Hiroyuki Yanagi

Anion Exchange Membrane and Ionomer for Alkaline Membrane Fuel Cells (AMFCs)

We newly developed the anion exchange membranes and ionomers for alkaline membrane fuel cell system. The AEMs consist of hydrocarbon type main chain and quaternary ammonium groups as ion exchanging site, and they show sufficient OH- conductivity and thermal durability. The ionomer also consists of hydrocarbon type main chain and quaternary ammonium groups. It shows applicable OH- conductivity for the catalyst layer of fuel cells. We evaluated the cell performance based on the developed membrane and ionomer . It shows sufficient cell output even if the ambient air was used as the oxidant.

Performance and Reliability of Deep-Ultraviolet Light-Emitting Diodes Fabricated on AlN Substrates Prepared by Hydride Vapor Phase Epitaxy

The reliability and output power of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) fabricated on AlN substrates prepared by hydride vapor phase epitaxy are reported. TEM analysis revealed that dislocation density in LED layers, except the p-GaN layer, was below 106 cm-2. DUV-LEDs emitting at 261 nm exhibited an output power of 10.8 mW at 150 mA. The lifetime of these LEDs was estimated to be over 10,000 h for cw operation at 50 mA. No significant acceleration of output power decay at higher operation currents was observed. The estimated lifetime at the operation current of 150 mA was over 5,000 h.

Light extraction enhancement of 265 nm deep-ultraviolet light-emitting diodes with over 90 mW output power via an AlN hybrid nanostructure

Deep-ultraviolet (DUV) aluminum gallium nitride-based light-emitting diodes (LEDs) on transparent aluminum nitride (AlN) substrates with high light extraction efficiency and high power are proposed and demonstrated. The AlN bottom side surface configuration, which is composed of a hybrid structure of photonic crystals and subwavelength nanostructures, has been designed using finite-difference time-domain calculations to enhance light extraction. We have experimentally demonstrated an output power improvement of up to 196% as a result of the use of the embedded high-light-extraction hybrid nanophotonic structure. The DUV-LEDs produced have demonstrated output power as high as 90 mW in DC operation at a peak emission wavelength of 265 nm.

High p-type conduction in high-Al content Mg-doped AlGaN

We report on the successful fabrication of highly conductive p-type Mg-doped Al0.7Ga0.3N thin films grown on sapphire substrates by metal-organic chemical vapor deposition. Photoluminescence measurements show that Mg doping for growth with a high V/III ratio and moderate Mg concentration can effectively suppress self-compensation by the formation of nitrogen vacancy complexes. The lowest electrical resistivity was found to be 47 Ω cm at room temperature. Moreover, the temperature dependence of the p-type conductivity in these high-Al content AlGaN films shows the extremely small effective activation energies of 47–72 meV at temperatures below 500 K.

In-situ Observation of CO2 through the Self-purging in Alkaline Membrane Fuel Cell (AMFC)

Introduction Recently alkaline membrane fuel cells (AMFCs) have attracted much attention because of its potential to use low cost catalysts, e.g. non-precious-metal catalysts, and to decrease cathodic overpotential. However, there are many problems to be solved for the practical use of AMFCs. One of the most important things is thought to be the understanding of CO2 effect on AMFC performance. We have already reported some interesting phenomena concerning CO2 absorption to alkaline membrane. That is, OH form alkaline membrane could absorb atmospheric CO2 very rapidly, to become to CO3 form, and further to become to HCO3 form almost in several ten hours. However , we also reported that even in the state of full exchange of OH to HCO3, the membrane returned to OH form through the self-purging, to make the AMFC performance higher. In this paper, to understand this phenomenon further, in-situ observation of CO2 during AMFC operation was investigated.

Determination of Carbonate Ion in MEA during the Alkaline Membrane Fuel Cell (AMFC) Operation

Measurements of the ion ratio (OH-, CO32- and HCO3-) in MEA during the operation was reported. The ratio of ions in MEA depended on the current density. The amount of CO32- in MEA could be reduced in the case of using clean air for the oxidant. On the other hand, the CO32- ratio in MEA did not change during the long time operation in the case of using ambient air for the oxidant. There is a possibility to enhance the cell performance with ambient air oxidant by boosting the release of CO2 from anode.

Properties of ultra-large CaF2 crystals for the high NA optics

CaF2(Calcium fluoride) lens materials are required for the most important component of the ArF laser lithography stepper for the reason of its excellent transparency in DUV region and excellent laser durability as compared with quartz. Last year we reported to succeed in growing both <111> and <100> crystals, which had 210m diameter and 150mm length by the Czochralski (CZ) method with high productivity1). The obtained CaF2 crystal had low stress birefringence by way of the optimized annealing process. Although, for the higher NA system, larger CaF2 single crystals are required for the lens materials having the high quality and high productivity. To meet the above mentioned demands, we made efforts to produce and succeeded the first in the world ultra-large (φ300mm over) and high quality CaF2 single crystal by the CZ method with high productivity. The crystal had very low stress birefringence, good transparency in DUV region and good homogeneity. It was also easy to control the orientation of the crystal by the selection of seed crystal.

Diode-type Gas Sensors Fabricated with a Titania Film on a Ti Plate and Pd-Pt Electrodes ?Effects of Polymer Coating on the Hydrogen-sensing Properties?

H2 responses of a diode-type gas sensor fabricated with a TiO2 film prepared by anodization of a Ti plate and Pd-Pt electrodes (Pd-Pt/TiO2) and the effects of polymer coating on the Pd-Pt/TiO2 sensor were investigated in this study. The H2 response of the Pd-Pt/TiO2 sensor in dry N2 was larger than that in dry air at 250?C, but the addition of moisture into the atmosphere reduced O2 concentration dependence of H2 response. The responses decreased drastically at lower temperature (50?C), but the responses in N2 were larger than those in air under both dry and wet conditions. The coating of polymer on the Pd-Pt/TiO2 sensor increased the H2 responses in wet air and N2 and reduced O2 concentration dependence of H2 responses.

Recent Advances in Nonprecious Metal Catalysts for Oxygen Reduction Reaction in Fuel Cells

Non-precious metal catalysts (NPMCs) are developed for oxygen reduction in alkaline fuel cell (AFC). The performance of the catalyst in alkaline electrolyte is studied by rotating disk electrode (RDE). The NPMC prepared with carbon-supported metal-nitrogen composite precursor and subjected to heat-treatment shows comparable activity for oxygen reduction when compared with Pt/C catalyst. The fuel cell performance of the catalyst was studied using anion exchange membrane (AEM) from Tokuyama Corporation. The NPMC exhibits an open circuit potential (OCP) of 0.97 V and a maximum power density of 177 mW cm -2 at 50 °C.

Properties of large CaF2 crystals grown by CZ method for lens materials

CaF2 (Calcium fluoride) lens materials are required for the composition of F2 laser lithography stepper. Recently, it is reported that both <111> crystal and <100> crystal are necessary for the lens blanks, which can resolve the intrinsic birefringence of CaF2. Although CaF2 single crystal has been produced by Bridgman method, some problems are pointed out on the optical properties and production yield especially on <100> crystal with large diameter. So it is worried that the amount of the supply of CaF2 will be short when F2 stepper will start on a large scale. To resolve the above mentioned problems, we tried to grow a large CaF2 single crystal by Czochralski (CZ) technique, because we expected that CZ technique could provide higher productivity and higher quality which mean lower residual stress than conventional method. CZ technique can also easily control the growing crystal axis by the selection of seed crystal. Consequently we succeeded in growth both <111> and <100> direction single crystal which has 210mm diameter and 150mm length. The obtained crystal is a single crystal over a whole boule and it shows high transparency in vacuum ultraviolet region. Moreover it shows very low birefringence value and good homogeneity after annealing process. We hope our challenge should prompt the development of F2 lithography.