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CeO2 decorated CoOx rod-like hybrid, supported onto holey reduced graphene (CoOx/CeO2/RGO) composite, was fabricated via a surfactant-assisted route. Its corresponding electrocatalytic performance towards oxygen reduction/evolution reactions (ORR and OER) was systematically investigated in alkaline electrolyte. Structural, morphological and compositional studies revealed changes in electronic and surface properties when CeO2 was introduced as an oxygen buffer material. The oxygen vacancies effectively enhanced the electrocatalytic activity, while the synergistic effect of co-catalyst CeO2, CoOx active-centers, and defective graphene with many voids facilitate the charge/mass transfer, making CoOx/CeO2/RGO an efficient and stable bifunctional electrocatalyst for OER/ORR with ΔE = 0.76 V (ΔE = E10 mA cm-2, OER – E1/2, ORR). This parameter is 70 mV and 270 mV lower than CoOx/RGO and the benchmark Pt/C, respectively. In addition, the OER/ORR bifunctionality of CoOx/CeO2/RGO composite outperforms that of Pt/C catalyst in a H2-O2 micro fuel cell platform.

Platinum nanoparticles (NPs) were photo-deposited on SnO2-C nanocomposites prepared by sol-gel method. Surface morphology of the prepared materials, examined by scanning electron microscopy (SEM) and transmission electron microscopy, confirmed selective deposition of Pt NPs on SnO2 nanoclusters formed on carbon surface. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) analysis, cyclic voltammetry (CV) and CO stripping experiments revealed modification of the electronic properties of the Pt NPs photo-deposited on the oxide-carbon composite in comparison to Pt/C prepared by the carbonyl chemical route. Rietveld refinement was employed to identify existing phases of catalysts and to determine the crystallite size. Micro-strain and intrinsic stacking fault increased and decreased, respectively, as a function of crystallite size. Pt loadings were determined by inductively coupled plasma mass spectrometry (ICP-MS). The oxygen reduction reaction (ORR) activity of the electrocatalysts was investigated in acid media using the rotating disk electrode (RDE) system. Accelerated durability test (ADT) results showed that photo-deposited Pt nanoparticles onto SnO2-C nanocomposite are more durable than those chemically deposited on carbon.

Flower-like hierarchical three-dimensional NiFe layered double hydroxides hollow microspheres (3D NiFe-LDH HMS), as one kind of novel non-noble metal electrocatalysts, have been fabricated in a template-free route for water oxidation. Both of the concentration of ammonium fluoride and the reaction time are adjusted to obtain a series of NiFe-LDH microspheres, with different internal structures from massive to hollow generated during the hydrothermal treatment, which improve the electrocatalytic activity of the NiFe-LDH catalysts towards the evolution reaction of oxygen. The optimized NiFe-LDH-0.4M HMS show the excellent OER performance in alkaline electrolyte with η = 290 mV@10 mA cm−2, and a Tafel slope of 51 mV dec−1, which outperforms the benchmark RuO2 catalyst. The possible reason is attributed to the more exposure of active sites, and fast ion transport resulting from the hierarchical hollow structure.

Direct ethanol fuel cells are highly promising energy conversion devices, but the complete oxidation of ethanol to CO2 at low temperatures is still one of the main challenges. Titanium oxycarbide (TiO1-xCx) powder is investigated as stable and synergistic support for Pt nanoparticles during the ethanol oxidation reaction (EOR) in acidic electrolytes. EOR products are quantitatively detected online with differential electrochemical mass spectrometry. At room temperature, Pt/TiO1-xCx has a CO2 efficiency maximum of 8.9%, while only 1.7% are measured for Pt nanoparticles on Vulcan carbon (Pt/C). The reaction pathway is channeled towards the formation of C1 products, while C2 product formation is suppressed. This effect is expected to be much enhanced at elevated temperatures which makes TiO1-xCx a highly interesting catalyst support material in general.

MOF(Ni/Fe) nanosheets were grown in situ vertically on three-dimensional (3D) nickel foam (NF). To induce a chemical coupling effect, defective CeO2-x nanoparticles (NPs) were chemically decorated on the surfaces of the MOF(Ni/Fe)/NF nanosheets. This phenomenon confirmed a positive effect for oxygen evolution in alkaline medium. The oxygen evolution reaction (OER) performance of the electrocatalysts reached an overpotential of ∼254 mV at j = 50 mA cm−2 with a Tafel slope of ∼34 mV dec−1.

The impact of sp2 sites of amorphous carbon and carbon nanotubes toward the hydrogen evolution/oxidation reactions on Pt nanoparticles, in alkaline medium, is described. The kinetic enhancement is given through the induced UV-photons of selectively photo-deposited platinum nanoparticles (Pt NPs) onto sp2 domains. The, henceforth, induced sp2 strong metal support interaction favors the electronic, and the oxophilic effects boosting the kinetics of hydrogen reactions.

Summary The phenomenon to restrain electrocatalytic particle agglomeration, while boosting the activity of multi-electron charge transfer reactions, known as strong-metal support-interaction, is reviewed. The main insights of this phenomenon are outlined. In this respect, the connection of a photo-induced process, to anchor metal centers, contributes to the electrocatalytic activity enhancement. Selected examples are given.

Platinum nanoparticles were photo-deposited on acid-treated multi-walled carbon nanotubes (CNTs) and SnO2-coated CNTs. The SnO2-CNT nanocomposite was synthesised by a chemical method. Scanning and scanning transmission electron microscopy results indicated that the CNTs surface is partially covered by the SnO2 layer. The surface morphology of the Pt catalyst depends on the nature of the support material. For instance, porous Pt aggregates of various sizes are formed at specific nucleation sites on the CNT surface, while a selective deposition of Pt was observed on the metal oxide part of the SnO2-CNT. Cyclic voltammetry and CO stripping investigations in 0.1 M HClO4 solution confirmed different surface electrochemistry of the Pt catalysts. It is revealed that photo-deposition induces the formation of Pt-Sn nanoalloys due to increased interaction at the oxide interfaces. Both Pt/CNT and Pt/SnO2-CNT catalysts showed remarkable activity towards the electroreduction of oxygen in acid media. Durability measurement showed that photo-deposited Pt nanoparticles are more resistant to degradation. The corrosion-resistant nature of the SnO2-CNT support further improves the catalysts stability. Pt/CNT and Pt/SnO2-CNT catalysts retained 86% and 88% of the initial surface area respectively, after 10,000 potential cycles between 0.6 and 1.2 VRHE.

Herein, a series of three-dimensional Ni2Fe-SDS-LDH/CFP non-precious metal electrocatalysts in a simple hydrothermal route using sodium dodecyl sulfonate (SDS) as an interlayer spacer agent, and carbon fiber paper (CFP) as a conductive substrate was tailored. The electrocatalytic performance towards oxygen evolution reaction (OER) in alkaline medium was investigated. The results demonstrate that the OER activity improvement is mainly related to the increased interlayer distance from 0.76 nm to 2.49 nm depending on the intercalated amount of SDS in Ni2Fe-LDH, and resulting in the enhanced superior surface characteristics (e.g., larger specific surface area, bigger pore size and pore volume). Among all the samples, the Ni2Fe-SDS-LDH/CFP (molar ratio SDS/Fe = 1.5) showed the best OER performance (η@10 mA cm−2 = 289 mV, Tafel slope = 39 mV dec−1) comparable with the commercial IrO2 catalyst, which corresponded to the largest interlayer space of 2.49 nm.

We fabricated a NiFeO x /CoN y -C nanocomposite derived from CoPcTs-intercalated Ni 2 Fe-layered double hydroxides (Ni 2 Fe-CoPcTs-LDH), which served as high-efficiency, low-cost, and long-durability bifunctional oxygen electrocatalyst in half-cell, and a H 2 -O 2 laminar flow unitized regenerative micro-cell (LFURMC) in alkaline media. Based on the synergistic effect between Co-N y and NiFeO x centers, the non-noble hybrid catalyst NiFeO x /CoN y -C achieves a ΔE (η@jOER,10 - η@jORR,-3) = 0.84 V in alkaline solution, outperforming the commercial Pt/C, and very close to that of IrO x /C. In the fuel cell mode, the performance of NiFeO x /CoN y -C with the maximum power density of 56 mW cm −2 is similar to that of Pt/C (63 mW cm −2 ) and IrO x /C (58 mW cm −2 ); in the electrolysis mode, the calculated maximum electrical power consumed on NiFeO x /CoN y -C (237 mW cm −2 ) is more than 3 times that on Pt/C (73 mW cm −2 ), similar with that of IrO x /C. More importantly, the NiFeO x /CoN y -C shows a remarkable stability in alternating modes in a LFURMC system.

Mesoporous Co3O3.87◻0.13 (◻ represents oxygen vacancies) and Co3O3.87F0.13 electrocatalysts, integrating advantages of oxygen vacancies and fluorine anion, were deployed. Co3O3.87◻0.13 and Co3O3.87F0.13 showed enhanced oxygen evolution reaction (OER) with overpotentials of 440 mV and 430 mV at 10 mA cm−2, Tafel slopes of 56 mV dec-1 and 56 mV dec-1, turnover frequency (TOFη= 400 mV) of 0.023 s-1 and 0.042 s-1 respectively, as compared to Co3O4 (520 mV, 64 mV dec-1, 0.0005 s-1) in the alkaline medium. Physicochemical characterizations showed that oxygen vacancies and the substituted fluorine modified the electronic structure, leading to the enhanced activity for OER process, consistent with the theoretical calculation. This approach provides ideas for rational design of new defective fluorinated oxide, with the feasible extension of such an approach to a wide variety of transition metal oxides.

International audience; TiO2 Brookite, and Anatase powders were prepared by a facile and low temperature solution based method. XRD diffractometry was performed to confirm their phase composition and crystallinity. Morphology was further confirmed by TEM. N2 adsorption was used to determine surface area and pore size distribution. The difference in capacitive properties of both materials and the determination of the flat band position was obtained by Mott-Schottky analysis. Diffuse reflectance and Tauc plots allowed to obtain the band gap value. The degradation of Indigo Carmine dye with both catalysts in a photo-electrochemical microreactor was assessed by UV–vis, and Raman spectroscopy. Both materials were more active than the benchmark commercial Degussa P25 sample in the order P25 < Anatase < Brookite and explained in terms of energy band positions.

Nanostructured palladium (Pd) supported on carbon (Vulcan XC-72) substrate, prepared via carbonyl chemical route, showed Pd-mass depending morphology, reflected on the surface electrochemistry via cyclic, CO-stripping voltammograms, and performance in direct formic acid and direct methanol micro laminar flow fuel cell arrangement. Comparison was done with commercial Pd/C (30 wt.%, ETEK) catalyst. The formic acid oxidation reaction (FAOR) studied in different acid media (0.1 M HClO 4 , 0.5 M H 2 SO 4 and 0.5 M H 3 PO 4 ), indicated an enhanced FAOR activity on nanowire-like as compared to nanoparticles and nanorods as well as the commercial one in each electrolyte. Besides, the nanowire-like Pd/C catalyst also favored methanol (MOR) in 0.1 M KOH. These facts confirm favorable morphological effect of nanowires for organic fuel oxidation in both acid and alkaline media.

International audience; This work summarizes the advanced materials developed by various research groups for improving the stability of platinum (Pt), and Pt-based catalysts center toward the oxygen reduction reaction (ORR) in acid medium. The ORR stability enhancement of Pt catalytic center can be classified according to the different nature of the supporting materials, namely, carbon-, oxide-based-, and oxide-carbon composites. The enhancement and stability of a catalytic center can be related to either its electronic modification induced by a strong interaction with the support, another metal (alloy), or to geometric effects. In addition, other parameters come into play, the size, the morphology of the catalytic center, the temperature, the dispersion, and mass loading, along with the measuring methods. This mini-review mainly focusses on the stability improvement, depending on the substrate nature. This latter can be further modified via functionalization or by the chemical interaction nature between the substrate and catalyst.

International audience; A passive silicon microfabricated direct methanol fuel cell employing a polymer anion exchange membrane has been identified as a promising integrable power supply for portable devices in the MEMS field. In this work the fabrication steps of the different components: silicon current collectors and membrane-electrode assembly (MEA), as well as the mounting approach and performance evaluation for the whole passive alkaline micro air-breathing direct methanol fuel cell (mu ADMFC) are shown. This system, with a small active area of 0.25 cm(2), was tested near of the real application conditions with totally passive fueling and at room temperature. Different MEA configurations and methanol and KOH concentrations were compared. Best performance was observed for the MEA with a previously sprayed catalytic layer on carbon cloth instead of the MEAs with the catalytic layer deposited directly onto the alkaline membrane. A maximum power density of 2.2 mW cm(-2) was achieved for 15 mu L of 1 M methanol + 4 M KOH fuel solution.

International audience; The electroreduction of nitrogen species in alkaline medium was performed on platinum nanoparticles (1-2 nm) with metal loadings of 5 and 10 wt% Pt, synthesized by the chemical carbonyl route. The electrochemically active surface analysis evidences that the real surface area is concomitant to the Pt-loading in the support. The electrochemical analysis put in evidence that nitrite ions were reduced from -0.6 to -0.78 V and the charge transfer step is attributed to the NO2-/NO redox couple. The Tafel slope analysis confirms that from E-p to -0.78 V the reduction of NO occurs via an ECE mechanism. An analysis of Nicholson-Shain schemes and NO-saturated in solution verified these results. (C) 2012 Elsevier Ltd. All rights reserved.

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.

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.

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.

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.

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.

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.

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.

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.

A novel metal chalcogenide cluster material (RuxSey) was investigated in situ using X-ray absorption spectroscopy at grazing angles (GIXAS). The electrocatalyst in form of thin films was deposited onto conducting glass substrates (SnO2:F) from colloidal solution. The detected signal was the result of X-ray reflection from the substrate. The in situ measurements at different atmospheres in the electrochemical system (Ar or N2, and O2) as a function of the applied electrode potential provided evidence for surface structure dynamics in electrocatalysis. Although the detected signals were at the limit of detection due to the small quantity of deposited catalyst material, we conclude that the co-ordination of oxygen to the catalytic centres enhances the local disorder. The change in the distance amounts to circa 12% at the vicinity of the ruthenium. This change decreases when changing to N2 or Ar (non electrocatalytic conditions), therefore, giving strong evidence of reversibility.

The series of Ru chalcogenide compounds is obtained by varying the nature of the chalcogen with the transition metal (Ru) matrix. The EXAFS technique reveals that the electrocatalytic centre is Ru in a cluster matrix. Furthermore, a reversible change in the structure of the active centre as a function of the applied electrode potential appears.

The reactivity with water and methanol of oxygen-reducing (Ru 1− x Mo x SeO z ) and oxygen (from water)-evolving eletrocatalysts (RuS 2 , RuO 2 ), which permit electron transfer via ruthenium d-states, was studied using electrochemical techniques and differential electrochemical mass spectroscopy (DEMS). In contrast to platinum, which is depolarised by methanol, ruthenium compounds show a high reactivity with water species and an extremely low reactivity with methanol. We conclude that the ruthenium-centred coordination chemical reactivity with water channels electrochemical currents, thus producing kinetic selectivity. The reason for the higher reactivity with water of Ru d-states as compared to platinum is seen in the higher density of d-states near the Fermi level as shown by this comparative study.

Composite layers consisting of a polyaniline (PANI) matrix and a molybdenum-doped ruthenium selenide (MRS) dispersed phase have been tested as cathodes for O2 reduction in 0.5 M H2SO4. The investigation, carried out on rotating disc electrodes using steady-state techniques, shows that a 4-electron reduction of O2 is efficiently carried out on PANI+MRS composites. The onset potential is close to 0.5 V (SCE) and a current plateau is observed at E

We report on a photoelectrochemical cell based on polymers (electrolyte and sensitizer) and TiO 2 . Poly(epichlorohydrin-co-ethylene oxide) filled with NaI/I 2 was used as electrolyte and poly( o -methoxy aniline) doped with p -toluenesulfonic (PoAni-TSA) as dye. The short-circuit current and open-circuit voltage obtained with illumination at 120 mW cm −2 are 12.2 μA cm −2 and 0.048 V, respectively, indicating that the ionic conductive elastomer is appropriated for assembling a totally solid device. The monochromatic photon-to-current conversion efficiency decreases from 1.3% to 0.1%, from 410 to 600 nm, respectively, showing that the conducting polymer acts as a dye for TiO 2 , injecting electrons into its conduction band.

The photoelectrochemical behaviour of the oxygen evolving n-RuS 2 ∣ H 2 SO 4 interface was investigated with the help of the scanning microscope for semiconductor characterization. Electrolyte electroreflectance and photovoltage digital images were obtained as a function of the pretreatment of the RuS 2 surface (polishing and electrochemical etching). Polishing gives rise to an inhomogeneous, scarcely photoactive surface, while electrochemical etching destroys the damaged overlayer generated by polishing, leaving an inhomogeneous, highly photoactive surface in contact with the electrolyte. In general, more photoactive zones are characterized by a higher electrolyte electroreflectance signal (EER-s) generated at the interfacial hydroxide layer, and a smaller signal coming from the space charge layer. According to the observed influence of the donor concentration on the EER-s signal amplitude, the contrast observed in the EER-s image was attributed to lateral heterogeneities in the donor concentration. The difficulty of modulating the electric field in the hydroxide layer at relatively high frequencies was attributed to the low relaxation time constant of surface states involved in the EER-s signal. The fact that at low light modulation frequencies those zones with the highest EER-s amplitude also show the highest photovoltage indicates that the photovoltage intensity depends on the time constant.

The electrochemical reduction of carbon dioxide at copper in a hydrogen carbonate electrolyte saturated with CO{sub 2} was investigated using differential electrochemical mass spectroscopy and improved experimental and data processing techniques. The poisoning effects were investigated and it is shown that the deactivation of the copper cathode could be decreased by application of anodic pulses to the cathode and/or by addition of Cu{sup 2+} ions into the electrolyte. A soluble CO{sub 2} reduction product of yet unknown structure with a very low vapor pressure was found in the electrolyte. The accumulation of this compound led to a remarkable decrease of the activity of copper electrodes. It is confirmed that methane and ethene are the main reduction products on the copper cathode. A new product which gave a mass signal of m/e = 31 was detected. The activity of methane and ethene production and the stability of the copper electrode are influenced by the nature of the alkali ion in the hydrogen carbonate electrolyte. The course of deactivation as a function of the nature of the alkali ion as well as impedance measurements give information about the mechanism of the electrochemical CO{sub 2}-reduction at copper cathodes. 23 refs., 8 figs.

The photo-induced anodic STM currents measured with water photo-oxidizing RuS 2 single crystals (100) were found to be strongly dependent on the relative H 2 O humidity and thus on the presence of adsorbed water molecules. Since humidity-dependent currents and photocurrents were not found with highly oriented pyrolithic graphite (HOPG) and have not been reported for other semiconductors, the phenomenon seems to be related to the semiconductor's ability to photoreact with water. This hypothesis was confirmed by verifying a similar effect with (oxygen evolving) TiO 2 . The conclusion is reached that adsorbed water species, which capture photogenerated holes from the semiconductor, are acting as efficient traps for electrons provided by the tunneling tip. The surface states involved can be detected by STM spectroscopy and their peaks estimated to be situated approximately 0.5 V above the valence band edge. Their concentration can be reversibly controlled by the degree of humidity. The described phenomenon is of interest for the understanding of STM currents and may additionally provide a new experimental approach to interfaces which are catalytic for water oxidation.