Ethanol electro-oxidation on carbon-supported Pt, PtRu and Pt3Sn catalysts: A quantitative DEMS study (original) (raw)
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Journal of Power Sources, 2009
The electrocatalytic activity of commercial carbon supported PtRu/Vulcan and Pt 3 Sn/Vulcan bimetallic catalysts (E-TEK, Inc.) for ethanol oxidation under well defined electrolyte transport conditions and their selectivity for complete oxidation were evaluated using cyclic voltammetry combined with on-line differential electrochemistry mass spectrometry (DEMS) measurements and compared to the activity/selectivity of standard Pt/Vulcan catalysts. The main reaction products CO 2 , acetaldehyde and acetic acid were determined quantitatively, by appropriate calibration procedures, current efficiencies and product yields were calculated. Addition of Ru or Sn in binary Pt catalysts lowers the onset potential for ethanol electro-oxidation and leads to a subtle increase of the total activity of the Pt 3 Sn/Vulcan catalyst. It does not improve, however, the selectivity for complete oxidation to CO 2 , which is about 1% for all three catalysts under present reaction conditions-incomplete ethanol oxidation to acetaldehyde and acetic acid prevails on all three catalysts. The results demonstrate that the performance of the respective catalysts is limited by their ability for CC bond breaking rather than by their activity for the oxidation of poisoning adsorbed intermediates such as CO ad or CH x,ad species.
Renewable Energy and Power Quality Journal
Direct ethanol fuel cells (DEFCs) operate at low temperature, which makes the oxidation and reduction reactions slower, requiring electrocatalysts able to accelerate these reactions. In the present work, commercial Vulcan carbon (V) supported Pt and Pd catalysts were compared as electrocatalysts for ethanol oxidation reaction (EOR) in acidic and alkaline medium, respectively. Cyclic voltammetries obtained in presence of ethanol showing a better catalytic performance for the Pd/V electroctalyst compared to the Pt/V electrocatalyst. The maximum current density related with the EOR in a 1.0 mol L-1 ethanol + 1.0 mol L-1 NaOH solution was 236.9 A g Pd-1 for Pd/V. The better performance of the Pd/V electrocatalyst can be associated with a lower Pd nanoparticles sizes and higher particles dispersion onto the Vulcan carbon surface in the Pd/V electrocatalyst. The onset potential for the EOR was 0.2 V vs. SCE for the Pt/V sample and-0.6 V vs. Hg/HgO for the Pd/V sample.
Electrochimica Acta, 2012
Carbon supported Pt-Sn catalysts were prepared by reduction of Pt and Sn precursors with formic acid and characterized in terms of structure, morphology and surface properties. The electrocatalytic activity for ethanol oxidation was studied in a direct ethanol fuel cell (DEFC) at 70 • C and 90 • C. Electrochemical and physico-chemical data indicated that a proper balance of Pt and Sn species in the near surface region was necessary to maximize the reaction rate. The best atomic surface composition, in terms of electrochemical performance, was Pt:Sn 65:35 corresponding to a bulk composition 75:25 namely Pt 3 Sn 1 /C. The reaction products of ethanol electro-oxidation in single cell and their distribution as a function of the nature of catalyst were determined. Essentially, acetaldehyde and acetic acid were detected as the main reaction products; whereas, a lower content of CO 2 was formed. The selectivity toward acetic acid vs. acetaldehyde increased with the increase of the Sn content and decreased by decreasing the concentration of the reducing agent used in the catalyst preparation. According to the recent literature, these results have been interpreted on the basis of ethanol adsorption characteristics and ligand effects occurring for Sn-rich electrocatalysts. (A.S. Aricò).
CO and Ethanol Electro-Oxidation on Pt-Rh/C
Journal of the Brazilian Chemical Society, 2014
Neste trabalho foi estudado o efeito da composição e tratamento térmico em H 2 , de materiais de Pt-Rh/C com proporções atómicas Pt:Rh de 3:1, 1:1 e 1:3 e 40% em massa de metal com relação a carbono, para a oxidação de CO ads e a oxidação de etanol. Os catalisadores foram preparados utilizando redução química com ácido fórmico e caracterizados fisicamente pelas técnicas de energia dispersiva de raios-X (EDX), retroespalhamento de elétron (EBS) e microscopia eletrônica de transmissão (TEM), mostrando relações Pt:Rh muito próxima às previstas, tamanhos de partícula médios similares e uma apropriada distribuição do metal sobre o suporte de carbono na micro e nano escala. Experimentos de voltametria cíclica mostraram um enriquecimento da superfície em Pt, devido à instabilidade termodinámica do sistema na temperatura experimental. A normalização das correntes foi feitas utilizando a carga de dessorção oxidativa de CO permitindo observar as diferenças entre os níveis atuais gerados exclusivamente pelos efeitos eletrônicos do Rh na Pt. O tratamento térmico dos catalisadores de Pt-Rh em uma atmosfera de H 2 , mostrou grande estabilidade dos materiais e também um notório incremento nos níveis de corrente para as reações de eletrooxidação de CO e etanol. Isto sugere a necessidade de melhor explorar os efeitos dos tratamentos térmicos na eletrocatálise da reação de oxidação do etanol. In this work we studied the effect of the composition and thermal treatment in H 2 of Pt-Rh/C materials with atomic ratios close to Pt:Rh 3:1, 1:1 and 1:3 and metal loading of 40 wt.%, for the CO ads and ethanol oxidation. Catalysts were prepared by chemical reduction with formic acid and physically characterized by energy dispersive X-rays spectroscopy (EDX), electron backscattering (EBS) and transmission electron microscopy (TEM), showing Pt:Rh ratios close to the nominals values, similar average particle sizes and an appropriated distributions of metal on carbon support at micro and nano scale. Cyclic voltammetry experiments showed a surface enriched in Pt due to the termodinamically unstable Pt-Rh system at the experimental temperature. The currents were normalized using the charge of oxidative desorption of CO allowing to observe differences among the current levels generated exclusively by the Rh electronic effects on the Pt. The thermal treatments of the Pt-Rh catalysts in a hydrogen atmosphere showed greater stability of the materials and notorious increases of the current levels for CO and ethanol electro-oxidation reactions. This suggests the necessity of better exploring the effects of thermal treatments in the electrocatalysis of the ethanol oxidation reaction.
Journal of Power Sources, 2006
We present results of a comparative study on the interaction of ethylene glycol (EG) with carbon supported Pt, PtRu and Pt 3 Sn nanoparticle catalysts, employing electrochemical and quantitative differential electrochemical mass spectroscopy (DEMS) measurements under continuous reaction and continuous electrolyte flow conditions. For all three catalysts EG adsorption is inhibited at very cathodic adsorption potentials, dissociative adsorption starts above 0.06 V and increases with increasing potential. Based on the electron yield per formed CO 2 molecule and on the similarity with the CO ad stripping characteristics CO ad is identified as the main stable adsorbate; the relative coverage in terms of adsorbed C1 species, relative to that of a saturated CO adlayer on the respective catalyst, reaches a maximum of ca. 0.6 at around 0.4 V on Pt/Vulcan, ca. 0.2 at around 0.2 V on PtRu/Vulcan and ca. 0.4 at around 0.35 V on Pt 3 Sn/Vulcan. Bulk EG electrooxidation under steady-state conditions shows a very small current efficiency for CO 2 formation of below 6% for 0.1 M EG on all three catalysts, the oxidation of EG mainly generates partly oxidized C2 by-products. Catalyst modification by Ru or Sn improves the activity for EG oxidation at low potentials (≤0.56 V), but does not lead to better selectivities for complete EG oxidation to CO 2 at potentials with significant oxidation rates. Hence, CC bond breaking is rate limiting for complete oxidation under present reaction conditions for all three catalysts. The data are consistent with a parallel pathway reaction mechanism, with formation and subsequent oxidation of CO ad in the one pathway and partial oxidation, via a sequence of reaction steps, to increasingly oxidized C2 species in the other pathway.
Journal of Electroanalytical Chemistry, 2012
One of the key objectives in fuel cell technology is to reduce Pt loading by the improvement of its catalytic activity towards alcohol oxidation. Here, a sol-gel based method was used to prepare ternary and quaternary carbon supported nanoparticles by combining PtARu with Mo, Ta, Pb, Rh or Ir, which were used as electro-catalysts for the methanol and ethanol oxidation reactions in acid medium. Structural characterization performed by XRD measurements revealed that crystalline structures with crystallites ranging from 2.8 to 4.1 nm in size and with different alloy degrees were produced. Tantalum and lead deposited as a heterogeneous mixture of oxides with different valences resulting in materials with complex structures. The catalysts activities were evaluated by cyclic voltammetry and by Tafel plots and the results showed that the activity towards methanol oxidation was highly dependent of the alloy degree, while for ethanol the presence of a metal capable to promote the break of CAC bond, such as Rh, was necessary for a good performance. Additionally, the catalysts containing of TaO x or PbO x resulted in the best materials due to different effects: the bi-functional mechanism promoted by TaO x and a better dispersion of the catalysts constituents promoted by PbO x .