Reduction Of SnO2 Research Articles

Solid phase growth of tin oxide nanostructures

a b s t r a c t For the first time, single-crystalline SnO2 nanostructures comprising of nanobelts, nanowires and nanosheets have been synthesised by solid phase crystal growth from tin oxide single crystals. The product was characterised by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, selected area electron diffraction, and Raman spectroscopy. The procedure consisted of two stages. In the first stage, a mixture of SnO2 polyhedral single crystals attached with graphite particles were produced by heating a mixture of SnCl2 and graphite. Then, the SnO2 single crystals were grown into nanobelts, nanowires and nanosheets by further heating. The role of graphite in the process is also discussed to be the surface reduction of SnO2 into oxides with lower oxygen content which provide a driving force for surface diffusion and subsequent crystal growth of tin oxide into the one and two dimensional nanostructures. The results provide insights for both fundamental research as well as technological production of SnO2 nanostructures.

Electrochemical Deposition of Zn3P2 Thin Film Semiconductors Based on Potential–pH Diagram of the Zn-P-H2O System

In this paper, we report on our attempt to make a thin film of Zn3P2 compound semiconductor by electrodeposition from aqueous solutions containing zinc and phosphorus species. First of all, we constructed the potential-pH diagram of the Zn-P-H2O system at 363 K and found out the wide stable region of Zn3P2 at lower potentials. In the cyclic voltammetry on SnO2 glass substrate, two cathodic current changes and an anodic peak were observed. This is similar results to Soliman et al., where the electrodeposition of Zn3P2 was succeeded. Consequently, the potentiostatic electrolysis thus was carried out to clarify the reduced substance and the reduction of SnO2 was only observed. When Au electrode was used as an inert electrode, the formation of Zn3P2 was not also observed, while the Au-Zn compound was confirmed. It is considered that the precipitation of zinc predominantly occurs and the reduction of phosphate ions are kinetically difficult from the results of the cyclic voltammetry.

Mechanism of an AZO-coated FTO film in improving the hydrogen plasma durability of transparent conducting oxide thin films for amorphous-silicon based tandem solar cells

An Al-doped ZnO (AZO)/F-doped SnO2 (FTO) film structure in an amorphous silicon solar cell (a-Si:H) was studied under exposure to hydrogen (H) plasma treatment via a simple spray pyrolysis. A radio-frequency magnetron sputtering method was used to deposit the FTO film first and the subsequent AZO overlayer on top of the FTO. The results of this approach suggest that the AZO film acts as a protection layer for the underlying FTO film and thus provides an excellent interface that protects the film from the direct bombardment with H+ ions and radicals. Even under exposure to H-plasma, the optical (UV-Vis) and electrical properties (Hall measurement) of the AZO/FTO double layer film show improvement in plasma stability in comparison with a single FTO film. Without the AZO overlayer, the reduction of SnO2 to metallic Sn and sub-oxidized SnO can occur in the FTO film. However, after a post-annealing treatment at 400 °C, the degradation of the FTO can be reversed by reoxidizing the Sn–O bonds. This interpretation of the H+ ion diffusion and the Sn–O redox process is confirmed via XPS and SIMS analysis. This investigation provides an opportunity to study the H+ ion diffusion mechanism in a metal oxide matrix in the presence of plasma and thermal effects. The study thus provides an alternative to the conventionally used FTO-based Si solar cells.

Catalytic properties of SnO2-TiO2 compositions in total methane oxidation

Tin and titanium dioxides and their compositions were studied as catalysts for the reaction of complete oxidation of methane. The catalytic activity of the test samples was compared in terms of first-order reaction rate constants with reference to the unit surface area of a catalyst. The crystal structures and specific surface areas of the obtained compositions were characterized. The thermal stability of SnO2 was investigated. Data on the temperature-programmed reduction of SnO2 and the composition Sn0.70Ti0.30O2 in hydrogen were given.

Electrochemical properties of SnO2/carbon composite materials as anode material for lithium-ion batteries

SnO2/carbon composite anode materials were synthesized from SnCl4·5H2O and sucrose via a hydrothermal route and a post heat-treatment. The synthesized spherical SnO2/carbon powders show a cauliflower-like micro-sized structure. High annealing temperature results in partial reduction of SnO2. Metallic Sn starts to emerge at 500°C. High Sn content in SnO2/carbon composite is favorable for the increase of initial coulombic efficiency but not for the cycling stability. The SnO2/carbon annealed at 500°C exhibits high specific capacity (∼400mAhg−1), stable cycling performance and good rate capability. The generation of Li2O in the first lithiation process can prevent the aggregation of active Sn, while the carbon component can buffer the big volume change caused by lithiation/delithiation of active Sn. Both of them make contribution to the better cycle stability.

Reduction of SnO<SUB>2</SUB> with Hydrogen

This study deals with the reduction of tin oxide by hydrogen in the temperature range of 773∼1023 K and the hydrogen partial pressure of 30.4∼101.3 kPa. It aims to investigate the kinetics of the reaction between tin oxide and hydrogen. The hydrogen reduction of tin oxide is to be related with the efforts to extract tin metal with decreasing the emission of carbon dioxide which causes global warming. The experiments were carried out under isothermal condition in hydrogen atmosphere using TGA equipment. The reduction rate of tin oxide to tin metal by hydrogen was found to be relatively fast under the whole conditions until the reduction ratio of SnO2 approaches to about 0.95. As an example, at 1023 K under a hydrogen partial pressure of 101.3 kPa, almost 100% of tin oxide was reduced to tin metal in 10 min. The nucleation and growth model yielded a satisfactory fit to these experimental data. The reaction was first order with respect to hydrogen partial pressure and had an activation energy of 62.5 kJ/mol (15.0 kcal/mol).

Controlled synthesis of SnO2@carbon core-shell nanochains as high-performance anodes for lithium-ion batteries

A new low-flow-rate inert atmosphere strategy has been demonstrated for the synthesis of perfect SnO2@carbon core-shell nanochains (SCNCs) by carbonization of an SnO2@carbonaceous polysaccharide (CPS) precursor at a relatively high temperature. This strategy results in the thorough carbonization of CPS whilst avoiding the carbothermal reduction of SnO2 at 700 °C. It has been investigated that a moderate carbon content contributes to the 1-D growth of SCNCs, and the thickness of the carbon shell can be easily manipulated by varying the hydrothermal treatment time in the precursor process. Such a unique nanochain architecture could afford a very high lithium storage capacity as well as resulting in a desirable cycling performance. SCNCs with about 8 nm carbon shell synthesized by optimized routes were demonstrated for optimal electrochemical performances. More than 760 mAh g¬1 of reversible discharge capacity was achieved at a current density of 300 mA g−1, and above 85% retention can be obtained after 100 charge-discharge cycles. TEM analysis of electrochemically-cycled electrodes indicates that the structural integrity of the SnO2@carbon core-shell nanostructure is retained during electrochemical cycling, contributing to the good cycleability demonstrated by the robust carbon shell.

One-Pot Synthesis of Carbon-Coated SnO2 Nanocolloids with Improved Reversible Lithium Storage Properties

We report a simple glucose-mediated hydrothermal method for gram-scale synthesis of nearly monodisperse hybrid SnO2 nanoparticles. Glucose is found to play the dual role of facilitating rapid precipitation of polycrystalline SnO2 nanocolloids and in creating a uniform, glucose-derived, carbon-rich polysaccharide (GCP) coating on the SnO2 nanocores. The thickness of the GCP coating can be facilely manipulated by varying glucose concentration in the synthesis medium. Carbon-coated SnO2 nanocolloids obtained after carbonization of the GCP coating exhibit significantly enhanced cycling performance for lithium storage. Specifically, we find that a capacity of ca. 440 mA h/g can be obtained after more than 100 charge/discharge cycles at a current density of 300 mA/g in hybrid SnO2-carbon electrodes containing as much as 1/3 of their mass in the low-activity carbon shell. By reducing the SnO2-carbon particles with H2, we demonstrate a simple route to carbon-coated Sn nanospheres. Lithium storage properties of the latter materials are also reported. Our results suggest that large initial irreversible losses in these materials are caused not only by the initial, presumably irreversible, reduction of SnO2 as generally perceived in the field, but also by the formation of the solid electrolyte interface (SEI).

In situ investigation of Pt100−xAuxand Pt100−ySnynanoalloys

Dispersed sols of 1-10 nm sized Pt(100--x)Au(x) and Pt(100--y)Sn(y) nanoalloys have been prepared separately at various x and y above and below the miscibility limit in the bulk metals. Pt(100--x)Au(x) was derived from trisodium citrate reduction of aqueous solutions of H2PtCl6 and HAuCl4. Pt(100--y)-Sn(y) was produced by (i) complexing Sn2+ with glucose at 323 K at pH > 7, (ii) neutralising this with H2PtC16 addition and (iii) reducing the bimetallic precursor with glucose on raising the temperature to 373 K. For Pt(100--x)Au(x (where both metals were zero-valent) as x increased the average size of nanoalloy particles increased. These particles adsorbed onto graphite, where the extent of hydrogen chemisorption at 298 K decreased by 67% at 9 at % Au. Pt/SnO2 nanoparticles (<3 nm in size) were adsorbed onto alumina. The Pt interacted with and catalysed the reduction of SnO2, with some Pt(100--y)Sn(y) nanoalloy formation at about 673 K which even in the bulk occurs over a wider range of compositions than Pt-Au) and enhanced H2 chemisorption at 17-33 at % Sn. Nevertheless some Sn must remain in a positive oxidation state on the alumina surface. The ratio of rates of 2MP/ 3MP formation from MCP and n-hexane may be informative in chemically fingerprinting (and revealing fundamental differences in) these nanoalloy surfaces. The reasons for this are seen in terms of the surface structures on these two types of nanoalloy particles (i.e. the availability of contiguous asymmetric pairs of active surface atoms *, which, as expected, is found to pass through a maximum or decrease beyond specific values of x and y).

Tin–carbon composites as anodic material in Li-ion batteries obtained by copyrolysis of petroleum vacuum residue and SnO 2

Composite materials with tin nanoparticles surrounded by a “muffling” carbon matrix are formed simultaneously by adding 20% SnO 2 to a vacuum residue and following carbonisation between 700 °C and 1000 °C. The primary purpose of the carbonaceous material is the reduction of SnO 2, giving rise to SnS and Sn as nanoparticles. The homogenous distribution of both components induces therefore a synergetic effect on the properties of the electrode material, not only from the electrochemical point of view but also from that mechanical. Thus, the carbon matrix hinders the agglomeration of Li–Sn alloys during long term cycling and, simultaneously, tin particles improve the conductivity of the material and increase the overall capacity as compared with the reference carbon. In addition, a CVD treatment increases the performance of the material. 119Sn Mössbauer and 7Li MAS NMR spectroscopies allow a detailed study of partially charged/discharged samples and, therefore, the phases, steps and mechanisms occurring during the electrochemical process.

Study of the interactions between carbon monoxide and high specific surface area tin dioxideThermogravimetric analysis and FTIR spectroscopy

The interactions of CO with a high specific surface area tin dioxide was investigated by FTIR spectroscopy and thermogravimetric analysis. FTIR study of CO interactions have shown that CO can adsorb on cus (coordinatively unsaturated sites) Sn4+ cation sites (band at 2201 cm-1). In addition, CO reacts with surface oxygen atoms. This leads to the partial reduction of SnO2 surface and to the formation of ionised oxygen vacancies together with the release of free electrons, which are responsible for the loss of transmission. Formed CO2 can chemisorb on specific surface sites: on basic sites to form carbonates species and on acidic sites (Sn4+-CO2 species) which is in competition with the formation of Sn4+-CO species. TG experiment have shown that the reduction of SnO2 by CO at 400°C occurs in two steps. First, the reduction of SnO2 surface, which is a quick phenomenon. This has allowed to evaluate that more than 12% of reducible surface oxygens can react with CO, essentially because of the presence of a large amount of surface hydroxyl groups. The second step of the reduction of SnO2 would be the progressive reduction of SnO2 bulk by the slow diffusion of oxygen atoms from the bulk to the surface.

Self-Assembled Nanowire−Nanoribbon Junction Arrays of ZnO

We report the synthesis and characterization of nanowire−nanoribbon junction arrays of ZnO, which were grown by thermal evaporation of the mixture of ZnO and SnO2 powders at 1300 °C through a vapor−liquid−solid process. The Sn particles produced by the reduction of SnO2 act as the catalyst; the structure is formed due to a fast growth of ZnO nanowires along [0001] and the subsequent “epitaxial” radial growth of the ZnO nanoribbons along the six 〈011̄0〉 directions around the nanowire. The “liana” shape nanostructure could be a candidate for fabricating ultrahigh sensitive sensors.

Effect of atmosphere and dopants on sintering of SnO2

Tin oxide is an n type semiconductor material with a high covalent behavior. Mass transport in this oxide depends on the surface state promoted by atmosphere or by the solid solution of aliovalent oxide doping. The sintering and grain growth of this type of oxide powder is then controlled by atmosphere and by extrinsic oxygen vacancy formation. For pure SnO2 powder the surface state depends only on the interaction of atmosphere molecules with the SnO2 surface. Inert atmosphere like argon or helium promotes oxygen vacancy formation at the surface due to reduction of SnO2 to SnO at the surface and liberation of oxygen molecules forming oxygen vacancies. As a consequence surface diffusion is enhanced leading to grain coarsening but no densification. Oxygen atmosphere inhibits SnO2 reduction by decreasing the surface oxygen vacancy concentration. Addition of dopants with lower valence at the sintering temperature creates extrinsic charged oxygen vacancies that promote mass transport at the grain boundary leading to densification and grain growth of this polycrystalline oxide.

Sintering of tin oxide and its applications in electronics and processing of high purity optical glasses

Tin oxide is an n type semiconductor material with a high covalent behavior. Mass transport in this oxide depends on the surface state promoted by atmosphere or by the solid solution of aliovalent oxide doping. The sintering and grain grow of this type of oxide powder is then controlled by atmosphere and by extrinsic oxygen vacancy formation. For pure SnO2 powder the surface state depends only in the interaction of atmosphere molecules with the SnO2 surface. Inert atmosphere like argon promotes oxygen vacancy formation at the surface due to the reduction of SnO 2 to SnO at surface and liberation of oxygen molecules forming an oxygen vacancy. As a consequence, surface diffusion is enhanced leading to grain coarsening, but no densification. Oxygen atmosphere inhibits the SnO2 reduction decreasing the surface oxygen vacancy concentration. Additions of dopants with lower valence at sintering temperature create extrinsic charged oxygen vacancies that promote mass transport at grain boundary leading to densification and grain growth of this polycrystalline oxide. Cobalt and niobium doped SnO2 ceramics exhibit varistor behavior, which can be applied in electronics. Moreover, SnO2 ceramics are chemically inert and can be applied in form of crucibles to melt some optical glasses.

Performance of 2,4-dinitrophenol as a positive electrode in magnesium reserve batteries

Anodes derived from oxides of tin have, of late, been of considerable interest because, in principle, they can store over twice as much lithium as graphite. A nanometric matrix of Li2O generated in situ by the electrochemical reduction of SnO2 can provide a facile environment for the reversible alloying of lithium with tin to a maximum stoichiometry of Li4.4Sn. However, the generation of the matrix leads to a high first-cycle irreversible capacity. With a view to increasing the reversible capacity as well as to reduce the irreversible capacity and capacity fade upon cycling, tin–tin oxide mixtures were investigated. SnO2, synthesized by a chemical precipitation method, was mixed with tin powder at two compositions, viz., 1:2 and 2:1, ball-milled and subjected to cycling studies. A mixture of composition Sn:SnO2 = 1:2 exhibited a specific capacity of 549 mAh g−1 (13% higher than that for SnO2) with an irreversible capacity, which was 7% lower than that for SnO2 and a capacity fade of 1.4 mAh g−1 cycle−1. Electrodes with this composition also exhibited a coulombic efficiency of 99% in the 40 cycles. It appears that a matrix in which tin can be distributed without aggregation is essential for realizing tin oxide anodes with high cyclability.

Microstructure and electrical properties of the SnO2 glass composite containing Cu particles precipitated by reducing copper oxides – Effect of particle size of reducing agent

An attempt was made to improve the electrical properties of SnO2 glass composites by dispersing metal particles having low resistivity and positive temperature coefficient of resistance (TCR) in the glass matrix. Cu metal particles were precipitated by reducing Cu2O by adding LaB6O as a reducing agent. The effects of LaB6O content and particle size on the microstructure and electrical properties of the SnO2 glass composites were monitored. When coarse LaB6O particles were used, the amount of the precipitated metal particles was large because SnO2 was also reduced as well as Cu2O during firing. However, in this case, the glass composite showed a porous microstructure including large pores because of the simultaneous evaporation of SnO formed as an intermediate product by reduction of SnO2. On the other hand, the glass composite prepared using fine LaB6O particles showed a dense microstructure uniformly dispersed with small pores. The porosity of the glass composite decreased by increasing the LaB6O content at first and then increased by further addition of LaB6O. The minimum of the porosity occurred at 2 wt % and 3 wt % LaB6O for the samples containing coarsest (4.81 μm) and finest (0.15 μm) LaB6O, respectively. Electrical conductivity (σ) and TCR of the glass composites containing LaB6O were higher and closer to zero, respectively, than those of a LaB6O free sample. The samples containing 2–3 wt % LaB6O showed 5–7 times higher σ and 50–70% smaller TCR in comparison with the sample without LaB6O. However, at high LaB6O content above 3–4 wt %, σ decreased and TCR moved in the negative direction with increase in LaB6O content. Especially, when coarse LaB6O was used, the declines σ and TCR at high LaB6O contents were remarkable. This was due to the decrease in the continuity of conductive paths related to the increase in number of the large pores caused by the evaporation of SnO.

Effect of atmosphere and dopants on sintering of SnO2

Tin oxide is an n-type semiconductor material with a high covalent behavior. Mass transport in this oxide depends on the surface state promoted by atmosphere or by the solid solution of a non-isovalent oxide doping. The sintering and grain growth of this type of oxide powder is then controlled by atmosphere and by extrinsic oxygen vacancy formation. For pure SnO2 powder the surface state depends only on the interaction of atmosphere molecules with the SnO2 surface. Inert atmosphere like argon or helium promotes oxygen vacancy formation at the surface due to reduction of SnO2 to SnO at the surface and liberation of oxygen molecules forming oxygen vacancies. As consequence surface diffusion is enhanced leading to grain coarsening but no densification. Oxygen atmosphere inhibits the SnO2 reduction decreasing the surface oxygen vacancy concentration. Addition of dopants with lower valence at sintering temperature creates extrinsic charged oxygen vacancies that promote mass transport at grain boundary leading to densification and grain growth of this polycrystalline oxide.

水素プラズマ曝露によるＳｎＯ２薄膜の還元

水素プラズマ曝露によるＳｎＯ２薄膜の還元

Ellipsometry and x-ray photoelectron spectroscopy study of SnO2 reduction at the interface with sputtered a-Si:H

Very thin layers of hydrogenated and unhydrogenated amorphous silicon have been deposited on tin oxide substrates under different temperatures and H2 partial pressures by dc magnetron sputtering. The deposition processes are monitored by real time in situ ellipsometry. We observe the reduction reaction of the SnO2 exposed to a H- or Si-containing deposition flux in the early stages of film growth by real time ellipsometry. The chemical states of Sn at the a-Si:H (or a-Si)/SnO2 interface have been studied by x-ray photoelectron spectroscopy (XPS). XPS confirms that a Si flux alone can reduce SnO2 to elemental Sn, and that this reaction is temperature dependent. However, the contribution of Si is secondary to that of H atoms in the reduction reaction.

Photoemission study on the SnO 2/P a-SiCx:H interface

Ultraviolet and X-ray photoemission spectroscopies (UPS and XPS) have been employed to SnO2 and its interface with P-type a-SiCx:H. The HeI valence band spectra of SnO2 show that the valence band maximum (VBM) shifts from 4.7 eV to 3.6 eV below the Fermi level (E(F)), and the valence band tail (VBT) extends up to the E(F), as a consequence of H-plasma treatments. The work function difference between SnO2 and P a-SiCx:H is found to decrease from 0.98 eV to 0.15 eV, owing to the increase of the work function of the treated SnO2. The reduction of SnO2 to metallic Sn is also observed by XPS profiling, and it is found that this leads to a wider interfacial region between the treated SnO2 and the successive growth of P a-SiCx:H.