Hiroyasu Iwahara

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 .

Technological challenges in the application of proton conducting ceramics

Abstract This paper describes technological challenges in the application of proton conducting ceramics developed in our laboratory. The proton conducting ceramics used here were perovskite-type oxide solid solutions based on cerate or zirconate. Galvanic cell type sensors for detecting hydrogen and other hydrogen-containing compounds could be fabricated using this kind of ceramics. Laboratory-scale hydrogen fuel cells, steam electrolyzers for hydrogen production, hydrogen extractors from gas mixtures and membrane reactors for organic compound gases were made by way of experiment using the ceramics as a solid electrolyte, and they were positively verified to work.

Protonic conduction in calcium, strontium and barium zirconates

Electrical conduction in sintered oxides based on calcium, strontium or barium zirconate at high temperature was investigated electrochemically. When Zr in MZrO 3 (M=Ca, Sr or Ba) was partially replaced by trivalent element such as In, Sc, Y, etc., the resultant solid solutions exhibited protonic conduction under hydrogen-containing atmosphere at elevated temperatures. In general, the protonic conductivities of BaZrO 3 - and SrZrO 3 -based ceramics were higher than those of CaZrO 3 -based one although the values were low compared to those of SrCeO 3 or BaCeO 3 -based ceramics. Clear isotope effects in IR spectrum and conductivity were observed between protonated and deuteronated SrZro 0.95 Y 0.05 O 3-α

Oxide ion conductors based on bismuthsesquioxide

Abstract Oxide ion conductive solid electrolytes based on bismuthsesquioxide are reviewed. These electrolytes are characterized by their conductivities more than ten times higher than those of conventional oxide ion conductors such as stabilized zirconias.

Proton conducting ceramics and their applications

High temperature protonic conductors based on perovskite-type oxides are reviewed concerning their electrical properties and possible applications. These ceramics are unique in respect of the fact that they have no protons as a host component, but incorporate protons via reactions with the atmosphere. Defect equilibria for proton formation in these kind of oxides are discussed citing some experimental results. Possible electrochemical devices using proton conducting ceramics are briefly introduced.

High oxide ion conduction in sintered oxides of the system Bi2O3-WO3

The ionic conduction in sintered oxides of the system Bi2O3-WO3 was investigated by measuring conductivities and ion transference numbers under various conditions. The ion transference number was measured by an oxygen concentration cell employing the specimen tablet as the electrolyte.It was found that a compound 3Bi2O3 WO3 and its solid solution were high oxide ion conductors, the conductivities of which were about one order of magnitude higher than those of the well-known oxide ion conductors such as stabilized zirconias. In contrast to pure Bi2O3 which is a completely electronic conductor below 730°C, these materials showed high oxide ion conduction even below 700°C accompanied by little electronic conduction. 3Bi2O3 WO3 has the face centered cubic structure, probably of the fluorite type, and the oxide ion conduction was thought to be attributed to the migration of oxide ion vacancies in the crystal.

Performance of Solid Oxide Fuel Cell Using Proton and Oxide Ion Mixed Conductors Based on BaCe1 − x Sm x O 3 − α

BaCe[sub 1 [minus] x]Sm[sub x]O[sub 3 [minus] [alpha]](x = 0.05, 0.10, 0.15) ceramics were synthesized and their ionic conduction was investigated. These ceramics showed protonic and oxide ionic mixed conduction under fuel cell condition. While protonic conduction was predominant below 1,027 K, oxide ionic conduction became significant as the temperature increased. Using these oxides as solid electrolyte, hydrogen-air fuel cell could be constructed. BaCe[sub 0.9]Sm[sub 0.1]O[sub 3 [minus] [alpha]] exhibited the best cell performance among the electrolytes examined. The maximum short-circuit current density was about 900 mA/cm[sup 2] at 1,273 K. The polarization at each electrode was low. Porous nickel could be used as anode material instead of expensive platinum and La[sub 0.6]Ba[sub 0.4]CoO[sub 3] as cathode material.

Protonic conduction in SrZrO3-based oxides

Abstract Proton conduction in SrZrO 3 -based oxides which were doped with aliovalent cations such as Yb 3+ , Y 3+ , Ga 3+ , Al 3+ and In 3+ was investigated. These ceramics showed proton and hole mixed conduction in water vapor containing atmosphere at relatively high oxygen partial pressure at high temperature. Hydrogen concentration cell using these oxides as a solid electrolyte could be constructed and showed stable EMF close to theoretical value calculated from Nernsts equation. Electrochemical hydrogen permeation could be carried out at high temperature using these oxides as a solid electrolyte. Hydrogen evolution rate was close to the value calculated from Faradays law.

Proton conduction in sintered oxides based on CaZrO3

Abstract CaZrO 3 -based ceramics, in which trivalent cations such as In, Ga and Sc were substituted for Zr, were synthesized. Proton conduction in these oxides was investigated using some electrochemical methods under various conditions at high temperature. These ceramics showed proton and hole mixed conduction in water vapor containing atmosphere. Hydrogen concentration cell using these oxides as a solid electrolyte showed stable EMF which was close to theoretical value. Proton could electrochemically permeate through these ceramics according to Faradays law. The charge carrier of these ceramics is proton and their transport number is almost unity in hydrogen atmosphere.

High oxide ion conduction in sintered Bi2O3 containing SrO, CaO or La2O3

Ionic conduction in sintered oxides of the system Bi2O3-SrO was investigated by measuring the conductivity and ion transference number under various conditions. The ion transference numbers were measured by an oxygen concentration cell employing the specimen as the electrolyte.It was found that the solid solution containing 20≈40 mole% SrO which had a rhombohedral structure was an almost pure oxide ion conductor under a relatively high partial pressure of oxygen, and that the conductivity was several times higher than that of stabilized zirconias at the same temperatures up to 800°C. Oxide ion conduction was confirmed also by quantitative determination of generated O2 from the anode of the oxygen concentration cell during discharge.The sintered specimens of the systems Bi2O3-CaO and Bi2O3-La2O3 were found also to be oxide ion conductors, and the ion transference numbers were greater than 0.9.