Catalytic Activity For Methanol Oxidation Research Articles

Nanostructure PtRu/MWNTs as Anode Catalysts Prepared in a Vacuum for Direct Methanol Oxidation

Platinum and ruthenium nanoparticles that are uniformly dispersed on multiwalled carbon nanotubes (MWNTs) were synthesized by vacuum pyrolysis using Pt(acac)2 and Ru(acac)3 as the metal precursors. The resulting nanocomposites were characterized by transmission electron microscopy and X-ray diffraction. The Pt, Pt45Ru55, and Ru nanoparticles had mean diameters of 3.0 +/- 0.6, 2.7 +/- 0.6, and 2.5 +/- 0.4 nm and the same mole number as their metal precursors at 500 degrees C. The electrocatalytic activity of the Pt/MWNTs and PtRu/MWNTs was investigated at room temperature by cyclic voltammetry and chronoamperometry. All of the electrochemical results showed that the PtRu/MWNTs exhibited a high level of catalytic activity for methanol oxidation as a result of the large surface area of the supporting carbon nanotubes and the wide dispersion of the Pt and Ru nanoparticles. Compared with the Pt/MWNTs, the onset potential for methanol oxidation of the PtRu/MWNTs was significantly lower, and the ratio of the forward anodic peak current to the reverse anodic peak current during methanol oxidation was somewhat higher. The Pt45Ru55/MWNTs displayed the best electrocatalytic activity of all of the carbon-nanotube-supported Pt and PtRu catalysts.

Monodisperse PtRu Nanoalloy on Carbon as a High-Performance DMFC Catalyst

The highly monodisperse PtRu (1:1) colloidal nanoalloy was prepared by the co-reduction of Pt(acac)2 and Ru(acac)3 precursors, deposited on a Vulcan carbon (Vc) support and subsequently treated by acetic acid to generate active PtRu/Vc catalyst, which showed a remarkable performance of catalytic activity in methanol oxidation.

Electrodeposited PtRu on cryogel carbon–Nafion supports for DMFC anodes

For a high catalytic activity of the anodes in DMFC at low noble metal content a fine dispersion of PtRu on carbon supports is required and to this purpose we prepared and investigated high specific surface area cryogel carbons of controlled mesoporosity. Two carbons CC1 and CC2 with pore-size distribution centered at 6 and 20 nm were obtained by sol–gel polycondensation of resorcinol and formaldehyde, followed by a freeze-drying procedure, a versatile and low-cost method to provide after pyrolysis carbons of controlled porosity. Electrodeposited PtRu on CC2-Nafion support with ca. 100 μg cm −2 of Pt displayed a good catalytic activity for methanol oxidation of 85 mA mg −1 of Pt after 600 s at 492 mV versus NHE and 60 °C in H 2SO 4 0.1 M–CH 3OH 0.5 M when the Pt-to-C mass ratio was ca. 10%. The catalytic activity tests and XRD and SEM analyses demonstrated the stability of the prepared electrodes upon catalysis in the time scale of our measurements. Strategies to further increase the catalytic activity of the PtRu/cryogel carbon–Nafion electrodes for methanol oxidation are discussed.

Segmented Pt/Ru, Pt/Ni, and Pt/RuNi Nanorods as Model Bifunctional Catalysts for Methanol Oxidation

Five-segment (Pt-Ru-Pt-Ru-Pt, Pt-Ni-Pt-Ni-Pt, and Pt-RuNi-Pt-RuNi-Pt) nanorods with the same overall rod length and the same total Pt segment length were prepared by sequential electrodeposition of the metals into the pores of commercially available anodic aluminum oxide (AAO) membranes. Field-emission scanning electron microscopy (FESEM) showed that the nanorods were about 210 nm in diameter and about 1.5 microm in length. The alternating Pt and oxophilic metal(s) segments could be easily differentiated in backscattered-electron images. X-ray diffraction (XRD) analysis of the nanorods indicated that Pt and Ni were polycrystalline with fcc structures, Ru was hcp, and the co-deposited RuNi adopted the nickel fcc structure with some negative shifts in the Bragg angles. The chemical states of Pt, Ru, and Ni on the nanorod surface were assayed by X-ray photoelectron spectroscopy (XPS), and the presence of Pt(0), Pt(II), Pt(IV), Ru(0), Ru(VI), Ni(0), and Ni(II) was observed. The nanorods were catalytically active for the room-temperature electrooxidation of methanol in acidic solutions. The relative rates of reaction showed the Pt-RuNi pair sites as having the lowest overpotential to dissociate water, the highest catalytic activity in methanol oxidation, and the strongest CO-tolerance in the potential window employed. The use of segmented nanorods with identifiable Pt-oxophilic metal(s) interfaces removes many of the ambiguities in the interpretation of experimental data from conventional alloy catalysts, thereby enabling a direct comparison of the activities of various types of pair sites in methanol oxidation.

Preparation and characterization of aqueous colloids of Pt–Ru nanoparticles

A synthetic method for platinum–ruthenium (PtRu) nanoparticles in aqueous media is proposed. This method employs citric acid as a capping agent and NaBH 4 as a reducing agent with the aid of pH control. The number-averaged size of the PtRu nanoparticles was ca. 2 nm. The crystal phase and chemical composition of the nanoparticles was investigated by X-ray diffraction measurement and scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis, which indicated that the nanoparticles mainly consisted of an alloy of Pt and Ru. Electrochemical measurement showed that the PtRu nanoparticles had catalytic activity for methanol oxidation.

Highly efficient electrode catalysts prepared with ordered nanoporous carbons with tunable pore sizes as catalyst supports

AbstractOrdered uniform nanoporous carbons with pore sizes in the range of 10 – 600 nm were synthesized against removable colloidal crystalline templates by carbonization of phenol and formaldehyde as a carbon precursor. The porous carbons have high surface areas, large pore volumes, and three-dimensionally interconnected uniform pore structures, and thus were used as a support of a Pt(50)-Ru(50) alloy catalyst to study their effect on the anodic performance of the catalyst in direct methanol fuel cell. The use of the ordered uniform porous carbon allowed higher degree of dispersion of the catalysts and efficient diffusion of reagents, resulting in much improved catalytic activity for methanol oxidation in the fuel cell. In general, the smaller pore sizes the porous carbons have, the higher surface areas and the better catalytic activity for methanol oxidation they showed.

Catalytic activity of Pt–Ru alloys synthesized by a microemulsion method in direct methanol fuel cells

Nanostructured Pt–Ru/C catalysts with different particle sizes have been synthesized by a microemulsion method. The particle size and morphology of the samples have been characterized by X-ray diffraction and transmission electron microscopy (TEM), and the electrochemical performances have been evaluated both in half cells with a mixture of 1 M sulfuric acid and 1 M methanol and in single cell direct methanol fuel cells (DMFC). Some of the Pt–Ru/C catalysts prepared by the microemulsion method show higher catalytic activity for methanol oxidation than the commercial Pt–Ru/C (ETEK) catalyst. It is found that the samples prepared with water to surfactant molar ratio ( W) of 10 exhibits the maximum mass activity with the least charge transfer resistance with an optimum particle size of around 5.3 nm. The mass activity decreases and the charge transfer resistance increases as the value of W decreases or increases from 10.

Ordered uniform porous carbons as a catalyst support in a direct methanol fuel cell

Ordered uniform porous carbon frameworks were synthesized against removable colloidal silica crystalline templates by carbonization of phenol and formaldehyde as a carbon precursor in the presence of sulfuric acid. These highly ordered uniform porous carbons when used as a catalyst support, resulted in much improved catalytic activity for methanol oxidation in fuel cell probably due to their three-dimensionally interconnected uniform pore structures and high surface areas.

Electrocatalytic properties of supported platinum–cobalt nanoparticles with uniform and controlled composition

Platinum–cobalt nanoparticles were prepared from water/Triton X-100/propanol-2/cyclohexane reverse microemulsions. The Pt:Co ratio in the nanoparticles was well controlled by the initial concentrations of Pt and Co in the precursor solution. The nanoparticles were characterized by transmission electron microscopy, X-ray diffractometry and energy dispersive X-ray analysis. The Pt–Co nanoparticles supported on a carbon electrode possessed high dispersion and high catalytic activity for methanol oxidation in alkaline solution at room temperature. The optimum Pt:Co ratio for methanol oxidation was determined to be 1:0.5.

Ordered Porous Carbons with Tunable Pore Sizes as Catalyst Supports in Direct Methanol Fuel Cell

Ordered uniform porous carbon frameworks with pore sizes in the range of 10 to ∼1000 nm were synthesized against removable colloidal silica crystalline templates by carbonization of phenol and formaldehyde as a carbon precursor. The porous carbons were used as supports for a Pt(50)−Ru(50) alloy catalyst to study their supporting effect on the anodic performance of the catalyst in a direct methanol fuel cell (DMFC). The use of the ordered uniform porous carbons resulted in much improved catalytic activity for methanol oxidation in the fuel cell probably due to their high surface areas, large pore volumes, and three-dimensionally interconnected uniform pore structures, which allow a higher degree of dispersion of the catalysts and efficient diffusion of reagents. In general, the smaller the pore sizes in the porous carbons were, the better the catalytic activity for methanol oxidation was. In addition, as pore sizes are getting smaller, the structural integrity with good pore interconnection seems to be get...

Methanol Electrooxidation on Carbon-Supported Pt3Ru2Sn Ternary Catalyst

Abstract The electrocatalytic methanol oxidation over Pt–Ru–Sn/C ternary alloy catalysts was investigated. The catalytic activity of Pt3Ru2Sn/C was significantly higher than that of PtRu/C. Sn in ternary alloy catalyst modified the Pt electronic structure without the large increase of Pt–Pt bond distance, which may enhance the catalytic activity for methanol oxidation by improving CO tolerance.

Fabrication of ordered uniform porous carbon networks and their application to a catalyst supporter.

Ordered uniform porous carbon frameworks showing interesting morphology variations were synthesized against removable colloidal silica crystalline templates through simply altering acid catalyst sites for acid-catalyzed polymerization. These highly ordered uniform porous carbons as a catalyst supporter resulted in much improved catalytic activity for methanol oxidation in a fuel cell.

Voltammetric investigation of platinum oxides. I. Effects of ageing on their formation/reduction behavior as well as catalytic activities for methanol oxidation

The formation and reduction behavior of platinum oxides on various titanium-platinized electrodes was investigated by means of cyclic voltammetry (cv) in H 2SO 4 with and without methanol. The cv results indicated that PtOH ads with the coexistence of bare Pt atoms and the presence of hydroxyl Pt(IV) species are responsible for the electrocatalytic oxidation of methanol in the potential ranges of premonolayer and monolayer oxide formation, respectively. The electrocatalytic activity of PtOH ads was found to be enhanced by ageing of the Pt deposits through means of either repeated cv or immersion in water for 15 days although the ageing processes would decrease their surface area. Scanning electron microscope (SEM) was used to examine any changes in surface morphology of the Pt deposit after ageing. X-ray photoelectron spectroscopic (XPS) spectra revealed a negative shift in binding energy of the surface Pt atoms after a repeated potential cycling. X-ray diffraction (XRD) patterns revealed a change in crystalline structure from polycrystalline to amorphous after this ageing treatment.

MoO 3 supported on montmorillonite type pillared clays: Characterization, surface acidity and catalytic properties towards the oxidation of methanol

Two different MoO 3 catalysts (30 wt%) supported on montmorillonite type pillared clays have been synthesized by (i) impregnation with an ammonium molybdate solution (sample Mo-APC-i) and (ii) mechanical mixing with MoO 3 (sample Mo-APC-m). After preparation both catalysts were calcined at 400°C. It has been established by X-ray phase analysis, temperature programmed reduction and IR spectroscopy that impregnation leads to a better dispersion of molybdenum oxide on the support, which ensures (i) a higher concentration of Brønsted acid sites (measured by adsorption of pyridine) and (ii) a higher catalytic activity in methanol oxidation of the Mo-APC-i catalyst.

Dispersion of phosphovanadates on silica gel chemically modified with silane coupling agents having an amino group and their catalytic activities for methanol oxidation

Phosphotetradecavanadate (PV14) was dispersed on a silica gel chemically modified with a silane coupling agent (AnPS-SiO2) by an equilibrium adsorption method. The PV14 contents approximately correlated with the V(IV) spin contents by ESR. PV14 dispersed on AnPS-SiO2 resulted in a quite high selectivity for formaldehyde such as 97% in methanol oxidation.

High platinum electrocatalyst utilizations for direct methanol oxidation

The influence of platinum crystallite dispersion on the electrocatalytic oxidation of methanol in sulphuric acid has been examined with different carbon black supports. There are no platinum “crystallite size” effects, even for crystallites as small as 1.4 nm in diameter, which corresponds to ca. 70% dispersion of the platinum. The mass activity increased proportionally with the specific surface area of the platinum crystallites. No inter-crystallite distance effect for platinum on the catalytic activity was found either, unlike the electroreduction of oxygen found previously. Therefore, increasing the dispersion of platinum on carbon surfaces is a significant factor for achieving a much higher catalytic activity of methanol oxidation than the present level.

V 2O 5K 2SO 4-silica system: The structure and activity of silica-supported V 2O 5K 2SO 4 catalysts

Silica-supported V 2O 5K 2SO 4 catalysts containing up to 70 wt% of the total active phase, calcined at 550 °C for 6 hr, have been studied by means of electron microscopy, DTA, TGA, X-ray, and BET studies. The correlation of measured physicochemical properties with the catalytic activity for methanol oxidation was investigated. X-Ray and electron microscope observations have indicated the presence of V 2O 5K 2SO 4 in all the catalyst samples without any interaction between them. The results of the thermal analyses showed that K 2SO 4 was not dissolved in the V 2O 5 matrix. Electron microscopy indicated the presence of needle-type V 2O 5 crystals. These needle structures, which depend on K 2SO 4 concentration, appear to be more active for the methanol oxidation. The values of average pore radius and surface area simultaneously play an important role in the activity of the catalyst. Electron microscopy and X-ray analysis of a spent catalyst showed that the fundamental components of the fresh catalyst were completely retained. However, the needle structures and other large particles partially disintegrated during catalysis over extended runs.