Direct Ethanol Fuel Cells Def Cs


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Renewable energy, Ethanol electrooxidation, anode and cathod catalyst

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Direct Ethanol Fuel Cells Def Cs

  1. 1. Direct Ethanol Fuel Cells DEFCs: Review A. M. Sheikh
  2. 2. Abstract• DEFCs: alternative energy sources recently• Emreging DEFC technology has challenges• Many improvements have been made.• Yet, there are deep needs for addressing current challenges.
  3. 3. Introduction• Direct Alcohol Fuel Cells DAFCs are from the Alkaline Fuel Cells AFCs family• AFCs give higher energy density than PEMFC• Non-noble metal catalysts can be used in AFCs• DAFCs: (methano, ethanol, ethelyne glycol, 2- propanol)• DAFCs use both alkaline (electrooxidation ) and acitic (CO2 , performenace ) media.
  4. 4. DAFCs challenges• Poor peformenace electrocatalysts (Low T)• Anode surface poisoning (intermediates CO)• Some cells: acidic & alkaline media(1.14 V)
  5. 5. DMFC vs DEFC• Sluggish reactions kinetics for methanol oxid.• Methanol crossover through nafion membrane• Anode poisoning by CO• Ethanol: less toxic• Ethanol: higher energy density• Ethanol: agriculture biomass products• Ethanol: lower crossover rate
  6. 6. Direct ethanol fuel cell
  7. 7. DEFC challenges- crossover• Crossover: the permeation of ethanol from the anode through the electrolyte membrane to the cathode.• Crossover effect: cathode potential and cathode depolarization, reducing cell efficiency• Crossover occurs when acetic acid, CO 2 &acetaldehyde (%) > O2 (%) in cathode.
  8. 8. Effect of current density on the crossover rate at differenttemperatures and different ethanol concentrations
  9. 9. The plot of ethanolcrossover rateversus ethanolconcentration withdifferenttemperature anddifferent heliumflow rate
  10. 10. Challenges= slow kinetics• Its deduced the best DEFC performenace temperature is 90 C
  11. 11. Challenges = heat management• Temperature = performenace• Ethanol conversion with current & T The effect of operating discharge cell current and temperature on ethanol conversion
  12. 12. Challenges= water management• Cathode reaction: the major water source & ethanol dilution in the anode• Water can generate cell resistence (performenace) (management needed)• water can be removed through the cathode or transferred to the anode & eleminated• Water uptake from polymer membrane: (T, disscoiation, counter ions type, elasticity, hydrophobicity
  13. 13. Solutions thought • contineous flow field • Hydrophibic filters • Cathode floodingTypical water distribution in alkaline DEFC
  14. 14. Challenges: durability & stability• According to MEA coditions• Some research: 60h concluding the catalysts aggolimeration and cathode flooding are the major causes of degredation• Ethanol is not giving the desirable performenace• Pd can replace PtRu catalyst• Breaking C-C bond is obstacle to form CO2
  15. 15. Challenges: fabrication & design
  16. 16. The cell componentsAnode Gas Difusion layer GDL, Anode catalystlayer, Electrolyte membrane, Cathode catalystlayer, & Cathode GDL Two alternative routes always used for (MEA) preparation: a) fixing the catalyst layer directly onto the membrane &b) the separate electrode method
  17. 17. Schematic presentation of the detailed electrode preparation procedures7/26/2012 (a) the conventional method (b) the decal transfer method 18
  18. 18. Good membrane should have:• High proton conductivity• Low electron conductivity• Resistant to oxidation• Low fuel crossover• Adequate mechanical, thermal & chemical stability• Good water water management
  19. 19. ElectrooxidationPathways ethanol in alkaline media Reaction pathways DEFC using Pt in acidic media
  20. 20. Cathode catalysts• Ag-W2 C, Pd, Pt-Ru• Pt-Co/C, Pt-Pd/C• At MEA foam layer of (Ni-Cr)Performance ranking of PtRuNi/C,PtSnNi/C, PtRu/C & PtSn/C in DEFC
  21. 21. DEFC applications
  22. 22. DEFC applications