Chemical Science Lesson Plan

Title: Hydrogen Fuel Cell

Grade Level: High School

Prepared by: John Shapley and Pat Shapley
Science standards

Science background for teachers

Introduction

Activity procedure

Materials

Summary and discussion


Objectives: Students will learn:
  • how water can be converted to hydrogen and oxygen gases with electrical energy
  • gas properties of hydrogen and oxygen
  • to apply the ideal gas law to a real problem
  • about efficiency of engines


Science standards

11.B.4a Identify a technological design problem inherent in a commonly used product.

12.C.5a Analyze reactions (e.g., nuclear reactions, burning of fuel, decomposition of waste) in natural and man-made energy systems.

Science background for teachers

Hydrogen is the most abundant element in the universe. Earth's primordial atmosphere was probably similar to the gas cloud that created the sun and planets. It consisted mainly of hydrogen and helium, along with methane, ammonia, and water. Elemental hydrogen is a diatomic molecules with a single H-H bond. This molecule stores a great deal of chemical energy and we may use this to fuel automobiles and generate electricity in the future.



Atomic hydrogen has 1 proton in its nucleus and 1 electron in a 1s atomic orbital. Deuterium is a stable isotope hydrogen with 1 neutron in the nucleus along with the proton. Tritium is a radioactive isotope with 2 neutrons in its nucleus.

The 1H nucleus behaves as if it were spinning (with a nuclear spin of 1/2). As you know from physics, a spinning charged particle generates a magnetic field. When a hydrogen nucleus is placed in an external magnetic field, it's lowest energy state has the hydrogen magnetic field opposite to the external field separated by a small energy gap from the state with the hydrogen magnetic field aligned with the external field. Because the hydrogen magnetic field is slightly changed by the electrons around the nucleus, 1H NMR spectroscopy can provide information about the environment of hydrogen atoms in many molecules.

Molecular Properties

Two hydrogen atoms can combine their electrons to form a 2-electron bond. Elemental hydrogen, H2, is the simplest of the molecules. What do we know about hydrogen?
  • Hydrogen is a lighter-than-air, flammable, diatomic gas. It is colorless and only sparingly soluble in solvents.

  • It boils at -253.5 deg C.

  • Platinum metal or heat can catalyze the reaction of hydrogen with oxygen to form water.

  • In hydrogen fuel cells, the chemical oxidation of hydrogen to water produces electricity. (This is an area of intense activity of inorganic chemists because fuel cells may replace fossil fuels to power automobiles and reduce our reliance on petroleum. We need better inorganic materials to store hydrogen, separate components of the fuel cell, and catalyze the oxidation/reduction reactions.)



Combustion of Hydrogen for Electricity

The combustion of hydrogen produces only water vapor and gives off 286 kJ/mol of energy, or 229 kJ/mol for combustion to liquid water.

H2 + 1/2 O2 H2O


Hydrogen can be used in standard power plants, in place of natural gas or coal, to heat water and drive a turbine. A hydrogen power plant would not contribute to air pollution.

An electric power plant fueled by hydrogen went online in 2006 in Finland. A power plant planned by BP and Edison Internation for Carson, California will burn the hydrogen produced from coal gasification by 2011.

The Futuregen project, supported by the Department of Energy and a consortium of energy companies, chose Mattoon, Illinois as the site of a clean, hydrogen-from-coal electric power plant. However, the DOE recently cancelled the project.

Hydrogen as a Transportation Fuel

Hydrogen can be burned in an internal combustion engine. Hydrogen can also produce electricity to power a vehicle through hydrogen fuel cells.

There are no commercially available cars that run on hydrogen because of the supply problem. We don't have hydrogen filling stations throughout the country.

Automobiles that run on hydrogen are currently being tested in California and automakers plan commercial vehicles for the future.

Hydrogen Fuel Cells

A hydrogen fuel cell is an electrochemical cell that uses the a spontaneous redox reaction to produce current that can do work. The net reaction is exothermic. Combining the 2 half cell potentials for the electrochemical reaction gives a positive cell potential.
H2 + 1/2 O2 H2OGf = -229 kJ/mol
H2 2 H+ + 2 e-E0= 0.00 V
O2 + 4 e- + 4 H+ 2 H2OE0= 1.23 V
The hydrogen flows to a platinum catalyst connected to the anode. Molecular hydrogen is dissociated to atomic hydrogen on the metal surface and the atomic hydrogen is oxidized. The protons travel through a solid electrolyte, the polymer electrolyte membrane or PEM, and the electrons travel through the external circuit. Molecular oxygen is reduced at the cathode and combined with protons to form water.

Hydrogen Storage

Hydrogen can be compressed and stored in tanks. Chemists are working on the syntheses of new materials that could store hydrogen gas at lower pressure. There are some interesting results on the storage of hydrogen in carbon nanotubes and in metal hydrides.

Introduction

The United States consumes almost a quarter of the world's total energy production. Per person, we use more energy than any other country. Most of this energy is non-renewable, from fossil fuels.

Renewable energy sources, such as solar energy and wind energy, produce electricity. Some automobile fuel comes from corn (bioethanol) and soybeans (biodiesel), but it requires energy from petroleum and agricultural chemicals, also from petroleum, to grow these crops.

Can we power automobiles with electricity? There are some new electric cars coming on the market soon, the Chevy Volt for example. However, these cars need large, heavy batteries to power them and their range is only about 40 miles.

One possibility is to use electricity to convert water into hydrogen gas and oxygen gas. This requires 229 kJ for every mole (about 6 x 1023 molecules) of hydrogen produced. At room temperature at sea level, a mole of hydrogen has a volume of about 25 L.

H2O H2 + 1/2 O2 Gf = 229 kJ/mol


Hydrogen can be burned in air. This is similar to burning gasoline in a typical car. Another possibility is to use a device call a hydrogen fuel cell to convert H2 and O2 into H2O and electrical energy. This can power an electric car. A hydrogen fuel cell car could be lighter than other electric cars because it wouldn't require batteries and it would be able to travel much longer distances.

In this activity, you will generate hydrogen by the electrolysis of water and use the hydrogen to power a toy car.

Research question: How does the energy contained in the H2 compare to the amount of energy required to move the car?

Materials

  1. one hydrogen fuel cell model car and controller per group
  2. one water electrolyzer
  3. 2 test tubes
  4. 6 thin wood splints
  5. tape measure
  6. a plastic bottle filled with distilled water (200 mL)
  7. balance
  8. paper towels
  9. waste container


Activity procedure

Download the labsheet here.

Part 1 (demonstration):
    Fill the electrolyzer with distilled water and plug it into a power socket.

    Capture a sample of each gas formed in a separate test tube.

    Light one of the splints with a match and blow it out. It should still glow. Then put the end of the splint in one of the test tubes. Note the response. Repeat this procedure with the second tube.

Part 2:
    Fill the reservoir (green balloon) with the gas you identified as hydrogen.

    How can you estimate the fuel energy of the hydrogen in the balloon? (Math help is below.)

    How far does the car go with this amount of hydrogen fuel?

    The energy use of a typical 1000 kg electric vehicle is 0.3 kWatt-hr/mile. Assuming this value scales by mass for the model car, calculate its expected energy use in joules/ft. How many feet could the car travel on the chemical energy of the hydrogen contained? How does this calculated distance compare with what you measured?

Equations, Conversions
Volume of a cylinder, V = h r2 where r is the radius and h is the height.

Circumference, C = 2 r

1 kWatt-hr = 3600 kJ = 3600000 J

1 mile = 5280 ft

229 kJ released per mol H2 consumed



Summary and discussion

  1. Describe what happened when the splints were inserted into the gas samples. How does this relate to the expected properties of the gases?

  2. What relative volumes of the two gases would you expect upon electrolysis?

  3. From the volume of hydrogen in the balloon, what was the energy content of the fuel?

  4. What is the efficiency of the engine in the car?

  5. Where could energy be lost?

EnLIST Chemistry Workshop, University of Illinois, 2010