Nanocomposite based on depositing platinum nanostructure onto carbon nanotubes through a one-pot, facile synthesis method for amperometric sensing

Platinum nanoparticles (Pt NPs) were deposited onto multi-walled carbon nanotubes (MWNTs) through direct chemical reduction without any other stabilizing agents. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry were employed to characterize the morphology of the as-prepared nanocomposite (noted as Pt NPs-MWNTs) and further identify the Pt NPs on the surface of MWNTs. The nanocomposite demonstrated the ability to electrocatalyze the oxidation of hydrogen peroxide and substantially raises the response current. A sensitivity of 591.33 mu A mM(-1) cm(-2) was obtained at Pt NPs-MWNTs modified electrode. Thus, we immobilized glucose oxidase (GOD) as a model enzyme on the nanocomposite-based electrode with a thin layer of Nafion to fabricate a glucose biosensor, which showed sensitive and fast response to glucose. The influence of the GOD loading was investigated and the biosensor with an enzyme loading concentration of 10 mg/mL shows optimal performance for glucose detection, that is, a detection limit of 3 mu M and a response time of 3 s, respectively.

Nanoelectrocatalyst based on high-density Au/Pt hybrid nanoparticles supported on a silica nanosphere

A high-efficiency nanoelectrocatalyst based on high-density Au/Pt hybrid nanoparticles supported on a silica nanosphere (Au-Pt/SiO2) has been prepared by a facile wet chemical method. Scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy are employed to characterize the obtained Au-Pt/SiO2. It was found that each hybrid nanosphere is composed of high-density small Au/Pt hybrid nanoparticles with rough surfaces. These small Au/Pt hybrid nanoparticles interconnect and form a porous nanostructure, which provides highly accessible activity sites, as required for high electrocatalytic activity. We suggest that the particular morphology of the AuPt/SiO2 may be the reason for the high catalytic activity. Thus, this hybrid nanomaterial may find a potential application in fuel cells.

Monodisperse, submicrometer-scale platinum colloidal spheres with high electrocatalytic activity

Monodisperse, submicrometer-scale platinum (Pt) colloidal spheres were prepared through a simple direct chemical reduction of p-phenylenediamine (PPD)-chloroplatinic acid (H2PtCl6) coordination polymer colloids. It was found that the prepared Pt colloids had the similar size and morphology with their coordination polymer precursors, and the prepared Pt colloids with rough surfaces were three-dimensional (3D) structured assemblies of high-density small Pt nanoparticles. The electrochemical experiments confirmed that the prepared Pt colloids possessed a high electrocatalytic activity towards mainly four-electron reduction of dioxygen to water, making the prepared Pt colloids potential candidates for the efficient cathode material in fuel cells.

Room temperature preparation of carbon supported Pt-Ru catalysts

A carbon supported Pt-Ru (Pt-Ru/C-T) catalyst can be prepared by a chemical reduction method in an aqueous solution with tetrahydrofuran (THF) at room temperature. The Pt-Ru particles possess high alloying, small average size and a low relative crystallinity. The electrocatalytic activity of the prepared Pt-Ru/C catalyst for methanol oxidation is much higher than that of commercial Pt-Ru/C (Pt-Ru/C-E) catalysts which have a similar average size and relative crystallinity, but the alloying extent is much lower than that in our Pt-Ru/C-T catalyst. The results illustrate that the alloying extent of Pt and Ru in the Pt-Ru/C catalyst plays an important role in the electrocatalytic activity of the Pt-Ru/C catalyst for methanol oxidation.

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).

Electrochemical performance of mixed ionic-electronic conducting oxides as anodes for solid oxide fuel cell

Mixed ionic-electronic conducting (MIEC) oxides, SrFeCo0.5Ox, SrCo0.8Fe0.2O3-delta and La0.6Sr0.4Fe0.8Co0.2O3-delta have been synthesized and prepared on yttria-stabilized zirconia as anodes for solid oxide fuel cells. Power output measurements show that the anodes composed of such kinds of oxides exhibit modest electrochemical activities to both H-2 and CH4 fuels, giving maximum power densities of around 0.1 W/cm(2) at 950 degrees C. Polarization and AC impedance measurements found that large activation overpotentials and ohmic resistance drops were the main causes for the relative inferior performance to the Ni-YSZ anode. While interlayered with an Ni-YSZ anode, a significant improvement in the electrochemical performance was observed. in particular, for the SrFeCo0.5Ox oxide interlayered Ni-YSZ anode, the maximum power output reaches 0.25 W/cm2 on CH,, exceeding those of both SrFeCo0.5Ox and the Ni-YSZ, as anodes alone. A synergetic effect of SrFeCo0.5Ox and the Ni-YSZ has been observed. Future work is needed to examine the long-term stability of MIEC oxide electrodes under a very reducing environment. (C) 1999 Elsevier Science B.V. All rights reserved.

短时微重力条件下燃料电池性能实验研究

开展了不同重力情况下燃料电池性能的实验研究.利用微重力落塔,对常重力和微重力条件下燃料电池发电时其内部的两相流动开展了可视化现场观测.对重力因素对燃料电池内部传质过程的影响进行了分析和讨论.实验结果表明:当电流密度较大时,在微重力环境中燃料电池性能较常重力环境中的有较明显下降.由于微重力条件下浮升力的消失导致气体不能及时从流道中排出,进而对直接甲醇燃料电池内的传质过程产生负面影响.

质子交换膜燃料电池短时微重力性能实验研究

利用落塔开展了不同重力情况下质子交换膜燃料电池性能的实验研究.对常重力和微重力条件下质子交换膜燃料电池发电时其阴极蛇形流场内部的两相流动开展了可视化现场观测.对重力因素对质子交换膜燃料电池内部传质过程的影响进行了分析和讨论.实验结果表明:在常重力环境中,液态水堆积在竖置流道的底部,无法有效排出.聚集在流道内的液态水与反应气体在流道内形成气/液两相流动.在微重力环境中,液态水在气体推动力的作用下从流道的底部上升并沿流道向出口流动.聚集在流道内的液态水排除后,减小了反应气体(氧气)从流道向催化层的传递阻力,从而使质子交换膜燃料电池的性能得到提高.

Enhanced Proton Conduction in Polymer Electrolyte Membranes as Synthesized by Polymerization of Protic Ionic Liquid-Based Microemulsions

Proton-conducting membranes were prepared by polymerization of microemulsions consisting of surfactant-stabilized protic ionic liquid (PIL) nanodomains dispersed in a polymerizable oil, a mixture of styrene and acrylonitrile. The obtained PIL-based polymer composite membranes are transparent and flexible even though the resulting vinyl polymers are immiscible with PIL cores. This type of composite membranes have quite a good thermal stability, chemical stability, tunability, and good mechanical properties. Under nonhumidifying conditions, PIL-based membranes show a conductivity up to the order of 1 x 10(-1) S/cm at 160 degrees C, due to the well-connected PIL nanochannels preserved in the membrane. This type of polymer conducting membranes have potential application in high-temperature polymer electrolyte membrane fuel cells.

Effects of treatment in different atmosphere on Pt3Sn/C electrocatalysts for ethanol electro-oxidation

Pt3Sn/C catalyst was prepared by a modified polyol process and treated in air, H-2/Ar, and Ar atmosphere, respectively. XRD analyses indicate that all of these catalysts have face-centered cubic (fcc) crystal structure. Temperature-programmed reduction (TPR) experiments show that more Sn exists in zero-valence in the Ar-treated PtSn catalyst than in the others. Cyclic voltammetry (CV), chronoamperometry (CA) experiments, and the performance tests of direct ethanol fuel cell (DEFC) indicate that the catalytic activity of PtSn/C for ethanol oxidation was affected significantly by the chemical state of Sn in catalyst particles. The as-prepared PtSn/C gives the higher power density, while Ar-treated PtSn/C shows the lower cell performance. It seems that the multivalence Sn rather than the zero-valence Sn in the PtSn catalyst is the favorable form for ethanol oxidation. Energy dispersion X-ray analysis (EDX) of the PtSn/C-as prepared and PtSn/C (after stability test) shows the active species (platinum, tin, and oxygen) composition changed to a different extent. Further attempt to improve the catalyst stability is needed.

Influence of catalyst layer structure on the current distribution of PEMFCs

A modified subcell approach was adopted to evaluate the current density distributions of proton exchange membrane fuel cells (PEMFCs) with different electrodes. Conventional hydrophobic electrodes showed better performance under flooding conditions compared to hydrophilic electrodes. The thin-film hydrophilic electrode performed better in the absence of liquid water, but it was more readily flooded. A composite catalyst layer was designed with 2/3 of the area from the inlet prepared hydrophilic and the remaining 1/3 area hydrophobic. The composite catalyst layer with commercial scale dimension showed notable enhanced performance in the concentration polarization region. (C) 2004 The Electrochemical Society.

The mechanism studies of ethanol oxidation on PdO catalysts by TPSR techniques

The paper studies the direct oxidation of ethanol and CO on PdO/Ce0.75Zr0.25O2 and Ce(0.75)Zr(0.2)5O(2) catalysts. Characterization of catalysts is carried out by temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR) techniques to correlate with catalytic properties and the effect of supports on PdO. The simple Ce0.75Zr0.25O2 is in less active for ethanol and CO oxidation. After loaded with PdO, the catalytic activity enhances effectively. Combined the ethanol and CO oxidation activity with CO-TPD and ethanol-TPSR profiles, we can find the more intensive of CO2 desorption peaks, the higher it is for the oxidation of CO and ethanol. Conversion versus yield plot shows the acetaldehyde is the primary product, the secondary products are acetic acid, ethyl acetate and ethylene, and the final product is CO2. A simplified reaction scheme (not surface mechanism) is suggested that ethanol is first oxidized to form intermediate of acetaldehyde, then acetic acid, ethyl acetate and ethylene formed going with the formation of acetaldehyde, acetic acid, ethyl acetate; finally these byproducts are further oxidized to produce CO2. PdO/Ce0.75Zr0.25O2 catalyst has much higher catalytic activity not only for the oxidation of ethanol but also for CO oxidation. Thus the CO poison effect on PdO/Ce0.75Zr0.25O2 catalysts can be decreased and they have the feasibility for application in direct alcohol fuel cell (DAFC) with high efficiency.

Magnet-assisted assembly of 1-dimensional hollow PtCo nanomaterials on an electrode surface

In this work, rapid and controllable confinement of one-dimensional (1D) hollow PtCo nanomaterials on an indium tin oxide (ITO) electrode surface was simply realized via magnetic attraction. The successful assembly was verified by scanning electron microscopy (SEM) and cyclic voltammetry, which showed that a longer exposure time of the electrode to the suspension of these 1D hollow nanomaterials (magnetic suspension) led to a larger amount of attached 1D hollow PtCo nanomaterials.

Carbon nanotubes decorated with Pt nanocubes by a noncovalent functionalization method and their role in oxygen reduction

Combined with polymer wrapping and layer-by-layer techniques, a noncovalent functionalization method is developed to disperse Pt nanocubes (NCs) onto carbon nanotubes (CNTs). By adjusting the relative ratio of Pt NCs to CNTs, nanotubes with different Pt NC loadings are produced. The composites exhibit excellent electrocatalytic activity towards oxygen reduction.

Preparation of Pd/C catalyst for formic acid oxidation using a novel colloid method

A novel colloid method using (WO3)(n)center dot xH(2)O as colloidal source was developed to prepare Pd/C catalyst for formic acid oxidation. Transmission electron microscopy image shows that the Pd/C nanoparticles have an average size of 3.3 nm and a narrow size distribution. Electrochemical measurements indicate that the Pd/C catalyst exhibits significantly high electrochemical active surface area and high catalytic activity with good stability for formic acid oxidation compared with that prepared by common method.