The function of ruthenium oxides in Pt-Ru catalysts for methanol electro-oxidation at low temperatures (original) (raw)
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Journal of Power Sources, 1999
The electrocatalytic activities of different ternary platinum-ruthenium Pt-Ru-metal-oxides have been investigated in half cell experiments, by cyclic voltammetry and stationary current-voltage measurements. The results are compared to binary Pt-Ru alloy Ž catalysts. The materials have been prepared using a modification of the Adams method. X-ray analytical methods X-ray diffraction,. XRD; energy dispersive X-ray spectroscopy, EDX; X-ray photoelectron spectroscopy, XPS have been used to characterize the composition, particle size and crystallinity of the catalysts, and their surface areas have been determined by the Brunauer-Emmet-Teller Ž. BET method. The catalyst materials consist of varying amounts of metal oxides and Pt-Ru alloy particles. BET surface areas of 80-120 m 2 rg have been measured corresponding to particle diameters of the order of 3-5 nm. The results of electrochemical measurements Ž. demonstrate that introduction of a transition metal oxide WO , MoO , VO leads to an improvement of the catalytic activity towards x x x methanol oxidation.
Catalysis Today, 2009
A relationship between the chemical state of Ru on bimetallic PtRu bulk samples and their performance in both CO and methanol electrooxidation has been established. The nature of the Ru species in the bimetallic samples has been scrutinized by means of XPS, XRD and TPR. The following Ru species were detected; reduced ruthenium (Ru0), anhydrous RuO2 and hydrous Ru oxide. The actual nature of the latter species consists of two amorphous oxides of general formula RuO2·xH2O and RuOx(OH)y as determined from the XPS analysis. Irrespective of the Ru phases, all PtRu catalyst studied display a similar CO oxidation pattern. However, methanol electrooxidation was found dependent on the Ru phases. Thus, catalysts containing Ru0 are more active in the methanol oxidation reaction, at least during the early stages of the reaction. More stable catalyst are obtained if amorphous Ru oxide phases are the predominant ones.
Investigation of Pt–Ru nanoparticle catalysts for low temperature methanol electro-oxidation
Journal of Solid State Electrochemistry, 2007
Pt-Ru nanoparticle-based methanol electro-oxidation catalysts with high concentration of metallic phase on carbon black have been synthesised by a low-temperature colloidal preparation route. Amorphous Pt-Ru oxide nanoparticles were deposited on carbon and subsequently reduced in hydrogen stream at different temperatures to obtain crystalline phases with tailored particle size. The electro-catalytic activity for methanol oxidation was investigated in half-cell from 30 to 60°C. The results were interpreted in terms of particle size, crystallographic structure, degree of alloying and carbon monoxide adsorption properties. The best performance was achieved for the catalyst with intermediate particle size in the investigated range. Furthermore, it is observed that the optimal properties for these catalysts depend on the operating temperature.
Journal of Power Sources - J POWER SOURCES, 2008
The effect of variations in the composition for ternary catalysts of the type Ptx(Ru–Ir)1−x/C on the methanol oxidation reaction in acid media for x values of 0.25, 0.50 and 0.75 is reported. The catalysts were prepared by the sol–gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption spectroscopy (AAS) and energy dispersive X-ray (EDX) analyses. The nanometric character (2.8–3.2nm) of the sol–gel deposits was demonstrated by XRD and TEM while EDX and AAS analyses showed that the metallic ratio in the compounds was very near to the expected one. Cyclic voltammograms for methanol oxidation revealed that the reaction onset occur at less positive potentials in all the ternary catalysts tested here when compared to a Pt0.75–Ru0.25/C (E-Tek) commercial composite. Steady-state polarization experiments (Tafel plots) showed that the Pt0.25(Ru–Ir)0.75/C catalyst is the more active one for methanol oxidation as revealed by the shift ...
IrO2 as a promoter of Pt–Ru for methanol electro-oxidation
Physical Chemistry Chemical Physics, 2014
A multifunctional catalyst may represent a valid route to enhance methanol electro-oxidation. Ternary catalysts based on Pt modified with both Ru and Ir oxides show better performance for methanol electro-oxidation than bi-metallic Pt-Ru catalysts.
Different carbon-supported Pt-Mo and Pt-Ru materials were synthesized and a systematic study was carried out in order to evaluate their catalytic activity towards methanol oxidation. Direct current methods were applied in sulfuric acid and methanolcontaining electrolytes, in order to evaluate the electrochemical response of the studied electrodes. Pt-Mo catalysts reveal similar performances and, in some cases, higher than Pt-Ru materials. For both catalysts series, it was found that low loadings of the promoting metal (Ru or Mo) improve the methanol oxidation activity. Characterizations by means of transmission electron microscopy and X-Ray Diffraction allowed to measure mean particle sizes below 10 nm for all phases. The Pt-Ru catalysts consist of metallic Pt and metallic ruthenium, while in the The Pt-Mo materials platinum is present in its metallic state and MoO 3 is the predominant molybdenum species.
Pt$z.sbnd;Ru anodes for methanol electrooxidation: A ruthenium-99 M�ssbauer study
Journal of Catalysis, 1990
99Ru M6ssbauer spectra have been obtained for a series of Pt-Ru methanol oxidation anodes. For the most catalytically active sample, XPS and M6ssbauer data indicate the presence of Ru(IV) species with a small quadrupole splitting. For highly dispersed samples the M6ssbauer data indicate that the Ru is present as a mixture of rutile-phase RHO2 and a second Ru(IV) species. Comparison with electrocatalytic results suggests that the second Ru(IV) species is the active catalytic copromoter. The possible identity of this species is discussed.
Frontiers in Chemistry, 2014
Ternary Pt-Ru-Ni deposits on glassy carbon substrates, Pt-Ru(Ni)/GC, have been formed by initial electrodeposition of Ni layers onto glassy carbon electrodes, followed by their partial exchange for Pt and Ru, upon their immersion into equimolar solutions containing complex ions of the precious metals. The overall morphology and composition of the deposits has been studied by SEM microscopy and EDS spectroscopy. Continuous but nodular films have been confirmed, with a Pt ÷ Ru ÷ Ni % bulk atomic composition ratio of 37 ÷ 12 ÷ 51 (and for binary Pt-Ni control systems of 47 ÷ 53). Fine topographical details as well as film thickness have been directly recorded using AFM microscopy. The composition of the outer layers as well as the interactions of the three metals present have been studied by XPS spectroscopy and a Pt ÷ Ru ÷ Ni % surface atomic composition ratio of 61 ÷ 12 ÷ 27 (and for binary Pt-Ni control systems of 85 ÷ 15) has been found, indicating the enrichment of the outer layers in Pt; a shift of the Pt binding energy peaks to higher values was only observed in the presence of Ru and points to an electronic effect of Ru on Pt. The surface electrochemistry of the thus prepared Pt-Ru(Ni)/GC and Pt(Ni)/GC electrodes in deaerated acid solutions (studied by cyclic voltammetry) proves the existence of a shell consisting exclusively of Pt-Ru or Pt. The activity of the Pt-Ru(Ni) deposits toward methanol oxidation (studied by slow potential sweep voltammetry) is higher from that of the Pt(Ni) deposit and of pure Pt; this enhancement is attributed both to the well-known Ru synergistic effect due to the presence of its oxides but also (based on the XPS findings) to a modification effect of Pt electronic properties.
In Situ X-Ray Absorption Studies of a Pt-Ru Electrocatalyst
Journal of The Electrochemical Society, 1995
X-ray absorption studies (XAS) were done on a carbon supported Pt-Ru electrocatalyst in 1 M HC1Q. Results at the Pt L3 and L~ edges confirmed that the Pt was alloyed with Ru and that the Ru content was about 25 atomic percent. There was a large excess of unalloyed Ru, with only about 10% of the Ru alloyed with the P t. The Pt XAS indicated that the R u increased the Pt d band vacancies and decreased the Pt-Pt bond distances from 2.77 A to values between 2.71 and 2.73 A. The bifunctional mechanism for methanol oxidation on Pt-Ru electrocatalysts needs to be modified to account for the effect of these electronic changes on the adsorption of H and CO residues from methanol decomposition. There are significant changes in the Pt XAS in going from the reversible hydrogen potential to 0.24 V. This may be due to the onset of the formation of RuOH species on the alloy. Further fine tuning of the electronic structure and the electrocatalysis may be possible through the use of ternary alloys.