In this review the phenomenon of proton conductivity in materials and the elements of proton conduction mechanismsproton transfer, structural reorganization and diffusional motion of extended moietiesare discussed with special emphasis on proton chemistry. This is characterized by a strong proton localization within the valence electron density of electronegative species (e.g., oxygen, nitrogen) and self-localization effects due to solvent interactions which allows for significant proton diffusivities only when assisted by the dynamics of the proton environment in Grotthuss and vehicle type mechanisms. In systems with high proton density, proton/proton interactions lead to proton ordering below first-order phase transition rather than to coherent proton transfers along extended hydrogen-bond chains as is frequently suggested in textbooks of physical chemistry. There is no indication for significant proton tunneling in fast proton conduction phenomena for which almost barrierless proton transfer is suggest...

Proton Conductivity: Materials and Applications

▪ Abstract The structural and chemical parameters determining the formation and mobility of protonic defects in oxides are discussed, and the paramount role of high-molar volume, coordination numbers, and symmetry are emphasized. Symmetry also relates to the structural and chemical matching of the acceptor dopant. Y-doped BaZrO3-based oxides are demonstrated to combine high stability with high proton conductivity that exceeds the conductivity of the best oxide ion conductors at temperatures below about 700°C. The unfavorably high grain boundary impedances and brittleness of ceramics have been reduced by forming solid solutions with small amounts of BaCeO3, and an initial fuel cell test has demonstrated that proton-conducting electrolytes based on Y-doped BaZrO3 provide alternatives for separator materials in solid oxide fuel cells (SOFCs). These materials have the potential to operate at lower temperatures compared with those of conventional SOFCs, and the appearance of chemical water diffusion across the...

Proton-conducting oxides

1. Introduction 46372. Theoretical Methodologies and Simulation Tools 46402.1. Ab Initio Quantum Chemistry 46412.2. Molecular Dynamics 46422.2.1. Classical Molecular Dynamics and MonteCarlo Simulations46432.2.2. Empirical Valence Bond Models 46442.2.3. Ab Initio Molecular Dynamics (AIMD) 46452.3. Poisson−Boltzmann Theory 46452.4. Nonequilibrium Statistical Mechanical IonTransport Modeling46462.5. Dielectric Saturation 46473. Transport Mechanisms 46483.1. Proton Conduction Mechanisms 46483.1.1. Homogeneous Media 46483.1.2. Heterogeneous Systems (ConfinementEffects)46553.2. Mechanisms of Parasitic Transport 46613.2.1. Solvated Acidic Polymers 46613.2.2. Oxides 46654. Phenomenology of Transport inProton-Conducting Materials for Fuel-CellApplications46664.1. Hydrated Acidic Polymers 46664.2. PBI−H

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Transport in proton conductors for fuel-cell applications: simulations, elementary reactions, and phenomenology.

Fuel cell materials and components

The increasing world population and the need to improve quality of life for a large percentage of human beings are the driving forces for the search for sustainable energy production systems, alternative to fossil fuel combustion. Among the various types of alternative energy production technologies, solid oxide fuel cells (SOFCs) operating at intermediate temperatures (400–700 °C) show the advantage of possible use both for stationary and mobile energy production. To reach the goal of reducing the SOFC operating temperature, proton-conducting oxides are gaining wide interest as electrolyte materials. This critical review provides a broad overview of the most recent progresses obtained tailoring the properties of proton-conducting oxides for fuel cell applications, analyzing and comparing the different strategies proposed to match high-proton conductivity with good chemical stability (170 references).

Materials challenges toward proton-conducting oxide fuel cells: a critical review

Proton conductive properties of gadolinium-doped barium cerates at high temperatures

Endurance against moisture for protonic conductors of perovskite-type ceramics and preparation of practical conductors

The performance and the long-term operating properties of solid oxide fuel cells (SOFCs) using BaCeO{sub 0.8}GdO{sub 0.2}O{sub 3{minus}{alpha}} (BCG) ceramics as the electrolyte have been investigated. A hydrogen-air fuel cell using BCG electrolyte with a thickness of 0.5 mm exhibited good performance at 800 C. Its short-circuit current was 0.9 A/cm{sup 2}, and there was hardly any degradation of BCG electrolyte in 1,600 h of operation. When a quasi-fuel gas containing 8% CO{sub 2}, which was expected by the reformation of the city gas (CH{sub 4}) at 800 C, was supplied to this cell, its short-circuit current was 0.63 A/cm{sup 2} and the cell worked stably under the discharge current density of 100 mA/cm{sup 2} for 2,500 h. Some sintered metals (Fe, Co, Ni) were examined as a anode material for this electrolyte. Ni is a promising anode material for BCG electrolyte from the point of view of performance and durability.

Operating Properties of Solid Oxide Fuel Cells Using BaCe0.8Gd0.2 O 3 − α Electrolyte

This invention provides a solid electrolyte fuel cell operable with high efficiency even in the temperature range of about 850° to 650° C., The invention is characterized by the use of a novel perovskite double oxide of the composition A X B Y O 3- α. The fabrication of the electrolyte, air electrode and fuel electrode layers by tape casting has contributed to marked improvement in processability and productivity.

Solid electrolyte fuel cell and method for manufacture of same

The present invention relates to a mixing ion conductive material for use in an electrochemical device such as a fuel cell or a sensor and more particularly to the super ion conductive material based on protons or oxide cations and also to a synthesizing method of the mixing ion conductive material. A mixing ion conductive oxide which has a proton conductivity and/or oxide cation conductivity and has a composition comprising 1 mol of barium oxide, 1-x mol of cerium oxide and x mol of gadolinium oxide; wherein 1>x>0.1. When x=0.2, the mixing ion conductive material shows a conductivity shown in FIG. 2. The oxide sintered body mentioned above has a density higher than 96.5% of the theoretical density and a grain size of 0.1 to 10 micron. The synthesizing method of the oxide sintered body is characterized by that the powders for use in the final heat treatment is crushed into a particle size less than 3 micron and is subjected to a vacuum drying process. Further, the sintering temperature is specified to a temperature between 1635° C. and 1665° C.

Noboru Taniguchi

Papers

Proton conductive properties of gadolinium-doped barium cerates at high temperatures

Endurance against moisture for protonic conductors of perovskite-type ceramics and preparation of practical conductors

Operating Properties of Solid Oxide Fuel Cells Using BaCe0.8Gd0.2 O 3 − α Electrolyte

Solid electrolyte fuel cell and method for manufacture of same

Mixed ionic conductors