Electrodes and fuel cells cases and visions

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1 Electrodes and fuel cells cases and visions Peter Holtappels Head of Programme Electrochemistry Fuel Cells and Solid State Chemistry Division Risø National Laboratory for Sustainable Energy Technical University of Denmark With contributions from: Carlos Bernuy-Lopez, Peter Blennow, Kent Kammer Hansen, Trine Klemensø, Alfred Samson, Anders Smith

2 Where is Risø DTU? DTU Campus Lyngby Risø DTU Roskilde København Malmö København Fuel Cells & Solid State Chemistry

3 Content Fuel Cells and Solid State Chemistry Division, Risø DTU Risø DTU activities on Solid Oxide Fuel Cells (SOFCs) The role of electrodes in SOFCs Electrode structures & processes Development of nano structured t electrodes Air electrodes (cathode) Metal supported cells Ceramic anodes Special application: Fluegas purification enhancing electrocalatytic selectivity

4 The Division in brief Functional ceramics for energy related technologies 130 people ceramic materials with special electrical, magnetic, thermal, chemical or electrochemical properties Our research span from fundamental investigations to component manufacture Focus on industrial collaboration and industrially relevant processes

5 Research Ceramic processes Materials development Characterization Advanced test Modelling

6 Technologies Solid Oxide Fuel Cells High temperature electrolysis Magnetic refrigeration Membranes for oxygen or hydrogen separation Flue gas purification Thermoelectrics

7 Solid Oxide Fuel Cells Direct conversion of chemically bound energy in a fuel to electricity High efficiency i Fuel flexibility (natural gas, hydrogen, ammonia, ethanol, biofuels, diesel) Low emissions Consists of thin layers of ceramics and possibly metal

8 Market-entry applications Distributed generation for, e.g, ships or hospitals (up to 250 kw e ) Micro-CHP (1-5 kw e ) Auxiliary power units (APUs) for trucks (5-10 kw e ) Risø DTU, Technical University of Denmark Update2011 Energy/Materials

9 Solid Oxide Fuel Cell - Principles e - Air: O 2 /N 2 N 2 Metallic IC cathode electrolyte anode O O x Electrocatalytic activity Nano/atomic scale Ionic conductivity Nano/atomic scale Electronic conductivity Nano/atomic/micro scale anode support (Open) porosity Microscale Metallic IC Fuel: CH 4 /H 2 O e e - CO 2 /H 2 O Risø DTU, Technical University of Denmark Update2011 Energy/Materials

10 Development trends in SOFCs LSM+YSZ YSZ Ni+YSZ LSM+YSZ S YSZ Ni+YSZ MIEC CGO ScYSZ Ni+YSZ MIEC ScYSZ Cermet - Infiltrate FeCr Ceramic-Supported Brittle Metal-Supported Robustness Raw materials

11 Air electrodes (cathodes) processes O 2,gas + 2V O,ely + 4e - 2O 2- ely LSM e - O 2 O y x,ad Cathode materials electronically cond. oxides (La,Sr) Mn O 3 (La,Sr) (Fe,Co)O 3 e - O 2 O 2 O o x YSZ V O O O x Risø DTU, Technical University of Denmark Update2011 Energy/Materials

12 Cell manufacture Raw materials Slurries Shaping Sintering Risø DTU, Technical University of Denmark Update2011 Energy/Materials

13 Lowering SOFC operating temperature At lower temperatures (<750C) the cathode accounts for the larger part of the losses of a SOFC In order to improve performance at lower temperatures, cathode development is needed *Barfod et al, Fuel Cells, 2006, 6, No. 2, Risø DTU, Technical University of Denmark Update2011 Energy/Materials

14 Impregnation/Infiltration Advantages Nano-scale particles are readily obtained which have large electrochemically active area leads to relatively low ASR Low calcination temperature minimize possible reactions between inifltrated and scaffold phases Improved control over resulting microstructures Independendent of other sintering steps during processing avoid problems due to thermal expansion mismatch Risø DTU, Technical University of Denmark Update2011 Energy/Materials

15 Impregnated cathodes A. Samson et al., Journal of The Electrochemical Society, 158 (6) B650-B659 (2011) Risø DTU, Technical University of Denmark Update2011 Energy/Materials

16 Electrochemical performance of LSC infiltrated electrodes A. Samson et al., Journal of The Electrochemical Society, 158 (6) B650-B659 (2011) Risø DTU, Technical University of Denmark Update2011 Energy/Materials

17 SOFC fuel electrodes: Ni-YSZ cermets H 2 /Ni-YSZ//YSZ Three percolating phases Ni / YSZ / pores H 2 O H 2 e - CTE adapted to YSZ YSZ- support structure avoids Ni-Agglomeration O o x Percolated Ni: current pick-up Active electrode areas: three phase boundary volume in vicinity of solid YSZ layer Risø DTU, Technical University of Denmark Update2011 Energy/Materials

18 Metal supported SOFC MIEC CGO ScYSZ Ni+YSZ MIEC ScYSZ Cermet - Infiltrate FeCr Wet ceramic processing Co-sintering (YSZ) High T in air Cathode barrier layer High T in air Cathode High T in air Risø DTU, Technical University of Denmark Update2011 Energy/Materials

19 Optimised metal support cell design MIEC CGO ScYSZ Cermet - Infiltrate FeCr CGO by spin-coat CGO by PVD type 1 CGO by PVD type 2

20 Metal supported cells Test of 16 cm 2 cells 650 C, H 2-4%H 2 O, Air 650 C, 0.25 Acm -2, H 2-4%H 2 O, Air, OU-FU < 5% ASR of corresponding button cell = 0.56 cm 2 Power output 0.28 Wcm 2 [A] J. Power Sources (2010) doi: /j.powsour /j Risø DTU, Technical University of Denmark Update2011 Energy/Materials

21 Ceramic fuel electrodes (anodes) Overcome the persisting drawbacks of state-of-the-art the art Ni-cermet electrodes Improved sulphur tolerance Improved re-oxidation stability Low coking activity La/Sr-titanates are a promising materials class Matching physical and chemical properties with other cell components Small stationary SOFC systems Combined heat and power

22 Special application: Fluegas purification Fluegas pollutants Particulate matter sulphur oxides nitrogen oxides carbon monoxide hydrocarbons

23 Enhancing selectivity for Nox reduction O 2,gas + 2V O,ely + 4e - 2O 2- ely 2NO x,gas + mv O,ely + ne - N 2 + mo 2- ely Alkaline earth oxide infiltration

24 Example KNO 3 -infiltration (300 0 C) Porous cell stack 11 layers T = 300 C

25 Summary & Outlook Reducing the operating temperature for solid oxide fuel cells down to below 600 C requires improved, better performing electrodes Nanostructuring the electrode improves the activity Reducing the particle size down to nano powders in conventional ceramic processing raises fabrictaion problems (Top down approach) By infiltration a ceramic structure is formed from precursor solutions (Bottom up approach) Infiltration/impregnation is an alternative and has succesfully applied to: activate ceramic air and fuel electrodes application in metal supported cells modify the selectivity for Nox conversion

26 Acknowledgements Colleagues at the Fuel Cell and Solid State Chemistry Department and Topsoe Fuel Cell Our Sponsors: The Danish National Advanced Technology Foundation EU Framework Programmes ( Energinet.dk Den Strategiske Forskningsråd JTI FCH JU Risø DTU, Technical University of Denmark Update2011 Energy/Materials

27 The Team