Ethanol oxidation on carbon supported (PtSn)alloy/SnO2 and (PtSnPd)alloy/SnO2 catalysts with a fixed Pt/SnO2 atomic ratio: Effect of the alloy phase characteristics

To evaluate the effect of the alloy phase characteristics on the ethanol oxidation activity, carbon supported (PtSnPd)_alloy/SnO₂ catalysts were prepared and their electrocatalytic activity compared with that of carbon supported (PtSn)_alloy/SnO₂. Pt-Sn-Pd/C samples in the atomic ratio (1:1:0.3) and (1:1:1) were characterized by energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD analysis shows the presence of fcc Pt reflexions, shifted to lower angles, and SnO₂ reflexions. By comparison with the XRD patterns of carbon supported Pt-Sn (1:1) and Pt-Pd (3:1) samples, prepared by the same method, the formation of ternary PtSnPd alloys is postulated. The crystallite size of the ternary catalysts is smaller than that of both binary Pt-Sn/C (1:1) and Pt-Pd/C (3:1) catalysts. Chronoamperometry experiments and tests in direct ethanol fuel cells of the as-prepared catalysts shows that the activity for ethanol oxidation of (PtSn)_alloy/SnO₂ is higher than that of (PtSnPd)_alloy/SnO₂. This result, obtained with the same Pt/SnO₂ atomic ratio in all the samples, indicates the critical role of the alloy phase characteristics of these catalysts on their activity for ethanol oxidation.     

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%.     

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.     

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.     

Electrodeposited Ni-Cr2O3 nanocomposite anodes for ethanol electrooxidation

Nanocomposite coatings of Ni-Cr₂O₃ supported on carbon electrodes have been prepared by electrodeposition technique from nickel Watts bath in presence of Cr₂O₃ nanoparticles. Their electrochemical catalytic activities have been evaluated towards electrooxidation of ethanol in 1.0 M NaOH solution by using cyclic voltammetry, chronoamperometry and Tafel plots. The performance of the prepared anodes towards electrooxidation of ethanol as a function of co-deposited Cr₂O₃ content was studied. The catalytic activity of fabricated electrodes increases with increasing the volume fraction percent (V_f%) of Cr₂O₃ in the deposited film up to 7V_f%. The Ni-Cr₂O₃/C (7V_f%) electrode displayed significantly enhanced catalytic activity and stability towards electrooxidation of ethanol compared with Ni/C electrode. The kinetic parameters of Ni(OH)₂/NiOOH and ethanol oxidation at Ni/C and Ni-Cr₂O₃/C electrodes have been evaluated.     

Hydrogenation of CO2 over Co supported on carbon nanotube,carbon nanotube-Nb2O5, carbon nanofiber,low-layered graphite fragments and Nb2O5

CO₂ hydrogenation was studied with catalysts containing 1.5–35 wt% Co supported on carbon nanotubes, nanofibers, low-layered graphite fragments and composites of carbon nanotube-Nb₂O₅. All catalytic processes with Co/supported catalysts were investigated using XRF, DSC, TGA, H₂-TPR, TEM, SEM and XPS. Based on obtained results, it is indicated that the products from CO₂ hydrogenation were CH₄ and/or CO under reaction conditions pressure of 1.5 MPa and temperature of 200–500 °C, as well as the size of the particles of Co and their phase state directly affected on the catalysts activity. 3 wt% Co catalyst supported on carbon nanotubes has shown catalytic inactivity due to amorphous state of metal. It is possible to activate them during Co crystallization after thermal treatment. It is shown, that the size of Co particles supported on carbon nanotubes is 4–6 nm. The methods of fictionalization the surface of carbon nanomaterials ensuring an additional stability of metal nanoparticles is recommended.     

Electrochemical behaviour of carbon supported Pt electrocatalysts for H2O2 reduction

Carbon supported bimetallic Pt-alloys (Pt_0.75M_0.25/C, with M = Ni or Co) are investigated as novel electrode materials for H₂O₂ reduction in acid solution. The alloy electrocatalysts, Pt_0.75Ni_0.25/C and Pt_0.75Co_0.25/C, as well as carbon supported Pt (Pt/C) are characterised using cyclic voltammetry. The electrocatalytic activity of the materials is studied using a rotating disc electrode system with a combination of linear scan voltammetry and chronoamperometry. It is found that the activity of Pt_0.75M_0.25/C electrocatalysts for H₂O₂ reduction is comparable to the activity of Pt/C electrocatalyst, with Pt_0.75Co_0.25/C exhibiting the best performance.     

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.     

Selective CO oxidation on Cu promoted Pt/Al2O3 and Pt/Nb2O5 catalysts

Pt–Cu catalysts supported on Al₂O₃ and Nb₂O₅ were studied for use in selective CO oxidation. The addition of copper enhanced the activity and selectivity of Pt–Cu/Nb₂O₅ at lower temperatures when compared to Pt/Nb₂O₅. On the other hand, copper addition was not beneficial in the case of Al₂O₃ supported catalysts.     

Evaluation of the corrosion of Sb-doped SnO2 supports for electrolysis systems

The corrosion behaviour and electrochemical stability of two different electrocatalyst supports based on Sb-doped SnO₂ (ATO) were evaluated in an acidic medium over a wide potential range (0–1.8 V vs. NHE). The results were compared with those from a commercial Vulcan carbon XC-72 (254 m² g⁻¹) support. ATO (85 m² g⁻¹) and modified-ATO (216 m² g⁻¹) were synthesized by the sol–gel method and were then characterized by XRD, BET and TEM. The modification of the ATO consisted of adding dodecylamine as a surfactant to generate a surface area similar to that of Vulcan carbon. The electrochemical characterization conditions were chosen to match the operating conditions of a proton exchange membrane fuel cell (PEMFC) and a solid polymer electrolyser (SPE), where the oxygen-evolution reaction takes place at a potential near 1.6 V with respect to normal hydrogen electrode (NHE). The results show good chemical stability when the ATO and the modified-ATO are subjected to these conditions, whereas Vulcan carbon corrodes easily. This indicates that Sb-doped SnO₂ is a good candidate for electrocatalyst supports for energy-conversion systems such as electrolysers and unified regenerative fuel cells.     

Enhanced electrocatalytic performance for methanol oxidation of Pt nanoparticles on Mn3O4-modified multi-walled carbon nanotubes

We report the preparation of well-dispersed Pt nanoparticles depositing on Mn₃O₄-modified multi-walled carbon nanotubes (Mn₃O₄-MWCNTs) that can be taken as high performance catalyst in methanol electro-oxidation. Various spectrometry techniques such as FT-IR, Raman, XRD, TEM and XPS measurements were performed, revealing that the Pt nanoparticles were highly dispersed on the surface of Mn₃O₄-modified MWCNTs with a narrow size distribution between 1.7 nm and 3.9 nm. Compared the Pt/MWCNT catalyst without Mn₃O₄ modification, the Pt/Mn₃O₄-MWCNT composite catalyst not only shows relative large electrochemical active surface area (EAS), high catalyzing activity toward methanol electro-oxidation, but also exhibits very high stability with apparent anti-poisoning tolerance to the incomplete oxidized species during methanol oxidation.     

CNT-based catalysts for H2 production by ethanol reforming

Hydrogen production by steam reforming of ethanol (SRE) was studied using steam-to-ethanol ratio of 3:1, between the temperature range of 150–450 °C over metal and metal oxide nanoparticle catalysts (Ni, Co, Pt and Rh) supported on carbon nanotubes (CNTs) and compared to a commercial catalyst (Ni/Al₂O₃). The aim was to find out the suitability of CNTs supports with metal nanoparticles for the SRE reactions at low temperatures. The idea to develop CNT-based catalysts that have high selectivity for H₂ is one of the driving forces for this study. The catalytic performance was evaluated in terms of ethanol conversion, product gas composition, hydrogen yield and selectivity to hydrogen. The Co/CNT and Ni/CNT catalysts were found to have the highest activity and selectivity towards hydrogen formation among the catalysts studied. Almost complete ethanol conversion is achieved over the Ni/CNT catalyst at 400 °C. The highest hydrogen yield of 2.5 is, however, obtained over the Co/CNT catalyst at 450 °C. The formation of CO and CH₄ was very low over the Co/CNT catalyst compared to all the other tested catalysts. The Pt and Rh CNT-based catalysts were found to have low activity and selectivity in the SRE reaction. Hydrogen production via steam reforming of ethanol at low temperatures using especially Co/CNT catalyst has thus potential in the future in e.g. the fuel cell applications.     

Formation of ultrafast-switching viologen-anchored TiO2 electrochromic device by introducing Sb-doped SnO2 nanoparticles

Ultrafast-switching viologen-anchored TiO₂ electrochromic device (ECD) was developed by introducing Sb-doped SnO₂ (Sb_xSn_1−xO₂, ATO) as counter electrode (CE), and the switching behavior of the fabricated ECD was investigated as a function of Sb-doping concentration. About 9-nm-sized Sb_xSn_1−xO₂ (x=0–0.3) nanoparticles were synthesized by a solvothermal reaction of tin (IV) chloride and antimony (III) chloride at 240 °C, and employed to fabricate 2.4-μm-thick transparent CE. Working electrode (WE) was formed from the 7-nm-sized TiO₂ nanoparticle by a doctor blade method, and the thickness of the nanoporous TiO₂ electrode was 4.5 μm. The phosphonated viologen, bis(2-phosphonylethyl)-4,4′-bipyridinium dibromide, was then adsorbed on the prepared films for the construction of the ECD. The response time was strongly dependent on the doping concentration of Sb in ATO, and the fastest switching response was observed at 3 mol%. At this composition, the coloration time was 5.7 ms, and the bleaching time was 14.4 ms, which is regarded as one of the best results so far reported.     

High efficiency Pt-CeO2/carbon nanotubes hybrid composite as an anode electrocatalyst for direct methanol fuel cells

Pt-CeO₂/carbon nanotubes (Pt-CeO₂/CNTs), based on glucose polymerization in the inner pores of anodic aluminum oxide templates under hydrothermal conditions followed by carbonization at high temperature, were synthesized using as precursors H₂PtCl₆ reduced by NaBH₄ and CeCl₃ deposited by NaOH. Pt nanoparticles and CeO₂ units were inserted onto the outer surfaces and inner surfaces of the as-prepared carbon nanotubes (CNTs). The resulting structures were characterized by scanning electron microscopy (SEM). The electrocatalytic performances of the Pt-CeO₂/CNTs modified glass carbon electrodes were investigated for methanol oxidation by cyclic voltammetric and chronoamperometric measurements. It was found that compared with Pt/CNTs, the hybrid Pt-CeO₂/CNTs electrodes showed superior catalytic performance when the molar ratio of Pt to CeO₂ in the catalyst was about 2:1. The increased catalytic efficiency of Pt is likely to result from its combination with CeO₂.     

Electrooxidation of ethanol and glycerol on carbon supported PtCu nanoparticles

Four carbon supported PtCu nanostructured catalysts with Pt:Cu atomic ratios of 1:3.20, 1:2.23, 1:0.61 and 1:0.35 were synthesized by a two-step route, involving the chemical reduction of Cu ions on the carbon support, followed by the partial galvanic replacement of Cu atoms by Pt. Bimetallic nanostructured particles with average sizes in the range of 2.3–3.2 nm were obtained. The bimetallic catalysts with surface Pt contents between 20 and 55 at. % were formed by a Cu-rich core surrounded by a Pt-Cu shell, while that with the highest Pt content presented a uniform alloy structure instead of a core-shell arrangement. The electrocatalytic performance of the as-prepared materials toward ethanol electrooxidation in acid and alkaline media and glycerol oxidation in alkaline environment was investigated by cyclic voltammetry and chronoamperometry. It was observed that the electrocatalytic activity of PtCu nanoparticles was found to depend on the surface composition, platinum utilization efficiency, structure and Pt ensemble. Among the as-prepared catalysts, Pt_0·62Cu_0·38/C core-shell material showed the best performance for ethanol oxidation in both acid and alkaline environments, while Pt_0·24Cu_0·76/C and Pt_0·31Cu_0·69/C core-shell catalysts exhibited the highest activity for glycerol oxidation in alkaline medium. The electrochemical results showed that the catalytic activity of the bimetallic Cu@PtCu core-shell nanostructured nanoparticles is between four and ten times higher than that of a commercial Pt_0·51Ru_0·49/C catalyst.     

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.     

Atomic layer deposition assisted Pt-SnO2 hybrid catalysts on nitrogen-doped CNTs with enhanced electrocatalytic activities for low temperature fuel cells

Nitrogen doped carbon nanotubes (CN_x) of a high nitrogen concentration were synthesized directly on carbon paper as the skeleton of a 3D composite electrode. Ultra-fine SnO₂ nanoparticles about 1.5 nm were deposited on CN_x with atomic layer deposition (ALD) technique. Pt nanoparticles from 1.5 to 4 nm were deposited on CN_x/carbon paper and SnO₂/CN_x/carbon paper with ethylene glycol reduction method. Three dimensional Pt/CN_x/carbon paper and Pt-SnO₂/CN_x/carbon paper composite electrodes were obtained, respectively. They were characterized over oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) for low temperature fuel cells. With similar sizes of Pt nanoparticles, the electrochemical surface area (ECSA) of Pt-SnO₂/CN_x/carbon paper is larger than that of Pt/CN_x/carbon paper. Pre-deposited SnO₂ nanoparticles promote the electrocatalytic activity of Pt toward ORR, carbon monoxide (CO) stripping and MOR. The underlying mechanisms for the enhanced activities are discussed.     

Flame co-synthesis of LiMn2O4 and carbon nanocomposites for high power batteries

A novel method to produce LiMn₂O₄/carbon nanocomposites in a rapid, one-step and industrially scalable process is presented. A flame spray and a diffusion flame are combined to continuously produce LiMn₂O₄ nanoparticles and carbon black, respectively. Powder carbon content is varied by adjusting the diffusion flame conditions. The powders are characterized by X-ray diffraction (XRD), transmission electron microscopy, cyclic voltammetry and galvanostatic cycling for a range of current densities. These LiMn₂O₄/carbon nanocomposites retain over 80% of their initial galvanostatic discharge capacity for current densities ranging from 5 to 50C-rates, significantly better than pure LiMn₂O₄ nanoparticles mixed conventionally with commercial carbon blacks. The improved performance of the LiMn₂O₄/carbon nanocomposites is attributed to the carbon particle contact and/or film coating of the freshly-made LiMn₂O₄ nanoparticles. This additional well-distributed carbon provides an electrically conductive network that induces a more homogeneous charge transfer throughout the electrode. The suitability of these nanocomposites as a hybrid material is discussed by considering the layout of a thin-layer lithium-ion battery containing these flame-made nanocomposites as positive electrode and LiC₆ as negative electrode. The battery’s specific energy is calculated to be 78 Wh kg⁻¹ (50C-rate) based on the results of lithium-ion insertion capacity experiments and reasonable engineering assumptions on the lithium-ion battery design.     

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.     

Carbon supported Pt hollow nanospheres as anode catalysts for direct borohydride-hydrogen peroxide fuel cells

The carbon supported Pt hollow nanospheres were prepared by employing cobalt nanoparticles as sacrificial templates at room temperature in aqueous solution and used as the anode electrocatalyst for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties of the as-prepared electrocatalysts were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry (CV), chronoamperometry (CA), chronopotentiometry (CP) and fuel cell test. The results showed that the carbon supported Pt nanospheres were coreless and composed of discrete Pt nanoparticles with the crystallite size of about 2.8 nm. Besides, it has been found that the carbon supported Pt hollow nanospheres exhibited an enhanced electrocatalytic performance for BH₄⁻ oxidation compared with the carbon supported solid Pt nanoparticles, and the DBHFC using the carbon supported Pt hollow nanospheres as electrocatalyst showed as high as 54.53 mW cm⁻² power density at a discharge current density of 44.9 mA cm⁻².