Teruaki Nomiyama

Photo-rechargeable battery with TiO2/carbon fiber electrodes prepared by laser deposition

Abstract A photo-rechargeable battery which has two functions of the opto-electric conversion and the storage of the electrochemical energy was investigated for TiO 2 /carbon fibers (CFs) compound electrodes. The laser deposition method was used to produce TiO 2 fine particles on the surface of CFs to improve the photo-rechargeable performances. Some of the electrodes prepared in He gas had the photo-charged quantity 10–100 times as large as those in vacuum and those prepared by the sintering method. The difference of the mechanism of the charge was discussed.

Coating effect of electrospun nanofibers of Nb-doped TiO2 mixed in photoelectrode of dye sensitized solar cells

Electrospun nanofibers (NFs) of Nb doped TiO2 (TNO) were added as a conductive agent to TiO2 mesoporous layer in dye sensitized solar cells. In order to improve the mobility of carriers in NFs by reducing the barrier at grain boundaries among constituent nanoparticles in NFs, the surface of TNO-NFs was coated with a thin TNO layer by pulsed laser deposition with changing the deposition time td. It was found that the inter-grain space was filled first at td ≤ 5 min, and the diffusion velocity vD of carriers was increased by more than 10 times. Since Jsc showed an increase of ∼15% while vD and the electron lifetime τe decreased at td > 10 min, the carrier injection from dye/TiO2 nanoparticles to TNO-NFs was considered to be promoted.

Photoexcited-Charge Transfer and Energy–Storage Reaction of Photorechargeable TiO2/Carbon Fibers Composite Electrodes

A TiO2/carbon fibers (CFs) composite electrode is a solar device that converts photon energy to electrochemical energy and stores it in situ. The photoexcited-charge transfer and energy–storage reaction were studied. The results of photoelectrochemical measurements showed that the photoexcited electrons generated in TiO2 moved to CFs via ohmic contact. From a frequency response analysis of the electrochemical impedance, it was found that the electrical energy storage was realized by the formation of lithiated carbons at the CFs side. Since a large time constant was observed in the time variation of photo-emf, it was concluded that the low formation rate of lithiated carbons was one of the causes of small photocharged quantities.

Photorechargeability of TiO2/Carbon Bilayer Electrodes Prepared by Laser Deposition

The electrodes of TiO2/carbon bilayer films were prepared by laser deposition to investigate the effects of the bonding state of carbon on photorechargeability. The carbon layer was fabricated at different substrate temperatures from room temperature to 400°C. Experimental results of X-ray diffraction, optical absorption, electrical resistivity, X-ray photoelectron spectroscopy and atomic force microscopy showed that the sp2/sp3 ratio in the carbon layer increased with substrate temperature. The photocharged quantity increased with sp3 ratio, while the photo-emf was almost constant. The facts imply that dangling bonds play an important role in the storage of Li+ ions with low photo-emf characteristic in the case of TiO2.

Charge transfer in photorechargeable composite films of TiO2 and polyaniline

A photorechargeable battery (PRB) is a photovoltaic device having an energy storage function in a single cell. The photoactive electrode of PRB is a bilayer film consisting of bare porous TiO2 and a TiO2–polyaniline (PANi) mixture that work as a photovoltaic current generator and an electrochemical energy storage by ion dedoping, respectively. To study the charge transfer between TiO2 and PANi, the photorechargeable quantum efficiency QE ([electron count on discharge]/[incident photon count on photocharge]) was measured by varying the thickness LS of the TiO2–PANi mixture. The quantum efficiency QEuv for UV photons had a maximum of ~7% at LS ~ 7 µm. The time constant τTP for the charge transfer was about 10−1 s, which was longer ten times or more than the lifetime of excited electrons within TiO2. These facts reveal that the main rate-limiting factor in the photocharging process is the charge transfer between TiO2 and PANi.

Thermally assisted flux flow excited by ultrasound in superconducting thin films

Abstract A new ultrasonic method has been proposed for the investigation of the depinning line of superconducting thin films. The motion of the depinned flux lines is detected as the excess flux-flow voltage caused by the excitation of pinned flux lines through the ultrasonic vibration of pinning centers. When a strain related to the tilt modulus C 44 of flux-line lattice was applied to YBa 2 Cu 3 O 7−δ thin films in a parallel magnetic field, a maximum of the excess flux-flow voltage was observed below the superconducting transition temperature. To explain the maximum observed, a theory is proposed in which thermally assisted flux flow and ultrasonic attenuation due to the depinning of flux lines are taken into account. The discrepancies between the experimental and the theoretical results are discussed with the ultrasonic frequency and amplitude dependence of the depinning temperature.

Flux flow excited by ultrasonic deformation of flux line lattice in high temperature superconducting ceramics

Abstract To investigate the flux pinning behavior in HTSC against various kinds of deformation of flux line lattice (FLL), the flux flow excited by ultrasonic deformation of FLL was measured for bulk sintered samples of Bi2Sr2Ca2Cu3Oy. The compressional, tilt and shear ultrasonic deformations, which are associated with the elastic moduli of C11, C44 and C66 of FLL in isotopic superconductors, were applied to FLL. A peak of the flux flow resistivity was observed at a temperature Tp at which the dissipation of ultrasonic energy became the maximum. The differences in Tp and the peak height obtained for the three kinds of deformation were small, against the theoretical prediction with the model of thermally assisted flux flow. The results suggest that most flux lines are bent due to the pinning at insulating layers and/or grain boundaries.

Effect of n=1 Buffer Layers on n=2 and n=3 Thin Films of Bi 2Sr 2Can-1CunOy

The effect of n=1(2201) buffer layers on n=2(2212) and n=3(2223) thin films of Bi2Sr2Can-1CunOy was investigated to reduce the strain caused by the lattice mismatch between the films and the substrates. The bilayer thin films of 2223/2201 and 2212/2201 were grown epitaxially on SrTiO3 (100) substrates by dc sputtering. When the thickness of the buffer layer was 10–25 nm, the superconducting transition temperature increased by ~20 K for 2223/2201 and by ~6 K for 2212/2201. The increase was attributed to the reduction of the strain from the experimental results of the full width at half-maximum of X-ray diffraction peaks, the length along the c-axis and the roughness of the film surface.