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Pt–Mo alloy electrocatalysts were prepared by an arc-melting furnace process to investigate the origin of their enhanced activity toward ethanol oxidation. Two Mo contents were chosen in zones of the binary phase diagram where they are supposed to form either a pure alloy mixture or a solid solution. Pt–Mo alloy catalysts were more active than Pt-alone. Gradual Mo dissolution at the electrode surface was observed after voltammetric and chronoamperometric measurements. The dissolved Mo contributed to the catalytic effect of the electrode as underpotentially deposited (upd) adatoms. This dissolution probably also leads to an increase in the electrode surface roughness. Low molybdenum content in the electrode material enhances the activity toward ethanol oxidation when compared to Pt-alone. Ethanol oxidation was also investigated by in situ infrared reflectance spectroscopy in order to determine the presence of adsorbed intermediates like CO species. Acetaldehyde, acetic acid and CO2 were also found by spectroscopic experiments. [ABSTRACT FROM AUTHOR]

Abstract: Carbon-supported Pt-based nanosized electrocatalysts can be synthesized for methanol and ethanol electrooxidation. The electrocatalytic activity of Pt can be greatly enhanced by using Pt-Ru/C for methanol oxidation or Pt-Sn/C for ethanol oxidation. In situ IR reflectance spectroscopy is a convenient tool to better understand the importance of the different adsorption steps involved in the mechanisms of electrooxidation. With Pt/C, it appears clearly that linearly adsorbed CO is the poisoning species formed during methanol and ethanol oxidation. In the case of methanol, even with Pt-Ru/C (the most active catalyst), adsorbed CO is also a reactive intermediate. The enhancement of activity observed in such a case is due to the possibility to activate water at lower potentials in the presence of Ru. With Pt-Sn/C, the mechanism of the electrooxidation of ethanol is strongly modified. If at low potentials, poisoning with adsorbed CO still exists (as with Pt/C), the oxidation of ethanol at potentials greater than 0.4V versus RHE occurs through an adsorbed acetyl species which can lead to the formation of acetaldehyde and acetic acid as final products in addition to carbon dioxide. [Copyright &y& Elsevier]

Abstract: Improvement of Pt activity for electrocatalytic reactions is possible by modifying Pt nanoparticles with other metals able to activate water. Selected examples are discussed with the electrooxidations of methanol and ethanol or the electroreduction of dioxygen. Nanoparticles electrodes of Pt–Ru (for methanol oxidation), of Pt–Sn (for ethanol oxidation) or of Pt–Cr (for oxygen reduction) supported on carbon powder can be prepared from colloidal precursors. This kind of preparation allows varying the composition and/or the structure of the electrode. The formulation of improved electrodes can be obtained after complete study of the reaction mechanism by “in situ” spectroscopic experiment. [Copyright &y& Elsevier]

The electrochemical oxidation of formaldehyde is studied on dimensionally stable anodes prepared by thermal decomposition of precursors (the corresponding chlorides). The working electrodes used were: Ti/Ir0.3Ti0.7O2, Ti/Ru0.3Ti0.7O2 and Ti/Ir0.2Ru0.2Ti0.6O2. The electrolyses were performed galvanostatically in a filter press cell with 0.5 mol L-1 H2SO4 solutions with initial formaldehyde concentration equal to 100 mmol L-1. The concentration of formaldehyde decreases fast with the electrolysis time, with the ternary anode (Ir + Ru + Ti) presenting the best performance for this step. The anode containing only Ir, despite presenting the higher superficial charge, is the one with the lowest electrocatalytic activity. For the formic acid oxidation step, the presence of iridium in the anode composition does not promote the process, the anode containing only ruthenium being the most effective for this step.

Abstract: Conventional electrochemical methods have been applied to study the oxidation of a possible alternative fuel for a direct oxidation fuel cell. The electrooxidation of dimethoxymethane (DMM) was investigated on the three low index planes, (100), (110) and (111) of platinum single crystals and compared with its oxidation on a platinum polycrystalline electrode. Among platinum electrodes, electroreactivity of DMM observed is Pt(111)>Pt(100)>Pt(110)∼Pt poly. Hydrogen adsorption is limited by the presence of DMM, except for Pt(111) plane. In situ IR experiments show the presence of bands of COads with all electrodes except Pt(111). This work shows that the mechanism of DMM electrooxidation is structure sensitive. A path takes place on Pt(100) and Pt(110) which is favourable to the formation of COads. Another path proceeds on Pt(111), where COads is not present and reaction does not occur at low potential. Results indicate that peak intensities are higher in perchloric acid than in sulphuric acid. So DMM adsorption is dependent on the specific adsorption of the anions. In situ IR reflectance spectroscopy identified some intermediates and reaction products of DMM adsorption and electrooxidation on Pt electrodes: COL (linearly bonded) and COB (bridge bonded), adsorbed CHO and CH3O species, methanol and CO2. The electrochemical and spectroelectrochemical experiments suggest a complex mechanism of DMM electrooxidation. [Copyright &y& Elsevier]

Abstract: The electrooxidation of dimethoxymethane (DMM) was studied on polycrystalline platinum electrode. Cyclic voltammetry has shown that the behaviour of DMM electrooxidation depends on scan rate, DMM concentration and the nature of anion of the supporting electrolyte. At a low scan rate or at a high DMM concentration, the electrode is strongly poisoned during DMM electrooxidation, which is an anion-sensitive reaction. Using electrochemical and in situ IR experiments, a multistep mechanism was proposed with DMM adsorption as the first and rate-determining step. At a low potential range, adsorbed CO is slowly formed. COads inhibits the DMM electrooxidation until it is full oxidized to CO2. Conversely, for lower adsorbed CO coverage, oxidation starts earlier and CO2 formation is observed. In situ infrared reflectance spectroscopy experiments were carried out to identify these adsorbed species intermediates and reaction products of DMM adsorption and oxidation. In addition to adsorbed COL (linearly bonded CO), adsorbed HCO, CH3O species and CO2 were detected suggesting a complex mechanism of the electrooxidation of DMM, with parallel paths involving methanol and formaldehyde electrooxidation. [Copyright &y& Elsevier]

Abstract: Most of the electrochemical reactions involved in fuel cell are structure sensitive. Moreover, for the electrooxidation of small organic molecules catalysts have to be multifunctional. For these reasons, the development of various synthesis methods of multimetallic electrocatalysts allowing to control the atomic composition and the microstructure is needed in order to improve the electrocatalytic activity. For this purpose, several methods for the preparation of nanostructured catalysts have been developed in our laboratory (impregnation–reduction method, colloidal route, carbonyl route, microemulsion and electrochemical methods), which allow to prepare multimetallic particles. These catalysts were characterized using physical and physico-chemical methods (XRD, TEM, EDX, electrochemical methods, etc.) in order to check their composition, structure, dispersion, active surface area, etc. Amongst the developed methods, some of them can lead to the formation of alloyed or non-alloyed multimetallic compounds depending on the synthesis procedure. XRD analysis allows us to discriminate the catalyst structures. The influence of the atomic composition and of the nature of foreign metals added to platinum is discussed in terms of electrochemical activity towards oxidation of small organic molecules of interest in energy storage and production. In particular, it appears that non-alloyed Pt–Ru catalysts display higher electroactivity towards methanol oxidation. Electrochemical and DEMS measurements were used to study and to evaluate the influence of the electrocatalyst structure on its electroactivity. The effect of the composition in terms of foreign metal atoms and atomic content of platinum based and platinum–tin based catalysts towards the electrooxidation of ethanol is also discussed from electrochemical experiments and fuel cell test results. [Copyright &y& Elsevier]

Abstract: The electrooxidation of ethylene glycol at nanostructured platinum based catalysts was studied in alkaline medium. The optimum metals loading and atomic composition for ethylene glycol electrooxidation were determined. The addition of Bi to platinum leads to decrease the onset potential of EG electrooxidation of about 70mV and to achieve higher current densities in the whole studied potential range. The ternary catalyst PtPdBi/C does not change the onset potential of EG oxidation, but leads to increase the current densities compared to PtBi catalysts. The EG electrooxidation enhancement with binary and ternary catalysts was confirmed in SAMFC (solid alkaline membrane fuel cell) experiments, the open circuit voltage (ocv) increasing from 0.66 to 0.83 and 0.81V and the maximum achieved power density raising from 19 to 22 and 28mWcm−2 with Pt, PtBi and PtPdBi catalysts, respectively. An attempt to explain the change in catalytic behavior was made by analysis of SAMFC reaction products in the anode outlet and by in situ FTIR spectroscopy measurements. It was shown that the addition of foreign atoms to platinum led to decrease the ability of the catalyst to break the C–C bond, likely due to dilution of surface platinum atoms. But, in the same time, catalyst containing Pd and Bi seems to activate the oxidation of EG in oxalate compared to pure platinum. The role of Bi and Pd was discussed. It was proposed that Bi mainly favors the adsorption of OH species but also affects the product distribution by changing the composition of chemisorbed species, whereas Pd only limits the poisoning of Pt sites by changing the composition of chemisorbed species. [Copyright &y& Elsevier]

Abstract: The electrooxidation of methoxy methane (dimethyl ether) was studied at different Pt-based electrocatalysts in a standard three-electrode electrochemical cell. It was shown that alloying platinum with ruthenium or tin leads to shift the onset of the oxidation wave towards lower potentials. On the other hand, the maximum current density achieved was lower with a bimetallic catalyst compared to that obtained with a Pt catalyst. The direct oxidation of dimethoxy methane in a fuel cell was carried out with Pt/C, PtRu/C and PtSn/C catalysts. When Pt/C catalyst is used in the anode, it was shown that the pressure of the fuel and the temperature of the cell played important roles to enhance the fuel cell electrical performance. An increase of the pressure from 1 to 3bar leads to multiply by two times the maximum achieved power density. An increase of the temperature from 90 to 110°C has the same effect. When PtRu/C catalyst is used in the anode, it was shown that the electrical performance of the cell was only a little bit enhanced. The maximum power density only increased from 50 to 60mWcm−2 at 110°C using a Pt/C anode and a Pt0.8Ru0.2/C anode, respectively. But, the maximum power density is achieved at lower current densities, i.e. higher cell voltages. The addition of ruthenium to platinum has other effect: it introduces a large potential drop at relatively low current densities. With the Pt0.5Ru0.5/C anode, it has not been possible to applied current densities higher than 20mAcm−2 under fuel cell operating conditions, whereas 250 and almost 400mAcm−2 were achieved with Pt0.8Ru0.2/C and Pt/C anodes. The Pt0.9Sn0.1/C anode leads to higher power densities at low current densities and to the same maximum power density as the Pt/C anode. [Copyright &y& Elsevier]

Abstract: In order to point out the effect of the second metal in platinum-based catalysts, a synthesis method by colloidal route derived from that of Bönnemann was used to prepare non-alloyed Pt1−x Cr x /C electrocatalysts active towards the oxygen reduction reaction (ORR). The non-alloyed character of the catalysts was showed by XRD analysis. The Pt/Cr electrocatalyst having an nominal atomic ratio, as determined by EDX then corresponding to bulk composition and not surface composition, close to (0.8:0.2) showed higher activity for ORR in methanol-free oxygen saturated electrolyte, whereas the catalyst having an atomic ratio of (0.7:0.3) displayed higher activity for ORR at low overpotentials in saturated oxygen electrolyte containing 0.1M methanol. Correlation of XRD and electrochemical results allows us to point out the effect of electronic interactions in catalyst activity towards ORR. It was also shown that adding chromium to platinum does not alter the reaction mechanism of oxygen reduction, and that in presence of low methanol concentration, the ORR occurs via the four-electron process according to the same mechanism as in methanol-free solution. [Copyright &y& Elsevier]

Ethanol is an alternative choice as a fuel in a direct combustion fuel cell. Its non toxicity and its availability from biomass resources advocate its use in a direct ethanol fuel cell (DEFC), even if the actual performance obtained are slightly lower than those observed with methanol. By modifying the composition of the platinum anode by adding tin, it was confirmed that the overall electrocatalytic activity is greatly enhanced at low potentials. The optimum composition in tin is in the range 10–20 at.%. With this composition, it was demonstrated that poisoning by adsorbed CO coming from the ethanol dissociative chemisorption is greatly reduced leading to a significant enhancement of the electrode activity. However, it seems that the oxidation of ethanol is not complete leading to the formation of C2 products. These observations made in half-cell experiments are fully confirmed during electrical tests in a single direct ethanol fuel cell. [Copyright &y& Elsevier]