Well-dispersed Platinum Nanoparticles Research Articles

Ethanol Electro-Oxidation on Catalysts with S-ZrO2-Decorated Graphene as Support in Fuel Cell Applications.

Direct ethanol fuel cells (DEFCs) are considered the most suitable direct alcohol fuel cell (DAFC) in terms of safety and current density. The obstacle to DEFC commercialization is the low reaction kinetics of ethanol (C2H5OH) oxidation because of the poor performance of the electrocatalyst. In this study, for the first time, graphene nanoplates (GNPs) were coated with sulfated zirconium dioxide (ZrO2) as adequate support for platinum (Pt) catalysts in DEFCs. A Pt/S-ZrO2-GNP electrocatalyst was prepared by a new process, polyol synthesis, using microwave heating. Field emission scanning electron microscope (FESEM) imaging revealed well-dispersed platinum nanoparticles supported on the S-ZrO2-GNP powder. Analysis of the Fourier transform infrared (FTIR) spectrometry confirmed that sulfate modified the surfaces of the sample. In X-ray diffraction (XRD), no effect of S-ZrO2 on the crystallinity net in Pt was found. Pt/S-ZrO2-GNP electrode outperformed those with unsulfated counterparts, primarily for the higher access with electron and proton, confirming sulfonating as a practical approach for increasing the performance, electrocatalytic activity, and carbon monoxide (CO) tolerance in an electrocatalyst. A considerable decrease in the voltage of the CO electrooxidation peak from 0.93 V for Pt/C to 0.76 V for the Pt/S-ZrO2-GNP electrode demonstrates that the new material increases activity for CO electrooxidation. Moreover, the as-prepared Pt/S-ZrO2-GNPs electrocatalyst exhibits high catalytic activity for the EOR in terms of electrochemical surface area with respect to Pt/ZrO2-GNPs and Pt/C (199.1 vs. 95 and 67.2 cm2.mg−1 Pt), which may be attributed to structural changes caused by the high specific surface area of graphene nanoplates catalyst support and sulfonating effect as mentioned above. Moreover, EIS results showed that the Pt/S-ZrO2-GNPs electrocatalyst has a lower charge transfer resistance than Pt/ ZrO2-GNPs and Pt/C in the presence of ethanol demonstrating an increased ethanol oxidation activity and reaction kinetics by Pt/S-ZrO2-GNPs.

Metal-Organic Framework-Based Nanoheater with Photo-Triggered Cascade Effects for On-Demand Suppression of Cellular Thermoresistance and Synergistic Cancer Therapy.

Nanomedicine with stable light-heat conversion and spatiotemporally controllable drug activation is crucial for the success of photothermal therapy (PTT). Herein, a metal-organic framework (MOF)-based nanoheater with light-triggered multi-responsiveness is engineered to in-situ and on-demand sensitize cancer cells to local hyperthermia. Well-dispersed platinum nanoparticles synthesized inside nanospaces of the MOF are employed as the near-infrared (NIR)-harvesting unit with stable and high light-heat conversion performance. A conformation switchable polymer shell is constructed as a secondary light-responding unit to gate the targeted activation of a molecular inhibitor against thermoresistance. By cascade transformation of light stimuli to downstream signals, the nanoheater enables inhibitor release to go with local heating at the same time restricted in lesion sites to maximize efficacy and minimize systemic toxicity. The efficient photothermal conversion and the blockage of cellular heat-protective pathways provide a dual-mode of action which selectively sensitizes cancer cells to hyperthermia in a spatiotemporally controlled manner. With NIR as the remote switch, the MOF-based nanosystem demonstrates localized and boosted PTT efficacy against cancer both in vitro and in vivo. These results present nanosized MOFs as tailorable and versatile platforms for synergistic and precise cancer therapy.

Size-tunable green synthesis of platinum nanoparticles using chlorogenic acid

A facile green synthesis of platinum nanoparticles (PtNPs) using chlorogenic acid (CGA) as a reducing agent and stabilizing agent has been reported here for the first time to the knowledge of the authors. Well-dispersed PtNPs are synthesized in spherical shapes and are tuned in size by simply changing the molar ratio of H2PtCl6 to CGA, with the same salt, temperature and solvent. The average sizes of the particles were 16.9 ± 4.7, 13.3 ± 4.0, 10.8 ± 3.4, and 7.5 ± 2.3 nm, respectively, corresponding to molar ratios of the initial H2PtCl6/CGA of 1:1, 1:2, 1:3 and 1:4 and decreased with an increase in CGA concentration. Transmission electron microscope; energy-dispersive spectrometer; UV–visible absorption spectra (UV–Vis); and Fourier transmission infrared spectra were used to characterize the PtNPs. Additionally, the advantage of CGA for possible synergistic biological activity was studied through the in vitro antioxidant activity of PtNPs by CGA for capture of free radicals. Our results indicate that CGA is an excellent reducing and stabilizing agent in green synthesis of PtNPs, and these size-tunable PtNPs can provide potential applications in the field of biomedicines.

Facile Construction of a Highly Dispersed Pt Nanocatalyst Anchored on Biomass-Derived N/O-Doped Carbon Nanofibrous Microspheres and Its Catalytic Hydrogenation.

With the depletion of nonrenewable resources and the increasingly serious "white pollution" caused by nondegradable plastics, using renewable biomass resources such as chitin to fabricate materials is a green and sustainable pathway. Herein, for the first time, we used N/O-doped carbon nanofibrous microspheres (CNMs) derived from renewable chitin as carriers to successfully construct a highly dispersed platinum nanocatalyst via a facile way. Various physicochemical characterizations provided reliable evidence for the ultrafine and well-dispersed platinum nanoparticles with an average diameter of 2.3 nm. As the supporting framework, the CNM with interconnected nanofibrous networks and a large surface area facilitated the adhesion and dispersion of Pt particles. Meanwhile, the inherent N/O-containing functional groups and the defects in carbonized chitin could anchor the platinum tightly. The CNM/Pt catalyst was further examined for hydrogenation, and it exhibited promising catalytic activity and stability (∼5 runs, 91%) and a broad applicability. This utilization of biomass resources to build catalyst materials would be important for the green and sustainable chemistry.

In Situ One-Step Synthesis of Platinum Nanoparticles Supported on Metal-Organic Frameworks as an Effective and Stable Catalyst for Selective Hydrogenation of 5-Hydroxymethylfurfural.

A facile in situ one-step route for the preparation of platinum nanoparticles supported on metal–organic frameworks (MOFs) without adding stabilizing agents was developed. The obtained 10% Pt@MOF-T3 material possessed a large surface area and high crystallinity. Meanwhile, uniform and well-dispersed platinum nanoparticles were formed inside the cavities of MOFs, which could be attributed to the efficient complexation and stabilization effect derived from the dipyridyl groups. The as-synthesized 10% Pt@MOF-T3 sample showed high activity and selectivity in the hydrogenation of 5-hydroxymethylfurfural (HMF). This excellent catalytic performance could be attributed to the synergistic effects of well-dispersed platinum nanoparticles and electron donation offered by MOFs. Meanwhile, the presence of bipyridine ligands in the MOF framework avoided the irreversible adsorption of the hydrocarbon compounds, leading to the enhanced catalytic efficiency. Besides, it was easily recycled and reused at least five times, showing good recyclability.

Minimum and well-dispersed platinum nanoparticles on 3D porous nickel for highly efficient electrocatalytic hydrogen evolution reaction enabled by atomic layer deposition

Conformal deposition and effective use of catalysts based on 3D electrode architectures are of great importance in electrocatalytic applications. In this work, 3D porous Ni substrate is first fabricated through a hydrogen bubbles dynamic templated method, and well-dispersed Pt nanoparticles are loaded on the substrate subsequently via atomic layer deposition. The 3D porous Ni/Pt is utilized as an efficient hydrogen evolution reaction catalyst. The 3D and high surface area structure is realized through the hydrogen bubbles dynamic templated method. The synergistic effect between atomic-layer-deposited Pt and the 3D structure of porous Ni substrate finds a new approach of minimal yet effective utilization of Pt for much enhanced HER activity. The 3D porous Ni/Pt samples show comparable activity performance with commercial 20 wt% Pt/C. Furthermore, according to the Pt mass-based calculation, only ~0.1 wt% Pt was deposited on 3D porous Ni substrate electrocatalysts which exhibits a much higher activity than the commercial 20 wt% Pt/C catalyst.

Selective Conversion of Renewable Furfural with Ethanol to Produce Furan-2-acrolein Mediated by Pt@MOF-5

The selective conversion of furfural (FUR) with ethanol to produce furan-2-acrolein has been successfully performed in the presence of O2, in which metal organic framework (MOF) supported platinum nanoparticles (Pt@MOF-5, Pt@UIO-66, and Pt@UIO-66-NH2) were used as the catalysts. Under the optimal conditions, 84.1% conversion of FUR and 90.1% selectivity of furan-2-acrolein was obtained with Pt@MOF-5 as the catalyst. Moreover, the catalysts were characterized by XRD, H2-TPR, HRTEM, HRSEM, and XPS techniques, with the synergetic effect of well-dispersed platinum nanoparticles in the MOF-5 channel. In addition, the results of the recycling experiment exhibited that there was no significant loss after the catalyst was reused 5 times.

Nucleation and growth process of atomic layer deposition platinum nanoparticles on strontium titanate nanocuboids

Uniform, well-dispersed platinum nanoparticles were grown on SrTiO3 nanocuboids via atomic layer deposition (ALD) using (methylcyclopentadienyl)trimethylplatinum (MeCpPt(Me)3) and water. For the first half-cycle of the deposition particles formed through two sequential processes: initial nucleation and growth. The final particle size after a single complete ALD cycle was dependent on the reaction temperature which alters the net Pt deposition per cycle. Additional cycles resulted in further growth of previously formed particles. However, the increase in size per cycle during additional ALD cycles, beyond the first, was significantly lower as less Pt was deposited due to carbonaceous material that partially covers the surface and prevents further MeCpPt(Me)3 adsorption and reaction. The increase in particle size was also temperature dependent due to changes in the net Pt deposition. Pt nanoparticles increased in size by 59% and 76% after 15 ALD cycles for reaction temperatures of 200 °C and 300 °C, respectively. There was minimal change in the number of particles per unit area as a function of reaction time, indicating that there was minimal Ostwald ripening or secondary nucleation for the reaction conditions.

Synthesis and stabilization of Pt nanoparticles in core cross-linked micelles prepared from an amphiphilic diblock copolymer

In this study, an amphiphilic poly(ethylene glycol)methyl ether-block-poly(glycidyl methacrylate) diblock copolymer (MPEG-b-PGMA) was synthesized via atom transfer radical polymerization (ATRP), and its micellar solution was prepared in acetone/water mixture. Core cross-linked (CCL) micelles were synthesized by cross-linking the epoxy functional group of poly(glycidyl methacrylate) block with ethylenediamine. These CCL micelles were used in the synthesis and stabilization of platinum nanoparticles (PtNPs) in aqueous media. Transmission electron microscopy (TEM) images showed that well-dispersed PtNPs with a diameter of around 5 nm were formed within the MPEG-b-PGMA spherical CCL micelles having 22.0 ± 3.0 nm diameters. The mean TEM diameter of the PtNPs is of the order of several nanometers, which is consistent with the plasmon absorption peaks observed at around 205 and 261 nm. The catalytic activity of CCL micelle-PtNP dispersion was also investigated in the reduction of p-nitrophenol to p-aminophenol in the presence of NaBH4. The results showed that the PtNPs exhibit a good catalytic activity toward reduction of p-nitrophenol. CCL micelle-stabilized PtNP dispersions were stable for long periods of time without changing properties at room temperature. CCL micelles found to be good hostage or stabilizer for the NPs in aqueous media.

Well-dispersed platinum nanoparticles supported on hierarchical nitrogen-doped porous hollow carbon spheres with enhanced activity and stability for methanol electrooxidation

Hierarchical nitrogen-doped porous hollow carbon spheres (HNPHCS) with porous-thin mesoporous shell and hollow macroporous core structure have been prepared via in-situ oxidation polymerization method using polyaniline as the precursor. After carbonization at 900 °C, the average diameter of HNPHCS is ca. 140 nm with shell thickness of ∼1 nm. Pt nanoparticles with high dispersion and small size have been successfully deposited on the HNPHCS by a microwave-assisted polyol process to synthesize Pt/HNPHCS catalyst. The obtained samples are characterized by physical characterization and electrochemical measurements. Electrochemical studies reveal that the prepared Pt/HNPHCS catalyst possesses notably higher catalytic activity and CO-tolerance, and better stability toward methanol electrooxidation in comparison with Pt/nitrogen-doped porous carbon and the commercial Pt/C catalysts. It is likely that enhanced catalytic properties of the Pt/HNPHCS could be due to the high dispersion of small Pt nanoparticles, the presence of nitrogen species, developed porous-thin mesoporous shell and hollow macroporous core structure of support HNPHCS. As a result, the as-developed Pt/HNPHCS present attractive advantages for the application in fuel cell electrocatalyst.

A two-step reduction method for synthesizing graphene nanocomposites with a low loading of well-dispersed platinum nanoparticles for use as counter electrodes in dye-sensitized solar cells

Low Pt-loaded graphene nanocomposites were prepared using a two-step reduction process. Graphene dispersion was first prepared from graphene oxide using hydrazine hydrate as a reducing agent. Pt-reduced graphene oxide composites were then synthesized in the aqueous graphene dispersion at 90 °C without the need for another reductant. Pt/graphene composite films were then deposited on fluorine-doped tin oxide substrates using a simple drop-casting method at room temperature and subsequently used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). Cyclic voltammetry and electrical impedance analysis show that the composite electrodes have high electrocatalytic activity toward iodide/triiodide reduction. The energy conversion efficiency of the Pt/graphene CE-based DSSC was found to be 1.9 % lower than that of cells with a Pt-based CE.

Electrospinning of silica sub-microtubes mats with platinum nanoparticles for NO catalytic reduction

Silica sub-microtubes loaded with platinum nanoparticles have been prepared in flexible non-woven mats using co-axial electrospinning technique. A partially gelated sol made from tetraethyl orthosilicate was used as the silica precursor, and oil was used as the sacrificial template for the hollow channel generation. Platinum has been supported on the wall of the tubes just adding the metallic precursor to the sol–gel, thus obtaining the supported catalyst by one-pot method. The silica tubes have a high aspect ratio with external/internal diameters of 400/200nm and well-dispersed platinum nanoparticles of around 2nm. This catalyst showed a high NO conversion with very high selectivity to N2 at mild conditions in the presence of excess oxygen when using C3H6 as reducing agent. This relevant result reveals the potential of this technique to produce nanostructured catalysts onto easy to handle conformations.

TiO<sub>2</sub> Nanotube Film as the Support of Platinum Electro-Catalyst with Enhanced Electrochemical Activity for Methanol Oxidation

A facile method to prepare well-dispersed Platinum nanoparticles (Pt NPs) on FTO and TiO2 nanotube (TNTs) film was reported. The so-prepared Pt/FTO and Pt/TNT film electrodes are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD). The results show Pt NPs have been dispersed on the supporting matrixs uniformly. Electrochemical investigations indicate that Pt/TNT has higher electrocatalytic activity and better tolerance to poisoning species in methanol oxidation than Pt/FTO, which can be ascribed to the high dispersion of Pt NPs on the TiO2 nanotubes surface. The present method is promising for the design of high performance catalysts for direct methanol fuel cells.

Well-Dispersed Platinum Nanoparticles Supported on Nitrogen-Doped Hollow Carbon Microspheres for Oxygen-Reduction Reaction

Well-Dispersed Platinum Nanoparticles Supported on Nitrogen-Doped Hollow Carbon Microspheres for Oxygen-Reduction Reaction

Characterization and Electrochemical Properties of Nitrogen-Doped Ordered Microporous Carbons Containing Well-Dispersed Platinum Nanoparticles

Ordered high surface area microporous carbon molecular sieves containing well-dispersed platinum nanoparticles have been prepared by chemical vapor deposition method. Acetonitrile was employed as carbon and nitrogen precursors to yield N-doped carbon molecular sieves. N-doped carbons have an average nitrogen content of ~ 4.1 wt%. Electrochemical tests showed that the rectangular-shaped CVs of N-doped carbons could be well retained over a wide range of scan rates (5~100 mV/s), and the CV curves presented a steep current change at the switching potentials. N-doped carbons exhibited excellent performance as an electrochemical supercapacitor with a calculated specific capacitance of 168 F/g. Meanwhile, it was noticed that a reasonable Pt loading would help to improve the capacitance. It was proposed that the polarizability or surface state modification by nitrogen doping and regular interconnected porous structure might contribute to the improvement of N-doped carbons’ electrochemical properties.

Electrodeposition of monodispersed platinum nanoparticles on a glassy carbon electrode for sensing methanol

A facile, one-step and template-free method has been developed for the electrodeposition of well-dispersed platinum nanoparticles (Pt-NPs) on a glassy carbon electrode. The effects of various inorganic anions and overpotential on the morphologies and dimensions of the final products were investigated. The resulting Pt-NPs show high electrocatalytic activity towards methanol oxidation and are less easily poisoned by carbon monoxide.

Size-, and Shape-Selective Synthesis of Platinum Nanoparticles from Pt(<I>β</I>-Diketonate)<SUB>2</SUB> Complexes in Organic Media

Preparation of platinum nanoparticles from two beta-diketonate complexes of platinum, Pt(hfac)2 and Pt(acac)2 (hfac: hexafluoroacetylacetonate, acac: acetylacetonate) in organic media will be presented in the contribution. Nearly spherical, well-dispersed platinum nanoparticles were fabricated by thermally-induced reduction of Pt(hfac)2 in the presence of teraalkylammonium salts as the stabilizing agents in several organic solvents. Particle sizes ranging from 9 to 15 nm can be controlled by variation of the surfactant, the concentrations of precursor and surfactant, as well as reaction temperature. Heating the solution of Pt(acac)2 complex in 1-octanol at appropriate temperatures provided the platinum nanocubes and the influence of reaction temperature on the particle shape was investigated.

Ordered micro-porous carbon molecular sieves containing well-dispersed platinum nanoparticles for hydrogen storage

Ordered micro-porous carbon molecular sieves containing highly dispersed platinum nanoparticles with tunable sizes from 1 to 6 nm are synthesized in this work. The synthesis is simply realized by nanocasting of furfuryl alcohol precursor on Pt-impregnated NaY zeolite hard templates and complemented by chemical vapor deposition by propylene gas. During the carbonization, Pt ions can be reduced to form highly dispersed Pt nanoparticles on the carbon matrixes. This method allows a very high Pt-loading up to 40 wt % while maintaining a high metal dispersion. X-ray diffraction and transmission electron microscopy measurements reveal the existence of uniformly dispersed Pt nanoparticles and microstructural regularity. Nitrogen adsorption isotherms show that the ordered micro-porous carbon molecular sieves possess a high surface area around 2750 m 2/g, large micro-pore volume 1.38 cm 3/g, and narrow pore size distribution (∼1 nm) in the micropore-range. A high hydrogen uptake up to 2.8 wt% at 77 K and 1 bar is observed. A high and relatively homogeneous value of hydrogen adsorption heat 11 kJ/mol in 1% Pt contained carbon was obtained, which exceeds the literature reported values for other carbon based adsorbents or metal organic framework compounds and is very close to the optimal value, 15 kJ/mol, recommended in the literature, suggesting a great potential for hydrogen storage or fuel cell applications.

Highly dispersed platinum–carbon aerogel catalyst for polymer electrolyte membrane fuel cells

Platinum loaded carbon aerogel catalysts for application in polymer electrolyte membrane fuel cells have been synthesized from the alcoholic sol–gel reaction of phloroglucinol with furfural using propylene oxide as a reducing agent of platinum salt, followed by supercritical drying with carbon dioxide. Subsequent carbonization of the platinum–organic aerogels under a reducing gas flow produced platinum–carbon aerogels. X-ray diffraction and transmission electron microscopy analyses of the platinum–carbon aerogel catalysts indicate the formation of well-dispersed platinum nanoparticles having sizes of about 3 nm. Surface characterization of the platinum–carbon aerogel by X-ray photoelectron spectroscopy reveals that 60% of the platinum is present in its metallic state. Electrochemical characterization by hydrogen adsorption/desorption cyclic voltammetry and CO stripping voltammetry indicates that the electrochemical active surface areas of the platinum–carbon aerogel are comparable to those of commercial catalysts.

Pt/C Catalyst Preparation Using Rotating Disk-Slurry Electrode (RoDSE) Technique

The Pt/C catalyst preparation by electrodeposition was done using a rotating disk electrode technique. The electrodeposition was carried out in a solution containing carbon black (Vulcan XC-72R), K2PtCl6 and 0.1M H2SO4 using a glassy carbon electrode for the potential applied. The convection of the technique and the applied potential permits the deposition at different sides of the carbon powder particle. The Pt deposition was analysed by TEM, nano XRF, and XRD. The TEM image showed Pt particles with sizes {greater than or equal to} 3 nm. The nano XRF and XRD confirm the presence of platinum nanoparticles showing the characteristic peak of this element. The use of the rotating disk-slurry technique was an effective method for the platinum electrodeposition because we can obtain well-dispersed platinum nanoparticles over the carbon powder support.