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International audience; Yttrium oxide and gadolinium oxide modified platinum nanoparticles supported on carbon (Vulcan XC-72), noted as Pt-M2O3/C (M=Y and Gd), were synthesized by water-in-oil nanoemulsion chemical route, followed by heat treatment at 100 and 300 degrees C under hydrogen/nitrogen (H-2/N-2) atmosphere and tested as electrocatalysts for the oxygen reduction reaction (ORR). As revealed by powder X-ray diffraction analysis, all obtained catalysts showed solely Pt face-centered-cubic structure, and absence of a secondary phase before and after heat treatments, indicating that Y2O3 and Gd2O3 are highly disordered (amorphous) and dispersed clusters. The surface Pt:M ratio (M=Y and Gd), as revealed by X-ray photoelectron spectroscopy, increased after heat treatment with respect to the value of as-prepared samples, for which the ratio was 1:1. Microstrain data extracted from Williamson-Hall plots for Pt-M2O3/C (M=Y and Gd) catalysts surprisingly increased after heat treatment at 100 degrees C, remaining nearly constant after heat treatment at 300 degrees C, whereas the value of pure Pt nanoparticles, noted as Pt/C, decreased after heat treatments. The mean particle size derived from TEM images for Pt-M2O3/C (M=Y and Gd) was almost unchanged after heat treatments, at variance with the Pt/C case where a clear increase is observed. Surface specific activity and mass activity towards ORR obtained with as-prepared Pt-M2O3/C (M=Y and Gd) catalysts were higher than those of as-prepared Pt/C catalyst. After heat treatment, the ORR activity of Pt-M2O3/C (M=Y and Gd) augmented, whereas that of Pt/C diminished. Moreover, after 6000cycles between 0.5 and 0.95V versus reversible hydrogen electrode (vs. RHE), Pt-M2O3/C (M=Y and Gd) catalysts retained a large active surface area and a high kinetic current density at 0.9V vs. RHE in comparison with Pt/C samples. These facts assess a positive effect of the interaction between M2O3 (M=Y and Gd) and Pt catalytic centers both on the catalytic activity of the material towards ORR and on its durability.

Chalcogenide electrocatalysts are very active and tolerant for the oxygen-reduction reaction (ORR) in electrolytes containing small organics. This property of tolerance allows them to be used as tolerant cathodes of direct methanol fuel cells (DMFC) that use highly concentrated methanol. Platinum chalcogenide-based cathodes of direct methanol fuel cells can overcome the problem of the formation of a mixed-potential due to the fuel crossover [Alonso-Vante et al., Patent-FR 12 55944, Appl. Filed 22 June 2012]. In this study, a comprehensive investigation on the origin of the tolerance of Pt chalcogenide electrocatalyst to small organic molecules such as methanol is provided. The XPS spectrum of Se 3d region in PtxSey/C revealed a shift of the selenium emission peak to lower binding energy as compared to a Se/C sample. This negative shift can be explained by charge transfer from the platinum surface atoms to the selenium, which is at the origin of the improved tolerance of Pt towards ORR in the presence of methanol. The physical chemical properties and electrochemical performances in half-cell and mixed-reactant microfluidic fuel cells are discussed.

Name that tune: A simple and new method to produce a methanol-tolerant Pt chalcogenide catalyst for the oxygen reduction reaction (ORR) is developed. The catalyst is tuned by electrochemical stripping of the Se atoms on the surface of the catalyst. The resulting electrode nanomaterial is PtSe0.2, and it shows the highest activity ever reported for the ORR in solutions containing methanol.

Herein, some chemical approaches to the tailoring of nanodivided materials are highlighted. Transition-metal materials in nanodivided form are essentially devoted to study the electrocatalytic reduction of molecular oxygen (ORR) in acid medium. This Minireview focuses on the physical and chemical structures of platinum-based and non-platinum-based materials. Due to the research dynamism in this field, the discussion is limited to a comprehensive review of ORR cathode materials investigated in the author's laboratory as well as to some relevant work obtained in other laboratories concerning the electrochemical ORR pathway and substrate effects.

This review covers the electrocatalytic activities, the corresponding influence factors and the synthesis methods of nonprecious-metal electrocatalysts towards oxygen-reduction reaction (ORR) for fuel-cell systems. In particular, the chalcogenides and the macrocycles containing Co or Fe metals have been focused upon. Due to the scarcity of Pt metal, the Co- and Fe-based chalcogenides are potentially interesting substitutes of Pt although they still show lower catalytic activities for ORR and lower electrochemical and chemical stability in the present fuel-cell electrolytes. Compared to Pt electrocatalysts, the Co- and Fe-based macrocycles, such as TMPP, TPP, Pc and TAA, are among the most promising substitutes for Pt because of their comparable catalytic activities towards ORR and the higher insensitivity to methanol (in direct methanol fuel cells – DMFC) although they still have some drawbacks, namely lower stability and shorter durability. Novel catalyst synthesis methods, modification techniques of catalysts as well as supporting substrates are expected to be developed in the future to satisfy the requirements of commercial fuel cells. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In recent years, a number of carbonyl clusters have been used as precursors to synthesize electrocatalysts of the nanolength scale for fuel cell reactions. This short review aims to delineate the concepts underlying the synthesis of these type of materials, highlighting the rationale of this type of research. Some selected examples regarding fuel cell reactions at the anode and the cathode are discussed.

A comparative study between carbon supported Platinum–Tin (Pt–Snsyn), synthesized via the carbonyl route, and the commercial (Pt3Sn) from E–TEK is reported. The electro-oxidation of methanol and adsorbed CO, in sulphuric acid medium, were used as probes to evaluate the performance of these electrocatalysts. In-line differential mass spectrometry (DEMS) was used for this purpose. Both nanoparticulate materials had a mean particle size of = 1.68 ± 0.72 nm, and = 3.58 ± 1.94 nm, respectively. It is demonstrated that, under the same experimental conditions, our homemade Pt–Snsyn is less sensitive to poisoning by CO. This observation was again verified during the oxidation of methanol. These results are discussed in terms of the local disorder of the particles surface atoms, favourably induced by size effect and the preparation route employed.

This chapter covers the process of oxygen-reduction reaction (ORR) for fuel-cell systems of nonprecious electrocatalyst centers explored since the 1960s, showing the progress achieved with regard to their catalytic activity and stability. The catalytic centers investigated so far are transition metal chalcogenides and metal-macrocycles; in particular, the chalcogenides and the macrocycles containing cobalt or iron metals. The chapter also displays the progress made via theoretical studies on non-noble metal chalcogenides made in understanding of the ORR mechanism and factors that affect the ORR activity and stability.

Semiconducting mixed cluster Chevrel compounds (Mo 4 Ru 2 Se 8 ) catalyze the reduction of molecular oxygen in acid medium

Single crystals of Re 6 Se 8 Br 2 and Re 6 S 8 Br 2 were synthesized by chemical vapour transport reactions. The latter was crystallized. X-ray structure analysis reveals that Re 6 S 8 Br 2 is isostructural to Re 6 Se 8 Br 2 . Both semiconducting cluster materials were photoelectrochemically characterized and showed p-type behaviour. From the photocurrent action spectra, their estimated band gaps are 0.84 eV and 1.65 eV for the selenide and sulphide, respectively, with a probably indirect optical transition.

The oxygen reduction reaction (ORR) activity of a Ru 1.92 Mo 0.08 SeO 4 catalyst, a Vulcan XC72-supported Ru catalyst and, for comparison, a Vulcan XC72-supported Pt catalyst was studied with a rotating ring-disk electrode. The very similar reaction characteristics of the two Ru catalysts in pure and CH 3 OH-containing H 2 SO 4 electrolyte, which differ markedly from those of the Pt catalyst, indicate that the reactive centers in both Ru catalysts must be identical. They are highly selective (>95%) toward reduction to H 2 O (four electron pathway), independent of the presence of methanol. In the latter case, they are 100% selective toward the ORR, i.e., completely methanol tolerant, while the ORR on Pt catalysts is accompanied by significant CH 3 OH oxidation. Based on mass specific current densities, however, the Ru catalysts are significantly less active than the standard Pt catalysts. Only at methanol concentrations above 10-30 mM does their methanol tolerance make them more active than Pt/Vulcan. Implications for their use as cathode catalysts in a direct methanol fuel cell are discussed.

Carbon-supported CoSe2 nanoparticles, as non-precious metal cathodic catalyst, were prepared via the in situ surfactant-free method with the conventional heating. Structural and electrochemical properties of the obtained 20 wt.-% CoSe2/C nanoparticles were investigated by means of powder X-ray diffraction (PXRD), differential thermal gravimetric analysis (DTA-DTG) and rotating disc electrode (RDE) techniques. CoSe2 nanoparticles have two kinds of crystal structure after heat treatment under nitrogen at different temperature: orthorhombic at 250 and 300 °C; cubic at 400 and 430 °C. The latter structure has higher oxygen reduction activity than the former in 0.5 M H2SO4. CoSe2/C nanoparticles after heat treatment from 250 to 430 °C, have an onset potential from 0.78 to 0.81 V versus the reference hydrogen electrode (RHE) in O2-saturated 0.5 M H2SO4 at 25 °C. 20 wt.-% CoSe2/C nanoparticles, after heat treatment at 300 °C, promote ca. 3.5 electrons, per oxygen molecule, transferred during the oxygen reduction process. They have an oxidation wave centred at 0.96 V versus RHE and display higher methanol tolerance as compared to 20 wt.-% Pt/C (E-TEK).

We report the results of an investigation of the interaction between Se and Ru in Ru−Se electrocatalysts showing high activity and methanol tolerance in the oxygen reduction reaction (ORR). The res...