Electrical and mass transport processes in molten oxide membranes

Fedorov

2016

Fuel Cells

We suggest a novel molten oxide fuel cell (MOFC) concept. The MOFC is based on the oxygen-ion-conducting solid/ molten oxide electrolyte (so-called liquid-channel-grainboundary-structure, LGBS, material) consisting of TeO 2 solid grains and chemically compatible TeO 2 +Te 4 Bi 2 O 11 liquid electrolyte at the grain boundaries. The intergranular liquid channels provide the LGBS mechanical plasticity (ductility), which makes it easy to shape and alleviates problems due to thermal incompatibility with electrodes (CTE), and high ionic conductivity. The volume fraction of liquid varied from 0.15 to 0.17 at 600-640°C. The cell performance has been examined by standard electrochemical methods. With air used as a cathode gas, the single cell showed the power 11.5 mW cm -2 at the current density 90 mA cm -2 , electrolyte thickness 2.5 mm, and temperature 640°C.

Section: Introductionmentioning

confidence: 99%

A Novel Molten Oxide Fuel Cell Concept

Fedorov

2016

Fuel Cells

“…They play important roles in geological processes . Molten oxide electrolysis is considered as a promising route to oxygen generation for extraterrestrial exploration. , There is a large amount of work on molten electrolytes and molten metal/molten oxide composite electrodes for battery and SOFC applications. − Recently, the molten oxide fuel cell (MOFC) and molten oxide membrane (MOM) concepts have been proposed. , MOFCs are a new type of intermediate temperature fuel cells, which combine the advantages of both solid oxide fuel cells (SOFCs, air at cathode side) and molten carbonate fuel cells (MCFCs, highly conductive molten electrolyte) and could be used for efficient electric power generation. MOMs are a new group of ion transport membranes (ITMs) for separation of ultrahigh purity oxygen from air .…”

Section: Introductionmentioning

confidence: 99%

“…In the first step, a ceramic composite is sintered. In the second step, so-called a liquid-channel grain-boundary structure (LGBS) is formed by the grain boundary (GB) wetting method . Making the ceramic composite includes pressing of the respective powder mixtures and subsequent sintering at a temperature below eutectic melting in air.…”

Section: Introductionmentioning

confidence: 99%

“…Formation of the LGBS material includes heating the ceramic composite above the eutectic temperature, which leads to the appearance of the liquid existing in equilibrium with the solid. While being heated, the ceramic composite experiences GB wetting by a chemically compatible liquid at eutectic temperature resulting in LGBS material (or molten oxide material) . The LGBS contains solid grains and intergranular liquid channels.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Next-Generation Electrochemical Energy Materials for Intermediate Temperature Molten Oxide Fuel Cells and Ion Transport Molten Oxide Membranes

2017

Acc. Chem. Res.

Self Cite

High temperature electrochemical devices such as solid oxide fuel cells (SOFCs) and oxygen separators based on ceramic materials are used for efficient energy conversion. These devices generally operate in the temperature range of 800-1000 °C. The high operating temperatures lead to accelerated degradation of the SOFC and oxygen separator materials. To solve this problem, the operating temperatures of these electrochemical devices must be lowered. However, lowering the temperature is accompanied by decreasing the ionic conductivity of fuel cell electrolyte and oxygen separator membrane. Therefore, there is a need to search for alternative electrolyte and membrane materials that have high ionic conductivity at lower temperatures. A great many opportunities exist for molten oxides as electrochemical energy materials. Because of their unique electrochemical properties, the molten oxide innovations can offer significant benefits for improving energy efficiency. In particular, the newly developed electrochemical molten oxide materials show high ionic conductivities at intermediate temperatures (600-800 °C) and could be used in molten oxide fuel cells (MOFCs) and molten oxide membranes (MOMs). The molten oxide materials containing both solid grains and liquid channels at the grain boundaries have advantages compared to the ceramic materials. For example, the molten oxide materials are ductile, which solves a problem of thermal incompatibility (difference in coefficient of thermal expansion, CTE). Besides, the outstanding oxygen selectivity of MOM materials allows us to separate ultrahigh purity oxygen from air. For their part, the MOFC electrolytes show the highest ionic conductivity at intermediate temperatures. To evaluate the potential of molten oxide materials for technological applications, the relationship between the microstructure of these materials and their transport and mechanical properties must be revealed. This Account summarizes the latest results on oxygen ion transport in potential MOM materials and MOFC electrolytes. In addition, we consider the rapid oxygen transport in a molten oxide scale formed on a metal surface during catastrophic oxidation and show that the same transport could be used beneficially in MOMs and MOFCs. A polymer model explaining the oxygen transport in molten oxides is also considered. Understanding the oxygen transport mechanisms in oxide melts is important for the development of new generation energy materials, which will contribute to more efficient operation of electrochemical devices at intermediate temperatures. Here we highlight the progress made in developing this understanding. We also show the latest advances made in search of alternative molten oxide materials having high mixed ion electronic and ionic conductivities for use in MOMs and MOFCs, respectively. Prospects for further research are presented.

“…1,2 Recently, the molten oxide membrane (MOM) materials have been developed. 14,15 This MOM materials consist of solid grains and intergranular liquid channels. The intergranular liquid channels provide the membrane material high ionic conductivity, gas tightness, and ductility.…”

mentioning

confidence: 99%

Oxygen Ion Transport in Molten Oxide Membranes for Air Separation and Energy Conversion

Климашин

2017

J. Electrochem. Soc.

Molten oxide membranes (MOMs) are a new class of ion transport inorganic membranes which demonstrate superior oxygen selectivity and permeability and could be used in electrochemical devices such as molten oxide fuel cells (MOFCs) and oxygen separators for energy conversion and air separation, respectively [Acc. Chem. Res., 50, 273 (2017)]. However, oxygen ion transport mechanisms in MOM materials are not clear enough. Understanding the oxygen ion transport mechanisms in molten oxides is important for the discovery of new MOM materials with enhanced performances that can enable the operation of the electrochemical devices more efficiently. Here we suggest an approach that adapts a dynamic polymer chain model, developed for specific molten oxides, to a wide range of melts. This generic model can evaluate the oxygen permeation fluxes through different MOM materials that are comparable to experimental data. The study of ion transport membrane (ITM) materials and processes is a rapidly expanding research interest field. This is due to the fact that the ITM-based technology modules have the potential to improve the efficiency and environmental performances of energy generation systems.1,2 ITM can separate high purity oxygen from air at elevated temperatures and have the potential to reduce the cost of oxygen production in comparison with the conventional cryogenic process.3 The mixed-conducting perovskite-type compounds, 4,5 ceramic composites, 6-9 and cermets 10-13 are used as ITM materials. The practicalities for incorporating ceramic membrane materials into industrial processes are discussed in comprehensive reviews. 1,2Recently, the molten oxide membrane (MOM) materials have been developed. 14,15 This MOM materials consist of solid grains and intergranular liquid channels. The intergranular liquid channels provide the membrane material high ionic conductivity, gas tightness, and ductility. This last property allows us to deal successfully with the problem of thermal incompatibility (difference in coefficient of thermal expansion, CTE).There 14,15 Transport properties (electrical conductivity, oxygen ion transport number, and oxygen and nitrogen permeation fluxes) of these MOM materials have been measured. [16][17][18][19][20] These membrane materials showed high oxygen selectivity and permeability. The ease of the MOM materials fabrication, combined with competitive oxygen permeability and superior oxygen selectivity, demonstrates a promising application.Understanding the oxygen ion transport mechanisms in molten oxides is important for the discovery of new MOM materials that can enable the oxygen separation and energy conversion more efficiently. Recently, a dynamic polymer chain model for oxygen ion transport in molten V 2 O 5 has been developed. [21][22][23] In this paper, we suggest an approach that adapts the dynamic polymer chain model to a wide range of melts. This generic model can predict the gas permeation fluxes through molten oxide 14,15 and carbonate [24][25][26][27][28][29] membrane materials that a...