In order to grasp properly PEFC power generation performances, it is necessary to know data for water management, such as diffusion coefficient of water D and electro-osmotic coefficient nd of water through the membrane. In this study, we have measured D for both membrane electrode assembly (MEA) and gas diffusion layer (GDL), and nd for MEA used in our experiment by our own simple method under a wide range of relative humidity. Measured D for MEA was 1–10×10−3 cm2 s−1 and nd for MEA was 1.0–1.5. Comparison of our data with other published data shows that our measured data exists between the upper and lower published data. Measured D for GDL gave the approximate value of porosity divided by tortuosity of 0.21.
The tunnel growth mechanism of aluminum foil was studied in order to control the etching morphology. The growth of tunnels with a reversed taper followed by the tapered tunnel growth was observed only in acid solution. We proposed a model of the self-corrosion of aluminum for the reversed taper growth, and verified it by comparison of the current efficiency with the measured value made by ICP-ES to the simulation obtained from the results of the reversely tapered tunnel structure. From results of the early tunnel growth with a reversed taper, we discussed the relation between the limit length of the tunnel and width of the tunnel. It was expected that a uniform length of the tunnels should be obtained by controlling the width at the tunnel mouth to the same size.
The static and dynamic characteristics of the electrodissolution of steel covered with an organic layer as well as of plain steel are studied in aqueous solutions of various NaCl concentrations. Anodic polarization and electrochemical impedance spectroscopy for plain steel indicate that active dissolution takes place in a potential region close to the open circuit potential where the current is less than 10−4 A. Similar experiments for coated steel suggest the adsorption of ionic species and the formation of a surface layer on the metal substrate. This layer results in a negative faradaic resistance, i.e. a potential region where the faradaic current is a decreasing function of the potential. This region of negative faradaic resistance is related to the occurrence of current oscillations. These oscillations, of a period ranging from 100 to 1200 s, might be attributed to the formation/dissolution of a salt precipitant within the pores of the organic layer.
We investigated the dependence of the properties, crystal structure and electrode characteristics on the Li content of LixCo1/3Ni1/3Mn1/3O2+δ. The crystal structure was determined by Rietveld analysis using neutron diffraction. The electron density images were determined by X-ray diffraction, Rietveld analysis and Maximum Entropy Method. The cycle performance was slightly lower, but the discharge capacity increased at x=1.122. From the crystal structure analysis, the amount of cation mixing was changed by the Li content, that is, a small amount of Ni2+ ions is present in the lithium layers (3a) and extra Li is located in transition metal layer (3b). Ni2+ ions occupied about 4% of the 3a site and Li is located in the 3b site at 0.915≤x≤1.052. On the other hand, Ni2+ ions occupied about 1.2% of the 3a site for x=1.122. In other words, 12% of the total amount of Ni existed in the 3a site at 0.915≤x≤1.052, but, 3.8% of the total amount of Ni existed in the 3a site for x=1.122. The bond length between 3b and 6c (oxygen site) increased with the increasing Li content. From the results, the discharge capacity increased with the decreasing Ni in the 3a site.
Electrochemical reduction of substituted (alkylamino)phosphonium salts under the presence of phenylisocyanate was carried out to confirm the generation of iminophosphoranes and phosphorus ylides. The reactions of the generated iminophosphorane with phenylisocyanate gave a phosphine oxide and a carbodiimide as the products of the Aza-Wittig-type reactions. When the ylide generation is favorable, the generated phosphorus ylide reacted with phenylisocyanate to give the intermediate betaines as the result of Wittig-type reaction and succeeding H-shift leads to more stable phosphorus ylides. To elucidate the mechanisms of selective synthesis of the iminophosphoranes and phosphorus ylides from a single (alkylamino)phosphonium salt, the theoretical density functional calculations were performed by using B3LYP with the 6–31+G(d) basis set.
Polymer Electrolyte Fuel-Cell (PEFC) systems are being developed at JAXA for applications to transfer vehicles for short-term missions and larger spacecraft in the future. For space applications in a closed environment, we developed a system in which the fuel is perfectly consumed and the oxygen is recycled. We prepared a fuel-cell stack, gas circulator, and dehydrator; combined them; and operated the fuel-cell system without external humidification. Our system concept of the fuel cell operated under the closed environment was verified for 250 hours. We observed the stable average output voltage over 0.75 V while PEFC continuously generated 60 A. We then varied the current level from 30 to 150 A and continued the test for 400 hours. We operated fuel cell system with constant gas circulation rate at the various load level, and observed stable performance of our PEFC system in a closed gas circulation system without external humidification.