A hydrogen fuel cell is an energy conversion device that turns chemical energy directly into electrical energy. It uses hydrogen as the fuel and oxygen from the air as the reactant. The main products are electricity, heat, and water, so the cell can power devices with very low pollution at the point of use.
Fuel cells matter because they can support clean transportation, backup power, and energy storage when the hydrogen is produced using renewable electricity.
Inside the cell, hydrogen enters the anode side and oxygen enters the cathode side. A catalyst splits hydrogen molecules into protons and electrons, and the membrane lets protons pass through while forcing electrons to travel through an outside circuit. That electron flow is the electric current that can power a motor, light, or other load.
At the cathode, oxygen, protons, and electrons combine to form water, completing the reaction.
Key Facts
- Overall reaction: 2H2 + O2 -> 2H2O + electrical energy + heat
- Anode reaction: H2 -> 2H+ + 2e-
- Cathode reaction: O2 + 4H+ + 4e- -> 2H2O
- Electrons move through the external circuit, creating electric current.
- Protons move through the proton exchange membrane from anode to cathode.
- A single PEM fuel cell usually produces about 0.6 V to 0.8 V under load, so cells are stacked for higher voltage.
Vocabulary
- Fuel cell
- A device that converts chemical energy from a fuel and an oxidizer directly into electricity, heat, and reaction products.
- Anode
- The electrode where hydrogen is split into protons and electrons in a hydrogen fuel cell.
- Cathode
- The electrode where oxygen combines with protons and electrons to form water.
- Proton exchange membrane
- A thin material that allows protons to pass through but blocks electrons and separates the fuel from the oxygen.
- Catalyst
- A substance that speeds up a chemical reaction without being used up by the reaction.
Common Mistakes to Avoid
- Thinking a fuel cell stores electricity like a battery is wrong because a fuel cell produces electricity as long as fuel and oxygen keep flowing.
- Sending electrons through the membrane is wrong because the membrane is designed to pass protons while electrons must travel through the external circuit.
- Forgetting oxygen in the reaction is wrong because hydrogen alone cannot produce water or complete the fuel cell reaction.
- Assuming the only output is electricity is wrong because real fuel cells also release heat and produce water.
Practice Questions
- 1 A fuel cell stack contains 50 cells, and each cell produces 0.70 V under load. What is the total stack voltage if the cells are connected in series?
- 2 A small fuel cell delivers a current of 4.0 A at a voltage of 12 V. What electrical power does it produce in watts?
- 3 Explain why a proton exchange membrane fuel cell needs an external circuit for the electrons, and describe what would happen if electrons could pass directly through the membrane.