High Dispersion Of Pt Nanoparticles Research Articles

Direct covalent thiolation of carbon nanotube supports to enhance the durability of highly loaded Pt electrocatalysts

Carbon corrosion is one of the most important issues for commercialization of fuel cell. We introduce a new approach to enhance the corrosion tolerance of carbon nanotube supports and simultaneously obtain high dispersion of Pt nanoparticles with a direct covalent functionalization method by using succinic acid radicals.

Graphene growth on nanodiamond as a support for a Pt electrocatalyst in methanol electro-oxidation

A core/shell structure nanodiamond/graphene (ND/G) was prepared by annealing ND in a vacuum at the temperatures of 1200 and 1500°C. ND/G with a controllable few-layer graphene covering on the ND surface was achieved. The prepared ND/G was used as a support for a platinum (Pt) electrocatalyst in direct methanol fuel cells. A higher dispersion of Pt nanoparticles was observed on ND/G compared to pristine NDs and the material showed better catalytic activity and greater stability for methanol electro-oxidation than Pt/ND.

Bucky diamond produced by annealing nanodiamond as a support of Pt electrocatalyst for methanol electrooxidation

Bucky diamond (BD) with a nanoscale diamond core surrounded by a fullerene shell was used as a support of Pt electrocatalyst for methanol electrooxidation. BDs were prepared by annealing detonation-synthesized nanodiamond (ND) powders in 10−3 Pa vacuum at 900–1100 °C. The electrochemical properties of the BD powders in aqueous solution were investigated. The BDs and NDs supported platinum (Pt) electrocatalysts were prepared using a microwave-assisted reduction method. Higher dispersion of Pt nanoparticles was observed on the BDs than the pristine NDs, indicating a high affinity between BDs and Pt metal. The Pt/BD catalyst had better catalytic activity and higher stability for the methanol electrooxidation in comparison to the Pt/ND prepared at the same conditions. This provides a novel nanoparticle with a high conductivity and a high stability for electrochemical applications.

Synthesis and characterization of Pt nanoparticles on sulfur-modified carbon nanotubes for methanol oxidation

Pt nanoparticles supported on carbon nanotubes (Pt/CNTs) have been synthesized from sulfur-modified CNTs impregnated with H 2PtCl 6 as Pt precursor. The dispersion and size of Pt nanoparticles in the synthesized Pt/CNT nanocomposites are remarkably affected by the amount of sulfur modifier (S/CNT ratio). The results of X-ray diffraction and transmission electron microscopy indicate that an S/CNT ratio of 0.3 affords well dispersed Pt nanoparticles on CNTs with an average particle size of less than 3 nm and a narrow size distribution. Among different catalysts, the Pt/CNT nanocomposite synthesized at S/CNT ratio of 0.3 showed highest electrochemically active surface area (88.4 m 2 g −1) and highest catalytic activity for methanol oxidation reaction. The mass-normalized methanol oxidation peak current observed for this catalyst (862.8 A g −1) was ∼ 6.5 folds of that for Pt deposited on pristine CNTs (133.2 A g −1) and ∼ 2.3 folds of a commercial Pt/C (381.2 A g −1). The results clearly demonstrate the effectiveness of a relatively simple route for preparation of sulfur-modified CNTs as a precursor for the synthesis of Pt/CNTs, without the need for tedious pretreatment procedures to modify CNTs or complex equipments to achieve high dispersion of Pt nanoparticles on the support.

Highly dense and uniformly dispersed platinum nanoparticles on poly(acrylic acid) modified multi-walled carbon nanotubes for methanol oxidation

Poly(acrylic acid) modified multi-walled carbon nanotubes (PAA-MWNTs) were synthesized through in situ radical polymerization in acetone and the PAA-MWNTs were used as supporting material for platinum nanoparticles. Platinum nanoparticles were deposited on the surface of PAA-MWNTs with high loading and high dispersion through ethylene glycol reduction. The size of Pt nanoparticles on PAA-MWNTs can be tuned by the water content in the reaction system and the loading amount can be adjusted by the mass ratio of H 2PtCl 6 to PAA-MWNTs. The electrocatalytic properties of the Pt/PAA-MWNTs catalyst were evaluated by methanol oxidation. The results of cyclic voltammetry show that the Pt/PAA-MWNTs composite possesses high electrocatalytic activity, good long-term stability and storage property, which can be attributed to the small particle size and high dispersion of Pt nanoparticles as well as the nature of MWNTs.

Dehydrogenation of isobutane over Sn/Pt/Na-ZSM-5 catalysts: The effect of SiO2/Al2O3 ratio, amount and distribution of Pt nanoparticles on the catalytic behavior

Sn/Pt/Na-ZSM-5 was used as catalyst for the dehydrogenation of isobutane, and the effect of SiO2/Al2O3 ratio and the dispersion of Pt nanoparticles on the conversion and product selectivity were studied under atmospheric pressure at 848 K. The catalysts were characterized by various techniques such as H2 chemisorption, TEM, SEM, EDX, XRD, FT-IR, TG/DTG, elemental analysis by XRF and ICP techniques. Higher dispersion of Pt nanoparticles in the catalyst with SiO2/Al2O3 ratio of 40 resulted in higher selectivity for isobutene.

Highly dispersed platinum nanoparticles on carbon nanocoils and their electrocatalytic performance for fuel cell reactions

Highly graphitic carbon nanocoils (GCNC) were synthesized through the catalytic graphitization of carbon microspheres obtained by the hydrothermal carbonization of different saccharides (sucrose, glucose and starch) and were used as a support for Pt nanoparticles. The Pt nanoparticles were deposited by means of a polymer mediated-polyol method. The Pt catalysts were characterized both physically (XRD, TEM, HRTEM and XPS) and electrochemically (electrooxidation of methanol in an acid medium). The electrocatalysts thus prepared show a high dispersion of Pt nanoparticles, with diameters in the 3.0–3.3 nm range and a very narrow particle size distribution. These catalytic systems possess high electroactive Pt surface areas (up to 85 m 2 g −1 Pt) and they exhibit large catalytic activities towards methanol electrooxidation (up to 201 A g −1 Pt). Moreover, they have a high resistance against oxidation, which is considerably greater than that of the Pt/Vulcan system.

Preparation, Characterization and Electrocatalytic Properties of Promoted PtMoSi/C Catalysts

PtMoSi/C nanocatalysts were prepared by chemical reduction using formaldehyde, H2, and hydrazine as reducing agents, respectively. The nanocomposites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). XRD patterns showed a face-centered cubic crystal structure, and TEM images indicated that the nanoparticles that were uniformly dispersed on carbon were 3-4 nm in diameter. XPS analysis revealed that the catalysts contained mostly Pt(0), Mo(VI), and Si(IV). The effects of preparation methods and additives on the catalytic activity were then studied by linear sweep voltammetry (LSV) and cyclic voltammetry (CV). It was found that the PtMoSi/C nanocatalysts ( n Pt: n Mo=3:1 was the optimal ratio of Pt to Mo) prepared using formaldehyde as reducing agent showed higher electrocatalytic activity and better tolerance to poisoning species in methanol oxidation than the homemade PtRu/C and the commercial E-TEK PtRu/C catalysts, and this could be ascribed to the high dispersion of Pt nanoparticles on the carbon by the addition of silicomolybdic acid.

Surface thiolation of carbon nanotubes as supports: A promising route for the high dispersion of Pt nanoparticles for electrocatalysts

This paper introduces a unique method for achieving high dispersion of precious metal nanoparticles on carbon nanotube supports for electrocatalysts: the surface thiolation of multiwall carbon nanotubes (MWNT). The high dispersion of Pt nanoparticles [i.e., small average particle size (1.5 nm) and narrow size distribution] was obtained by the surface thiolation of MWNT as supports, despite a considerably large Pt load (40 wt% Pt to MWNT) and the use of MWNT with a relatively small surface area as supports to common activated carbon. In particular, EXAFS and XPS data revealed that the interaction between Pt nanoparticles and surface thiol groups on MWNT was the reason for the high dispersion. These highly dispersed Pt nanoparticles showed enhanced and stable electrocatalytic activity in methanol oxidation and oxygen reduction reactions. This result indicates that the surface thiolation of supports is an effective way to obtain highly dispersed precious metal nanoparticles to enhance electrocatalytic activity.

Preparation of mesoporous carbon templated by silica particles for use as a catalyst support in polymer electrolyte membrane fuel cells

Mesoporous carbons were prepared using commercial silica particles and a formaldehyde–resorcinol resin as a template and carbon precursor, respectively. By changing the molar ratio of template to carbon precursor, mesoporous carbons with different mesoporosities (MC- X, X represents the molar ratio of template to carbon precursor) were produced. The resulting MCs had a high-surface area and large pore volume. In particular, the highest mesoporosity was observed for MC-3. Pt catalysts-supported on MC- X were prepared using formaldehyde as a reducing agent for use as a cathode catalyst in a polymer electrolyte fuel cell (PEMFC). The size of Pt crystallite was dependent on the properties of corresponding carbon support. As a whole, a carbon support with a high-surface area and high-mesoporosity served the best in terms of a high-dispersion of Pt nanoparticles. In a unit cell test of the PEMFC, a Pt catalyst with a high-mesoporosity and fine dispersion of metal showed an enhanced performance. The findings indicate that the surface area combined with the mesoporosity had a positive influence on the metal dispersion and the distribution of ionomer, leading to the enhanced cell performance.

Controllable Pt Nanoparticle Deposition on Carbon Nanotubes as an Anode Catalyst for Direct Methanol Fuel Cells

We report a novel process to prepare well-dispersed Pt nanoparticles on CNTs. Pt nanoparticles, which were modified by the organic molecule triphenylphosphine, were deposited on multiwalled carbon nanotubes by the organic molecule, which acts as a cross linker. By manipulating the relative ratio of Pt nanoparticles and multiwalled carbon nanotubes in solution, Pt/CNT composites with different Pt content were achieved. The so-prepared Pt/CNT composite materials show higher electrocatalytic activity and better tolerance to poisoning species in methanol oxidation than the commercial E-TEK catalyst, which can be ascribed to the high dispersion of Pt nanoparticles on the multiwalled carbon nanotube surface.

Preparation of highly active 40 wt.% Pt/C cathode electrocatalysts for DMFC via different routes

A series of 40 wt.% Pt/C electrocatalysts were prepared by a modified polyol process and an improved aqueous impregnation method with different impregnation time. The characterization results of TEM and XRD identically reveal that the size and distribution of Pt nanoparticles on carbon are controllable by modifying impregnation time in both routes. High dispersion of Pt nanoparticles on carbon is achieved by both methods with 15 min impregnation, while aggregation of Pt nanoparticles takes place with prolonging the impregnation time to 36 h, especially in the aqueous impregnation procedure. UV–vis spectroscopy measurements verified that the redox reaction between PtCl 6 2− and formaldehyde could take place at a slow rate under ambient conditions via a two-step reaction path, where PtCl 4 2− serves as an intermediate. On the other hand, PtCl 6 2− anion can be directly reduced to Pt 0 above 333 K in the modified polyol process through an autocatalytic pathway. The short-time-impregnated 40 wt.% Pt/C as cathode electrocatalysts in direct methanol fuel cell performs better than that of long-time-impregnated electrocatalysts. Experimental evidence provides clues for fundamental understanding of elementary steps of the redox reactions, which helps guiding the design and preparation of highly dispersed Pt catalyst with high metal loadings for fuel cells.