Renewable energy, Ethanol electrooxidation, anode and cathod catalyst

1. Direct Ethanol Fuel Cells DEFCs:
Review
A. M. Sheikh
ahmad.elsheikh@hotmail.com

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. 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. DAFCs challenges
• Poor peformenace electrocatalysts (Low T)
• Anode surface poisoning (intermediates CO)
• Some cells: acidic & alkaline media(1.14 V)

6. 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

7. Direct ethanol fuel cell

8. 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.

9. Effect of current density on the crossover rate at different
temperatures and different ethanol concentrations

10. The plot of ethanol
crossover rate
versus ethanol
concentration with
different
temperature and
different helium
flow rate

11. Challenges= slow kinetics
• Its deduced the best DEFC
performenace temperature
is 90 C

12. Challenges = heat management
• Temperature = performenace
• Ethanol conversion with current & T
The effect of operating
discharge cell current and
temperature on ethanol
conversion

13. 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

14. Solutions thought
• contineous flow field
• Hydrophibic filters
• Cathode flooding
Typical water distribution in alkaline DEFC

15. 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

16. Challenges: fabrication & design

17. The cell components
Anode Gas Difusion layer GDL, Anode catalyst
layer, Electrolyte membrane, Cathode catalyst
layer, & Cathode GDL
Two alternative
routes always
used for (MEA)
preparation: a)
fixing the
catalyst layer
directly onto the
membrane &b)
the separate
electrode method

18. Schematic presentation of the detailed electrode preparation procedures
7/26/2012
(a) the conventional method (b) the decal transfer method
18

19. 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

20. Electrooxidation
Pathways ethanol in
alkaline media
Reaction pathways DEFC
using Pt in acidic media

21. 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

22. DEFC applications

23. DEFC applications