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Pt-Sn anodic catalysts supported on multiwall carbon nanotubes, mesoporous carbon and Vulcan carbon were prepared using a deposition-reduction technique with sodium borohydride, characterized by different techniques and tested as anodes in a single direct methanol fuel cell at low temperatures. Characterization and CO stripping results indicate the presence of promoting effects of Sn over Pt in catalysts supported on Vulcan carbon and carbon nanotubes. This would mainly be caused both by geometric modifications induced by Sn placed in the surroundings of the active metal phase and probable electronic effects. These promoting effects make the oxidation of CO to CO2 at low potentials easier, thus improving the CO tolerance of the anodic electrocatalyst. On the other hand, Pt-Sn catalysts supported on mesoporous carbon do not show a proper metallic phase needed for a good electrochemical behavior. When catalysts were tested in a DMFC, Pt-Sn catalysts supported on Vulcan carbon and carbon nanotubes gave a better power density than a commercial one mainly when working at low current densities. [ABSTRACT FROM AUTHOR]

Abstract: A simple model is proposed to evaluate the contribution of alloyed and non-alloyed platinum and tin to the ethanol oxidation reaction on Pt–Sn/C catalysts for direct ethanol fuel cells. On the basis of the model, the ethanol oxidation on partially alloyed catalysts occurs through a dual pathway mechanism, separately involving the Pt3Sn phase and Pt–SnO x . The model, validated by experimental data, can predict the performance of a single direct ethanol fuel cell by varying the Sn content and/or the degree of alloying of Pt–Sn/C catalysts used as the anode material. [ABSTRACT FROM AUTHOR]

This manuscript reviews the complex behavior of the electrochemical oxidation of adsorbed CO (CO stripping) on Pt nanoparticles in acid media. While on low-index Pt single crystals the so-called CO stripping generally exhibits a single, narrow, and well-defined oxidation peak, its oxidation on Pt nanoparticles may produce multiple peaks instead, whose origin is still not fully understood. The issue of peak multiplicity is reviewed based on published articles in the field of electrocatalysis and also on new experimental results. The aim of the present contribution is to highlight the extreme sensitivity of this reaction with respect the state of the surface, microstructure and discuss some other important related features, including the role played by the experimental protocol itself. The influence of the index of crystallografic planes exposed to the electrolyte, particle size, particle agglomeration, CO surface diffusion, adsorbed anions, catalyst support, among other factors on the CO electro-oxidation are presented and discussed. In turn, the ideas presented herein would help scientists to avoid misinterpretation of the experimental results, better design experimental procedures and thus advance in the required knowledge for tuning the Pt nanoparticles to fulfill the requirements for specific applications, such as fuel cell catalysts resistant to CO poisoning. [ABSTRACT FROM AUTHOR]

Abstract: Binary Pt–Sn/C (1:1) and ternary Pt–Sn–Ru/C (1:1:0.3 and 1:1:1) catalysts were synthesized by reduction of precursors with formic acid, and their activity for ethanol oxidation was compared with that of commercial Pt/C and Pt–Ru/C catalysts. Linear sweep voltammetry measurements at 40 and 90°C showed that for potentials higher than 0.3V vs. RHE, the Pt–Sn–Ru/C (1:1:0.3) catalyst presents the highest activity for ethanol electro-oxidation, while the electrochemical activity of the Pt–Sn–Ru/C (1:1:1) catalyst was lower than that of both the binary Pt–Sn/C and Pt–Ru/C catalysts. Tests in a single direct ethanol fuel cell confirmed the superior performance of the Pt–Sn–Ru/C (1:1:0.3) electrocatalyst. The positive effect of the Ru presence in the Pt–Sn–Ru/C (1:1:0.3) catalyst was ascribed to the interactions between Sn and Ru oxides. [Copyright &y& Elsevier]

Carbon-supported platinum-tin electrocatalysts (Pt–Sn/C) are known to be the most efficient fuel cell anode material to oxidize ethanol in the so-called Direct Ethanol Fuel Cells (DEFC). However, the platinum-tin binary system presents distinct phases depending on the amount of Sn (i.e., the Pt:Sn ratio) and on the thermal annealing temperatures, as well as the presence of oxides (e.g. SnO 2) whose influence on the performance of DEFCs is not well understood. In this work, Pt–Sn catalysts presenting distinct Pt:Sn ratios were prepared, characterized and tested in a single DEFC. The combined results from DEFC tests and structural characterization techniques showed that increasing the amount of Sn dissolved into the Pt structure enhances DEFC performance but also that Sn content alone does not explain the overall behavior. Microstructural effects on the DEFC response was further investigated by performing a comprehensive study using high intensity X-ray Diffraction and in situ –X-Ray Absorption Spectroscopy provided by synchrotron light on Pt 3 Sn 1 /C samples subjected to thermal treatments in a reducing H 2 atmosphere at temperatures of 100, 200, 300, 400, and 500 °C. The results showed that best DEFC performance depends on a balance between the amount of Sn dissolved in Pt, the formation of a new phase (PtSn) and also on the presence of tin oxides, yielding a material with an optimized modified 5d-band electronic structure, which was obtained with a thermal treatment at 200 °C. Image 1 • Pt–Sn catalysts with distinct Pt:Sn ratios were prepared and tested in a single DEFC. • The Sn content dissolved in the Pt lattice enhances DEFC performance. • Thermal treatment of Pt 3 Sn 1 /C in H 2 atmosphere increases DEFC response. • High intensity XRD and in situ –XAS was used to probe structural/electronic properties. • DEFC response depends on the amount of Sn in Pt but also on the PtSn and SnO 2 phase. [ABSTRACT FROM AUTHOR]

Platinum–nickel electrocatalysts prepared by a simple and cost-effective procedure have been investigated for the oxygen reduction reaction (ORR) in direct methanol fuel cells (DMFCs). The formic acid method was used to deposit well-dispersed Pt x Ni y nanoparticles (x:y = 3:2) on the surface of a carbon black support (Ketjenblack). Carbothermal reduction of the as-prepared catalyst in an inert gas (Ar) at 900 °C produced an alloy and a partial modification of the crystalline structure from the face centered cubic, typical of Pt, to a tetragonal structure of PtNi alloy. An acid leaching treatment was carried out to partially remove unalloyed surface nickel atoms in the outermost layers, leading to an enrichment of Pt concentration (x:y = 2:1). Cyclic voltammetry analysis in acidic medium indicated a relatively high electrochemical active surface area (> 70 m 2 g − 1 ) for both untreated and thermally treated Pt x Ni y catalysts. The activity towards the ORR was evaluated in half-cell configuration (0.5 M H 2 SO 4 ) using the rotating disk electrode technique. Similar behavior towards the ORR was found for the untreated and thermally treated PtNi/C catalysts, with an increase in activity compared to a commercial Pt/C catalyst. A remarkably better tolerance to methanol was observed for both PtNi/C cathode catalysts compared to the commercial Pt/C catalyst. [ABSTRACT FROM AUTHOR]

Abstract: Bimetallic PtGe and PtIn catalysts (Ge/Pt and In/Pt molar ratios = 0.33, 17 wt.% Pt loading) were prepared over carbonaceous supports (carbon Vulcan, carbon nanotubes and structured mesoporous carbon). The liquid phase deposition–reduction method by using 0.4 M sodium borohydride as a reducing agent was employed. The electrocatalytic activity for methanol oxidation was compared with a commercial Pt/CV E-TEK catalyst. The onset potential of the CO oxidation was shifted to less positive values for carbon Vulcan and carbon nanotubes supported catalysts and with a smaller effect in the case of mesoporous carbon supported ones. The best electrocatalytic performance was obtained by using carbon Vulcan as support of bimetallic catalysts, followed by carbon nanotubes. The performance of mesoporous carbon as a support was not adequate. PtGe/CV, PtGe/NT and PtIn/CV catalysts displayed the best performance in DMFC. The good performance of these catalysts could be due to the presence of small particle sizes with a narrow distribution, and to geometric effects (observed from different characterization techniques) related to a probable decoration of Ge or In around the small Pt particles. [Copyright &y& Elsevier]

Abstract: In direct alcohol fuel cells, ethanol crossover causes a less serious effect compared to that of methanol because of both its smaller permeability through the Nafion® membrane and its slower electrochemical oxidation kinetics on a Pt/C cathode. The main interest in direct ethanol fuel cells (DEFCs) is to find an anode catalyst with high activity for the oxidation of ethanol. However, due to the low activity of pure platinum for the oxygen reduction reaction (ORR), research on cathode electrocatalysts with improved ORR and the same or improved ethanol tolerance than that of Pt are also in progress. In this work, a commercial carbon supported Pt–Co (3:1) electrocatalyst (E-TEK) was investigated as cathode material in DEFCs and the activity compared to that of Pt. In the cathodic potential region (0.7–0.9V versus RHE) Pt/C and Pt–Co/C showed the same activity for the oxidation of crossover ethanol. But the performance of Pt–Co/C as cathode material in DEFCs in the temperature range 60–100°C is better than that of Pt/C both in terms of mass activity and specific activity, due to an improved activity of the alloy for oxygen reduction. [Copyright &y& Elsevier]