physics 470 lecture hydrogen fuel cells may 9, 2012 1
TRANSCRIPT
4
Features of a fuel cell
Sir William Grove invented the fuel cell in 1839
Hydrogen gas is fed to the negative terminal (the anode)
A catalyst helps the hydrogen to split, sending its electrons through an external circuit and the protons through an electrolyte
22H 4H 4e
5
Features of a fuel cell
Oxygen combines with the electrons at the positive terminal (the cathode) and protons to form water
The overall reaction combines hydrogen
and oxygen to produce electricity and water.
2 2O 4 4H 2H Oe
2 2 22H O 2H O
6
The proton exchange membrane fuel cell
Has a high power density and low operating temperature
The electrolyte is a specially treated polymer (chemically related to Teflon) that conducts only positive ions
The membrane must be hydrated (7 water molecules for every proton conducted!)
The membrane is “poisoned” by carbon monoxide
7
The proton exchange membrane fuel cell
The anode-membrane-cathode assemblies are stacked for higher voltage
10
Other types of fuel cells
Phosphoric Acid Molten Carbonate Solid Oxide Alkali See comparison chart from the
Department of Energy
12
Fuel cell problems
PEM cells: Hydration of the membrane requires careful water control and/or pressurization (adds weight, complexity). New membranes such as PBI may require less water.
For all fuel cells, drawing large currents reduces performance
13
Fuel cell losses
Ohm’s Law Applet
0V I R E
14
Which of the following statements is FALSE?
A. Catalysts help fuel cells increase the gas transport rate to the electrodes.
B. Fuel cells operate on the chemical reaction that combines hydrogen and oxygen.
C. Fuel cells are like a battery with a continuous supply of chemical reactants.
D. The only outputs of a fuel cell are water and electrical energy.
15
Which of the following statements is FALSE?
A. Catalysts help fuel cells increase the gas transport rate to the electrodes.
B. Fuel cells operate on the chemical reaction that combines hydrogen and oxygen.
C. Fuel cells are like a battery with a continuous supply of chemical reactants.
D. The only outputs of a fuel cell are water and electrical energy.
16
Suppose a fuel cell has an internal resis-tance of 0.025 . What is the output voltage when the ideal voltage is 12.0 V and the current is 30 A ?
A. 0.30 V
B. 0.75 V
C. 9.00 V
D. 11.25 V
17
Suppose a fuel cell has an internal resis-tance of 0.025 . What is the output voltage when the ideal voltage is 12.0 V and the current is 30 A ?
A. 0.30 V
B. 0.75 V
C. 9.00 V
D. 11.25 V
30A 0.025
12V 0.75V
11.25 V
12V
V
V
IR
18Suppose a fuel cell has an internal resis-tance of 0.025 . What fraction of the power is lost when the ideal voltage is 12.0 V and the current is 30 A ?
A. 2.5%
B. 3.6%
C. 6.25%
D. 12.0%
19Suppose a fuel cell has an internal resis-tance of 0.025 . What fraction of the power is lost when the ideal voltage is 12.0 V and the current is 30 A ?
A. 2.5%
B. 3.6%
C. 6.25%
D. 12.0%
2loss
2
loss
30A 0.025
22.5 W
22.5 W% loss
12V 30A
22.5 W100 6.25%
360 W
P I R
P
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Stationary Power Fuel Cells
Fuel Cell power plant, Santa Rita Jail, Dublin, CA
Biogas-powered fuel cell power plant, Sierra Nevada Brewing Co, Chico, CA
200 kW fuel cell, Central Park, NY police station
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Fuel Cell-Powered Zero Emission Vehicles
Ford Focus FC5 Fuel Cell Car
Hyundai FC Tucson
Honda FCX Clarity
Thor UTC Bus
Several other fuel cell cars in this 2008 article. More links at fueleconomy.gov.
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Fuel cell airplane
Boeing fuel cell aircraft first flight: April 3, 2008. It used a battery to assist the takeoff.
DLR Antares, the world’s first fuel-cell-only aircraft, takes off July 7, 2009 in Hamburg, Germany.