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GDR ITSOFC-PACTE Tours 8-10 juin 2009

The Electrochemical and thermal performances of Ca 3 Co 4 O 9-δ as a cathode material for IT-SOFCs. K. Nagasawa 1) , O. Mentré 2) , S. Daviero-Minaud 2) , N. Preux 2) , A. Rolle 2) and H. Nakatsugawa 1)

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GDR ITSOFC-PACTE Tours 8-10 juin 2009

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  1. The Electrochemical and thermal performances of Ca3Co4O9-δ as a cathode material for IT-SOFCs K. Nagasawa1), O. Mentré2), S. Daviero-Minaud2), N. Preux2), A. Rolle2) and H. Nakatsugawa1) 1)Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya Word, Yokohama, Kanagawa, 240-8501, Japan 2) UCCS - Unite de Catalyse et de Chimie du Solide – UMR CNRS 8181, Ecole Nationale Superieure de Chimie de Lille, Batiment C7a – BP.90, 108, 59652, Villeneuve d'Ascq cedex, France GDR ITSOFC-PACTE Tours 8-10 juin 2009

  2. Outline • Background • Disposition for Ca3Co4O9-δ • Cell Manufacturing • Thermal Dilatometory • Chemical Compatibility • Electrode Deposition • Preliminary Electrochemical Tests • Conclusions GDR ITSOFC-PACTE Tours 8-10 juin 2009

  3. Back ground Cobalt Oxide in Cathode materials for IT-SOFC • showing promising cathode performances. 3D Perovskite 2D Perovskite Sm0.5Sr0.5CoO3 La1-xSrxCoO3 Ba0.5Sr0.5Co1-xFexO3 　　　・ 　　　・ YBaCo4O7 GdBaCo2O5 • 　mechanical incompatibilitywith electrolyte in TEC • 　chemical incompatibility reactivity with zirconia ( IT) GDR ITSOFC-PACTE Tours 8-10 juin 2009

  4. CoO2 Hexagonal layer High electrical conduction layer Co valence 3+/4+ Cf. NaxCoO2-yH2O  Ca3Co4O9 σ > 100 S/cm Ca2CoO3 Rock salt layer Co valence 2+/ 3+ Oxygen Vacancy δ ～ 0 – 0.15 Possible ionic conduction O O Crystal structure and oxygen vacancy in Ca3Co4O9-δ 2D misfit layered structure X2/m(0 p 0)s0 [Ca2CoO3]pCoO2 GDR ITSOFC-PACTE Tours 8-10 juin 2009

  5. . . ΔL/L0 (-) Thermal expansion coefficient (10-6ºC-1) Temperature (ºC) Thermal dilatometry • CGO → TEC = 11-12 x 10-6 (ºC-1) Experimental Value • Ca3Co4O9 → TEC = 9-10 x 10-6 (ºC-1) • 30CGO-Ca3Co4O9 → TEC = 10-11 x 10-6 (ºC-1) Caliculated Theoretical Value from HT-XRD • Ca3Co4O9 → TEC = 13 x 10-6 (ºC-1) GDR ITSOFC-PACTE Tours 8-10 juin 2009

  6. 5.00 μm 5.00 μm 5.00 μm 5.00 μm Optimizing grain size by ball milling times initial condition (0 hour) 9 hours 12 hours 24 hours Mean grain size 0～12 h →1.5-4 m24 h →0.5-1 m GDR ITSOFC-PACTE Tours 8-10 juin 2009

  7. Reaction test with electrolyte YSZ(a) 750℃ 100 hours or Ca3Co4O9 + CGO(b) YSZ CGO GDR ITSOFC-PACTE Tours 8-10 juin 2009

  8. Experimental Test Cell preparation Ball milling CaCO3 Calcination 880℃　12h Sintering 880℃ 24h + 30 wt% CGO Ball milling Co3O4 + dispersant + acetone Deposit CGO pellet Heat treating 700℃ Drying in air ink + binder + acetone <Cell size> 10-11 mm in diameter 1.5-2 mm thick ・XRD ・Thermal dilatometry ・SEM ・Impedance measurement GDR ITSOFC-PACTE Tours 8-10 juin 2009

  9. 70%Ca3Co4O9-30%CGO resin resin CGO Ca3Co4O9 CGO 20.0 μm 50.0 μm SEM image • Cross section of the cell • Cell surface <Ca3Co4O9-δelectrode cell> GDR ITSOFC-PACTE Tours 8-10 juin 2009

  10. Impedance spectraof Ca3Co4O9-δ [ in air ] [ at 700 ºC ] 0 1 2 -1 6 0 -1 <HF> <LF> [ 700 ºC in air ] ASR = 4.00 Ω.cm2 GDR ITSOFC-PACTE Tours 8-10 juin 2009

  11. Impedance spectraof 30CGO-Ca3Co4O9-δ [ in air ] [ at 700 ºC ] 0 1 1 2 0 1 -1 -1 -1 6 6 <HF> <LF> [ 760 ºC in air ] ASR = 1.05 Ω.cm2 [ 700 ºC in air ] ASR = 1.42 Ω.cm2 GDR ITSOFC-PACTE Tours 8-10 juin 2009

  12. Activation energy →Improve low activation energy by added 30% CGO GDR ITSOFC-PACTE Tours 8-10 juin 2009

  13. Conclusions • Good chemical compatibility with CGO (TEC, Chemical reactivity). • Good adherence between electrode and electrolyte, no crack surface. • Relatively Low ASR value of Ca3Co4O9 and 30CGO-Ca3Co4O9 cell. • the limiting stage is the ionic conductivity for Ca3Co4O9  Necessity for optimization of the microstructure. (grain size optimization, use of cellulose for porosity)  Optimization of the Oxygen conductivity (doping, … measurement of the permittivity under investigation (SPS- Toulouse, France) GDR ITSOFC-PACTE Tours 8-10 juin 2009

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