A hydrogen fuel cell generates electricity through an electrochemical reaction using hydrogen and oxygen. In simplified terms it works like this: Hydrogen is sent into one side of a proton exchange membrane (PEM). The hydrogen proton travels through the membrane, while the electron enters an electrical circuit, creating a DC electrical current. On the other side of the membrane, the proton and electron are recombined and mixed with oxygen from room air, forming pure water.
Because there is no combustion in the process, there are no other emissions, making fuel cells an extremely clean and renewable source of electricity.