Yoshitsugu Sone

Proton Conductivity of Nafion 117 as Measured by a Four‐Electrode AC Impedance Method

Nafion 117{reg_sign} is a proton conducting ion-exchange membrane which is now receiving much attention due to its use as an electrolyte in the polymer-electrolyte-membrane fuel cell (PEMFC), which is of great interest for electric vehicle propulsion. The proton conductivity of Nafion 117 was measured under various conditions of humidity and temperature using a four-electrode ac impedance method. The conductivity of this membrane without heat-treatment was ca. 7.8 {times} 10{sup {minus}2} S/cm at ambient temperature and 100% relative humidity; it varied strongly with the humidity and heat-treatment of the membrane. After heat-treatment, the membrane showed a slight dependence of conductivity on temperature. From 21 to 45 C, its conductivity at a given relative humidity decreased with increasing temperature, while from 45 to 80 C it increased with temperature.

Understanding Volume Change in Lithium-Ion Cells during Charging and Discharging Using In Situ Measurements

Because structural change in lithium cobalt oxide (LiCoO 2 ) cathode is primarily responsible for the performance degradation of lithium-ion cells in simulated satellite operation, it is important to investigate the operating-condition effect on cell-volume change. In this work, we used in situ strain-gauge measurement to probe the total volume change during charging and discharging of five 50 Ah-class lithium-ion cells with graphite anodes and LiCoO 2 cathodes. Some interesting phenomena concerning the correlation of the taper voltage with the strain change at the end of the charge were found in the strain trend curve. To explain these phenomena, we examined the strain change of a commercial 0.65 Ah-class lithium-ion polymer cell with the same electrodes as a function of taper voltage by using in situ load-cell measurement and were able to deduce that the cell-volume change during charging correlated to the structure transition of the LiCoO 2 cathode from the initial hexagonal phase (H1) to a new hexagonal phase (H2) at a taper voltage near 4.00 V. We conclude that the taper voltage should be maintained below 4.00 V to maximize the cycle life of lithium-ion cells with graphite anodes and LiCoO 2 cathodes during practical satellite operation.

New Additives to Improve the First-Cycle Charge–Discharge Performance of a Graphite Anode for Lithium-Ion Cells

We tested the effect of two new additives, cyclo hexane (CH) and l-methyl-2-pyrrolidinone (NMP), on the cycling performance of a carbon-coated artificial graphite (AG) anode on a lithium-ion cell to investigate suppression of irreversible capacity loss of the graphite anode during the first-cycle charge. Both CH and NMP additives effectively increased the coulombic efficiency of the graphite anode during the first cycle. We attribute this phenomenon to the dissolution of the poly (vinylidene fluoride) (PVdF) binder of the AG anode due to CH or NMP addition, which improved the PVdF elasticity and reduced the contact area between the AG particles and the electrolyte. Consequently, adding CH or NMP reduced the loss of lithium ions in the first-cycle charge. Cycle-performance testing of the Li/AG half-cell indicated that we could achieve maximum discharge capacity and coulombic efficiency by applying an additive amount ranging from 2 to 5% for both CH and NMP. The cycling performance testing of the LiCoO 2 half-cell suggested that these two additives also have good oxidation stability and are therefore worth applying in lithium-ion cells with graphite anodes.

Air Revitalization in Orbit Demonstration for a Future Long-Duration Manned Mission

Various space agencies are currently considering the moon and asteroids as way stations for astronauts bound for Mars. Under JAXA’s long-term vision, JAXA2025, the agency will by 2015 finalize its development plans for the next period of manned space activity. To establish supporting technologies, JAXA is researching systems that will be indispensable for manned space activities beyond low earth orbit, including water and air recycling. Three types of assemblies are necessary for recycling air: a carbon dioxide separator to remove exhaled carbon dioxide from a spacecraft’s atmosphere, a carbon dioxide reduction assembly to produce water from the separated carbon dioxide and added hydrogen, and water electrolysis equipment for oxygen production. This paper describes a carbon dioxide removal assembly and a water electrolysis assembly designed for operation in microgravity.

CO 2 Methanation on Co-sputtered Ru–Metal Oxides Catalysts Prepared Using the Polygonal Barrel-Sputtering Method

CO2 methanation catalysts were prepared by co-sputtering with Ru and metal oxides such as TiO2 and ZrO2 using the polygonal barrel-sputtering method. The co-sputtering technique not only resulted in the decrease in the reaction temperature but also maintained the deposition of smaller Ru particles during the reaction at higher temperature.Graphical Abstract

Air Revitalization Demonstration on the JEM (KIBO) for a Manned Space Exploration

To further advance manned space exploration, a critical issue that must be addressed is recycling of resources, especially air revitalization and water reclamation. Japan is already a leader in terrestrial environmental technologies, and aims to apply this know-how to develop air and water recycling technologies for space applications. To support proposed post-ISS missions such as manned lunar or asteroid exploration and an Earth-Moon Lagrange point (EML1) space station, JAXA is developing an air revitalization system for an on-orbit demonstration on the International Space Station (ISS) early in the extended ISS operation period (2015–2020). The requirements for this technical demonstrator have been investigated and its specifications established. Regenerative life support functions include oxygen recovery from carbon dioxide using a combination of CO2 reduction by a Sabatier process and O2 generation by electrolysis. Each air and water re-vitalization subsystem is planned to be transported to the ISS separately by successive H-II Transfer Vehicle (HTV) launches in the sequence Water Reclamation → Water Electrolysis → CO2 Reduction. This paper presents the air re-vitalization system developed by JAXA, and gives details of water electrolysis in microgravity.

Study for the Reduction of Carbon Dioxide Using Sabatier Reaction

The Sabatier reaction with a titanium dioxide (TiO2)-supported ruthenium (Ru) catalyst (Ru/TiO2) was investigated with the goal of scaled-up carbon dioxide (CO2) methanation at lower temperatures than conventional catalysts. The catalytic reaction of stoichiometric amounts of CO2 and hydrogen (H2) without any diluting was conducted over a 0.75 wt% Ru/TiO2 (Ru/TiO2(0.75)) at several flow rates. The CO2 reduction was achieved with catalyst temperatures less than 300°C in good to excellent conversions. Transmission electron microscopy (TEM) and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) images of Ru/TiO2(0.75) revealed highly dispersed Ru nanoparticles having one to a few nanometers’ diameter on the TiO2 supports. The physical properties of Ru metals are considered to contribute the decrease of the reaction temperature.

Study of Regenerative Fuel Cells for Aerospace Missions of Japan

A fuel cell (FC) /regenerative fuel cell (RFC) for space utilization has special system requirements, such as operational conditions and designs, because of its isolated low gravitational and closed environment, which differs greatly from that for terrestrial use. Over 1,000 h continuous and stable operation of PEFC using the developed prototype system was achieved. During conditions of no thermal control, no external humidifier, and low current density operation under low pressure, the voltage was maintained at a constant level under such low temperatures. No cross-leak or flooding phenomena were observed from these results: good performance was also obtained. These results suggest that the polymer electrolyte and other components used in this study were stable in such conditions.