曽根 理嗣

Water electrolysis cell in which the product gases was separated from liquid water on the surface of the electrode was developed. In order to realize the separation between gas and water, interdigitated diffusion layer (GDL) was designed, and the surface of the GDL was covered by catalyst to form electrode. When the pressurized water was supplied, the water directly made a contact to the proton conductive membrane. Due to the hydrophobic surface condition of the GDLs, gas/water separation along the surface of the electrode was completed. (C) The Author(s) 2020. Published by ECSJ.

The satellite REIMEI was launched in August 2005, this is one of the first satellites to use Li-ion batteries. REIMEI is a small scientific satellite designed for carrying out aurora observations using three different cameras. The main scientific mission of the satellite ended in 2013. More than 14 years have passed, and the batteries have experienced over 78,100 charge/discharge cycles. REIMEI remains in operation with a new mission dedicated to analyzing its Li-ion battery. In this work, we present a durability analysis for the REIMEI battery based on telemetry data. (C) The Author(s) 2020. Published by ECSJ.

Commercially available 18650 Li-ion cells were exposed to charge-discharge cycling at 0 degrees C using two different charging protocols: constant current-constant voltage (CC-CV) and constant current (CC). The effect of the charge process protocol on the Li-ion cell performance is shown and analyzed. After exposing the cells to low temperature charging, a high voltage plateau appeared at the beginning of the discharge. This high voltage plateau is related to the occurrence of lithium plating during the charging process. Interestingly, the intensity of the observed high voltage plateau decreased with cycling. In addition, the Li-ion cells that were charged using a CC protocol exhibited a larger capacity fade in comparison to those that were charged using a CC-CV protocol. Furthermore, electrochemical impedance spectroscopy (EIS) measurements were carried out during cycling. It was shown that the internal impedance of the cells increased with charge-discharge cycling, indicating the formation of an interphase layer during low temperature cycling. (C) The Author(s) 2020. Published by ECSJ.

In order to elucidate the impact of calendar degradation on charge-discharge cycling under low temperature, we evaluated and compared the performance of fresh and calendar degraded LiFePO4-Graphite Li-ion cells during cycling at -5 degrees C. After exposing fresh and calendar degraded cells to low temperature cycling, the fresh cell exhibited a relatively good performance, while in the case of the calendar degraded cell a poor performance was observed. In addition to this, a high voltage plateau, which usually appears at the beginning of the discharge profiles as a consequence of the occurrence of lithium plating, was not observed in the discharge profiles of the fresh cell. However, in the case of the calendar degraded cell a high voltage plateau appeared at the beginning of the discharge profiles, indicating that lithium plating is more likely to occur in degraded Li-ion cells exposed to low temperature charging. Our investigation results show that calendar degradation can compromise the safety and performance of Li-ion cells during low temperature cycling. (c) 2019 The Electrochemical Society.

In this work, we introduce a water electrolysis and CO2 hydrogenation tandem system which focuses on methane generation. The concept consists of a water electrolyzer thermally coupled to a CO2 hydrogenation reactor, where the power required to generate hydrogen comes from renewable energy. A thermodynamic analysis of the tandem system was carried out. Our analysis exposes that it is possible to increase the exergy efficiency of the water electrolyzer and CO2 hydrogenation system by thermal coupling, where the thermal energy required to split water into H-2 and O-2 during the electrolysis process is compensated by the heat generated during the CO2 hydrogenation reaction. Here, the conditions at which high exergy efficiency can be achieved were identified.

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.[GRAPHICS].

The Japan Aerospace Exploration Agency is now developing life support systems for closed environments in space. The reduction reaction of carbon dioxide is an important technique for the sustainable manned operation in space. Recently, Umeda et al. [J. Appl. Phys. 114, 174908 (2013)] from the Nagaoka University of Technology reported that the reduction reaction of carbon dioxide (CO2) proceeded using a fuel cell under the existence of CO2 and H-2 by supplying those gases to the cathode and the anode, respectively. We observed stable reaction when Pt/Ru-C was used as a catalyst for the cathode and Pt-C for the anode. Different organic materials were obtained depending on the alternated potential and temperature. Furthermore, a fuel cell stack with 8 cells connected in series was tested to demonstrate the stable energy generation by feeding CO2 to the cathode and H-2 to the anode. Published by AIP Publishing.

Copyright © 2018 by the International Astronautical Federation (IAF). All rights reserved. The satellite 'REIMEI' was launched in August 2005; this satellite is one of the first spacecraft to use Li-ion batteries. The orbit of the satellite is a low earth orbit, over 65000 charge/discharge cycles have been reached and REIMEI is still operating. We are trying to estimate the remaining useful capacity and state of health for the REIMEI Li-ion batteries. However, the estimation of remaining useful life for Li-ion cells is not trivial, since their degradation is caused by many physical and chemical processes which get accelerated depending on the working environment and operating conditions. The satellite uses 2 batteries, each battery consists of 7 cells. The cells use LiMn2O4 and graphite as the positive and negative electro-active materials, respectively. The rated capacity of each cell is 3 Ah. In this work we analyse the performance of the REIMEI batteries based on telemetry data.

Lithium-ion secondary cells are widely used for the space applications, today. Among these applications, REIMEI, which was launched in 2005, was one of the first satellites using lithium-ion battery. The off-the-shelf type cells designed using spinel manganese oxide for the positive and the graphitized carbon for the negative electrode were used. The cell case was made of aluminum laminated film and the structure was reinforced by the aluminum case filled with epoxy resin. Today, ten years has passed, and the battery experienced 55,000 cycles for charge and discharge. The current distribution between two batteries almost coincided together even after the long term operation, which revealed the stable performance of the lithium-ion secondary cells under the microgravity in space. (C) The Electrochemical Society of Japan, All rights reserved.

The Japan Aerospace Exploration Agency (JAXA) is developing polymer electrolyte fuel cell (PEFC) systems that can be operated under isolated low-gravity and closed environments. In the present study, we combine the PEFC with an electrolyzer in order to realize a regenerative fuel cell. Ideally, if a single cell can be operated as a fuel cell and the cell can be made reversible through the electrolysis reaction, then compact, lightweight regenerative fuel cell systems can be realized. A unitized regenerative fuel cell was prepared, and its operability was demonstrated. During 100-W class operations, a stable fuel cell and electrolysis reaction was observed. (C) 2011 Elsevier B.V. All rights reserved.

The Japanese spacecraft, HAYABUSA, was launched on May 9, 2003 and spent more than 2.5 years approaching the asteroid ITOKAWA. This spacecraft used 13.2 Ah lithium-ion secondary cells. After HAYABUSA touched down on ITOKAWA in December 2005, it could not communicate for seven weeks due to a malfunction of the attitude control. During this period, four of 11 lithium-ion secondary cells were over-discharged, and solar power was unavailable due to the spacecraft's tumbling motion. However, the battery power was still indispensable for sealing the container with the asteroid sample. The seven remaining healthy cells were slowly recharged using minimum current. During this time, ground simulation tests using similarly-built and intentionally short-circuited cells were carried out to evaluate the battery's operational safety. After its safety was confirmed, the lithium-ion secondary battery was used to transfer, latch, and successfully seal the sample container into the reentry capsule. The necessary power for these actions was supplied by the battery.

Polymer electrolyte fuel cell (PEFC) systems targeting applications to transfer vehicles for short-term missions and larger spacecraft in the future are being developed at NASDA. First, we designed and manufactured a system with a 100 W class fuel cell. Through our tests, we found that a humidifier is not necessary when using pure hydrogen and oxygen supplied from opposite directions. In a closed simulated environment, the tests could also demonstrate the stable operation of the fuel cell system where the oxygen was recycled and the hydrogen stream was dead-ended. © 2004 Elsevier B.V. All rights reserved.

Polymer Electrolyte Fuel Cell (PEFC) systems are being developed at JAXA for applications to transfer vehicles for shot-term missions and larger spacecraft in the future. For space applications in a closed environment, we are developing a system in which the fuel is perfectly consumed and the oxygen is recycled. We prepared a six-cell-stack fuel cell with a gas-water separator and demonstrated its performance without external humidification. The effective surface area of the Pt catalyst layer on the MEA was 162 cm2. The performance of the fuel cell was checked for 1,000 hours while it nominally generated 60 A. We also demonstrated the fuel cell performance through the simulated Space Shuttle operations. The PEFC performed stably during these operations, providing its applicability for future space missions.

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 × 10-2 S cm-1 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.