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Separator for Fuel Cells

#3140


Development of an Integrated Separator for Direct Reforming of Hydrocarbons in High-Temperature Fuel Cells

Tech Area / Field

  • CHE-IND/Industrial Chemistry and Chemical Process Engineering/Chemistry
  • NNE-FCN/Fuel Conversion/Non-Nuclear Energy

Status
8 Project completed

Registration date
26.10.2004

Completion date
29.01.2008

Senior Project Manager
Mitina L M

Leading Institute
VNIIEF, Russia, N. Novgorod reg., Sarov

Supporting institutes

  • Boreskov Institute of Catalysis, Russia, Novosibirsk reg., Akademgorodok

Collaborators

  • University of Twente / Faculty of Science and Technology, The Netherlands, Enschede\nKarlsruhe University / Institut fur Technische Chemie und Polymerchemie, Germany, Karlsruhe

Project summary

Power plants (PP) based on a fuel cell stack (FCS) are being actively developed at present, since they possess a number of unquestionable advantages, i.e. high efficiency factor, low noise level etc.

The overwhelming majority of power plants applies methane as a fuel, which is catalytically reformed in the PP fuel conditioning system and converted into a gas mixture enriched with hydrogen that is used in the FCS for the electrochemical reaction of oxidation. Steam reforming of methane is the most well studied, efficient, and, as a result, the most widely applied method of hydrogen production in the FC PP. In most FC PPs, catalytic steam reforming is effected in fuel processors. The fuel processor is a complex device, which needs a heat power source to maintain heat modes thereof. As a heat power source there serve, as a rule, the FCS operation products, i.e. gas mixtures containing a certain amount of combustible components, such as hydrogen, carbon monoxide and methane residues. For efficient combustion of these mixtures, complex multi-stage catalytic combustion apparatuses are applied.

This makes the PP design more complicated, increases its cost and, finally, decreases commercial attractiveness thereof.

To simplify the PP design and improve its efficiency, the FCS with internal reforming is applied, wherein catalytic reforming apparatuses are integrated in the FCS as discrete elements containing a catalytically active component and alternating with FC groups. The required heat power for steam reforming is provided via heat release as a result of the electrochemical reaction of hydrogen oxidation in the FCS. This integration is efficient in power plants based on high-temperature fuel cells, such as MCFC.

Most efficient is the integration directly in each fuel cell of the FCS. Since steam reforming requires efficient heat supply with high power density to the reaction zone, we think the integration of the catalytically active component with a metal separator to be most reasonable. The said separator, due to a high relatively the other MCFC components (anode, cathode, electrolyte) heat conductivity, would allow to lower temperature gradients that are conditioned by non-uniformity of the electrochemical reaction in the FC with large area and to prevent local overheating.

The catalytically active component, in particular, and the separator, in whole, are to operate under severe operating conditions. In particular, most critical are the following factors: a corrosive gas medium in the form of humid hydrogen with carbon dioxide at temperatures within 575-675oC and the contact in the gas-liquid phase with the electrolyte in the form of eutectic mixture of Li/Na/Ba/Ca carbonates.

The Project goal is the development of an integrated separator for direct reforming of hydrocarbons in high-temperature MCFC, which would possess a high corrosion resistance while operation within the FCS.

The above goal is to be attained via application of a multilayer coating for the separator.

The coating will have, at least, two layers.

The first layer will have a high level of adhesion to the metal surface and the normalized thickness of 10-15 microns due to the layer formation before its operation within the fuel cell. This layer is formed with composite metal oxides with the specific electric resistance of at most 120 mОm/cm2. The porosity of the first layer will be minimal to prevent gas diffusion of the FCS functioning products and anode gases into the separator material within the temperature range of 575-675 oC.

The second layer will have the normalized thickness of at least 100 microns, open porosity with the specific surface within 100-150 m2/g and the pore size within 50-150 Ao. This layer is formed, mainly, with composite oxides of transition metals possessing both high activity in the reaction of natural gas oxidation with water vapor as well as stability to the deactivating action of alkali metal carbonate vapors within the temperature range of 575-675 oC.

While the Project implementation, a protective coating for the separator will be developed while using the technique of plasma spraying in inert mediums/vacuum on the basis of manganites, chromites and cobaltites of rear-earth elements doped with Sr and/or Y that would possess high electric conductivity and corrosion resistance. Finished manganites, cobaltites and chromites of rare-earth metals will be sprayed on metallic surfaces with protective layer while varying the mode of plasma jet flow (laminar or turbulent), physical and chemical properties of the coatings will be studied by X-ray analysis and scanning electronic microscopy methods. Finished manganites, cobaltites and chromites of rare-earth metals doped with Sr and Ca will be sprayed on metallic surfaces while varying the mode of plasma jet flow (laminar or turbulent), physical and chemical properties of the coatings will be studied by X-ray analysis and scanning electronic microscopy methods.

A technique of synthesis in the plasma jet of manganites, cobaltites and chromites of rare-earth elements from predecessors (simple oxides or salts) and their simultaneous fixing on the metallic surface will be developed. Physical and chemical properties of the coatings will be studied by X-ray analysis and scanning electronic microscopy methods; and difference in properties of the given coatings and the ones obtained by spraying of finished materials will be revealed.

The catalytic activity of source finished manganites, cobaltites and chromites of rare-earth elements; finished manganites, cobaltites and chromites of rare-earth elements doped with Sr and Ca and the separator coatings in the methane oxidation reaction will be measured. A mathematical model of heat transfer in the fuel cell of planar construction with direct oxidation of hydrocarbons in the FC anode area during the electrochemical reaction will be developed.

The composition of the separator coatings will be elaborated upon results of physical and chemical studies and measurements of the coatings’ activity.

The technique will be worked over on one of Russian production facilities while using the separator materials being developed within the ISTC Project 2281p.

The work results will be of a scientific and practical value and will serve as a step towards commercialization of one of the most fast-developing areas of the power industry.

The Project will be carried out by a team of highly qualified specialists, the majority of which being involved in the development of defense products. The team includes Doctors and Candidates of Science, specialists in chemistry, physics, science of materials, catalysis, automation of experimental research and mathematical modeling.

The labor efforts of weapon scientists make up 3490 man/day (57 % from the total scope of works).

Technical issues will be constantly discussed with Project Collaborators in order to obtain a practical result available for commercial application just after the Project completion. Joint experiments and calculations can be carried out.

The proposed Project meets the ISTC goals and objectives and allows to support applied research in the area of FC PP technology development that are promising apparatuses for converting chemical energy of hydrocarbon fuel into electric and heat energy while meeting the current environmental requirements.


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