Hydrogen Power in the Classroom

Materials

Introduction

Over 50 years ago advertisements appeared trying to sell attachments that would allow your car to burn water as a fuel. Although those inventions and claims were nonsense, if you use electrolysis to break water into hydrogen and oxygen gas, and use a proton exchange membrane (PEM) fuel cell to power the car, you CAN run a car on water. Even better, there are no exhaust pollutants, and the only emission is pure water!

Currently this process is not practical because of the high cost of the PEM systems, but hydrogen technology is definitely here to stay. It is already used in space vehicles and space stations and in remote locations on earth where the supplying of traditional fuels would be costly.

The following demonstration allows your students to see the results of energy transfer from light to electricity to chemical, and then back to electrical, using a reversible fuel cell. Students can also see a potential application by converting light into mechanical energy to turn the wheels of a model car. The dynamic experience lends itself to enthusiastic discussions about the nearly limitless possibilities of fuel cell technology.

This investigation addresses many of the National Science Content Standards for Grades 5-8, including Content Standard A: Science as Inquiry, Content Standard E: Science and Technology, and Content Standard F: Science in Personal and Social Perspectives. The objective of the investigation is to show students that hydrogen can produce an electrical current when used in a fuel cell. Specifically, students

Record that electrical energy is produced when hydrogen is used to power a fuel cell
Note that repeating an experiment produces similar results
Use data to produce a graph, which allows them to predict the duration of wheel rotation for a given volume of hydrogen gas
Demonstrate correct safety procedures for this investigation

Background

Here is a car that actually runs on water! The hydrogen car system (Fig. 1) contains a source of hydrogen (the electrolyzer) and a way of storing it (the gas cylinder). It also includes a source of oxygen, but it could use air, which of course consists of 20% oxygen.

The hydrogen car contains a reversible fuel cell. If electricity and water are supplied to the reversible fuel cell, it behaves as an electrolyzer, producing hydrogen and oxygen gases. If the reversible fuel cell is connected to an electrical load, i.e., an electric motor, and the hydrogen and oxygen gases are supplied to the anode and cathode of the fuel cell respectively, electricity will flow through the electric circuit. The hydrogen and oxygen gases recombine to form water, releasing electricity in the process. You could diagram this as follows:

Electricity + Water => Hydrogen + Oxygen
Hydrogen + Oxygen => Water + Electricity

What a wonderful solution to the air pollution problem, as hydrogen fuel cell power would add only water vapor to our atmosphere while using pure water and electricity as the source of the hydrogen needed to power the fuel cell. This useful technology is already in use by astronauts living in space stations. With the use of an initial supply of water, fuel cells, solar cells, and electrolyzers, astronauts have a source of electricity and oxygen as well as an abundant source of the hydrogen used for fuel, which produces electricity and water again. In the hydrogen car, stored hydrogen produces electricity that powers the motor and turns the wheels. Because the electric motor spins very quickly, a gearbox reduces the speed of the motor shaft and powers the rear wheels of the car to drive it forward at a slower speed.

Teacher Notes

This investigation requires that the electrolyzers be hydrated and able to produce bubbles of hydrogen soon after the lesson begins. Therefore the electrolyzers must be filled with distilled water before beginning the experiment. There is no problem leaving them filled overnight for use on the subsequent day. If several classes are to do the investigation in succession, do not empty the electrolyzers between sessions.

To avoid damaging the solar panel by overheating from the light source, teachers MUST specify the minimum distance from the solar panel to the light source. If you work in bright sunlight, the experiment can be done in a much shorter time, or it may be repeated 2 or 3 times within a 45-minute period.

Try out the system beforehand to see how many times students may repeat the experiment to get more data. In a sample trial, 2 repetitions took about 40 minutes with a standard 100-W light source in a desk lamp 15 cm away from the solar panel. The panel warmed but was not overly heated. It should not be left in this position indefinitely, however.

Remind your students to measure volumes very carefully to ensure reproducible results. To read the graduations on the hydrogen storage cylinder accurately, students must get at eye level with the electrolyzer. The amount of energy required to turn the wheels is considerably more than is required to run the electrolyzer. You can demonstrate the powering of the car by the solar panel alone, but the solar panel must be very close to the light source. The solar panel turns the wheels easily if it is in bright sunlight. Just remember to limit the time to only a few seconds to avoid heat damage to the solar panel.

The Experiment

Setting up the Hydrogen Fuel Cell Model Car

Put on your safety goggles. They will protect you only if you wear them properly.
Fill the electrolyzer with distilled water as per the instructions and connect the solar panel so the light source is exactly perpendicular to the solar panel at the distance your teacher recommends. Begin producing hydrogen and oxygen.
Place your car support under the hydrogen car base
When the hydrogen storage cylinder is filled to a little more than 4 mL, carefully remove the solar panel from the system by gently pulling out the jumper cables from the electrolyzer.
Carefully attach the gas-filled electrolyzer to the car base. Be sure the red and black contacts are to the front of the car. Hold the red and black cables running from the motor to the side so they do not prevent the electrolyzer from being fully down.
Make sure the car is supported so the wheels are free to turn, and carefully insert the black cable into the black connection on the electrolyzer.
Hold your car so it cannot slip off the support, and connect the red cable into the red connection on the electrolyzer. Watch what happens.
Watch the level of gas in the hydrogen storage cylinder and start a stopwatch (or note the time) when the gas level reaches exactly 4 mL. This marks the beginning of your timing. Record the times again when the gas level has been reduced to 3 mL, to 2 mL, and to 1 mL. When the hydrogen storage cylinder reads 0 mL note the time exactly. Keep recording any extra time the wheels turn after the 0 mL mark. Keep this extra time as a separate note. Do not graph it.
Repeat step 8 as many times as your teacher suggests, calculating the duration your wheels were able to turn for each filling. Make sure you begin your timing when the gas level is at exactly 4 mL.
Graph your results, plotting mL of gas against time of wheel rotation.
Disassemble and put away the equipment, and then take off your goggles.

Review Questions

Why do you set up the solar panel exactly perpendicular to the light source?
Why is it important to fill the hydrogen gas cylinder with exactly 4 mL each time you measure the duration of the wheels turning?
What happens to the level of gas in the hydrogen storage cylinder as the wheels turn? Why does this occur?
What do you think is happening inside the membrane in the fuel cell?
Could you power the electric motor with electricity produced by the solar panel? What is the advantage of powering a car with hydrogen fuel rather than with a solar panel connected directly to the electric motor?

Answers to the Review Questions

The solar panel is exactly perpendicular to the light source to maximize the amount of electricity produced.
If I want to compare the amount of time the wheels turn for each mL of hydrogen gas used, it is important to begin exactly at the 4mL mark each time.
The volume of gas in the hydrogen storage cylinder decreases because electricity is used to power the electric motor and turn the wheels. The hydrogen gas combines with the oxygen gas to form water and produce electricity.
I think the hydrogen gas is combining with the oxygen gas inside the membrane of the fuel cell.
Yes, I think you could power the electric motor with electricity produced by the solar panel. Powering a car with hydrogen fuel rather than a solar panel means you could drive the car when there was not enough light for a solar panel to work.

Resources

Activity created by Brian Herrin, Heliocentris North America, Vancouver, BC Canada