Most current hydrogen fuel cells utilize a polymer electrolyte membrane (PEM) design, also known as Proton Exchange Membrane Fuel Cells. These cells consist of thin layers (less than 20 microns) of a material similar to plastic wrap.

The catalyst is applied to both the anode and cathode sides of the fuel cell. On the anode side, hydrogen molecules are separated into protons and electrons. The protons combine with an ion-conducting polymer (ionomer) and pass through the membrane to the cathode, where the oxygen reduction reaction occurs, generating the electrical energy required to power the vehicle’s motor.

Fuel cells also feature additional layers of carbon paper called Gas Diffusion Layers (GDLs), which help divert water vapor components away from the reactive layers of the fuel cell and into the vehicle’s exhaust system.

Since hydrogen fuel cell systems do not produce electricity until they reach a temperature of 50ºF, hydrogen-powered vehicles like the Toyota Mirai are equipped with a lithium-ion battery to aid in initiating the electrochemical reaction.