Activity Of Pt Nanoparticles Research Articles

Sonication induced peptide-appended bolaamphiphile hydrogels for in situ generation and catalytic activity of Pt nanoparticles

The self-assembly of peptide based bolaamphiphiles is investigated upon sonication. We show the ability of peptide bolaamphiphiles 1 and 2 to form strong and rigid self-supporting hydrogels under physiological conditions upon sonication. The self-assembly of higher order supramolecular structures occurs through a synergic effect of hydrogen bonding and π-stacking interactions. Phenylalanine rich peptide bolaamphiphile 2 self-assembles into well-defined nanoribbons whereas tyrosine rich functional material 1 self-assembles into nanofibrillar structures that can be used as a template for in situ generation of platinum nanoparticles. Furthermore, hydrogenation reactions are catalyzed by in situ synthesized Pt nanoparticles such as p-phenylenediamine, which is prepared by the reaction of p-nitroaniline with Pt nanoparticles.

A strategy for signal amplification using an amperometric enzyme immunosensor based on HRP modified platinum nanoparticles

A novel sandwich-type electrochemical enzyme immunosensor for sensitive detection of α-1-fetoprotein (AFP) using a signal amplification strategy based on the enzyme and the catalytic activity of Pt nanoparticles (PtNPs) is investigated in this work. Sensitivity was greatly amplified by the detection mode which was based on dual signal amplification: (1) secondary antibody labeled HRP-functionalized PtNPs were introduced on the electrode surface through biotin–avidin interactions; (2) the biotin-labeled HRP was further attached to HRP-functionalized PtNPs to assemble a dense HRP film, which resulted in significant enhancement of the current response. The adjusted (but not random) orientation of anti-AFP on the nanohybrid film of gold nanoparticles/multi-walled carbon nanotubes (AuNP/MWNT) was accomplished using an avidin–biotin immobilization technique. The nanohybrid film AuNP/MWNT can improve the response of the immunosensors due to its higher exposed surface area, high catalytic activity which facilitates electron transfer and excellent biocompatibility. The performance of the amperometric immunosensor was evaluated and optimized for best performance. The detection limit for AFP was found to be 0.08 ng/mL at S/ N = 3 and the detection concentration were in the range between 0.25 and 100 ng/mL.

Rotating disk electrode study of Cs 2.5H 0.5PW 12O 40 as mesoporous support for Pt nanoparticles for PEM fuel cells electrodes

The catalytic activity of Pt nanoparticles supported by zeolite-type mesoporous Cs 2.5H 0.5PW 12O 40 solid super-acid towards oxygen reduction has been explored. Pt(IV) impregnated Cs 2.5H 0.5PW 12O 40 was prepared by titration of an aqueous solution of phosphotungstic acid and a known quantity of H 2PtCl 6 with a solution of cesium carbonate. The H 2PtCl 6 impregnated insoluble salt was subsequently chemically or electrochemically reduced to form supported Pt nanoparticles. HRTEM micrographs show that the reduced composites Pt–Cs 2.5H 0.5PW 12O 40 (Pt–Cs 2.5PW 12) contains Pt nanoparticles of average dimensions 2–5 nm, embedded into the porous structure of the insoluble salt. RDE and RRDE studies and fuel cell polarization data performed using thin layer composite films of Pt–Cs 2.5PW 12 chemically or electrochemically reduced show that the catalyst is very stable and rather efficient for oxygen reduction (ORR). The oxygen reduction wave is shifted by 60–70 mV towards more positive potentials with respect to the one obtained using electrodes prepared with a standard catalyst such as E-Tek 20% Pt–Vulcan. Analysis of the voltammetric curves demonstrates that the electrocatalytic activity of the composite electrodes is higher than that of the standard catalyst. This indicates that the solid state super-acid Cs 2.5H 0.5PW 12O 40 acts as co-catalyst by providing a proton rich environment in the vicinity of the Pt nanoparticles that enhances their catalytic activity towards oxygen reduction.

Enhanced electrocatalytic activity of Pt nanoparticles modified with PPy-HEImTfa for electrooxidation of formaldehyde

A facile approach to improve the electrocatalytic properties of Pt nanoparticles (nm-Pts) has been developed. nm-Pts are deposited on substrate electrode Pt sheet using cyclic voltammetry in sulfuric acid containing H 2PtCl 6 to get nm-Pt electrode, and then are modified with polypyrrole in an ionic liquid 1-ethylimidazolium trifluoroacetate (PPy-HEImTfa) to obtain the electrode PPy-HEImTfa/nm-Pt. The electrocatalytic performance of PPy-HEImTfa/nm-Pt towards the oxidation of formaldehyde in acidic solution has been studied by cyclic voltammetry and in situ FTIR spectroscopy. Results show that PPy-HEImTfa/nm-Pt exhibits high electrocatalytic activity and stability, as compared with nm-Pt electrode or PPy-HEImTfa modified with nm-Pts (nm-Pt/PPy-HEImTfa) under the similar preparation conditions. In situ FTIR spectroscopic measurements confirm that PPy-HEImTfa film on the surface of nm-Pts help to catalyze the oxidation of the adsorbed CO and reduced the poisoning effect of CO on nm-Pt catalyst.

Highly dispersed uniformly sized Pt nanoparticles on mesoporous Al-SBA-15 by solid state impregnation

Highly dispersed Pt nanoparticles on modified mesoporous Al-SBA-15 were obtained by a solid state impregnation (SSI) methodology, which consisted of a physical mixture of Al-SBA-15 support with a given amount of Pt(acac)2 in order to have 1wt.% of Pt on the final solid. The solid mixture was ground vigorously and annealed at 180°C (e.g. the sublimation point of Pt(acac)2) for 0.5h and then at 400°C in inert atmosphere, to decompose the organic ligand. The materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) by applying high angle annular dark field (HAADF) technique, nitrogen physisorption, pyridine adsorption by infrared spectroscopy (FTIR), X-ray photoelectronic spectroscopy (XPS) and FTIR of CO adsorption. Catalytic activity of Pt nanoparticles was evaluated in naphthalene hydrogenation (HYD) as test reaction. The results were compared with those obtained on Pt nanoparticles dispersed on Al-SBA-15 by wet impregnation (WI) method. Both SSI and WI methods produce significant differences in the population of flat and edge sites on the Pt nanoparticles with dimensions around 1.0nm. However, Pt nanoparticles obtained by SSI showed higher activity upon naphthalene HYD than those obtained by WI method, which was explained by the higher density of edge sites measured by FTIR of CO adsorption.

Enhancement of activity of platinum towards oxidation of ethanol by supporting on titanium dioxide containing phosphomolybdate-modified gold nanoparticles

A new concept of utilization of titanium dioxide matrix in electrocatalysis by admixing it with polyoxometallate modified gold nanoparticles is described here. The approach utilizes Keggin-type phosphododecamolybdate (PMo 12O 40 3−) adsorbates capable of modifying, activating and stabilizing Au nanoparticles of the sizes of 30–40 nm. Ultra-thin films of phosphomolybdates on nanostructured gold are characterized by well-defined fast (reversible) multi-electron electrochemical reactions. By dispersing platinum black over the Au-containing TiO 2, the electrocatalytic activity of Pt nanoparticles towards oxidation of ethanol has been enhanced. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account improvement of overall conductivity (due to the presence of nanostructured gold) at the electrocatalytic interface (including TiO 2-support), as well as and possibility of specific Pt–TiO 2 or Pt–Au electronic interactions and existence of active hydroxyl groups (on titanium dioxide or polyoxometallate surfaces) in the vicinity of catalytic Pt sites.

Electrocatalytic activity of Pt nanoparticles on a karst-like Ni thin film toward methanol oxidation in alkaline solutions

The study prepared rugged Ni thin films for the study on electrocatalytic methanol oxidation reaction (MOR) in alkaline solutions. The rugged Ni thin film has a karst-like morphology, which provides a large surface area for Pt nanoparticle loading by pulse electrodeposition. Cyclic voltammetry measurements showed that the Pt/karst-Ni electrode had a high electrocatalytic activity toward MOR and CO tolerance in the KOH electrolyte. Ni(OH)2 formed on the Ni support during the potential scan can enhance CO tolerance of Pt nanoparticles via the bi-functional mechanism. The Langmuir–Hinshelwood and the Eley–Rideal mechanisms are used to elucidate the role of OH surface groups on the Ni support and OH− ions in the electrolyte, respectively, in the enhancement of the CO tolerance. XPS analysis indicates that negative charges transfer from the Ni support to Pt nanoparticles. The electronic interaction may modify adsorption properties of CO adspecies on the Pt catalyst; the modification allows easy CO electro-oxidation by OH species surrounding the Pt nanoparticles, either from the Ni support or from the alkaline solution. The synergistic effect of the bifunctional mechanism and the electronic interaction makes the Pt/karst-Ni structure a good catalytic electrode for MOR in the KOH solution.

Size-Dependent Methanol Electro-oxidation Activity of Pt Nanoparticles with Different Shapes

We report a comparative electrochemical investigation of size-dependent methanol electro-oxidation activity on cubic vs. octahedral/tetrahedral Pt nanoparticles. The size range for the former was 9.5 nm to 5.6 nm to 4.5 nm and for the latter was 9.7 nm to 6.0 nm to 5.0 nm. Different trends were observed: the methanol activity increased as the nanoparticle size decreased on the cubic Pt nanoparticles but decreased on the octahedral/tetrahedral Pt nanoparticles. Although the presence of residual polyvinylpyrrolidone that was used as stabilizing ligand during the nanoparticles synthesis did complicate the mechanistic understanding of the observed trends, these observations nonetheless highlighted the fundamental and practical importance and the necessity of investigating and understanding, in a controllable fashion, the orientational sensitivity of catalytic activity at nanoscale in conjunction with size.

Size‐ and Shape‐Dependent Activity of Metal Nanoparticles as Hydrogen‐Evolution Catalysts: Mechanistic Insights into Photocatalytic Hydrogen Evolution

The catalytic activity of Pt nanoparticles (PtNPs) with different sizes and shapes was investigated in a photocatalytic hydrogen-evolution system composed of the 9-mesityl-10-methylacridinium ion (Acr(+)-Mes: photocatalyst) and dihydronicotinamide adenine dinucleotide (NADH: electron donor), based on rates of hydrogen evolution and electron transfer from one-electron-reduced species of Acr(+)-Mes (Acr·-Mes) to PtNPs. Cubic PtNPs with a diameter of (6.3±0.6) nm exhibited the maximum catalytic activity. The observed hydrogen-evolution rate was virtually the same as the rate of electron transfer from Acr·-Mes to PtNPs. The rate constant of electron transfer (k(et)) increased linearly with increasing proton concentration. When H(+) was replaced by D(+), the inverse kinetic isotope effect was observed for the electron-transfer rate constant (k(et)(H)/k(et)(D)=0.47). The linear dependence of k(et) on proton concentration together with the observed inverse kinetic isotope effect suggests that proton-coupled electron transfer from Acr·-Mes to PtNPs to form the Pt-H bond is the rate-determining step for catalytic hydrogen evolution. When FeNPs were used instead of PtNPs, hydrogen evolution was also observed, although the hydrogen-evolution efficiency was significantly lower than that of PtNPs because of the much slower electron transfer from Acr·-Mes to FeNPs.

Size Effect of Au Nanoparticle on Electrocatalytic Activity of Pt-Au/C Composite Catalysts for Methanol Oxidation

The carbon-supported 30Pt-10Au/C composite nanoparticles (NPs) catalysts with Au NPs of three different sizes were synthesized by the successive reduction of HAuCl4 and H2PtCl6 precursors. The size effect of the Au NPs on the electrocatalytic activity of the 30Pt-10Au/C catalysts for methanol oxidation was examined by cyclic voltammetry in a 1 M H2SO4 and 1 M CH3OH aqueous solution. The Au NPs improved the catalytic activity of Pt NPs for methanol oxidation based on the bi-functional catalytic mechanism, and this effect of Au NPs accelerated remarkably with decreasing Au NP size.

Enhancement of electrochemical stability and catalytic activity of Pt nanoparticles via strong metal-support interaction with sulfur-containing ordered mesoporous carbon

Pt nanoparticles on sulfur-containing ordered mesoporous carbon (Pt/S-OMC) are obtained with 3 nm in size and 60 wt.% loading. XPS analysis shows that there is a strong metal-support interaction between Pt nanoparticles and S atoms embedded on the OMC support. This strong metal-support interaction fastens Pt nanoparticles upon the support and alters the electronic state of Pt from Pt 0 of bulk Pt to a slightly charged state of Pt δ+ . These features result in an improvement both in electrochemical stability and oxygen reduction reaction kinetics compared to Pt/OMC where the OMC does not have sulfur atoms. The approach of tuning the electronic state and the interaction of Pt on carbon supports by embedding heterogeneous atoms into the OMC can effectively improve the stability and catalytic activity of Pt nanoparticles.

Electrocatalytic Activity of Pt Nanoparticles on Karst-Rock Shaped Ni Thin Films toward Methanol and Ethanol Oxidation in Alkaline Solutions

We prepared Ni thin films with a karst-rock topography on the Si substrate and used the thin film as the electrocatalyst support for the study of methanol and ethanol oxidation in alkaline media. Well-dispersed Pt nanoparticles were pulse-electrodeposited on the rugged Ni thin film, which provided a very large surface for the Pt loading. The cyclic voltammertry (CV) showed that the Pt/Ni electrode had a high electrocatalytic activity toward methanol oxidation compared with blanket Pt. Nanosized Pt particles electrodeposited on the rugged surface of the Ni thin film provide a large amount of electrocatalytic sites for methanol oxidation. Hydroxyl surface groups bound on the Ni karst-rock nanostructures in the alkaline solution may greatly enhance CO electro-oxidation in terms of the bifunctional mechanism. The study demonstrates that the karst-rock shaped Ni thin film is a potential candidate as the Pt electrocatalyst support for direct methanol alkali fuel cells.

Tuning the electrocatalytic activity of Pt nanoparticles on carbon nanotubes via surface functionalization

Polyelectrolytes with various characteristic functional groups as interlinkers to anchor Pt nanoparticles were used to functionalize carbon nanotubes (CNTs) as Pt electrocatalyst support. It was found that polyanions (poly(styrenesulfonic acid) (PSS), and poly(acrylic acid sodium) (PAA)) have a beneficial effect on methanol electrooxidation on Pt nanoparticles supported on carbon nanotubes via modifying their electronic structure through charge transfer from polyanions to Pt sites and supply of oxygen-containing species. The increased electron density around Pt sites by the charge transfer from polyanions would cause partial filling of Pt 5 d-bands, resulting in the downshift of d-band center and weaker chemisorption with oxygen-containing species (e.g. CO ad). The weakened chemisorption of CO on Pt nanoparticles would promote the methanol electrooxidation. On the contrary, polycations would have an opposite effect on the electronic structure and chemisorption properties of Pt nanoparticles.

Electrocatalytic activity of Pt nanoparticles on bamboo shaped carbon nanotubes for ethanol oxidation

Recently, bamboo shaped carbon nanotubes (BCNTs) have received increased attention for its bamboo shaped structure associated properties and its application in direct methanol/ethanol fuel cell. In this work, the potential to use BCNTs as the support material of high loaded Pt nanoparticles for improving the efficiency of ethanol/methanol fuel cell is explored. The structure and nature of the resulting Pt-BCNTS composite were characterized by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) spectrum, it was found that Pt nanoparticles were homogeneously dispersed on the BCNTs surfaces with 23.5% by weight. Cyclic voltammogram (CV) indicated that the Pt-BCNTs catalyst displayed excellent electrocatalytic activity and long-term stability toward ethanol oxidation. The excellent performance may be attributed to the high dispersion of nanoscale Pt catalysts and the unique nature of BCNTs. The results imply that doping N atom introduces some defective sites and active sites onto the surface of CNTs. In general, this paper demonstrates that BCNTs are promising support material for Pt-nanoparticles catalyst and can be used to enhance the efficiency of fuel cell.

Computational Study of Electrocatalytic Activity of Pt(100) Surfaces for Oxygen Reduction Reaction and Its Implications for the Activity of Pt Nanoparticles

not Available.

Formic Acid Oxidation on Bi-modified Pt Nanoparticles of Various Sizes

This work presents oxidation of formic acid on Bi-modified Pt nanoparticles of various sizes. The sizes of the studied Pt nanoparticles range from 1.5 to 5.6 nm (detailed in Rhee, C. K.; Kim, B.-J.; Ham, C.; Kim, Y.-J.; Song, K.; Kwon, K. Langmuir 2009, 25, 7140-7147), and the surfaces of the Pt nanoparticles are modified with irreversibly adsorbed Bi. The investigated coverages of Bi on the Pt nanoparticles are 0.12 and 0.25 as determined by coulometry of the oxidation of adsorbed hydrogen and Bi, and X-ray photoelectron spectroscopy. The cyclic voltammetric behavior of formic acid oxidation reveals that the adsorbed Bi enhances the catalytic activity of Pt nanoparticles by impeding a poison-forming dehydration path with a concomitant promotion of a dehydrogenation path. The chronoamperometric results indicate that elemental Bi and partially oxidized Bi are responsible for the catalytic enhancement, when the Bi coverages on Pt nanoparticles are 0.12 and 0.25, respectively. The size effect of Bi-modified Pt nanoparticles in formic acid oxidation is discussed in terms of specific activity (current per unit surface area) and mass activity (current per unit mass).

Constructing a hierarchical graphene–carbon nanotube architecture for enhancing exposure of graphene and electrochemical activity of Pt nanoclusters

Stacking of individual graphene sheets (GS) is effectively inhibited by introducing one-dimensional carbon nanotubes to form a 3-D hierarchical structure which enhances the utilization of GS-based composites. From SEM images, CNTs are useful nanospacers for diminishing the face-to-face aggregation of GS. The specific electrochemically active surface area (SECSA) and specific double-layer capacitance (C S,DL) of Pt/GS–CNTs (127.9 m 2/g, 171.3 F/g) is much higher than that of Pt/GS (105.4 m 2/g, 104.7 F/g) and Pt/CNTs (51.5 m 2/g, 37.1 F/g), revealing the synergistic effects between GS and CNTs on enhancing the electrochemical activity of Pt nanoparticles and electrolyte-accessible surface area.

Effect of pore morphology of mesoporous carbons on the electrocatalytic activity of Pt nanoparticles for fuel cell reactions

In the present investigation, the role of the pore morphology of mesoporous carbons in the electrocatalytic activity of Pt nanoparticles for fuel cell reactions has been successfully revealed by adopting ordered mesoporous carbon CMK-3 and disordered wormhole-like mesoporous carbon (WMC) as the support material, respectively. Both materials possess very similar pore characteristics (pore volume, BET surface area, mesopore size) except pore morphology. It has been found that CMK-3 can provide Pt nanoparticles with more electrochemically active Pt sites and higher electrochemical surface area, and thus, Pt/CMK-3 exhibits superior fuel cell reactions activity compared to Pt/WMC, especially in the case of liquid reactants (e.g. ethanol). This could be attributed to the much easier mass transportation through CMK-3 support profiting from both the high ordered degree and the very good 3D interconnection of the nano-spacings of their hexagonally arrayed carbon nanorods (i.e. mesopores), thus leading to more accessibility of Pt nanoparticles. The above results demonstrates that the pore morphology of carbon supports plays a decisive role in the electrocatalytic activity of their supported Pt nanoparticles, although other structure parameters like pore size are very similar.

Role of Surface Steps of Pt Nanoparticles on the Electrochemical Activity for Oxygen Reduction

The design of highly active nanoscale catalysts for the oxygen reduction reaction (ORR) and oxidation of small molecules such as the methanol oxidation reaction (MOR) constitutes the grand scientific and technological challenge in fuel cells. Although increasing surface steps on Pt nanoparticles was shown recently to enhance the activity of electrochemical oxidation of carbon monoxide and methanol electro-oxidation, little is known about the role of surface steps of nanoparticles on ORR activity. Here, we report that the ORR activity of Pt nanoparticles of ∼2 nm is not influenced by surface steps, in contrast to MOR activity. Further, CO annealing experiments and in situ X-ray adsorption measurements clearly compare the role of surface step for ORR and MOR on Pt nanoparticles. The findings provide new insights to design highly active catalysts for proton exchange membrane fuel cells and direct methanol fuel cells.

Effect of polymeric stabilizers on the catalytic activity of Pt nanoparticles synthesized by laser ablation

The effect of polymeric stabilizers on the catalytic activity of Pt nanoparticles for an electron-transfer reaction between Fe ( CN ) 6 3 - and S 2 O 3 2 - was investigated. Pt nanoparticles were prepared by laser ablation of Pt plate in water, and then stabilized with typical stabilizing polymers such as poly(vinyl pyrrolidone) (PVP), poly(vinyl sulfate) (PVS), and polyethyleneimine (PEI). The catalytic reaction proceeds much faster with PEI-stabilized nanoparticles than PVP- or PVS-stabilized particles. The activity of nanoparticles also highly depends on pH and polymer concentration. These clearly demonstrate that the net charge of the stabilizers plays a decisive role for the nanoparticle-mediated electron transfer between charged reactants.