Shin-ichi Nagamatsu

μ-XAFS of a single particle of a practical NiOx/Ce2Zr2Oy catalyst

μ-XAFS analysis using an X-ray μ-beam (1000 nm (h) × 800 nm (v)) was successfully carried out on a single particle of a practical catalyst NiO(x)/Ce(2)Zr(2)O(y) (0 ≤x≤ 1, 7 ≤y≤ 8). The oxidation state and local coordination structure of the NiO(x)/Ce(2)Zr(2)O(y) particle were characterized by Ni K-edge μ-XANES and μ-EXAFS, which showed the catalytically active and inactive phases of a single catalyst particle.

Surface-Regulated Nano-SnO2/Pt3Co/C Cathode Catalysts for Polymer Electrolyte Fuel Cells Fabricated by a Selective Electrochemical Sn Deposition Method

We have achieved significant improvements for the oxygen reduction reaction activity and durability with new SnO2-nanoislands/Pt3Co/C catalysts in 0.1 M HClO4, which were regulated by a strategic fabrication using a new selective electrochemical Sn deposition method. The nano-SnO2/Pt3Co/C catalysts with Pt/Sn = 4/1, 9/1, 11/1, and 15/1 were characterized by STEM-EDS, XRD, XRF, XPS, in situ XAFS, and electrochemical measurements to have a Pt3Co core/Pt skeleton-skin structure decorated with SnO2 nanoislands at the compressive Pt surface with the defects and dislocations. The high performances of nano-SnO2/Pt3Co/C originate from efficient electronic modification of the Pt skin surface (site 1) by both the Co of the Pt3Co core and surface nano-SnO2 and more from the unique property of the periphery sites of the SnO2 nanoislands at the compressive Pt skeleton-skin surface (more active site 2), which were much more active than expected from the d-band center values. The white line peak intensity of the nano-SnO2/Pt3Co/C revealed no hysteresis in the potential up-down operations between 0.4 and 1.0 V versus RHE, unlike the cases of Pt/C and Pt3Co/C, resulting in the high ORR performance. Here we report development of a new class of cathode catalysts with two different active sites for next-generation polymer electrolyte fuel cells.

Performance and characterization of a Pt–Sn(oxidized)/C cathode catalyst with a SnO2-decorated Pt3Sn nanostructure for oxygen reduction reaction in a polymer electrolyte fuel cell

We have prepared and characterized a SnO2-decorated Pt-Sn(oxidized)/C cathode catalyst in a polymer electrolyte fuel cell (PEFC). Oxygen reduction reaction (ORR) performance of Pt/C (TEC10E50E) remained almost unchanged or even tended to reduce in repeated I-V load cycles, whereas the I-V load performance of the Pt-Sn(oxidized)/C prepared by controlled oxidation of a Pt-Sn alloy/C sample with the Pt3Sn phase revealed a significant increase with increasing I-V load cycles. The unique increase in the ORR performance of the Pt-Sn(oxidized)/C catalyst was ascribed to a promoting effect of SnO2 nano-islands formed on the surface of Pt3Sn core nanoparticles. Also in a rotating disk electrode (RDE) setup, the mass activity of an oxidized Pt3Sn/C catalyst was initially much lower than that of a Pt/C catalyst, but it increased remarkably after 5000 rectangular durability cycles and became higher than that of the fresh Pt/C. The maximum power density per electrochemical surface area for the Pt-Sn(oxidized)/C catalyst in a PEFC was about 5 times higher than that for the Pt/C catalyst at 0.1-0.8 A cm(-2) of the current density. In situ X-ray absorption near-edge structure (XANES) analysis at the Pt LIII-edge in increasing/decreasing potential operations and at the Sn K-edge in the I-V load cycles revealed a remarkable suppression of Pt oxidation compared with the Pt/C catalyst at higher potentials and no change in the Sn oxidation state, respectively, resulting in higher performance and stability of the Pt-Sn(oxidized)/C catalyst due to the SnO2 nano-islands under the PEFC operation conditions. The SnO2 nano-island decorated Pt-Sn(oxidized)/C catalyst with a Pt3Sn alloy nanostructure is regarded as a promising candidate for a PEFC cathode catalyst.

Mapping Platinum Species in Polymer Electrolyte Fuel Cells by Spatially Resolved XAFS Techniques

There is limited information on the mechanism for platinum oxidation and dissolution in Pt/C cathode catalyst layers of polymer electrolyte fuel cells (PEFCs) under the operating conditions though these issues should be uncovered for the development of next-generation PEFCs. Pt species in Pt/C cathode catalyst layers are mapped by a XAFS (X-ray absorption fine structure) method and by a quick-XAFS(QXAFS) method. Information on the site-preferential oxidation and leaching of Pt cathode nanoparticles around the cathode boundary and the micro-crack in degraded PEFCs is provided, which is relevant to the origin and mechanism of PEFC degradation.

Same-View Nano-XAFS/STEM-EDS Imagings of Pt Chemical Species in Pt/C Cathode Catalyst Layers of a Polymer Electrolyte Fuel Cell.

We have made the first success in the same-view imagings of 2D nano-XAFS and TEM/STEM-EDS under a humid N2 atmosphere for Pt/C cathode catalyst layers in membrane electrode assemblies (MEAs) of polymer electrolyte fuel cells (PEFCs) with Nafion membrane to examine the degradation of Pt/C cathodes by anode gas exchange cycles (start-up/shut-down simulations of PEFC vehicles). The same-view imaging under the humid N2 atmosphere provided unprecedented spatial information on the distribution of Pt nanoparticles and oxidation states in the Pt/C cathode catalyst layer as well as Nafion ionomer-filled nanoholes of carbon support in the wet MEA, which evidence the origin of the formation of Pt oxidation species and isolated Pt nanoparticles in the nanohole areas of the cathode layer with different Pt/ionomer ratios, relevant to the degradation of PEFC catalysts.

Direct Synthesis of Phenol from Benzene and O2, Regulated by NH3 on Pt/β and Pt‐Re/ZSM‐5 Catalysts

Phenol, which is an important intermediate in the manufacture of fine chemicals and plastics, is mainly produced by the threestep so-called “cumene process”, through the decomposition of a cumene hydroperoxide intermediate with sulfuric acid into phenol (in the liquid phase) with the equimolar formation of acetone. Compared to the cumene process, the direct synthesis of phenol from benzene in a one-step, gas-phase reaction is one of the most desirable catalytic reactions. Various oxidants have been examined for the direct benzene-into-phenol synthesis, such as O2, [1] H2O2, [2] N2O, [3] H2+O2, [4]

Multiple scattering approach to the theory of angular dependence of K-edge X-ray magnetic circular dichroism

We discuss the angular-dependent K-edge X-ray magnetic circular dichroism (XMCD) spectra based on the semi-relativistic short-range order full multiple-scattering theory, where 2-spinor formalism is used to describe spin-orbit coupling and spin-dependent exchange scattering. So far, most of the theoretical approaches have been limited to the simplest case where the circularly polarized X-ray propagation coincides with the direction of the magnetic field. Here we discuss more general cases using the above theoretical approaches. In addition to the well-known angular dependence, we have a new term with different angular dependence. This term can provide useful information on the symmetry lowering of magnetic atoms around the X-ray absorbing atom. This effect is expected to be experimentally observed. We separately discuss atomic, single and full multiple-scattering XMCD spectra, in particular, the anisotropic features of them are studied in detail. We found the spin-orbit coupling at neighboring atoms plays a minor role; however, spin-dependent exchange scatterings plays an important role in XMCD analyses.

Partitioning Method Applied to X-Ray Absorption Near Edge Structure Calculations

So far we have developed an efficient technique to calculate the X-ray absorption near edge structure (XANES) spectra based on partitioning method to include important full multiple scatterings but exclude unimportant scatterings. In this paper we discuss some techniques to obtain rapid convergence of partial summation and give some illustrative examples applied to medium size (about 50) and large clusters (>100 atoms). The best approach to obtain good convergence to full MS calculation and high efficiency depends on cluster size. Though full MS calculations need much time , that is drastically shortened to less than 10–30% for the large clusters by use of the present methods.

Multiple scattering approach to Co K-edge XMCD and XANES spectra in Gd-Co alloys

Abstract We have measured and analyzed Co K-edge X-ray absorption near edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) near edge spectra in crystalline and amorphous GdCo 2 alloys. We have used a semi-relativistic full multiple scattering approach to the analyses of the XMCD spectra. A general formula is obtained which is applicable to randomly oriented systems in space. Useful information is obtained on both the electronic and geometric structure around a Co atom. The difference in XANES and XMCD spectra between crystalline and amorphous GdCo 2 is well explained by models referring to the anomalous X-ray scattering result, where three Gd atoms in the second shell are removed away. The calculated XANES are not so sensitive to the electronic structure, whereas the calculated XMCD spectra are rather sensitive to the spin polarization on Co atoms. The result shows that the spin polarization on Co atoms in GdCo 2 alloys is smaller than that in Co metals.

Spatially Non-Uniform Degradation of Pt/C Cathode Catalysts in Polymer Electrolyte Fuel Cells Imaged by Combination of Nano XAFS and STEM-EDS Techniques

This account article treats with spatially non-uniform degradation events of Pt/C cathode catalysts in polymer electrolyte fuel cells involving the formation and dissolution of positively charged Pt ions and detachment of metallic Pt nanoparticles/clusters, which were visualized by the same-view nano XAFS and STEM-EDS imaging technique under humid N2 atmosphere.