Separator for Fuel Cells
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
8 Project completed
Senior Project Manager
Mitina L M
VNIIEF, Russia, N. Novgorod reg., Sarov
- Boreskov Institute of Catalysis, Russia, Novosibirsk reg., Akademgorodok
- European Materials Research Society (EMRS), France, Strasbourg\nEcole Polytechnique de Montreal / Centre for Research in Computational Thermochemistry, Canada, QC, Montreal\nEcobiofuel Inc., Canada, Alberta
Project summaryPower plants (PP) based on a fuel cell stack (FCS) are being actively developed nowadays, since they possess a number of unquestionable advantages, i.e. high efficiency, low noise level, etc.
Most power plants use methane as a fuel that is catalytically reformed in the PP fuel conditioning system and is converted into a gas mixture enriched with hydrogen to be used in the FCS for the electrochemical reaction of oxidation.
Steam reforming of methane is the most well studied, efficient and, as a result, most widely applied method of hydrogen production in the fuel cell-based power plants (FC PP). In most FC PPs, catalytic steam reforming is effected in fuel processors. The fuel processor is a complex device, which requires heat power sources to maintain thermal modes thereof. As a heat power source the FCS functioning products are generally used, i.e. gas mixtures containing a certain amount of combustible components, such as hydrogen, carbon monoxide and methane. For efficient combustion of these mixtures, complex multi-stage catalytic combustion apparatuses are applied.
This considerably complicates the PP design, increases its cost, and, finally, reduces commercial attractiveness thereof.
To make the PP design less complicated and improve the PP efficiency, the FCS with internal reforming is applied, where catalytic reforming units are integrated in the stack as discrete elements containing a catalytically active component and alternating with FC groups. The heat energy needed for steam reforming is provided via heat release in the result of the electrochemical reaction of hydrogen oxidation in the FCS. Such integration is effective in power plants based on high-temperature fuel cells, such as molten carbonate fuel cells (MCFC) and solid oxide fuel cells (SOFC). Most efficient is integration directly in each cell of the stack. In this case, the reforming catalyst in the form of discrete elements, e.g. granules of different shapes or porous foam materials, is placed in the FC zones, where anode gases are circulating. One of most significant structural elements in the FC that distributes the fuel and the oxidizer flows in the FC anode and cathode zones, respectively, and provides electric coupling of cells in the MCFC is a separator (in planar SOFC – interconnector). From design viewpoint, the separator/interconnector is a plate profiled from a flat metal sheet, where channels for distribution of gas flows are formed. Since steam reforming requires effective heat supply with high power density into the reaction zone, we think most reasonable to integrate the catalytically active component with a metal separator, which due to its high (in comparison with the other MCFC/SOFC components, i.e. anode, cathode and electrolyte) heat conductivity will allow to decrease temperature gradients caused by non-uniformity of the electrochemical reaction in the FC with large area, thus preventing local overheating.
We propose to prepare the catalytically active component in the form of a multilayer gas-permeable porous coating of the separator/interconnector.
The catalytically active component and the whole separator/interconnector are to operate in severe conditions. Most critical are the following factors:
- In MCFC conditions, in the area of Ni-Cr anode the contact in gas-liquid phase with the electrolyte in the form of eutectic mixture of Li/Na/Ba/Ca carbonates,
- In MCFC conditions, the action of corrosive gas medium in the form of wet hydrogen with carbon dioxide within the temperature range of 575-675оС,
- In planar SOFC conditions, the action of high temperatures - up to 900 оС.
The Project goal is development of an integrated separator/interconnector for direct reforming of hydrocarbons in high-temperature MCFC and planar SOFC, which will possess high lifetime characteristics while operation within the FCS.
The above goal is to be attained via using a multi-layer coating for the separator. The coating will have at least two layers. The first layer will have a high degree of adhesion to the metal surface, the normalized thickness of 25-30 microns due to the layer formation before operation within the fuel cell and will be formed, basically, with metal oxides and intermetallides having the specific electrical resistance of at most 120 mΩ/cm2. The first layer porosity 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 оС. 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 it will be formed, mainly, with complex 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 оС. In addition, it will possess high activity in hydrocarbons oxidation reactions within the temperature range up to 900 оС while operation in planar SOFC conditions.
Multilayer coatings will be developed while using combinations of simple and complex oxides of transition metals and Ni and Al oxides – a group of natural/synthetic materials with high thermal stability and catalytic activity in the reaction of hydrocarbons oxidation. Promising Ni-Cr-intermetallides will be used as coatings for sub-layers improving adhesion strength. As protective coatings to be used as catalyst supports most promising are the following spinel types: Al2О3·(MgO)x and Al2О3·(MgO)x·(CeO2)y. As porous catalytically active multi-layer coatings, the following systems are promising: NiO·(Al2О3)x·(MgO)y; NiO·(Al2О3)x·(MgO)y·(CeO2)z and NiO·(Al2О3)x·(MgO)y·(La2O3)z.
The proposed works are related to the Applied Research and Technology Development Categories, since the Project works will result in:
First of all, enhancement and improvement of existing plasma spraying techniques via developing a gas-dynamic plasma spraying technique of multi-layer protective and catalytic coatings;
Secondly, development of several compositions of multi-layer protective and catalytic coatings for direct reforming of hydrocarbons in high-temperature MCFC and planar SOFC.
The Project mission is integration of the processes of hydrocarbons reforming into high-temperature fuel cells via applying multi-layer protective and catalytic coatings on the surface of the metal separator/interconnector profiled in the form of channels and effecting the reforming process directly in said separators/interconnectors while using the heat released by the fuel cell during the electrochemical reaction.
Realization of the above mission will allow:
- To reduce the FC PP weight-dimension characteristics and improve the FC PP reliability owing to a simpler design;
- To extend the FC PP lifetime via improving the durability of FC constructional elements in severe operating conditions.
In the result, commercial attractiveness of fuel cell-based power plants will be improved that will facilitate their entry into the energy market.
The Project works are aimed, primarily, at improvement of the available manufacturing process of coating application using plasma spraying and cold gas-dynamic spraying techniques. The improvement will consist in application of multi-layer protective catalytic coatings on the surface of the metal separator/interconnector of high-temperature MCFC and planar SOFC profiled in the form of channels.
Most promising metals and alloys with an optimal set of characteristics and best manufacturability will be used as materials for separators/interconnectors, including those patented by the Project participants and mastered by the metallurgical industry.
Based on the improved technique, two main consumer products will be created, namely:
- A composition of low-porous protective coating and processing methods of coating application to profiled metal plates using plasma spraying and cold gas-dynamic spraying techniques;
- A composition of porous catalytic coating and processing methods of coating application to profiled metal plates using the plasma spraying techniques.
These products are commercially attractive both in the market of fuel cell-based power plants and components thereof, as well as in other market segments.
In the motor-car industry, most promising applications are catalytic neutralizers and electric neutralizers of ICE exhaust gases, protective coatings for the working surface of high-temperature manifolds of exhaust systems.
In the chemical industry, most promising applications are high-temperature hydrocarbons reforming and synthesis reactors, protective coatings for the working surface of high-temperature accessories.
In the metallurgical industry, most promising areas are protective coatings for the working surface of high-temperature ovens and foundry equipment.
While the Project implementation, the technique will be developed and tested on industrial equipment that will allow by the Project end to create a production line on application of various coatings using the plasma spraying technique for mass production of environmentally friendly fuel cell-based power plants for residential and commercial applications.
Intellectual property to be generated within the Project frames will be protected via publications in scientific journals, and, in case of patentability, via patenting in Russia and abroad, including joint patenting with the Project Collaborators. By present, no information has been revealed that could impede the Project results use.
The labor efforts of weapon scientists make up 3510 man/day (62 % 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.
While the Project implementation recommendations on the Project results implementation will be worked out, and specialists from RFNC-VNIIEF and BIC will conduct marketing studies in Russia and abroad and will develop a business plan on technology implementation and a commercialization strategy. While marketing studies, contacts with Collaborators and other potential consumers will be established that will allow coatings characteristics and research directions to meet most completely the consumer requirements.
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.
The International Science and Technology Center (ISTC) is an intergovernmental organization connecting scientists from Kazakhstan, Armenia, Tajikistan, Kyrgyzstan, and Georgia with their peers and research organizations in the EU, Japan, Republic of Korea, Norway and the United States.
ISTC facilitates international science projects and assists the global scientific and business community to source and engage with CIS and Georgian institutes that develop or possess an excellence of scientific know-how.