Effects of the electrodeposition potential and temperature on the electrochemical capacitance behavior of ordered mesoporous cobalt hydroxide films

Novel ordered mesoporous cobalt hydroxide film (designated H_I-e Co(OH)₂) has been successfully electrodeposited from cobalt nitrate dissolved in the aqueous domains of the hexagonal lyotropic liquid crystalline phase of Brij 56. Experimental electrodeposition parameters such as deposition potentials and deposition temperatures are varied to analyze their influences on the electrochemical capacitor behavior. The films are physically characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to determine the effects of deposition potentials and temperatures on the surface morphology and nanostructure. Electrochemical techniques such as cyclic voltammetry (CV) and chronopotentiometry are applied to systematically investigate the effects of deposition potentials and temperatures on the capacitance of the films. The results demonstrated that the capacitive performance of the H_I-e Co(OH)₂ film achieved the highest value when it is electrodeposited at −0.75 V under the deposition temperature of 50 °C.     

Influence of the substrate's surface structure on the mechanism and kinetics of the electrochemical UPD formation of a copper monolayer on gold

The copper electrodeposition process was studied onto different gold substrates, single crystal (1 1 1) and polycrystalline, using electrochemical techniques. It was found, from the analysis of the experimental current density transients, that the potentiostatic formation of a full copper monolayer onto the gold electrode under UPD conditions follows the same mechanism, regardless of the crystallinity of the substrate. The mechanism involved the simultaneous presence of an adsorption process and of two 2D nucleation processes, progressive and instantaneous, respectively.     

Morphology and structure of the passive interphase formed during aqueous electrodeposition of polypyrrole coatings on steel

An iron(II) oxalate dihydrate passive interphase was electrodeposited on steel substrate from aqueous oxalate solutions prior to the electrochemical polymerization of pyrrole. The effect of electrochemical process parameters on the morphology and structure of the passive interphase was systematically investigated by scanning electron microscopy(SEM) and X-ray diffractometry (XRD). Our results reveal that the passive interphase is composed of a monolayer of closely packed crystals. The size of the crystals is dependent on the experimental conditions. The iron(II) oxalate dihydrate interphase formed on steel by electrochemical deposition has an orthorhombic structure irrespective of the reaction condition. The unit cell dimensions of the passive interphase formed by electrodeposition are slightly different from those formed by conventional chemical process.     

电沉积制备多孔Ni-Fe-Sn合金电极及其析氧性能

采用直流电沉积法在铜箔表面合成了多孔结构的Ni–Fe–Sn合金,用扫描电子显微镜、X射线能谱仪和X射线衍射仪对合金的微观组织形貌和相态进行了表征,用电化学工作站测试了合金电极在碱性环境中的析氧性能。结果表明,Ni–Fe–Sn合金电极主要由Ni3Sn2和FeNi3相组成,电极表面形成了多孔结构。在30wt% KOH溶液中,Ni–Fe–Sn合金的析氧过电位仅为261 mV(电流密度10 mA/cm2),Tafel斜率为69.9 mV/dec。电极在10 mA/cm2电流密度下能稳定工作12 h以上,具有良好的电化学稳定性。     

Development of HA-CNTs composite coating on AZ31 Magnesium alloy by cathodic electrodeposition. Part 2: Electrochemical and in-vitro behavior

The carbon nano-tubes (CNTs) reinforced hydroxyapatite (HA), with various functionalized CNTs concentration ranging from 0 to 1.5?wt%, were deposited on AZ31 magnesium alloy by direct and pulse cathodic electrodeposition methods. The corrosion resistance of the coatings was tested in simulated body fluid (SBF) using different electrochemical methods such as open circuit potential, polarization and electrochemical impedance spectroscopy. The in-vitro behavior, changes in solution pH as well as the amount of evolved hydrogen of these coatings were also evaluated during five days immersion in SBF. The results indicated that the pulse deposited HA having 1% CNTs coating was the optimum condition which decreased the corrosion current density of AZ31 magnesium alloy from 44.25?µA/cm² to 0.72?µA/cm². Moreover, it stabilized the alkalization behavior of AZ31 alloy and caused a tenfold decrease in the amount of hydrogen generation in SBF. Additionally, the formation of new hydroxyapatite layer on the surface of the pre-exist coatings after five days immersion in SBF was confirmed by SEM characterization.     

Pulsed electrodeposition of bismuth telluride films: Influence of pulse parameters over nucleation and morphology

Pulsed electrodeposition methods were applied to the preparation of bismuth telluride films. Over the potential ranges from −170 mV to −600 mV, the formation of Bi₂Te₃ nuclei proceeded through a three-dimensional instantaneous nucleation mode. The nuclei densities for several values of potential were ranged between ∼10⁶ nuclei cm⁻² and ∼10⁸ nuclei cm⁻². For a pulsed galvanostatic electroplating, the best covering percentage and a stoichiometry close to the desired Bi₂Te₃ were obtained with the parameters t_on, t_off and J_c, respectively, equal to 10 ms, 1000 ms and −100 mA cm⁻².     

Optical and electrochemical evaluation of colloidal Au nanoparticle-ITO hybrid optically transparent electrodes and their application to attenuated total reflectance spectroelectrochemistry

Colloidal Au nanoparticle monolayers covalently deposited on conductive layers of indium tin oxide (ITO) were fabricated and evaluated as optically transparent electrodes (OTEs) for spectroelectrochemical applications. Specifically, the electrodes were characterized using UV-Vis spectroscopy and cyclic voltammetry; comparisons are made with other types of hybrid ITO optically transparent electrodes. The optical modulation of surface-bound colloidal Au in response to potential cycling over a wide potential window (0.6 to −1.0 V) was acquired in an attenuated total reflectance (ATR) spectroelectrochemical cell. Finally, uptake of a model analyte, tris-(2,2′-bipyridyl)ruthenium(II) chloride, into a Nafion charge selective film spin coated onto the colloidal Au-ITO hybrid electrode was examined using ATR absorbance spectroelectrochemistry. Dependence of uptake on film thickness is addressed, and non-optimized detection limits of 10 nM are reported.     

Vapor-Phase Epoxidation of Propene over Au/Ti-MCM-41 Catalysts: Influence of Ti Content and Au Content

Ti-MCM-41 samples were used for propene epoxidation using H₂ and O₂ after Au deposition by deposition--precipitation. Au nanoparticles supported on Ti-MCM-41 with Ti incorporated hydrothermally followed by post-synthesis grafting gave higher propene oxide yields than Ti-MCM-41 with Ti incorporated hydrothermally or by grafting. Au L₃-edge EXAFS spectra show the presence of metallic Au for the low Au content (0.21 wt%) catalyst which is more selective to epoxidation, while at high Au loadings (0.42 wt%) oxidic Au species are observed and the catalyst shows lower epoxide selectivity.     

Development of HA-CNTs composite coating on AZ31 magnesium alloy by cathodic electrodeposition. Part 1: Microstructural and mechanical characterization

Magnesium alloys are considered as a new class of biodegradable alloys having many favorable properties to overcome the problems of currently used biomedical materials. Hydroxyapatite (HA) containing carbon nano-tubes (CNTs), with concentration ranging from 0 to 1.5?wt.%, coated on AZ31 magnesium alloy by direct and pulse cathodic electrodeposition methods. The coating properties including phase analysis, chemical bonding, morphology, and thickness were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FESEM), respectively. Nano-indentation, micro-hardness and adhesion tests were also used to evaluate the mechanical properties of the coatings. The results showed that a dense and fine coating structure was obtained by pulse deposition method. Moreover, the presence of carbon nanotubes in composite coating increased crystallization, presumably due to the increase in nucleation sites affecting the growth direction of hydroxyapatite crystals. The optimum condition having high crystallinity (71.2%) along with an uniform structure was the pulse deposited hydroxyapatite coating containing 1?wt.% CNTs. The elastic modulus and hardness of this sample increased by approximately 42% and 130% compared to the pure HA coating, respectively. Furthermore, the fracture toughness of pulse deposited HA–1wt % CNTs on AZ31 alloy reaches 1.96 ± 0.72MPa/m^0.5 which is in the range of compact bone.     

Hydrogen evolution during the oxidation of formaldehyde on Au:: The influence of single crystal structure and Tl-upd

Hydrogen evolution during formaldehyde oxidation in alkaline solution has been monitored by Differential Electrochemical Mass Spectrometry on Au(111) and polycrystalline gold. The current efficiency for hydrogen evolution increases with higher concentration and is in the same range on both, polycrystalline Au and Au(111) electrode. The onset potentials and half-wave potentials are higher on Au(111). Reaction orders for the faradaic current on the bare gold electrodes have been determined as 0.21 for higher and 0.76 for lower concentrations. Reaction orders for hydrogen evolution during formaldehyde oxidation are 1.4 times higher in each case. Tafel slopes in the range of 140–160 mV are found. This signifies that the first reaction step involving the formation of adsorbed hydrogen is largely determining the overall reaction rate. In the presence of thallium adlayers hydrogen evolution from formaldehyde oxidation is largely suppressed. On the thallium modified polycrystalline Au, formaldehyde oxidation is shifted for 100 mV to higher potentials where Tl is partially desorbed and hydroxide is coadsorbed on the modified surface. On thallium modified Au(111), a similar process takes place, but in the same potential region as the onset of formaldehyde oxidation on the bare surface and therefore the formaldehyde oxidation is only slightly shifted. Tafel slopes are decreased to 80 mV/dec in the presence of thallium. In the presence of adsorbed thallium, the first reaction step is in equilibrium, the coverage with adsorbed hydrogen is smaller and its recombination to H₂ is largely suppressed.     

Preparation of Pt–Ru bimetallic anodes by galvanostatic pulse electrodeposition: characterization and application to the direct methanol fuel cell

The electrodeposition of platinum and ruthenium was carried out on carbon electrodes to prepare methanol anodes with different Pt/Ru atomic ratios using a galvanostatic pulse technique. Characterizations by XRD, TEM, EDX and atomic absorption spectroscopy indicated that most of the electrocatalytic anodes consisted of 2 mg cm^–2 of Pt–Ru alloy particles with the desired composition and with particle sizes ranging from 5 to 8 nm. Electrochemical tests in a single DMFC show that these electrodes are very active for methanol oxidation and that the best Pt/Ru atomic ratio in the temperature range used (50–110 °C) is 80:20. The influence of the relaxation time t _off was also studied and it appeared that a low t _off led to smaller particle sizes and higher performances in terms of current density and power density.     

Influence of metal oxides on the catalytic behavior of Au/Al2O3 for the selective reduction of NOx by hydrocarbons

The reduction of NO by propene in the presence of excess oxygen over mechanical mixtures of Au/Al₂O₃ with a bulk oxide has been investigated. The oxides studied were: Co₃O₄, Mn₂O₃, Cr₂O₃, CuO, Fe₂O₃, NiO, CeO₂, SnO₂, ZnO and V₂O₅. Under lean C₃H₆-SCR conditions, these oxides (with the exception of SnO₂) convert selectively NO to NO₂. When mechanically mixed with Au/Al₂O₃, the Mn₂O₃ and Co₃O₄ oxides and, to a much greater extent, CeO₂ act synergistically with this catalyst greatly enhancing its SCR performance. It was found that their synergistic action is not straightforwardly related to their activity for NO oxidation to NO₂. The exhibited catalytic synergy may be due to the operation of either remote control or a bifunctional mechanism. In the later case, the key intermediate must be a short-lived compound and not the NO₂ molecule in gas-phase.     

Electrodeposition of Ag and Pd on a reconstructed Au(1 1 1) electrode surface studied by in situ scanning tunneling microscopy

Electrochemical deposition of Ag and potential-induced structural change of the deposited Ag layer on a reconstructed surface of Au(1 1 1) electrode were followed by in situ scanning tunneling microscope (STM). A uniform Ag monolayer was formed on a reconstructed Au(1 1 1) surface in a 50-mM H₂SO₄ solution at +0.3 V (vs. Ag/AgCl) after adding a solution containing Ag₂SO₄ so that the concentration of Ag⁺ in the STM cell became ca. 2 μM. No characteristic height corrugation such as the Au reconstruction was observed on the surface, indicating that the lifting of the substrate Au reconstruction occurred by Ag deposition. The formed Ag monolayer was converted to a net-like shaped Ag nano-pattern of biatomic height when the potential was stepped from +0.3 to −0.2 V in the solution containing 2 μM Ag⁺. This result indicates that the substrate Au(1 1 1)-(1 × 1) surface was converted to the reconstructed surface even in the presence of Ag adlayer. Quite different structure was observed for Pd deposition on a reconstructed surface of Au(1 1 1) electrode at +0.3 V and the origin for this difference between Ag and Pd deposition is discussed.     

Influence of anode material on the electrochemical oxidation of 2-naphthol: Part 1. Cyclic voltammetry and potential step experiments

The anodic oxidation of 2-naphthol has been studied by cyclic voltammetry and chronoamperometry, using a range of electrode materials such as Ti-Ru-Sn ternary oxide, lead dioxide and boron-doped diamond (BDD) anodes. The results show that polymeric films, which cause electrode fouling, are formed during oxidation in the potential region of supporting electrolyte stability. IR spectroscopy verified the formation of this organic film. While the Ti-Ru-Sn ternary oxide surface cannot be reactivated, PbO₂ and BDD can be restored to their initial activity by simple anodic treatment in the potential region of electrolyte decomposition. In fact, during the polarization in this region, complex oxidation reactions leading to the complete incineration of polymeric materials can take place on these electrodes due to electrogenerated hydroxyl radicals. Moreover, it was found that BDD deactivation was less pronounced and its reactivation was faster than that of the other electrodes.     

Evolution of hierarchically formed petal-like 3 dimensional layer structures for SnS2 via ratio control of Sn/thiourea and their electrochemical charge storage behavior

Herein, the successful synthesis of tin sulfide compounds by a facile one-step solvothermal method is reported, and its evolution of hierarchically formed petal-like 3-dimensional layer structures for SnS₂ via ratio control of Sn/thiourea(TU) is systematically investigated. With the increase of TU content, the two-dimensional layered structure is clearly changed from discrete to hierarchically dense nanostructure. Thus, among various conditions, SnS₂ with 1:2 ratio (SNS12) shows superior electrochemical performance associated with its discrete nanostructure. In this study, sample SNS12 shows a high specific capacitance of 1403 F g^-1 at 1 mVs^-1, a high power density of 456.42 W h kg^-1 at an energy density of 46.84 W kg^-1 with the stable cyclic performance of 85.87% up to 5000 cycles. The enhanced electrochemical performances are attributed to its unique ultrathin petal discrete structure, which allows for fast ion/electron transfer, high active sites, short diffusion distance, and more electrolyte/electrode interface access. Moreover, a fabricated symmetric supercapacitor device has a high capacity to operate commercial LED, leading to the validation of its practical operation durability for synthesized material on a device-level application. This study suggests that favorably layered 3D SnS₂ electrode materials and their controllable protocols via Sn/TU ratio modulation could be one of the beneficial direction for the envisioned energy storage applications.     

碱处理制备介孔-微孔沸石分子筛的影响因素及其应用研究进展

综述了碱处理制备介孔-微孔沸石分子筛的影响因素,包括碱处理条件、沸石分子筛硅铝比和模板剂对碱处理脱硅形成介孔的影响。评述了碱处理所制备介孔-微孔沸石分子筛在应用方面所取得的进展,重点介绍了它们在烷基化、异构化、裂化和醇烃化等催化反应中的应用。通过碱处理引入介孔可极大地缩短分子在沸石微孔道中的扩散距离,从而增强表观催化反应活性及提高催化剂的稳定性。提出了今后研究的重点为：阐明碱处理引入介孔的形成机理和碱处理对分子筛骨架结构、酸性的影响,拓展碱处理制备介孔-微孔沸石分子筛的应用 范围。     

Hydrogen evolution during the oxidation of formaldehyde on Au:: The influence of single crystal structure and Tl-upd

Hydrogen evolution during formaldehyde oxidation in alkaline solution has been monitored by Differential Electrochemical Mass Spectrometry on Au(111) and polycrystalline gold. The current efficiency for hydrogen evolution increases with higher concentration and is in the same range on both, polycrystalline Au and Au(111) electrode. The onset potentials and half-wave potentials are higher on Au(111). Reaction orders for the faradaic current on the bare gold electrodes have been determined as 0.21 for higher and 0.76 for lower concentrations. Reaction orders for hydrogen evolution during formaldehyde oxidation are 1.4 times higher in each case. Tafel slopes in the range of 140-160 mV are found. This signifies that the first reaction step involving the formation of adsorbed hydrogen is largely determining the overall reaction rate. In the presence of thallium adlayers hydrogen evolution from formaldehyde oxidation is largely suppressed. On the thallium modified polycrystalline Au, formaldehyde oxidation is shifted for 100 mV to higher potentials where Tl is partially desorbed and hydroxide is coadsorbed on the modified surface. On thallium modified Au(111), a similar process takes place, but in the same potential region as the onset of formaldehyde oxidation on the bare surface and therefore the formaldehyde oxidation is only slightly shifted. Tafel slopes are decreased to 80 mV/dec in the presence of thallium. In the presence of adsorbed thallium, the first reaction step is in equilibrium, the coverage with adsorbed hydrogen is smaller and its recombination to H₂ is largely suppressed.     

Adsorption of mercaptopropionic acid onto Au(1 1 1): Part I. Adlayer formation, structure and electrochemistry

The adsorption of 3-mercaptopropionic acid (MPA) on Au(1 1 1) in 0.1 M H₂SO₄ was studied by cyclic voltammetry, capacitance measurements and in situ scanning tunneling microscopy (STM). The formation of a self-assembled monolayer under electrochemically controlled conditions was monitored for the first time with an STM. A two-step adsorption process has been found, beginning with the adsorption of MPA to form a disordered film, which lifts the () reconstruction of Au(1 1 1), followed by an ordering of the MPA adlayer into two different dense structures. Concomitantly with the second step, formation of the well-known vacancy islands is observed. This formation is explained by an adsorbate-induced compression of the gold substrate. Two distinctly different structures of the dense MPA monolayer on Au(1 1 1) were observed. One () structure with p=3.6-4.8 and a second structure consisting of two unit cells of () and () symmetry. In part II, the effect of the MPA on the copper electrodeposition onto Au(1 1 1) is discussed.     

Influence of Pd on the structure and electrochemical hydrogen storage properties of Mg50Ti50 alloy prepared by ball milling

High-energy ball milling was used to modify the physico-chemical and the electrochemical hydrogenation properties of Mg₅₀Ti₅₀ alloy via the addition of Pd. This was done by first ball milling Mg and Ti together for (20 − x) hours. 3.3 at.% Pd was then added and ball milling was resumed for x hours. X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that the alloying of Pd with pre-milled Mg₅₀Ti₅₀ was initiated after only a few minutes and was completed after 5 h of milling. The maximum discharge capacity of the Mg₅₀Ti₅₀-3.3 at.% Pd electrode increased significantly with the milling time (from 35 mAh g⁻¹ for 5 min to 480 mAh g⁻¹ for 20 h of milling). The exchange current density increased with the milling time and was directly related to the Pd surface concentration, suggesting that Pd plays a key role in facilitating the charge-transfer reaction. In contrast, the incorporation of Pd had a minor effect on the hydrogen diffusion coefficient. The electrochemical pressure-composition isotherms revealed a significant destabilization of the hydride as the milling time with Pd increased. No significant improvement in the hydrogen storage properties of Mg₅₀Ti₅₀-Pd electrodes was observed for Pd concentrations higher than 3.3 at.%.