CO Coverage/Oxidation Correlated with PtRu Electrocatalyst Particle Morphology in 0.3 M Methanol by In Situ XAS (original) (raw)
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Journal of Electroanalytical Chemistry, 1998
In situ X-ray absorption studies were done in 1 M HClO , with and without 0.3 M MeOH, on several well-defined carbon-supported Pt 4e lectrocatalysts with particle sizes in the range of 25 to 90 A. Data were obtained at several potentials in the range of 0.0 to 1.14 V vs. RHE. The results show that as the particle size is reduced below 50 A, the strength of adsorption of H, OH and C , moieties such as CO is 1 increased. The strong adsorption of OH explains the reduced specific activity for oxygen reduction on small particles. The reduced activity for methanol oxidation on the small particles is due to a combination of the increased strength of adsorption of both CO and OH. The strong adsorption of H at negative potentials on small Pt particles is sufficient to induce reconstruction and morphological changes in the Pt particles. Both XANES and EXAFS data on a 53 A particle at 0.84 V indicate that formation of PtOH is the rate determining step in the oxidation of methanol. All these affects are due to an increase in the number of Pt sites with low coordination on the small particles.
Journal of The Electrochemical Society, 2005
An analysis of X-ray absorption spectroscopy ͑XAS͒ data ͓X-ray absorption near-edge structure ͑XANES͒ and extended X-ray absorption fine structure ͑EXAFS͔͒ at the Pt L 3 edge for Pt-M bimetallic materials ͑M = Co, Cr, Ni, Fe͒ and at the Co K edge for Pt-Co is reported for Pt-M/C electrodes in HClO 4 at different potentials. The XANES data are analyzed using the ⌬ method, which utilizes the spectrum at some potential V minus that at 0.54 V reversible hydrogen electrode ͑RHE͒ representing a reference spectrum. These ⌬ data provide direct spectroscopic evidence for the inhibition of OH chemisorption on the cluster surface in the Pt-M. This OH chemisorption, decreasing in the direction Pt Ͼ Pt-Ni Ͼ Pt-Co Ͼ Pt-Fe Ͼ Pt-Cr, is directly correlated with the previously reported fuel cell performance ͑electrocatalytic activities͒ of these bimetallics, confirming the role of OH poisoning of Pt sites in fuel cells. EXAFS analysis shows that the prepared clusters studied have different morphologies, the Pt-Ni and Pt-Co clusters were more homogeneous with M atoms at the surface, while the Pt-Fe and Pt-Cr clusters had a "Pt skin." The cluster morphology determines which previously proposed OH inhibition mechanism dominates, the electronic mechanism in the presence of the Pt skin, or lateral interactions when M-OH groups exist on the surface.
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.
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.
Fuel, 2023
In this work, we report PtRu alloy system supported on Co 3 O 4-activated carbon (Co 3 O 4-C) prepared by direct reduction of H 2 PtCl 6 and RuCl 3 solutions as a highly active and durable electrocatalyst for methanol oxidation reaction. The electrochemical activity of the electrocatalysts was evaluated using electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), cyclic voltammetry (CV), and chronoamperometry (CA). The formation of PtRu alloy on the Co 3 O 4-C matrix, as well as their electronic interactions, is confirmed by employing X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. The electrocatalysts showed distinct electrocatalytic activity in alkaline medium, depending on whether the catalysts contained PtRu alloy and whether they were supported on the hybrid Co 3 O 4-C, proving their unique contributions to the electrocatalytic reaction. Benefiting from the strong metal-support interaction (SMSI) and electronic interaction between Pt and Ru, the PtRu/Co 3 O 4-C displayed a highly efficient electrocatalytic performance with a mass activity of 6709 mAmg − 1 Pt , a substantial improvement compared to the commercial Pt-based benchmark catalyst, which achieved only 212 mAmg − 1 Pt. Furthermore, the PtRu/Co 3 O 4-C showed excellent stability after 10 000 s, high durability after 500 cycles retaining 94 % of current density, and higher tolerance for CO. This enhanced catalytic performance can be attributed to the small nanoparticle sizes, high dispersion, large ECSA of 102.1 m 2 /g, and the synergy resulting from electronic coupling interactions.
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.
Frontiers in Energy, 2017
A method is described to determine the internal structure of electrocatalyst nanoparticles by in situ X-ray absorption spectroscopy (XAS). The nondestructive spectroscopic technique typically utilizing synchrotron radiation as the source measures changes in the X-ray absorption coefficient as a function of energy. The bulk technique has found its use for materials characterization in all scientific areas, including nanomaterials. The analysis of the internal structure of nanoparticles reveals interatomic distances and coordination numbers for each element, and their values and mutual relations indicate whether the elements form a homogeneous or heterogeneous mixture. The core-shell heterogeneous structure in which certain elements are predominantly located in the core, and others form the encapsulating shell is of particular importance in catalysis and electrocatalysis because it may reduce the amount of precious metals in nanoparticles by replacing the atoms in the core of nanoparticles with more abundant and cheaper alternatives. The examples of nanoparticle structures designed in the laboratory and the approach to model efficient catalysts through systematic analysis of XAS data in electrochemical systems consisting of two and three metals are also demonstrated.
Physical Chemistry Chemical Physics, 2007
PtRu (1 : 1) catalysts supported on low surface area carbon of the Sibunit family (S BET = 72 m 2 g À1) with a metal percentage ranging from 5 to 60% are prepared and tested in a CO monolayer and for methanol oxidation in H 2 SO 4 electrolyte. At low metal percentage small (o2 nm) alloy nanoparticles, uniformly distributed on the carbon surface, are formed. As the amount of metal per unit surface area of carbon increases, particles start coalescing and form first quasi two-dimensional, and then three-dimensional metal nanostructures. This results in a strong enhancement of specific catalytic activity in methanol oxidation and a decrease of the overpotential for CO monolayer oxidation. It is suggested that intergrain boundaries connecting crystalline domains in nanostructured PtRu catalysts produced at high metal-on-carbon loadings provide active sites for electrocatalytic processes.
The Journal of Physical Chemistry C, 2009
In this work, methanol oxidation was studied on carbon-supported Pt-Ru nanocatalysts, where the amounts of alloyed and oxide phases were modified by heat treatments in different atmospheres. Because particle growth was avoided using mild temperature conditions, the study reported here was conducted in the absence of particle size effects. All samples were characterized by X-ray diffraction and transmission electron microscopy. The general electrochemical behavior of the nanocatalysts was evaluated by cyclic voltammetry, and the electrocatalytic activity for the oxidation of methanol was studied in 0.5 mol L -1 methanol acid solutions by linear potential sweeps and chronoamperometry. The results obtained clearly evidence that the presence of oxide species is necessary to enhance the electrocatalytic activity for methanol oxidation. Oxidation of adsorbed CO was also measured. Both reactions, methanol and adsorbed CO oxidation, were found to be very sensitive to the surface changes produced by the heat treatments. Interestingly, the best catalyst for methanol oxidation was not found to be the most efficient for the oxidation of adsorbed CO. Electrocatalytic activities correlate well with oxidation states and electronic properties analyzed by X-ray photoelectron spectroscopy and in situ dispersive X-ray absorption spectroscopy.