羰基簇合物途径制备的碳载Pt-Co催化剂阴极抗甲醇性能

通过Pt和Co羰基簇合物途径制备了碳载Pt Co(Pt Co/C)复合催化剂.其金属粒子的平均粒径小,相对结晶度很低.与商业化的E TEKPt/C催化剂相比,该催化剂具有较好的抗甲醇性能和电催化氧还原活性.

Perpendicular exchange bias in IrMn/Pt/[Co/Pt](3) multilayers with cone magnetization

The perpendicular exchange bias and magnetic anisotropy were investigated in IrMn/Pt/[Co/Pt](3) multilayers through the analysis of in-plane and out-of-plane magnetization hysteresis loops. A phenomenological model was used to simulate the in-plane curves and the effective perpendicular anisotropies were obtained employing the area method. The canted state anisotropy was introduced by taking into account the first and second uniaxial anisotropy terms of the ferromagnet with the corresponding uniaxial anisotropy direction allowed to make a nonzero angle with the film`s normal. This angle, obtained from the fittings, was of approximately 15 degrees for IrMn/[Co/Pt](3) film and decreases with the introduction of Pt in the IrMn/Pt/[Co/Pt](3) system, indicating that the Pt interlayer leads to a predominant perpendicular anisotropy. A maximum of the out-of-plane anisotropy was found between 0.5 and 0.6 nm of Pt, whereas a maximum of the perpendicular exchange bias was found at 0.3 nm. These results are very similar to those obtained for IrMn/Cu/[Co/Pt](3) system; however, the decrease of the exchange bias with the spacer thickness is more abrupt and the enhacement of the perpendicular anisotropy is higher for the case of Cu spacer as compared with that of Pt spacer. The existence of a maximum in the perpendicular exchange bias as a function of the Pt layer thickness was attributed to the predominance of the enhancement of exchange bias due to more perpendicular Co moment orientation over the exponential decrease of the ferromagnetic/antiferromagnetic exchange coupling and, consequently, of the exchange-bias field. (C) 2011 Elsevier B.V. All rights reserved.

Electrocatalysis of oxygen reduction on carbon-supported Pt-Co nanoparticles with low Pt content

The oxygen reduction reaction (ORR) was investigated on carbon-supported Pt-Co nanoparticle electrocatalysts with low Pt content in alkaline electrolyte. High resolution transmission electron microscopy, In situ X-ray absorption spectroscopy, and X-ray diffraction analysis evidenced large structural differences of the Pt-Co particles depending oil the route of the catalyst synthesis. It was demonstrated that although the Pt-Co materials contain low amounts of Pt, they show very good activities when the particles are formed by a Pt-rich shell and a Pt-Co core, which was obtained after submitting the electrocatalyst to a potential cycling in acid electrolyte. The high activity of this material was due to a major contribution from its higher surface area, as a result of the leaching of the Co atoms from the particle Surface. Furthermore, its high activity was ascribed to a minor contribution from the electronic interaction of the Pt atoms, at the particle surface, and the Co atoms located in the beneath layer, lowering the Pt cl-band center. As these electrocatalysts presented high activity for the ORR with low Pt content, the cost of the fuel cell cathodes could be lowered considerably. (c) 2009 Elsevier B.V. All rights reserved.

Carbon-supported Pt-Co catalysts prepared by a modifled polyol process as cathodes for PEM fuel cells

In this work, carbon-supported Pt70Co30 nanoparticles were prepared by a polyol process using a long-chain diol as reducer (hexadecanediol) and oleic acid and oleylamine as stabilizers. Depending on the synthesis conditions, Pt70Co30/C nanocatalysts with very small particle size (1.9 +/- 0.2 nm) and narrow distribution homogeneously dispersed on the carbon support and having a high degree of alloying without the need of thermal treatments were obtained. The as-prepared catalyst presents an excellent performance as proton exchange membrane fuel cells (PEMFC) cathode material. In terms of mass activity (MA), the Pt70Co30/C electrocatalysts produced single fuel cell polarization response superior to that of commercial catalyst. To analyze alloying effects, the result of thermal treatment at low temperatures (200-400 degrees C) was also evaluated and an increase of average crystallite size and a lower degree of alloying, probably associated to cobalt oxidation, were evidenced.

Large extraordinary Hall effect in [Pt/Co]5/Ru/[Co/Pt]5 multilayer

This Brief Report presents giant extraordinary Hall effect (EHE) in the Ru-mediated antiferromagnetically coupled [Pt/Co]5/Ru/[Co/Pt]5 multilayers (MLs) compared with those MLs without the Ru spacer. The enhancement of the EHE is attributed to the strong Ru/Co interface scattering. Through the variation in the Pt layer thickness and the temperature, we determine the relation between the Hall voltage and the longitudinal resistivity. It is found that the conventional scaling analysis has difficulties in consistently interpreting our data.

吸附在Pt/C催化剂上Eu~(3+)对CO电氧化的促进作用

引言目前影响质子交换膜燃料电池(PEMFC)迅速发展并商业化的主要问题之一是阳极催化剂抗CO的毒化能力。Pt因其对氢的氧化具有高的催化活性而广泛地用作PEMFC的阳极催化剂,也有人研究将其它金属用于PEMFC阳极催化剂,但催化活性要比Pt低得多[1~4]。而Pt作PEMFC的阳极催化剂一个问题是痕量的CO,如10~100ppm就可以使Pt催化剂中毒[5,6]。现在的PEMFC一般用高压氢作为燃料,有很大的不安全性。人们提出用两种方法来解决这个问题,一是用甲醇、甲烷或汽油现场重整制氢作燃料的方法,但用这种制氢方法制得的氢气中含有大量的CO,即使经过纯化,也会含有ppm级的CO。另一个方法是直接用小分子醇类化合物,如甲醇作燃料,被称为直接醇燃料电池(DAFC)[7~11],但醇类化合物在阳极氧化时会有中间产物,如CO的产生,容易使阳极Pt催化剂中毒。因此,研究抗CO中毒的阳极催化剂已成为PEMFC和DAFC中一个很重要的研究课题。许多文章已报道Pt与其它贵金属或过渡金属的合金催化剂,或Pt与过渡金属氧化物的复合催化剂有一定的抗CO中毒能力。如Pt鄄Ru[12~16]、Pt鄄Bi[17]、Pt鄄Sn[17~19]...

Electrocatalytic activity of Ru-modified Pt(111) electrodes toward CO oxidation

The electrochemical deposition of Ru on Pt(111) electrodes has been investigated by electron diffraction, Auger spectroscopy, and cyclic voltammetry in a closed UHV transfer system. At small coverages Ru formed a monatomic commensurate layer, at higher coverage mostly small islands with a bilayer height were detected. When the Pt was almost completely covered by Ru, three-dimensional clusters developed. The island structure of Ru changed upon electrooxidation of CO, reflecting an enhanced mobility of Ru. Adsorption and electrooxidation of CO have been studied on such Ru-modified Pt(111) electrodes using cyclic voltammetry and in situ FTIR spectroscopy. Compared to the pure metals, the Ru-CO bond is weakened, the Pt-CO bond strengthened on the modified electrodes. The catalytic activity of the Ru/Pt(111) electrode toward CO adlayer oxidation is higher than that of pure Ru and a PtRu alloy (50:50). It is concluded that the electrooxidation of CO takes place preferentially at the Ru islands, while CO adsorbed on Pt migrates to them. © 1999 American Chemical Society.

Density functional theory study of the interaction between CO and on a Pt surface:CO/Pt(111), O/Pt(111), and CO/O/Pt(111)

Ab initio total energy calculations within the Density Functional Theory framework were carried out for Pt(111), Pt(111)-p(2x2)-CO, Pt(111)-p(2x2)-O, and Pt(111)-p(2x2)-(CO+O) to provide an insight into the interaction between CO and O on metal surfaces, an important issue in CO oxidation, and also in promotion and poisoning effects of catalysis. The geometrical structures of these systems were optimized with respect to the total energy, the results of which agree with existing experimental values very well. It is found that (i) the local structures of Pt(111)-p(2x2)-(CO+O), such as the bond lengths of C-O, C-Pt, and O-Pt (chemisorbed O atom with Pt), are almost the same as that in Pt(111)-p(2x2)-CO and Pt(111)-p(2x2)-O, respectively, (ii) the total valence charge density distributions in Pt(111)-p(2x2)-(CO+O) are very similar to that in Pt(111)-p(2x2)-CO, except in the region of the chemisorbed oxygen atom, and also nearly identical to that in Pt(111)-p(2x2)-O, apart from in the region of the chemisorbed CO, and (iii) the chemisorption energy of CO on a precovered Pt(111)-p(2x2)-O and the chemisorption energy of O on a precovered Pt(111)-p(2x2)CO are almost equal to that in Pt(111)-p(2x2)-CO and Pt(111)-p(2x2)-O, respectively. These results indicate that the interaction between CO and chemisorbed oxygen on a metal surface is mainly shore range in nature. The discussions of Pt-CO and Pt-O bonding and the interaction between CO and the chemisorbed oxygen atom on Pt(111) are augmented by local densities of states and real space distributions of quantum states.

Investigation of the CO tolerance mechanism at several Pt-based bimetallic anode electrocatalysts in a PEM fuel cell

The electrocatalysis of CO tolerance of Pt/C, PtRu/C, PtFe/C, PtMo/C, and PtW/C at a PEM fuel cell anode has been investigated using single cell polarization and online electrochemical mass spectrometry (EMS) measurements, and cyclic voltammetry, X-ray diffraction (XRD), in situ X-ray absorption near edge structure (XANES) analyses of the electrocatalysts. For all bimetallic electrocatalysts, which presented higher CO tolerance, EMS results have shown that the production of CO(2) start at lower hydrogen electrode overpotentials as compared to Pt/C, confirming the occurrence of the so-called bifunctional mechanism. On the other hand, XANES results indicate an increase in the Pt 5d-band vacancies for the bimetallic catalysts, particulary for PtFe/C, this leading to a weakening of the Pt-CO bond, helping to increase the CO tolerance (the so-called electronic effect). For PtMo/C and PtRu/C supplied with H(2)/CO, the formation of CO(2) is observed even when the cell is at open circuit, confirming some elimination of CO by a chemical process, most probably the water gas shift reaction. (C) 2008 Elsevier Ltd. All rights reserved.

Mikrostruktur und Magnetisierungsdynamik feinmodulierter Co/Pt-Heterostrukturen

Gegenstand dieser Arbeit ist die Untersuchung der strukturellen und magnetischen Eigenschaften von (111)-texturierten epitaktischen dünnen Co/Pt-Vielfachschichten und Pt/Co/Pt-Heterostrukturen. Mit Hilfe von Röntgen-Diffraktions-Experimenten wurde der Einfluß der Oberflächenqualität des MgO (111) Substratmaterials auf die Zwischenlagenstruktur und die kristalline Ordnung in den Filmen analysiert. Es konnte nachgewiesen werden, daß die Unordnung an der Co/Pt-Grenzfläche unterhalb einer Längenskala von 6 nm allein durch die Wachstums- und Interdiffusionsprozesse zwischen der Co- und der Pt-Lage bestimmt ist, unabhängig von der Qualität der Substratoberfläche. Demgegenüber zeigte sich, daß durch eine besondere Substratbehandlung eine langreichweitige kristalline Kohärenz der Schichten und eine Unterdrückung der Verzwillingung aus abc- und acb-Wachstumsdomänen des fcc-Platin erzielt werden können. Anhand integraler Messungen des magneto-optischen Kerr-Effektes wurde ein direkter Zusammenhang zwischen der Substrat-induzierten Defektdichte der Filme und der Nukleation magnetischer Domänen während der Ummagnetisierung nachgewiesen. Pt/Co/Pt-Dreifachlagen mit Kobalt-Dicken bis zu 1 nm besitzen eine senkrechte magnetische Anisotropie und zeigen magnetische Domänen mit Größen von bis zu einigen hundert Mikrometern, die mit Hilfe optischer Kerr-Mikroskopie visualisiert wurden. In Pt/Co/Pt-Dreifachschichten mit weniger als drei Monolagen Kobalt, welche auf vicinalen MgO (111)-Substraten aufgebracht wurden, treten während der Ummagnetisierung aufgrund anisotroper Domänenwandbewegung charakteristische dreieckige Domänenformen auf. Es wurde ein mikroskopischer Mechanismus vorgeschlagen, welcher dieses anisotrope Pinning von magnetischen Domänenwänden an mesoskopischen Stufen-Strukturen der Substratoberfläche beschreibt. Zur quantitativen Beschreibung der anisotropen Domänenwandbewegung wurden zweidimensionale numerische Simulationen durchgeführt, basierend auf einem modifizierten Random-Field-Ising-Modell mit einem Ginzburg-Landau-artigen Hamiltonian, in dem der Einfluß der Stufenkanten auf den Ordnungsparamter durch ein neu eingeführtes effektives anisotropes Feld G(r) repräsentiert ist. Unter Annahme einer lateralen Anordnung der Stufenkanten in Form eines Fischgrätenmusters konnten im Rahmen dieses Modells die experimentell beobachteten charakteristischen anisotropen Domänenformen sowie die Skaleneigenschaften der Domänenwände in exzellenter Weise numerisch reproduziert werden.

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.

固相反应法制备Pt-Ru/C催化剂对乙醇氧化的电催化活性研究

引言近年来,直接甲醇燃料电池(DMFC)由于其燃料来源丰富、价格低廉、甲醇携带和储存安全方便等独特的优越性而越来越受到重视[1]。但是甲醇具有一定的毒性,因此要想实现DMFC在诸如手机、笔记本电脑以及电动车等可移动电源领域的应用,必须探索新的液体燃料以替代有毒性的甲醇。其中乙醇很易从农作物中大量生产,又无毒,因此很有可能用作替代甲醇的质子交换膜燃料电池燃料。近年来乙醇的电催化氧化已被众多的研究者从电催化和乙醇燃料电池的角度进行了广泛的研究[2,3]。但是乙醇在Pt电极上的氧化易导致强吸附物种CO毒化催化剂,Pt鄄Ru合金是目前强吸附毒化物种CO易氧化为CO2的最有效的电催化剂,因此近年来也有一些关于Pt鄄Ru合金催化剂对乙醇的电化学氧化的研究[4~6]。我们研究组首次用固相反应法制备了Pt/C催化剂,发现所制得的Pt/C催化剂对甲醇[7]和乙醇[8]氧化的电催化性能要比用传统的液相反应法制得的Pt/C催化剂好很多。但Pt/C催化剂对甲醇和乙醇氧化的电催化活性还是较低,因此,本文首次研究了用固相反应法制备Pt鄄Ru/C催化剂及这种催化剂对乙醇氧化的电催化性能,发现用固相反应法制备的Pt鄄Ru/C催化剂对乙醇氧...

CO在铂修饰的氧化钛电极上电催化氧化行为的研究

通过阴极还原 -阳极氧化法制备了 Pt-Ti O2 /Ti电极 ,研究了 CO在该电极上的电化学行为和电极制备条件对 CO电催化氧化的影响 .结果表明 ,与 Pt电极相比 ,CO在 Pt-Ti O2 /Ti电极上的氧化峰峰电位负移了1 0 0 m V,并且表现出较好的稳定性 .通过 XPS技术对 Pt-Ti O2 /Ti电极进行了表征 ,发现 Pt以金属形式存在 ,Ti以 Ti O2 形式存在 .Pt-Ti O2 /Ti电极能抗 CO中毒的原因可能是因为 Ti O2 的掺杂使引起催化剂中毒的桥式吸附的 CO物种在复合催化剂上的吸附率较低所致.