Fuel Cell Research Activities at the University of Leoben Focus: Solid Oxide Fuel Cells. Werner Sitte

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1 Fuel Cell Research Activities at the University of Leoben Focus: Solid Oxide Fuel Cells Werner Sitte Chair of Physical Chemistry, University of Leoben, Austria IEA Workshop Advanced Fuel Cells, TU Graz,

2 State-of-the-art and motivation for research on IT-SOFCs Lifetime/degradation Reduced degradation rate of thermally activated cell degradation mechanisms Reduced corrosion rate of chromium-based alloys and steels for interconnects Metal, metal-ceramic (compressible) seals and non crystallizing glass Stability of contact coatings Lower sensitivity for combined thermal-redox cycles Costs Lifetime Cheap interconnect chromium alloys / steels and BOP materials Industrial, cost effective manufacturing processes Fuel flexibility and high efficiency H 2 and reformates Internal reforming of NG (simplest and most efficient system) - Low catalytic activity for carbon deposition IEA Workshop Advanced Fuel Cells, TU Graz,

3 Participation of University of Leoben in the Integrated Project SOFC600 ( ) Project Consortium 7 Universities 11 R&D organisations 3 Industrial companies, all SMEs ECN Netherlands HTceramix Switzerland CEA France EMPA Switzerland FZJ Germany Imperial College United Kingdom Uni Karlsruhe Germany Uni St.Andrews United Kingdom Uni Oxford United Kingdom Uni Leoben Austria CNRS Bordeaux France TOFC Denmark AECA (NTDA-SOFC) Spain NRC Canada DICP China IPMS Ukraine SJTU China BIC Russia PMI Belarus VTT Finland Risø - DTU Denmark IEA Workshop Advanced Fuel Cells, TU Graz,

4 Cell housing SOFC600: Component and cell development Cell temperature Contacting Porosity NN CO 2 YDC LNF Grain size LSC-GCO LSCF LN PN PVD J-V curve Kinetics PSCF LSC 20GCO Screen printing Nano-LSC Layer Thickness Lateral conductivity Reactivity Stability Wet deposition Powder Barrier Layer Cell housing Current collector grid Area specific resistance Cr-resistance cm 2 cell ASR < 0.5 ohm.cm 2 Degradation rate < 1 mohm.cm 2 /khr Ceria Sintering Ni-salt Cell area Gas flow Co-firing Sealing S-tolerance Reference cells Impedance Expansion Anode substrate EB-PVD Cell integration Cell composition Oxide anode Phase transition Coking Ni/YSZ Microstructure Impregnation Ionic radius Dopant Yb-Zr MgO LST Catalyst Integrated Project SOFC600 (SES ), F. van Berkel Hf-Zr Ni/GCO Grain boundary Partial oxygen pressure Grain size Ni/ScZ Y-Ce-Sc-Zr Particle size Milling S/C Oxygen ionic conductivity Ce-reduction Internal reforming Milling SYT 10Sc1CeZr Polarisation Redox Robustness Poreformer Aging Thin film LiMOCVD 8YSZ Dilatometry

5 Overall Achievements Cell Development SOFC600 SOFC cell at 600 o C Area Specific Resistance (ASR) below 0,5 Ω.cm 2 Degradation rate below 0.05% / 1000 hours (1 mohm.cm 2 /khr) Robustness: 200 redox cycles, internal reforming capability, reduced coke formation activity status 2003/04 (CORE-SOFC) Aim for components: ASR / mω cm tentative status 2005 (REALSOFC) Anode (WP1.1) < 0.3 ohm.cm 2 Cathode (WP1.2) < 0.15 ohm.cm 2 Electrolyte (WP1.3) < 0.1 ohm.cm project target Cell (WP1.4) < 0.5 ohm.cm Temperature / C IEA Workshop Advanced Fuel Cells, TU Graz,

6 University of Leoben: SOFC Activities SOFC Cathodes Oxygen exchange properties of BSCF, LSCF, NDN including long time stability in real atmospheres poröses NiO/YSZ dichtes YSZ poröses dotiertes CeO 2 e - e - H 2 e - H 2 O O 2- SOFC Electrolytes Sc-ZrO 2 bulk and grain boundary conductivity = f(t, po 2 ) ageing studies poröses LSCF O 2 e - e - e - Quelle: ECN Niederlande IEA Workshop Advanced Fuel Cells, TU Graz,

7 SOFC cathodes: BSCF BSCF in different atmospheres CO 2 -free atmosphere: Reversible oxygen exchange of perovskite phase (ABO 3-δ ) 1 2 O [V 2 O (g) + ] = δ V = O + 2e f(t,po 2 ) O x O CO 2 -rich atmosphere: Onset of oxygen exchange shifted towards higher T E. Bucher et al., in Proc. 8 th Eur. SOFC Forum, 2008, p. A0603. IEA Workshop Advanced Fuel Cells, TU Graz,

8 SOFC cathodes: LSCF vs. NDN Long term stability of the oxygen exchange kinetics of Nd 2 NiO 4+δ (NDN) and La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) in dry and wet atmospheres at 700 C T=700 C A. Egger et al., J. Electrochem. Soc., in press (2010) IEA Workshop Advanced Fuel Cells, TU Graz,

9 Sc-doped zirconia electrolytes Impedance spectra in oxidizing and reducing atmospheres (300 C) Y 0.2 O 7.60 Ce 0.12 Y 0.08 O L ss R bulk R gb R el L ss R bulk R gb R el CPE bulk CPE gb CPE el CPE bulk CPE gb CPE el -Z'' / MΩ cm p(o 2 ) = 0.21 bar, T = 300 C 1%-H 2 /Ar, T = 300 C -Z'' / MΩ cm p(o 2 ) = 0.21 bar, T = 300 C 1%-H 2 /Ar, T = 300 C Z' / MΩ cm Z' / MΩ cm [W. Preis, A. Egger, J. Waldhäusl, W. Sitte, E. de Carvalho, J.T.S. Irvine, SOFC XI, ECS Transactions 25 (2009) ] IEA Workshop Advanced Fuel Cells, TU Graz,

10 Sc-doped zirconia electrolytes Bulk conductivity as a function of temperature in oxidizing and reducing atmospheres Comparison between Y 0.2 O 7.60 and Ce 0.12 Y 0.08 O 7.66 : heating in air (oxidizing conditions) and cooling in 1%-H 2 /Ar after reduction at 700 C for approx. 4 days Y 0.2 O 7.60 Ce 0.12 Y 0.08 O 7.66 heating in air ( C) cooling in 1% - H 2 / Ar ( C) heating in air ( C) cooling in 1% - H 2 / Ar ( C) 4 2 = (0.99 ± 0.03) ev 560 < T/ C < = (0.92 ± 0.02) ev 560 < T/ C < 700 ln(σt / S cm -1 K) = (0.99 ± 0.03) ev = (1.27 ± 0.01) ev 560 < T/ C < < T/ C < 560 = (1.27 ± 0.01) ev 300 < T/ C < 560 ln(σt / S cm -1 K) = (1.24 ± 0.01) ev = (1.05 ± 0.02) ev 300 < T/ C < < T/ C < 700 = (1.27 ± 0.01) ev 300 < T/ C < (T / K) (T / K) -1 IEA Workshop Advanced Fuel Cells, TU Graz,

11 Sc-doped zirconia electrolytes Grain boundary conductivity as a function of temperature in oxidizing and reducing atmospheres Comparison between Y 0.2 O 7.60 and Ce 0.12 Y 0.08 O 7.66 : heating in air (oxidizing conditions) and cooling in 1%-H 2 /Ar after reduction at 700 C for approx. 4 days Y 0.2 O 7.60 Ce 0.12 Y 0.08 O heating in air ( C) cooling in 1% - H 2 / Ar ( C) 6 heating in air ( C) cooling in 1% - H 2 / Ar ( C) ln(σt / S cm -1 K) = (1.30 ± 0.01) ev = (1.27 ± 0.01) ev ln(σt / S cm -1 K) = (1.28 ± 0.01) ev = (1.28 ± 0.01) ev (T / K) (T / K) -1 IEA Workshop Advanced Fuel Cells, TU Graz,

12 Sc-doped zirconia electrolytes Electrical conductivity as a function of p(o 2 ) at 700 C Bulk conductivity Total (bulk + gb) conductivity T = 700 C σ bulk / S cm Y 0.20 O 7.60 Ce 0.08 Y 0.12 O 7.64 Ce 0.10 Y 0.10 O 7.65 σ total / S cm Y 0.20 O 7.60 Ce 0.08 Y 0.12 O 7.64 Ce 0.10 Y 0.10 O 7.65 Ce 0.12 Y 0.08 O 7.66 Ce 0.12 Y 0.08 O 7.66 Ce 0.16 Y O 7.68 Ce 0.16 Y O 7.68 Ce 0.20 O 7.70 Ce 0.20 O log[p(o 2 ) / bar] log [p(o 2 ) / bar] All samples containing ceria show a remarkable decrease of the ionic conductivity at p (O 2 ) < bar This effect is even more pronounced for grain boundaries IEA Workshop Advanced Fuel Cells, TU Graz,

13 Sc-doped zirconia electrolytes Aging study of (CeO 2 ) 0.01 (Sc 2 O 3 ) 0.10 (ZrO 2 ) 0.89 at 700 under 1%-H 2 /Ar air 1%-H 2 /Ar 0.04 σ / S cm bulk grain boundaries total (= bulk + gb) t / hours [W. Preis, A. Egger, J. Waldhäusl, W. Sitte, E. de Carvalho, J.T.S. Irvine, SOFC XI, ECS Transactions 25 (2009) ] IEA Workshop Advanced Fuel Cells, TU Graz,

14 Outlook: Research on SOFC components for stationary and mobile applications SOFC Cathodes Cathodes for solid oxide fuel cells with respect to long term stability under real operating conditions including failure analysis of degraded cathodes - Partners: AVL List GmbH and FZ Jülich Structure-property relations of thin film SOFC cathodes (oxygen exchange properties, defect chemistry) - Partners: Joanneum Research Forschungsgesellschaft mbh, TU Wien SOFC Electrolytes Development of co-doped Sc-zirconia electrolytes (bulk and grain boundary conductivity as function of temperature and oxygen partial pressure, defect chemistry, ageing studies) - Partner: University of St. Andrews, UK IEA Workshop Advanced Fuel Cells, TU Graz,

15 Acknowledgment Research Co-operations... Financial Support IEA Workshop Advanced Fuel Cells, TU Graz,

16 Thank you for your attention! IEA Workshop Advanced Fuel Cells, TU Graz,