1. Integrated Micropower Generator Sossina M. Haile, Zongping Shao, Chan Kwak, Peter Babilo California Institute of Technology, Materials Science Micro- SOFC Swiss Roll Combustor + High Efficiency Thermal Management

2. Integrated MicroPower GeneratorReview, Oct 18, 2002 Caltech Materials Science Tasks 1. Swiss Roll Optimization 2. Electrolyte Selection 3. Fuel Selection – with all others 4. (a) Anode Development - NWU 4. (b) Cathode Development 5. SCFC Model Development 6. Catalyst Optimization – with USC [later] 7. Stand Alone Swiss Roll Fabrication & Characterization 8. SCFC Fabrication – LBNL 9. First generation IMG Fabrication & Characterization  10. Evaluation and Redesign  11. Second Generation IMG Fab. & Characterization 

3. Integrated MicroPower GeneratorReview, Oct 18, 2002 SCFC Electrolytes Oxygen Ion Conductors Doped CeO 2 (La,Sr)(Ga,Mg)O 3 Proton Conductors Doped Ba(Ce,Zr)O 3 Doped SrCeO 3 Anode CH 4 + ½ O 2  CO + 2H 2 H 2 + O =  H 2 O + 2e - CO + O =  CO 2 + 2e - Cathode ½ O 2 + 2e -  O = Chemical and Electrochemical Reactions Electrolytes for 300-600C: 10 -2 S/cm at 500C, t ion ~ 1 Anode CH 4 + ½ O 2  CO + 2H 2 H 2 O + CO  CO 2 + H 2 H 2  2H + + 2e - Cathode ½ O 2 + 2H + + 2e -  H 2 O H 2 O recirculation required with proton conductor

4. Integrated MicroPower GeneratorReview, Oct 18, 2002 Electrolyte and Fuel Selection Electrolyte Oxygen ion conductors –Most literature demonstration based on such electrolytes –Our initial investigations of proton conducting electrolytes were not promising Specific choice: doped CeO 2 –Samaria doped (SDC) –Excellent conductivity –Good chemical stability –Low electronic conductivity –Experience with this material Fuel Choices –Methane, ethane –Propane, butane –Alcohols Selection: Propane –Demonstrated in SCFCs –Only ethane gives slightly higher power –Acohols very poor –Compatible with micro- aspirator –Good vapor pressure even at low temperature

5. Integrated MicroPower GeneratorReview, Oct 18, 2002 Electrode Materials and Catalytic Activity Cathode –Sr 0.5 Sm 0.5 CoO 3 (SSC) –SSC + SDC + Pt –SDC + Pt –La 0.2 Sr 0.8 Co 0.6 Fe 0.4 O 3 (LSCF) consider as catalyst instead Anode –Ni + SDC Characterization –Catalytic activity –X-ray diffraction (stability) –Fuel cell performane C 3 H 8 + O 2 + He or Ar GC analysis Thermocouple Catalyst dispersed in inert materials Catalytic Reactor furnace

6. Integrated MicroPower GeneratorReview, Oct 18, 2002 Gas Phase Reactivity Propane: 10ml/min, Oxygen: 50ml/min, Helium: 200ml/min Empty reactorSilica granules, 1.5 g = inert dispersant C 3 H 8 :O 2 = 1:5; Stoichiometric combustion ratio Note: C 3 H 8 :O 2 = 1:1.5 is stoichiometric for partial oxidation

7. Integrated MicroPower GeneratorReview, Oct 18, 2002 Catalytic Activity of Ni-SDC Anode Powder Ni-SDC 0.2g C 3 H 8 : 2 ml/min; O 2 : 3ml/min; He 12 ml/min C 3 H 8 :O 2 = 1:1.5C 3 H 8 :O 2 = 1:3 Ni-SDC 0.2g C 3 H 8 : 2 ml/min; O 2 : 6ml/min; He 24 ml/min [CO]  as T , 35 – 45% yield at 500C; higher yield at lower O 2

8. Integrated MicroPower GeneratorReview, Oct 18, 2002 XRD Characterization of Anode Powder Ni-SDC after catalytic reactor testing –Ni is not reoxidized Pretreatment of the anode before fuel cell test (650C) –C 3 H 8 & O 2 cannot reduce NiO –Pure C 3 H 8  heavy coking – Brief H 2 exposure

9. Integrated MicroPower GeneratorReview, Oct 18, 2002 Catalytic Activity of (SSC) Cathode Powder 1:3 Reactants concentrated Reactant diluted

10. Integrated MicroPower GeneratorReview, Oct 18, 2002 Catalytic Activity of SSC Cathode Powder Reactants concentratedReactants diluted 1:5 1:1.5 1:5 Reactants concentratedReactants diluted 1:1.5

11. Integrated MicroPower GeneratorReview, Oct 18, 2002 Characteristics of SSC Cathode Powder Some combustion at 350  C Higher conversion as O 2  Erratic dilution dependence Higher conversion as T  Not suitable at T >600  C Chemical stability by X-ray diffraction SSC is stable under SCFC conditions (after catalytic reactor testing) C 3 :O 2 diluteconc.diluteconc. 1:5179.44640 1:313143980 1:1.511103130 Propane conversion % 500C600C

12. Integrated MicroPower GeneratorReview, Oct 18, 2002 Fuel Cell Performance Measurements C3H8C3H8 O2O2 He Keithley 2420 Thermocouple Furnace Fuel cell Anode Cathode Electrolyte GC analysis Anode Electrolyte Bi-layer double dry press Co-sinter Reduce Bi-Layer Cathode Tri-layer paint Co-sinter Cell Fabrication Test Station Cells examined –[1] Ni-SDC | SDC | SSC –[2] Ni-SDC | SDC | Pt-SDC –[3] Ni-SDC | SDC | SSC-Pt-SDC –1500m | 40-60m | 50m H2H2 Ar

13. Integrated MicroPower GeneratorReview, Oct 18, 2002 SEM images of the double pressed cells SDC NiO-SDC SSC SDC 60 wt% NiO 20-40% porous 37 m 10 m 3 m

14. Integrated MicroPower GeneratorReview, Oct 18, 2002 [1] Ni-SDCSDCSSC. OCV depends on O 2 :C 3 H 8 –Optimum is 3:1 Peak power density –At 600C, 48 mW/cm 2 –At 400C, 28 mW/cm 2 600C Open circuit voltagePolarization curves O 2 :C 3 = 3:1 Hibino: 450C, 41 ml/min C 3 ; 54 ml/min O 2 ; 205 ml/min N 2, 1.5mm SDC  240 mW/cm 2 O 2 :C 3 H 8 = 1.3:1 !! C 3 : 10 ml/min He: 240 ml/min

15. Integrated MicroPower GeneratorReview, Oct 18, 2002 Cell Design Challenge Ni+SDC SSC SDC C 3 H 8, CO, H 2, O 2, H 2 O Inlet gases can sweep partial oxidation by- products to cathode side, lower cell voltage Partial oxidation occurs on ‘edge’ of anode C 3 H 8 + O 2 Ni+SDC SSC SDC Coke formed primarily on leading edge of anode C 3 H 8 + H 2 O  CO + H 2 + H 2 O + CO 2

16. Integrated MicroPower GeneratorReview, Oct 18, 2002 [2] Ni-SDCSDCPt-SDC O 2 :C 3 = 3:1, reactants concentrated less concentrated 475C 525C 500C 600C

17. Integrated MicroPower GeneratorReview, Oct 18, 2002 Strong impact of dilution on fuel cell performance Even without SSC, Pt is better cathode than Ni Optimal operation temperature ~550 – 600C  [2] Ni-SDCSDCPt-SDC Less concentrated Reactants concentrated 625  C 475  C

18. Integrated MicroPower GeneratorReview, Oct 18, 2002 [2] Ni-SDCSDCPt-SDC Outlet gas composition at open circuit C 3 H 8 : 10ml/min, O 2 : 30ml/min, He: 120ml/min (concentrated) At T > 625C –insufficient oxygen at cathode –> 90% converstion At T < 475C –insufficient anode activity

19. Integrated MicroPower GeneratorReview, Oct 18, 2002 AB C [3] Ni-SDCSDCSSC-Pt-SDC A and C: C 3 H 8 : 10 ml/min, O 2 : 30 ml/min, He:120 ml/min, B: He: 240 ml/min Best power density : 68 mW/cm 2 SSC-Pt-SDC > SSC, SDC-Pt Stability depends on quality of (cathode) processing O 2 :C 3 = 3:1, reactants concentrated O 2 :C 3 = 3:1, less concentrated

20. Integrated MicroPower GeneratorReview, Oct 18, 2002 Summary All fuel cells function only in a small temperature range (400-650C), otherwise OCV is nearly zero O 2 :C 3 H 8 ratio had significant effect on the fuel cell performance –Optimal oxygen to propane ratio = 3:1 Power density varied from several to ~ 70mW/cm 2 –Maximum at 600C (initial) for Ni-SDC|SDC|SSC-Pt-SDC) –SSC-Pt-SDC cathode preferable to SSC or SDC-Pt Carbon coking occurred only on the leading anode edge Fuel cell power stability depends on fabrication –Occasional short circuit through electrolyte –Delamination of cathode  colloidal deposition, painting

21. Integrated MicroPower GeneratorReview, Oct 18, 2002 Where to go from here Modification of Ni + SDC anode with Rh, Pd, Ru etc. –Highly active catalysts for partial oxidation –Initial results with Rh very promising –Enable reduced temperature operation, ~ 400C –Task for Northwestern Design modifications –Prevent/limit flow of partial oxidation products to cathode –Together with Goodwin, LBNL group Cathode development –Active oxygen reduction catalyst –Inactive towards propane –Initial results with Bi 2 V 0.9 Cu 0.1 O 6- + Ag promising