RuxTi1−xO2 as the support for Pt nanoparticles: Electrocatalysis of methanol oxidation (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.
A single-Pt-atom-on-Ru-nanoparticle electrocatalyst for CO-resilient methanol oxidation
Nature Catalysis
Single Pt atom catalysts on non-active carbon supports have been key targets for electrochemical reactions because the high exposure of active Pt leads to record-high activities. PtRu alloy catalysts are the most active for the methanol oxidation reaction (MOR) as the Ru atoms decrease CO poisoning of the active Pt. To combine the exceptional activity of single atom Pt catalysts with the bene ts of an active Ru support we must overcome the synthetic challenge of forming single Pt atoms on noble metal nanoparticles. We have developed a concept to grow and spreads Pt islands on faceted Ru branched nanoparticles to make single Pt atom on Ru catalysts. By following the spreading process with in situ TEM, we show that the formation of single atoms is thermodynamically driven by the formation of strong Pt-Ru bonds and a lowering of surface area. The single Pt atom on Ru catalysts successfully limit CO poisoning during MOR to produce record current density and mass activity over time. Main The methanol oxidation reaction (MOR) is the limiting reaction for the direct methanol fuel cell because CO-poisoning prevents high current densities over time 1. CO poisoning is one of the most signi cant issues limiting the long-term use of catalysts for reactions such as MOR, ethanol oxidation and formic acid oxidation, where CO intermediates form 2,3. Pt is the most active MOR catalyst, however CO ads intermediates bind strongly to poison the Pt sites, thus preventing access of methanol to these active sites 4. CO poisoning occurs by the formation of CO ads bound on top of three Pt atoms in a triangular arrangement 5,6. As a consequence, single atom catalysts are a promising target to overcome CO poisoning if Pt atoms can be dispersed on a support without formation of these triangular arrangements of Pt atoms.
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.
A Pt/Ru nanoparticulate system to study the bifunctional mechanism of electrocatalysis
Journal of Electroanalytical Chemistry, 2005
The reduced sensitivity of Pt-Ru alloys towards CO poisoning results from two effects: the ligand effect and the bifunctional mechanism. Although these have been known for many years, their applicability to nanoparticle electrocatalysts remains unclear. Furthermore, it is not known if the formation of a Pt-Ru alloy is necessary to improve the catalyst tolerance to CO or if the presence of Ru in immediate proximity to Pt nanoparticles (non-alloy systems) brings about a significant change. A new approach to the detailed investigation of the underlying mechanisms is presented by using mixtures of surfactant-stabilised Pt and Ru nanoparticles attached to an oxidised glassy carbon electrode. After CO activation the particle-decorated carbon surfaces become active for the methanol oxidation reaction as a result of the removal of part or all of the surfactant shell. However, despite this activation the onset potential and the peak maximum for both CO and methanol oxidation remain unchanged, independently of the mixture composition, whereas the maximum current decreases with increasing Ru content. Scanning transmission electron microscopy (STEM) investigations confirmed the close proximity between Pt and Ru nanoparticles on the electrode surface. However, no enhancement of activity was observed which may be due to the presence of small amounts of capping ligands preventing direct metal contact between the Ru and Pt nanoparticles.
Revue Roumaine de Chimie, 2020
A catalytic coating composed of a mixture of RuO 2 and Pt nanocrystals was prepared by a thermal procedure on a titanium substrate and used for the electrochemical oxidation of methanol. The adsorption of the intermediate CO, formed by methanol oxidation on Pt nanocrystals, depended on potential and the coating composition. An increase in the RuO 2 content decreased the rate of methanol dehydrogenation and increased the rate of oxidation of the strongly bound intermediate CO ad. This caused a decrease in the maximum coverage of Pt nanocrystals with CO ad and a shift of the rapid linear drop in CO ad coverage to more negative potentials.
Single Pt atoms on Ru nanoparticles for CO-resistant methanol oxidation reaction electrocatalysis
2021
Single Pt atom catalysts on non-active carbon supports have been key targets for electrochemical reactions because the high exposure of active Pt leads to record-high activities. PtRu alloy catalysts are the most active for the methanol oxidation reaction (MOR) as the Ru atoms decrease CO poisoning of the active Pt. To combine the exceptional activity of single atom Pt catalysts with the benefits of an active Ru support we must overcome the synthetic challenge of forming single Pt atoms on noble metal nanoparticles. We have developed a concept to grow and spreads Pt islands on faceted Ru branched nanoparticles to make single Pt atom on Ru catalysts. By following the spreading process with in situ TEM, we show that the formation of single atoms is thermodynamically driven by the formation of strong Pt-Ru bonds and a lowering of surface area. The single Pt atom on Ru catalysts successfully limit CO poisoning during MOR to produce record current density and mass activity over time.
Journal of Solid State Electrochemistry, 2003
The electrocatalytic activities of different binary Pt-Ru(ox) catalysts have been investigated in halfcell experiments by cyclic voltammetry and stationary current-potential measurements. The materials have been prepared using a modification of the Adams method. X-ray analytical methods (X-ray diffraction, XRD, and energy dispersive X-ray spectroscopy, EDX) as well as thermogravimetric analysis (TGA) have been used to characterize the composition and the catalysts' content of the crystalline phases, and their surface areas have been determined by the BET method. It is found that the composition of the catalyst is strongly influenced by the synthesis temperature, which is varied between 400 and 600°C. In contrast, the particle size of the metallic phases of the catalysts is not significantly affected for synthesis temperatures below 600°C, as investigated by transmission electron microscopy. Synthesis temperatures of ‡500°C favor the formation of crystalline RuO 2 phases, whereas at synthesis temperatures below 500°C the presence of metallic alloy and of hydrous oxides was derived by the combined XRD and EDX measurements. The stationary current-potential curves show a correlation with the different synthesis temperatures. It can be concluded that both the presence of an alloyed metallic Pt-Ru phase as well as the presence of amorphous hydrated Ru oxides are favorable for the electrocatalytic oxidation of methanol. Keywords Anode catalysts AE Electro-oxidation AE Hydrous ruthenium oxides AE Methanol