Yusuke Ayato

Study of Pt Electrode/Nafion Ionomer Interface in HClO4 by In Situ Surface-Enhanced FTIR Spectroscopy

Pt electrode/Nafion interface has been characterized in HCIO 4 aqueous solutions using surface-enhanced infrared absorption spectroscopy (SEIRAS) with the aim of investigating the structure of the interface which plays a crucial role in the performance of polymer electrolyte fuel cells (PEFCs). A potential dependent band was found around 1100 cm - 1 and assigned to the symmetric vibration of the -SO - 3 groups of the ionomer membrane. Electric field driven orientation/adsorption of the ionomer membrane at the interface was suggested from the potential dependence of the band intensities of -SO - 3 groups. It was inferred that the -SO - 3 groups act like counterions at the Pt/ionomer interface to form the electric double layer.

Direct Electrochemistry of Hemoglobin Molecules Adsorbed on Bare Indium Tin Oxide Electrode Surfaces

The direct electrochemistry of hemoglobin (Hb) molecules adsorbed on bare indium tin oxide (ITO) electrodes was investigated by voltammetric methods. A pair of redox peak currents, which is attributed to a heme Fe(III)/Fe(II) couple in Hb molecules, was found at Hb-adsorbed ITO electrodes in phosphate-buffered saline (PBS; pH 7.4) solutions. Slab optical waveguide (SOWG) spectroscopy, which is one of the attenuated total reflection (ATR) techniques, was employed to observe the Soret band of Hb molecules adsorbed on the bare ITO electrode surfaces. The obtained spectra indicated that directly adsorbed Hb molecules were not significantly denatured on the bare ITO electrode surfaces.

A simple biofuel cell cathode with human red blood cells as electrocatalysts for oxygen reduction reaction

A red blood cell (RBC) from human exhibited direct electron transfer (DET) activity on a bare indium tin oxide (ITO) electrode. A formal potential of -0.152 V vs. a silver-silver chloride saturated potassium chloride (Ag|AgCl|KCl(satd.)) was estimated for the human RBC (type AB) from a pair of redox peaks at around 0.089 and -0.215 V (vs. Ag|AgCl|KCl(satd.)) on cyclic voltammetric (CV) measurements in a phosphate buffered saline (PBS; 39 mM; pH 7.4) solution. The results agreed well with those of a redox couple for iron-bearing heme groups in hemoglobin molecules (HbFe(II)/HbFe(III)) on the bare ITO electrodes, indicated that DET active species were hemoglobin (Hb) molecules encapsulated by a phospholipid bilayer membrane of the human RBC. The quantity of electrochemically active Hb in the human RBC was estimated to be 30 pmol cm(-2). In addition, the human RBC exhibited oxygen reduction reaction (ORR) activity in the dioxygen (O2) saturated PBS solution at the negative potential from ca. -0.15 V (vs. Ag|AgCl|KCl(satd.)). A single cell test proved that a biofuel cell (BFC) with an O2|RBC|ITO cathode showed the open-circuit voltage (OCV) of ca. 0.43 V and the maximum power density of ca. 0.68 μW cm(-2).

One-Step Liquid-Phase Synthesis of Carbon Nanotubes: Effects of Substrate Materials on Morphology of Carbon Nanotubes

Effects of substrate materials and shapes have been investigated in the one-step liquid-phase (OS-LP) synthesis of carbon nanotubes (CNTs). Similar highly aligned multi-walled CNT (MWCNT) arrays (HACNTAs) with a height (ha) of ~30 µm were synthesized on the substrates of commercially available stainless steel and Inconel® alloy by a resistance heating method in methanol containing cobaltocene, whereas aligned MWCNT arrays (ha≈10 µm) with slightly poor alignment were formed on the titanium substrate, compared with those of the former two. On the other hand, very short, non-aligned MWCNTs with a length of ~1 µm were deposited on a silicon substrate. The different morphologies depending on the substrate materials are related with interaction between the pyrolytically-generated Co atoms and the surface oxide layers of the substrates. In addition, we have for the first time demonstrated that the OS-LP synthesis is suitable for CNT-coating onto intricately-shaped substrates like stainless steel mesh.

In Situ Observation of Time Dependent Electrochemical Activity of Cytochrome c at Bare Indium-Tin-Oxide Electrodes by Cyclic Voltammetry and Slab Optical Waveguide Spectroscopy

In situ observation of electrochemical activity and time dependent characteristics of cytochrome c (cyt c) was carried out in 0.01 M phosphate buffered saline (PBS, pH 7.4) containing 20µM cyt c solutions at bare indium-tin-oxide (ITO) electrodes by using a cyclic voltammetry (CV) and a slab optical waveguide (SOWG) spectroscopy. The bare ITO electrodes could retain the electrochemical activity of cyt c in the PBS solutions, indicating the great advantage of using ITO electrodes against other electrode materials, such as gold (Au). The CV curves and simultaneously observed the time-resolved SOWG absorption spectra in the consecutive cycles implied that the cyt c molecules could retain its own electrochemical function for a long time.

Evidences for Adsorption of Heptyl Viologen Cation Radicals in Thin Deposition Layers on ITO Electrodes by Slab Optical Waveguide Spectroscopy

In situ observations were mainly performed by using slab optical waveguide (SOWG) spectroscopy synchronized with potential step measurements to investigate the time dependent spectral change of the adsorbed heptyl viologen cation radicals (HV +· ) in thin deposition layer on indium-tin-oxide (ITO) electrodes. Several absorption bands, which indicated a monomer and dimer of HV +· were co-adsorbed on ITO electrode surface with a monolayer or a few layers deposition, were observed in UV-visible region. The time dependent spectra yielded some important molecular information for the adsorption phenomena of HV +· on the electrode surface. All observed absorption bands disappeared completely when the electrode potential of -200 mV vs. Ag/AgCl was applied, which indicated the adsorbed HV +· species were electrochemically reoxidized on the ITO electrode.

Performance of Intermediate Temperature Fuel Cells with Proton Conducting Electrolytes Synthesized with Diammonium Hydrogen Phosphate (1)

The (ZrO2-1.6P2O5)-PTFE composite electrolytes have been prepared by mixing PTFE powders with different particle sizes and the shell-core-type ZrO2-1.6P2O5 electrolyte, synthesized by solid state reaction with diammonium hydrogen phosphate, to improve the mechanical strength of the electrolyte. The H2 gas permeability decreased and the cell performances improved with decreasing PTFE-particle size. The aging at 0.4 V above 443 K enhanced the ITFC performance owing to the penetration of the electrolyte to the carbon paper. The maximum output power enhanced by 63% after 15 h of aging at 573 K.

Slab optical waveguide spectroscopy for in situ interfacial analysis

Recently we have developed a novel slab optical waveguide (SOWG) spectroscopy utilizing glycerol drop on a thin glass plate for light introduction, with which in situ absorption spectra of adsorbed materials in UV-visible range were measured. This SOWG system has some advantages such as a low loss, a broad-band transparency, an easy coupling, and high sensitivity under monolayer coverage. Additionally, we have utilized indium-tin-oxide (ITO) electrode thin film on a SOWG (ITO-SOWG) for in situ observation of electrochemical reactions on electrode surface. We have observed the adsorption behavior of proteins and dyes on solid/liquid interfaces and obtain the electrochemical responses of them.