文档介绍：Lecture #8
Fuel Cells Revisited
Fuel Cells
Chemical Rxn Electricity:
Net: H2 + 1/2O2 = H2O
A: H2 - 2e- = 2H+ OV
C: 2H+ + 2e- + 1/2O2 = H2O V
Desired voltage achieved by stacking cells (in series)
Fuel reformer
Natural gas, alcohol, hydrocarbons H2 + CO
anode
cathode
H2 (fuel)
H2O
O2 (oxidant)
Separator (porous)
Load
Choice of Fuels
Hydrogen
Hydrazine
toxic
expensive
Natural gas/petroleum
catalytic stream reforming (900oC)
remove CO by shift reaction
How Different from Battery?
Battery internal supply of fuel and oxidizer
Significance: must be replenished/recharged
EX:
Alkaline cell (primary battery)
discharge and discard
Car battery (primary and secondary)
discharge (primary) and recharge (secondary)
Fuel Cells - Why?
No moving parts
Long lifetime/reliability
High efficiency (40 - 70%)
No Carnot cycle limitations (efficiency independent of size)
heat available for cogeneration
Low emissions
PAFC: < 1 ppm Nox, 4 ppm CO, < 1 ppm non-methane anic gases
Fuel Cells - Why (cont’d)
Quiet
No moving parts
Long device petitive price
1 g Pt/1 kW cell = $20-$50/kW)
Relatively low weight and small size
1 kg/kW
Efficiency
Heat engine
Second Law - Carnot cycle
Top efficiency 40%
Higher temperatures, higher efficiency
Fuel Cell
No such limitations
Fuel Cells - Why Not?
High initial cost - difficult to enter market
Technology unfamiliar to power industry
No existing infrastructure
Regulatory
History
1839 Sir William Grove
Electrolysis of water
“Father” of the Fuel Cell
1889 Ludwig Mond and Charles Langer
“fuel cell”
First practical device based on Pt
1932 Francis Bacon
Alkali=electrolyte
Nickel=electrodes
Hart, .; Womack, . Fuel Cells: Theory and Application Chapman and Hall: London, 1967.
History (Cont’d)
1912-1942 Bauer
Molten alkali carbonate electrolyte, solid C anode @ 10000C
1945 Davtyan
Mixed carbonates and oxides with sand separator
work basis for post-war fuel cell work
1950’s NASA