Inside the fuel cell stack, hydrogen - stored in a tank under extremely high pressure - and oxygen are mixed, and the process produces electricity, with the only emission being water (five litres for every 60 miles you travel).
The electricity generated is either sent directly to the electric motors that drive the wheels, or to a battery for storage and later use.
The battery and fuel cell in the Scenic ZEV H2 can work independently of each other or in tandem, a bit like a petrol-electric hybrid.
The batteries are used when the car is travelling at low speed, and electricity directly from the fuel cell is used when cruising. When extra power or acceleration is needed, power from both is used.
Under braking, the electric motor recharges the battery, and the electricity generated in the fuel cell is also sent to the batteries when the car is at a standstill.