What is the temperature range for low- and high-temperature fuel cells respectively?
Low: 60-200°C
High: 600-1000°C
Provide an overview of the type of electrolyte, what ion the electrolyte transports, theoperating temperature, type of catalyst and fuel for PEM, alkaline and SOFC fuelcells, respectively
What are the anode reactions, the cathode reactions and the total reactions for alkaline and SOFC fuel cells
Alkaline:
Anode: 2H2 + 4OH- -> 4H20 + 4e-
2
Kathode: O2 + 4e- +2H2O -> 4 OH-
2H2 +O2 -> 2H2O
SOFC: (Hydrogen fuel)
Anode: 2H2 + 2O2- -> 2H2O+
Kathode: O2 + 4e- -> 2O2-
Total: 2H2 + O2 -> 2H2O
(carbon fuel)
Anode: 2CO + 2O2- -> 2CO2 + 4e-
total: 2CO + O2 -> 2 CO2
What are the advantages of alkaline fuel cells compared to PEM and SOFC?
alkine pros:
• Lower cost of components
• low temperature
• low startig time due to low temperature
• Precious metal for catalyst is not required
• Activation overpotential (cathode) is lower for AFC → not nesccesary with precious metal catalyst for the cathode
• Electrolyte can easily be replaced PEM efficiency: 50-60 % (LHV), AFC 70 % (LHV)
SOFC pros:
• Ni withstands more sulfur than precious metal, withstands CO
• High temperature leads to faster reactions
• (activation overpotential is reduced)
• Anode can be used as a catalyst for internal reforming→ SOFC can use many typar fuels (methane, CO, methanol,ammonia)In hybrid systems, such as PEM combined with SOFC and steam reforming, one can achieve high overall efficiency (~ 80-85 %*)
What are the main differences between SOFC and the other two types of fuel cells?
the high temperature
the electrolyte materials
Fuel Compatibility:
SOFCs: Solid Oxide Fuel Cells can operate with a variety of fuels, including hydrogen, natural gas, and even certain liquid fuels.
PEMFCs: Polymer Electrolyte Membrane Fuel Cells primarily use pure hydrogen as a fuel.
AFCs: Alkaline Fuel Cells typically use pure hydrogen or solutions of alkali metal hydroxides as fuels.
What can we do to mitigate issues with CO2 in AFC?
-Use oxygen
- Purify air
- Recycle electrolyte and remove carbonate precipitate
- Use AEM
What are the pros and cons of SOFC fuel cells?
Advantages of SOFC:
• Anode can be used as a catalyst for internal reforming→ SOFC can use many typar fuels (methane, CO, methanol,ammonia)In hybrid systems, such as PEM combined with SOFC and steam reforming, onecan achieve high overall efficiency (~ 80-85 %*)
Diadvantages with SOFC:
• High temperature places demands on material selection and seals
• Long start-up time (due to high temperature). Should be run for extended periods withoutstart/stop.
• Short service life. Some of the largest fuel cell producers have given up on SOFC.
• High weight and require large area due to BOP (balance of plant)
Describe the three phase boundary in SOFC. How can its structure be improved?
The three phase boundary in SOFC. Its structure may be improved by extending the three phase boundary.
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