Electrooxidation of Methanol on Carbon Supported Pt-Ru Nanocatalysts Prepared by Ethanol Reduction Method (original) (raw)
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Electrochimica Acta, 2006
The methods developed and described in paper-part I are employed to prepare nanometer size Pt-Ru particles on a Vulcan ® XC72R substrate with controlled metal loading. Transmission Electron Microscopy (TEM) confirmed uniform particles size (average diameter 2 nm) and homogeneous dispersion of the particles over the substrate. Energy Dispersive X-ray absorption (EDX) analysis confirmed the compositional homogeneity. The catalytic activity of these supported nanoparticles with regard to methanol electrooxidation is investigated using cyclic voltammetry (CV), chronoamperometry (CA) and CO-stripping voltammetry techniques at temperatures between 25 and 60 • C. Such investigation concerns supported catalysts prepared with ca. 10 and 18 wt.% overall metal loading (Pt + Ru) onto the Vulcan ® XC72R substrate. Comparative testing of our catalysts and a commercial Pt-Ru/Vulcan reveals markedly superior activity for our catalysts. In fact, we observe for the latter a five-fold increase of the oxidation current as compared to a commercial Pt-Ru/Vulcan with equal metal loading. One of the reasons for the greater activity is found to be the very high dispersion of the metals over the substrate, i.e. the large surface area of the active phase. Other reasons are plausibly ascribable to the varied Pt/Ru composition and/or reduced presence of contaminants at the catalyst surface. (V. Tricoli). with respect to state of the art nanocatalysts based on binary Pt-Ru alloy.
Carbon supported Pt, Ru and Mo catalysts for methanol electrooxidation
International Journal of Hydrogen Energy, 2012
Methanol electrochemical oxidation on carbon supported electrocatalysts was studied on platinum, ruthenium and molybdenum as active phases. Pt/C, PtRu/C, PtMo/C and PtRuMo/ C catalysts were synthesized with 20% metal loading by chemical reduction. These catalysts were physical and electrochemical characterized by Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), cyclic voltammetry and CO anodic stripping voltammetry. Chronoamperometry was used to analyze and compare the catalysts activities after an electrochemical surface activation. The platinum active area was determined by anodic stripping CO voltammetry, exhibiting a different electrochemical profile for each catalyst. PtMo/C CO oxidation profile exhibited two peaks and clearly depicted the lowest onset potential value. The electrochemical methods revealed an enhanced performance of PtMo/C catalysts for methanol oxidation in comparison with the others catalysts studied. After the integration of chronoamperometric plots over 20 min in methanol acid media at 450 mV, PtMo/
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.
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.
Methanol electro-oxidation on Pt-Ru-P/C and Pt-Ru-P/MWCNT in acidic medium
Pt-Ru-P was prepared by the chemical reduction method using sodium hypophoshite as a reducing agent on Vulcan XC 72 and multi-walled carbon nano-tubes (MWCNTs). Sodium citrate was added as the stabilizer during electro-catalyst preparation. The electro-catalytic activity towards methanol oxidation in acidic medium was studied by cyclic voltammetry and linear sweep voltammetry. Pt-Ru-P/MWCNT showed excellent activity than Pt-Ru-P/C. This may be attributed to the effectiveness of the MWCNTs acting as good catalyst support material. The particle size of both electro-catalysts obtained with the transmission scanning electron microscopy (TEM) ranged between 2-4nm desirable for the direct methanol fuel cells.
Applied Catalysis B: Environmental, 2008
In this study, a carbon nanotube-supported PtRu electrocatalyst (PtRuCNT) was prepared, characterized and investigated for methanol electro-oxidation by catalytic activity enhancement using an electrochemical treatment. From XPS analyses, the as-prepared catalyst was found to mainly composed of Pt(0)/Pt(II) states for the Pt element and Ru(0)/Ru(IV) states for the Ru element. When the electrocatalyst was subjected to an enhancement treatment, the Ru(IV) state increased substantially from 29.50% to 44.11%. Both CO-stripping experiments and open-circuit cell voltage measurements indicated that the treated PtRuCNT has given rise to an improved performance on methanol electrooxidation caused mainly by the increase of the Ru(IV) state in this particular case. The single-cell test also revealed that a direct methanol fuel cell (DMFC) can be put into its full operation in a short time. A direct application of this finding is to significantly shorten the activation time of a new DMFC stack. However, the electrochemically treated PtRuCNT catalyst still needs a continuous enhancement mechanism to sustain its enhanced activity. A promotional model is proposed to explain the phenomenon observed and a remedial approach is also suggested to solve the problem for practical applications. ß
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.
Electrochimica Acta, 2006
Two types of Pt/Ru electrocatalysts, which have different structural characteristics, were prepared with different synthetic routes. That is, Pt/Ru electrocatalysts were synthesized by the coreduction and successive deposition methods, respectively. The structural and catalytic properties of Pt/Ru electrocatalysts were characterized by XRD, TEM, voltammetry and chronoamperometry. From the XRD analysis, coreduced and successively deposited Pt/Ru electrocatalysts had an alloyed structure.
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.
RuxTi1−xO2 as the support for Pt nanoparticles: Electrocatalysis of methanol oxidation
2015
Two binary Ru-Ti oxides, Ru 0.1 Ti 0.9 O 2 and Ru 0.7 Ti 0.3 O 2 , were synthesized by the sol-gel method and used as an electrocatalyst support. The system was characterized by XRD, EDS, TEM and cyclic voltammetry. The Ru 0.1 Ti 0.9 O 2 and Ru 0.7 Ti 0.3 O 2 consist of two phases of anatase and rutile structure. An average size of the Pt nanoparticles supported on them is ∼3.5 nm and they are deposited on both Ru and Ti-rich domains. The supports exhibited good conductivity and electrochemical stability. The onset potentials of CO ads oxidation on the synthesized catalysts and on commercial PtRu/C are similar to each other and lower than that on Pt/C. This suggests that in Pt/Ru 0.1 Ti 0.9 O 2 and Pt/Ru 0.7 Ti 0.3 O 2 the Pt nanoparticles are in close contact with Ru atoms from the support, which enables the bifunctional mechanism. The activity and stability of the catalysts for methanol oxidation were examined under potentiodynamic and potentiostatic conditions. While the activity of Pt/Ru 0.1 Ti 0.9 O 2 is unsatisfactory, the performance of Pt/Ru 0.7 Ti 0.3 O 2 is comparable to PtRu/C. For example, in the potentiostatic test at 0.5 V the activities after 25 min are 0.035 mA cm −2 and 0.022 mA cm −2 for Pt/Ru 0.7 Ti 0.3 O 2 and PtRu/C, respectively. In potentiodynamic test the activities at 0.5 V after 250 cycles are around 0.02 mA cm −2 for both catalysts. (S.Lj. Gojković). metal oxides as the catalyst support . Among the oxides, TiO 2 distinguishes itself due to high stability in acid media . In the past several years TiO 2 has been successfully tested as a Pt catalyst support as a pure mesoporous oxide , doped by Nb or as binary oxides such as Ti 0.7 W 0.3 O 2 [16], Ru x Ti 1−x O 2 [17], hydrous and anhydrous TiO 2 -RuO 2 [18] and Ti 0.7 Ru 0.3 O 2 . The addition of foreign atoms into the TiO 2 crystal lattice increases the conductivity of otherwise low-conducting TiO 2 but can also promote the catalyst activity, i.e., transform a catalyst support to a co-catalyst.