Mixed Proton Conductors Research Articles

Electrochemical Substitution of Sodium Ions in Tungsten Phosphate Glass with Protons

A novel technique was developed to inject proton carriers into phosphate glass. Sodium ions in the sodium tungsten phosphate glass were electrochemically substituted with protons. A glass plate with a deposited Pd anode was placed on the molten tin cathode and heated at a temperature below glass transition temperature under DC-bias in hydrogen containing atmosphere. Protons were injected from the palladium anode and substituted the sodium ions in the glass. The sodium ions migrated to the cathode and discharged to the molten tin cathode by capturing an electron from the external circuit. The atomic sodium dissolved into the cathode and reacted with CO2 impurities in the atmosphere resulting deposition of sodium carbonate on the tin cathode surface. After almost all of the sodium ions were discharged from the glass, the proton concentration in the glass reached 4.3 × 1021 cm−3. The proton conductivity was found to be 1 × 10−3 Scm−1 at 350°C. The injected protons were stable at temperatures below 400°C. The glass obtained by this technique behaves as a mixed conductor of protons and electrons with a proton transport number of 0.30. A possible means to suppress the electronic conductivity was discussed.

Partial Conductivities and Chemical Diffusivities of Mixed Protonic–Electronic Conducting CaZr0.9Y0.1O3 − δ

The electrical properties of (CZY) were studied as a function of both oxygen partial pressure and water vapor partial pressure in the temperature range of and the partial conductivities of protons, holes, and oxygen vacancies were calculated from the defect model. In a wet atmosphere, CZY was a mixed conductor of protons, holes, and oxygen ions. No conduction transition from protons to holes and/or oxygen ions occurred even as temperature was increased up to . The calculated activation energy of proton transport was . The standard solution enthalpy for water dissolution was best fitted with a slope of . The twofold conductivity relaxation behavior that was observed at during hydration/dehydration was interpreted in terms of decoupled ambipolar diffusion of oxygen vacancies and protons by holes. The best-estimated chemical diffusivities of oxygen and hydrogen were several orders of magnitude lower than that reported for other proton-conducting perovskite oxides due to the relatively low ion conductivity of CZY.

Partial conductivities of mixed conducting BaCe 0.65Zr 0.2Y 0.15O 3–δ

The electrical properties of BaCe 0.65Zr 0.2Y 0.15O 3–δ (BCZY) were studied as a function of both oxygen partial pressure and water vapor partial pressure in the temperature range of 500–800 °C, and the partial conductivities of protons, holes, and oxygen vacancies were calculated from the defect model. P-type conduction was dominant in an oxidative atmosphere. In a wet atmosphere, BCZY was a mixed conductor of protons, holes, and oxygen ions. A conduction transition from protons to holes and/or oxygen ions was found with increasing temperature. The calculated activation energy of oxygen ion transport was 0.71 eV. The standard solution enthalpy for water dissolution was best fitted with a slope of −120.19 kJ/mol, which is somewhat smaller in absolute terms than that of BaCe 0.9Y 0.1O 3–δ and of BaCe 0.8Y 0.2O 3–δ. This result also agrees well with the literature reports that the Ba, rather than Sr, occupation of A-site and the Ce, rather than Zr, occupation of B-site in perovskite proton conductors induce more negative hydration enthalpies due to the increasing basicity of the corresponding oxides.

Ionic conduction in Ba xCe 0.8Pr 0.2O 3–α

Ba x Ce 0.8Pr 0.2O 3– α ( x=0.98–1.03) ceramics were prepared by high temperature solid-state reaction. X-ray diffraction (XRD) patterns showed that the materials were perovskite-type orthorhombic single phase. By using gas concentration cell and AC impedance spectroscopy methods, the electrical conduction behavior of the materials was investigated in different gases at 500–900 °C. The influence of nonstoichiometry in the materials with x≠1 on conduction properties was studied and compared with that in the material with x=1. The results indicated that Ba 1.03Ce 0.8Pr 0.2O 3– α was a pure protonic conductor, and Ba 0.98Ce 0.8Pr 0.2O 3– α was a mixed conductor of protons and electrons in wet hydrogen at 500–900 °C. BaCe 0.8Pr 0.2O 3– α was a pure protonic conductor in 500–600 °C, and a mixed conductor of protons and electrons above 600 °C in wet hydrogen. In 500–900 °C, they were all mixed conductors of oxide ions and electronic holes in dry air, and mixed conductors of protons, oxide ions and electronic holes in wet air. Both the protonic and oxide ionic conductivities increased with increasing barium content in the materials in wet hydrogen, dry air and wet air, respectively.

Ionic Conduction in Ba0.95Ce0.8Ho0.2O3‐α.

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Ionic Conduction in Ba0.95Ce0.8Ho0.2O3−α

AbstractBa0.95Ce0.8Ho0.2O3−α was prepared by high temperature solid‐state reaction. X‐ray diffraction (XRD) pattern showed that the material was of a single perovskite‐type orthorhombic phase. Using the material as solid electrolyte and porous platinum as electrodes, the measurements of ionic transport number and conductivity of Ba0.95Ce0.8Ho0.2O3−α were performed by gas concentration cell and ac impedance spectroscopy methods in the temperature range of 600–1000 °C in wet hydrogen, dry and wet air respectively. Ionic conduction of the material was investigated and compared with that of BaCe0.8Ho0.2O3−α. The results indicated that Ba0.95Ce0.8Ho0.2O3−α was a pure protonic conductor with the protonic transport number of 1 during 600–700 °C in wet hydrogen, a mixed conductor of protons and electrons with the protonic transport number of 0.97–0.93 in 800–1000 °C. But BaCe0.8Ho0.2O3−α was almost a pure protonic conductor with the protonic transport number of 1 in 600–900 °C and 0.99 at 1000 °C in wet hydrogen. In dry air and in the temperature range of 600–1000 °C, they were both mixed conductors of oxide ions and electronic holes, and the oxide‐ionic transport numbers were 0.24–0.33 and 0.17–0.30 respectively. In wet air and in the temperature range of 600–1000 °C, they were both mixed conductors of protons, oxide ions and electronic holes, the protonic transport numbers were 0.11–0.00 and 0.09–0.01 respectively, and the oxide‐ionic transport numbers were 0.41–0.33 and 0.27–0.30 respectively. Protonic conductivity of Ba0.95Ce0.8Ho0.2O3−α in both wet hydrogen and wet air was higher than that of BaCe0.8Ho0.2O3−α in 600–800 °C, but lower in 900–1000 °C. Oxide‐ionic conductivity of the material was higher than that of BaCe0.8Ho0.2O3−α in both dry air and wet air in 600–1000 °C.

Electrical Properties of p-Type Electronic Defects in the Protonic Conductor SrCe0.95Eu0.05 O 3 − δ

The electrical properties of were studied as a function of both oxygen partial pressure and water vapor partial pressure in the temperature range of 500-800°C, and the partial conductivities of protons, holes, and oxygen vacancies were calculated from the proposed defect model. P-type conduction was dominant in an oxidative atmosphere. It was shown that, in a wet atmosphere, is a mixed conductor of protons, holes, and oxygen ions. A conduction transition from protons to holes and/or oxygen ions was found as temperature increased. The calculated activation energy of oxygen ion transport was 0.67 eV; standard solution enthalpy of water dissolution was −164 kJ/mole, which is larger than that of The effect of dopants on the conduction mechanism is explained by a hopping mechanism. © 2003 The Electrochemical Society. All rights reserved.

Mixed alkali metal selenate proton conductors: Phase transitions and crystal structure of [Rb0.54(Nh4)0.46]3H(SeO4)2

Optical birefringence, calorimetric, thermal expansion, powder and single crystal X-ray diffraction investigations of mixed proton conductors [Rb1-x(NH4)x]3H(SeO4)2 were performed with the aim of studying the influence of partial substitution of cations on the superprotonic phase transition, on the atomic structure and on other characteristic features of this type of crystals.

Humidity Sensor with SrCe0.95Yb0.05 O 3 Solid Electrolyte for High Temperature Use

A sensing system for humidity was operated at with both and gases at 873–1273 K. The system design was Pt, (reference electrode), Pt. The EMF of the sensor had good reversibility and rapidly responded to the changes of humidity and temperature. Because the solid electrolyte was a mixed conductor of protons, oxygen ions, and positive holes, the EMF for , air, , or Ar with humidity was expressed taking into account mixed conduction bywhere is the equilibrium constant of the reaction of . The was determined experimentally, and was measured by an oxygen sensor with solid electrolyte. For gas in both electrodeswhere the superscript means reference electrode. The was determined experimentally.