Development of Novel Anode Material for Intermediate Temperature SOFC (IT-SOFC)

Transcription

1 Development of Novel Anode Material for Intermediate Temperature SOFC (IT-SOFC) Amit Sinha *, D. N. Miller and J.T.S. Irvine School of Chemistry, University of St Andrews North Haugh, St Andrews KY16 9ST UK * as304@st-andrews.ac.uk

2 Introduction Objective: Development of rare-earth free electrode materials for IT-SOFC Candidate Material Titanium oxycarbide Why Ti-oxycarbide? Multi-functional material Combination of metallic and ceramic properties High electronic conductivity ~16 % of metallic and nonmetallic sites vacant Key Issues: Phase purity Stability under oxidising and reducing environments Interaction with electrolyte materials Electrochemical performance

3 Synthesis of titanium oxycarbide powders TiO and TiC Mixing Powder Mixture Reaction-Sintering under vacuum TiO x C 1-x Solid State Synthesis of TiO x C 1-x (x=0.2, 0.5 and 0.8)

4 In te n s ity (A.U.) (3 1 1 ) (2 2 2 ) (1 1 1 ) (2 2 0 ) (2 0 0 ) Characterisation of oxycarbide powders Phase purity TiO 0.8 C 0.2 TiO 0.5 C 0.5 TiO 0.2 C ( o ) XRD patterns of TiO x C 1-x powders

5 Intensity (AU) Characterisation of oxycarbide powders Phase purity Rietveld refinement pattern of TiO 0.5 C 0.5 powder 4000 Y Obs 3000 Y Calc Y Obs - Y Calc Bragg Position TiO 0.5 C 0.5 unit cell 0 Lattice Parameters (Å) ( o ) a = b=c = (8) Reliability parameters of the refinement: R p :8.73% R wp :11.3% R exp : 12.91%

6 L a ttic e P a ra m e te r ( ) S lo p e a s p e r V e g a rd 's L a w J C P D F D a ta b a s e P re s e n t S tu d y O x y g e n c o n te n t o f T io x C 1 -x (x ) Lattice parameters of TiO x C 1-x as a function of oxygen content (x)

7 TiO 0.2 C 0.8 Fracture surface of reaction-sintered TiO 0.2 C 0.8 specimen TiO 0.2 C 0.8

8 TiO 0.2 C 0.8 X=0.2 TiO 0.5 C 0.5 X=0.5 TiO 0.8 C 0.2 X=0.8 Av. Grain Size of oxycarbide (TiO x C 1-x ) increases with increase in oxygen content (x) 10 µm Ti-Compound Melting Point ( o C) TiO 1750 TiC 3140

9 TEM photomicrographs of TiO 0.2 C 0.8 powder along with its SAED pattern with their corresponding crystal planes

10 In te n s ity (A.U.) Stability under reducing environment powder after heating at 900 C for 18 h in 5% H 2 T io 0.2 C 0.8 As synthesised Powder ( o ) XRD patterns of TiO 0.2 C 0.8 powder before and after heat treatment under reducing environment at 900 C

11 TG/% DTG Stability under oxidising environment TiO 0.2 C 0.8 TiO 0.5 C 0.5 TiO 0.8 C Temp ( o C) TGA/DTG plots of titanium oxy-carbides under flowing air

12 Raw material : TiO and TiC Solid state synthesis of oxycarbide Mechanism of formation of oxycarbide At room temperature TiO is monoclinic while TiC is cubic Monoclinic TiO Ti 5/6 O 5/6 (Ti 0.83 O 0.83 ) or Ti 5 O 5 (Ti 5 1 O 5 1 ) where and represent titanium and oxygen vacancies The monoclinic TiO contains metal and oxygen vacancies of the order of 16.7% each. XRD pattern of starting TiO powder (monoclinic) m-tio

13 Intensity (A.U.) Phase transformation of TiO m-tio m-tio room temperature Monoclinic crystal structure of TiO 4000 room temperature o C room temperature 800 o C ( o ) 2 ( o ) XRD pattern of TiO after heating at 800 C under Ar+5H 2

14 Intensity (A.U.) Phase transformation of TiO cubic-tio 1000 o C ( o ) XRD pattern of m-tio after heating at 1000 o C under Ar+5H 2 Cubic ordered phase from monoclinic ordered phase Std. Pattern of ordered Cubic TiO from: Valeeva et al., JETP Letters, 71 (2000)

15 TiO Monoclinic Cubic Transformation Room Temperature (Ti 5 1 O 5 1 ) 1000 o C (Ti 5 1 O 5 1 )

16 TiO-- Monoclinic Cubic Transformation

17 Out of 24 Metal sub-lattice 4 sites are vacant Out of 24 nonmetal sublattice 4 vacant (1/6) or 16.7 % vacancy both in metal and non-metal sublattices Six unit cell of Cubic TiO (Ti 20 4 O 20 4 )

18 Ti 20 O 16 C 4 Ti 20 O 10 C 10 TiO 0.8 C 0.2 TiO 0.5 C 0.5

19 Compatibility of titanium oxycarbide with electrolyte materials

20 Compatibility of Titanium Oxycarbide with Electrolyte Materials Oxygen ion conductors 1. LSGM 2. Gadolina doped Ceria (GDC) 3. Yttria stabilized zirconia 4. Ca-doped GdAlO 3 TiO x C 1-x and Electrolyte powder (1: 1) Mixing Powder Mixture Heat Treatment under Ar+5%H o C for 18 h Phase analysis through XRD

21 In te n s ity (A.U.) Interaction Study with LSGM-1020 LSGM1020 +TiO 0.2 C 0.8 heated at 900 o C under Ar+ 5% H 2 for 18 h LSGM1020 TiO 0.2 C ( o ) No Interaction with LSGM1020 at 900 o C

22 In te n s ity (A.U.) Interaction Study with gadolina doped Ceria (GDC) GDC+TiO 0.2 C 0.8 heated at 900 o C under Ar+ 5% H 2 for 18 h GDC+TiO 0.2 C 0.8 Mixture GDC TiO 0.2 C ( o ) No Interaction with GDC at 900 o C GDC: 10 mol% Gd-doped Ceria

23 TEM photomicrograph of GDC Powder TEM photomicrograph of TiO 0.2 C 0.8 GDC composite powder after heat-treatment at 900 for 18 h in Ar+5% H 2

24 Intensity (A.U.) Interaction Study with YSZ TiO 0.5 C 0.5 +YSZ mixture after heat treatment at 900 o C under 5%H 2. YSZ TiO 0.5 C ( o )

25 Interaction Study with Ca-doped GdAlO 3 Counts jtsi21_1 Ca- doped GdAlO 3 is an oxygen Lattice ion conductor parameters: 3000 conductivity close to that of YSZ [1,2] a/ Å: (2) b/ Å: (3) c/ Å: (2) 2000 Powder prepared through combustion synthesis 1000 Phase pure powder directly after combustion Position [ 2Theta] (Copper (Cu)) Peak List [1] A. Sinha, H. Näfe, B.P. Sharma, P, Gopalan, J. Electrochem. Soc. 155 (2008) B309 [2] A. Sinha, H. Näfe, B.P. Sharma, P, Gopalan, Electrochim. Acta 55 (2010) 8766

26 Interaction Study with Ca-doped GdAlO 3 No interaction with Tioxycarbide XRD pattern of Gd 0.85 Ca 0.15 AlO 3 -TiO 0.2 C 0.8 composite heat treated at 900 o C for 18 h under 5 %H 2 +Ar atmosphere

27 Electrochemical performances

28 C e ll V o lta g e (V ) P o w e r D e n s ity (m W /c m 2 ) C e ll V o lta g e (V ) Electrochemical Performance with GDC Electrolyte GDC+TiO 0.2 C OCV of Unit Cell ` GDC GDC+LSCF T e m p ( o C) o C o C o C Plot of OCV as a function of operating temperature utilising moist hydrogen as fuel and ambient air as oxidant Power o C mw/cm 2 C u r r e n t D e n s ity (A /c m 2 )

29 -Z // (o h m.c m 2 ) -Z // (o h m.c m 2 ) -Z // (o h m.c m 2 ) o C Fracture surface of GDC Electrolyte k Z / (o h m.c m 2 ) o C k Z / (o h m.c m 2 ) Electrolyte-anode bilayer o C 200k Z / (o h m.c m 2 ) Nyquist Plots of planar cell under fuel cell measuring conditions 1

30 Fabrication of titanium oxycarbide tube

31 In te n s ity (A.U.) Fabrication of titanium oxycarbide tubes TiO 2 (Anatase) crystallite size = 26 nm Hydrated TiO 2 and Graphite Wet- Mixing Powder Mixture XRD Pattern of hydrous titania Tube making (CIP) G ra p h ite Reaction-Sintering under vacuum TiO x C 1-x Tubes ( o )

32 Lattice parameter a/ Å: (14) Cell Vol (4) Composition TiO 0.2 C 0.8 XRD Pattern of Ti oxycarbide Titanium oxycarbide tube

33 Summary

34 Summary Phase pure titanium oxycarbide Formation mechanism of oxycarbide Compatibility study with oxygen ion conductors Electrochemical characterisation Fabrication of titanium oxycarbide tube

35 Prof. JTS Irvine JTSI Group BARC, Mumbai H2FC Supergen

36 Thank You