Preparation of MoO3/Pt electrodes by electrodeposition for a direct methanol fuel cell

MoO₃/Pt binary catalysts with various Mo/Pt ratios were prepared by an electrodeposition method for use as the anode in a direct methanol fuel cell. Pt was electrodeposited onto indium tin oxide (ITO) substrate, and then MoO₃ was electrodeposited from an Mo-peroxo electrolyte on the top of Pt with different deposition times. The crystallinity of synthesized films was analyzed by X-ray diffraction (XRD), and the oxidation state of both the platinum and molybdenum were determined by X-ray photoelectron spectroscopy (XPS) analyses. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM/EDS) was employed to investigate the surface morphology and composition. The catalytic activity and stability for methanol oxidation were measured using cyclic voltammetry and chronoamperometry in a mixture of 0.5 M H₂SO₄ and 0.5 M CH₃OH aqueous solution. Electrocatalytic activity for CO oxidation was also evaluated in a 0.5-M H₂SO₄ solution. The addition of a proper amount of MoO₃ was found to significantly improve both the catalytic activity and stability for methanol oxidation.     

Atomic layer deposition of crystalline molybdenum oxide thin films and phase control by post-deposition annealing

Molybdenum forms a range of oxides with different stoichiometries and crystal structures, which lead to different properties and performance in diverse applications. Herein, crystalline molybdenum oxide thin films with controlled phase composition are deposited by atomic layer deposition. The MoO₂(thd)₂ and O₃ as precursors enable well-controlled growth of uniform and conformal films at 200–275 °C. The as-deposited films are rough and, in most cases, consist of a mixture of α- and β-MoO₃ as well as an unidentified suboxide MoO_x (2.75 ≤ x ≤ 2.89) phase. The phase composition can be tuned by changing deposition conditions. The film stoichiometry is close to MoO₃ and the films are relatively pure, the main impurity being hydrogen (2–7 at-%), with ≤1 at-% of carbon and nitrogen. Post-deposition annealing is studied in situ by high-temperature X-ray diffraction in air, O₂, N₂, and forming gas (10% H₂/90% N₂) atmospheres. Phase-pure films of MoO₂ and α-MoO₃ are obtained by annealing at 450 °C in forming gas and O₂, respectively. The ability to tailor the phase composition of MoO_x films deposited by scalable atomic layer deposition method represents an important step towards various applications of molybdenum oxides.     

Preparation and Characterization of Molybdenum Oxide Thin Films by Sol-Gel Process

This paper presents a new sol-gel process to prepare molybdenum oxide thin films. A molybdenum acetylacetonate sol was prepared by employing the system CH₃COCH₂COCH₃/MoO₃/C₆H₅CH₃/HOCH₂CH₂OCH₃. A molybdenum acetylacetonate gel was prepared by addition of aqueous NH₃. Thermal gravimetry (TG) and differential thermal analyses (DTA) of the gel suggested that crystallization of MoO₃ occurs in a 140 K temperature range around 508°C. MoO₃ films were prepared on fused silica, Si (111) and Al₂O₃ (012) substrates by annealing spin coating films of the sol in oxygen environment at 508°C. X-ray diffraction (XRD) showed that all films crystallize in -MoO₃ structure, and crystallites on fused silica substrate are arbitrarily oriented while those on Si (111) and Al₂O₃(012) substrates oriented in the (010) direction. SEM investigations showed that MoO₃ grains of all films are randomly distributed, with a longitudinal dimension of about 1–5 m and the film thickness is about 1 m.     

Electrochemical formation and composition analysis of Zn x Cd1-x Se solid solutions

The direct growth of ZnSe–CdSe solid solution onto metallic cathodes by electrodeposition from acidic aqueous sulphate solutions is described. The plating process is studied by simple voltammetry, while the structure and composition of the electrolytic deposits are investigated by X-ray diffraction. The experimental d-spacing values of the as-grown mixed lattice are compared to data from reference Zn _x Cd_1-x Se pellets of standard composition, produced by a sintering method. The findings are supplemented with energy-dispersive X-ray (EDX) elemental analysis. Thereupon, the variation of the mole fraction x in Zn _x Cd_1-x Se, and the solid phase constitution of the electrodeposits are determined and correlated to the electrochemical conditions of growth. The resulting films contain admixtures of CdSe compound and metallic Cd.     

Electrodeposition of Zn–TiO<Subscript>2</Subscript> nanocomposite films—effect of bath composition

Zn–TiO₂ nanocomposite films were prepared by pulsed electrodeposition from acidic zinc sulphate solutions on a Ti support. The influence on the composite structural and morphological characteristics of Zn²⁺ and TiO₂ concentrations in the deposition bath has been investigated. The characterisation of the samples was made by X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS). For all the obtained coatings, the anatase and rutile phases’ most intense diffraction lines were observed between 24° and 28° 2θ, confirming the formation of the Zn–TiO₂ nanocomposite. X-ray diffraction data show that the presence of the TiO₂ nanoparticles plays a remarkable influence on the preferred orientation of the metal matrix. For the more diluted solution, a dependence between the metallic matrix grain size and the concentration of TiO₂ in bath is observed. The grain size decreases with the increasing on the nanoparticle amounts. The SEM results for Zn and Zn–TiO₂ deposits indicate that the nanoparticles have a strong influence on the deposit surface morphology, which is caused by the changes on the deposition mechanism.     

Electrochemical deposition of molybdenum oxide into films of poly(3,4-ethylenedioxythiophene) conducting polymer on glassy carbon substrates

Electrochemical deposition of molybdenum oxides from molybdate-containing solutions onto glassy carbon electrodes and the same electrodes coated with a film of poly(3,4-ethylenedioxythiophene) conducting polymer was studied. The morphology of the deposited molybdenum oxides was examined by scanning electron microscopy. The method of X-ray photoelectron spectroscopy was used to determine the state of molybdenum in surface molybdenum oxides and a conclusion was made that the oxide MoO₂ is mostly present.     

Influence of electrodeposition conditions on the properties of CdTe films

The results of the influence of electrodeposition conditions on the structural, compositional, optical, and photoelectrochemical properties of CdTe thin films deposited in one-step electrochemical method are presented. The CdTe films were prepared electrochemically from aqueous acidic solution with low ratios of Cd²⁺ ions to Te(IV) ions concentration. Instead of commonly used TeO₂, water-soluble Na₂TeO₃ was used as a source of tellurium ions. The cathodic deposition of CdTe was performed at different constant potentials from solutions containing different cadmium and tellurium ions concentration. As-deposited CdTe thin films were studied by different analytical techniques. The X-ray photoelectron spectroscopy spectra exhibited CdTe formation on the electrode with some amount of tellurium oxides and cadmium oxides. The best quality CdTe deposits, free of TeO₂, were formed in bath containing excess of Cd²⁺ ions and at the potential of ?0.65 V vs. saturated calomel electrode, slightly more positive than E _eq of Cd/Cd²⁺ system. Structural X-ray diffraction studies revealed polycrystallinity of deposits with the highest content of the (111)-oriented cubic (111) form. Optical band gap energy values were found in the range from 1.36 to 1.6 eV for CdTe films prepared at various synthesis conditions. The preliminary photoelectrochemical studies have shown that the variation of the deposition potential as well as bath composition leads to the formation of p- or n-type CdTe films. As-deposited CdTe films were not stable in polysulfide solution under illumination.     

Composite films of polyaniline and molybdenum oxide formed by electrocodeposition in aqueous media

Composite films of polyaniline (PANI) and molybdenum oxide (MoO_x) were afforded through a convenient route of electrocodeposition from aniline and (NH₄)₆Mo₇O₂₄. The composite films showed characteristic redox behaviors of PANI and MoO_x, respectively, on the cyclic voltammograms. Chlorate and bromate were catalytically electroreduced with an enlarged current on the composite film at a potential ca. 0.2 V more positive than that on MoO_x. The potential window for the composite film to display pseudocapacitive properties in 1.0 mol·dm⁻³ NaNO₃ was −0.6 ∼ 0.6 V vs SCE. The cathodic potential limit shifted at least 0.4 V negatively from that of polyaniline (PANI)-based materials reported so far. The specific capacitance was 363.6 F·g⁻¹ when the composite film was charged–discharged at 1.5 mA·cm⁻², about two times of that of the similarly prepared PANI. The composite film was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Molybdenum existed in a mixed state of +5 and +6 in the composite film based on XRD and XPS investigations. Figure PANI and (MoO_x) were electrocodeposited in aqueous solutions from aniline and (NH₄)₆Mo₇O₂₄. The composite film obtained displayed catalytic activities toward the electroreduction of oxoanions. The pseudocapacitance of the composite film is nearly two times of that of PANI with the potential window extended negatively up to −0.6 V vs SCE     

Solution preparation of the amorphous molybdenum oxysulfide MoOS2 and its use for catalysis

Acid condensation of aqueous MoO₂S₂²⁻ anion yields amorphous MoOS₂ oxysulfide. This compound possesses tubular morphology and when freshly precipitated is soluble in polar organics such as acetone and ethanol. The ensemble of characterizations (IR, UV-visible, EXAFS spectroscopy) suggests that it contains cyclic or short linear oligomers of neutral molybdenum (V) oxysulfide MoOS₂ core. Thermal decomposition of MoOS₂ under inert atmosphere leads to the formation of a mixture of MoO₂ and MoS₂ phases. Promotion of MoOS₂ with cobalt followed by sulfidation leads to highly active HDS catalysts.     

On the Reduction of MoO3 to MoO2: A Path to Control the Particle Size and Morphology

During the reduction of molybdenum trioxide (MoO₃) to metallic molybdenum, the first reduction step yielding molybdenum dioxide as an intermediary product is of crucial importance. In this study, we examined the impact of the parameters reduction temperature, water influx, and potassium content on the hydrogen reduction of this first reaction step. Beginning from the same starting material, the chemical vapor transport mechanism was utilized to yield the phase pure MoO₂. Analyses including powder X-ray diffraction, inductively coupled plasma-mass spectrometry, scanning electron microscopy, and high performance optical microscopy were performed on the product phases. Modulations of the specific surface areas of molybdenum dioxide ranging from 2.28 to 0.41 m²/g were possible. Furthermore, a distinct shift from small plate-like grains to cuboid-like forms was achieved.     

CuInS2：两步电沉积制备及性能

采用恒电位沉积法制备铜铟合金预制膜,并存管式炉中通过固态源蒸发硫化预制膜得到CuInS:薄膜.通过扫描电镜(SEM)、能量色散谱仪(EDS)和X射线衍射仪(XRD)对CuInS2薄膜的表而形貌、截面厚度、成分组成和薄膜的组织结构进行了研究,并利用紫外可见光吸收谱仪(UV-Vis)研究了不同硫化温度对CuInS:薄膜的形貌及其光学吸收性质的影响.结果表明:不同的退火温度能够影响CuInS:薄膜的表面形貌以及带隙的大小,从而影响其光学吸收特性.     

Studies on electrodeposition of Zn–MoS<Subscript>2</Subscript> nanocomposite coatings on mild steel and its properties

Pure zinc and Zn–MoS₂ composite coatings were prepared by electrodeposition from zinc sulfate–chloride bath containing uniformly dispersed MoS₂ nanoparticles. The effect of MoS₂ on the deposition properties morphology, crystallographic orientation, and corrosion behavior were studied. The electrokinetic properties (zeta potential) and size distribution statistics in plating bath for the particles were evaluated using dynamic light scattering experiments. The Zn and Zn–MoS₂ deposition process was studied by linear polarization and cyclic voltammetry. Scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction analysis, and potentiodynamic polarization measurements were used to characterize the coatings. The addition of MoS₂ to the electrolyte significantly changed the microstructure and crystallographic orientation of the zinc deposits and enhanced the corrosion resistance of the coatings. The morphological and electrochemical properties of the zinc coatings were observed to be significantly affected by the incorporation of MoS₂ particles into the zinc matrix.     

Thin film nonstoichiometric chromium oxide-based cathode material for rechargeable and primary lithium batteries

The application of nonstoichiometric chromium oxide-based thin film cathodes in lithium rechargeable and primary batteries operating at high rates has been demonstrated. Films of varying composition have been obtained by anionic Cr (VI) species electrodeposition on a 1X18N10Т grade stainless steel cathode from fluoride-containing electrolytes. The effect of film doping by Li⁺ ions during its electrosynthesis has been сonsidered. As-prepared films were studied by scanning and transmission electron microscopies, 3D optical profiler, thermogravimetric analysis, chemical analysis, and X-ray diffraction (XRD). The main phase components of the electrodeposited films regardless of Li⁺ in an electrolyte are Cr₂O₃, α-CrOOH, β-CrOOH, and metallic chromium as shown by XRD pattern refinement. The electrochemical reduction rate in a non-aqueous electrolyte (1 M LiClO₄ in PC/DME) correlates with the chromium oxide-hydroxide component content of film. Primary CrO _x -Li CR2325 mock-up cathode coating can be discharged in a pulsed mode at 10 Ω external resistance with 80–84 mA cm^?2 current densities for 10–100 ms. Thin film cathodes electrodeposited in the presence of lithium ions become rechargeable when the lithium content of the film reaches 0.02 wt.%. Mock-ups of CR2325 coin battery with a thin film cathode doped with lithium ions can be discharged more than 40 times with 136 mAh g^?1 specific capacity, 461 Wh kg^?1 specific energy and 154 W kg^?1 power density at 30 kΩ external resistance. The simplicity of thin film preparation makes this technology promising for thin film lithium batteries.     

The photocatalytic properties of Ti–Mo oxides prepared by a simple sol–gel route

Powders containing mixtures of titania and molybdite in different ratios were prepared by sol–gel processing. The sols were dried and subsequently calcined at 300, 500 and 700 °C. Depending on the ratio of Ti and Mo in the initial sol and the calcination temperature, Ti-doped MoO₃, TiO₂/MoO₃ or Mo-doped TiO₂ have been formed. The as prepared samples were characterised by scanning electron microscopy with attached X-ray dispersive energy analysis, X-ray diffractometry, Raman spectroscopy, gas adsorption and optical characterisation by ultraviolet/visible spectroscopy. The latter was used for the analysis of the photocatalytic properties on the decolourisation of methylene blue solutions under visible light irradiation. The phase composition, the specific surface and the photocatalytic activity were influenced by the molybdenum content and the calcination temperature. The final molybdenum content in the samples additionally depends on the calcination temperature. The optimum photocatalytic properties were observed or Ti-doped MoO₃.     

Growth and characterization of molybdenum oxide thin films prepared by photochemical metal–organic deposition (PMOD)

Molybdenum oxide thin films have been successfully prepared by direct UV irradiation of amorphous films of a molybdenum dioxide acetylacetonate complex on Si(1 0 0) substrates. Photodeposited films were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and the surface morphology examined by Atomic Force Microscopy (AFM). It was found that as-photodeposited films are uniform and smooth, with thickness of 350 nm, with rms surface roughness of 28 nm and contain non-stoichiometric oxides (MoO_3−x). The results of XRD analysis showed that post-annealing of the films in air at 450 °C transforms the sub-oxides to α-MoO₃ phase with a much rougher surface morphology (rms = 144 nm). The as-photodeposited MoO_3−x films are amorphous, and exhibit better optical quality than annealed films.     

Layered molybdenum oxide thin films electrodeposited from sodium citrate electrolyte solution

Molybdenum oxide thin films were prepared electrochemically onto the selenium predeposited tin oxide-coated glass substrates using 0.22 M sodium citrate (C₆H₅Na₃O₇) solution (pH 8.3) and sodium molybdate as a precursor. Cyclic voltammetry was used to determine the deposition potential effects on molybdenum compound speciation, while quantitative thin film composition was obtained from X-ray photoelectron spectroscopy depth profiles. Thin molybdenum film growth and composition was potential dependant. Predominant molybdenum species was Mo(IV) at all deposition potentials and deposition times. Optical properties of the molybdenum oxide thin films were determined using UV–VIS spectroscopy. The absorption edge varied between 560 and 650 nm, whereas optical band gap values—between 1.79 and 2.19 eV—well within the limits for solar light-induced chemical reactions.     

Electrochemistry of MoO3–K2MoO4 melts: a chance to control the nature of reduced molybdenum oxides

Cathodic electrodeposition of oxides on platinum from MoO₃–K₂MoO₄ (3.85–75?mol% MoO₃) under DC and pulsed galvanostatic modes is discussed in combination with voltammetry data. Characteristic potential values (as related to oxygen evolution onset) are reported for Mo(VI/IV) redox processes, as well as for electrochemical equilibria with participation of molybdenum metal and Pt–Mo alloys. On the basis of scan rate effects and results for various potential limits, and also of voltammetry with preliminary potentiostatic accumulation of products, molybdate reduction mechanism complicated by a chemical step of Mo metal oxidation is proposed. This qualitative assumption is verified in preparative electrolysis experiments with products identification by means of X-ray diffractometry, scanning electron microscopy, and EDX local analysis. Deposition under pulsed mode is found to be useful tool to adjust the duration of chemical step and by these means to alter the composition of final products. The conditions supporting the formation of MoO₂ and more reduced oxides are formulated.     

Hydrothermal synthesis of potassium molybdenum oxide bronzes: structure-inheriting solid-state route to blue bronze and dissolution/deposition route to red bronze

The hydrothermal syntheses of the alkali metal molybdenum bronzes from starting solids (H_xMoO₃) with structural affinities to the desired products were investigated. Single-phase potassium blue and red bronzes were prepared by the hydrothermal treatments at around 430 K, and characterized by powder X-ray diffraction, IR spectroscopy, and SEM. The formation processes of these two bronzes during the hydrothermal treatments were found to differ. The blue bronze was formed by a structure-inheriting solid-state route from H_xMoO₃ with x<0.3, whereas the red bronze was formed for x>0.3 through a solution dissolution/deposition route via the formation of MoO₃+MoO₂.     

Preparation and properties of rare-earth-molybdenum(V) oxides Ln3MoO7

Phase equilibrium studies in Ln₂O₃MoO₂MoO₃ systems indicate, for a Ln₂O₃:Mo ratio of 3:2, the existence of a new molybdenum (V)-rare-earth oxide Ln₃MoO₇. Ternary oxides have been prepared for Ln ≡ La-Ho and Y. For Ln ≡ La-Eu, Ln₃MoO₇ compounds form at 1473 K under oxygen partial pressures ranging from 10^−7.3 to 10^−11.6 atm. For Ln ≡ Gd-Ho and Y compounds form above 1573 K and at 1473 K the stability range is about 10⁻⁹ to about 10⁻¹⁰ atm. Lattice parameters deduced from X-ray diffraction patterns are reported. For the large Ln cations, lanthanum to europium, all reflections could be indexed in an orthorhombic C-centred cell isotypic to Nd₃NbO₇. For Ln ≡ Gd-Ho and Y, strong f.c.c.-type reflections show that the structure is defect fluorite. Stability ranges in terms of oxygen partial pressure and crystal chemical properties are discussed with respect to the rare-earth elements. Magnetic susceptibility measurements of La₃MoO₇ confirm the oxidation state + 5 for molybdenum.     

Effect of heat treatment on electrochromic properties of TiO<Subscript>2</Subscript> thin films

Electrochromic titanium oxide (TiO₂) films were deposited on ITO/glass substrates by chemical solution deposition (CSD). The stock solutions were spin-coated onto substrates and then heated at various temperatures (200–500 °C) in various oxygen concentrations (0–80%) for 10 min. The effects of the processing parameters on the electrochromic properties of TiO₂ films were investigated. X-ray diffraction measurements demonstrated that the amorphous TiO₂ films were crystallized to form anatase films above 400 °C. The electrochromic properties and transmittance of TiO₂ films were measured in 1 M LiClO₄–propylene carbonate (PC) non-aqueous electrolyte. An amorphous 350 nm-thick TiO₂ film that was heated at 300°C in 60% ambient oxygen exhibited the maximum transmittance variation (ΔT%), 14.2%, between the bleached state and the colored state, with a ΔOD of 0.087, Q of 10.9 mC/cm², η of 7.98 cm²/C and x in Li _x ClO₄ of 0.076 at a wavelength (λ) of 550 nm.