Hydrogen Fuel Cells
Heliocentris: Science education through
fuel cells 1
Trends in the Use of Fuel
Wood
Coal
Oil
Natural
Gas
Hydrogen
Percentage of hydrogen content in fuel
19th century:
steam engine
20th century:
internal combustion engine
21st century: fuel cells
The History of Fuel Cells
Electrolyser
Grove’s Gas Battery
(first fuel cell, 1839)
(after Larminie and Dicks, 2000)
Photo courtesy of University of Cambridge
Bacon’s laboratory in 1955
Photo courtesy of NASA
NASA Space Shuttle fuel cell
Applications for Fuel Cells
Transportation vehicles
Photo courtesy of DaimlerChrysler
NECAR 5
ApplicationsDistributed
for Fuel Cells
power stations
Photo courtesy of Ballard Power Systems
250 kW distributed cogeneration power plant
Applications for Fuel
Cells
Home
power
Photo courtesy of Plug Power
7 kW home cogeneration power plant
Portable
power
Applications for Fuel
Cells
50 W portable fuel cell with metal hydride storage
The Science of Fuel Cells
Alkaline
(AFC)
Polymer
Polymer
Electrolyte
Electrolyte
Membrane
Membrane
(PEMFC)
(PEMFC)
Phosphoric
Acid
(PAFC)
Types of
Fuel Cells
Molten Carbonate
(MCFC)
DirectMethanol
Methanol
Direct
(DMFC)
(DMFC)
SolidOxide
Oxide
Solid
(SOFC)
(SOFC)
PEM Fuel Cell Electrochemical Reactions
Anode:
H2
2H+ + 2e- (oxidation)
Cathode:
1/2 O2 + 2e- + 2H+
H2O (l) (reduction)
Overall Reaction:
H2 + 1/2 02
H2O (l)
ΔH = - 285.8 kJ/mole
A Simple PEM Fuel Cell
Hydrogen + Oxygen  Electricity + Water
Water
Membrane Electrode Assembly (MEA)
Catalysis
Oxidation
4e -
Tran spo rt
H2
Platinumcatalyst
2H2
4H+
Resistance
Naf ion
O2
H2 O
Anode
H+
PlatinumKcatalyst
Cathode
Polymer
electrolyte
(i.e. Nafion)
Reduction
4e -
O2
N afion
Carbon cloth
Carbon cloth
4H+
2H2 O
N afion
2
Polymer Electrolyte Membrane
Polytetrafluoroethylene (PTFE) chains
Water collects
around the
clusters of
hydrophylic
sulphonate
side chains
Sulphonic Acid
50-175 microns
(2-7 sheets of paper)
(after Larminie and Dicks, 2000)
Thermodynamics of PEM Fuel Cells
Change in enthalpy (ΔH)
= - 285,800 J/mole
Gibb’s free energy (ΔG)
= ΔH - TΔS
ΔG at 25° C:
= - 285,800 J - (298K)(-163.2J/K)
= - 237,200 J
Ideal cell voltage (Δ E)
ΔE at 25º C
= - ΔG/(nF)
= - [-237,200 J/((2)(96,487 J/V))]
= 1.23 V
ΔG at operating temperature (80º C):
= - 285,800 J - (353K)(163.2 J/K)
= - 228,200 J
ΔE at 80º C
= - [-228,200 J/((2)(96,487 J/V))]
= 1.18 V
Characteristic Curve
Power Curve
activation losses
+ internal currents
1.2
1
0.8
P
1.5
0.4
1
0.2
0.5
0
0
1
2
3
4
x
2
concentration
losses
V 0.6
0
MPP
2.5
ohmic
losses
0
1
2
I
Factors Affecting Curve:
• activation losses
• fuel crossover and
internal currents
• ohmic losses
• mass transport or
concentration losses
3
4
I
Max Power Point (MPP):
dP
0
dI
5
Hydrogen Storage
56 L
14 L
9.9 L
Compressed gas
(200 bar)
Liquid hydrogen
Liters to store 1 kg hydrogen
MgH2
metal hydride
Hydrogen: Energy Forever
H2
Fuel tank
Reformer
Hydrogen bottles
H2
H2
Algae
H2
Hydrogen bottles
Electrolyser
Solar panel
H2
H2
Hydrogen bottles
Renewable Energy Sources
Oxygen
H2
Storage
Solar Cell
Oxygen
Fuel
Cell
Electrolyzer
Wind
Water
Water
Micro hydro
As long as the sun shines, the wind blows, or the rivers flow, there
can be clean, safe, and sustainable electrical power, where and
when required, with a solar hydrogen energy system
The Benefits of Fuel Cells
Clean
Modular
Quiet
Benefits of
Fuel Cells
Safe
Sustainable
Efficient
Our Fragile Planet.
We have the responsibility to mind the planet so
that the extraordinary natural beauty of the Earth
is preserved for generations to come.
Heliocentris: Science education through
fuel cells 22
Photo courtesy of NASA
Presentation courtesy of Heliocentris