Chromium impact on Strontium and Manganese-free cathode materials

Transcription

1 Chromium impact on Strontium and Manganese-free cathode materials M.K. Stodolny a B.A. Boukamp b D.H.A. Blank b G. Rietveld a F.P.F. van Berkel a a University of Twente, Department of Science and Technology & MESA +, Institute for Nanotechnology b Energy Research Centre of the Netherlands Presented at the 2 nd International Workshop on Degradation Issues of Fuel Cells,21-23 September 2011, Thessaloniki, Greece ECN-L NOEMBER 2011

2 Chromium impact on Strontium and Manganese-free cathode materials Maciej K. Stodolny a,*, B. A. Boukamp b, D. H. A. Blank b, G. Rietveld a, F. P. F. van Berkel a a Energy research Centre of the Netherlands (ECN) b Dept. of Science and Technology & MESA + Institute for Nanotechnology, University of Twente * stodolny@ecn.nl 2 nd International Workshop On Degradation Issues Of Fuel Cells; Thessaloniki, Greece;

3 Outline Aim: Understanding degradation mechanisms of the Cr-poisoned LNF cathode Introduction: Cost-effective SOFC stack cheap metallic interconnects Cr-poisoning of SoA SOFC cathodes Promises of the La(Ni,Fe)O 3 material PhD research: LNF stability in the presence of Cr species Solid-state reactivity of LNF+Cr 2 O 3 Gas transport of Cr and impact on LNF Explanation of the Cr-poisoning mechanism

4 SOFC cells Stack Industrial CHP SOFC stack design interconnect Fe-Cr alloy cost-effectiveness, workability, corrosion resistance, TEC cathode: (La,Sr)MnO 3 (La,Sr)(Co,Fe)O 3 Cr-poisoning susceptible PROBLEM: Cr-species originating from the Fe-Cr interconnects poison SoA SOFC cathodes

5 Strontium and Manganese-free cathode materials Perovskites: La(Ni,Fe)O 3 (Komatsu et al., Zhen et al., Stodolny et al., ) Ruddlesden-Popper nickelates: - La 2 NiO 4 (Hildenbrand et al., Bassat et al., ) - Nd 2 NiO 4 (Schuler et al., Bucher et al., ) (authors taking Cr-poisoning into account) 4

6 Endurance LNF testing in all ceramic housing Promises of La(Ni,Fe)O 3 material: LaNi 0.6 Fe 0.4 O 3 cathode was reported to have high Cr-resistance [Komatsu et al., Zhen et al.] Improved electrochemical performance of LNF [Stodolny et al.] Optimised LNF air xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx I- xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx fuel stable and well performing

7 Endurance LNF testing with metallic interconnect Promises of La(Ni,Fe)O 3 material:?!? LaNi 0.6 Fe 0.4 O 3 cathode was reported to have high Cr-resistance [Komatsu et al., Zhen et al.] Improved electrochemical performance of LNF [Stodolny et al.] Optimised LNF air Ferritic steel interconnect xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx I- post-test analysis?!? xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx performance degradation fuel Cr tolerance questionable!?! M. K. Stodolny, F. P. F. van Berkel, J. P. Ouweltjes, ECN Internal Communication, to be submitted for publication.

8 Post-test analysis of a Cr-poisoned LNF cathode SEM micrograph SEM-EDX Cr mapping cathode 120 mm barrier layer electrolyte anode Cr tolerance questionable!?! Complex! [Cr] ~ f (T, t, j, flow, po 2 ph 2 O, )

9 PhD research aims Understanding of the LNF chemical stability in the presence of Cr species Explanation of the Cr-poisoning mechanism Lit: Transport of Cr-species via: To investigate: - direct solid state diffusion solid-state reactivity between LNF and Cr 2 O 3 - vapor phase transport vapor transport of Cr-species and impact on LNF properties

10 Cell oltage [] ROAD MAP of experiments To investigate: solid-state reactivity: LaNi 0.6 Fe 0.4 O 3 +Cr 2 O 3? solid-state reactivity Cr gas transport solid-state reactivity Cr gas transport and impact on: conductivity f (t) f (microstructure) f (gas atmosphere) electrochemistry f (t, (J)) Current Density [ma/cm 2 ]

11 solid-state reactivity: LaNi 0.6 Fe 0.4 O 3 +Cr 2 O 3? La-Cr-Fe-Ni-O system phase diagram - tetrahedron ½ Cr 2 O 3 solid-state reactivity: 10LNF + 5Cr 2 O 3 10LNF + 3Cr 2 O 3 Cr addition LaCr 10LNF + 1Cr 2 O 3 LaNi 0.6 Fe 0.4 O 3 ½ Fe 2 O 3 LaFe ½ La 2 O 3 LaNi NiO composition expressed as the mole fractions of the metallic components

12 solid-state reactivity: LaNi 0.6 Fe 0.4 O 3 +Cr 2 O 3? 10LNF + 1Cr 2 O 3 ½ Cr 2 O 3 Relative stability of the perovskites: LaCrO 3 > LaFeO 3 > LaNiO 3 J. Cheng et al., J. Mater. Res., 20, No.1, 191 (2005). LaCr LaNi 0.28 Fe 0.4 Cr 0.32 O 3 LaFe ½ Fe 2 O 3 ½ La 2 O 3 NiO LaNi predicted phases Check experimental XRD

13 LNF and Cr 2 O 3 reactivity at 800ºC for 200h 10LNF+1Cr 2 O 3 200h/800 C Perovskite: orthorhombic rhombohedral precipitated NiO 10LNF+1Cr 2 O 3 only mixed Perovskite: rhombohedral unreacted Cr 2 O 3 ٠ M.K. Stodolny, B.A. Boukamp, D.H.A. Blank, F.P.F. van Berkel, J. Electrochem. Soc. 158 (2), B112 (2011). M. Stodolny, F.P.F. van Berkel, B.A. Boukamp, ECS Transactions, 25 (2) (2009).

14 LNF and Cr 2 O 3 reactivity Thermodynamic equilibrium verification ORTHORHOMBIC ~La(Fe,Cr)O 3 Reactivity in progress equilibrium LaNi 0.28 Fe 0.4 Cr 0.32 O 3 orthorhombic 10LNF + 1Cr 2 O 3 orthorhombic Ni Cr e (!) Initial Thermodynamic 10LNF + 1Cr 2 O 3 orthorhombic + rhombohedral LNF (LaNi 0.6 Fe 0.4 O 3 ) rhombohedral X-ray Diffraction spectra Le Bail fit RHOMBOHEDRAL LaNiO 3 LaNi 0.6 Fe 0.4 O 3

15 Cell oltage [] ROAD MAP of experiments solid-state reactivity: LaNi 0.6 Fe 0.4 O 3 +Cr 2 O 3 solid-state reactivity Cr gas OC 800 o C air Cr gas transport and impact on: conductivity electrochemistry f (t) f (microstructure) f (gas atmosphere) f (t, (J)) Current Density [ma/cm 2 ]

16 Gas transport of Cr-species experimental approach The electronic conductivity measurements while exposed to a Cr-source (ITM-14 porous foam) The fractured cross-section of the as-prepared LNF-GDC-3YSZ

17 Conductivity evolution at 800 ºC for the Cr-free and Cr-exposed LNF layers LNF-A M.K. Stodolny, B.A. Boukamp, D.H.A. Blank, F.P.F. van Berkel, Journal of Power Sources 196 (2011)

18 ICP-OES Resistance increase at 800 ºC in correlation with the amount of deposited Cr pcro x < pcro x > ~(Mn,Cr) 2 O 4 ~Cr 2 O 3

19 Cr distribution in a Cr-exposed LNF layer SEM-EDX

20 Cr distribution in a Cr-exposed LNF grain TEM-EDX Relative stability of the perovskites: LaCrO 3 > LaFeO 3 > LaNiO 3 J. Cheng et al., J. Mater. Res., 20, No.1, 191 (2005).

21 Cr-exposed LNF grain - electron diffraction Rhombohedral Orthorhombic Similarly to solid state reactivity of LNF with chromia: M. Stodolny, F.P.F. van Berkel, B.A. Boukamp, ECS Transactions, 25 (2) (2009). M.K. Stodolny, B.A. Boukamp, D.H.A. Blank, F.P.F. van Berkel, J. Electrochem. Soc. 158 (2), B112 (2011). (LaNiO 3 La Ni 0.6 Fe 0.4 O 3 ) ~La(Fe,Cr)O 3

22 Conductivity loss triggered by the Cr-intrusion Cr-substituted LNF LNF Cr-LNF LNF LNF Cr-LNF LNF LNF

23 Cell oltage [] ROAD MAP of experiments solid-state reactivity Cr gas OC air 800 o C Cr gas transport and impact on: conductivity electrochemistry f (t) f (microstructure) f (gas atmosphere) f (t, (J)) Current Density [ma/cm 2 ]

24 Influence of LNF microstructure on the Cr-poisoning impact (800 ºC) fine particles D(50)=0.38 µm LNF-D LNF coarse particles D(50)=0.54 µm LNF-A LNF

25 Affected Area Cr-content M.K. Stodolny, B.A. Boukamp, D.H.A. Blank, F.P.F. van Berkel, Solid State Ionics, submitted for publication Influence of LNF microstructure on the Cr-poisoning impact (800 ºC) fine particles D(50)=0.38 µm LNF-D Cr-LNF LNF 70% 4.3at% coarse particles D(50)=0.54 µm LNF-A 0.8at% Cr-LNF LNF 33% Time [h]

26 Cell oltage [] ROAD MAP of experiments solid-state reactivity Cr gas OC 800 o C various air [CrO x (OH) y ] Cr gas transport and impact on: conductivity electrochemistry f (t) f (microstructure) f (gas atmosphere) f (t, (J)) Current Density [ma/cm 2 ]

27 Influence of gas atmosphere on the Cr-poisoning impact (800 ºC) LNF-B Cr 0.2 at% dry N % O 2 high flow Cr 3.8 at% [CrO x (OH) y ] dry air semi-stagnant Cr 5.9 at% humid air semi-stagnant M.K. Stodolny, B.A. Boukamp, D.H.A. Blank, F.P.F. van Berkel, to be submitted for publication.

28 Cell oltage [] ROAD MAP of experiments Cr gas load solid-state reactivity Cr gas OC Cr gas transport and impact on: conductivity f (t) f (microstructure) f (gas atmosphere) electrochemistry f (t, (J)) Current Density [ma/cm 2 ] complete SOFC 3-electrode testing Preliminary results only! Not published yet!

29 Typical 3-electrode geometries

30 3-electrode setup (Square planar geometry with coplanar reference electrodes) idea: 3-el. cell preparation dedicated cell-housing I Cr I WE Cr CE WE CE I Electrolyte Counter electrode block RE RE WE I WE RE RE CE on the backside CE on the backside Screen design Working electrode block

31 Laser added electrode alignment um DE misalignment <10μm!!! alignment deviation <10μm! line straightness <5μm!

32 Overpotential [m] Overpotential [m] Endurance LNF testing with/without Cr source mA/cm 2 at 800 o C SO06 CEL_A_2 SO06 CEL_A_2 SO06 CEL_A_3 SO06 CEL_A_2 SO06 CEL_A_3 SO06 CEL_A_3 Proof of principle Reference test (all ceramic) Burn-in; non-linear linearity region Time [h] With Cr source WE-REF1 WE-REF2 I Cr WE -150 CE h 200 h 400 h 400 h I WE

33 Cr-poisoning impact on the electrochemistry of LNF R pol With Cr source R ohm I Cr WE CE M.K. Stodolny, B.A. Boukamp, D.H.A. Blank, F.P.F. van Berkel, to be submitted for publication. I WE

34 Summary of the proposed Cr-poisoning mechanism Both solid Cr 2 O 3 and Cr vapor species directly reacts with LNF at 800 o C The Cr-attack results in a replacement of Ni by Cr in the LNF perovskite lattice The segregated nickel forms Ni-rich metal oxide precipitates in the pores The drop of the LNF conductivity is due to formation of a low-conductive Cr-rich phase

35 Promising... LNF and Cr 2 O 3 reactivity at 600ºC 10LNF + 5Cr 2 O 3 10LNF + 3Cr 2 O 3 10LNF + 1Cr 2 O h at 600 o C no reaction detected! M.K. Stodolny, B.A. Boukamp, D.H.A. Blank, F.P.F. van Berkel, J. Electrochem. Soc. 158 (2), B112 (2011).

36 Promising... Influence of temperature on the Cr-poisoning impact (600 and 800 ºC case) M.K. Stodolny, B.A. Boukamp, D.H.A. Blank, F.P.F. van Berkel, J. Power Sources 196 (2011)

37 Summary and outlook Understanding of solid-state reactivity between LNF and Cr 2 O 3 Gas transport of Cr and its impact on the LNF properties established Cr-poisoning is dependent on: LNF microstructure Operating temperature Cr atmosphere Cr-tolerant? SOFC: Coarse cathode microstructure (+activation) Low operating temperature Low Cr-evaporation (coatings, ) Outlook Impedance data deconvolution In-depth explanation of Cr-poisoning on LNF Suggestions for Cr-resistant cathode

38 Research priorities on the degradation issues Cr-poisoning may not be fully avoidable Synergetic approach: Minimize presence of Cr volatile species Interconnect protective coatings Dry air at high flow velocities seek for a more Cr-tolerant cathode Reconsider thermodynamics Comparative unified testing procedure