Pulsed-spray Evaporation Chemical Vapor Research Articles

Insight into one-step synthesis of active amorphous La-Co thin films for catalytic oxidation of CO

Active amorphous lanthanum-based thin films were synthesized through one-step pulsed spray evaporation chemical vapor deposition (PSE-CVD) technique at 320 °C for CO oxidation. The obtained films were characterized in terms of phase, composition and morphological properties. X-ray diffraction (XRD) analysis revealed an amorphous nature of the deposited catalysts; and scanning electron microscope (SEM) showed a transition of morphology due to Co doping from sharp to round shaped edges. Chemical composition analysed by EDS and XPS disclose similar trends in amount of cobalt increment and lanthanum decrement. XPS deconvolution revealed pure lanthanum sample (La100) constitutes mainly of lanthanum oxide and lanthanum hydroxide; while, doping with 10% of cobalt (La90Co10) introduces formation of cobalt ions (Co3+ and Co2+) together with La3+ions and low formation of oxygen lattice. Increment of Co to 20% (La80Co20) resulted increasing of Co2+/Co3+, CO32−/OH−formation ratios and oxygen lattice (Olat) content, which may play a key role in the catalytic activity. Complete oxidation of CO was evaluated by online-FTIR. Based on light-off curves, La80Co20 catalyst exhibited the most efficient catalytic activity with T90 of 203 °C, due to increment of lattice oxygen (Olat), Co2+/Co3+ and CO32−/OH−; while, La90Co10 catalyst exhibited lowest catalytic activity which is linked to low Olat and inhibited catalytic effect of water formed at the surface. Thus, the doping strategy of La by Co at low temperature is a good approach for CO abatement. Moreover, DFT calculations demonstrated that amorphous lanthanum oxide is very feasible for CO adsorption.

SnS2 Nanowall Arrays toward High-Performance Sodium Storage.

Cost-effective sodium ion batteries (SIBs) are emerging as a desirable alternative choice to lithium ion batteries in terms of application in large-scale energy storage devices. SnS2 is regarded as a potential anode material for SIBs because of its unique layered structure and high theoretical specific capacity. However, the development of SnS2 was hindered by the sluggish kinetics of the diffusion process and the inevitable volume change during repeated sodiation-desodiation processes. In this work, SnS2 with a unique nanowall array (NWA) structure is fabricated by one-step pulsed spray evaporation chemical vapor deposition (PSE-CVD), which could be used directly as binder-free and carbon-free anodes for SIBs. The SnS2 NWA electrode achieves a high reversible capacity of 576 mAh g-1 at 500 mA g-1 and enhanced cycling stability. Attractively, an excellent rate capability is demonstrated with ∼370 mAh g-1 at 5 A g-1, corresponding to a capacity retention of 64.2% at 500 mA g-1. The superior sodium storage capability of the SnS2 NWA electrode could be attributed to outstanding electrode design and a rational growth process, which favor fast electron and Na-ion transport, as well as provide steady structure for elongated cycling.

Rational design of metal oxide nanocomposite anodes for advanced lithium ion batteries

Metal-oxide anodes represent a significant future direction for advanced lithium ion batteries. However, their practical applications are still seriously hampered by electrode disintegration and capacity fading during cycling. Here, we report a rational design of 3D-staggered metal-oxide nanocomposite electrode directly fabricated by pulsed spray evaporation chemical vapor deposition, where various oxide nanocomponents are in a staggered distribution uniformly along three dimensions and across the whole electrode. Such a special design of nanoarchitecture combines the advantages of nanoscale materials in volume change and Li+/electron conduction as well as uniformly staggered and compact structure in atom migration during lithiation/delithiation, which exhibits high specific capacity, good cycling stability and excellent rate capability. The rational design of metal-oxide nanocomposite electrode opens up new possibilities for high performance lithium ion batteries.

Low-temperature deep oxidation of olefins and DME over cobalt ferrite

This work reports the facile synthesis of cobalt ferrite catalysts by pulsed spray evaporation chemical vapor deposition (PSE-CVD) for low-temperature oxidation of dimethyl ether and olefin exhaust emission. To better understand the structure–performance relationship, the prepared thin films were comprehensively characterized in terms of phases, surfaces and redox properties. A well-crystallized inverse spinel structure was revealed by both XRD and Raman analyses. Helium ion microscopy (HIM) images show that the obtained films have cauliflower structure with apparent open porosity. The catalytic performance of the as-prepared cobalt ferrite was evaluated with a fixed-bed quartz reactor–FTIR system. The results indicate that the cobalt ferrites were very active for the total oxidation of propene, n-butene and DME at low temperature and no CO was observed during the oxidation processes. The attractive performance of cobalt ferrite catalysts is attributed to a redox mechanism which involves the synergistic effect of the morphology, reducibility, and lattice oxygen mobility.

Abnormal behaviors in electrical transport properties of cobalt-doped tin oxide thin films

Electrical transport behaviors of SnO2-based oxides are absolutely essential, either for the understanding of physiochemical properties, or their practical applications. In this paper, an abnormal change in electrical transport is reported upon cobalt doping. A far-from-equilibrium technique—pulsed spray evaporation chemical vapor deposition (PSE-CVD), is investigated for the fabrication of Sn1−xCoxO2−δ (x = 0–0.18) thin films. Upon cobalt doping, the Hall mobility improves gradually and a ten-fold enhancement was noticed for Sn0.82Co0.18O2−δ relative to pure SnO2 films. This unexpected effect induces a dramatic drop in the electrical resistivity. Post-annealing treatment and XPS investigation indicate that the occurrence of surface-stabilized tin interstitials may be the primary reason for the unusual enhancement in conductivity. Cobalt doping not only generates the interstitial tin cations, but also stabilizes to a great extent their presence at the surface. This study may help to illumine new insight for the understanding of doping strategies, and offer a potential route for transport-related applications.

Unusual enhancement in electrical conductivity of tin oxide thin films with zinc doping

Electrical conductivity of SnO(2)-based oxides is of great importance for their application as transparent conducting oxides (TCO) and gas sensors. In this paper, for the first time, an unusual enhancement in electrical conductivity was observed for SnO(2) films upon zinc doping. Films with Zn/(Zn + Sn) reaching 0.48 were grown by pulsed spray-evaporation chemical vapor deposition. X-Ray diffraction (XRD) shows that pure and zinc-doped SnO(2) films grow in the tetragonal rutile-type structure. Within the low doping concentration range, Zn leads to a significant decrease of the crystallite size and electrical resistivity. Increasing Zn doping concentration above Zn/(Zn + Sn) = 0.12 leads to an XRD-amorphous film with electrical resistivity below 0.015 Ω cm at room temperature. Optical measurements show transparencies above 80% in the visible spectral range for all films, and doping was shown to be efficient for the band gap tuning.

CVD of Ru, Pt and Pt-based alloy thin films using ethanol as mild reducing agent

Noble metal thin films (Pt and Ru) were grown at 250 °C, using commercially available precursors, by the pulsed spray evaporation chemical vapor deposition (PSE-CVD) technique. The growth process relies on the thermally activated reaction of ethanol with the metal acetylacetonate precursors. The synthesized polycrystalline films are pure metal phase and crystallize in hexagonal (Ru) and cubic (Pt) structures. The formation of an interfacial silicide phase was noticed in the case of the Pt growth on silicon substrates. The films are smooth, continuous and show a steady growth without any noticeable incubation time. The single-step growth of Pt-based alloys, Pt–Co and Pt–Cu, with controlled composition was performed by simply adjusting the composition of the liquid feedstock.

Investigation of Growth, Structural and Optical Properties of CeO<SUB>2</SUB> Nanocrystalline Thin Films Prepared by Pulsed Spray-Evaporation Chemical Vapor Deposition (PSE-CVD)

Investigation of Growth, Structural and Optical Properties of CeO<SUB>2</SUB> Nanocrystalline Thin Films Prepared by Pulsed Spray-Evaporation Chemical Vapor Deposition (PSE-CVD)

Tailoring the properties and the reactivity of the spinel cobalt oxide

Pulsed spray evaporation chemical vapor deposition (PSE-CVD) was employed for the synthesis of cobalt-based spinel oxide thin films, Co(3-x)Fe(x)O4 with x = 0-1.56. XRD, Raman scattering and FTIR emission spectroscopy show that the normal spinel structure was retained for 0 < or = x < or = 0.65 by the selective insertion of Fe3+ in the octahedral sites. The spinel inversion was noticed above this range, whereas the insertion of Fe2+ was first indicated with x > or = 1. The room-temperature electrical resistivity of the thin films was controlled between 9 and 0.007 Omega cm by the adjustment of iron doping concentration. Furthermore an improvement of the thermal stability of the spinel was noticed upon doping by iron. The reducibility of the spinel in the presence of molecular hydrogen was efficiently adjusted by a shift of the reduction temperature by up to 110 degrees C upon the controlled insertion of iron in the octahedral sites of the spinel. The investigation of the catalytic oxidation of CO and ethanol over Co(3-x)Fe(x)O4 films with controlled structural modification enabled the confirmation of the Mars-van Krevelen mechanism for the oxidation of CO and the tight correlation between the selectivity of the conversion of ethanol to acetaldehyde and the abundance of surface basic sites. The controlled iron doping was demonstrated to be an efficient strategy to tune the reactivity and the selectivity of the cobalt-based spinel oxide. The doping-induced transition from normal to inverse spinel was observed to induce a clear discontinuity in the trend of all investigated physicochemical properties.