Using Hydrogen as Fuel (College Board AP® Environmental Science): Study Guide

Hydrogen fuel cells

What is a fuel cell?

• A fuel cell is a device that converts chemical energy into electrical energy through an electrochemical reaction

• Fuel cells function like batteries, but they don’t lose power or need recharging

• They produce electricity and heat cleanly and efficiently, providing there is a fuel supply

• Fuel cells are versatile and can run on different types of fuels

• They can be used in many ways to power anything from a big power plant to a small laptop

The hydrogen-oxygen fuel cell

• The hydrogen-oxygen fuel cell produces electricity by feeding hydrogen to the negative anode electrode and air to the positive cathode electrode

• Both elements release energy, heat and water as byproducts, which makes this a clean energy technology

Main components

• Anode: this is the negative electrode where hydrogen gas is supplied and oxidized

• Cathode: this is the positive electrode where oxygen gas reacts with hydrogen ions

• Electrolyte: this allows hydrogen ions (protons) to flow between the anode and cathode while preventing direct mixing of hydrogen and oxygen

• External circuit: this connects the anode and cathode, allowing electrons to flow and generate electricity

• The diagram below shows the setup of a hydrogen fuel cell 

  • The air entering provides the oxygen

  • The fuel entering is hydrogen

  • The only chemical product made is water 

Hydrogen fuel cell 

Process of generating electricity

• When hydrogen passes through the anode, the electrolyte turns it into charged particles, leading to the movement of protons and electrons

• Protons move through the liquid to the cathode, while electrons are pushed through an outside circuit, creating electric current

• At the cathode, protons and electrons come together with oxygen from the air to create water

• This is the byproduct from the reaction, making hydrogen fuel cells a clean and effective way to produce energy

Types of hydrogen fuel cells

• There are different kinds of hydrogen fuel cells, such as:

  • proton exchange membrane (PEM) fuel cells

  • phosphoric acid fuel cells

  • liquid carbonate fuel cells

• Each type has its own specific features and is best for different uses

PEM fuel cells

• These are the most popular type of hydrogen fuel cells

• They are mainly used in vehicles and portable electronics

• They work at a low temperature (about 80 °C) and are very powerful, which makes them good for mobile uses

Phosphoric acid fuel cells

• These are usually used in static applications, such as power plants and cogeneration systems

• They work at a higher temperature (about 200 °C) and have less power output than PEM fuel cells

Molten carbonate fuel cells

• These are mainly used in big stable setups, like power plants

• They work at really high temperatures (about 650 °C) and are very efficient

• However, they are very expensive and the most complicated type of hydrogen fuel cell

Is hydrogen a renewable energy source?

• Hydrogen is not considered a renewable energy source because it is not available in its pure form in nature, unlike solar or gas

• External energy is needed to extract hydrogen from other sources like water through electrolysis

• This makes hydrogen an energy carrier rather than a primary energy source

• Electrolysis can generate significant carbon emissions if the electricity used is fossil fuel-based

• Hydrogen can be made renewable if it is produced using renewable energy sources

• This type of hydrogen is known as 'green hydrogen' or 'renewable hydrogen'