Koji Katahira

Protonic conduction in Zr-substituted BaCeO3

Abstract Zr-substituted BaCeO 3 (BaCe 0.9− x Zr x Y 0.1 O 3− α ) was synthesized and its electrical conduction behavior and chemical stability were investigated. Single phases were confirmed over the whole range of x values (0.0≤ x ≤0.9). These oxides exhibited pure protonic conduction in hydrogen-containing atmosphere while they showed protonic, oxide ionic and electronic mixed conduction under high oxygen partial pressure at elevated temperatures. The chemical stability against CO 2 increased with an increase in zirconium content, although the protonic conductivity decreased with increasing x .

Protonic-Electronic Mixed Conduction and Hydrogen Permeation in BaCe0.9 − x Y 0.1Ru x O 3 − α

The protonic-electronic mixed conductors are of great interest for their potential applications particularly for the hydrogen separation that is essential for hydrogen production from hydrocarbons. This paper deals with the mixed conduction properties of BaCe 0 . 9 - x Y 0 . 1 Ru x O 3 - α (x = 0-0.1) in which Ru is partially substituted for Ce in the high-temperature proton conductor, BaCe 0 . 9 Y 0 . 1 O 3 - α . Appreciable hydrogen permeation through the Ru-doped materials was observed and is attributed to ambipolar diffusion. The mixed conducting mechanism is discussed in terms of the defect chemistry and electronic structures revealed by the electrochemical and spectroscopic measurements.

Extraction and production of hydrogen using high-temperature proton conductor

Abstract An electrochemical hydrogen pump using the SrCe 0.95 Yb 0.05 O 3− α proton conductor has been applied to hydrogen extraction and production. The extraction of hydrogen from dilute hydrogen and synthesis gases, and hydrogen production by water vapor electrolysis are demonstrated. The extraction of hydrogen could be operated with a current efficiency close to unity, while some electronic conduction appeared in the water vapor electrolysis. The introduction of water vapor into the cathode compartment was effective to extend the current density. These results, together with the problems to be solved, are mainly discussed in terms of electrode reactions and ionic transport numbers.

Hydrogen Extraction Using One-end Closed Tube Made of CaZrO3-based Proton-conducting Ceramic for Tritium Recovery System

In a nuclear fusion reactor, tritium and its compounds must be recovered for the purpose of fuel recycling and hydrogen gas must be separated from a gas mixture with hydrogen compounds and other molecules. Proton-conducting ceramics have the proper characteristics to aid in this separation. The present paper describes the performance of a hydrogen pump using the one-end closed tube made of a proton-conducting ceramic (CaZr0.9In0.1O3-α, Effective electrode area: 47 cm2) at 800°C. Hydrogen gas was selectively extracted from Ar-H2 mixed gas at the rate of Faradays low under an applied voltage of 3.5 V. This test apparatus could also electrolyze water vapor and/or decompose methane at the anode to generate hydrogen at the cathode. In the case of argon gas with 0.1% hydrogen, 0.1% methane and 1.2% water vapor, the hydrogen evolution rate was 0.34m1/min at 3.5 V. The current density was 1.2 mA/cm2 and the current efficiency was 79%. Experimental data suggest that water vapor has an important role for the hydrogen extraction from the mixture with methane.

Application of Proton-conducting Ceramics and Polymer Permeable Membranes for Gaseous Tritium Recovery

In order to carry out deuterium plasma experiments on the Large Helical Device (LHD), the National Institute for Fusion Science (NIFS) is planning to install a system for the recovery of tritium from exhaust gas and effluent liquid. As well as adopting proven conventional tritium recovery systems, NIFS is planning to apply the latest technologies such as proton-conducting ceramics and membrane-type dehumidifiers in an overall strategy to ensure minimal risk in the tritium recovery process. Application of these new technologies to the tritium recovery system for the LHD deuterium plasma experiment is evaluated quantitatively using recent experimental data.

A solid electrolyte steam sensor with an electrochemically supplied hydrogen standard using proton-conducting oxides

Abstract A high temperature solid electrolyte steam sensor with an electrochemically supplied hydrogen as a standard was designed and investigated. Two discs of proton-conducting oxide with porous platinum electrodes were stacked and a small hole was made in order to leak the gas at the interface. Constant voltage was applied to one cell in order to pump up hydrogen from water vapor in atmosphere. EMF of the other cell was measured using the pumped hydrogen as a standard gas. On applying a certain voltage, good EMF response against water vapor pressure was observed over a wide range of PH2O at 700°C.

Electrochemical properties of junction between protonic conductor and oxide ion conductor

Abstract A dense and tightly contacted thin layer of SrZrO 3 -based solid solution could be formed on yttrium stabilized zirconia, YSZ, by high temperature chemical reaction. A water vapor concentration cell using this SrZrO 3 -YSZ junction showed a stable e.m.f. when the SrZrO 3 side was exposed to wet air, whereas it exhibited no e.m.f. when the SrZrO 3 was exposed to dry air, suggesting protonic conduction in SrZrO 3 . An oxygen concentration cell showed lower e.m.f. than that of the theoretical at 600°C. A hydrogen–oxygen fuel cell showed asymmetric behavior regarding the used gases. Higher current could be drawn when the SrZrO 3 film was exposed to hydrogen. Higher current passed through the junction when a positive voltage was applied on the SrZrO 3 side. This rectifying behavior did not appear in dry argon.

Application of New Technologies for Gaseous Tritium Recovery and Monitoring

In order to realize the deuterium plasma experiments by using the Large Helical Device (LHD), NIFS is planning to install the system for tritium recovery from exhaust gas and effluent liquid. With the case of adopting generally used tritium recovery systems, NIFS has also made the development plans for the compact and less waste generating recovery system by applying the latest technologies such as tritium gas extraction with a proton conducting ceramic and tritiated water vapor removal with a membrane type dehumidifier. Applicability of these new technologies on the tritium recovery system for the LHD deuterium plasma experiment are evaluated quantitatively using the latest experimental data. Mock-up tests of the membrane type dehumidifier are carried out and verified the way of automated operation and stable dehumidifier performance during a long time operation.

Effect of Plated Platinum Electrode on Hydrogen Extraction Performance Using CaZrO3-based Proton-Conducting Ceramic for Tritium Recovery System

In a nuclear fusion device, hydrogen isotopes and their compounds in the vacuum exhaust gas must be separated from other gaseous species and recovered as hydrogen isotope gases for tritium recycling. We have proposed the use of proton-conducting ceramics for the hydrogen recovery. By sending a direct current to an electrochemical cell including the proton-conducting ceramic as an electrolyte, hydrogen is pumped selectively from the anode compartment to the cathode at high temperature. Hydrogen is ionized at the anode to produce protons, which are transported and deionized to form hydrogen at the cathode by the following reactions: H2 ! 2Hþ þ 2e (at anode) ð1Þ 2Hþ þ 2e ! H2(at cathode): ð2Þ

Hydrogen Extraction Characteristics of Proton-conducting Ceramics under a Wet Air Atmosphere for a Tritium Stack Monitor

For the purpose of designing a tritium monitoring system combined with proton-conducting ceramics as a membrane separator, the hydrogen pump characteristics of CaZr0.9In0.1O3–α proton-conducting ceramics were evaluated. In the experiments, argon gas containing 20.7% oxygen and 1.2% water vapor was fed to the anode at a rate of 47–137 ml/min at 600–800°C and an applied voltage until 3.5 V. The resulting hydrogen evolution rate reached maximally 0.67ml/min and the hydrogen recovery rate was 60%. However, the proton transport number decreased to 0.52 because the electron-hole current increased along with protonic current according to the defect equilibrium reaction occurring under a wet atmosphere containing oxygen. During operation, the hydrogen evolution rate fluctuates over time by at least 0.1 ml/min, which is approximately 20% of the hydrogen evolution rate. Additionally, the hydrogen evolution rate increased with an increase in the partial pressure of water vapor at the anode. It is important to design the tritium monitoring system taking into consideration the fluctuation in hydrogen evolution rate.