H. Iwahara

Proton conduction in sintered oxides and its application to steam electrolysis for hydrogen production

Abstract Some sintered oxides based on SrCeO3 were found to exhibit proton conduction on exposing them to a hydrogen-containing atmosphere at high temperature. The verification of proton conduction was made by studying the emf of various gas cells using the specimen diaphragm as an electrolyte. These materials could be applied to the electrolyte for steam electrolysis to produce hydrogen gas.

Proton Conduction in Sintered Oxides Based on BaCeO3

Some sintered oxides based on were found to exhibit appreciable proton conduction under hydrogen‐containing atmosphere at high temperature. The verification of proton conduction was made by studying the EMF of various gas cells using the specimen ceramics as the solid electrolyte. The protonic conductivity in the doped was higher than that in the proton conductor found previously by us. These materials could be applied to the solid electrolyte for a hydrogen fuel cell, a hydrogen pump, and a steam electrolyzer to produce hydrogen.

Relation between proton and hole conduction in SrCeO3-based solid electrolytes under water-containing atmospheres at high temperatures

Abstract Electrical conduction in the solid proton electrolyte based on SrCeO3 was studied under water-containing atmospheres at high temperatures. The change of conductivity was measured systematically as a function of the concentration of the dopant or of the partial pressures of water vapor and oxygen. Since the conduction in the oxides was not purely protonic but partially electronic, these conductivities were determined separately using a steam concentration cell. It was observed that the proton conductivity increased in proportion to P 1 2 H2O and was independent of PO2. It was also recognized that the electronic conduction present in the oxides was due to holes and the hole conductivity followed the P 1 4 O2 law. A possible model for the proton formation in the oxides is discussed and it is proposed that the protons might be produced from water vapor at the expense of holes.

High Temperature Solid Electrolyte Fuel Cells Using Perovskite‐Type Oxide Based on BaCeO3

Using perovskite‐type oxide based on as a solid electrolyte, small‐size high‐temperature fuel cells were constructed and cell performances were examined. The Nd‐doped ceramic electrolyte exhibited a mixed conduction of proton and oxide ion. Mixtures of water vapor and some gases such as methanol vapor or methane were used as a fuel by internal reforming to liberate hydrogen in the anode compartment. These fuel cells worked stably above 900°C. At 1000°C, the overvoltage at both electrodes was very small and the performances of the cells were limited mainly by ohmic resistance of the solid electrolyte. Besides platinum, porous nickel was a promising anode material for this electrolyte.

High temperature proton conducting oxides and their applications to solid electrolyte fuel cells and steam electrolyzer for hydrogen production

High temperature proton conducting oxides are favorable materials for direct energy conversion, hydrogen extraction and the sensing of hydrogen. As such materials, we found the SrCeO3-based ceramics which have appreciable protonic conduction under hydrogen-containing atmosphere at high temperatures. In this paper, the conduction properties of these oxides and their applications to a high temperature fuel cell and a steam electrolyzer for hydrogen production are described referring to the experimental results obtained in our laboratory.

High temperature type proton conductor based on SrCeO3 and its application to solid electrolyte fuel cells

Abstract Some electrical properties of the high temperature type proton conductor SrCeO.95 -Yb0.05O3−α found by us were investigated in various atmospheres. Transient conduction behavior of this material suggested that the rate of proton formation at oxide surface and proton diffusion into the bulk were fairly fast at high temperatures. Using thin disc of this ceramic as a solid electrolyte diaphragm and various metals or oxide electronic conductors as electrode materials, fuel cells were constructed by way of experiment and their performances were examined. Nickel as well as platinum were of promising materials for the anode, and some perovskite-type oxide electronic conductors comprised the cathode. Water vapor was confirmed to evolve at the cathode and its evolution rate was in proportion to the discharge current indicating that protons were the charge carriers in this ceramic.

Formation of protons in SrCeO3-based proton conducting oxides. Part II. Evaluation of proton concentration and mobility in Yb-doped SrCeO3

Abstract In order to evaluate the proton concentration in SrCeO3-based oxides, protons in the oxides were expelled in the form of water vapor by raising temperature in a flowing oxygen gas and the total amount of water vapor evolved was measured. While the solubility of water vapor in pure SrCeO3 was negligibly small, Yb-doped proton-conducting oxides dissolved an appreciable amount of water vapor. The determined proton concentration for SrCe0.95Yb0.05O3−α was about 2 mol% at 600°C and about 1 mol% at 1000°C. The equilibrium constant for proton and hole formation and their mobilities were estimated, and these parameters fitted to the conduction behavior measured previously by us.

Mixed conduction and oxygen permeation in the substituted oxides for CaTiO3

Mixed conduction in substituted perovskite-type oxides CaTi1−xMxO3−α (M=Fe, Co and Ni) was studied by means of electrochemical methods. Of these materials, Fe-substituted oxides showed the highest oxide ion conductivity as well as high electronic conductivity. The oxide ion transport numbers of the oxides were lower than 0.6 over the whole composition range measured in air. Electrochemical oxygen permeation in such a material could be confirmed by gas chromatography. Extraction of oxygen from air was carried out using the mixed conductor. The oxygen extraction rate in this method was higher than that using a silicone film.

Studies on solid electrolyte gas cells with high-temperature type proton conductor and oxide ion conductor

Abstract Various types of gas cells are studied using high-temperature-type proton and oxide ion conductors as the solid electrolyte. Steam and hydrogen concentration cells could be constructed using the SrCeO 3 -based proton conductive solid electrolyte. Using the oxide ion conductor, YSZ, the steam concentration cell could also be constructed in hydrogen atmosphere. Some characteristics of these cells are discussed.

High temperature fuel and steam electrolysis cells using proton conductive solid electrolytes

Abstract High-temperature-type proton conductive solids are favorable materials as electrolytes for fuel cells and steam electrolysis cells for the production of hydrogen gas. An attempt has been made to construct a high temperature fuel cell and a steam electrolysis cell using an SrCeO3-based solid electrolyte, which we found to be a protonic conductor in the presence of hydrogen or water vapor. Both cells could be operated stably at 800 – 1000 °C. The major limitation of the cell system was the resistance of the solid electrolytes.