Pt/C催化剂中纳米Pt颗粒团聚效应的小角X射线散射

应用小角X射线散射(SAXS)技术,对乙二醇合成法、浸渍还原法和微波加热法制备的Pt/C催化剂粉体内纳米Pt颗粒的团聚效应进行了研究,得到了不同方法制备的Pt颗粒及其团聚体的特征尺寸、体积分布、表面积变化、团聚程度等信息,并利用透射电镜（TEM）对3种样品进行了测试。实验结果表明:微波加热法制备的催化剂中,Pt颗粒较好地分散于C载体上,且Pt颗粒具有尺度小、分布范围窄、总表面积大和团聚体较少等特征;常规浸渍和乙二醇还原两种方法制备的催化剂中Pt颗粒大小分布相似,但乙二醇还原法制备的催化剂总表面积和团聚体尺度更大,数量也更多。     

Pt/C催化剂中纳米Pt颗粒团聚效应的小角X射线散射

 应用小角X射线散射(SAXS)技术,对乙二醇合成法、浸渍还原法和微波加热法制备的Pt/C催化剂粉体内纳米Pt颗粒的团聚效应进行了研究,得到了不同方法制备的Pt颗粒及其团聚体的特征尺寸、体积分布、表面积变化、团聚程度等信息,并利用透射电镜（TEM）对3种样品进行了测试。实验结果表明:微波加热法制备的催化剂中,Pt颗粒较好地分散于C载体上,且Pt颗粒具有尺度小、分布范围窄、总表面积大和团聚体较少等特征;常规浸渍和乙二醇还原两种方法制备的催化剂中Pt颗粒大小分布相似,但乙二醇还原法制备的催化剂总表面积和团聚体尺度更大,数量也更多。     

SiO2 stabilized Pt/C cathode catalyst for proton exchange membrane fuel cells

This paper describes the preparation of SiO₂ stabilized Pt/C catalyst (SiO₂/Pt/C) by the hydrolysis of alkoxysilane, and examines the possibility that the SiO₂/Pt/C is used as a durable cathode catalyst for proton exchange membrane fuel cells (PEMFCs). TEM and XRD results revealed that the hydrolysis of alkoxysilane did not significantly change the morphology and crystalline structure of Pt particles. The SiO₂/Pt/C catalyst exhibited higher durability than the Pt/C one, due to the facts that the silica layers covered were beneficial for reducing the Pt aggregation and dissolution as well as increasing the corrosion resistance of supports, although the benefit of silica covering was lower than the case of Pt/CNT catalyst. Also, it was observed that the activity of the SiO₂/Pt/C catalyst for the oxygen reduction reaction was somewhat reduced compared to the Pt/C one after the silica covering. This reduction was partially due to the low oxygen kinetics as revealed by the rotating-disk-electrode measurement. Silica covering by hydrolysis of only 3-aminopropyl trimethoxysilane is able to achieve a good balance between the durability and activity, leading to SiO₂/Pt/C as a promising cathode catalyst for PEMFCs.     

H2/Pt/Ce0.9Gd0.1O1.95/Pt/O2 fuel cell operated in the intermediate temperature range 500 – 700°C

Ce_0.9Gd_0.1O_1.95 (GCO), is one of the potential candidate electrolytes for intermediate temperature Solid Oxide Fuel Cells (ITSOFC). GCO has high oxide ion conductivity in the intermediate temperature range (500 – 700 °C) compared to other Ce_1−yGd_yO_2-2/y compositions and the Gd³⁺ ion is the most appropriate dopant material compared to other rare earth materials such as Sm³⁺, Y³⁺, Zr³⁺, etc. Our results show that the fuel cell H₂/Pt/Ce_0.9Gd_0.1O_1.95/Pt/O₂ operated in the temperature range 500 – 700°C gives the maximum power densities 0.0049 W/cm² at 500 °C and 0.0126 W/cm² at 650 °C for cell voltages 0.6275 V and 0.6278 V, respectively, where the electrolyte was kept in 5% H₂ (+ Argon) for 12 hours before use in the fuel cell. Maximum power densities are 0.0038 W/cm² at 500 °C and 0.0270 W/cm² at 650 °C for cell voltages 0.5986 and 0.5913 V, respectively, where the electrolyte was kept in 2 % O₂ (+ Argon) for 12 hours before use in the fuel cell. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

PdNi-decorated manganite nanocatalyst for electrooxidation of ethylene glycol in alkaline media

PdNi bimetallic nanoparticles coated onto manganite (MN) nanocatalyst was used for ethylene glycol (EG) and glycerol (Gly) electrooxidation in alkaline media. The MN nanorods were prepared by hydrothermal method, and the PdNi was coated on the rods by an in situ reduction method. The prepared nanocomposite was characterized by scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), Energy dispersive X-ray spectroscopy (EDS), and electrochemical methods. The SEM and TEM images exhibit the formation of nanorods of 10?nm and also show the formation of nanocrystalline PdNi on the walls of the MN nanorods. This study shows that the MN nanorods can be excellent support material and they supply oxygen to the catalyst, by which the catalytic activity is enhanced. The electrooxidation reactions in strong alkaline condition containing various concentrations of EG have been studied. Among the different concentrations, 9?M KOH/6?M EG exhibits the highest activity. PdNi/MN nanocatalyst exhibits better activity even in higher electrolytic concentrations of EG and alkali.     

Nanoparticulate TiO2-promoted PtRu/C catalyst for methanol oxidation

To improve the electrocatalytic properties of PtRu/C in methanol electrooxidation, nanoparticulate TiO₂-promoted PtRu/C catalysts were prepared by directly mixing TiO₂ nanoparticles with PtRu/C. Using cyclic voltammetry, it was found that the addition of 10 wt% TiO₂ nanoparticles can effectively improve the electrocatalytic activity and stability of the catalyst during methanol electrooxidation. The value of the apparent activation energy (E _a) for TiO₂-PtRu/C was lower than that for pure PtRu/C at a potential range from 0.45 to 0.60 V. A synergistic effect between PtRu and TiO₂ nanoparticles is likely to facilitate the removal of CO-like intermediates from the surface of PtRu catalyst and reduce the poisoning of the PtRu catalysts during methanol electrooxidation. Therefore, we conclude that the direct introduction of TiO₂ nanoparticles into PtRu/C catalysts offers an improved facile method to enhance the electrocatalytic performance of PtRu/C catalyst in methanol electrooxidation.     

Electrochemical codeposition of Pt/graphene catalyst for improved methanol oxidation

Pt/graphene electrocatalyst was uniformly deposited on a glassy carbon substrate using a pulsed galvanostatic electrodeposition method, which facilitated the simultaneous electrochemical reduction of graphene oxide and formation of Pt nanoparticles. Compared to the commercial carbon-supported Pt electrocatalyst, the electrochemically reduced Pt/graphene (Pt/ERG) catalyst exhibited improved electrocatalytic activity for methanol oxidation due to the synergistic effects of an increase in the number of catalytic reaction sites and an enhancement of the charge transfer rate.     

A HREELS/TDS study of the intermediate formed by the reaction of C2N2 with H2 on Pt(111)

We report vibrational spectroscopy data (HREELS) and thermal desorption spectroscopy results on the molecular intermediate which is formed when cyanogen and hydrogen are coadsorbed on Pt(111). The reaction of cyanogen with adsorbed hydrogen becomes appreciable at ∼ 250 K. The vibrational spectrum of the surface species which is formed is consistent with a di-imine species (HNCHCHNH). The di-imine decomposes at a surface temperature of 430 K resulting in the desorption of cyanogen and hydrogen.     

Tunable interface anisotropy in a Pt/C01-xFex/Pt multilayer

Interfacial magnetic anisotropy in a Pt/CO1-xFex/Pt multilayer is tuned by doping iron atoms into the cobalt layer. The perpendicular magnetic anisotropy and out-of-plane coercivity are found to decrease with increasing x. For a specific x, the out-of-plane coercivity acquires a maximal value as a function of the thickness of the CoFe layer. At low temperature, the coercivity is enhanced. Small coercivity but reasonably large perpendicular magnetic anisotropy can be obtained by controlling the x and CoFe layer thickness.     

Effect of borohydride as reducing agent on the structures and electrochemical properties of Pt/C catalyst

In this paper, we found that boron deposited on the surface of support when sodium borohydride used as reducing agent during the preparation of Pt/C catalyst. The deposition of boron markedly reduces particle size of Pt, raises electrochemical active surface (EAS) area of catalyst and electrochemical activity for hydrogen evolution or oxygen reduction reaction (ORR) compared with which prepared using other reducing agents (hydrogen and formaldehyde).     

Search for phonon anomalies in the intermediate valence compound CeSn3

The phonon dispersion relations of the intermediate valence compound CeSn₃ and the integral valence reference compound LaSn₃ were measured by inelastic neutron scattering. They are quite similar and no phonon anomalies due to valence fluctuations in CeSn₃ were detected. Likewise no line broadening was observed. Model calculations revealed, that the influence of the “breathing” deformability of the rare earth ions on the lattice dynamics is only moderate; moreover the breathing force constant turned out to be equal for both CeSn₃ and LaSn₃.     

Rapid growth of nanocrystalline CuInS2 thin films in alkaline medium at room temperature

Layer-by-layer (LbL) deposition of CuInS₂ (CIS) thin films at room temperature (25 °C) from alkaline CuSO₄ + In₂(SO₄)₃ and Na₂S precursor solutions was reported. The method allowed self-limited growth of CIS films with nanocrystalline structure and composed of densely packed nanometer-sized grains. The as-deposited CIS film was 250 nm thick and composed of closely packed particles of 20-30 nm in diameter. The alkaline cationic precursor solution was obtained by dissolving CuSO₄ and InSO₄ in deionized water with a appropriate amount of hydrazine monohydrate (H-H) and 2,2′,2″-nitrilotriethanol (TEA). CIS films were annealed at 200 °C for 2 h and effect of annealing on structural, optical, and surface morphological properties was thoroughly investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-vis spectrometer, C-V, and water contact angle techniques, respectively.     

Ordered charge asphericity around dysprosium and structural deformation in DyB2C2

The orbitally ordered phase of DyB2C2 has been studied by nonresonant x-ray diffraction with high-brilliance synchrotron radiation. From the condition of diffraction, the symmetry property of the charge distribution around dysprosium has been concluded at the quadrupolar level. The quantitative inspection, furthermore, indicates that the observed signals cannot be interpreted as arising only from the 4f electrons of dysprosium responsible for the ordering; instead, the experiment can be described rather well by considering a distortion of the metaloid network concomitant with the ordering.     

Monte Carlo simulations of FTIR studies during CO oxidation on a Pt/SiO2 catalyst

A Monte Carlo (MC) simulation of the reaction of CO with an oxygen covered Pt surface and oxygen with a CO covered Pt surface is presented in this paper. The effect of the adsorption, desorption, reaction, and surface migration rates on the formation of CO clusters is analyzed in terms of the CO frequency shift in the IR spectrum. The MC simulation calculates the CO frequency shifts according to a dipole-dipole interaction model. The IR frequency shifts predicted by the simulation depend on the value of the various kinetic processes considered. The simulation indicates that the CO migration on the surface is important at low pressure but is inhibited at high pressure. The IR frequency shifts predicted by the simulation agree qualitatively with experimental values obtained during CO oxidation on a Pt catalyst.     

Any-polar resistive switching behavior in Ti-intercalated Pt/Ti/HfO2/Ti/Pt device

The special any-polar resistive switching mode includes the coexistence and stable conversion between the unipolar and the bipolar resistive switching mode under the same compliance current. In the present work, the any-polar resistive switching mode is demonstrated when thin Ti intercalations are introduced into both sides of Pt/HfO₂/Pt RRAM device. The role of the Ti intercalations contributes to the fulfillment of the any-polar resistive switching working mechanism, which lies in the filament constructed by the oxygen vacancies and the effective storage of the oxygen ion at both sides of the electrode interface.     

Carbon-silica composites supported Pt as catalyst for asymmetric hydrogenation of ethyl 2-oxo-4-phenylbutyrate

Mesoporous carbon-silica composites supported Pt nanoparticle catalysts (Pt/MCS) were firstly applied to the heterogeneous asymmetric hydrogenation of ethyl 2-oxo-4-phenylbutyrate (EOPB). A series of different silica contents were investigated in the fabrication of this mesoporous material. When the volume of added tetraethyl orthosilicate (TEOS) during the preparation of composites is 8 mL, Pt/MCS-8 holds carbon and silica as the main components and possesses relatively strong acidity, mesoporous structures with micropores, appropriate Pt nanoparticle size and high dispersibility showing by XRD, XPS, TPD, N₂ sorption and TEM. These properties cause its good catalytic performance in the heterogeneous asymmetric hydrogenation of EOPB with the enantiomeric excess value and conversion up to 85.6% and 97.8%, respectively.     

High catalytic performance of Pt nanoparticles on plasma treated carbon nanotubes for electrooxidation of ethanol in a basic solution

Nanosized Pt particles deposited on plasma treated multi-walled carbon nanotubes have been used in electrocatalytic oxidation of ethanol in a basic solution. These Pt nanoparticles have very narrow size distribution and exhibit significant higher catalytic activities, higher Pt utilization efficiency (93.77%) and improved durability in comparison to the commercial available Johnson Matthey Pt/C catalyst.     

Correlation between diode polarization and resistive switching polarity in Pt/TiO2/Pt memristive device

We have investigated the correlation between diode polarization and switching polarity in electroformed Pt/TiO₂/Pt memristive device. Before forming, the diode direction of the Pt/TiO₂/Pt device is reversible under the current pulses with varying current amplitude. The diode polarization arises from oxygen vacancy migration in fully depleted Pt/TiO₂/Pt films. The measurement results indicated that only the polarized diode can be electroformed and the metallic suboxide filament is created in parallel to the diode with a switching polarity dependent on the polarization of stack prior to forming. The non‐polar state inhibits field concentration at either end of the device at the specified current, preventing the electroforming. On and off state currents are measured at 0.2 V for 5 × 10⁴ s showing good retention, which is promising for non‐volatile memory application. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Effect of Co substitution for Fe in Sr2FeMoO6 on electrocatalytic properties for oxygen reduction in alkaline medium

Double perovskites Sr₂Fe_1???x Co _x MoO₆ (x?=?0, 0.25, 0.5, 0.75 and 1) have been investigated as cathode material for oxygen reduction reaction (ORR) in 0.5 M NaOH at 25 °C using the rotating disk electrode. The electrocatalytic powders were prepared by a solid-state process and characterised by X-Ray powder diffraction, scanning electron microscopy and infrared spectroscopy. The electrochemical techniques considered are linear voltammetry, steady-state polarization and impedance spectroscopy. The electrocatalysts Sr₂Fe_1???x Co _x MoO₆/C consisting of the double perovskite oxides and carbon (Vulcan XC-72) were mixed and spread out into a thin layer on a glassy carbon substrate. The electrocatalytic activity was strongly influenced by the Co substitution at room temperature. The relation between catalytic performance and the degree of Co content was examined. The Co-containing catalysts exhibited lower activity attributed to their high resistivity, and the highest activity toward oxygen reduction was observed for Sr₂CoMoO₆.