These are a complete departure from the engine and turbocharger concept and work by creating electricity directly by combining hydrogen and oxygen using hydrogen or a hydrocarbon fuel. The electricity is then used to power an electric motor. Their major advantage is that they produce only water as an emission. The potential applications for such systems are many. Applications to mobile vehicles are still at the advanced development stage, the major problems being hydrogen fuel storage in the small available space in passenger cars or hydrogen conversion from liquid fuel. A hydrogen fuel infrastructure has been proposed, which would also allow more conventional reciprocating engines to use this fuel with consequent emissions benefits.