H. Uchida

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.

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.

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.

High temperature type protonic conductor based on SrCeO3 and its application to the extraction of hydrogen gas

Protonic and electronic conductivities of SrCe0.95Yb0.05O3−α ceramic in hydrogen gas were investigated at high temperatures. The protonic conductivity was 2 orders of magnitude higher than electronic conductivity. When the ceramic was exposed to hydrogen gas on one sinde and to oxygen gas on another side (fuel cell condition), the electronic conductivity increases with increasing partial pressure of oxygen suggesting that the charge carriers were positive holes. Using this ceramic as a solid electrolyte diaphragm, electrochemical hydrogen extractor was constructed by way of experiment and we could extract hydrogen from the pyrolyzed gas of CO + H2O mixture, ethane or steam. A bench-scale steam electrolyzer was fabricated using the protonic conductor, and pure hydrogen gas could be extracted in a rate of a few l/hr.

Formation of protons in SrCeO3-based proton conducting oxides. Part I. Gas evolution and absorption in doped SrCeO3 at high temperature

Abstract In order to clarify the equilibrium of proton formation in SrCeO3-based sinters at high temperature, the evolution and absorption of water vapor and/or oxygen were studied as a function of temperature and partial pressure. When the water vapor pressure was increased, an oxygen evolution associated with an increase in proton concentration was observed for Yb-doped SrCeO3. It was verified that three equilibria are simultaneously established between the oxide and the atmosphere (i.e. V o . + 1 2 O 2 ⇄ O o + 2 h . , H 2 O + 2 h . ⇄ 2 H . + 1 2 O 2 and H2O + Vo.. ⇄ 2 H. + Oo). It was also recognized that these equilibria had a tendency to shift to left side with increase of temperature.

Dissolution of water vapor (or hydrogen) and proton conduction in SrCeO3-based oxides at high temperature

In order to clarify the process of the dissolution of water vapor (or hydrogen) to generate protons in SrCeO3-based oxides at high temperature, the evolution and the absorption of water vapor and/or oxygen were studied by changing temperature or partial pressure in a flow of wet or dry gases. It was verified by such series of experiments that three equilibria were simultaneously established between the oxide and the atmosphere (i.e. V..o+12O2⇇OO+2h., H2O+2h.⇇2H.+12O2 and H2O+V..O⇇2H.+OO. By a thermal desorption method, the proton concentration in SrCe0.95Yb0.05O3−α was determined to be 2 mol% at 600°C and 1.1 mol% at 1000°C. The equilibrium constant for proton formation and the proton mobility were also estimated in this study.