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NOVA scienceNOW: Fuel Cells

Viewing Ideas


Before Watching

  1. Write the definition of energy on the board. (Energy is the capacity to do work.) Make a two-column chart on the board similar to the one below and have students brainstorm examples for each form of energy.

    Form of Energy

    Example

    Chemical

    sugar being metabolized or fuel being burned

    Electrical

    electric pencil sharpener

    Mechanical

    swinging a bat

    Heat

    warmth from light bulb

    Sound

    drum being hit

    Nuclear

    radioactive decay

    Electromagnetic

    visible light

  2. A fuel cell is a type of battery and has the same parts as a household battery. From the Web or in a textbook, find a diagram of a battery for students to look at. Ask students how they think a battery generates electricity. Discuss the points below.

    • A battery converts chemical energy into electrical energy.

    • Batteries have two electrodes—an electron donor and an electron acceptor. The anode (the electron donor) is made of a material that gives up electrons easily, and the cathode (the electron acceptor) is made of a material that accepts electrons easily.

    • The anode and cathode are surrounded by a mix of chemicals (called electrolytes) that help produce an electric charge. Different kinds of batteries use different electrolytes.

    Ask students to describe characteristics important for batteries (e.g., long-lasting, inexpensive, light in weight, safe, easy to use, and rechargeable).

  3. Similar to household batteries, fuel cells power electrical circuits. Remind students that electricity is the flow of electrons and that a circuit provides a path for electrons to flow from the anode to the cathode. On the board, draw a simple circuit that includes a battery, bulb, and wires. (Alternatively, find a circuit diagram on the Web or in a textbook.) Trace how electrons flow through the circuit. (Electrons leave the battery's negative, electron-donating terminal [anode], travel through the wires toward the positive, electron-accepting terminal [cathode]. Along the way, they pass through the filament in the bulb.) Have students annotate the diagram to show where energy is being converted from one form to another.

    Part of the Circuit

    Energy Conversion Taking Place

    Battery

    Chemical to electrical

    Wires

    Heat as a waste product

    Light bulb

    Electrical to light and heat

  4. Fuel cells use hydrogen and oxygen to generate electricity. Ask, "What is the most common substance that contains hydrogen and oxygen?" (Water) Ask students to name some gases that are presently used as a fuel source (e.g., propane, natural gas) and the precautions that must be taken when using them as a fuel. (They require proper handling and storage to prevent an explosion.)

    As an extension for students studying chemistry, have them locate hydrogen and oxygen on the periodic table and state their atomic mass and number. Draw students' attention to the number of electrons in the outer shell of both elements and discuss how these electrons influence their reactivity. (Both gases are highly reactive. To achieve a more stable atomic state, hydrogen readily donates its electron and oxygen readily accepts two electrons.) Discuss how hydrogen and oxygen bond covalently to produce water.


After Watching

  1. Have students list ways a fuel cell and household battery are alike and different. (Batteries and fuel cells both have anodes and cathodes and produce electricity. However, their chemicals differ.) Print the NOVA scienceNOW fuel cell diagram (pbs.org/wgbh/nova/sciencenow/3210/01-fcw.html) and discuss with students how it works. Divide the class into teams and ask them to construct model fuel cells that include an anode, cathode, proton-exchange membrane (conducts positively charged ions and blocks electrons), and catalyst (material that facilitates the reaction between oxygen and hydrogen). Supply teams with common materials to make their models (e.g., foam sheets, cardboard, plastic wrap, foil, pipe cleaners, and string). Have teams display their models and explain how their fuel cells work.

  2. Have students visit the clickable fuel-cell car on the NOVA scienceNOW Web site (pbs.org/wgbh/nova/sciencenow/3210/01.html), or download the printable version of the car. Ask student pairs to identify the energy conversions that occur in a fuel-cell car and share their list of conversions.

  3. Draw a two-column chart on the board and have students brainstorm the pros and cons of hydrogen fuel cells, including where they would be most and least viable. (Providing a reliable supply of hydrogen and oxygen for small-scale or mobile uses, such as cars, necessitates solving a host of storage and distribution issues related to these reactive gases. These include developing a system of high-pressure tanks and pipelines, finding convenient ways to fill a fuel cell's gas tanks, and minimizing the risk of burns and explosions. Producing hydrogen and oxygen on-site avoids many of the challenges associated with transporting and storing these gases.) Assign students a place where fuel cells could be used: a car, train, home, apartment complex, or factory. Ask them to create an advertising poster that promotes the use of fuel cells as an energy source for their assigned location.

    4. Robert Krulwich made the statement that there is plenty of hydrogen on Earth, but that it is always stuck to other stuff (i.e., other atoms). "It's in the foods we eat, the fuels we burn, the beverages we drink, and the plastics and plant materials we use to construct our world. In fact, hydrogen is so chemically reactive that it does not naturally occur as a pure element on Earth." To give students a sense of how challenging it is to produce hydrogen and oxygen by splitting water, have them do one of the electrolysis activities suggested in the Links and Books section. These include:

    • Collect oxygen and hydrogen using a battery or DC power supply to provide the energy.

    • Collect oxygen and hydrogen using a hand-crank generator to provide the energy. Students will experience—and likely be surprised by—just how much energy is required to produce a small amount of gas.


Links and Books

Web Sites

Collecting the History of Fuel Cells
americanhistory.si.edu/fuelcells/
Explains how different fuel cells work and offers historical information about each type, including proton-exchange membranes.

Fuel Cells 2000
www.fuelcells.org/
Offers information on fuel-cell basics and includes a section on hydrogen fuel cells.

Scientific American Frontiers—Electrolysis activity
pbs.org/saf/1403/teaching/teaching4.htm
Presents an electrolysis activity recommended for grades 9-12.


Books

Alternative Energy by Marek Walisiewicz. Dorling Kindersley, 2002.
Focuses on the future of energy technology, including hydrogen fuel cells.

Energy by Jack Challoner. Dorling Kindersley, 1998.
Provides an overview of energy and how it is used.

Teacher's Guide
NOVA scienceNOW: Fuel Cells
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