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FABRICATION AND EVALUATION OF SMALL (~ 100W) SOFC REACTORS.

Objective

LARGE AREA (> 100 CM2) CERAMIC ELECTROLYTE COMPONENTS AND IMPERMEABLE FLAT PLATE CERAMIC BIPOLAR UNITS BASED ON LACR (MG)03 COMPOSITIONS WILL BE FABRICATED. THESE COMPONENTS WILL BE INTEGRATED WITH HONEYCOMB POROUS ELECTRODE STRUCTURES TO ENABLE MULTI-CELL SOFC STACKS TO BE ASSEMBLED WITH APPROXIMATELY 100W POWER OUTPUT. THE PERFORMANCE OF THESE STACKS WILL BE EVALUATED, AND ADDITIONAL STUDIES ON INTERNAL REFORMING AND CHEMICAL CO-GENERATION WILL ALSO BE UNDERTAKEN.
Research was carried out with the objective of assembling a small multicell solid oxide fuel cell (SOFC) stack with the capability of approximately 100 W power output. As well as evaluating the performance of these stacks, additional studies were carried out on internal reforming and chemical cogeneration.

Participating laboratories failed to supply electrolyte sheets and bipolar plates in time but a small 2-cell stack was eventually assembled which gave a satisfactory performance. Total output was 3 W or a power density of 0.12 W cm{-2} (0.7 V at 175 mA cm{-2}) at 950 C.

Further investigations were required before SOFC design and configuration could be finalized. These involved:
evaluation of mechanical property data for electrolyte sheets involving cyclic fatigue and slow crack growth at elevated temperatures;
optimization of electrolyte sheet size;
evaluation of mechanical properties of lanthanum (calcium) chromium oixde bipolar plate at elevated temperatures (it is important to establish whether segregation of calcium oxide in steam atmospheres can lead to excessive rates of stress corrosion);
reduction of electrode and bipolar interfacial resistances and current collection problems by careful selection of materials;
preparation of stable nickel zirconium oxide anodes.

Techniques for the preparation of lanthanum (strontium) manganese oxide porous cathodes is well established and impedance spectroscopy has become an important technique for acquisition of electrode performance data. Experiments have demonstrated that Macor is not suitable as a cell holder in steam and methane environments and preliminary experiments on the internal reforming of methane as nickel zirconium oxide anodes provide encouraging data.
THE RESEARCH PROGRAMME INVOLVES FOUR PRINCIPAL ACTIVITIES. COLLABORATION WITH SIEMENS IS EMPHASIZED AND DIFFERENCES IN THE OBJECTIVES AND APPROACHES ARE SUMMARIZED IN APPENDIX 1.

3.1. FABRICATION OF ELECTROLYTE COMPONENTS.

IN THE CURRENT PROJECT EN3E/167/E EXPERTISE WILL HAVE BEEN GAINED ON THE FABRICATION OF CERAMIC ELECTROLYTE HONEYCOMB STRUCTURES, FLAT PLATES AND RIBBED PLATES UPTO AN APPROXIMATED AREA OF 25 CM2. COMMERCIAL POWDERS ARE BEING USED AND THEIR PROPERTIES OPTIMIZED FOR USE IN TAPE CASTING OR EXTRUSION PROCESSES. IN THE PRESENT PROJECT THIS EXPERTISE WILL BE USED TO PRODUCE LARGER AREAS OF FLAT PLATE, AND RIBBED PLATE CERAMIC ELECTROLYTE COMPONENTS. INITIALLY THESE AREAS WILL BE 100.0 CM2 (10X10) BUT THE AREA WILL BE INCREASED IN STAGES UPTO 500 CM2. THE PROPERTIES OF THESE CERAMIC ELECTROLYTE PLATES INC. STRENGTH, TOUGHNESS, WEIBULL MODULUS, PERMEABILITY, AND ELECTRICAL CONDUCTIVITY WILL BE MONITORED. IT IS ALSO INTENDED THAT THESE PLATES WILL BE SUPPLIED TO SIEMENS (PROJECT EN3E/D2/406D) FOR EVALUATIONS AS WELL AS PROVIDING THE BASIS FOR THE ASSEMBLY OF THE 100W STACKS (SECTION 3.3).

3.2.PREPARATION OF CERAMIC BI-POLAR PLATES

ALL DESIGNS OF SERIES CONNECTED PLANAR MONOLITHIC MULTICHANNEL REACTORS REQUIRE THE INCORPORATION OF AN IMPERMEABLE BI-POLAR PLATE.

A DEVELOPMENT PROJECT WILL THEREOFRE BE INITIATED INTO THE FABRICATION OF IMPERMEABLE LACR(MG)03 PLATES WITH INITIAL DIMENSIONS OF APPROXIMATELY 5X5 CM2 AND 100 UM THICKNESS. HEATING ELEMENTS FABRICATED FROM LACR(MG)03 ARE NOW COMMERCIALLY AVAILABLE AND SO THE FABRICATION OF LACR(MG)03 BI-POLAR PLATES APPEARS TO BE A REALISTIC OBJECTIVE. IF SUFFICIENT PROGRESS CAN BE MADE, THEN EXPERIMENTS WILL ALSO BE CONDUCTED INTO THE FABRICATION OF LARGER AREAS (E.G.LACR(MG)03). IN PARALLEL WITH THIS PROJECT APPROPRIATE CONFIGURATIONS OF POROUS CERAMIC CATHODE (LA(SR)MN03) AND ANODES (NI - ZR02) WILL ALSO BE PREPARED. A VARIETY OF SHAPES CAN BE ENVISAGED FOR THESE POROUS ELECTRODE STRUCTURES (SEE ARGONNE MOD O DESIGN ABOVE) BUT PROBABLY WE SHALL EXPLOIT OUR EXPERTISE IN EXTRUSION TECHNOLOGY WHICH IS BEING USED TO PREPARE HONEYCOMB ZIRCONIA ELECTROLYTE STRUCTURES IN THE CURRENT MULTICHANNEL SOFC REACTORS (EN3E/167/E).

IF ALTERNATIVE APPROPRIATE OXIDE MATERIALS BECOME AVAILABLE DURING THE PERIOD OF THIS PROJECT THEN THESE WILL ALSO BE EVALUATED.

IT SHOULD BE EMPHASIZED THAT THERE WILL BE A REGULAR EXCHANGE OF INFORMATION WITH SIEMENS (PROPOSED PROJECT EN3E/D2/406D) WHICH IS DEVELOPING METALLIC AND NON OXIDE BI-POLAR MATERIALS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE
Address
South Kensington Campus
London
United Kingdom

Participants (4)

British Gas plc
United Kingdom
Address
152 Grosvenor Road
SW1V 3JL London
Business Unit of TNO Built Environment and Geosciences
Netherlands
Address
Van Mourik Broekmanweg 6
2628 XE Delft
Foundation for Research and Technology-Hellas
Greece
Address
Stadiou 18, Platani
26500 Patras
GEC Alsthom Ltd
United Kingdom
Address
Lichfield Road
ST17 4LN Stafford