EXPERIMENT
7-Addtion
How Can We Use a Hydrogen Fuel
Cell to Generate Clean Energy and
Connect Chemistry to the Real
World?
INTRODUCTION
A Brief Summary
This new fuel cell lab has been developed to illuminate connections between chemical energy,
thermodynamics, electrolysis and a hydrogen based transportation economy. In this fuel cell lab, hydrogen
(H2) and oxygen (O2) gases will be generated by electrolysis and then be put into a fuel cell to power a
model car and a small cell phone vibrator. As shown in the equation below, electrolysis of water (H 2O)
requires an input of electrical energy to produce H2 and O2 whereas a hydrogen fuel cell converts the
chemical energy stored in H2 and O2 into electrical energy. Since O2 and H2 react to form H2O, hydrogen
fuel cells generate clean energy without any pollution to the environment.
In this lab, a fuel cell will be used to power small electric devices such as a model car or mini cell phone
vibrator and the net energy output as well as energy efficiency of hydrogen fuel cell will be determined.
You will learn how the fuel cell converts chemical energy directly into electrical energy, which can then be
converted to mechanical energy to do physical work. The aim of this experiment is to use fuel cell to help
you develop a tangible understanding of concepts introduced in the lecture, such as chemical and electrical
energy, electrochemistry, and thermodynamics.
In your current experiment 7, only electrolysis of water in a beaker is discussed. This new addition focuses
on the fuel cell which provides electric work. Before we start to discuss the experimental details, we
review several basic concepts in the following to help you to understand the experiment. More information
will be found in your prelab questions/answers on Mycourse website.
Electrochemistry and Hydrogen Fuel Cells
Electrochemistry, the study of interchange of chemical and electrical energy, primarily involves two
processes: the generation of an electric current from a chemical reaction and the opposite process, the use
of an electricity to produce chemical energy. A battery is a device for generating electricity from chemical
reaction; whereas an opposite device called electrolyzer can be utilized to generate chemicals from electric
current such as electrolysis of water to produce O2 and H2.
A fuel cell is a type of galvanic cells (batteries) where spontaneous chemical reactions that convert
chemical energy of a fuel (hydrogen, natural gas, methanol, gasoline, etc.) and an oxidant (air or oxygen)
into electric energy. There are many types of fuel cells. In this lab we will focus on the study of hydrogen
fuel cell that uses H2 as fuel and oxygen as an oxidant. Unlike a traditional battery that is a closed system,
fuel cell operates with a continuous flow of reactants (fuel and oxygen) through the cell whereas a
traditional battery eventually runs out of fuel or oxidants. In principle, a fuel cell does not run down or
The PEM “Reversible” Fuel Cell
There are many types of fuel cells out there to choose from but the one that can
demonstrate most of a fuel cell’s characteristics as well as be affordable, easy to use and
require recharging as long as fuel and an oxidizer are supplied while a battery’s current runs lower and
safetill
is itthe
PEM
reversible
cell. PEM can mean Proton Exchange Membrane or
lower
can
no longer
supplyfuel
electricity.
Polymer Electrolyte Membrane, take your pick, and both refer to the part that separates
the hydrogen
protons
andcells
electrons
electricity
1). demonstrate
The reversible
There
are many types
of fuel
out theretotoproduce
choose from
but the (Figure
one that can
most part
of a fuel
cell’s
characteristics
as well
as bean
affordable,
easy to
and safe
is the hydrogen
PEM “reversible”
fuel cell.
means
that it serves
as both
electrolyzer
foruse
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as Unlike
thewell
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in experiment
7, Adevice
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with this
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as
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to
separate
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hydrogen
protons
and
electrons
produce
rechargeable battery. The main difference is that the electrolyte is external andtodoes
not
electricity. The “reversible” means that it serves as both an electrolyzer (for electrolysis of water to
get used up in the process of generating [DC] electricity, and it can continue to generate
hydrogen and oxygen) and a fuel cell (that uses hydrogen and oxygen). You get the best of both worlds
electricity
as as
long
as hydrogen
and oxygen
available.
with
this device
it mimics
a rechargeable
battery.are
However,
the main difference is that the fuel is
externally supplied and does not get used up in the process of generating DC electricity, and such fuel cell
Acontinue
reversible
PEM fuel
cell operates
distinct
Electrolysis
can
to generate
electricity
as long in
as two
hydrogen
and modes
oxygen –are
available. Mode and Fuel
Cell Mode. There are also two chemical processes involved – oxidation and reduction.
A “reversible” PEM fuel cell operates in two distinct modes – Electrolysis Mode and Fuel Cell Mode.
There are also two chemical processes involved – oxidation and reduction.
Electrolysis Mode
( +)
( +)
(-)
(Anode)
Fuel Cell Mode
(Cathode)
Figure 1
Figure 2 – Electrolysis Mode
(-)
(Cathode)
(Anode)
Figure 2
Figure 3 – Fuel Cell Mode
In the Electrolysis Mode (Figure 1) water is introduced to both sides of the fuel cell where it is electrolyzed
into hydrogen at the cathode (negative) and oxygen at the anode (positive) by a small voltage less than 1.5
volts (called the water decomposition voltage). The water is oxidized into oxygen and hydrogen ions on
the anode and then hydrogen ions on the anode pass through the membrane to gain electrons to form
hydrogen at the cathode. Electrolysis of pure water requires excess energy in the form of over-potential to
overcome various activation barriers. Without the excess energy, the electrolysis of pure water occurs very
slowly if at all. This is in part due to the limited self-ionization of water because pure water has an
electrical conductivity about one millionth that of seawater. Nevertheless, electrolysis can be accomplished.
Copyright
and Volts
Magazine
May
2010electrolysis:
Page 2
The
following©
areNuts
the chemical
reactions
occurring
during
Electrolysis Mode Reactions
In the Fuel Cell Mode (Figure 2) the process is reversed along with the polarities of the anode and cathode.
As hydrogen flows into the fuel cell on the anode (negative), the hydrogen molecules lose electrons to form
hydrogen ions on the anode and then hydrogen ions pass through the membrane to the cathode where
oxygen molecules on the cathode (positive) gain electrons and combine with hydrogen ions to form water.
The electrons, which cannot pass through the membrane, flow from the anode to the cathode through an
external load such as a car motor or a mini cell-phone vibrator, which consumes the power generated by the
fuel cell. The overall electrochemical process of a fuel cell mode is called "reverse electrolysis," or the
opposite of electrolyzing water to form hydrogen and oxygen. Once again, here are the chemical reactions:
Fuel Cell Mode Reactions
Thermodynamics and Electrochemistry in Fuel Cells
(The related information can be found from Zumdahl, chapter 11.3)
Electric Work
Wel = -E q
(E is fuel cell voltage in Volts, q is charge or transferred electron quantity in Columbus),
Or Wel = -E n F
(n is transferred electron quantity in moles, F is Faraday’s constant)
Remember that the electric work is done by consuming H2 fuel. For each mole consumption of H2 fuel,
the transferred electron (n) is 2 moles.
Gibbs Free Energy
Based on thermodynamic laws, the maximum possible useful work obtainable from a fuel cell at constant
temperature and pressure is equal to the change in Gibbs free energy of electrochemical reaction, so
ΔG rxn = Wel max = - E n F (Wel is measureed at a maxium cell potential or an open circuit potential)
This equation relates the electrochemistry with thermodynamic parameter. So for each mole consumption
of H2 in fuel cell, we can determine the Gibbs free energy change by the electric work performed.
Efficiency of Fuel Cell
In hydrogen fuel cell, an overall reaction is that H2 and O2 are converted to H2O like in “combustion”.
However, unlike a true combustion reaction, the energy is not transferred to heat, but to electric energy.
Since the traditional method of measuring efficiency in combustion engines cannot be applied to a fuel cell,
the most useful way of determining efficiency is by comparing the work done by the fuel cell with the
energy released by the combustion of the fuel (the reaction enthalpy of an overall reaction):
η = | Wel / ΔH rxn |
The maximum fuel cell efficiency is ηmax = |Wel max / ΔH rxn | = |ΔG rxn / ΔH rxn |.
For combustion of each mole of H2 fuel under standard condition, the reaction enthalpy is known as
ΔH rxn = - 286 kJ/mol H2
Entropy Change
Fuel cell efficiency in providing electrical power supply is usually in the range of 35 to 55%, so difference
between the theoretical energy (-ΔH rxn) and actual electrical work (Wel or -ΔG rxn) would generate heat and
cause entropy increase of the fuel cell. By thermodynamic basics, we have
ΔH rxn = ΔG rxn + T ΔS rxn
Basic Concepts in Electrical Measurements
Ohm’s Law
I = E / R (I is current through the conductor in Amperes, E is potential in Volts,
R is the resistance of the conductor in units of ohms.)
Electrical Power
P = E ×I
(P is the electrical work per second, in unit of Watts)
PROCEDURE (WORK IN TEAMS)
Wear safety glasses at all times to protect eyes from injury. Although the fuel cell
car set is supposed to be very safe, follow the instructions and do not use the
materials for other purposes. When running the electric circuit, take care in
handling the vibrator and the car motor.
Materials
Fuel Cell Car Kit
Fuel cell
Special Equipment
Circuit board containing:
Car motor attached to the

Switch
car chassis with 4 wheels

Cell phone vibrator
2 graduated cylinders (H2 and O2)
2 inner chambers
 0.1  resistor
Wires
2 short tubing with red or black caps
Multimeter
2 long tubing
2 alligator clips
1 syringe
Battery Charger
NOTE: Be extremely careful when handling and connecting parts. Avoid damage of the fuel cell
due to the wrong connections (fuel cell is expensive). Use distilled water throughout the entire
experiment. Ask your TA check all connections before you turn on the charger and the fuel cell.
Points for the whole group will be taken off if the fuel cell is damaged.
This is a team collaboration experiment. Every member should participate and contribute equally to the
testing of the fuel cell. For example, student A may set up the preparation; student B watch the change of
gas volume and roughly record the time; student C control the battery charger and hydrolysis; student D
take the electric measurement.
Figure 3 below shows a photo of a fuel cell car with major parts labeled in order to give you an overall
picture of what a fuel cell car looks like in this experiment.
1.
2.
3.
4.
Insert the fuel cell into the rectangular slot located on the car chassis with “O2” “H2” symbols upside.
Remove the small red cap from a short tube connected to the oxygen side of fuel cell. Use the syringe
and inject about 1-2 ml of distilled water (no tap water) into the fuel cell through the short tube. Make
sure that water pass through the oxygen-side chamber in front of the screen to humidify the membrane
and the whole chamber is wet with water (Figure 4). Record the starting time for humidifying the fuel
cell on your notebook.
Fill the hydrogen and oxygen storage cylinders with distilled water up to the “0” line. Insert the
inner cylinders into the outer cylinders. The inner cylinders should be filled with water without any gas
bubbles at top. In case you cannot get any large bubble out by adding water into the cylinders, ask the
TA for help. Also ensure that they fit firmly onto the plastic rim and the two notches (small openings) at
bottom of the inner cylinders are not blocked by the inner plastic rims.
Firmly attach the long tubes onto the top nozzles of inner storage H 2 and O2 cylinders (if they are not
already attached) and the opposite ends to the lower nozzles located on the lower positions of the H2 and
O2 sides of fuel cell, respectively. Make sure the tubes are connected correctly to the corresponding
sides of the fuel cell.
Make sure that the battery charger is at “off” position. Insert the red banana plug from battery
charger into the red banana socket on the fuel cell, and the black plug into the black banana socket. The
colors must match. When reversed black and red wires accidentally connect to the power, you will
destroy the fuel cell and you and your team members will have significant points off from your lab
report grades!
ASSEMBLY GUIDE
atteries= 2 U n its
W ater= 1 0 0 m l
Scisso rs
rubber tubing
Connect the short tubes completely onto the
short H2/O2 intake nozzles located on the
lower sections of both "H2" and "O2" sides of
the fuel cell.
k pin into the
pie ces.
ver. Push and
H 2 sid e
screw tightly
O 2 sid e
AA
Ba
ry
tte
Fu el C ell
n before you
de could
, or create
se.
Remove the cap from the tube connected to
the oxygen side of the fuel cell. Using the
syringe, inject distilled water into the fuel cell
until the fuel cell is HALF filled with water.
First add water up to the "0" line.
*WARNING:
The polymer membrane is an
Place inner containers into outer cylinders minding that the
are not blocked
by inner
plastic rims.
Make sure the
importantgapspart
of the
proton
exchange
water is still level to the “0” line. If not, remove some water
membrane
(PEM)
cell, theit tubing
should
with the
syringe. fuel
Then connect
to the be
inner
containers.
Make
there
is nowith
air trapped
inside the
Figure
3 A drying
fuelsure
cell
car
a built-in
prevented
from
out.
f the chassis until
ocated on the car
ers into the round
inner containers and the water is level to the "0" line.
electric circuit board for measuring voltage and current of a
fuel cell.
Distilled water
O
2
Figure 4 Injecting water into the oxygen side of the fuel cell
(on the left); connecting tubing (on the right)
sid e
5.
Ask your TA to check your setup and check the
time recorded in your notebook to see if you humidify
your fuel cell for more than 5 minutes. Once TA
approves and your fuel cell is humidified for more than
5 minutes, you can turn on the battery charger to initiate
hydrolysis process. You will observe the hydrogen and
Connect the red and black cables to the solar
oxygen gases coming from the fuel cell into the inner
panel, and connect the other ends to the red
and black sockets on the fuel cell.
cylinders
soon
after
electrolysis
Watch hydrogen
For solar panel:
remove
the cables
connecting thestarts.
solar
to the fuel cell.
and oxygen gases being generated and stored in the panel
inner
storage
cylinders,
the
water
levels
in these
Turn the switch on the battery box to “off” and remove the
cables from the cable sockets located on the fuel cell.
left si
de
inner cylinders
would
decrease.
Keep the battery box switched to the "off " position except
After
during the time you are performing electrolysis.
water injection
Record the room
temperature in your lab notebook
while waiting for hydrolysis. When the inner
chambers are completely filled with hydrogen, gas bubbles will come out from the bottom notch of the
Remove the red and black cables connected to the fuel
hydrogen cylinder (This is a good indication for the cell
completion
of the electrolysis since sometimes it is
in "step 10".
Insert the banana plug cables from the car’s motor into the
difficult to tell if H2 completely fill up the inner cylinder).
first observe the H2 gas bubbles
red and blackWhen
plugs on theyou
fuel cell.
Make sure the colors of the plugs and cables are inserted
coming out from the inner cylinder, turn off the battery
charger
and
the cables of a battery
into plug socket
of the same
color disconnect
as in "step 10".
motor should begin to power the car. The estimated
charger from the fuel cell. If it takes longer than 10The
minutes
to
finish
electrolysis,
please notify TA.
driving time on one charge is about 3 to 5 minutes.
The following step is to measure the open circuit potential to calculate the maximum work of the
fuel cell. Write down the serial number of multimeter on your notebook (e.g. TE549254). Take the
O 2 sid e
two probe cables from the multimeter (if a multimeter has no cables attached, you need to insert a black
pin into the “COM” and red pinBattery
to “V sockets on the multimeter); plug the black cable from “COM”
Pack
into the hydrogen side banana socket and the red one from “V into the oxygen side of the fuel cell.
Procedure for repeated gas production: Disconnect the
small plugs from the tubes connected to the nozzles on the
reversible fuel cell. This will allow water into the inner
cylinders to replace the gasses and reset water levels to “0”
line. Re-insert the plugs into the tubes and repeat electrolysis again.
te: Th e tu b in g
u ld n o t to u ch
w h eels.
ssis
Connect the pre-cut tubes firmly onto the inner
storage cylinders short nozzle, connect the tubes
opposite end to the upper nozzles located on the
upper positions of both "H2" and "O2" sides of fuel cell
shown here. Make sure the tubes are connected
correctly to the corresponding sides of the fuel cell.
6.
7.
b en d th e
tu b e th is w ay
ALTERNATE OPTION:
Connect the red cable from the battery pack to
the red socket on the fuel cell and connect the
black cable to black socket.
Switch the battery pack to the "on" position.
Electrolysis of water should begin with oxygen
Turn on the multimeter and set the scale to voltage “2V” range. Take three measurements within 20
seconds and record the voltage values up to 3 decimal points.
8.
A circuit board (shown in Figure 3) with cell phone vibrator had already been mounted on the
front of the car and connected to the car motor. Connect two power plugs from the circuit board to the
banana sockets on both sides of the fuel cell (color matching). Ask your TA to check your connection.
To measure the voltage through the fuel cell while cell phone vibrator is running, use an alligator clip to
connect between the positive probe cable from the multimeter to “V+” terminal on the circuit board and
the negative probe cable to the “V-“ terminal on the board. The switch on the circuit board has a three
positions: “Down” position for cell phone vibrator, “middle” for off position, and “UP” position for fuel
cell car. Turn the switch on the circuit board to the “Down” position for running the cell phone vibrator.
Take three voltage measurements within 20 seconds and record the values up to 3 decimal points in
your lab notebook. To obtain the current during the fuel cell operation for running a mini cell phone
vibrator, we measure the voltage across a fixed 0.1  resistor built in the circuit instead. The voltage of
the fixed 0.1  resistor can be measured by connecting multimeter (in the same manner as the voltage
measurement) to “VR+” and “VR-” on the circuit board. Change the scale to “200 mV” range in your
multimeter. Measure the voltages in units of mV for three times within 20 seconds and record the
values up to 1 decimal points in mV. From voltage and resistance, you can calculate the current using
Ohm’s law
9.
Finally, after all the measurements, it is time to play with the car! Check the volume level of the H2
and O2 gas in the inner cylinders. Turn the switch on the circuit board to the “UP” position to power the
car motor and watch the hydrogen fuel cell-powered car running! Please turn the switch to the
“middle” position to power off the car after 3 minutes!!! A fuel cell has a limited lift time and we need
to save the time for other students. Watch the decrease in O 2 and H2 gasses after running the car.
10.
After finishing the experiment, turn off the switch and disconnect the cables. Put the fuel cell back
into the small plastic bag and leave the short tubes connected with the fuel cell. Make sure the Ziploc
bag is not broken (if necessary, obtain a new bag from the stockroom) and sealed well to keep the cell
under humidified condition. Make sure that you put everything including tubes and small components
back into the box. Before leaving, ask the TA to check the car kit.
11.
Back to the classroom area for about 10 minutes' group discussion. Discuss and work out one of the
following questions. The same questions are given in your lab report. Each group may submit the same
answer summing up the ideas of all members for your lab report.
a) Why efficiency (η, %) can hardly equal 100% in this fuel cell experiment?
b) List more than one differences between the electrolysis using the fuel cell and the electrolysis in Part
A experiment 7.
Lab 7 Fuel Cell Lab Report Fall ‘11
How Can We Use a Hydrogen Fuel Cell to Generate Clean Energy and Connect
Chemistry to the Real World?
You can type your lab report on a separate page or write by hand. Please attach the
following pages to the front page of your lab report for experiment 7 Part A from the
lab manual. You need to show all your work to get full credits. Your report needs to
include:
Your Name____________
TA_________________
Lab Section_____________
Group Members________________________________________________________________________
I. Describe the purpose of the experiment with a few sentences. You can find the
information from the introduction, but do not copy them directly.
II. Summarize the experimental results.
a) Fill in the following table with your data.
Voltage (V)
1st time
2nd time
3rd time
Average
Open circuit
1.4232 V
1.4204 V
1.4166 V
1.4184 V
Fuel cell powering the
mini vibrating motor
0.7779 V
0.7807 V
0.7804 V,
(4th) 0.7810 V
0.7800 V
0.1 Ω resistor
4.93 mV
4.91 mV
4.90 mV
4.90 mV
b) According to the Ohm’s law, use the average voltage of the 0.1 Ω resistor to
calculate the average current of the circuit for running a cell phone mini vibrator:
c) Calculate related parameters from your result above. For electric current and
potential, take the average of your measurements. Please show all your work below
the table (hint: The current for the open circuit is zero)
Load
Open Circuit
Vibrating Mini
Motor
Current (A)
00000
0
0.4900 A
Fuel cell
potential (V)
Fuel cell power
(Watts)
1.4184 V
///
0.7893 V
0.0389 W (2)
III) Calculate the following electric and thermodynamic parameters:
1)Calculate the standard reaction HOrxn and GOrxn (in KJ/mole of H2) for the
following fuel cell reaction from their standard HOf and GOf. (see Zumdahl
Appendix four)
H2 (g)+ 1/2 O2 (g)  H2O (l)
2)The overall hydrogen fuel cell reaction: H2 (g)+ 1/2 O2 (g)  H2O (l). Write down
the two half reactions and calculate the standard fuel cell potential Eo (or open
circuit potential) using their standard half cell reduction potentials (see Zumdahl
Appendix five)
3) Calculate the following values for per mole consumption of H2:
A) Maximum electric work (Wel max) using GOrxn from question 1)
B) The standard open circuit voltage Eoopen using GOrxn from question 1)
C) The maximum efficiency performed for a reversible fuel cell under the standard
condition using GOrxn and HOrxn from question 1)
4) Calcaute the maximum electric work (in KJ/mol of H2) using an experimental measured
open circuit cell potential from the previous table assuming only reversible electrical work
is performed at constant temperature and pressure. Compare with the Wel max under
standard condition calculated using GOrxn from question 3) and explain the difference.
5) Electrons moving at fuel cell potential (E, in unit of V) provide the electricity work,
Wel (in J/mol of H2). Suppose the fuel cell output voltage is stable within a short period of
powering the vibrator, calculate the electricity work done and
the fuel cell when it is running a cell phone motor.
III. Discussion
Write a short response to explain one of the following questions (less than 150
words):
i.Why efficiency (η, %) can hardly equal 100% in this fuel cell experiment?
ii.List more than one differences between the electrolysis using the fuel cell and
the electrolysis in Part A experiment 7.