Other Fuel Cell Technology Options Flashcards
1
Q
High Temperature Polymer Electrolyte Fuel Cells - Quick Facts
A
- Challenges:
- durability limited due to high corrosion rates at these temperatures
- limited power densities observed
- limitations of membranes - Membrane made of phosphoric acid- doped Polybenzimidazole PA-PBI
2
Q
HT PEFC - Electrolyte
A
- main difference to standar PEFC
- instead of sulfonated membranes, other proton exchange membranes (PEMs) withstanding higher T operation are employed
- PA/PBI (phosphoric acid- doped Polybenzimidazole)
- ion pair membranes
- challenges
- PA-PBI: low stability at low T due to acid leaching -> impacts other components
- phosphate-based ion pairs: poisoning of catalysts due to phosphate anions > slows down ORR
- general: thin (but stable) HT-membranes to decrease ohmic losses over electrolyte
3
Q
HT-PEFC Advantages over standard PEFC
A
- membrane conductivity without humidification -> no water management needed
- higher operating T -> easier thermal management
- overall potential for reduction of BoP (all components except stack itself) weight
- higher CO tolerance of catalyst at higher T
4
Q
HT-PEFC Disadvantages over standard PEFC
A
- lower electrode power density
- component corrosion due to HT & PA
- limited durability
- limited conductivity of coatings
- limited membrane stability -> PA leaching when liquid water is present (cold start)
5
Q
Recent developments of HT-PEFCs
A
- improved acid retention
- improved performance in kinetic regime (less catalyst poisoning)
- lightweight BP & sealants; don’t corrode in acidic environment at elevated T
- enhanced T flexibility
6
Q
Proton Conducting Ceramic Fuel Cell - Quick Facts
A
- challenges
- high mass/ion-transport associated resistances within cell -> limited performance - membrane made of Proton Conducting Ceramic
7
Q
PCFC - Electrolyte
A
- main difference to SOFC: electrolyte & ion conducted
- proton conducting ceramics
- ion conductivity reaches technically usable values at temperatures lower than in the SOFC (start at 400°C)
- materials
- perovskites
- (fluorite-structured) oxides
8
Q
PCFC Advantages over standard SOFC
A
- lower operating T
- enables wider material choice for sealing, interconnecting
- reduces thermally induced strain & corrosion
- potential for improved lifetimes
9
Q
PCFC Disadvantages over standard SOFC
A
- actual cell performances < 550 °C currently limited
- still at low technology readiness level
10
Q
Recent developments of PCFC
A
- electrolyte -> improved conductivity; special focus on temperatures < 400°C
- cathode materials for higher electrode power density
- fabrication/manufacturing strategies for
- larger cell areas
- thin, but robust layers
11
Q
More Fuel Cells
A
- number of other fuel cell types have been developed
- differ in:
- Electrolyte/ion transport
- Fuel
- Operating Conditions (p,T)
- Cell Structure & materials
12
Q
Other Types
A
- Alkaline Fuel Cells
- liquid alkaline electrolyte
- Phosphoric Acid Fuel Cell
- liquid, phosphoric acid used as electrolyte
- Molten Carbonate Fuel Cell
- molten carbonate salts are used as electrolyte (6:4 mixture of lithium & potassium)
- Direct Methanol Fuel Cell
- struct
13
Q
Take Away Messages F)
A
- more T-stable proton-conductive membranes give opportunity to increase PEFCs operating T above 100 (- ~220°C)
- current cell performance inferior to PEFC
- advantages when it comes to thermal & water management - not only oxygen conducting, but also proton conducting ceramics exist -> can be used as electrolytes in “PCFCs”
- enable lower T than standard SOFC electrolytes facilitating material choices & reducing thermomechanical degradation
- at limited development level - number of other FC technology options exist with limited relevance to high power mobile applications
- fuel cell types differ in a number of parameters among them:
- electrolyte/ion transported
- fuel (flexibility)
- operating conditions (p,T..)
- cell structure & materials
