Kazumi Tanimoto

Density, Surface Tension, and Electrical Conductivity of Ternary Molten Carbonate System Li2CO3 – Na2CO3 – K2CO3 and Methods for Their Estimation

The density, surface tension, and electrical conductivity of the ternary molten salt mixtures of Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 system have been measured. The molar volumes of the ternary mixtures agreed well with those estimated by additivity arguments within 0.7%. It was found that the surface tension of a ternary carbonate mixture can be predicted from known surface tension of binary carbonates, and the mixing of two molten carbonate mixtures of the same surface tension makes a mixture of almost equal surface tension before mixing in this ternary system. We have succeeded in predicting the equivalent conductivity of the ternary carbonate mixtures using the cationic radii and the equivalent conductivities of the pure carbonates.

Proton conduction in (La0.9Sr0.1)MIIIO3−δ (MIII=Sc, In, and Lu) perovskites

Abstract The electrical conductivity of A 3+ B 3+ O 3 -type perovskites, (La 0.9 Sr 0.1 )M III O 3− δ (M III =Sc, In, and Lu) (LSM), was investigated under controlled atmospheres between 573 and 1273 K. At P (O 2 )>10 −5 atm, all the compounds showed the predominant proton conduction below 873 K under wet conditions; at P (O 2 ) −10 atm, the Sc and In compounds below 873 K and the Lu-one at all temperatures under hydrogen-containing conditions. The Sc compound showed the highest proton conductivity of ca. 4×10 −3 S· cm −1 at 873 K in the presence of water vapor or hydrogen. The proton conductivity of LSM decreased with increasing the size of B-site (M III ) cation.

Electrical Conductivity of Molten Li2CO3 – X2CO3 (X: Na, K, Rb, and Cs) and Na2CO3 – Z2CO3 (Z: K, Rb, and Cs)

The electrical conductivities of the molten binary salt mixtures Li 2 CO 3 -X 2 CO 3 (X: Na, K, Rb, and Cs) and Na 2 CO 3 -Z 2 CO 3 (Z: K, Rb, and Cs) were measured using an ac two-probe technique and electrochemical impedance spectroscopy. The electrical conductivities of the eutectic compositions of (Li 0.52 Na 0.48 ) 2 CO 3 and (Li 0.62 K 0.38 ) 2 CO 3 at 923 K were 2.06 and 1.31 S cm -1 , respectively. The conductivity of molten Li 2 CO 3 -X 2 CO 3 (X: Na, K, Rb, and Cs) and Na 2 CO 3 -Z 2 CO 3 (Z: K, Rb, and Cs) decreases with an increase in the ionic radius of X or Z. We have succeeded in correlating the equivalent conductivity of a binary carbonate mixture A, with the composition (x A and x B ), the equivalent conductivities of the pure components A and B (A A and Λ B ), and two parameters (λ A and λ B ) as Λ = x 2 A Λ A + x 2 B Λ B + x A x B (λ A x A + λ B x B ). The pair of interaction parameters (λ A and λ B ) can be estimated for a binary system of molten carbonates using the relationship between the cationic radii and the equivalent conductivities of the pure carbonates.

Density, molar volume, and surface tension of molten Li2CO3-Na2CO3 and Li2CO3-K2CO3 containing alkaline earth (Ca, Sr, and Ba) carbonates

The density, molar volume, and surface tension of binary, ternary, and quaternary molten carbonate mixtures of Li 2 CO 3 -Na 2 CO 3 and Li 2 CO 3 -K 2 CO 3 containing alkaline earth (Ca, Sr, and Ba) carbonates were measured using a maximum bubble pressure technique. The addition of alkaline earth carbonates resulted in increases in the density and surface tension of the molten carbonate mixtures. The apparent molar volume of a component carbonate in mixtures can be derived from the density data, assuming additivity, and inversely be used to estimate the molar volume and density of mixtures within an error of 1 %. The surface tensions of alkali-alkaline earth carbonates were proportional to the mole fraction of the added alkaline earth carbonate.

Optimum operating conditions of DIR-MCFC without vapor-phase carbonate pollution

Abstract In direct internal reforming-molten carbonate fuel cells (DIR-MCFC), deterioration of catalytic activity takes place in the anode channel due to both liquid-phase pollution and vapor-phase pollution. Although the liquid-phase pollution can be solved by installing protective barrier, an effective defense method and a reactivation method of vapor-phase polluted catalyst have not established yet. In order to study the reactivation method, the adhesion form of potassium compounds in the polluted catalyst under the various gas conditions was evaluated by using a thermogravimetric analyzer in which water vapor can feed. Additionally, the activity of the treated catalyst was also tested by a differential reactor. As a result, KOH changes to K 2 CO 3 under a CO 2 concentration of 25% or more. KOH becomes a solid-phase from the liquid-phase when it is changed into K 2 CO 3 . Therefore, the catalyst can not be reactive because K 2 CO 3 chokes pores of the catalyst. However, the activity of the polluted catalyst is revived to 80% of the initial activity by controlling the gas species concentration, especially CO 2 . Moreover, the catalytic activity can be revived under a steam–carbon ratio of 2.0 or more. Based on the results obtained by these fundamental experiments, the reactivation methods of catalyst polluted are proposed as follows: (i) catalyst should be loaded more upstream in the anode; (ii) in order to reactivate the polluted catalyst, the DIR-MCFC should maintain a steam–carbon ratio of 2.0 or more; (iii) gas conditions to activate the catalyst should be applied regularly.

Analysis of transient voltage response on a 4 × 4 cm molten carbonate fuel cell by a current pulse method

A voltage drop and recovery analysis method is developed in this paper to estimate the different contributions to the transient behavior of a molten carbonate fuel cell (MCFC) based on the assumption that the gas diffusion and electrode polarization are the two main functions of the transient voltage response. It is shown that the model predictions are in reasonable agreement with the experiment data. Hence, the method developed provides an efficient tool to analyze the characteristics of an MCFC.

XAFS Analysis of Pt and Pt‐Ru Catalysts for PEFCs by In‐Situ Measurements under Operating Conditions in the Fluorescence Mode

In‐situ X‐ray absorption fine structure (XAFS) is one of powerful spectroscopic techniques to analyze valence state and chemical bonding in Pt and Pt‐Ru electrocatalysts under fuel cell operating conditions. We measured Pt L3 and Ru K‐XAFS of Pt and Pt‐Ru electrocatalysts in fluorescence mode under different operation voltages using pure H2 or 97 ppm CO containing H2 as fuel gases that were fed to the anode. The radial structure functions that derived from the obtained XAFS spectra showed that the local structure around Pt and Ru atoms in the electrocatalysts changes depending on the operation voltage and shows difference with the existence of CO in the fuel gas.

Visualization and Measurement of Dynamic Water Behavior in PEFC by Neutron Radiography

Hydrogen gas and air are supplied in saturated moist condition to keep a membrane wet in a PEFC. Condensation may occur in the cathode by the FC reaction, since air is saturated moist condition. The condensed water may affect on the fuel cell performance. It is very important for the design to know the water behaviors. In this study, in-situ visualization of an operating PEFC was carried by neutron radiography with the cell voltage measurements. A JARI standard cell was improved for the visualization with the same performance. Water distribution in the fuel cell could be quantitatively measured from visualized images via some image processing methods. The relationships between the water distributions and cell voltage fluctuations were clearly shown from the visualization and measurement results. The difference in water distribution for three types of gas supply channel was clearly shown.Copyright

Visualization of Electrolyte Volatile Phenomenon in MCFC

Volatilizing of molten carbonate as electrolyte in Molten Carbonate Fuel Cell (MCFC) is one of degradation factors. The Volatilization of the molten carbonate brings the cross-leak and the corrosion of the metallic materials. Moreover, the piping blockage caused by solidification of the volatile chemical species in piping will be happened at lowering temperature. Especially, since the reforming catalysts filled to the anode channel in Direct Internal Reforming Molten Carbonate Fuel Cells (DIR-MCFC) are polluted by volatile species from the molten carbonate, volatilizing of the molten carbonate is an important issue. However, the behavior of molten carbonate volatile issue has been not elucidated, since the volatilization volume is too small amount to analyze them. Last symposium, we informed that at anode side, amount of volatilized particle was increasing with increasing current density. Although volatilization phenomenon was observed at cathode side, there was no relationship between amount of volatilized particle and current density. The volatile chemical species from anode and cathode were potassium rich composition.

Solubility of LiCoO/sub 2/ in molten carbonates

The solubility of LiCoO/sub 2/ was proportional to Pco/sub 2//sup 3/2/ and Po/sub 2//sup -1/4/ in (Li/sub 0.52/Na/sub 0.48/)/sub 2/CO/sub 3/. It obeys the acidic dissolution mechanism. This result was the same dependence as that in (Li/sub 0.62/K/sub 0.38/)/sub 2/CO/sub 3/. The solubility of LiCoO/sub 2/ in (Li/sub 0.52/Na/sub 0.48/)/sub 2/CO/sub 3/ was about a half of that in (Li/sub 0.62/K/sub 0.38/)/sub 2/CO/sub 3/. The solubility of LiCoO/sub 2/ decreased with Li content in Li-K carbonate system. The solubility of LiCoO/sub 2/ was lower than that of NiO even under the pressurized cathode condition of MCFC.