Jean-Michel Léger

Recent advances in the development of direct alcohol fuel cells (DAFC)

Abstract Recent developments into technology of proton exchange membrane fuel cells (PEMFC) now allow serious consideration to be given to a direct alcohol fuel cell (DAFC) based on a PEMFC, in which alcohol is used directly as the fuel. This is particularly advantageous for mobile applications, since this will avoid the use of a bulky and expensive reformer. However, the relatively complex reaction mechanism, leading to a low electroreactivity of most alcohols, even methanol, needs the investigation of new platinum-based electrocatalysts, particularly active for breaking the Cue5f8C bond when alcohols other than methanol are to be used. Moreover, in order to overcome the deleterious effect of alcohol crossover through the proton exchange membrane, it is necessary to develop new oxygen reduction electrocatalysts insensitive to the presence of alcohols.

Structural effects in electrocatalysis: A comparative study of the oxidation of CO, HCOOH and CH3OH on single crystal Pt electrodes

Abstract The electrocatalytic oxidation of CO, HCOOH and CH3OH is compared on Pt(100), Pt(110) and Pt(111) single crystals. The similarity of behaviour of CH3OH and CO on the three single crystal planes leads to the conclusion that the oxidation of both compounds involves CO-like intermediates. On the other hand, HCOOH behaves quite differently, particularly on Pt(100) and Pt(111) electrodes, i.e its oxidation involves different adsorbed intermediates, some of them being poisoning species formed in the hydrogen region.

Electrocatalytic oxidation of methanol on platinum-based binary electrodes

Abstract Four platinum-based binary catalysts (Pt+Sn, Pt+Pb, Pt+Re, Pt+Ru) used for the electrochemical oxidation of methanol were investigated by linear and cyclic voltammetry. Except for the Pt+Ru system, which always gives an enhanced electrocatalytic activity when compared to pure metals, thus leading to a synergistic effect, the other ad-atom+Pt systems show an increased activity only for some concentration ranges of the precursor salts, and for some ranges of electrode potentials. Outside of these experimental conditions, the three metal ad-atoms behave as relatively strong catalytic poisons. An explanation of these effects is suggested on the basis of a competitive adsorption between the second-metal ad-atoms, the adsorbed hydrogen and the strongly bound residue of methanol adsorption.

Oxidation of methanol on a platinum electrode in alkaline medium: Effect of metal ad-atoms on the electrocatalytic activity

Abstract A mechanistic investigation of the electrochemical oxidation of methanol was worked out in alkaline medium in order to interpret the effect of some foreign metal ad-atoms (Pb. Bi, Cd, Tl) on the electrocatalytic activity of platinum. The rate-determining step being a surface reaction between adsorbed hydroxyls and a methanol chemisorption intermediate, the positive effect met with Pb and Bi may be explained through the bifunctional theory of electrocatalysis, whereas the negative effect met with Cd and Tl may come from the inhibiting behaviour of these latter ad-atoms.

Synergistic effect in the electrocatalytic oxidation of methanol on platinum+palladium alloy electrodes

Abstract The electrocatalytic oxidation of methanol has been investigated on platinium+palladium alloy electrodes of different compositions in acid, neutral and alkaline aqueous solutions. The surface characteristics (composition and roughness factor) of the alloys and the stability of the electrodes in contact with different electrolytic solutions have been studied using cyclic voltammetry. In particular, a surface enrichment in platinum due to a preferential dissolution of palladium and an increase of the roughness factor with an increase of the palladium content has been shown. The electrocatalytic activity of different alloys for methanol oxidation has been characterized by exchange current densities obtained from extrapolation of Tafel lines of calculated equilibrium potential. The plot of these current densities vs. the surface composition leads to a synergistic effect, particularly important in alkaline medium. A reasonable explanation of this enhanced electroactivity at about 15 at.% in Pd is given on the basis of a decrease of electrode poisoning.

Carbon monoxide electrosorption on low index platinum single crystal electrodes

Abstract The electrooxidation of carbon monoxide previously adsorbed at a given potential and during various adsorption times was carried out on the three low index planes of platinum single crystals. The I(E) profiles obtained display at least two oxidation peaks which can be attributed to the oxidation of different adsorbed CO species. Comparison with the results at the solid—gas interface and calculation of the quantity of electricity involved for each peak suggest that these two kinds of adsorbed CO may be linearly bonded CO and bridge or multibonded CO. A third CO species might occur on the Pt (110) surface. These results allow the I(E) profile for a polycrystalline electrode closely covered by adsorbed CO to be simulated as the weighted contribution of the oxidation current of linearly bonded CO on each single crystal plane.

Direct Methanol Fuel Cells: From a Twentieth Century Electrochemist’s Dream to a Twenty-first Century Emerging Technology

1. Energy Conservation and Environmental Friendliness-the Incentive for Fuel Cell Development The fuel cell is a nineteenth century invention; in the twentieth century it became the “heart” of an electrochemical power plant and power source, which is now in a stage of advanced technology development. Its first and only application since the early 1960s, has been as an auxiliary power source for space flights by the National Aeronautics and Space Administration (NASA). During the past decade, development for terrestrial (civilian and defense) applications has led to its commercialization and research on utilization in a variety of applications. Programs in the United States, Japan, Europe, and some other countries are focused on the development of fuel cell power plant/power sources for (1) base-load,

Electrocatalytic Oxidation of Oxygenated Aliphatic Organic Compounds at Noble Metal Electrodes

The investigation of electrocatalytic processes involved in the electrooxidation of organic compounds became a subject of growing interest at the beginning of the 1960s. A tremendous effort was undertaken to develop fuel cells, which theoretically have the ability to directly convert the chemical energy of hydrocarbons into electrical energy without the limitations due to Carnot’s theorem (i.e., with a high energy efficiency), an advantage which is particularly attractive for autonomous power sources.1–3 In such applications the rate of conversion of the organic compound by oxidation into carbon dioxide has to be as high as possible, in order to obtain the maximum energy available from the fuel and thus the maximum efficiency. However, the incomplete oxidation of organic compounds is of great interest as well, if one considers the potential applications for organic electrosynthesis, so that many attempts have been made in this field as well. Rigorous control of the experimental conditions may allow such reactions to become highly selective, leading to the development of industrial processes based on electrochemical reactions for the production of chemicals.4,5

A voltammetric study of the formation on hydroxides and oxyhydroxides on nickel single crystal electrodes in contact with an alkaline solution

The formation of the hydroxides, α-Ni(OH)2, β-Ni(OH)2, and of the oxyhydroxides, NiOOH, on Ni(100), Ni(110), Ni(111), in contact with 0.1M NaOH was studied by linear sweep cyclic voltammetry. Structural effects are only observed in the hydroxide region, where the formation of α-Ni(OH)2 and its reduction to metallic nickel depend on the crystallographic plane. Conversely, as soon as the irreducible hydroxide, β-Ni(OH)2 is formed, there is no more structural effects, and the oxyhydroxide region is similar for the three low index planes.

An EMIRS study

Abstract The nature of the adsorbed species formed by chemisorption of aqueous methanol at platinum electrodes has been reexamined, particularly by taking into consideration the EMIRS vibrational spectra obtained below 1050 cm −1 , a spectral range not investigated before. Apart from the bands due to adsorbed CO (linearly and bridge or multi-bonded to the surface) which was previously identified and recognized as a poisoning species, several other bands, corresponding to weakly adsorbed species, have been detected. Their interpretation led us to assign them tentatively to methoxy radicals, formate and formyl intermediates. Further structural information has also been obtained. It is suggested that methoxy species are bonded to the metal surface via the oxygen atom and that two types of formate intermediates result, linked by a single or by two oxygen atoms to platinum.