Particle Size Of Pt Nanoparticles Research Articles

CeOx‐induced oxygen vacancy‐enhanced Pt‐based titanium silicalite‐1 catalysts for selective conversion of levulinic acid

The selective conversion of levulinic acid (LA) obtained from lignocellulosic biomass represents a crucial pathway for producing the key value‐added chemical compound γ‐valerolactone (GVL). Herein, we constructed a series of Pt‐based titanium‐silicalite‐1 (TS‐1) bifunctional catalysts modified with rare earth metal Ce through a simple spin‐coating impregnation method, and the catalytic performance was significantly improved compared to the unmodified Pt1.2/TS‐1. Pt0.7‐Ce0.5/TS‐1 exhibited the best aqueous‐phase catalytic activity (with a GVL yield of 99.4%). The introduction of CeOx can reduce the particle size of Pt nanoparticles and promote the formation of electron‐rich Pt species while delivering abundant oxygen vacancies (OV) for the catalysts. The characterization and testing results highlight the synergistic effect of OV and electron‐rich Pt sites on the oriented adsorption and selective hydrogenation of LA, providing new insights into constructing more efficient noble metal‐based zeolite catalysts for biomass conversion.

Total oxidation of propane using titania-supported platinum nanoparticles prepared through sol-immobilization

A set of mono-metallic nanoparticles catalysts, including palladium, platinum, and gold supported on titania, were prepared via the sol-immobilization technique, and evaluated for the total oxidation of propane as a model reaction of volatile organic compounds (VOCs) oxidation, which is a wide-ranging group of organic pollutants that contribute to serious atmospheric problems. The results showed that 1 wt.% Pt/TiO2 was the most active catalyst toward CO2, as the catalyst was very active, and the complete conversion of propane was achieved with full selectivity toward CO2. The effect of the support type was investigated through the immobilization of platinum nanoparticles on CeO2 and γ-Al2O3. The results indicated that the catalytic activity follows the order 1% Pt/TiO2 > 1% Pt/CeO2 > 1% Pt/Al2O3. For the Pt/TiO2 catalyst, the influence of the calcination temperature and metal loading on the catalytic activity was investigated. There is a slight increase in the Pt particle size when raising the calcination temperature from 300 °C to 500 °C, which enhances the catalytic activity of 1% Pt/TiO2 at 500 °C. Furthermore, increasing the metal loading from 0.1 to 1 wt.% enhances the catalytic activity as a result of the increase in particle size. Different characterization techniques were utilized, including XRD, TEM, XPS, and MP-AES, to determine the structure-activity relationship, and together they indicate that the catalytic activity is influenced more by the particle size of Pt nanoparticles than by the oxidation state.

(Digital Presentation) The Utilization of Platinum Catalysts Deposited on Carbon Support Synthesized from Coffee Grounds in a Polymer Electrolyte Membrane Fuel Cell

Exploring alternative sources for platinum catalyst carbon support material is vital for the further development of polymer electrolyte membrane fuel cells (PEMFC).1 The support material and the method of depositing Pt nanoparticles are crucial for defining the catalytic properties of the catalyst. In this study, carbon support material, derived from coffee grounds was used in the preparation of Pt catalysts for PEMFC application. The carbon material was synthesized using ZnCl2 activated pyrolysis method2 and the Pt nanoparticles were deposited onto carbon support by two methods: using ethylene glycol3 or hydrogen4 as a reducing agent.The physical properties of the support material, as well as catalysts were analysed through thermogravimetric analysis (TGA), dynamic light scattering, X-ray diffraction (XRD), N2 sorption analysis and high-resolution scanning electron microscopy (HR-SEM) methods. The electrochemical activity, as well as the electrochemically active surface area (ECSA) of the catalysts were determined in a completed PEMFC. The properties and performance of catalysts synthesised were compared with the catalyst which was deposited onto commercial carbon (Ketjenblack, EC-300J).TGA displayed that carbon derived from coffee grounds contained 6.9 % of impurities by mass in the form of metal oxides and that the coffee carbon Pt catalyst contained 60 wt% of Pt. The Pt crystallite size was determined through XRD and it was 1.4 nm. HR-SEM analysis displayed that the average particle size of Pt nanoparticles on the coffee carbon catalyst was 4.7±2.5 nm. Results from N2 sorption analysis showed that all materials were micro-mesoporous, with coffee ground carbon having a specific surface area of 590 m2 g-1. The coffee carbon Pt catalyst produced smaller results of 370 m2 g-1 compared to the carbon support, due to the Pt nanoparticles depositing in the micropores, however still had a larger specific surface area than the commercial carbon catalyst with a specific surface area of 300 m2 g-1.Catalysts deposited on coffee ground carbon produced comparable electrochemical results to catalysts deposited on commercially available carbon. The coffee carbon catalyst produced a higher ECSA of 64 mPt 2 gPt -1, compared to the commercial carbon catalyst with an ECSA of 51 mPt 2 gPt -1. The current density of the Pt catalyst deposited onto coffee carbon was 0.68 A cm-2 at 670 mV, whilst in the same conditions commercial carbon peaked at 0.70 A cm-2. Both coffee and commercial carbon Pt catalysts produced similar power density maximums with the coffee Pt catalyst producing 0.56 W cm-2 and the commercial Pt catalyst producing 0.60 W cm-2.Physical and electrochemical characterizations displayed that higher ECSA values were strongly correlated to smaller Pt crystallite size. Other techniques to increase fuel cell performance were also experimented with, such as covering the gas diffusion layer with catalyst instead of Nafion membrane and adding additional Nafion layers, with both methods producing promising results.This study displays that there is a lot of potential in improving the catalytic performance of Pt catalysts by depositing on support materials derived from alternative sources. The methods of boosting PEMFC performance could be further investigated for catalysts deposited on different carbon supports. Acknowledgements This work was supported by the EU through the European Regional Development Fund TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011), Personal Research Grant PRG676 and by private limited company AuVe Tech LLTKT20148 “Production of Polymer Electrolyte Membrane Fuel Cells”. The SEM measurements were conducted using the NAMUR+ core facility funded by the Estonian Research Council (TT 13). References S. Shahgaldi and J. Hamelin, Carbon, 94, 705-728 (2015). M. Härmas, PhD thesis, University of Tartu, Tartu, Estonia (2020). Y. Shao, S. Zhang, R. Kou, X. Wang, C. Wang, S. Dai, V. Viswanathan, J. Liu, Y. Wang, Y. Lin, J. Power Sources 195, 1805-1811 (2010). Y. Zheng, Z. Dou, Y. Fang, M. Li, X. Wu, J. Zeng, Z. Hou, S. Liao, J. Power Sources, 306, 448-453 (2015).

Ammonia sensing characteristics of a cerium oxide thin film coated with platinum nanoparticles

This paper reports on ammonia (NH3) sensing characteristics of a new semiconducting metal oxide (SMO) sensor. employing a cerium oxide (CeO2) thin film and platinum (Pt) nanoparticles (NPs) as a sensing layer. The thickness of CeO2 thin film is 30 nm and the particle size of Pt NPs is about 4–6 nm. Based on the enhanced surface area/volume (SA/V) ratio and catalytic ability of Pt metal, the sensing behaviors are efficiently improved owing to the smaller Pt NPs. A high sensing response of 5.81 under 1000 ppm NH3/air gas and a low detectable content of 1 ppm NH3/air are acquired at 275 ℃. In addition, a relatively fast sensing action with the response (recovery) times of 15 s (85 s) and 6 s (25 s) are observed upon exposure to 1000 and 1 ppm NH3/air gas, respectively, at 300 ℃. The Langmuir isotherm is used to study the related surface coverage under introduced ammonia gas. The proposed Pt NP/CeO2 sensor shows prominent stability for long-term operation without intentional passivation treatment. The proposed sensor device’s benefits include a simple device structure, relatively easy manufacturing, a wide sensing range of ammonia gas content (1–1000 ppm NH3/air), and lower cost.

Achieving uniform Pt deposition site by tuning the surface microenvironment of bamboo-like carbon nanotubes

The surface microenvironment of supports, including surface state and constitution, are crucial adjective factors to the dispersibility and particle size of Pt nanoparticles (NPs) on carrier, follow-up affecting their catalytic activities for methanol oxidation reaction (MOR). Here an in-situ pyrolysis approach is reported for preparing bamboo-like N doped carbon nanotubes coupled with fewer metallic particles (M@N-CNTs (M = Co, Ni and Fe3C)), enabled tunable surface state and constitution of carbon layers. Combined experimental and theoretical investigation, as fabricated Co@N-CNTs provide optimal surface of backbone for Pt deposition with narrowest particle size distribution and minimum size by virtue of dominated pyridinic-N, enriched defect, abundant wrinkle and fewer number of carbon layer, which exhibits superior MOR performance as well as long-lifespan. Our findings not only exhibit some new insights for accurate modulation and optimization of carbon skelecton at the atomic scale in fundamental, but also reveal the structural and compositive origin of the enhanced catalytic activity towards to MOR.

Particle Size Effect on Platinum Dissolution: Practical Considerations for Fuel Cells.

The high costs of polymer membrane electrolyte fuel cells (PEMFCs) remain a roadblock for a competitive market with combustion engine vehicles. The PEMFC costs can be reduced by decreasing the size of Pt nanoparticles in the catalyst layer, thereby increasing the Pt dispersion and utilization. Furthermore, high-power performance loss due to O2 transport resistance is alleviated by decreasing the particle size and increasing dispersion. However, firm conclusions on how Pt particle size impacts durability remain elusive due to synthetic difficulties in exclusively varying single parameters (e.g., particle size and loading). Therefore, here the particle size of Pt nanoparticles was varied from 2.0 to 2.8 and 3.7 nm while keeping the loading constant (30 wt %) on a Vulcan support using the two-step surfactant-free toolbox method. By studying the electrochemical dissolution in situ using online inductively coupled plasma mass spectrometry (online ICP-MS), mass-specific dissolution trends are revealed and are attributed to particle-size-dependent changes in electrochemically active surface area. Such degradation trends are critical for the start/stop of PEMFCs and currently require the implementation of potential control systems in consumer vehicles. Additionally, shifts in the onset of anodic dissolution and also oxidation to more negative potentials with decreasing particle size were observed. These results indicate a similar mechanism of anodic dissolution related to place-exchange when moving from extended polycrystalline Pt to nanoparticle scales. The negative shifts in the onset as the particle size decreases highlight a practical limitation for PEMFCs during load/idle conditions: without further material improvements, which inhibit Pt dissolution, reduction in costs and improvement in high-power performance via increased Pt utilization and dispersion will not be possible by decreasing particle sizes further.

Partially embedding Pt nanoparticles in the skeleton of 3DOM Mn2O3: An effective strategy for enhancing catalytic stability in toluene combustion

Polymethyl methacrylate-templating and ethylene glycol reduction methods were adopted to prepare the nanosized Pt catalysts (x wt% Pt/3DOM Mn2O3; x = 0.2–2.3) that were partially embedded in the skeleton of three-dimensionally ordered macroporous (3DOM) Mn2O3. These materials possessed a surface area of 33–36 m2/g, with the Pt NPs (3.6–4.4 nm in size) being well embedded in the skeleton of 3DOM Mn2O3. The 2.3 wt% Pt/3DOM Mn2O3 sample showed the best activity and the lowest apparent activation energy (41 kJ/mol) for toluene combustion, which was related to its high adsorbed oxygen species concentration and good low-temperature reducibility. Compared with 2.0 wt% Pt/3DOM Mn2O3-imp derived from the colloid adsorption method, 2.3 wt% Pt/3DOM Mn2O3 exhibited a better catalytic stability within 60 h of toluene combustion. After calcination at 650 °C for 3 h, the average particle size of Pt nanoparticles (NPs) in 2.3 wt% Pt/3DOM Mn2O3 grew up slightly from 4.3 to 4.9 nm and toluene conversions decreased slightly, while that of Pt NPs in 2.0 wt% Pt/3DOM Mn2O3-imp increased greatly from 4.4 to 13.7 nm and toluene conversions dropped significantly. Effects of H2O, CO2, and SO2 on activity of 2.3 wt% Pt/3DOM Mn2O3 and 2.0 wt% Pt/3DOM Mn2O3-imp were also examined. Partial deactivation induced by H2O or CO2 addition was reversible, whereas that due to SO2 introduction was irreversible. It is concluded that the strong interaction between Pt NPs and 3DOM Mn2O3 was responsible for excellent stability of the partially Pt-embedded 3DOM Mn2O3 sample in toluene combustion.

Facile preparation of Pt/CdS photocatalyst by a modified photoreduction method with efficient hydrogen production

A series of 0.75 wt% Pt/CdS photocatalysts were successfully synthesized via a modified photoreduction process, with the assistance of a protective agent (polyvinylpyrrolidone, PVP) and/or structural inducer (NaI, NaBr, and NaCl). The physicochemical properties of the obtained 0.75 wt% Pt/CdS photocatalysts were characterized in more detailed. Their photocatalytic efficiencies were evaluated by visible-light photocatalytic hydrogen production. The results show that the photocatalytic activities of 0.75 wt% Pt/CdS photocatalysts for H2 production mainly depend on the type of structural inducer. Furthermore, a suitable ratio of PVP/NaI is necessary to optimize the photocatalytic performance of Pt/CdS composites. Notably, 0.75 wt% Pt/CdS (PVP/NaI = 4:1) gains the highest hydrogen production activity with a rate of 1155.8 μmol h−1, which is 1.8 times higher than that of 0.75 wt% Pt/CdS obtained from the traditional photoreduction method (640.9 μmol h−1) and 17.3 times higher than that of the bare CdS sample (66.9 μmol h−1). The as-prepared 0.75 wt% Pt/CdS photocatalyst (PVP/NaI = 4:1) also exhibits a good stability. An optimum ratio of PVP/NaI not only causes a decrease in particle size of Pt nanoparticles but also leads to an increase in BET specific surface area of Pt/CdS and an enhanced electron transfer capability of Pt nanoparticles, which should be responsible for the enhanced photocatalytic performance.

Achievement of distinctively high durability at nanosized Pt catalysts supported on carbon black for fuel cell cathodes

We have established a method for the preparation of Pt nanoparticles (NPs) with a series of target mean-diameters (dm) and sharp size-distribution, supported on graphitized carbon black (GCB), Pt/GCB, without changing the mean interparticle distances (dPt-Pt), on GCB surfaces. This is achieved by the deposition of additional Pt-skin layer(s) on the NPs surfaces of the core Pt/GCB from its suspending aqueous solution, which contains precise amounts of Pt-complex equivalent to the projected thickness of Pt skin-layer(s), by simple bubbling of hydrogen, where the core Pt/GCB was prepared by the nanocapsule method that is able to provide NPs with highly uniform dispersion on the support with an extremely narrow size distribution. Contrary to the common view, we were able to demonstrate a lack of dependence of the long-term stability on the particle size of Pt NPs (dm<5nm) using test protocols for monitoring the load-change cycling and start/stop operation of polymer electrolyte fuel cells (PEFCs) at 65°C. This finding is evidence that the so-called “particle size effect” on the stability is not intrinsic but avoidable for the NP catalysts, in addition to our previous demonstration of the independence of the initial specific activity upon Pt NPs sizes for the oxygen electroreduction. This deviation from “common-sense,” i.e., the improvement of the activity and stability at Pt NPs by means of the sharp size distribution and their uniform dispersion on the GCB support, becomes extremely important as a guiding principle to develop cathode catalysts for practical PEFCs. The present unique achievement of the durability is probably brought about by the mitigation of nonuniform growth of Pt NPs via Ostwald ripening. This is most likely due to the uniform Pt dissolution/re-deposition among the uniformly sized and distributed nanoparticles.

Simulation of LSPR based fiber optic sensor utilizing layer of platinum nanoparticles

Analysis of localized surface plasmon resonance (LSPR) based fiber optic sensor using platinum (Pt) nanoparticles is carried out. For a fixed particle size of Pt nanoparticles, the sensitivity and figure of merit (FOM) increase with increase in thickness of Pt nanoparticles layer. Besides, sensitivity enlarges as the particle size increases from 5nm to 10nm and afterwards, it starts sinking with further increase in the particle size of Pt nanoparticles for all thicknesses of Pt nanoparticles layers. Optimized thickness and particle size of Pt nanoparticles layer are 50nm and 10nm respectively. 50nm thick Pt nanoparticles layer, particle size 10nm based sensor possesses sensitivity of 7450nm/RIU.

Pt/HZSM-5 catalyst synthesized by atomic layer deposition for aqueous-phase hydrogenation of levulinic acid to valeric acid

A Pt/HZSM-5 catalyst was prepared by atomic layer deposition (ALD) for aqueous-phase hydrogenation of levulinic acid (LA) to valeric acid (VA). 5Pt/HZSM-5 produced with 5 cycles of Pt ALD was identified as a highly active and stable bifunctional catalyst, and a high yield of VA (91.4%) was achieved in aqueous solution. A close interaction between Pt and acid sites of HZSM-5 is favor for the selective generation of VA. The microporous structure and the acid sites of HZSM-5 were not changed after Pt ALD, and some Pt nanoparticles were located in the micropore channel of HZSM-5. This reveals that the Pt ALD has the advantage to protect the structure of zeolite. The average particle size of Pt nanoparticles, electric state of surface Pt, and surface acid sites are nearly not changed with the increase of Pt ALD cycle number. However, the ratio of Pt in the pore channel to that out of the pore decreases with the increase of ALD cycle numbers, resulting in a decrease of TOF of VA yield. For comparison, Pt nanoparticles supported on HZSM-5 were also produced by impregnation. But the pore structure of HZSM-5 was damaged, and more micropore were formed by impregnation method for Pt loading. Moreover, it exhibited very low catalytic activity, selectivity of VA, and stability.

Influence of pH on performance of sodium phosphinate for decreasing the particle size

ABSTRACTTo clarify the influence of pH on performance of sodium phosphinate (NaPH2O2) for decreasing particle size of Pt nanoparticles, carbon-supported Pt nanoparticles that contained phosphorus (P–Pt/C) were synthesised by an electron-beam irradiation reduction method (EBIRM) under four different pH conditions (pH = 3, 6, 9, and 12) and under five different NaPH2O2 concentrations (0.0, 0.5, 1.0, 3.0, and 5.0 mM). The relationship among pH, NaPH2O2 concentration, average particle size of Pt nanoparticle, and Pt loading weight was investigated in this study. The average particle size of Pt nanoparticles was in the range of 0.8–3.4 nm and lower in the order; pH12 > pH3 > pH6 > pH9; for example, under the same NaPH2O2 concentrations of 3.0 mM, the particle size of P–Pt/C prepared at pH = 12 and pH = 9 was 1.5 and 0.8 nm, respectively. In addition, Pt loading weight was also lower in the order; pH12 > pH3 > pH6 > pH9. In summary, these results indicated that the pH in the precursor solution affected the performance of NaPH2O2. These findings would be useful for controlling the particle size of monometallic Pt and Pt-based bimetallic nanoparticles supported on carbon particles for fuel cell applications.

Self-assembled platinum nanoparticles on sulfonic acid-grafted graphene as effective electrocatalysts for methanol oxidation in direct methanol fuel cells.

In this article, sulfonic acid-grafted reduced graphene oxide (S-rGO) were synthesized using a one-pot method under mild conditions, and used as Pt catalyst supports to prepare Pt/S-rGO electrocatalysts through a self-assembly route. The structure, morphologies and physicochemical properties of S-rGO were examined in detail by techniques such as atomic force microscope (AFM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The S-rGO nanosheets show excellent solubility and stability in water and the average particle size of Pt nanoparticles supported on S-rGO is ~3.8 nm with symmetrical and uniform distribution. The electrocatalytic properties of Pt/S-rGO were investigated for methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). In comparison to Pt supported on high surface area Vulcan XC-72 carbon (Pt/VC) and Pt/rGO, the Pt/S-rGO electrocatalyst exhibits a much higher electrocatalytic activity, faster reaction kinetics and a better stability. The results indicate that Pt/S-rGO is a promising and effective electrocatalyst for MOR of DMFCs.

Effects of electron charge density and particle size of alkali metal titanate nanotube-supported Pt photocatalysts on production of H2 from neat alcohol.

Pt nanoparticles (PtNPs) in the range of 1.0-3.0 nm were deposited on alkali titanate nanotubes (MTNTs = M2-xHxTi3O7, M = Li(+), Na(+), K(+) and Cs(+)) by wet impregnation. While most of the physical properties of Pt/MTNTs remained almost constant, the oxidation state and size of PtNPs varied systematically with the size of the cations of MTNTs. XPS indicated that the binding energy of Pt in Pt/MTNTs was reduced to a lower value than that of Pt(0), yielding a Pt(δ-) oxidation state. Diffuse-reflectance infrared Fourier transform spectroscopy coupling with CO adsorption studies confirmed the formation of the Pt(δ-) state in Pt/MTNTs. Thus, electrons were transferred from MTNTs to PtNPs establishing an electric double layer at the interface between PtNP and MTNT supports, and the degree of electron transfer increased with the size of the cations in MTNTs. HRTEM revealed that the mean sizes of PtNPs followed the order, Pt/LiTNTs < Pt/NaTNTs < Pt/KTNTs < Pt/CsTNTs. TPR showed that the reducibility of PtOx/MTNTs determined the order of PtNPs size. In the photocatalytic production of H2 (2H(+) + 2e(-)→ H2), since H2 is produced at the interfacial Pt sites, the electron charge density and the particle size of PtNPs are the two competing factors in producing H2. Photoluminescence studies revealed that the initial increase in electron density on PtNPs reduced the recombination of h(+)-e(-) pairs and increased H2 yields, but a further increase in charge density enhanced the recombination of h(+)-e(-) pairs and lowered the H2 yield. PtNPs in Pt/KTNTs had a moderate charge density and a moderate particle size, and so, produced a maximum amount of H2 among Pt/MTNTs.

Preparation of Pt Nanoparticle-Adsorbed Carbon Nanotubes Using Room Temperature Ionic Liquid and Their Use as Electrocatalyst for Oxygen Reduction

Carbon nanotube (CNT) possesses unique characteristics with extremely high mechanical resistance. This conducting material is suitable to fabricate electrode materials. Also it is expected to utilize CNT as an ideal supporting material because of its large surface area-t-volume ratio. However, it is quite difficult to equip functional materials including catalysts with CNT having surface inertness. To immobilize materials on CNT, some modification of the CNT surfaces, such as partial oxidation, is required to generate functional groups, to which functional materials are anchored. In our previous studies, we found that metal sputtering onto room temperature ionic liquid (RTIL) under reduced pressure produces metal nanoparticles suspended in the ionic liquid.1-3 By this way, several kinds of nanoparticles including alloy4 and hollow nanoparticles5 have been synthesized, so far. In addition, putting Au nanoparticles suspended IL onto the inert surface of a highly oriented pyrolytic graphite (HOPG) followed by heating was found to immobilize firmly the nanoparticles on the HOPG surface.6 In the present research, attempts have been made to preparation of Pt nanoparticle-adsorbed carbon nanotubes (Pt-CNT) by the aforementioned method and electrocatalytic activities of the prepared Pt-CNT toward O2reduction was examined. RTILs used for the preparation of Pt nanoparticles were dried in vacuum prior to use. A glass plate (2.5 ×2.5 cm), on which RTIL (0.4 mL) was spread, was set in a Cressington 108 auto SE sputter coater. A Pt foil target (Φ5.7 cm, 99.98%) was placed on 4.5 cm above the glass plate. Sputter deposition onto RTIL was conducted with 40 mA of sputter current in dry Ar (99.999 %) atmosphere whose pressure did not exceed 7 ± 1 Pa. The sputtering was conducted at room temperature (298 ± 2 K). Preparation of Pt-CNT was attempted by agitating the Pt sputtered RTIL (0.4 mL) with untreated CNTs (1 mg) at 573 K for 5 h. The resultant mixture was rinsed by dry acetonitrile several times to remove RTIL, followed by drying in vacuo. A transmission electron microscope (TEM) image of the resulting CNT is given in Figure 1, which shows adsorption of numerous Pt nanoparticles on the surface of CNT. Chemical analysis of Pt-CNT revealed that RTIL worked as a paste to stick Pt nanoparticles on the CNT surface. The mean particle size of Pt nanoparticles on SWCNT was ca. 3.5 nm and the amount of Pt nanoparticle on the Pt-SWCNT composite was 32.9 wt%. We prepared three Pt-SWCNT composites whose amounts of Pt on SWCNT were 7.1, 16.0, 24.1 and 32.9 wt% in order to examine their electrocatalytic activities toward oxygen reduction. A rotating ring-disk electrode (RRDE) with glassy carbon disk and Pt ring electrodes was used. Pt-CNT (1 mg) was dispersed in 0.2 mL iso-propanol and 5 μL of the dispersion liquid was applied to the disk electrode and fixed by putting 5 μL of a Nafion iso-propanol solution. The prepared electrode was pretreated with multiple potential scans between 0.5 and 1.25 V vs. RHE in 0.1 M HClO4 aqueous solution under N2. The electrochemical surface areas (ECSAs) were measured from cyclic voltammograms, giving 34.4, 30.3, 40.2, and 48.7 m2g-1of ECSAs for Pt-CNTs with 7.1, 16.0, 24.1 and 32.9 wt% Pt. Figure 2 shows voltammograms of disk electrodes modified with four kinds Pt-CNTs and the corresponding voltammograms for the ring electrodes. The onset potential of oxygen reduction became positive with increment of the Pt loading amount. The ring electrode detects H2O2produced in oxygen reduction at the disk electrode, however its amount was quite low; generation rate was below 5 % for Pt-CNT with 24.1 wt% and 32.9 wt% Pt even at potentials negative than 0.4 V vs. RHE, and also it was close to 0% for all cases at potentials between 0.7 to 0.85 V. These results showed that Pt-CNT has a favorable electrocatalytic activities for oxygen reduction.

Improved catalysts for hydrogen/deuterium exchange reactions

The hydrogen isotope exchange reaction between hydrogen and water is a key process in water detritiation and heavy water production. To improve the characteristics of hydrophobic catalysts for this type of reaction, foamed and cellular structures of hydrophobic catalysts were successfully prepared by adding a blowing agent. The mean particle size of Pt nanoparticles was 2.3 nm. The proportions of elemental Pt and Pt oxides were 62% and 38%, respectively. The addition of polymethyl methacrylate powder decreased internal diffusion of water vapor and hydrogen inside the catalyst and improved active site utilization. As a result, the catalytic activities of the hydrophobic catalysts are significantly higher than those of conventional hydrophobic catalysts for hydrogen isotope exchange. All catalysts exhibited excellent hydrophobic performances after 30 days of testing. It was reasonable to mix Pt/C catalysts, polytetrafluoroethene and polymethyl methacrylate in a ratio of 1:2:1 before hydrophobic treatment. Finally, the mechanisms of hydrogen–water diffusion and exchange were investigated.

Platinum electrocatalysts attached to carbon nanotubes by atomic layer deposition with different cycle numbers

This study adopts an atomic layer deposition (ALD) process to prepare ultra-low Pt loading over the surface of carbon nanotubes (CNTs), showing superior power density in single-stack proton exchange membrane fuel cells (PEMFCs). The ALD cycle number (i.e., 50, 100, 200, and 400 cycles) serves as a key factor in controlling the particle size and the weight loading of Pt deposits. Two linear plots of the Pt loading and the particle size versus the ALD cycle number confirm the presence of self-limiting reaction steps. The growth rate is estimated to be 0.0013mg/cm2/cycle. The average particle size of Pt nanoparticles shows an increase with the ALD cycle, i.e., 2.49–25.5nm within 50–400 ALD cycles. The gas diffusion electrode (GDE) equipped with as-grown Pt catalysts, prepared from ALD 50 cycles, generates superior peak power density of 7.8kW/g at 75°C, showing a novel design of GDE for PEMFCs.

Ethanol electrooxidation on carbon-supported Pt nanoparticles catalyst prepared using complexing self-reduction method

A novel self-reduction of Pt-complex method is used to prepare Vulcan XC-72 carbon-supported Pt nanoparticles (Pt/C) catalysts by employing ethylenediamine-tetramethylene phosphonic acid (EDTMP) as a complexing reagent. During the preparation of Pt/C catalysts, the particle size of Pt nanoparticles (Pt–NPs) can be controlled effectively in the range of 1.7–13.5 nm by adjusting reaction solution pH values. TEM images demonstrate that the Pt–NPs well disperse on the Vulcan XC-72 carbon support with a relatively narrow particle size distribution by using the complex self-reduction method. Therefore, the Pt/C catalysts prepared by the same method are suitable for evaluating the size effect of the Pt–NPs on electrocatalytic performance for ethanol electrooxidation. A correlation between the electrocatalytic activity of ethanol oxidation and particle size of the Pt/C catalysts indicates that Pt–NPs with mean particle size of ca. 2.5 nm possesses the highest electrocatalytic performance for ethanol electrooxidation.

Platinum nanoparticle intercalated montmorillonite to enhance the char formation of polyamide 6 nanocomposites

Organically modified montmorillonite (OMT) was used to disperse catalytically active Pt nanoparticles that influence the char formation processes of polyamide 6 (PA6). The Pt nanoparticles of varying particle size are generated in organically modified montmorillonite (Pt–OMTs) which are subsequently melt blended with PA6. The average particle size of Pt nanoparticles ranges from 9.2 to 21.6 nm as found by X-ray diffraction and field emission scanning electron microscopy. The char formation mechanism is studied by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TG–IR). Infrared spectroscopy on the residue reveals the formation of unsaturated hydrocarbons during decomposition of PA6 nanocomposite which are crosslinked into a highly conjugated structure.

Electrocatalytic oxidation of methanol on a platinum modified carbon nanotube electrode

A thin film of poly(o-aminophenol) (POAP) was formed by electropolymerization on well-aligned multi-walled carbon nanotubes (MWNTs). The electrochemical properties of POAP/MWNTs nanocomposites have been investigated by cyclic voltammetry in 1.0 M H2SO4 and 5 mM K3[Fe(CN)6]/1 M KCl solutions. Platinum nanoparticles (PtNPs) were electrochemically deposited onto the POAP/MWNTs nanocomposites by potential cycling between +0.50 and −0.70 V at a scan rate of 50 mV sec−1 in 0.1 M NaCl solution containing 5 mM Na2PtCl6. The electrocatalytic oxidation of methanol at the nanocomposites of PtNPs/POAP/MWNTs was studied in a 0.2 M H2SO4 solution. Compared to bare MWNTs and POAP modified glassy carbon electrodes, POAP/MWNTs electrode significantly enhances the catalytic efficiency of Pt nanoparticles for methanol oxidation. This improvement in performance is due not only to the high surface area and the fast electron transfer rate of nanotubes, but also to a decrease of the average particle size of Pt nanoparticles and an increase of the specific surface of electrodes in the presence of the POAP film.