17 Nov08 Jorge Frade

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17 Nov08 Jorge Frade

  1. 1. Guidelines for materials selection and optimization in electrochemical conversion of fuels J.R.Frade University of Aveiro, Portugal Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008
  2. 2. Fuel cells Clean; High  Hydrocarbons Partial oxidation or Reforming e.g. CH 4 +1/2O 2  CO+2H 2 Electricity Chemicals Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008 Purification H 2
  3. 3. <ul><li>Effects of fuel/air atmospheres on cell materials </li></ul><ul><li>Redox behaviour </li></ul><ul><li>Stability limits under reducing conditions </li></ul><ul><li>Structural changes </li></ul><ul><li>Effects on transport properties, etc. </li></ul><ul><li>Effects on carbon deposition </li></ul><ul><li>Effects of contaminants (S-tolerance) etc.? </li></ul><ul><li>Thermochemical or thermomechanical failure </li></ul><ul><li>… </li></ul><ul><li>Interactions between cell materials </li></ul><ul><li>Processing </li></ul><ul><li>Operation </li></ul><ul><li>Maintenance, thermal cycling, etc. </li></ul>Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008
  4. 4. Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008 Reducing cnditions imposed by H 2 2H 2 + O 2  2H 2 O; Po 2 = (pH 2 O/pH 2 ) 2 exp(-  G/RT)
  5. 5. Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008 Reducing cnditions imposed by CH 4 , ...
  6. 6. Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008 Guidelines for redox tolerance of metallic electrocatalysts in H 2 atmospheres
  7. 7. Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008 Stability limits of SOFC cathode materials and catalysts under reducing conditions 2LaMnO 3  La 2 O 3 + 2MnO + 1/2O 2 2LaCoO 3  La 2 CoO 4 + CoO + 1/2O 2 ...
  8. 8. Structural changes and property degradation under reducing conditions LSMCT2 = (La 0.55 Sr 0.45 ) 0.95 Mn 0.5 Cr 0.3 Ti 0.2 O 3-δ ; LSMCT4 = (La 0.35 Sr 0.65 ) 0.95 Mn 0.5 Cr 0.1 Ti 0.4 O 3-δ ... Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008
  9. 9. Stability range estimated from sudden changes in conductivity and Seebeck coefficient. Stability limits Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008
  10. 10. Typical dependence of ionic and electronic conductivity of CGO20 solid electrolytes Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008
  11. 11. Predictions of methane conversion of ionic transport number and open cell voltage of a CGO-based cell Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008
  12. 12. Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008 Predictions of carbon deposition <ul><li>Strategies to minimize the risks of carbon deposition: </li></ul><ul><li>Steam reforming </li></ul><ul><li>Substitution of metallic catalysts by alternative catalysts </li></ul>
  13. 13. Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008 Better S-tolerance Poorer S-tolerance Is thermodynamics useful to predict Sulphur tolerance?
  14. 14. <ul><li>Thermal expansion mismatch </li></ul><ul><li>in a thin La 10 Si 5 AlO 26+x electrolyte layer on a thick LSMCT substrate, with firing at 1250ºC </li></ul><ul><li> L/L o =  T </li></ul><ul><li> E/(1-  ) </li></ul><ul><li>Typical for ceramics: E >100 GPa and  ≈ 0.3. </li></ul><ul><li>For  ≈ 2x10 -6 K -1 , and  T ≈ 1000ºC </li></ul><ul><li> ≈  0.002;  ≈ - 300 MPa (delamination!) </li></ul>Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008
  15. 15. Thermal expansion mismatch and ionic conductivity at 800ºC, in air Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008 Composition       I ;S/cm T, K E a (kJ/mol) La 2 Ni 0.8 Cu 0.2 O 4+  13.3 0.11* - - LSFC 12.9 0.01 1073-1223 206 LSM 11.7 1.3  10 -5 - - LSFC - 50 wt% CGO 12.6 0.04 1023-1223 82 LSM - 50 wt% CGO   11.7 0.03   1023-1223   104   La 10 Si 5 AlO 26.5   9.1 0.08   973-1223     56    
  16. 17. Chemical expansion under air/5%H 2 Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008  L/L o;  E/(1-  ) for  =0.005  200MPa (risks of fracture!)
  17. 18. EDS spectra showing cation diffusion accross the CGO buffer layer in apatite/CGO/ LSMCT4 and LSGM/CGO/LSMCT4 arrangements Interdiffusion between cell materials Economia de H 2 : Un desafio para Portugal, Vimeiro, Nov.17, 2008

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