Teruo Kodama

Structure and transport properties of polymer gel electrolytes based on PVdf-HFP and LiN(C2F5SO2)2

Abstract Gel polymer electrolytes composed of PVdF/HFP and a non-aqueous lithium electrolyte solution EC/DEC/LiN(C 2 F 5 SO 2 ) 2 (BETI) were prepared to investigate the conduction properties of the gel materials. Structural and micro-structural characterization was carried out by means of modulated differential scanning calorimetry (MDSC) and scanning electron microscopy (SEM). The samples with polymer/solution weight ratios higher than 0.5 contain at least an amorphous swollen gel phase and a crystalline one, while a pure liquid phase appears, which occupies cavities in the micrometer range in the gels with lower polymer content. The transport properties of the gels were investigated by means of impedance spectroscopy for conductivity and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) for diffusion coefficients. The results were compared with those of corresponding films prepared with LiN(CF 3 SO 2 ) 2 (TFSI). The BETI-based samples showed diffusion values lower than the TFSI-based ones. Estimation of the carrier concentration change with the gel composition revealed that the interaction between the host polymer and the electrolyte in the gel especially in the polymer rich region (>50 wt%).

Temperature and humidity ranges of some hydrates of high-proton-conductive dodecamolybdophosphoric acid and dodecatungstophosphoric acid crystals under an atmosphere of hydrogen or either oxygen or air

The temperature and humidity dependences of the hydration number of dodecamolybdophosphoric acid, H3Mo12PO40ṡmH2O, and dodecatungstophosphoric acid, H3W12PO40ṡnH2O, crystals are presented in the phase diagrams. The waters of crystallization of both acid crystals show a zeolitic nature, but they also show some definite hydrate in the dehydration process. The existence of the 29-, 18-, and 13-hydrate of dodecamolybdophosphoric acid and the 29-, 20-, 13-, and 6-hydrate of dodecatungstophosphoric acid is found in the range of 10–80°C and 30–95% relative humidity (RH) under an atmosphere of either oxygen or air. H3Mo12PO40ṡ29H2O is stable over 70% RH along the full range of temperatures. In comparison, H3W12PO40ṡ29H2O is stable above 20°C and over 83% RH. Other hydrates are stable under the indicated RH values. Also, the lower hydrates are stable at higher temperatures and lower RH levels. The phase diagrams of the stable ranges of these hydrates of the acid crystals were also obtained under a hydrogen atmosphere. Slight differences in these ranges are observed depending on which gas (hydrogen or either oxygen or air) is used in the atmosphere.

Cell performance of molten-carbonate fuel cell with alkali and alkaline-earth carbonate mixtures

Abstract Molten-carbonate fuel cells with two types of alkali carbonate mixture as the electrolyte have been operated. The resulting cell performances have been compared in order to optimize the composition of each carbonate mixture. One electrolyte type is a mixture of the high lithium eutectic ((Li 0.62 K 0.38 ) 2 CO 3 ) and an alkaline-earth carbonate, while the other is a mixture of the lithium-sodium eutectic ((Li 0.52 Na 0.48 ) 2 CO 3 ) and an alkaline-earth carbonate. Additions of CaCO 3 , SrCO 3 and BaCO 3 have been used. A small amount of each alkaline-earth carbonate to both eutectics does not influence the cell performance. On the other hand, larger amounts reduce the cell performance. The required content of each additive to provide optimum cell performance depends on both the additive itself and the host eutectic. The temperature dependence of cell performance in the presence of the different additives has also been investigated. There is little difference between the behaviour of ((Li 0.62 K 0.38 K 0.38 ) 2 Ca)CO 3 , ((Li 0.62 K 0.38 ) 2 Ba)CO 3 and ((Li 0.52 Na 0.48 ) 2 Ca)CO 3 . By contrast, high temperature dependence was found for ((Li 0.62 K 0.38 ) 2 Sr)CO 3 , ((Li 0.52 Na 0.48 ) 2 Sr)CO 3 and ((Li 0.52 Na 0.48 ) 2 Ba)CO 3 .

Dissolution behaviour of copper and nickel oxides in molten Li2CO3/Na2CO3/K2CO3

Abstract An Li 2 CO 3 /Na 2 CO 3 /K 2 CO 3 eutectic melt has been taken as a typical example of a molten carbonate system, and the dissolution behaviour of the oxides of nickel and copper in the melt have been investigated at 873 K. The solubility products of CuO and NiO in the melt have been estimated to be 8.9 × 10 −9 Mol 2 l −2 and 3.8(±0.6) × 10 −10 Mol 2 l −2 , respectively. The diffusion coefficients of Cu(II) and Ni(II) ions in the melt are approximately 7.2 × 10 −5 Cm 2 s −1 and 2.2(±0.5) × 10 −5 Cm 2 s −1 , respectively. When the oxide-ion concentration in the melt is high, two new peaks are observed in the voltammogram for CuO. These peaks have been attributed to the direct electrochemical reduction of particles of CuO and Cu 2 O.

Humidity sensor with sintered β-Ca(PO3)2 for high temperature use☆

Abstract A galvanic cell-type humidity sensor has been constructed from sintered β-Ca(PO 3 ) 2 which is a proton conductive solid. The EMF response as a function of the logarithm of water vapor is linear, reversible, reproducible, and very fast over a wide range of vapor pressure measured at 578, 678 and 776°C, respectively. The variation of observed EMF versus logarithm of water vapor is in good agreement with the theoretical EMF expected from the Nernst equation. Experimental results of steam-oxygen and steam-hydrogen concentration cells respectively employing β-Ca(PO 3 ) 2 as an electrolyte confirm proton conductivity and suggest the potential application of this material for high temperature galvanic cell-type humidity sensing.

The water content and humidity ranges of dodecamolybdophosphoric acid and dodecatungstophosphoric acid crystals

Abstract The water content of dodecamolybdophosphoric acid H 3 Mo 12 PO 40 ·29H 2 O and dodecatungstophosphoric acid H 3 W 12 PO 40 ·29H 2 O crystals were redetermined to be 29 molecules per formula unit. Also, these crystals were found to be stable between 70 and 95% and between 80 and 95% relative humidity in the above order from 15 to 80°C. 13- and 18-hydrates of dodecamolybdophosphoric acid and 6- and 20-hydrates of dodecatungstophosphoric acid were also found to be stable in the lower humidity levels.

Simple humidity control system

This note describes a control system for maintaining constant humidity by passing a gas through a saturated aqueous solution.

Cell performance of molten carbonate fuel cell with alkali carbonate eutectic mixtures

Abstract Molten carbonate fuel cells with four alkali carbonate eutectic mixtures of Li 2 CO 3 /Na 2 CO 3 /K 2 CO 3 in the proportions 62/0/38, 43/0/57, 43/32/25 and 52/48/0 (mol%), have been operated using electrolyte matrices fabricated by tape casting. When the ratio of electrolyte volume to matrix pore volume was optimized, all of the test cells gave similar good performance.

Determination of the dissociation constant of molten Li2CO3/Na2CO3/K2CO3 using a stabilized zirconia oxide-ion indicator

Abstract An Li2CO3/Na2CO3/K2CO3 eutectic melt has been selected as an example of a molten-carbonate system and the suitability of a stabilized zirconia—air electrode as an oxide-ion concentration indicator for this melt has been confirmed. With this indicator, the dissociation constant of the reaction CO32− (l) = CO2(g) + O2− (l) in this melt has been determined to be Kd = PCO2 [O2−] = 4.03 × 10−3 Pa at 873 K Reproducible measurements were obtained throughout the experiment and this method might find further application in the study of reactions related to the oxide ion in carbonate melts.

Corrosion study on ceramics for conductance measurements of molten carbonates

Abstract In order to find corrosion-resistant materials applicable to a conductance cell used in a conductance measurement apparatus for molten carbonates, several ceramics were examined for durability in both hydrochloric acid solution and carbonate melt. It was found that beryllia-based ceramics and alumina ceramics of high purity exhibited high corrosion-resistance against those agents, and could be applied in conductance cells. This article gives valuable criteria for the application of potential ceramic materials in carbonate melts.