and from the influence of the formed corrosion products. The multilayer structure of the obtained coatings also influenced coating morphology and the hardness of the obtained system.

Interfacial diffusion and exchange bias in the oxide multilayer Zn0.7Ni0.3Fe2O4/BiFeO3/SrTiO3

The aim of this work is to fabricate an all‐oxide spin valve using multiferroic BiFeO3 as the antiferromagnetic pinning layer, in the hope that we may be able to switch magnetoresistance electrically. The proposed architecture is Zn0.7Ni0.3Fe2O4/ Sr1–xLaxTiO3/ Zn0.7Ni0.3Fe2O4/ BiFeO3/ LaNiO3/SrTiO3. We have demonstrated that such a multilayer structure can be grown epitaxially by the RF magnetron sputtering. X‐ray diffraction showed that the films were indeed biaxially aligned with reasonable in‐plane and out‐of‐plane textures, under the growth conditions optimised for achieving good ferroelectric and magnetic properties. X‐ray photoelectron spectroscopy depth profiling showed that there was significant Bi diffusion across the interface if the BiFeO3 film was not stabilised in high oxygen ambience after deposition. High‐resolution transmission electron microscopy showed a tidy and sharp Zn0.7Ni0.3Fe2O4/ BiFeO3 boundary for the Zn0.7Ni0.3Fe2O4 films grown at 550 °C, while for the films grown at higher temperature an irregular interface was observed. Under the optimum growth condition, a clear exchange bias was achieved at the Zn0.7Ni0.3Fe2O4/ BiFeO3 interface. Copyright © 2011 John Wiley & Sons, Ltd.

Corrosion stability of electrodeposited cyclic multilayer Zn–Ni alloy coatings

This paper reports on a study of electrodeposition and characterisation of cyclic multilayer coatings of Zn–Ni alloy from a sulphate bath. Cyclic multilayer alloy coatings were deposited on mild steel through the single bath technique by appropriate manipulation of cathode current densities. The thickness and composition of the individual layers of the CMA deposits were altered precisely and conveniently by cyclic modulation of the cathode current during electrodeposition. Multilayer deposits with sharp change in composition were developed using square current pulses, using thiamine hydrochloride and citric acid as additives. Laminar deposits with different configurations were produced and their corrosion behaviours were studied by AC and DC methods in 5%NaCl solution. It was observed that the corrosion resistance of the CMA coating increased progressively with the number of layers (up to certain optimal numbers) and then decreased. The decrease in corrosion resistance at high degree of layering was attributed to interlayer diffusion due to less relaxation time for redistribution of metal ions at cathode during deposition. The coating configurations have been optimised for peak performance of the coatings against corrosion. It was found that CMA coating developed at cyclic cathode current densities of 3·0/5·0 A dm−2 with 300 layers showed the lowest corrosion rate (0·112×10−2 mm/year) which is ∼54 times better than that of monolithic Zn–Ni alloy, deposited from the same bath. The protection efficacy of CMA coatings is attributed to the difference in phase structure of the alloys in successive layers, deposited at different current densities, evidenced by X-ray diffraction analysis. The formation of multilayers and corrosion mechanism were examined by scanning electron microscopy.

Composition Modulated Multilayer Zn–Fe Alloy Coatings on Mild Steel for Better Corrosion Resistance

Composition modulated alloy (CMA) of Zn–Fe coatings were developed on mild steel galvanostatically from chloride bath containing sulphanilic acid (SA) and ascorbic acid (AA) through single bath technique (SBT). The properties of CMA coatings were found to depend on the thickness of individual layers and switching cathode current densities (SCCDs). The CMA (Zn–Fe) coating, having 120 layers, deposited at 20 and 50 mA cm−2, were found to show the least corrosion rate (1.545 × 10−2 mmy−1) compared to monolithic alloy (32.5 × 10−2 mmy−1) of the same thickness. The improved corrosion resistance of multilayered coatings was due to the fact that the defects and failures occurring in a single layer in the deposition process is covered by the successively deposited coating layers, and hence the corrosive agent path is extended or blocked. Further, the high corrosion resistance of CMA Zn–Fe coatings was attributed to the “dielectric barrier” of the coatings, evidenced by dielectric spectroscopy and Mott–Schottky's plot. The corrosion rate was found to increase at high degree of layering, and is attributed to less relaxation time for redistribution of metal ions in diffusion layer, during plating. In other words, at higher layer thickness, the CMA coating tends to become a monolithic. CMA coatings were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Electrolytic preparation of cyclic multilayer Zn–Ni alloy coating using switching cathode current densities

Cyclic multilayer alloy (CMA) coating of Zn–Ni was developed on mild steel using single bath technique, by proper manipulation of cathode current densities. The thickness and composition of the individual layers were altered precisely and conveniently by cyclic modulation of cathode current densities. Multilayer coatings, having sharp change in compositions were developed using square current pulses. Gelatin and sulphanilic acid (SA) acid were used as additives. Laminar deposits with different configurations were produced, and their corrosion behaviors were studied, in 5% NaCl solution by electrochemical methods. It was observed that the corrosion resistance of CMA coating increased progressively with number of layers (up to certain optimal numbers) and then decreased. Cyclic voltammetry study demonstrated the role of gelatin and SA in multilayer coating. The coating configuration has been optimized for the peak performance against corrosion. The substantial decrease of corrosion rate, in the case of multilayer coatings was attributed to the changed intrinsic electric properties, evidenced by Electrochemical Impedance Spectroscopy (EIS) study. The surface morphology and its roughness were examined by Atomic Force Microscopy (AFM). The surface and cross-sectional view of coatings were examined, using Scanning Electron Microscopy (SEM). X-ray photoelectron spectrum (XPS) study was carried out for surface analysis. The relative performance of pure Zn, monolithic and CMA coatings were compared and discussed.

Temperature-Induced Modifications of PdZn Layers on Pd(111)

Ultrathin PdZn surface alloys on Pd(111) are model systems well-suited for obtaining a microscopic understanding of the mechanisms of Pd/Zn-based catalysis for methanol steam reforming. The temperature-induced compositional and structural changes of these alloy films are investigated in the catalytically relevant temperature range. Heating of multilayer Zn films to 500 K results in the formation of multilayer PdZn alloy films with surface and near-surface composition close to 1:1. In the temperature regime above 550 K the subsurface layers deplete quickly in Zn due to diffusion of Zn atoms into the Pd bulk. In contrast, the composition of the surface layer changes only slightly, indicating formation of a PdZn film with strong monolayer character. This change in subsurface composition triggers a change of the original Zn-out/Pd-in surface corrugation, leading ultimately to a Pd-out/Zn-in situation for annealing temperatures beyond 700 K. The altered corrugation pattern is also obtained when submonolayer am...

Corrosion behavior of composition modulated multilayer Zn–Co electrodeposits produced using a single-bath technique

Composition modulated alloy (CMA) electrodeposits of Zn–Co were produced from acid chloride baths by the single-bath technique. Their corrosion behavior was evaluated as a function of the switched cathode current densities and the number of layers. The process was optimized with respect to the highest corrosion resistance. Enhanced corrosion resistance was obtained when the outer layer was slightly richer with cobalt. At the optimum switched current densities 40/55 mA cm−2, a coating with 600 layers showed ~6 times higher corrosion resistance than monolithic Zn–Co electrodeposit having the same thickness. The CMA coating exhibited red rust only after 1,130 h in a salt-spray test. The increased corrosion resistance of the multilayer alloys was related to their inherent barrier properties, as revealed by Electrochemical Impedance Spectroscopy. The corrosion resistance was explained in terms of n-type semiconductor films at the interface as supported by Mott–Schottky plots.

Development of compositionally modulated multilayer Zn–Ni deposits as replacement for cadmium

Compositionally modulated multilayer (CMM) Zn–Ni deposits were electrodeposited from single acidic bath (pH = 4.7) by using a potentiostatic sequence. The Zn and Ni composition in the alloy was tailored as a function of distance from the steel substrate. X-ray diffraction studies of the deposit showed the presence of γ-phase with a composition of Ni 5Zn 21. The corrosion properties of modulated multilayer coatings were studied in 5% NaCl solution using electrochemical corrosion techniques. The polarization resistance of the deposits varied as a function of Ni content between 1700 and 3440 Ω. CMM Zn–Ni with 20 wt% Ni exposed in ASTM B117 salt spray test did not show any red rust formation after 400 h.

Chemical reactions of [formula omitted] thin films

We report a combined temperature programmed desorption and Auger electron spectroscopy study of Zn and ZnO thin films on Cu, Cu 2O, and CuO surfaces. Multilayer Zn films desorb at 500 K with a pre-exponential factor of 10 12 s −1 and a desorption energy of 32 kcal mol , in excellent agreement with the heat of sublimation of bulk Zn metal. The bottommost layer of Zn atoms has a desorption energy that is 6 kcal mol larger, which is consistent with the heat of formation of dilute Cu Zn alloys. Films converted to ZnO by oxidation in air decompose with an apparent activation energy of 45 kcal mol , which is substantially smaller than the decomposition energy of bulk ZnO. Thin ZnO films can also be formed by evaporating multilayer coverages of Zn onto CuO or Cu 2O and then heating. When CuO is used as the substrate, the Zn film is oxidized by O atoms produced by the reduction of CuO to Cu 2O. When Cu 2O is used as the substrate, ZnO is produced by the reduction of Cu 2O to Cu, which migrates to the surface of the ZnO film.