Hideo Daimon

Dumbbell-like Pt−Fe3O4 Nanoparticles and Their Enhanced Catalysis for Oxygen Reduction Reaction

Monodisperse dumbbell-like Pt-Fe(3)O(4) nanoparticles are synthesized by epitaxial growth of Fe onto Pt nanoparticles followed by Fe oxidation. The nanoparticle size in the structure is tunable from 2 to 8 nm for Pt and 6 to 20 nm for Fe(3)O(4). Pt nanoparticles in the Pt-Fe(3)O(4) structure show a 20-fold increase in mass activity toward oxygen reduction reaction compared with the single component Pt nanoparticles and the commercial 3 nm Pt particles. The work proves that it is possible to maximize catalytic activity of the Pt nanoparticle catalyst through the control not only of Pt size and shape but also of its interaction with Fe(3)O(4) nanoparticles.

Multimetallic Au/FePt3 Nanoparticles as Highly Durable Electrocatalyst

We report the design and synthesis of multimetallic Au/Pt-bimetallic nanoparticles as a highly durable electrocatalyst for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. This system was first studied on well-defined Pt and FePt thin films deposited on a Au(111) surface, which has guided the development of novel synthetic routes toward shape-controlled Au nanoparticles coated with a Pt-bimetallic alloy. It has been demonstrated that these multimetallic Au/FePt(3) nanoparticles possess both the high catalytic activity of Pt-bimetallic alloys and the superior durability of the tailored morphology and composition profile, with mass-activity enhancement of more than 1 order of magnitude over Pt catalysts. The reported synergy between well-defined surfaces and nanoparticle synthesis offers a persuasive approach toward advanced functional nanomaterials.

Rational synthesis of heterostructured nanoparticles with morphology control.

Rational synthesis of Pt-Au(n) nanoparticles (NPs) has been achieved by overgrowing Au on Pt with n, the number of Pt-Au heterojunctions in each particle, controlled from 1 to 4, and the corresponding NPs in pear-, peanut-, or clover-like morphology. Monte Carlo simulation reveals that the morphology control can be correlated to a thermodynamic equilibrium of the Au coherence energy, the overall particle surface energy, and the heterogeneous Pt-Au interfacial energy in the composite system, which is manipulated by the seeding particle size and solvent polarity. The developed synthetic strategy together with the provided fundamental understanding of heterogeneous nucleation and heterostructure growth could have great potential toward the rational synthesis of composite nanomaterials with morphology control for advanced catalytic and other functional applications.

MAGNETIC PROPERTIES OF FE-CU AND FE-P ELECTRODEPOSITED ALUMITE FILMS

Cu and P were examined as additives to decrease the perpendicular coercivity of Fe-electrodeposited alumite film. Addition of Cu and P to the Fe particles decreased the coercivity to less than 1000 Oe, and P was a more effective additive than Cu in decreasing the coercivity. In the Fe-Cu system, Cu atoms are considered to be dispersed uniformly in the Fe matrix because no drastic changes in the morphological, crystallographical and magnetic properties were observed. In the Fe-P system, P is considered to be precipitated between Fe microcrystallites because the crystallographic continuity of the Fe particles was deteriorated, and distinct microstructure was observed in the Fe particles when P was added. Drastic decrease in the coercivity of Fe-electrodeposited alumite film is considered to be mainly due to the discontinuity of the Fe particles in a system containing P.

Platinum–Phosphorus Nanoparticles on Carbon Supports for Oxygen-Reduction Catalysts

Highly dispersed platinum nanoparticles on carbon supports were synthesized by electrochemical reducing platinum ions in an aqueous solution containing hypophosphite H3PO2 . Adding H3PO2 during the synthesis of the catalyst was effective for reducing platinum particle size, and the platinum particles with a mean size of 2.0–2.3 nm were obtained at a high platinum loading amount of over 50 wt %. The oxygen-reduction activity of the catalysts that added H3PO2 was higher than that of the catalyst that did not add H3PO2, which was due to the large surface area of the platinum in the former catalyst. According to the results of scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analysis, the phosphorus in the catalysts bonded with the surface of platinum particles as an oxide. The growth suppression of platinum particles was therefore attributed to the existence of a phosphorus oxide on the surface of platinum particles. But, adding H3PO2 excessively reduced the platinum surface area.

Magnetic and crystallographic study of Co electrodeposited alumite films

Magnetic properties and crystallographic structures of alumite films of which pores were filled with Co were investigated. The perpendicular magnetic anisotropy energy of the films was smaller than their shape anisotropy energy, which is due to the magnetocrystalline anisotropy of hcp‐Co particles in the pores. The c‐axis orientation of hcp‐Co particles was found to be influenced by the pH near the cathode and the ac frequency used in the deposition. The c axis rose from the in‐plane direction of the film to the normal one when the Co was electrodeposited into the pores at high pH value and low ac frequency, and the perpendicular magnetic anisotropy of the films increased. The deposition of Co at high pH value and low ac frequency was supposed to decrease the current density in the reduction process of Co2+ ions, which caused the preferred c‐axis orientation to the normal direction of the film.

Activity and Durability of PtRuP Catalysts and Their Atomic Structures

PtRuP catalysts were synthesized by electroless plating method and chelate ligand was added to the synthetic solution to narrow down difference of reduction potentials in Pt and Ru ions. XRD and XAFS analyses revealed that the addition of the ligand promoted alloying of Pt and Ru atoms in the PtRuP catalyst. Methanol oxidation activity and durability were improved by the well-alloyed PtRuP catalyst, which supported bi-functional mechanism. INTRODUCTION Based on bi-functional mechanism, an explanation for improvement of CO tolerance in Pt catalyst by addition of Ru proposed by Watanabe, Pt and Ru atoms in the PtRu catalyst should be well alloyed and Ru atom should be in close vicinity to Pt one at surface of the catalyst. However, Pt core/Ru shell structure is likely to be formed in wet syntheses such as alcohol reduction and electroless plating, because Pt ion is preferentially reduced due to difference of standard reduction potentials in Pt and Ru ions. In PtRuP catalyst synthesized by the alcohol reduction method, the highest methanol oxidation activity was achieved with composition of Pt78Ru22. The composition largely deviates from Pt50Ru50 commonly known as the best composition for the PtRu catalyst. This deviation is coming from the difference of the standard reduction potentials. Bulk composition of Pt in the catalyst should be higher than 50 at.% in order to make surface composition of the catalyst into 50 to 50, because Pt enriched core is formed by the preferential reduction of Pt ion in the alcohol reduction method. In this study, PtRuP catalysts were synthesized by electroless plating method. Chelate ligand was added in the synthetic solution to narrow down the difference of the reduction potentials. Effects of the ligand addition on methanol oxidation activity and on durability of the catalysts are reported in terms of atomic structures of the PtRuP catalysts. EXPERIMENTALS PtRuP catalysts were synthesized by electroless plating method by using NaPH2O2 as a reducing agent as well as source of P. H2PtCl6, RuCl3 and NaPH2O2 were dissolved in ion exchanged water and PtRuP catalyst was deposited on carbon support at 358 K. Chelate ligand was added in the synthetic solution to narrow down the difference of the reduction potentials. Methanol oxidation activity of the catalysts was evaluated by linear sweep volammetry (LSV). Durability of the catalysts was tested by repeated cyclic voltammetry (0.2-1.1 V vs. NHE). Atomic structures of the PtRuP catalysts were analyzed by XRD and by X-ray absorption fine structure (XAFS) of Pt-LIII and Ru-K edges. RESULTS AND DISCUSSION LSV measurements showed that methanol oxidation activity was improved in PtRuP catalyst synthesized with chelate ligand. Figure 1 shows XRD patterns of PtRuP and commercialized Pt catalysts. Diffraction angle from (111) plane of PtRuP catalyst synthesized without chelate ligand is almost same as that of Pt catalyst. On the other hand, the diffraction shifted toward higher angle in PtRuP catalyst synthesized with chelate ligand. This sift toward higher diffraction angle suggests that alloying of Pt and Ru atoms in the PtRuP catalyst was advanced, because lattice spacing of Pt decreases by alloying with Ru which has smaller atomic radius than that of Pt. Results of XAFS analysis are summarized in Table 1. Here, indexes of PRu and PPt (PRu=NRu-Pt/(NRu-Ru+NRu-Pt), NRu-Pt is Pt coordination number and NRu-Ru is Ru coordination one viewing from Ru atom, PPt is viewing from Pt atom) were introduced to compare frequency of neighboring Pt atom to Ru one. PRu and PPt of PtRuP catalyst synthesized with chelate ligand are larger than those of PtRuP catalyst synthesized without ligand, which indicates alloying of Pt and Ru atoms was advanced in the PtRuP catalyst synthesized with chelate ligand. Figure 2 shows durability of PtRuP and commercialized PtRu catalysts. It was found that addition of chelate ligand improved durability of PtRuP catalyst. Compositional analysis of the repeated CV tested solution showed that dissolution amount of Ru was smaller in PtRuP catalyst synthesized with chelate ligand, which also arises from well alloyed structure of the PtRuP catalyst synthesized with chelate ligand. In conclusion, addition of chelate ligand narrowed down difference of reduction potentials of Pt and Ru ions and well alloyed PtRuP catalyst was synthesized by electroless plating method. Methanol oxidation activity and durability were improved by the well-alloyed PtRuP catalyst. REFERENCES (1) M. Watanabe and S. Motoo, J. Electroanal. Chem. Interfacial Electrochem., 60, 267 (1975). (2) Daimon and Y. Kurobe, Catalysis Today, 111, 182 (2006). Fig.1 XRD Patterns of Catalysts. 34 36 38 40 42 44 2θ (deg.) In te ns ity (a .u .) Pt (111) PtRuP with chelate ligand PtRuP without chelate ligand

CO-P ELECTRODEPOSITED ALUMITE FILMS WITH IN-PLANE MAGNETIZATION

The magnetic properties and corrosion resistance of a magnetic alumite film, in which micropores are filled with Co, are investigated. It is found that in-plane magnetizatlon film is obtained by adding a small amount of P to the Co. For example, the effective anisotropy energy of the film changes from +0.44×105 erg/cm3 to -1.32×105 erg/cm3 by the addition of 8 at.% P. The in-plane coercivity of the film can be controlled between 340 Oe and 1350 Oe by the P content. The corrosion resistance of the film filled with Co94P6 under the atmosphere of 40°C, 90% R. H. with 10 ppm SO2 gas is tested. The corrosion resistance of the film under this condition is superior to that of sputtered Co-Ni thin film media with a carbon protective layer. Magnetic alumite film filled with Co-P alloy is considered to be a candidate for longitudinal magnetic recording media.

Magnetic and Microstructural Properties of Co–Cr Film Fabricated by Continuous Roll Coater

Co–Cr thin films with a Ge layer between the basefilm and Co–Cr film have been fabricated at a high deposition rate using a continuous roll coater. The effects of the Ge layer and deposition conditions on the magnetic properties and microstructures have been investigated. It is concluded that the Ge layer is remarkably effective in improving the preferred c-axis orientation and magnetic properties, even though the Co–Cr films are fabricated at an extremely high deposition rate. In addition, the tilting angle of the c-axis from the normal of the film plane, which is caused by the oblique incident of the vapor, is affected by the deposition temperature and rate as well as the incident direction of the vapor.

Study on the surface oxidation of Co-Cr films

The tribological properties of a Co-Cr thin film were greatly improved by surface oxidation. According to surface analyses, a Cr-rich oxidized region in which Cr is oxidized to Cr/sub 2/O/sub 3/ was formed near the surface of the film. This region plays an important role in improving the mechanical durability of the film. However, when the oxidation is carried out for a long time, a thick Co-rich oxidized region grows on the Cr-rich oxidized one. As a result, the durability deteriorates. >