SnO2 Support Research Articles

Highly stable RuO2/SnO2nanocomposites as anode electrocatalysts in a PEM water electrolysis cell

This work explores the opportunity to reduce the cost and enhance the stability of RuO2 as an oxygen evolution reaction catalyst by coating RuO2 on chemically stable SnO2 support. Nano-sized RuO2/SnO2 composites of different mass ratios of RuO2 to SnO2 (0.45:1, 0.67:1, and 1.07:1) were synthesized using solution-based hydrothermal method. The physicochemical properties of the RuO2/SnO2 were studied by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and N2 adsorption–desorption isotherms. The electrochemical activity of RuO2/SnO2 as anode electrocatalyst was investigated in a proton exchange membrane (PEM) water electrolysis cell of Pt/C cathode and Nafion membrane. Experimental results showed that RuO2/SnO2 of ratio (1.07:1) exhibit higher electrochemical activity compared to pure RuO2, resulting ~50% reduction of noble metal content. The extended life test of electrocatalysts for 240 h implied that RuO2/SnO2 (1.07:1) significantly improved the stability of electrode in comparison to pure RuO2 in oxygen evolution processes. Copyright © 2013 John Wiley & Sons, Ltd.

High surface electrochemical support based on Sb-doped SnO2

Sb-doped SnO2 (ATO) support is prepared by sol–gel method in the presence of dodecylamine as template. The synthesized powder presents the highest specific surface area until now reported (216.7 m2 g−1) with high electrical conductivity (0.202 S cm−1). The durability test accomplished by cyclic voltammetry in acid media (100 cycles between 0 and 1.7 V vs NHE) demonstrates that the ATO support maintains significantly its stability and the performance of the tested electrocatalyst compared to Vulcan XC-72. The ATO material is a promising support that can be used in several electrochemical applications where the use of carbon is not suitable.

SnO2‐Based Nanomaterials: Synthesis and Application in Lithium‐Ion Batteries

The development of new electrode materials for lithium-ion batteries (LIBs) has always been a focal area of materials science, as the current technology may not be able to meet the high energy demands for electronic devices with better performance. Among all the metal oxides, tin dioxide (SnO₂) is regarded as a promising candidate to serve as the anode material for LIBs due to its high theoretical capacity. Here, a thorough survey is provided of the synthesis of SnO₂-based nanomaterials with various structures and chemical compositions, and their application as negative electrodes for LIBs. It covers SnO₂ with different morphologies ranging from 1D nanorods/nanowires/nanotubes, to 2D nanosheets, to 3D hollow nanostructures. Nanocomposites consisting of SnO₂ and different carbonaceous supports, e.g., amorphous carbon, carbon nanotubes, graphene, are also investigated. The use of Sn-based nanomaterials as the anode material for LIBs will be briefly discussed as well. The aim of this review is to provide an in-depth and rational understanding such that the electrochemical properties of SnO₂-based anodes can be effectively enhanced by making proper nanostructures with optimized chemical composition. By focusing on SnO₂, the hope is that such concepts and strategies can be extended to other potential metal oxides, such as titanium dioxide or iron oxides, thus shedding some light on the future development of high-performance metal-oxide based negative electrodes for LIBs.

Synthesis and Characterization of Pt Catalysts on SnO2 Based Supports for Oxygen Reduction Reaction

The oxygen reduction reaction was studied at Pt nanocatalysts on two different tin oxide based supports, Sb-SnO2 and Ru-SnO2, in acid solution. Tin oxide based supports were synthesized by hydrazine reduction method. Physical characterization of the supports was performed by BET, X-ray diffraction and TEM techniques. SnO2 belonging peaks were detected in Sb-SnO2 powder, while Ru-SnO2 XRD diffraction patterns contained peaks of RuO2 and SnO2. The average crystallite sizes, determined by Scherrer equation, were 3 nm and 4 nm for Sb-SnO2 and Ru-SnO2, respectively. Pt catalysts on Sb-SnO2 and Ru-SnO2 supports were synthesized by borohydride reduction method. TEM analysis revealed homogeneous particle size distribution, with average particle size of 2.9 and 5.4 nm, for Sb-SnO2 and Ru-SnO2, respectively. Electrocatalytic activity and stability of these catalysts for oxygen reduction were studied by cyclic voltammetry and linear sweep voltammetry at rotating disk electrode (RDE). Pt catalysts on Sb and Ru doped SnO2 support exhibited catalytic activities comparable to Pt on commercial carbon based support. Stability tests were also performed. Determined small loss of electrochemical active surface area of the Pt catalyst on Sb doped tin oxide support, after repetitive cycling, indicated high stability and durability of this cathode for prospective fuel cells application.

Hierarchical structure SnO2 supported Pt nanoparticles as enhanced electrocatalyst for methanol oxidation

Hierarchical structure SnO2 with two-dimensional (2D) nanosheets building blocks was employed as support material for Pt nanoparticles (NPs). The SnO2 supported Pt catalyst was synthesized through a facile aqueous phase process using sodium borohydride as the reducing agent. The as-prepared Pt–SnO2 catalyst exhibited remarkably improved electrocatalytic activity and stability toward methanol oxidation, in comparison with that of the commercial Pt/C catalyst and the commercial SnO2 nanopowder supported Pt catalyst. The superior catalytic performance may arise from the unique multiscale structure and morphology of the SnO2 support, which process extraordinary promotional effect on Pt catalyst.

The effect of TiO2 doping on the catalytic properties of nano-Pd/SnO2 catalysts during the reduction of nitrate

The monometallic catalysts Pd/TiO2–SnO2 and Pd/SnO2 prepared by impregnation method were investigated for their ability to catalyze the reduction of nitrate with formic acid as the reducing agent and were characterized by X-ray diffraction (XRD), BET surface area, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Pd and TiO2 were in high dispersion on the surface of the SnO2 support when the mol fraction of TiO2 was less than 15%. The SnO2 crystal lattice was partially replaced by titanium ions, causing SnO2 lattice distortion and resulting in the increase of oxygen vacancies as catalytic active sites. The best catalytic properties of the formic acid–Pd/TiO2–SnO2 system were achieved at a mol fraction of 10% TiO2. Compared with the Pd/SnO2 catalyst, the catalytic activity of Pd/TiO2–SnO2 increased by 48% from 2.08mg/(mingcata) to 4.00mg/(mingcata), while the NH4+ concentration decreased from 13.0mg/L to 5.2mg/L. The catalytic activity, selectivity and stability of the Pd/TiO2–SnO2 catalyst were superior to those of Pd/SnO2 with the same Pd loading and formic acid concentration. The results of the XPS analysis indicated that the catalysts Pd/SnO2 and Pd/TiO2–SnO2 were of high oxygen vacancy. Pd/TiO2–SnO2 has better catalytic properties than Pd/SnO2 may attribute to the increased amount of oxygen vacancy after TiO2 doping.

Voltage enhancement in dye-sensitized solar cell using (001)-oriented anatase TiO2 nanosheets

A nanocrystalline TiO2 (anatase) nanosheet exposing mainly the (001) crystal faces was tested as photoanode material in dye-sensitized solar cells. The nanosheets were prepared by hydrothermal growth in HF medium. Good-quality thin films were deposited on F-doped SnO2 support from the TiO2 suspension in ethanolic or aqueous media. The anatase (001) face adsorbs a smaller amount of the used dye sensitizer (C101) per unit area than the (101) face which was tested as a reference. The corresponding solar cell with sensitized (001)-nanosheet photoanode exhibits a larger open-circuit voltage than the reference cell with (101)-terminated anatase nanocrystals. The voltage enhancement is attributed to the negative shift of flatband potential for the (001) face. This conclusion rationalizes earlier works on similar systems, and it indicates that careful control of experimental conditions is needed to extract the effect of band energetic on the current/voltage characteristics of dye-sensitized solar cell.

ChemInform Abstract: Efficient Heterogeneous Epoxidation of Alkenes by a Supported Tungsten Oxide Catalyst.

AbstractA heterogenous catalyst comprising of tungsten and zinc oxides (3.5 wt% W and 0.8 wt% Zn) on SnO2 support is found to efficiently promote the epoxidation of alkenes and the oxidation of amines, silanes, and sulfide by hydrogen peroxide.

An integrated approach to Deacon chemistry on RuO2-based catalysts

Rationally designed RuO2-based Deacon catalysts can contribute to massive energy saving compared to the current electrolysis process in chemically recycling HCl to produce molecular chlorine. Here, we report on our integrated approach between state-of-the-art experiments and calculations. The aim is to understand industrial Deacon catalyst in its realistic surface state and to derive mechanistic insights into this sustainable reaction. We show that the practically relevant RuO2/SnO2 consists of two major RuO2 morphologies, namely 2–4 nm-sized particles and 1–3-ML-thick epitaxial RuO2 films attached to the SnO2 support particles. A large fraction of the small nanoparticles expose {110} and {101} facets, whereas the film grows with the same orientations, due to the preferential surface orientation of the rutile-type support. Steady-state Deacon kinetics indicate a medium-to-strong positive effect of the partial pressures of reactants and deep inhibition by both water and chlorine products. Temporal Analysis of Products and in situ Prompt Gamma Activation Analysis strongly suggest a Langmuir–Hinshelwood mechanism and that adsorbed Cl poisons the surface. Under relevant operation conditions, the reactivity is proportional to the coverage of a specific atomic oxygen species. On the extensively chlorinated surface that can be described as surface oxy-chloride, oxygen activation is the rate-determining step. DFT-based micro-kinetic modeling reproduced all experimental observations and additionally suggested that the reaction is structure sensitive. Out of the investigated models, the 2ML RuO2 film-covered SnO2 gives rise to significantly higher reactivity than the (101) surface, whereas the 1ML film seems to be inactive.

Au nanoparticle-decorated porous SnO2 hollow spheres: a new model for a chemical sensor

Au nanoparticle-decorated porous SnO2 hollow spheres, which are different from the conventional noble metal-doped thick or thin semiconductor films, are prepared and systematically investigated as a new model for chemical gas sensors. The synthesized Au-decorated porous SnO2 hollow spheres are characterized by means of X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and inductively coupled plasma-optical emission spectroscopy. The Au content in the SnO2 support was determined as 5.63 wt% by XPS and 5.90 wt% by ICP, respectively, indicating the homogeneous dispersion of Au nanoparticles on SnO2 hollow spheres. Experimental results show that, by using ethanol as a probe molecule, this new model exhibits excellent sensing performances in terms of high response, fast response-recovery, superior selectivity and good stability. The enhanced sensing features are attributed to the improved gas diffusion and mass transport induced by the unique porous structure, the formation of conjugated electron depletion layers on both the outer and inner surfaces of the SnO2 hollow spheres and the catalytic effect of the Au nanoparticles. It is believed that the strategy of combining the porous nanostructure and catalytic activity of noble metals can further provide potential for other applications.

Preparation and electrocatalytic property of Au-Pt/SnO2/GC composite electrode

Au-Pt/SnO2/GC composite electrode was prepared by self-assembling Au-Pt nanoparticles on SnO2 film, which was deposited on actived glassy carbon (GC). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) images revealed that dense and uniform Au-Pt particles with 25-nm diameter were dispersed on SnO2 film. X-ray photoelectron spectroscopy (XPS) results proved that there was an interaction between Au-Pt nanoparticles and SnO2 support. Electrochemical experiments showed that Au-Pt/SnO2/GC composite electrode had a good electrocatalytic activity to the oxidation of methanol.

Molecular Wiring of Olivine LiFePO4 by Ruthenium(II)-Bipyridine Complexes and by Their Assemblies with Single-Walled Carbon Nanotubes

The undoped and carbon-free olivine, LiFePO4 was bonded with 5% PVDF, and deposited on F-doped SnO2 support (FTO). The electrodes were modified by a monolayer of three different complexes: NaRu(4,4′-dicarboxylic acid-2,2′-bipyridine)(4,4′-dinonyl-2,2′-bipyridine)(NCS)2, coded as Z-907Na, Ru-bis(4,4′-diethoxycarbonyl-2,2′-bipyridine)(4,4′-dicarboxylic acid-2,2′-bipyridine), coded Z-974, and Ru-bis(4,4′-dicarboxylic acid-2,2′-bipyridine)(4,4′-dinonyl-2,2′-bipyridine), coded Z-975. These complexes have redox potentials from 3.5 to 4.45 V versus Li/Li+ and are active for molecular wiring of LiFePO4. The Ru-complexes contacting FTO are reversibly oxidized, which allows the holes to be transported via the adsorbed monolayer across the olivine surface, where a subsequent chemical delithiation occurs toward FePO4. The supramolecular assembly of Z-907Na with single-walled carbon nanotubes (SWNT) is more active for molecular wiring than pure Z-907Na. In this case, the LiFePO4/FePO4 system can be charged/discharged by currents larger by 1 order of magnitude, and the performance of the assembly depends on the type of SWNT. This study improved our understanding of molecular wiring in general, and the enhancement of wiring activity by SWNT in particular.

Molecular Wiring of LiFePO4 (Olivine)

The carbon-free LiFePO4 (olivine) was modified by a monolayer coverage with [12-(2,5-di-tert-butyl-4-methoxy-phenoxy)-dodecyl]-phosphonic acid, coded DW. Thin film electrodes were bonded with 5% PVDF and deposited on F-doped SnO2 (FTO) support. The surface-modified LiFePO4 can be electrochemically charged via a mechanism called molecular wiring. The DW molecules contacting FTO are reversibly oxidized, which allows that the holes are transported from the FTO via the adsorbed DW monolayer across the whole olivine surface, where a subsequent chemical delithiation occurs toward FePO4. The sole cross-surface hole percolation via adsorbed DW was demonstrated on two reference systems, namely, TiO2 and LiMnPO4 (olivine), which are electrochemically inert in the potential region, where the DW oxidation occurs. The diffusion coefficient of hole transport across the LiMnPO4 surface equals 3 x 10(-9) cm(2)/s, which is ca. three times larger than the corresponding value for mesoporous TiO2. The undoped and carbon-free LiFePO4 can be charged by currents equivalent to ca. C/2 to C/10 exclusively via the monolayer of adsorbed molecules, but the process slows down when the charging progresses. The wiring current is roughly inversely proportional to the level of olivine charging by oxidative delithiation.

Nanoscopic Observation of Strong Chemical Interaction between Pt and Tin Oxide

Platinum catalysts supported on tin oxide were prepared by the impregnation method and were treated in several conditions. The change of their structure by the treatment was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. In the as-prepared catalyst, platinum particles with their mean size of ca. 3 nm were highly dispersed on SnO2 supports. After the treatment in reduction atmosphere, the intermetallic compounds ascribed to PtSn and Pt3Sn were formed, and the growth of particle by aggregation was observed. Moreover, the particles with core−shell nanostructure were observed in the catalyst reduced at higher temperatures. It was revealed that the core−shell structure was formed by the phase separation of Sn species from the intermetallic compound particles when the catalyst was treated by mild reoxidation such as exposure to air. On the other hand, after the reoxidation treatment, the mean particle size of the metal particle became smaller and cryst...

Electrochemical impedance spectroscopy of mesoporous Al-stabilized TiO2 (anatase) in aprotic medium

High-frequency electrochemical impedance spectroscopy was used to investigate the mesoporous film of Al-stabilized TiO2 on F-doped SnO2 support in 1 M Li(CF3SO2)2N in ethylene carbonate/dimethoxyethane (1:1 v/v). Kinetic parameters, viz. charge transfer resistance and chemical diffusion coefficient, were determined. Charge transfer resistance increased with time of contact of electrode in the above aprotic electrolyte solution. The increase followed exponential dependence, whereas the double layer capacitance, simultaneously, decreased exponentially with time. These effects were discussed in terms of the solid–electrolyte interface, which undergoes chemical changes upon contact with the electrolyte solution.

Benefits of mesopores in nanocristalline Pd/SnO2 catalysts for nitrate hydrogenation

Mesoporous nanocristalline SnO2 supports were synthesized by a modified sol-gel method starting from SnCl2?2H2O and citric acid at pH 2.0 and 9.5. Noble metal was introduced via wet impregnation using PdCl2 as active phase precursor. Catalysts activities in water denitration were correlated with their textural, structural and morphological properties using LTNA (BET), XRD and SEM/EDS analysis. Lower pH value during the catalyst synthesis resulted in a final material characterized with more developed porosity and higher surface area. Although both catalysts turned out to be tailored from nanoscale crystallites, higher pore fraction of mesopores resulting from the synthesis in acidic conditions, was found to be responsible for superior catalytic behavior.

Acid sites and oxidation center in molybdena supported on tin oxide as studied by solid-state NMR spectroscopy and theoretical calculation

Solid-state NMR spectroscopy and density functional theory (DFT) calculations were employed to study the structure and properties, especially the solid acidity, of molybdenum oxide supported on tin oxide. As demonstrated by solid-state NMR experiments, Mo species are mainly dispersed on the surface of SnO(2) support rather than significantly dissolved into the SnO(2) structure and Brønsted as well as Lewis acid sites are present on the MoO(3)/SnO(2) catalyst. Acid strength of the supported metal oxide is stronger than those of zeolites, e.g., HY and HZSM-5, though the concentration of acid sites is relatively lower. The DFT calculated (13)C chemical shift for acetone adsorbed on MoO(3)/SnO(2) is in good agreement with the experimental value, which confirms our proposed structure of -Mo-(OH)-Sn- for the Brønsted acid site. Reducibility of the supported metal oxide is also demonstrated by solid-state NMR experiments and an active oxidation center of this catalyst is proposed as well.

Combustion of Methane at Low Temperature over Pd and Pt Catalysts Supported on Al2O3, SnO2 and Al2O3-Grafted SnO2

Pd and Pt catalysts supported on alumina, tin(IV) oxide and tin(IV) oxide grafted on alumina were prepared, characterised and tested with respect to the low-temperature combustion of methane after reduction in H2 and ageing under reactants at 600°C. In the case of Pd, the use of SnO2 or SnO2-based supports led to catalysts slightly less active than Pd/Al2O3. In contrast, SnO2 was found to strongly promote the oxidation of methane over Pt catalysts with respect to Pt/Al2O3, even after ageing under reactants. When Pt was supported on SnO2 grafted on Al2O3, the activity was found at most similar to or, after ageing, lower than Pt/Al2O3. This negative effect was discussed, being partly related to the sintering of SnO2 under reactants observed by FTIR and XRD.

Surface grafting as a route to modifying the gas-sensitive resistor properties of semiconducting oxides: Studies of Ru-grafted SnO2

The phenomenon of electrical conductivity of an oxide being controlled by the chemical state of a surface grafted reactive centre, resulting in a room-temperature gas response, is demonstrated. Surface grafting of Ru centres onto SnO2 by reaction of [(η6-C6H6)Ru(acetone)3][BF4]2 with surface OH, followed by thermal decomposition in either H2/N2 or air resulted in additional electronic states in the SnO2 band gap associated with surface Ru species, revealed by XPS and correlated with resistance increase of the material. The samples were characterized by EXAFS to confirm the structure of the surface Ru species, TPD, UV–VIS spectroscopy, XPS and electrical measurements. Thermal decomposition in H2/N2 resulted in isolated Ru centres bound to SnO2. The chemical state of these Ru centres varied as a result of gas chemisorption (oxygen, water vapour, carbon monoxide and nitric oxide). An electronic interaction between grafted Ru centres and the SnO2 support was manifested in room-temperature conductivity being controlled by the surface state of the Ru and by gas adsorption onto these centres. Decomposition in air resulted in small surface-bound clusters of RuO2 and did not result in a gas-sensitive preparation. DFT molecular cluster calculations successfully illustrated the main features of the experimental results, supporting the interpretation that the conductivity changes were caused by gas interaction with surface Ru centres altering the trapping of conduction electrons on these centres. Oxygen, NO and CO were non-dissociatively adsorbed. The Ru centres slowly oxidised in air and hydroxylated in the presence of water vapour. Carbon monoxide and NO in ppm concentrations in air displaced oxygen from the Ru centres but the electrical response was strongly affected by the presence of water vapour in the atmosphere. In principle, surface-grafted reactive centres can be chosen to be specific to a particular gas, providing a route to new types of gas detector tailored for a particular application.