Hideki Matsune

High Durability of Carbon Nanotube-Supported Pt Electrocatalysts Covered with Silica Layers for the Cathode in a PEMFC

Multiwalled carbon nanotube (CNT)-supported Pt nanoparticles (Pt/CNT) were covered with silica layers by successive hydrolysis of 3-aminopropyl-triethoxysilane and tetraethoxysilane on CNTs with Pt metal precursors, followed by reduction with hydrogen. The Pt/CNT covered with silica layers (SiO 2 /Pt/CNT) was used as a cathode catalyst for a proton exchange membrane fuel cell (PEMFC). The activity of SiO 2 /Pt/CNT catalyst for the oxygen reduction reaction in a single-cell PEMFC was similar to that of Pt/CNT, in spite of the uniform coverage of Pt with silica layers, indicating that the coverage of Pt/CNT with silica layers did not appreciably decrease the catalytic activity. In addition, SiO 2 /Pt/CNT electrocatalyst showed high stability during potential cycling from 0.05 to 1.20 V vs reversible hydrogen electrode in an aqueous H 2 SO 4 electrolyte, whereas Pt/CNT significantly deactivated during the experiment. The structural change of Pt species in these electrocatalysts during potential cycling was investigated by transmission electron microscopy images and Pt L III -edge X-ray absorption fine structure. The crystallite size of Pt metal in SiO 2 /Pt/CNT did not change appreciably during the potential cycling, while Pt metal crystallites in Pt/CNT seriously aggregated. Silica layers enveloping Pt metal particles in SiO 2 /Pt/CNT prevent the dissolution and redeposition of Pt metal particles as well as the agglomeration of Pt metal particles on the supports.

Highly durable Pd metal catalysts for the oxygen reduction reaction in fuel cells; coverage of Pd metal with silica

Pd cathode catalysts for polymer electrolyte fuel cells have been covered with silica layers a few nanometres thick. The silica-coated Pd catalysts showed high activity and excellent durability for the oxygen reduction under the severe cathode conditions of PEFCs, while Pd catalysts without silica-coating were seriously deactivated under the same conditions. The coverage of Pd metal with silica prevents the diffusion of Pd species out of the silica layers.

Preparation of silica-coated Pt metal nanoparticles using microemulsion and their catalytic performance

Abstract Pt–SiO2 catalysts were prepared by using water-in-oil type microemulsion. The catalysts were prepared by hydrolysis of tetraethylorthosilicate in the microemulsion containing Pt species, followed by calcination in air and reduction with H2. This preparation method for Pt–SiO2 provided Pt metal nanoparticles with a diameter of ca. 6 nm covered uniformly with silica layers, while a conventional impregnation method formed Pt metal particles supported on the silica surface. The Pt catalysts coated with silica (coat–Pt) showed different catalytic performance for the competitive oxidation of mixed hydrocarbons from Pt catalysts supported on silica (imp–Pt), i.e. in the competitive oxidation of methane and iso-butane, coat–Pt catalysts preferentially oxidized methane, while iso-butane was oxidized selectively over imp–Pt catalysts. The results of the adsorption of Ar on coat-Pt showed that silica in coat-Pt had porous structures of pore diameters < 1 nm. Because the porous structure of silica, which wrapped Pt metal particles, controlled the diffusion rate of reactant molecules, coat-Pt showed a specific catalytic performance for competitive oxidation.

Carbon nanotube-supported Pd–Co catalysts covered with silica layers as active and stable cathode catalysts for polymer electrolyte fuel cells

Carbon nanotube-supported Pd catalysts (Pd/CNT) as the cathode for polymer electrolyte fuel cells (PEFCs) were modified with various transition metals (Fe, Co, Ni and Cu) to improve their catalytic activity for the oxygen reduction reaction (ORR). Modification with these transition metals enhanced the activity of Pd/CNT for the ORR, especially the activity of Pd–Co/CNT, which was 2 times higher than that of Pd/CNT. X-ray diffraction and X-ray absorption spectroscopy indicated that the metal species in Pd–Co/CNT was mainly present as a Pd–Co alloy, which acts as catalytically active sites for the ORR. However, the Pd–Co/CNT catalysts were rapidly deactivated for the ORR in 0.1 M HClO4 electrolyte due to the dissolution and diffusion of metal species out of the catalysts. Pd–Co/CNT was covered with silica layers with a thickness of a few nanometers, which prevented the diffusion of Co and Pd species into the HClO4 electrolyte. Thus, silica-coated Pd–Co/CNT catalysts exhibited high activity for the ORR and excellent durability under severe cathode conditions.

Highly active and durable silica-coated Pt cathode catalysts for polymer electrolyte fuel cells: control of micropore structures in silica layers

Carbon nanotube (CNT)-supported Pt catalysts (Pt/CNT) for use as cathode components in polymer electrolyte fuel cells (PEFCs) were covered with silica layers to prevent particle size increases during operation of the PEFC, either through the sintering of the Pt particles or the dissolution and redeposition of Pt ions. The formation of silica layers by the successive hydrolysis of 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) significantly improved the durability of the Pt/CNT catalysts under cathodic conditions, although the activity of the silica-coated material for the oxygen reduction reaction was slightly lower than that of the uncoated catalyst. In contrast, a silica-coated Pt/CNT catalyst prepared by the successive hydrolysis of APTES and TEOS in the presence of NH2–(CH2)n–NH2 (n = 6, 8 and 10) exhibited both high catalytic activity and excellent durability. The NH2–(CH2)n–NH2 added during the silica coating process worked as a template for the formation of micropores in the silica layers and the resulting pore structures enhanced the diffusion of both reactants and products during oxygen reduction on the silica-coated Pt/CNT catalysts.

Size-effect on fluorescence spectrum of perylene nanocrystal studied by single-particle microspectroscopy coupled with atomic force microscope observation

This paper presents single particle fluorescence spectroscopy of perylene nanocrystals coupled with AFM observation of their topographic shapes. The fluorescence spectra of individual nanocrystals confirmed clearly and precisely a blue-shift in the excimer emission maximum on the reduction of their volume. The result can be explained in terms of “lattice softening”, which makes intermolecular interaction weaker and modified the energy level of the excimer state in nanocrystal.

Highly durable carbon nanotube-supported Pd cathode catalysts covered with silica layers for polymer electrolyte fuel cells: Effect of silica layer thickness on the catalytic performance

Carbon nanotube-supported Pd catalyst (Pd/CNT) was covered with silica layers a few nanometers thick by successive hydrolysis of 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) to improve the durability of the Pd catalyst under cathode conditions of polymer electrolyte fuel cells (PEFCs). The coverage with silica layers resulted in the improvement of durability of Pd/CNT during the potential cycling between 0.05 and 1.20 V (vs. RHE) in aqueous HClO4 electrolyte. The catalytic activity and durability of silica-coated Pd/CNT strongly depended on silica layer thickness in the catalysts. The coverage with thicker silica layers improved the durability of Pd/CNT but the catalytic activity of the catalysts for the oxygen reduction reaction became lower with silica layer thickness. The coverage of Pd/CNT with silica layers of ca. 3 nm thickness is preferable from a viewpoint of the catalytic activity and durability.

Preparation of silica-coated Pt-Ni alloy nanoparticles using microemulsions and formation of carbon nanofibers by ethylene decomposition

Abstract Silica-coated Pt-Ni alloys were prepared using a water-in-oil-type microemulsion. The silica-coated Pt-Ni alloys prepared without thermal treatment decomposed ethylene to form nanocomposites of carbon nanofibers.

Relationship between degree of dynamic morphological change and proliferative potential of murine embryonic stem cells.

The degree of dynamic morphological change of murine embryonic stem cells is investigated through direct observation by microscopy. As a result, we find that the degree of dynamic morphological change is proportional to the increase in the ratio of the cellular population in subculture.