Carbon-supported PtRu Research Articles

On the influence of the metal loading on the structure of carbon-supported PtRu catalysts and their electrocatalytic activities in CO and methanol electrooxidation

PtRu (1:1) catalysts supported on low surface area carbon of the Sibunit family (S(BET) = 72 m(2) g(-1)) 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 (<2 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.

06/01906 Preparation of carbon-supported PtRu nanoparticles for direct methanol fuel cell applications — a comparative study: Deivaraj, T. C. and Lee, J. Y. Journal of Power Sources, 2005, 142, (1–2), 43–49

In direct methanol fuel cells (DMFCs), the optimum characteristics of ion-exchange membranes are investigated at high concentrations of methanol feed up to 7 M by modifying the diffusion coefficient and the ionic conductivity of the polyelectrolyte material. A Nafion membrane is modified by the incorporation of layered double hydroxide (LDH) nanoplatelets with different Mg2+:Al3+ ratios. When the feed concentration of methanol is lower than 3 M, the DMFC is controlled by the ionic conductivity of the polyelectrolyte membrane because methanol cross-over is not relatively significant. When the feed concentration is high, however, the diffusion coefficient of methanol is the key factor that determines the performance of the fuel cell. This is due to a high concentration gradient of methanol across the polyelectrolyte membrane. The open-circuit voltage is increased by the decreased diffusion coefficient in LDH/Nafion nanocomposite membranes at methanol feed concentrations up to 7 M; apparently because methanol cross-over is suppressed by the incorporation of LDH. The maximum power density of the DMFC is determined by the two competing transport processes of ion conduction and methanol diffusion, especially at a relatively high methanol concentration, that can provide optimum operating conditions in the membrane.

Synthesis and Structure−Activity Relationship Exploration of Carbon-Supported PtRuNi Nanocomposite as a CO-Tolerant Electrocatalyst for Proton Exchange Membrane Fuel Cells

A carbon-supported PtRuNi nanocomposite is synthesized via a microwave-irradiated polyol plus annealing synthesis strategy. The catalyst is characterized by transmission electron microscopy, powder X-ray diffraction, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. The data are discussed with respect to those for the carbon-supported PtRu nanocomposite prepared following the same way. The characterizations show that the inclusion of Ni in the PtRu system has only a small effect on the particle size, the structure, and the compositional homogeneity. CO-stripping voltammetry and measurements on the single proton exchange membrane fuel cells show that the PtRuNi/C catalyst has an improved activity for CO(ads) electro-oxidation. An accelerated durability test on the catalyst exhibits insignificant loss of activity in acidic media. On the basis of the exploration of the structure-activity relationship, a mechanism for the improved performance of the catalyst is proposed. It is suggested that the improved CO-tolerant performance of the PtRuNi/C nanocomposite should be related to the hydrogen spillover on the catalyst surface, the enhanced oxidation of CO(ads) by nickel hydroxides, and the high proton and electronic conductivity of the hydroxides. The nickel hydroxide passivated surface and/or anchoring of metallic nickel in the platinum lattice may contribute to the durability of the catalyst in acid solution.

Probing the Formation Mechanism and Chemical States of Carbon-Supported Pt−Ru Nanoparticles by in Situ X-ray Absorption Spectroscopy

The understanding of the formation mechanism of nanoparticles is essential for the successful particle design and scaling-up process. This paper reports findings of an X-ray absorption spectroscopy (XAS) investigation, comprised of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions, to understand the mechanism of the carbon-supported Pt-Ru nanoparticles (NPs) formation process. We have utilized Watanabe's colloidal reduction method to synthesize Pt-Ru/C NPs. We slightly modified the Watanabe method by introducing a mixing and heat treatment step of Pt and Ru oxidic species at 100 degrees C for 8 h with a view to enhance the mixing efficiency of the precursor species, thereby one can achieve improved homogeneity and atomic distribution in the resultant Pt-Ru/C NPs. During the reduction process, in situ XAS measurements allowed us to follow the evolution of Pt and Ru environments and their chemical states. The Pt LIII-edge XAS indicates that when H2PtCl6 is treated with NaHSO3, the platinum compound is found to be reduced to a Pt(II) form corresponding to the anionic complex [Pt(SO3)4]6-. Further oxidation of this anionic complex with hydrogen peroxide forms dispersed [Pt(OH)6]2- species. Analysis of Ru K-edge XAS results confirms the reduction of RuIIICl3 to [RuII(OH)4]2- species upon addition of NaHSO3. Addition of hydrogen peroxide to [RuII(OH)4]2- causes dehydrogenation and forms RuOx species. Mixing of [Pt(OH)6]2- and RuOx species and heat treatment at 100 degrees C for 8 h produced a colloidal sol containing both Pt and Ru metallic as well as ionic contributions. The reduction of this colloidal mixture at 300 degrees C in hydrogen atmosphere for 2 h forms Pt-Ru nanoparticles as indicated by the presence of Pt and Ru atoms in the first coordination shell. Determination of the alloying extent or atomic distribution of Pt and Ru atoms in the resulting Pt-Ru/C NPs reveals that the alloying extent of Ru (JRu) is greater than that of the alloying extent of Pt (JPt). The XAS results support the Pt-rich core and Ru-rich shell structure with a considerable amount of segregation in the Pt region and with less segregation in the Ru region for the obtained Pt-Ru/C NPs.

Multiwalled Carbon Nanotube Supported PtRu for the Anode of Direct Methanol Fuel Cells

The activity of the methanol oxidation reaction of a multiwalled carbon nanotube (MWCNT)-supported PtRu catalyst was investigated and compared with the Vulcan XC-72 carbon-supported catalyst. The PtRu nanoparticles with 1:1 and 7:3 atomic ratios (with similar PtRu loadings and morphological structures) were deposited both on the MWCNTs and on the carbon. Cyclicvoltammetry results demonstrated that the MWCNT-supported PtRu catalyst exhibited a higher mass activity (mA mg(-1) of PtRu) for the methanol oxidation reaction than the carbon-supported PtRu under the condition that both catalysts possess more or less the same PtRu loadings, particle sizes, dispersions, and electrochemical surface area. The direct methanol fuel cell performance test data showed that MWCNT-supported PtRu catalysts yielded about 35-39% higher power densities than the carbon-supported PtRu.

Preparation of carbon-supported PtRu nanoparticles for direct methanol fuel cell applications – a comparative study

Carbon-supported PtRu nanoparticles were prepared by different methods that involve the simultaneous chemical reduction of H 2PtCl 6 and RuCl 3 by NaBH 4 at room temperature ( PtRu-1), by ethanol under reflux ( PtRu-2), and by the thermal decomposition of a single-source molecular precursor [(bipy) 3Ru] (PtCl 6) ( PtRu-3). Transmission electron microscopy (TEM) examinations show that the mean diameter of the PtRu nanoparticles is lowest for PtRu-1 followed by PtRu-2 and PtRu-3. Measurements of electrocatalytic properties, however, reveal a different trend, namely: PtRu-3 > PtRu-1 > PtRu-2. This is attributed to the formation of a more homogenous alloy nanoparticle system from the thermolysis of the single-source molecular precursor. All three catalysts are more active than commercially available E-TEK (20 wt.%) Pt catalyst. PtRu-3 also displays the highest tolerance to carbon monoxide. Heat treatment of PtRu-1 and PtRu-2 only marginally affects their electrocatalytic performance, whereas the co-reduction of H 2PtCl 6 and RuCl 3 under alkaline conditions has more adverse outcomes.

A study of PtRuO 2 catalysts thermally formed on titanium mesh for methanol oxidation

Platinum-based catalysts, for the electro-oxidation of methanol, have been made by thermal decomposition of chloride precursors onto titanium mesh. The catalysed electrodes were successfully operated in acidic methanol electrolytes. Electrochemical characterisation has been carried out using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic polarisations. A complete analysis of the electrochemical results showed that the preliminary performance of the catalysed titanium mesh was comparable to that achieved with carbon-supported PtRu catalysts. The catalysts formed on titanium mesh by thermal decomposition also exhibited dimensional stability. Catalysed titanium mesh therefore appears to be a promising alternative to carbon-supported catalysts for certain fuel cell applications.

Size-selected synthesis of PtRu nano-catalysts: reaction and size control mechanism.

A rapid synthesis method for the preparation of PtRu colloids and their subsequent deposition on high surface area carbons is presented. The reaction mechanism is shown to involve the oxidation of the solvent, ethylene glycol, to mainly glycolic acid or, depending on the pH, its anion, glycolate, while the Pt(+IV) and Ru(+III) precursor salts are reduced. Glycolate acts as a stabilizer for the PtRu colloids and the glycolate concentration, and hence the size of the resulting noble metal colloids is controlled via the pH of the synthesis solution. Carbon-supported PtRu catalysts of controlled size can be prepared within the range of 0.7-4 nm. Slow scan X-ray diffraction and high-resolution transmission electron microscopy show the PtRu catalysts to be crystalline. The Ru is partly dissolved in the face-centered cubic Pt lattice, but the catalysts also consist of a separate, hexagonal Ru phase. The PtRu catalysts appear to be of the same composition independent of the catalyst size in the range of 1.2-4 nm. Particular PtRu catalysts prepared in this work display enhanced activities for the CH(3)OH electro-oxidation reaction when compared to two commercial catalysts.

Nonalloyed Carbon-Supported PtRu Catalysts for PEMFC Applications

PtRu(1:1)/C catalysts were prepared by a process that was claimed previously to lead to nonalloyed Pt and Ru particles, using two different precursors, Ru nitrosyl nitrate and Ru chloride hydrate. Both X-ray diffraction and characterization by cyclic voltammetry point toward Pt and Ru being present as separate phases in the prepared, nonannealed catalysts. In combination with a high dispersion, this results in proton exchange membrane fuel cell (PEMFC) anode electrocatalysts. These PEMFCs have improved hydrogen oxidation activity and CO tolerance. © 2004 The Electrochemical Society. All rights reserved.

Physical and Electrochemical Characterizations of Microwave-Assisted Polyol Preparation of Carbon-Supported PtRu Nanoparticles

PtRu nanoparticles supported on Vulcan XC-72 carbon and carbon nanotubes were prepared by a microwave-assisted polyol process. The catalysts were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). The PtRu nanoparticles, which were uniformly dispersed on carbon, were 2-6 nm in diameter. All PtRu/C catalysts prepared as such displayed the characteristic diffraction peaks of a Pt face-centered cubic structure, excepting that the 2theta values were shifted to slightly higher values. XPS analysis revealed that the catalysts contained mostly Pt(0) and Ru(0), with traces of Pt(II), Pt(IV), and Ru(IV). The electro-oxidation of methanol was studied by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. It was found that both PtRu/C catalysts had high and more durable electrocatalytic activities for methanol oxidation than a comparative Pt/C catalyst. Preliminary data from a direct methanol fuel cell single stack test cell using the Vulcan-carbon-supported PtRu alloy as the anode catalyst showed high power density.

Kinetic study of methanol oxidation on carbon-supported PtRu electrocatalyst

Methanol electrooxidation was investigated on the carbon-supported PtRu electrocatalyst (1:1 atomic ratio) in acid media. X-ray diffraction measurement indicated alloying of Pt and Ru. Cyclic voltammetry of the sample reflects the amount of Ru in the catalyst and its ability to adsorb OH radicals. Tafel plots for the oxidation of 0.02–3 M methanol in the solutions containing 0.05–1 M HClO 4 and in the temperature range 27–40 °C showed reasonably well-defined linear region with the slope of about 115 mV dec −1 at the low currents, irrespective of the experimental conditions employed. Reaction order with respect to methanol was found to be 0.5. A correlation between methanol oxidation rate and pseudocapacitive current of OH adsorption on Ru sites was established. It was proposed that bifunctional mechanism is operative with the reaction between methanol residues adsorbed on Pt sites and OH radicals adsorbed on Ru sites as the rate-determining step.

Nano-composite of PtRu alloy electrocatalyst and electronically conducting polymer for use as the anode in a direct methanol fuel cell

Nano-composites comprised of PtRu alloy nanoparticles and an electronically conducting polymer for the anode electrode in direct methanol fuel cell (DMFC) were prepared. Two conducting polymers of poly( N-vinyl carbazole) and poly(9-(4-vinyl-phenyl)carbazole) were used for the nano-composite electrodes. Structural analyses were carried out using Fourier transform nuclear magnetic resonance spectroscopy, AC impedance spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Electrocatalytic activities were investigated by voltammetry and chronoamperometry in a 2 M CH 3OH/0.5 M H 2SO 4 solution and the data compared with a carbon-supported PtRu electrode. XRD patterns indicated good alloy formation and nano-composite formation was confirmed by TEM. Electrochemical measurements and DMFC unit-cell tests indicate that the nano-composites could be useful in a DMFC, but its performance would be slightly lower than that of a carbon-supported electrode. The interfacial property between the PtRu-polymer nano-composite anode and the polymer electrolyte was good, as evidenced by scanning electron microscopy. For better performance in a DMFC, a higher electric conductivity of the polymer and a lower catalyst loss are needed in nano-composite electrodes.

Characterization of Differently Synthesized Pt-Ru Fuel Cell Catalysts by Cyclic Voltammetry, FTIR Spectroscopy, and in Single Cells

Carbon-supported Pt-Ru (1:1) catalysts were synthesized from aqueous solutions of Pt(IV) and Ru(IV) salts by two different reductive methods and characterized in comparison to a commercial Pt-Ru/C catalyst purchased from E-TEK, Inc. The three catalysts differ in particle size, dispersion, and degree of alloying, as determined by X-ray diffraction and transmission electron microscopy. Cyclic voltammetry in different methanol concentrations and CO-stripping experiments were conducted to check their electrocatalytic activity. The results obtained are in good agreement with single-cell measurements using mixtures with concentrations of 75 and 150 ppm CO. The synthesized catalysts show improved activities for low CO concentrations at 75°C cell temperature. In addition, for the synthesized catalysts only low CO coverages were found at the electrode surface by special in situ infrared reflectance techniques in contrast to the commercial one. © 2002 The Electrochemical Society. All rights reserved.

Catalysts for Direct Methanol Fuel Cells

The activity of in house prepared carbon-supported Pt-Ru catalysts for methanol oxidation and carbon-supported RuSe for the oxygen reduction reaction in direct methanol fuel cells (DMFCs) was investigated. The composition of Pt-Ru/C was varied both in terms of weight loading (ratio of total metal content to carbon) as well as the ratio of Pt to Ru. The measurements were carried out in a half cell arrangement in sulphuric acid at various temperatures. The weight loading and ratio of Pt to Ru were varied in order to find out the optimum weight loading of precious metal and the temperature dependence of Pt to Ru ratio on methanol oxidation reaction. It has been found that there exists an optimum in the weight loading at 60 wt.% for carbon-supported Pt-Ru catalyst towards its maximum mass activity. While 1:1 Pt to Ru ratio exhibits a higher activity than 3:2 Pt:Ru above 60 °C, 3:2 ratio exhibits a higher activity at lower temperature. It has been observed that RuSe is inactive towards methanol and it is realised that RuSe is a potential candidate as methanol tolerant oxygen reduction catalyst. The activity of carbon supported RuSe for oxygen reduction reaction (ORR) was tested in sulphuric acid in the presence of methanol. Even though the mass specific activity of the RuSe catalyst is somewhat lower than that of Pt/C, the surface activity of carbon-supported RuSe is superior than that of carbon supported Pt which indicate the unfavourable size distribution of RuSe/C catalyst.

Characterization of different Pt–Ru catalysts by X-ray diffraction and transmission electron microscopy

Carbon-supported Pt–Ru (1:1)-catalysts have been synthesized by two reduction methods in an aqueous phase and in a third way in an organic solution and characterized in comparison to a commercial Pt–Ru/C catalyst purchased from E-TEK. X-ray diffraction and transmission electron microscopy were carried out on the different samples in the as-synthesized state and after heat-treatment at 500°C in nitrogen and air atmospheres respectively. Powder patterns of the different catalysts in the as-synthesized state reveal a fcc pattern with d values matching or close to platinum. No evidence of metallic Ru or any oxide phases was found. After heat-treatment in nitrogen Ru reflections occur in the synthesized catalyst samples, backing the supposition of separate platinum and ruthenium particles instead of a Pt–Ru alloy.

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Distributions of Size and Composition in Carbon-Supported Pt-Ru Composite Metal Fine-Particle Catalysts.

金属錯体イオン対 [Pt3 (CO) 6] 42- と [(C6Me6) 2Ru] 2+ を前駆体とする炭素担持複合金属触媒が粒径も粒子組成も揃っているのに対して, K2PtCl4 と RuCl3 の水溶液混合物から含浸法で調製したものは, 広い粒径分布と拡がりのある粒子組成をもち, 大粒径は Ptリッチ, 小粒径は Ru リッチとなる傾向がみられた. 2-プロパノール液相脱水素反応に関しては, Pt-Ru モル比 1 : 1 組成の塩化物前駆体から調製したものが高活性を示し, 粒径分布・粒子組成よりも成分組成の方が重要な要因となることがわかった.