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FAMU-FSU College of Engineering
Department of Mechanical Engineering
EML 4930/5930
Spring 2007
Lab 3: PEM Fuel Cell Characterization
Prof. A. Krothapalli
Introduction
The majority of our electrical power is derived from the burning of fossil fuels.
During combustion, chemical potential energy in fuel is converted to thermal
energy. Using a heat engine, thermal energy is then converted into mechanical
energy. Because of the inefficiencies in each step of this process, the useful
electrical work output is much less than the chemical energy input.
In contrast, fuel cells convert chemical energy directly into electrical energy. In
this process, the electrons are transferred one at a time, thus resulting in less
irreversibility and therefore greater useful work output.
Objectives
In this lab you will gain hands-on experience in the operation and performance of
fuel cell power generators. You will characterize fuel cell performance by
generating polarization (V-I) and power curves. In addition, you will also calculate
the voltage, efficiency, and examine the effect of power output on cell efficiency.
The SERC Single Cell Fuel Cell
The fuel cell used in this experiment consists of the following components:
- Cathode endplate
- Anode endplate
- 2 rubber gaskets
- Collector plate
- Anode and cathode gas diffusion media (GDM)
- Membrane electrode assembly (MEA)
Gas Supply Requirements
To generate electricity with the SERC Single Fuel Cell, compressed hydrogen
and air will be used.
Air Supply Specifications
The air supply for the fuel cell must be clean and oil free. The cell needs to be
supplied with a flow rate of 0.5 to 1 standard liters per minute (slm). The cathode
side (air side) of the fuel cell is exposed to the atmosphere, therefore operating
just slightly above atmospheric pressure. The airflow must be sufficient to supply
the desired stoichiometric ratio of air, but not so great as to dry out the cell. To
help keep the cell from drying out, a humidifier is placed inline with the air supply.
In this experiment you will run the fuel cell with, and without a humidifier and
record the effects.
Hydrogen Supply Specifications
The hydrogen supply for the fuel cell must be of industrial grade (99.95% pure). It
needs to be supplied at a pressure of 1 pound per square inch gauge (psig), and
maintain a flow rate of no more than 0.1 slm. The hydrogen gas supply
manifold must be purged prior to connecting and operating the fuel cell.
The lab TA will perform this step.
.
Procedure
1. Connect voltmeters to a pair of brass bolts directly opposite one another.
(Failure to do so, i.e.- tapping non-paired brass bolts, will result in different
voltage readings due to uneven current distribution.)
2. Verify that the airflow from the air supply is approximately 500 standard cubic
centimeters (sccm).
3. Purge the hydrogen manifold and set the hydrogen delivery pressure to 1 0.5
psig.
* Steps 1 through 3 will be performed by the lab TA.
4. With no humidifier connected to the air supply, record the open circuit voltage
of the fuel cell and the temperature. (If voltage is less than 750 mV, step three
needs be repeated.)
5. Connect the resistive load in line with voltmeter, beginning with the highest
resistance (5 Ω). Record the temperature, voltage and current.
6. Repeat step 5 for remaining resistance loads.
7. Connect the humidifier to the air supply and repeat steps 4 (If voltage is less
than 750 mV, step three needs be repeated), 5 and 6.
8. Repeat steps 4 through 6 two more times with humidification. (Gives you three
polarization curves)
9. Remove load and close gas supply valves.
Analysis
1. Plot the polarization curves. What do these curves show you?
2. Plot the voltage and power vs current.
3. What trend does the data describe (are the voltages increasing or decreasing
with respect to current) and why?
4. At what voltage does the maximum power point occur?
5. Describe and explain any discrepancies between the polarization curves.
6. Calculate the efficiency at each data point on the polarization plot.
7. Plot power output vs efficiency.
8. What are the trade-offs between power and efficiency?
9. Where do you think the best operating curve is? Might it vary on application?
10. How is the efficiency of the system affected as the temperature increases?