At high speeds and under heavy loads, both the gas engine and electric motor drive the Prius. At low speeds, the electric motor alone runs the car. The battery charges during deceleration and braking, eliminating the need to recharge the vehicle in overnight. GM will unveil demonstrator models of full-size hybrid pickups this year. In the fuel cell, hydrogen and oxygen mix in the presence of a catalyst to create electricity that powers the car's engine.
Water vapor is the only emission.
Obstacles remain in fuel-cell technology. Storing hydrogen onboard a vehicle requires either a huge, pressurized tank or a cryogenic system capable of maintaining compact liquid hydrogen at extremely cold temperatures. Hydride storage is a promising alternative. However, until the advent of hydrogen-supplied filling stations, pure hydrogen won't be a practical fuel source. Currently, the three most practical fuels for reforming fuel cells are natural gas, methanol and gasoline.