Introduction

This lab introduces students to hydrogen as an energy carrier, meaning it can store energy that can later be converted into electricity or heat. Because energy production is a major source of carbon dioxide emissions, scientists and engineers are exploring alternative energy systems that can reduce or avoid direct carbon emissions. Hydrogen is of particular interest because it does not contain carbon or emit carbon dioxide when combusted, although the environmental impact of hydrogen depends on how it is produced.

In the first part of the activity, students examine different hydrogen production methods, commonly described using hydrogen color labels*. These labels refer to the processes used to produce hydrogen and help explain why some hydrogen pathways release significant amounts of carbon dioxide, while others result in much lower emissions. 

*Note: Hydrogen color labels are used in this activity as a simplified way to introduce hydrogen production pathways. In professional research and policy contexts, however, these labels are increasingly treated as informal shorthand, with lifecycle carbon intensity (CI)—the total greenhouse gas emissions associated with hydrogen production—serving as the primary metric for comparison and decision-making.

In the second and third parts of the activity, students focus on water electrolysis, a hydrogen production method that uses electrical energy to split water into hydrogen and oxygen gas. This hands-on investigation provides a foundation for understanding how electrolysis-based hydrogen is produced, and why, despite its low emission potential, it currently represents only a small share of global hydrogen production.

Student Objectives

Students will be able to

• Explain why different hydrogen production methods produce (or make, or result in) different amounts of carbon dioxide emissions.
• Explain how electrolysis uses electrical energy to drive a non-spontaneous chemical reaction.
• Identify oxidation and reduction reactions and locate them at the anode and cathode.
• Describe the electrolysis of water, including reactants, products, and half-reactions.
• Construct and operate a simple electrolytic cell.

Materials

Per Group

• Student Handout
• Beaker
• 2 clear plastic straws
• Ruler (or caliper, if available)
• 2 graphite pencils (sharpened at both ends)
• 2 jumper wires with alligator clips
• 9V battery
• Masking tape
• Hot glue (or alternative method for sealing straw)
• Waterproof marker
• Tap water
• Safety goggles

Safety Considerations (Electrolysis of Water Lab)

• Use low-voltage power only (9V batteries). Do not substitute wall power or power supplies.
• Hydrogen gas is produced and is flammable. Conduct the lab in a well-ventilated room and keep all flames, sparks, and heat sources away. Do not ignite or test the gas.
• Supervise the use of hot glue. Consider sealing straws in advance to reduce burn risk.
• Inspect jumper wires and batteries for damage before use. Disconnect batteries when the reaction period ends.
• Require safety goggles for all participants.
• Use graphite electrodes only. Do not allow students to add electrolytes (salt, acids, or bases) unless the activity has been modified and safety-reviewed.
• Monitor handling of sharpened pencils and scissors to prevent injury.
• Clean up water spills promptly to reduce electrical and slip hazards.

Procedure:

1. Context and Discussion
   • Provide each student with the Student Handout. 
   • Introduce the activity by explaining that students will first learn about hydrogen production methods and then carry out an experiment to produce hydrogen gas using electricity.
   • Guide a brief class discussion focused on how different energy production methods emit carbon dioxide, and why hydrogen is being explored as a potential low-carbon energy carrier.
2. Hydrogen and Electrolysis Background: Have students read and complete Parts 1 and 2 of the Student Handout, either individually or in pairs. Review and emphasize:
   • Why many hydrogen production methods release carbon dioxide.
   • The difference between hydrocarbon-derived hydrogen and electrolysis-derived hydrogen.
   • The role of electricity in water electrolysis and why its source matters.
   • Oxidation at the anode and reduction at the cathode (LEO goes GER).
   • The overall water decomposition reaction: 2H₂​O→2H_2​+O_2​
3. Electrolytic Cell Construction: Divide students into groups of 2 or 3. Students follow the instructions in Part 3 in the handout to build and run an electrolytic cell. Students will:
   • Prepare graphite electrodes using pencils.
   • Seal and position the drinking straw to collect gas at the cathode.
   • Assemble the electrolytic cell in the beaker of water. 
   • Correctly label the anode (+) and cathode (-). 
   • Record initial measurements.

Monitor groups to ensure correct electrode placement and secure electrical connections. 

4. Electrolysis Observation and Data Collection: Once the circuit is complete, students will: 
   • Allow the system to run for 10 minutes.
   • Record the height of the water in the beaker before and after.
   • Observe gas formation at the cathode.
   • Sketch or photograph their setup.

5. Analysis: Students complete the Analysis Questions section of the Student Handout.

Answer Key

Part 1: Hydrogen Fuel Comprehension Questions 

1. Gray hydrogen is made from hydrocarbons, usually natural gas, using a process called steam methane reforming (SMR). This process produces hydrogen, but it also emits carbon dioxide into the atmosphere. Blue hydrogen is made using the same process, but it includes carbon capture and storage (CSS). The carbon dioxide produced is captured and stored underground or used in other processes. However, some emissions may still occur.
2. Many current methods use fuels like natural gas or coal. Since these fuels contain carbon, carbon dioxide is formed and released during the chemical reactions used to produce hydrogen. 
3. Electrolysis is a process that uses electrical energy to split water into hydrogen and oxygen gas. The electricity provides the energy needed to break apart the water molecules. Without electricity, the reaction would not happen on its own.
4. Green hydrogen is made using electrolysis. It is considered “green” when the electricity comes from low-emission sources like wind, solar, or hydropower. Unlike gray or blue hydrogen, it does not directly produce carbon dioxide during production.
5. The graph shows that most hydrogen today is produced using natural gas. Hydrogen made using electrolysis makes up only a small percentage of total production both in the U.S. and worldwide.
6. Electrolysis currently makes up only a small share because it’s expensive and requires large amounts of electricity.

Part 2: Electrolysis Comprehension Questions

1. Oxidation is when a substance loses electrons. Reduction is when a substance gains electrons. In electrolysis, oxidation happens at the anode (positive electrode) and reduction happens at the cathode (negative electrode). 
2. In the electrolysis of water, water is broken down into hydrogen gas and oxygen gas. At the cathode, hydrogen ions gain electrons and form hydrogen gas. At the anode, water molecules lose electrons and form oxygen gas. Water is split into hydrogen (H₂) and Oxygen (O₂). 
3. Electrolysis is used to produce hydrogen gas, extract and purify metals, coat objects with metal (electroplating), produce chlorine gas, and produce sodium hydroxide.

Part 3: Building an Electrolytic Cell Analysis Questions

1. Answers will vary. If gas was collected, students should describe that gas bubbles formed and collected at the top or throughout the straw, displacing water inside the straw. They should describe the approximate volume of gas collected. 
2. If gas did not collect, possible set up errors may include the straw was not completely sealed, the graphite electrode was not snug in the straw, or loose/incorrect wire jumper connections. 
3. Hydrogen gas.
4. It was produced at the cathode (negative electrode). During electrolysis of water, reduction occurs at the cathode. Hydrogen ions gain electrons at the cathode and form hydrogen gas.
5. Answers will vary. Possible limiting factors include limited current from the 9V battery, lower conductivity of tap water, small surface area of the graphite electrodes, short reaction time, poor electrical connections, or gas leaks in the straw. 
   Since the amount of hydrogen collected depends on how much electric charge flows through the system, anything that reduces current or time will reduce hydrogen production.
6. Answers will vary. 
7. Answers will vary. Industrial systems could use efficient electrode materials, increase electrode surface area, improve cell design to reduce energy loss, and use low-carbon electricity sources such as wind, solar and hydropower. 
8. It would be classified as green hydrogen.