Heterostructure core PdSn–SnO2 decorated by Pt as efficient electrocatalysts for ethanol oxidation

To enhance the performance of heterostructure electrocatalysts for fuel cell and other applications, carbon-supported Pt decorating PdSn–SnO₂ nanoparticles are prepared and characterized by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. The electrochemical results show higher ethanol oxidation activity of heterostructured catalysts than that of Pt@PdSn/C, PtSn/C and PdSn–SnO₂/C catalysts. This result demonstrates significant potential for utilizing heterostructure-core synthesis in the preparation of novel core–shell catalysts.     

The performance of Pt nanoparticles supported on Sb2O5.SnO2, on carbon and on physical mixtures of Sb2O5.SnO2 and carbon for ethanol electro-oxidation

Pt nanoparticles were supported on Sb₂O₅.SnO₂ (ATO), on carbon and on physical mixtures of ATO and carbon by an alcohol-reduction process using ethylene glycol as reducing agent. The obtained materials were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their performance for ethanol oxidation was investigated at room temperature by chronoamperometry and in a direct ethanol fuel cell (DEFC) at 100 °C. Pt nanoparticles supported on a physical mixture of ATO and carbon showed a significant increase of performance for ethanol oxidation compared to Pt nanoparticles supported on ATO or on carbon.     

Carbon-supported PdSn–SnO2 catalyst for ethanol electro-oxidation in alkaline media

Carbon-supported PdSn–SnO₂ with high electrical catalytic activity for ethanol oxidation in alkaline solution was synthesized using an impregnation reduction method. XRD analysis of the as-prepared PdSn–SnO₂/C revealed that the Pd diffraction peaks shifted to lower 2θ values with respect to the corresponding peaks of the Pd/C catalyst, indicating that Sn doping could shrink the Pd crystalline lattice. XPS measurements confirmed the existence of Sn and SnO₂ in the PdSn–SnO₂/C catalysts. The prepared PdSn–SnO₂/C catalysts presented a remarkably higher electrocatalytic activity than that of the Pd–Sn/C and Pd/C catalysts. This was mainly because the easy adsorption-dissociation of OH_ads over the SnO₂ surface changed the electronic effect and accelerated the adsorption of ethanol on the surface of Pd, thus enhancing the overall ethanol oxidation kinetics and contributing to a significant improvement in the catalytic activity.     

Sulfated SnO2 modified multi-walled carbon nanotubes - A mixed proton-electron conducting support for Pt catalysts in direct ethanol fuel cells

We report on the synthesis of sulfated SnO₂ modified multi-walled carbon nanotubes (MWCNTs) composites as new supports of Pt catalyst (Pt-S-SnO₂/MWCNTs) with the aims to enhance electron and proton conductivity and also catalytic activity for ethanol oxidation. The Pt-S-SnO₂/MWCNTs catalyst is synthesized by a combination of improved sol-gel and pulse-microwave assisted polyol methods. The surface presence, morphology and structure of the Pt-S-SnO₂/MWCNTs catalyst are characterized by Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD), respectively. The electrocatalytic properties of the Pt-S-SnO₂/MWCNTs catalyst for ethanol oxidation reactions are investigated by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The results show that Pt-S-SnO₂/MWCNTs catalyst exhibits higher catalytic activity for ethanol oxidation than Pt supported on non-sulfated SnO₂/MWCNTs composites.     

Pt support of multidimensional active sites and radial channels formed by SnO2 flower-like crystals for methanol and ethanol oxidation

SnO₂ nanoflowers and nanorods have been synthesized by the hydrothermal method without using any capping agent. Both types of SnO₂ nanostructures are selected as a support of Pt catalyst for methanol and ethanol electrooxidation. The synthesized SnO₂ nanostructures and SnO₂ supported platinum (Pt/SnO₂) catalysts are characterized by X-ray diffraction, scanning electron microscope and high resolution transmission electron microscope. The electrocatalytic properties of the Pt/SnO₂ and Pt/C catalysts for methanol and ethanol oxidation have been investigated systematically by typical electrochemical methods. The influence of SnO₂ morphology on its electrocatalytic activity is comparatively investigated. The Pt/SnO₂ flower-shaped catalyst shows higher electrocatalytic activity and better long-term cycle stability compared with other electrocatalysts owing to the multidimensional active sites and radial channels of liquid diffusion.     

Ethanol oxidation reaction activity of highly dispersed Pt/SnO2 double nanoparticles on carbon black

Highly dispersed Pt and SnO₂ double nanoparticles containing different Pt/Sn ratios (denoted as Pt/SnO₂/CB) were prepared on carbon black (CB) by the modified Bönnemann method. The average size of Pt and SnO₂ nanoparticles was 3.1 ± 0.5 nm and 2.5 ± 0.3 nm, respectively, in Pt/SnO₂(3:1)/CB, 3.0 ± 0.5 nm and 2.6 ± 0.3 nm, respectively, in Pt/SnO₂(1:1)/CB, and 2.8 ± 0.5 nm and 2.5 ± 0.3 nm, respectively, in Pt/SnO₂(1:3)/CB. The Pt/SnO₂(3:1)/CB electrode showed the highest specific activity and lowest overpotential for ethanol oxidation reaction (EOR), and was superior to a Pt/CB electrode. Current density for EOR at 0.40 and 0.60 V vs. reversible hydrogen electrode for the Pt/SnO₂(3:1)/CB electrode decayed more slowly than that for the Pt/CB electrode because of a synergistic effect between Pt and SnO₂ nanoparticles. The predominant reaction product was acetic acid, and its current efficiency was about 70%, while that for CO₂ production was about 30%.     

Effect of Ni on Pt/C and PtSn/C prepared by the Pechini method

Different compositions of Pt, PtNi, PtSn, and PtSnNi electrocatalysts supported on carbon Vulcan XC-72 were prepared through thermal decomposition of polymeric precursors. The nanoparticles were characterized by morphological and structural analyses (XRD, TEM, and EDX). XRD results revealed a face-centered cubic structure for platinum, and there was evidence that Ni and Sn atoms are incorporated into the Pt structure. The electrochemical investigation was carried out in slightly acidic medium (H₂SO₄ 0.05 mol L⁻¹), in the absence and in the presence of ethanol. Addition of Ni to Pt/C and PtSn/C catalysts significantly shifted the onset of ethanol and CO oxidations toward lower potentials, thus enhancing the catalytic activity, especially in the case of the ternary PtSnNi/C composition. Electrolysis of ethanol solutions at 0.4 V vs. RHE allowed for determination of acetaldehyde and acetic acid as the reaction products, as detected by HPLC analysis. Due to the high concentration of ethanol employed in the electrolysis experiments (1.0 mol L⁻¹), no formation of CO₂ was observed.     

Catalytic activity,stability and impedance behavior of PtRu/C,PtPd/C and PtSn/C bimetallic catalysts toward methanol and formic acid oxidation

PtRu, PtPd and PtSn with weight ratios of (2:1) on carbon black (Vulcan XC-72) supported bimetallic catalysts were prepared by using microwave method via chemically reduction of H₂PtCl₆·6H₂O, RuCl₃, PdCl₂ and SnCl₂·2H₂O precursors with ethylene glycol (EG). These prepared catalysts were systematically investigated and obtained results were compared with commercial Pt black, PtRu black catalysts and with each other. The catalysts were characterized with XRD, ICP-MS, EDS and TEM. The electrocatalytic activities, stability and impedance of the catalysts were investigated in sulfuric acid/methanol and sulfuric acid/formic acid mixtures using electrochemical measurements. The results showed that PtSn/C catalyst showed comparable activity and durability with commercial Pt/C catalyst toward methanol oxidation. The synthesized PtRu/C catalyst was found to completely oxidize methanol and it showed more catalytic activity than commercial PtRu catalyst. Bimetallic PtPd/C catalyst gave better activity than both commercial Pt black and synthesized Pt/C catalyst for oxidation of formic acid. Higher electrochemical active surface areas were obtained with supported bimetallic catalysts.     

Electrospun TiO2/SnO2 nanofibers with innovative structure and chemical properties for highly efficient photocatalytic H2 generation

Innovative TiO₂/SnO₂ nanofibers were fabricated via electrospinning an innovated precursor solution and used for photocatalytic H₂ generation. The nanofibers exhibited greatly enhanced H₂ evolution rate compared to bare TiO₂ nanofiber and P25. The enhanced efficiency of the TiO₂/SnO₂ nanofibers was attributed to its excellent synergistic properties: (1) its good mesoporosity; (2) the red-shift of absorbance spectra to enhance light absorbance capability; (3) its long nanofibrous structure and (4) anatase TiO₂ – rutile TiO₂ – rutile SnO₂ ternary junctions favorable for the separation of electrons and holes. Based on our experimental results, the optimum ratio of TiO₂/SnO₂ nanofibers with 3% Sn demonstrated the highest efficiency in H₂ generation.     

Electrooxidations of ethanol,acetaldehyde and acetic acid using PtRuSn/C catalysts prepared by modified alcohol-reduction process

Well-dispersed ternary PtRuSn catalysts of various atomic ratios (60:30:10, 60:20:20 and 60:10:30) were deposited onto carbon using modified alcohol-reduction process for electrochemical oxidation of ethanol. The alloy phase structure and surface morphology for each variation of the PtRuSn/C catalysts were determined by XRD and HRTEM. In order to evaluate the contributions of Ru and Sn in the different stages of ethanol oxidation, electrochemical oxidations of adsorbed CO, ethanol, acetaldehyde and acetic acid were performed on each PtRuSn/C catalyst. The results indicated that the Ru-rich PtRuSn/C catalyst (60:30:10) exhibited the lowest onset potential for the electrooxidations of adsorbed CO, ethanol and acetaldehyde, revealing that the removal through oxidation of the intermediate C₁ and C₂ species from Pt sites is primarily attributed to the Ru and Pt₃Sn alloy structures. However, for the overall oxidation of ethanol, the Sn-rich PtRuSn/C catalyst (60:10:30) containing PtSn phase and SnO₂ structure is favorable for the activation of CC bond breaking, thereby generating higher current density (mass activity) at higher potentials. Moreover, in the electrooxidation of acetic acid, a remarkable improvement for oxidizing acetic acid to C₁ species was observed in the Sn-rich PtRuSn/C catalyst (60:10:30), while the Ru-rich PtRuSn/C catalyst (60:30:10) was almost incapable of breaking the CC bond to further oxidize acetic acid. The possible reasons for the different reactivities on the studied PtRuSn/C catalysts were discussed based on the removal of intermediates and activation of the CC bonds on the different surfaces.     

RuO2 supported on Sb-doped SnO2 nanoparticles for polymer electrolyte membrane water electrolysers

With a colloid method, RuO₂ was deposited on Sb-doped SnO₂ nanoparticles (ATO, Aldrich, 30-40 nm), which was employed as a novel support material for anode catalysts of polymer electrolyte membrane water electrolysers (PEMWE). Distinctive RuO₂ nanoparticles (10-15 nm) were stably deposited on ATO nanoparticles, which were characterized with XRD and SEM. RuO₂/ATO exhibited higher activity than unsupported RuO₂ for oxygen evolution. A PEMWE single cell with 10 mg cm⁻² 20 wt.% RuO₂/ATO achieved 1.56 V at 1 A cm⁻² at 80 °C.     

Hydrothermal synthesis of SnO2–V2O5 mixed oxide and electrochemical screening of carbon nano-tubes (CNT), V2O5, V2O5–CNT,and SnO2–V2O5–CNT electrodes for supercapacitor applications

Nano-scaled SnO₂–V₂O₅ mixed oxide is synthesized by a hydrothermal method in an autoclave. For comparative evaluation, V₂O₅ single oxide is prepared by a conventional process from ammonium vanadate. The capacitive behaviour of the following electrodes is studied by cyclic voltammetry in 0.1 M KCl solutions: carbon nano-tubes (CNT), V₂O₅, V₂O₅–CNT, and SnO₂–V₂O₅–CNT. At a scan rate of 100 mV s⁻¹, the SnO₂–V₂O₅–CNT electrode provides the best performance, viz., 121.4 F g⁻¹. The nano-scaled mixed oxide is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman spectra.     

Steam reforming of ethanol at moderate temperature: Multifactorial design analysis of Ni/La2O3-Al2O3, and Fe- and Mn-promoted Co/ZnO catalysts

Novel Co (10%) catalysts supported on ZnO and promoted with Fe and Mn (1%) were synthesized and characterized by high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS), X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS). Their catalytic activity for steam reforming of ethanol was compared with that of Ni catalysts supported on La₂O₃-Al₂O₃. Experiments at 400 and 500 °C, steam to carbon ratios of 2 and 4, and a wide interval of contact time were analyzed following a multifactorial experimental design. At 500 °C and a steam to carbon molar ratio of 4, complete conversion of ethanol was achieved above a contact time of 200 g min mol⁻¹ for all catalysts. The ratio of selectivity between hydrogen and methane was around 23 mol_H2/mol_CH4 in the Co catalysts, while it approached the thermodynamic equilibrium (5.7 mol_H2/mol_CH4) in the Ni catalysts. The Co catalysts do not promote methane-forming reactions like ethanol cracking and acetaldehyde decarbonilation, nor do they facilitate the reverse methane steam reforming reaction. The catalytic behavior of cobalt is enhanced by promotion with iron or manganese through the formation of bimetallic particles, which facilitates cobalt reducibility. This suggests that Co-Mn/ZnO and Co-Fe/ZnO catalysts have a good potential for their use for ethanol reforming at moderate temperature.     

Dual gas sensing properties of graphene-Pd/SnO2 composites for H2 and ethanol: Role of nanoparticles-graphene interface

In the present work, role of palladium (Pd) and tin oxide (SnO₂) nanoparticles (NPs) deposited on graphene has been investigated in terms of dual gas sensing characteristics of ethanol and H₂ between two temperatures. The incorporation of nanoparticles into graphene has been observed which results a large change in the sensing response towards these gases. It is investigated that, incorporation of isolated Pd NPs on the graphene facilitates the room temperature sensing of H₂ gas with fast response and recovery time whereas, isolated SnO₂ NPs on graphene enables the detection of ethanol at 200 °C. However, combination of isolated Pd and SnO₂ NPs on graphene shows improved sensitivity and good selectivity towards H₂ and ethanol, usually not observed in chemiresistive gas sensors. Catalytic PdH interaction and corresponding change in work function of nanoparticles on hydrogenation resulting in modifications in electronic exchange between Pd, SnO₂ and graphene are responsible for the observed behavior. These results are important for developing a new class of chemiresistive type gas sensor based on change in the electronic properties of the graphene and NPs interfaces.     

Photocatalytic H2 production from acetic acid solution over CuO/SnO2 nanocomposites under UV irradiation

The CuO/SnO₂ composites have been prepared by the simple co-precipitation method and further characterized by the XRD, FESEM and Raman spectroscopy. The photocatalytic H₂ production from acetic acid (HAc) solution over CuO/SnO₂ photocatalyst has been investigated at room temperature under UV irradiation. Effects of CuO loading, photocatalyst concentration, acetic acid concentration and pH on H₂ production have been systematically studied. Compared with pure SnO₂, the 33.3 mol%CuO/SnO₂ composite exhibited approximately twentyfold enhancement of H₂ production. The H₂ yield is about 0.66 mol-H₂/mol-HAc obtained under irradiation for prolonged time. The Langmuir-type model is applied to study the dependence of hydrogen production rate on HAc concentration. A possible mechanism for photocatalytic degradation of acetic acid over CuO/SnO₂ photocatalyst is proposed as well. Our results provide a method for pollutants removal with simultaneous hydrogen generation. Due to simple preparation, high H₂ production activity and low cost, the CuO/SnO₂ photocatalyst will find wide application in the coming future of hydrogen economy.     

SnO2-Au hybrid nanoparticles as effective catalysts for oxygen electroreduction in alkaline media

SnO₂ nanoparticles were synthesized by a facile electrochemical method based on anodic oxidation of a tin metal sheet. The resulting particles, with an average diameter of about 20 nm, were then loaded with varied amounts of HAuCl₄, forming SnO₂-Au(x) (x = 0, 0.095, 0.38, 0.76, 1.9, 3.0, and 3.8 at.%) hybrid nanoparticles after calcination at elevated temperatures (700 °C). X-ray diffraction (XRD) and transmission electron microscopic (TEM) measurements showed that the SnO₂ particles exhibited high crystallinity with a rutile structure, and spherical Au nanoparticles were dispersed on the surface of the SnO₂ support. Based on the TEM images and the width of the Au(2 0 0) XRD diffraction peak, the size of the Au nanoparticles was found to be between 15 and 35 nm in diameter and decrease with increasing loading of the original HAuCl₄ precursor. The electrocatalytic activity of the resulting SnO₂-Au(x) composite nanoparticles toward oxygen reduction reactions (ORR) was then evaluated by cyclic and rotating disk voltammetric measurements in alkaline solutions. It was found that the incorporation of gold nanoparticles led to apparent improvement of the catalytic activity of SnO₂ nanoparticles. Moreover, the ORR electrocatalytic activity exhibited a strong dependence on the gold loading in the hybrid nanoparticles, and the most active catalyst was found with a gold loading of 1.9 at.%, based on the reduction current density and onset potential of ORR. Furthermore, at this gold loading, oxygen reduction was found to follow the efficient four-electron reaction pathway, whereas at other Au loadings, the number of electron transfer involved in oxygen reduction varied between 1 and 3. Additionally, Tafel analysis suggested that at low overpotentials, the first electron transfer might be the limiting step in oxygen reduction, whereas at high potentials, oxygen adsorption appeared to play the determining role at the SnO₂-Au hybrid electrodes. These results indicate that the SnO₂-Au composite nanoparticles might serve as effective catalysts for oxygen electroreduction in alkaline media.     

Electro-oxidation of methanol on SnO2-promoted Pd/MWCNTs catalysts in alkaline solution

The methanol electro-oxidation (MEO) on Pd–SnO₂/MWCNTs catalysts prepared by microwave-assisted polyol reduction method has been investigated. The structure, morphology and electro-catalytic performances of the catalysts were characterized with XRD, TEM and cyclic voltammetry (CV). The results showed that the highly dispersed Pd nano-particles (PdNPs) with a narrow size distribution on MWCNTs were successfully synthesized. The catalytic activity of Pd–SnO₂/MWCNTs for MEO was up to 778.8 mA/mg Pd in 0.1 M KOH solution containing 1 M methanol, which was significant higher than that of Pd/C (414.2 mA/mg Pd) or Pd–SnO₂/C (566.7 mA/mg Pd). Moreover, the MEO on Pd–SnO₂/MWCNTs electrode displayed an irreversible behavior under a diffusion control giving an exchange current density (j⁰) of 3.76 × 10⁻⁴ A cm⁻² and a Tafel slope of 149 mV dec⁻¹ (α = 0.56) at 25 °C, which indicates that Pd–SnO₂/MWCNTs catalyst has a high electro-catalytic performance for the MEO in alkaline media.     

Platinum nanoparticles embedded in layer-by-layer films from SnO2/polyallylamine for ethanol electrooxidation

Self-assembled films from SnO₂ and polyallylamine (PAH) were deposited on gold via ionic attraction by the layer-by-layer (LbL) method. The modified electrodes were immersed into a H₂PtCl₆ solution, a current of 100 μA was applied, and different electrodeposition times were used. The SnO₂/PAH layers served as templates to yield metallic platinum with different particle sizes. The scanning tunnel microscopy images show that the particle size increases as a function of electrodeposition time. The potentiodynamic profile of the electrodes changes as a function of the electrodeposition time in 0.5 mol L⁻¹ H₂SO₄, at a sweeping rate of 50 mV s⁻¹. Oxygen-like species are formed at less positive potentials for the Pt–SnO₂/PAH film in the case of the smallest platinum particles. Electrochemical impedance spectroscopy measurements in acid medium at 0.7 V show that the charge transfer resistance normalized by the exposed platinum area is 750 times greater for platinum electrode (300 kΩ cm²) compared with the Pt–SnO₂/PAH film with 1 min of electrodeposition (0.4 kΩ cm²). According to the Langmuir–Hinshelwood bifunctional mechanism, the high degree of coverage with oxygen-like species on the platinum nanoparticles is responsible for the electrocatalytic activity of the Pt–SnO₂/PAH concerning ethanol electrooxidation. With these features, this Pt–SnO₂/PAH film may be grown on a proton exchange membrane (PEM) in direct ethanol fuel cells (DEFC).     

Direct ethanol fuel cells based on PtSn anodes: the effect of Sn content on the fuel cell performance

In the present work, several carbon supported PtSn catalysts with different Pt/Sn atomic ratios were synthesized and characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Both the results of TEM and XRD showed that all in-house prepared carbon supported Pt and PtSn catalysts had nanosized particles with narrow size distribution. According to the primary analysis of XPS results, it was confirmed that the main part of Pt of the as-prepared catalysts is in metallic state while the main part of Sn is in oxidized state. The performances of single direct ethanol fuel cells were different from each other with different anode catalysts and at different temperatures. It was found that, the single DEFC employing Pt₃Sn₂/C showed better performance at 60 °C while the direct ethanol fuel cells with Pt₂Sn₁/C and Pt₃Sn₂/C exhibited similar performances at 75 °C. Furthermore, at 90 °C, Pt₂Sn₁/C was identified as a more suitable anode catalyst for direct ethanol fuel cells in terms of the fuel cell maximum power density. Surface oxygen-containing species, lattice parameters and ohmic effects, which are related to the Sn content, are thought as the main factors influencing the catalyst activity and consequently the performance of single direct ethanol fuel cells.     

Novel inorganic precursors [Co4.32Zn1.68(HCO2)18(C2H8N)6]/SiO2 and Co4.32Zn1.68(HCO2)18(C2H8N)6]/Al2O3 for Fischer–Tropsch synthesis

The silica- and alumina-supported Co–Zn catalysts were synthesized by thermal decomposition of new inorganic precursors [Co_4.32Zn_1.68(HCO₂)₁₈(C₂H₈N)₆]/SiO₂ or Al₂O₃. A novel coordination polymer formulated as [Co_4.32Zn_1.68(HCO₂)₁₈(C₂H₈N)₆] (1) was prepared using the solvothermal technique and characterized by elemental analysis, FT-infrared spectroscopy. Thermal stability of the complex 1 was investigated by thermogravimetric analysis and differential scanning calorimetry, and its structure was determined by single-crystal X-ray diffraction. Characterization of catalysts was carried out using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET specific surface area. The catalysts were evaluated for Fischer–Tropsch synthesis (FTS) in the temperature range 200–300 °C. The results revealed that the synthesized catalysts have higher selectivity to the desired products at 260 °C. The performance of the catalysts was compared to those of catalysts constructed via impregnation method and the fabricated catalysts show higher activity and selectivity than the reference catalysts.