A hydrogen fuel cell propulsion system includes a fuel cell stack, which is layered with many individual fuel cells. Hydrogen from an onboard fuel source, and oxygen from the air are fed into the anode (negative) and cathode (positive), respectively. At the anode, the hydrogen molecules release electrons, which travel to the cathode via an external circuit,

creating an electrical current that powers the electric motor(s) and other system electronics. In an FCEV, the power generated by the fuel cell stack is used to drive the FCEV‘s electric motor(s), with additional power supplied when needed from a rechargeable battery. This battery is also used to store additional short-term energy generated in FCEVs equipped with regenerative braking.