1. Hector Colon, Prabhu Ganesan, Bala Haran, R. E. White and Branko Popov Department of Chemical Engineering University of South Carolina, Columbia, South Carolina 29208 Performance of Titanium Alloy and Co Plated Titanium Alloy for MCFC Current Collector

2. Outline Experimental Objective Lifetime Limitations Results Conclusions Materials Characterization

3. Component Material / PropertiesProblem/Solution Anode MaterialNi+10wt% Cr Pore size3 ~ 6  m Porosity 50~70% Thickness 0.5~1.5 mm Sp. Area0.1~1 m 2 /g Creep/Sintering - Ni-Al Alloy Cathode MaterialLithiated NiO Pore size6 ~ 9  m Porosity 80~85% as Ni Thickness 0.5~0.8 mm Sp. Area0.5 m 2 /g NiO dissolution - Stabilized NiO - LiCoO 2 cathode - Modified electrolyte Matrix Material  -LiAlO 2 Pore size0.2 ~ 0.5  m Porosity 50~60% Thickness 0.5 mm Sp. Area0.1~10 m 2 /g Sintering/Thermal Stability - Fiber or large particles Phase stability -  -LiAlO 2 Current Collector MaterialSS316 Chromium Dissolution - Nickel Cladding (Anode) - Fe-Al alloys Lifetime Limitations

4. Lifetime Limitations (SS 316)  Ni  Cr

5. SS 316 (After 350 hr of testing) Lifetime Limitations (SS 316)

6. Objective  To find a candidate that will has better corrosion resistance than the state of art current collector  To characterize the performance of a titanium alloy (Ti77.5/Mo12/Zr 4.5/Sn 4.5) with different surface treatments  Heat Treatment  Cobalt platting on the surface

7. Experimental  Heat treatment was performed in order to increase the thickness and form a more uniform protective corrosion layer  Kept at 400 ºC in 99 % N 2 & 1% O 2 atmosphere for 62 hr  Co plating was performed to reduce the possible dissolution of components and to improve the conductivity of the oxide layer  Cobalt chloride and sodium citrate bath  1 mA/cm 2 for 2.5 hours at pH 9.5

8. Materials Characterization Electrochemical Characterization: Linear Polarization-R P EIS Physical Characterizations: SEM – Microstructure Analysis XRD – Crystal Characterization AAS - Dissolution Studies

9. Results (Mo Dissolution) Dissolution of Mo from Titanium alloy at 650 o C  Heat Treated Ti Alloy  Bare Ti Alloy  Cobalt Coated Ti Alloy

10. Cobalt coated Titanium Alloy (Before testing) Results (SEM-Micrographs)

11. Bare Titanium Alloy (After 350 hr of testing) Results (SEM-Micrographs)

12. Heat Treated Titanium Alloy (After 350 hr of testing) Results (SEM-Micrographs)

13. Cobalt Coated Titanium Alloy (After 350 hr of testing)

14. Results (XRD-Pattern after 350 hr testing) Li 2 TiO 3 – Lithium Titamium Oxide LiTiO 2 – Lithium Titamium Oxide Titanium Alloys (After 350 hr of testing)

15. Results (Impedance Behavior with Time) Bare Titanium Alloy

16. Results (Impedance Behavior with Time) Heat Treated Titanium Alloy

17. Results (Impedance Behavior with Time) Cobalt coated Titanium Alloy

18. Results (Impedance Behavior with Time) SS 316

19. Conclusions  Immersion test indicate a decrease in molybdenum dissolution in the case of Cobalt coated Ti alloy  Surface mainly consist of Titanium oxides  The polarization resistance for this alloy is significantly higher than state of art current collector  Cobalt coated titanium alloy gives the highest corrosion resistance

20. Financial sponsors - Dept of Energy, National Energy Technology Laboratory Acknowledgements