Michihisa Koyama

Reaction model of dense Sm0.5Sr0.5CoO3 as SOFC cathode

Overpotential and AC impedance spectra were measured to study the reaction model of dense Sm0.5Sr0.5CoO3 (SSC) as SOFC cathode. From the PO2 dependence of interfacial conductivity, the rate determining step of dense SSC electrode was adsorption and desorption processes at the surface of the electrode. Rate constants of adsorption and desorption were calculated from the interfacial conductivity of the dense electrode to be 3×10−5 mol cm−2 s−1 atm−1 and 2×10−8 mol cm−2 s−1, respectively. These were approximately one order of magnitude larger than the corresponding values calculated for La0.6Sr0.4CoO3. These rate constants can elucidate the overpotentials of porous electrodes.

A Computational Chemistry Study on Friction of h-MoS2. Part I. Mechanism of Single Sheet Lubrication

In this work, we theoretically investigated the friction mechanism of hexagonal MoS(2) (a well-known lamellar compound) using a computational chemistry method. First, we determined several parameters for molecular dynamics simulations via accurate quantum chemistry calculations and MoS(2) and MoS(2-x)O(x) structures were successfully reproduced. We also show that the simulated Raman spectrum and peak shift on X-ray diffraction patterns were in good agreement with those of experiment. The atomic interactions between MoS(2) sheets were studied by using a hybrid quantum chemical/classical molecular dynamics method. We found that the predominant interaction between two sulfur layers in different MoS(2) sheets was Coulombic repulsion, which directly affects the MoS(2) lubrication. MoS(2) sheets adsorbed on a nascent iron substrate reduced friction further due to much larger Coulombic repulsive interactions. Friction for the oxygen-containing MoS(2) sheets was influenced by not only the Coulomb repulsive interaction but also the atomic-scale roughness of the MoS(2)/MoS(2) sliding interface.

Object-based modeling of SOFC system: dynamic behavior of micro-tube SOFC

A simulation model for a tubular solid oxide fuel cell (SOFC) was developed by the object-based approach to calculate the current distribution, gas concentration distribution, and temperature distribution at the steady states and transient operation states. The transient electrical and temperature response to a load change was simulated for the both cells with the diameter of 22 mm (standard cell) and the diameter of 2.4 mm (micro-tube cell). The time required to reach the new steady state as the operating voltage was changed from 0.7 to 0.5 V for the micro-tube cell was found to be 15 s, which is much shorter than that of the standard cell.

Applying ultra-accelerated quantum chemical molecular dynamics technique for the evaluation of ligand protein interactions

Ligand–protein interactions have been studied using several chemical information techniques including quantum chemical methods that are applied to truncated systems composed of the ligand molecule and the surrounding amino acids of the receptor. Fragmented quantum molecular chemical studies are also a choice to study the enzyme–ligand system holistically, however there are still restrictions on the number of water molecules that can be included in a study of this nature. In this work we adopt a completely different approach to study ligand–protein interactions accounting explicitly for as many solvent molecules as possible and without the need for a fragmented calculation. Furthermore, we embed our quantum chemical calculations within a molecular dynamics framework that enables a fundamentally fast system for quantum chemical molecular dynamic simulations (QCMD). Central to this new system for QCMD is the tight binding QC system, newly developed in our laboratories, which combined with the MD paradigm results in an ultra-accelerated QCMD method for protein–ligand interaction evaluations. We have applied our newly developed system to the dihydrofolate reductase (DHFR)–methotrexate (MTX) system. We show how the proposed method leads us to new insights into the main interactions that bind MTX to the enzyme, mainly the interaction between the amino group of MTX and Asp27 of DHFR, as well as MTX amino group with Thr113 of DHFR, which have been only elucidated experimentally to date.

Internet-Based Integrated Environmental Assessment Using Ontologies to Share Computational Models

Summary New advances in Internet technologies and computer modeling provide opportunities for collaborative systems to support research and development in the field of industrial ecology. In particular, new information technologies such as semantic search engines based on ontologies could help researchers to link fragments of knowledge generated at research centers from around the world. Using a storyline of four imaginary researchers who hope to find collaborators in order to develop their research findings, we illustrate two levels of a four-level architecture for an Internet-based knowledge integration and collaboration environment for integrated environmental assessment. The foundation of the proposed architecture is a belief that computational models are an effective medium for conveying expert knowledge of various phenomena. Drawing from this premise, the first level of the architecture stands on a base of computational models that in some way represent the expert knowledge of the model builder. At the second level, we provide markup and interface definition tools to describe the type of knowledge contained in each model, together with the types of information services that can be provided. The results of research at these two levels of an Internet-based knowledge integration environment for integrated environmental assessment in industrial ecology are presented in this article. Our work on the third level of model searching and matching and the fourth level of parametric model integration and solving will be presented in subsequent articles.

La0.6Ba0.4CoO3 as a Cathode Material for Solid Oxide Fuel Cells Using a BaCeO3 Electrolyte

The cathodic reaction mechanism of a solid oxide fuel cell (SOFC) was investigated for an electrode-electrolyte system of La{sub 0.6}Ba{sub 0.4}CoO{sub 3} (LBC)-BaCeO{sub 3}, under both the O{sup 2{minus}} conducting and H{sup +}/O{sup 2{minus}} mixed-ionic conducting conditions. AC impedance measurements were carried out, and the electrode interfacial conductivities were calculated. The experimental results revealed that the processes dominating the electrode resistance for the O{sup 2{minus}} conducting and the H{sup +}/O{sup 2{minus}} mixed-ionic conducting conditions are different. It was also found that the process dominating the electrode resistance changes at 700 C under H{sup +}/O{sup 2{minus}} mixed-ionic conducting conditions. The process dominating the electrode resistance above 700 C is postulated to be the reaction O{sub LBC} + H{sub LBC} {r{underscore}arrow} OH{sub LBC}. LBC showed high-performance cathode characteristics for a SOFC using BaCeO{sub 3} electrolyte.

Experimental and Molecular Dynamics Simulations of Tribochemical Reactions with ZDDP: Zinc Phosphate–Iron Oxide Reaction

Zinc phosphate glass is considered to be the main constituent of tribofilms generated under boundary lubrication with zinc dialkyldithiophosphate (ZDDP), a well-known antiwear additive. The reaction occurring during friction between zinc phosphate glasses and steel native iron oxide layer is investigated by both an experimental approach and by Molecular Dynamics simulations (MD). The importance of this “tribochemical” reaction in the general ZDDP antiwear process is discussed.

A Review of Molecular-Level Mechanism of Membrane Degradation in the Polymer Electrolyte Fuel Cell

Chemical degradation of perfluorosulfonic acid (PFSA) membrane is one of the most serious problems for stable and long-term operations of the polymer electrolyte fuel cell (PEFC). The chemical degradation is caused by the chemical reaction between the PFSA membrane and chemical species such as free radicals. Although chemical degradation of the PFSA membrane has been studied by various experimental techniques, the mechanism of chemical degradation relies much on speculations from ex-situ observations. Recent activities applying theoretical methods such as density functional theory, in situ experimental observation, and mechanistic study by using simplified model compound systems have led to gradual clarification of the atomistic details of the chemical degradation mechanism. In this review paper, we summarize recent reports on the chemical degradation mechanism of the PFSA membrane from an atomistic point of view.

The valence band structure of AgxRh1–x alloy nanoparticles

The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag0.5Rh0.5 alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.

Chemical Degradation Mechanism of Model Compound, CF3 ( CF2 ) 3O ( CF2 ) 2OCF2SO3H , of PFSA Polymer by Attack of Hydroxyl Radical in PEMFCs

To enhance the durability of perfluorosulfonic acid (PFSA) polymer for proton-exchange membrane fuel cells (PEMFCs), we theoretically analyzed the degradation mechanism of PFSA by the attack of a hydroxyl (OH) radical. We used CF 3 (CF 2 ) 3 O(CF 2 ) 2 OCF 2 SO 3 H as a model compound representing the PFSA side chain because the experimental result suggested that the ether group in the PFSA side chain is vulnerable to the OH radical attack. We performed density functional theory calculation to discuss the degradation reaction mechanism of the ether group in the model compound of the side chain and OH radical. Under high humidity condition, we clearly demonstrated the degradation mechanism and reactivity of C-0 bond cleavage in the ether group by the OH radical. This result shows reasonable agreement with the experimental one. However, the OH radical prefers the reaction of the sulfonic acid group to the ether group under the low humidity condition. We found the different reactivity of the OH radical under the low and high humidity conditions. To improve the durability of PFSA, we proposed four directions: (i) enhancement of deprotonation, (ii) protection of ether group by steric hindrance, (iii) enhancement of C-O bond strength, and (iv) substitution of the ether group by other chemical groups. The latter two directions have been theoretically explored more in detail.