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Double perovskites Sr2Fe1 − x Co x MoO6 (x = 0, 0.25, 0.5, 0.75 and 1) have been investigated as cathode material for oxygen reduction reaction (ORR) in 0.5 M NaOH at 25 °C using the rotating disk electrode. The electrocatalytic powders were prepared by a solid-state process and characterised by X-Ray powder diffraction, scanning electron microscopy and infrared spectroscopy. The electrochemical techniques considered are linear voltammetry, steady-state polarization and impedance spectroscopy. The electrocatalysts Sr2Fe1 − x Co x MoO6/C consisting of the double perovskite oxides and carbon (Vulcan XC-72) were mixed and spread out into a thin layer on a glassy carbon substrate. The electrocatalytic activity was strongly influenced by the Co substitution at room temperature. The relation between catalytic performance and the degree of Co content was examined. The Co-containing catalysts exhibited lower activity attributed to their high resistivity, and the highest activity toward oxygen reduction was observed for Sr2CoMoO6.

International audience; A Carbon-supported CoSe2 nanocatalyst has been developed as an alternative non-precious metal electrocatalyst for oxygen reduction reaction (ORR) in alkaline medium. The catalyst was prepared via a surfactant-free route and its electrocatalytic activity for the ORR has been investigated in detail in 0.1 M KOH electrolyte at 25 degrees C using rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. The prepared catalyst showed promising catalytic activity towards ORR in a four-electron transfer pathway and higher tolerance to methanol compared to commercial Pt/C catalyst in 0.1 M KOH. To some extent, the increase of CoSe2 loading on the electrode favors a faster reduction of H2O2 intermediate to H2O. (C) 2012 Elsevier Ltd. All rights reserved.

Platinum nanoparticles have been selectively deposited on composites of titanium oxide-carbon and tungsten oxide-carbon. Selectivity of the deposition made it possible to investigate changes in electronic properties of both platinum and oxide support, induced by the so-called strong metal–support interactions (SMSI). X-ray photoelectron spectroscopy (XPS) was used, and changes in binding energy of Pt 4f, Ti 2p, and W 4f core-levels and Pt 4f peak asymmetry were determined. These parameters allowed us to state the changes in local electron density, when Pt is deposited on oxide support. In all cases the binding energy of the Pt 4f signal for platinum deposited on an oxide support was significantly lower in comparison to samples where Pt was solely supported onto carbon. The increase in Pt 4f XPS signal asymmetry was observed. This suggests an increased electron density on Pt. No electron donor could be identified from the analysis of the oxide supports. To explain the observed data, at least two effects mu...

The preparation and testing for electrocatalytic activity of functionalized carbon nanotube (f-CNT) supported Pt and Au–Pt nanoparticles (NPs), and bilirubin oxidase (BOD), are reported. These materials were utilized as oxygen reduction reaction (ORR) cathode electrocatalysts in a phosphate buffer solution (0.2 M, pH 7.4) at 25 °C, in the absence and presence of glucose. Carbon monoxide (CO) stripping voltammetry was applied to determine the electrochemically active surface area (ESA). The ORR performance of the Pt/f-CNTs catalyst was high (specific activity of 80.9 μA cmPt−2 at 0.8 V vs. RHE) with an open circuit potential within ca. 10 mV of that delivered by state-of-the-art carbon supported platinum catalyst and exhibited better glucose tolerance. The f-CNT support favors a higher electrocatalytic activity of BOD for the ORR than a commercially available carbon black (Vulcan XC-72R). These results demonstrate that f-CNTs are a promising electrocatalyst supporting substrate for biofuel cell applications.

W-doped titanium dioxide is a promising candidate material for applications ranging from UV–VIS light photocatalytic reactions to catalyst support in proton-exchange membrane fuel cells, depending on the doping content. The present study reports on the possibility to synthesize substitutional Ti1−xWxO2 thin films with 0 ≤ x ≤ 1 by magnetron co-sputtering from Ti and W metallic targets. Two routes were investigated starting from 1) crystalline titanium tungsten alloys deposited in non-reactive (pure Ar) mode, and 2) amorphous titanium tungsten oxides deposited in reactive (Ar + O2 atmosphere) mode. The structure and phase stability after air annealing at 550 °C has been investigated by X-ray Diffraction (XRD). X-ray Reflectivity (XRR) was used to determine the change in film mass density upon annealing. Films of the non-reactive mode series could not be successfully fully oxidized into Ti1−xWxO2 form. For the reactive mode film series, ternary Ti1−xWxO2 oxides were obtained after air annealing and the crystal structure was changed from anatase to rutile with increasing W content in the range 0–33 at.%. Films with higher W content (0.33

The electrochemical reduction of nitrate ions was carried out on Pt-based nanoparticles supported on carbon Vulcan and deposited on a glassy carbon electrode. Different materials were evaluated: synthesized Pt10/C, Pt–Sny/C (y = 10, 20 wt.%) and commercial Ptx/C-ETEK (x = 10, 20 and 40 wt.%). Cyclic voltammetry technique was used for this purpose. It was found that the catalytic activity for hydrogen evolution reaction (HER) and nitrate electro-reduction (NER) follows the order Pt10/C > Pt40/C-ETEK > Pt–Sn20/C > Pt20/C-ETEK > Pt–Sn10/C > Pt10/C-ETEK. The electrochemically active surface area (ECSA), charge due to nitrate electro-reduction ( Q N O 3 − ) , and kinetic parameters were calculated in order to understand the catalytic behavior.

Pt and RuxSey nanoparticles were selectively deposited onto oxide sites of oxide–carbon composite substrates using the photo-deposition process and compared to conventional carbon support materials. The oxide was essentially anatase phase. Cyclic voltammetry and rotating disk electrode measurements for the oxygen reduction reaction (ORR) in formic acid containing-electrolyte showed a tolerance improvement for ORR of Pt supported on composite substrates. This positive substrate effect on platinum, turned out not to be favorable for RuxSey catalyst centers. On the other hand, the methanol tolerance for ORR was increased for both nanostructured materials supported on the oxide–carbon composite. Single H2/O2 fuel cell results were in agreement with half-cell electrochemical measurements on Pt, showing an improvement of the power density when using the oxide–carbon as substrate for the cathode. The composites were evaluated as cathode catalysts of an HCOOH laminar-flow fuel cell (LFFC) in which commercial Pd/C was used as an anode catalyst. The cathodes with RuxSey and Pt supported on TiO2/C improved the specific power density by 15% and 24%, respectively, with respect to carbon as support.

Titanium dioxide (anatase) and carbon composites were produced. The oxide was synthesized via the sol–gel technique in a carbon matrix. A chemical interaction was revealed by thermal differential analysis since the carbon decomposition temperature shifts in the presence of the oxide. Oxide–carbon composites were used as support for nanodivided platinum and ruthenium–selenide catalyst. The nanoparticles were selectively deposited onto the oxide by means of electron–hole pairs generated on the oxide sites under UV irradiation. A systematic study for Pt was performed as a function of the loading using the oxide–carbon composite substrate and carbon toward the oxygen reduction reaction. A specific activity (mA/cm2 Pt) enhancement of 30% to 40%, at 0.9 V per reversible hydrogen electrode, with respect to carbon-supported samples, was obtained. This effect was also observed on the Ru–Se system and can be attributed to a catalyst–substrate effect.

The preparation of carbon and titanium dioxide supported Pt catalysts through a photochemical and photocatalytic routes were investigated. The catalysts were prepared by irradiation with UV-light (365 nm) at room temperature using H2PtCl6 and C10H14O4Pt (Pt(acac)2) as platinum precursors. The kinetic studies revealed that H2PtCl6 produced metallic platinum faster than Pt(acac)2 and also showed that the amount of platinum deposited on TiO2 was higher than on carbon. The samples were characterized by X-ray diffraction, SEM/EDS and cyclic voltammetry. X-ray diffraction permitted to identify the crystallographic (111) and (200) planes from platinum metal on the catalysts synthesized, the intensity of peaks depends of the amount of platinum deposited. SEM/EDS test confirmed what it was found by the kinetics studies. The electrocatalytic activity was compared with a commercial Pt E-Tek catalyst (10 wt%). The electrochemical results showed that Pt/C-AA catalyst synthesized by liquid phase photo-deposition method has stability in acid media and high distribution of the actives sites on the electrode surfaces. It could be considered as a candidate for electro-catalyst for polymer electrolyte fuel cell. The Pt/TiO2 catalysts did not present electrochemical activity.

This work reports the electrochemical measurements of 20 wt.% Ru x Se y /C for oxygen reduction reaction (ORR) in presence of different concentration of HCOOH and its use as cathode catalyst in a microfluidic formic acid fuel cell ( μ FAFC). The results were compared to those obtained with commercial Pt/C. Half-cell electrochemical measurements showed that the chalcogenide catalyst has a high tolerance and selectivity towards ORR in electrolytes containing up to 0.1 M HCOOH. The depolarization effect was higher on Pt/C than on Ru x Se y /C by a factor of ca. 23. Both catalysts were evaluated as cathode of a μ FAFC operating with different concentrations of HCOOH. When 0.5 M HCOOH was used, maximum current densities of 11.44 mA cm −2 and 4.44 mA cm −2 were obtained when the cathode was Ru x Se y /C and Pt/C, respectively. At 0.5 M HCOOH, the peak power density of the μ FAFC was similar for both catalysts, ca. 1.9 mW cm −2 . At 5 M HCOOH the power density of the μ FAFC using Ru x Se y , was 9.3 times higher than the obtained with Pt/C.

This mini-review summarizes materials design methods, oxygen reduction kinetics, tolerance to small organic molecules and fuel cell performance of chalcogenide metal catalysts, particularly, ruthenium (RuxSey) and non-precious transition metals (MxXy: M = Co, Fe and Ni; X = Se and S). These non-platinum catalysts are potential alternatives to Pt-based catalysts because of their comparable catalytic activity (RuxSey), low cost, high abundance and, in particular, a high tolerance to small organic molecules. Developing trends of synthesis methods, mechanism of oxygen reduction reaction and applications in direct alcohol fuel cells as well as the substrate effect are highlighted.

We report on Pt selectively photodeposited on oxides sites of Ti-, and W-carbon composites. The change of the lattice parameter strongly suggests that the metal center alloys with the metal centers of the oxides with a concomitant change of electronic properties favorable for oxygen reduction reaction in acid medium. Keywords: ORR, XPS, Platinum, Titanium oxide, Tungsten oxide, Lattice strain

The oxygen reduction reaction (ORR) was investigated on carbon (XC-72) supported platinum nanoparticles, generated via the carbonyl chemical route and on oxide composites supported platinum generated via the UV-photo-deposition technique in sulfuric acid medium. The behavior of Pt/C was examined using a careful dosing of the catalyst loading spanning the range from 4.3 to 131 μg cm −2 . The ORR electrochemical response of Pt/C (in line with recent literature data) is put into contrast with the Pt/oxide-composite systems. Our results point out that it is possible to use smaller amounts of catalyst for the ORR when platinum atoms interact with the oxide (anatase) surface of the substrate composite. Evidence of the incipient metal–substrate interaction is discussed in the light of the results of XRD experiments.

Carbon-supported and non-supported cluster-like RuxSey were synthesized in aqueous media. The structure and morphology were analyzed by XRD and TEM, respectively. Particles dispersed uniformly on the support with an averaged size of 2.1 nm were obtained. The oxygen reduction reaction (ORR) in presence of HCOOH was investigated by means of rotating disk electrode at 25 °C on RuxSey nanoclusters. The kinetics of HCOOH oxidation for non-supported and carbon-supported RuxSey catalysts was analyzed. A reaction order of 1/1.4 and 1/1.6 was determined for RuxSey and RuxSey/C, respectively. This reaction order indicates that the reaction mechanism is similar to Pt/C. The chalcogenide catalyst showed a high tolerance and selectivity towards the ORR in electrolytes containing up to 0.1 M HCOOH. At the highest formic acid concentration (5 M) the potential, at e.g. current density of 0.2 mA cm−2, shifts to negative for non-supported and carbon-supported RuxSey by 0.24 V and 0.28 V, respectively. The results reported in this work are the basis for overcoming the negative impact of fuel cross-over in microfluidic formic acid fuel cells that currently use Pt as cathode catalyst.

Titanium dioxide is a low cost material, environmental friendly and one of the most attractive semiconductors, due to this it has a wide spectrum of applications in photocatalysis and photoelectrocatalysis. In this work, TiO2 nanoparticles in anatase and anatase-brookite phases were synthetized by sol-gel method, and deposited on multi-walled carbon nanotubes (MWCNT). A solution of Titanium (IV) Isopropoxide was mixed with MWCNT by ultrasonication, the suspension was kept in an ice bath (around 0o C), and water was added for the hydrolysis reaction. Anatase phase was obtained placing the so-gel product in a thermal treatment at 4000C during 2 hours. For anatase-brookite mixture, the sol-gel product was placed in a reflux system at 800C during 5 hours. Once the solution was cooled at room temperature, the pH was adjusted to 2. Finally, after a filtration process, the obtained material was dried and thermally treated at 4000C. In order to compare, anatase and anatase-brookite nanoparticles without MWCNT were synthesized. The materials were physically and chemically analyzed by scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, Raman spectroscopy, surface area analysis (BET method) and X-ray diffraction. For the photoelectrochemical measurements, a three electrode cell assembly was used having 0.5M H2SO4 as base electrolyte. The working electrode was prepared by depositing the synthetized materials in a conducting glass substrate. Ag/AgCl (KCl sat) electrode and a Pt wire was used as reference and counter electrode respectively. During the analysis the working electrode was irradiated with UV light and linear sweep voltammetry (LSV) was performed in order to obtain photocurrent values. Photocurrents transients were obtained by light chopping with on-off periods of 5s. An extensive analysis and discussion of the obtained physicochemical results as well as the photocatalytic performance will be presents at the conference.

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.

Platinum nanoparticles were selectively deposited on titania via a facile photochemical method. The anatase-type TiO2 nanostructure, prepared by sol-gel, is in intimate contact with the carbon (Vulcan XC-72) used as supporting material. The structural studies via XRD in the as prepared and heat-treated samples were evaluated and compared to the substrate without oxide. The lattice constant of platinum was found 0.6% less than the value in the bulk. This observation is accompanied by high internal strains, which are not present on the Pt/C system. A healing of such defects is achieved by the thermal treatment. The consequence of such observations is discussed in terms of a strong-metal nanoparticle oxide interaction, which is favorable for electrocatalysis. These studies suggest that Pt–TiO2–C might serve as an element of response to lower the amount of utilized platinum in low temperature H2/O2 fuel cells cathodes.

We investigated the effect of CoSe 2 /C nanoparticle loading rate on oxygen reduction reaction (ORR) activity and H 2 O 2 production using the rotating disk electrode and the rotating ring-disk electrode techniques. We prepared carbon-supported CoSe 2 nanoparticles with different nominal loading rates and evaluated these samples by means of powder X-ray diffraction. All the catalysts had an OCP value of 0.81 V vs. RHE. H 2 O 2 production during the ORR process decreased with an increase in catalytic layer thickness. This decrease was related to the CoSe 2 loading on the disk electrode. H 2 O 2 production also decreased with increasing catalytic site density, a phenomenon related to the CoSe 2 loading rate on the carbon substrate. The cathodic current density significantly increased with increasing catalytic layer thickness, but decreased with increasing catalytic site density. In the case of 20 wt% CoSe 2 /C nanoparticles at 22 μg cm −2 , we determined that the transfer process involves about 3.5 electrons.

In this work we compare the experimental results for “real” fuel cell carbon supported Pt–Ru catalysts with the literature data for well defined model surfaces. The spectroscopic carbon monoxide probing, in the infrared region, clearly reveals differences in the reactivity of single-grain metal nanoparticles and multi-grained nanostructures with high concentrations of grain boundary defect regions. We use structural, spectroscopic and electrochemical information in an effort to rationalize the particle size and grain boundary effects in electrocatalysis.

Synthesized carbon-supported Pt nanoparticles (10 wt% Pt/C) and their commercial counterpart (40 wt% Pt-Etek/C) have been used to study the electrochemical reduction of NOx- ions at different concentrations in alkaline and acid pH. A comparative study between nanostructured and massif platinum was evaluated. Cycling Voltammetry (CV), Rotating Disc Electrode (RDE) and Differential Mass Spectrometry (DEMS) were used for this purpose. Stationary current-potential curves indicate that the adsorption-desorption phenomena take place in two different regions of potential: the electrochemical reduction of NOx- ions for potentials ranging from -0.60 to -0.95 V/SCE, and the hydrogen evolution reaction (HER) at potential lower than -0.95 V/SCE. These results confirmed that the reduction of NOx- ions follows the order Pt/C > Pt-Etek/C > Pt-massif. DEMS demonstrated the formation of nitrogen species such as N2, NO, N2O and NO2.

The carbon monoxide molecule was used to probe the surface properties of PtRu(1:1)/C catalysts with 5, 30, and 60 wt % metal. The spectroscopic IR study performed in the external reflection configuration clearly showed that linearly bonded CO dominates the spectra for all catalysts, although the presence of bridged adsorbates was also revealed. These nanostructures, consisting of metal grains interconnected via grain boundaries, and formed at high metal loadings on carbon support, strongly influence the catalytic oxidation of the adsorbed carbon monoxide. It is proposed that in the potential interval 0.3 < E < 0.45 V, O(H)ads formation occurs preferentially at the active sites which are presumably located at the emergence of the grain boundaries at the particle surfaces. Dissolved CO strongly inhibits CO oxidation on multigrained materials while for highly dispersed isolated PtRu nanoparticles it shifts the oxidation onset negative. The spatial distribution of the adsorbed CO molecules on the catalyst sur...

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)

20 wt. % Co3S4/C nanoparticles as novel non-precious metal electrocatalysts were synthesized by two routes based on the in situ decomposition of cobalt carbonyl (Co2(CO)8) in p-xylene solvent: with the surfactants of oleic acid and trioctylphosphane oxide, and without surfactant directly using the supporting carbon (Vulcan XC-72) as the dispersing agent. The corresponding structure, thermal stability, electrochemical properties were investigated by means of powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and rotating disk electrode (RDE) techniques. The particles synthesized without surfactant show the higher electrocatalytic activities toward oxygen reduction reaction (ORR) with the onset potential ca. 0.7 V vs. RHE in 0.5 M H2SO4 relative to those synthesized with the surfactants with the onset potential ca. 0.3 V vs. RHE, possible resulting from the surfactants blocking the active sites on the surface of the electrocatalysts. The synthesized 20 wt. % Co3S4/C nanoparticles demonstrate the thermal stability below 360 oC under air atmosphere and the electrochemical stability in the acid medium below 0.8 V vs. RHE.

Partial replacement of Ru in chalcogenide nanoparticles (RuxSey) by a less noble metal, such as Fe, was studied by electrochemical and materials-characterization techniques. The synthesis of the nanoparticles consisting of Ru, Fe, and Se was performed using two different chemical routes, which led either to a combination of RuxSey with oxidized iron or a true alloying of iron with the RuxSey bulk. The physical-chemical properties of the different types of three-component system were subsequently examined. The electrochemical performance in oxygen reduction reaction (ORR) in acidic medium (0.5 M H2SO4) was evaluated relative to the iron-free catalyst. The results demonstrate that the reaction mechanism (four-electron charge transfer) is not perturbed at the modified metal center, even when Ru is replaced by 50 at.% of Fe.

We report on the synthesis of composites Polypyrrole/Carbon (PPy/C) to be used as matrix-support of platinum nanoparticles prepared by carbonyl chemical route. The composite materials with different PPy loading were characterized by physical chemical methods, such as elemental analysis, infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The catalysts: 20 wt. % Pt/composites were used as substrates for the oxygen reduction reaction in acid medium. For the same catalyst loading (50 µg cm-2), it was observed that the nature of the composite strongly influences the electrochemical activity of nanoparticulated platinum.

Research of nanometer scale range catalysts based on cluster-like mono-, bi-metallic, and chalcogenides for oxygen reduction reaction (ORR) as cathodes, a major challenge for polymer electrolyte membrane fuel cells (PEMFCs) nowadays, for facilitating efficient electron transfer using the carbonyl chemical route is reviewed. A strategy aimed at reducing the amount of expensive catalyst materials, giving the accessibility of non-noble materials and taking into account the activity and selectivity of cathodes for the ORR is devised as well.

The adsorption of nitrogen species, in neutral electrolyte solutions, onto boron-doped diamond (BDD) electrode surfaces from dissolved NO2, NO, and N2O gases was induced at 0 V/SCE. Modified BDD electrode surfaces showed a different electrochemical response toward the hydrogen evolution reaction than did a nonmodified electrode surface in electrolyte base solution. The formation of molecular hydrogen and nitrogen gaseous species was confirmed by the online differential electrochemical mass spectrometry (DEMS) technique. Among the three nitrogen oxides gases, NO2 substantially modifies the electrolyte via hydrolysis leading to the formation of NO3- and its adsorption on the BDD electrode surface. The BDD/(NO3-) interface was the only N2O and N2 species generating system.

The electrical performances of a membrane-less glucose/O2 biofuel cell was measured, using a biocathode composed of laccase co-immobilized with 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS2-) on the external face of a carbon porous tube, and Au-Pt alloy nanoparticles as anode. A 40 wt. % Au-Pt/C anode catalyst was dispersed in an ultrasonically homogenized ink to be immobilized on the inner face of a carbon tube by painting. Inserting the biocathode into the anode, which has a large internal diameter, assembled the cell. O2 diffuses by porosity through the inner carbon tube to react with laccase, while the top and the bottom of the cell are sealed with two Teflon gaskets. The electrolyte (phosphate buffer 0.2 M pH 7.4) containing 10 mM glucose was analyzed by ionic chromatography with a ternary gradient of elution necessary to separate the remaining glucose from gluconic, glucuronic and glucaric acids, which were the detected reaction products.

Conducting polypyrrole (PPy)/C (Vulcan XC-72) composite materials were synthesized by chemical polymerization method. These materials were used as matrix to support platinum nanoparticles, which were produced by the carbonyl chemical route. For the same catalyst loading (50 μg cm−2), it was observed that the nature of the composite strongly influences the electrochemical activity of nanoparticulated platinum toward the oxygen reduction reaction in acid medium. The variation of the PPy/C ratio determines the so-called substrate effect for electrocatalysis.

Oxygen reduction Ru/Se and Ru/S fuel cell surface chalcogenide catalysts were prepared via chemical reaction of reduced Ru nanoparticles with selenium and sulfur in xylenes [D. Cao, A. Wieckowski, J. Inukai, N. Alonso-Vante, J. Electrochem. Soc. 153 (2006) A869]. The chalcogenide samples – as well as the starting chalcogens-free Ru nanoparticle material – were immobilized on a gold disk for X-ray Photoelectron Spectroscopy (XPS) characterization. While we found oxygen in most of the samples, predominantly from Ru oxides, we conclude that the oxygen on Ru/S may be located in subsurface sites: the subsurface oxygen. We also found that the transformation of the oxidized Ru black to metallic Ru required intensive electrochemical treatment, including hydrogen evolution. In contrast, five cyclic voltammetric scans in the potential range from 0.00 and 0.75 V versus RHE were sufficient to remove the oxygen forms from Ru/Se and, to a large extent, from Ru/S. We therefore conclude that Ru metal is protected against oxidation to Ru oxides by the chalcogens additives. The voltammetric treatment in the 0.00 and 0.75 V range also removed the SeO 2 or SO x forms leaving anionic/elemental Se or S on the surface. Upon larger amplitude voltammetric cycling, from 0.00 to 1.20 V versus RHE, both Se and S were dissolved and the dissolution process was coincidental with the oxygen growth in/on the Ru samples.

The cluster-like RuxSey (x ≈ 2, y ≈ 1) compound can be prepared by simple pyrolysis of the carbonyl complex Ru4Se2(CO)11 in inert gas. We have observed this process in situ using X-ray diffraction. The clusters exhibit a disordered hcp-type structure with an average size of 1.7 nm. Selenium is probably coordinated at the surface of ruthenium nanoparticles. Up to 430 °C, these nanoparticles are stable in an inert ambient, except for a certain growth in size. Above this temperature, the system splits into two phases: hcp-type ruthenium particles, which are probably free of Se, and a ruthenium-diselenide phase: RuSe2. Using density functional theory (DFT), we studied the surface structure of RuSe2 and found a preference for Se-rich surfaces. Transferring to the nanoparticles, this might correspond to the picture of a Ru core and either a RuxSey- or a pure Se shell (adsorbate layer).

International audience; The synthesis of CoSe2 nanoparticles supported on nitrogendoped carbon nanohorns (CoSe2/NCNH) and the influence of the interaction of the metal centre with the NCNH on the oxygen reduction reaction (ORR) are reported. CoSe2/NCNH shows a 50 mV lower onset overpotential and a 150 mV positive shift in the half-wave potential compared to CoSe2 supported on carbon and carbon nanohorns. This suggests that the intrinsic activity and the density of active reaction centres of CoSe2 are modified by NCNHs. An air-breathing direct meth-anol microlaminar flow fuel cell (mLFFC) is constructed using CoSe2/NCNH as a methanol-tolerant cathode catalyst. A maximum power density of 10.05 mWcm(-2) and a maximum current density of 124.20 mAcm(-2) are achieved with CoSe2/NCNH compared to the non-doped catalyst, CoSe2/C and Pt/C with 5m methanol as the fuel. The improved activity of CoSe2/ NCNH is attributed to the peculiar morphology and the nitrogen doping of the carbon nanohorns. This catalyst could be a suitable alternative to Pt.

International audience; Carbon supported palladium nanostructures were synthesized via the carbonyl chemical route. Compared with nanostructured platinum, prepared via carbonyl chemical route, Pd nanomaterials showed mass-loading morphology, whereas particle size and morphology of Pt nanostructures was constant. The oxygen reduction reaction (ORR) on nanostructured Pd, with different morphology in both acid and alkaline medium was investigated. A relationship, based on X-ray diffraction structural analysis pattern, transmission electron microscope, with the Pd morphological effect on ORR activity was identified.

International audience; In this study, low-mass loadings (ca. 5 wt%) Pt/C catalysts were synthesized using the carbonyl chemical route allowing for the heterogeneous deposition of Pt nanoparticles on different carbon-based substrates. N-doped reduced graphene oxide, reduced graphene oxide, graphene oxide, graphite and Vulcan XC-72 were used for the heterogeneous deposition of Pt nanoparticles. The effect of the chemical nature of the carbon-based substrate on the Oxygen Reduction Reaction (ORR) kinetics at Pt nanoparticles surfaces was investigated. XPS results show that using N-doped reduced graphene oxide materials for the deposition of Pt nanoparticles leads to formation of Pt-N chemical bonds. This interaction between Pt and N allows for an electronic transfer from Pt to the carbon support. It is demonstrated that ca. 25% of the total amount of N atoms were bound to Pt ones. This chemical bond also revealed by the DFT analysis, induces changes in the oxygen adsorption energy at the platinum surface, engendering an enhancement of the catalyst activity towards ORR. In comparison with Vulcan XC-72, the mass activity at 0.9 V vs. RHE is 2.1 fold higher when N-doped reduced graphene oxide is used as substrate. In conjunction with the experimental results, DFT calculations describe the interaction between supported platinum clusters and oxygen where the support was modelled accordingly with the carbon-based materials used as substrate. It is demonstrated that the presence of N-species in the support although leading to a weaker O-2 adsorption, induces elongated O-O distances suggesting facilitated dissociation. Additionally, it is revealed that the strong interaction between Pt clusters and N-containing substrates leads to very slight changes of the cluster-substrate distance even when oxygen is adsorbed at the interfacial region, thus leading to a lower resistance for electron charge transfer and enabling electrochemical reactions.

We report on the analysis of the performance of each electrode of an air-breathing passive micro-direct methanol fuel cell (µDMFC) during polarization, stabilization and discharge, with CH3OH (2–20 M). A reference electrode with a microcapillary was used for separately measuring the anode the cathode potential. Information about the open circuit potential (OCP), the voltage and the mass transport related phenomena are available. Using 2 M CH3OH, the anode showed mass transport problems. With 4 and 6 M CH3OH both electrodes experience this situation, whereas with 10 and 20 M CH3OH the issue is attributed to the cathode. The stabilization and fuel consumption time depends mainly on the cathode performance, which is very sensitive to fuel crossover. The exposure to 20 M CH3OH produced a loss in performance of more than 75% of the highest power density (16.3 mW·cm−2).

We have recently developed a method for obtaining chalcogenide catalysts, which is based on surface modification of ruthenium black particles rather than the synthesis of a bulk metal-chalcogen compound [1]. Electrochemical, non- electrochemical and fuel cell testing have revealed high ORR activity and very good methanol tolerance of such surface chalcogenide catalysts [2,3]. Uniquely for Pt-free cathode catalysts, such surface chalcogenides also exhibit very good performance durability under fuel cell operating conditions at 70{degree sign}C. In this paper, we focus on hydrogen-air and direct methanol fuel cell performance of chalcogen-modified Ru blacks as well as on the mechanism of oxygen reduction on such catalysts, as determined in rotating ring disk-electrode (RRDE) studies.

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.

In this study, the electrochemical oxidation of acetaldehyde was investigated at activated massive DSA® electrodes in acid medium, using differential electrochemical mass spectrometry (DEMS) and high-performance liquid chromatography (HPLC). The electrodes were prepared either by platinum electrodeposition or by depositing a highly nanodispersive-supported catalyst (Pt and Pt-Ni) over electrode surfaces with a Ti/Ru0.3Ti0.7O2 nominal composition. Bulk electrolysis shows evidence of CO2 and acetic acid formation. The electrocatalytic efficiency of the electrode material was also investigated as a function of the amount of catalyst added over the DSA® electrode surface. The presence of RuO2-active sites on the DSA® substrate plays an important role in the reaction overall efficiency. The addition of platinum to DSA® enhances the oxidation of acetaldehyde to CO2. The role of the substrate on the direct activation of acetaldehyde oxidation is discussed on the basis of the direct application of the metal nanoparticle catalyst over conductive oxide surface based on Magneli phase (mixture of TinO2n−1 and other phases) from Ebonex®.

Ruthenium oxide-like (RuxOy) nanoparticles were prepared by the decomposition of carbonyl precursors in organic solvents under mild conditions. CO oxidation over the reduced particles was studied by combined in situ X-ray diffraction and gas-phase analysis. For a sample prepared in dichlorobenzene, in a flow of CO/O2 = 0.55, oxidation of CO started at ca. 70 °C with the simultaneous formation of amorphous surface oxide. On further heating, the CO2 production increased proportionally with the rate of formation of surface oxide. Below ca. 130 °C the catalyst can be reversibly reduced in CO to the disordered precursor state, average size ca. 2.8 nm. After catalytic performance for 3 h at 180 °C, reduction in CO of partially oxidized RuxOy is accompanied by a burst of CO2 partial pressure and induces particle growth to ∼5 nm∼5 nm due to the exothermic heat of the reaction. These results are comparable to earlier results for ruthenium single-crystal surfaces studied under low pressure conditions.

The electrochemical oxidation of ethanol in alkaline solution has been studied on Cu–PVC electrode and Ni/Cu–PVC composite electrodes modified by ruthenium nanoparticles. The techniques used were cyclic voltammetry (CV), steady-state potentiostatic method, on line differential electrochemical mass spectrometry (DEMS), and high-performance liquid chromatography (HPLC). The chemical products: acetaldehyde and acetic acid were detected measuring the proper mass charge (m/z) ratios. These products were also confirmed by HPLC. The surface modification of composite electrodes by ruthenium nanoparticles promotes the formation of acetaldehyde. As shown by DEMS, the surface modification shifts the onset potential for oxygen evolution reaction on the Cu–PVC composite electrode towards more anodic values.

Surface mesoscopic titanium dioxide (P25) films deposited onto conducting glass plates (SnO 2 :F) were modified by colloidal Ru x Se y nanoparticles (2 nm diameter). A decrease of the photocurrent was found upon modification of TiO 2 films. However, interfacial electron transfer kinetics to oxygen was favored. The increase of the catalyst surface concentration onto TiO 2 , shifts the onset of the photocurrent under UV-illumination, to 0.6 V/RHE in presence of oxygen dissolved in the electrolyte. Concomitant to this, the cathodic current becomes important and shifts to more positive potentials. This phenomenon allows the system to work catalytically under open circuit conditions. On non-modified TiO 2 , the application of a 0.3 V/RHE potential leads to an enhancement of the photooxidation of formic acid. Photocurrent images revealed a non-homogeneous distribution of the catalyst on the titanium dioxide films.

Vulcan XC-72 carbon-supported Pt−Ni alloy nanoparticle catalysts with different Pt/Ni atomic composition were prepared via the carbonyl complex route and their structure was studied by X-ray diffraction spectroscopy at wide angles (WAXS) and Debye function analysis (DFA). The very good agreement between the WAXS pattern and DFA simulation revealed that all the as-prepared Pt−Ni alloy catalysts have a unique and highly disordered face-centered cubic structure (solid solution) and that the lattice parameter decreases with the increase of the Ni content in the alloys. Transmission electron microscopy (TEM) images indicated that the as-prepared Pt−Ni alloy nanoparticles were well dispersed on the surface of the carbon support with a narrow particle size distribution and that their mean particle size slightly decreased with the increase in Ni content. Energy-dispersive X-ray analysis (EDX) confirmed that the catalyst composition was nearly the same as that of the nominal value. Thus, a comparative study was ma...

Structural and stability studies of bimetallic Pt−Sn (3:1) nanoparticles were performed in situ via X-ray diffraction at wide angles (WAXS). The homemade bimetallic catalyst (Pt−Sn) ccomp (ccomp = from carbonyl complex) was synthesized in mild conditions from a Pt−carbonyl chemical precursor. A relatively narrow size distribution (2.4 ± 0.9 nm) of such a bimetallic catalyst supported onto carbon Vulcan XC72 was obtained at room temperature. Its electrochemical behavior was compared to that of a commercial catalyst. The WAXS study revealed that such a catalyst, prepared via the carbonyl route, has a certain degree of surface disorder (high Debye parameter, B), which enhances the electrocatalytic activity for hydrogen adsorption. Furthermore, WAXS also demonstrated that the structural stability of this bimetallic catalyst is maintained at the annealing temperature employed (500 °C), although the particle size increases from 1.6 to 2.2 nm. Electrochemical underpotential deposition studies, via copper deposit...

The electrochemical response and electrode potential-dependent infrared spectra for CO-adsorbate oxidation on unsupported ruthenium cluster-like material (Ru x ), prepared in two organic solvents: (xylene (Xyl), and 1,2-dichlorobenzene (Dcb)) from tris–ruthenium dodecacarbonyl decomposition, are reported. In spite of a similar particle size (2 nm) of the materials, the interfacial pseudo-capacitance of Ru x (Xyl) is ca. four times higher than that of Ru x (Dcb). Wide angle X-ray spectroscopy (WAXS) analysis on Ru x (Xyl) and Ru x (Dcb) nanoparticles revealed a high degree of structural disorder on Ru x (Xyl) (J. Phys. Chem. B 105 (2001) 5238). The surface state of Ru x (Xyl) and Ru x (Dcb) used to oxidize CO, to form oxide-like (Ru x O y ) species, and used to recover the metallic nanoprecursor (under hydrogen annealing) can be inherently attributed to the degree of surface atom disorder. The CO absorption bands recorded on both types of surfaces are linear in nature and have apparently similar behavior to that observed on massive or well-defined ruthenium electrode surfaces.

The change in reflected microwave power due to the photoinduced change of the sample's average conductivity is measured. The resulting microwave reflection signal is proportional to the change of the integral over the excess carrier profile in the semiconductor sample. With a relation between this profile and the excess charge carrier concentration at the surface, the measured change in reflected microwave power is a measure for the change in surface concentration of excess carriers. With this link simultaneously recorded microwave reflection signal and photocurrent are combined to separate the surface recombination velocity from the charge transfer constant using a model for the microwave reflection signal containing these two parameters explicitly. For n-Si (4–5 × 1014 cm−3) in contact with dried propylene carbonate (PC) containing 0.1 M tetrabutylammonium perchlorate (TBAP) and 10 mM ferrocene/ferrocenium, these two quantities are measured under periodic illumination as a function of the applied potential. The approximation of the separated surface recombination velocity with a potential dependent Shockley–Read–Hall-formalism yields the capture cross sections for electrons (4 × 10−16 cm3s−1) and holes (4 × 10−18cm3s−1) of the relevant surface recombination levels.

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.

Structural studies and stability of cluster-like particles of Rux and RuxSey were performed in situ via X-ray diffraction at wide angles (WAXS). Both materials have a similar particle size (1.4−1.6 nm) in the reduced state. Whereas Rux particles are rather sensitive to oxygen from air, the chemical stabilization, against oxidation, of such metallic centers is obtained by the coordination of selenium atoms. The role of selenium atoms is also to stabilize the nanostructural nature (geometric effect) of the compound, as demonstrated by the temperature measurements (up to 300 °C) in the gas phase, and to provide the electronic effect for electrocatalysis.

A family of novel catalysts for oxygen electroreduction is presented, based on nanostructured Ru x X y chalcogenide compounds (X=S, Se, Te). EXAFS data suggest that the catalysts have a core of ruthenium atoms, which has triangular co-ordination and a direct metalmetal bond. Depending on the chalcogen, the Ru-cluster consists of two or three metal layers of different size and mutual co-ordination with chalcogen atoms co-ordinated to the periphery of the cluster. Variation of the chalcogen type affects the size of the Ru-cluster and the strength of its interaction with the chalcogen. This influences the interaction of Ru-clusters with oxygen and thus their activity in the reduction of molecular oxygen.

Novel cluster Ru chalcogenide materials MoxRuySez and RuxTey were studied in situ using EXAFS in the transmission mode during the oxygen reduction reaction. Reversible changes in the structure of the active center were revealed for the electrochemical reaction as a function of the applied electrode potential. The shift of the potential in the anodic direction from 0.08 to 0.78 V versus rhe (reference hydrogen electrode) in the presence of oxygen resulted in an increase of the Ru−O and simultaneous decrease of the Ru−Ru coordination numbers in the first coordination shell of Ru. Along with the variation of the coordination numbers, we observed reversible changes of the coordination distances: a decrease of the Ru−O and an increase of the Ru−Ru distance with the positive polarization. These changes witness the distortion of the catalytic center upon oxygen adsorption. A tentative mechanism of oxygen activation on RuxXy cluster materials is proposed on the basis of the in situ EXAFS data.