From
http://www.eia.doe.gov/kids/energyfacts ... rogen.html
"There are currently about 200 hydrogen-fueled vehicles in the United States – mostly in California. Most of these vehicles are buses and automobiles powered by electric motors. They store hydrogen gas or liquid on board and convert the hydrogen into electricity for the motor using a fuel cell. Only a few of these vehicles burn the hydrogen directly (producing almost no pollution).
Hydrogen vehicles are starting to move from the laboratory to the road. One California family has recently leased a hydrogen car for personal use. The U.S. postal service, a package delivery company, a few Florida Park rangers, and a few private utility companies are also using hydrogen vehicles. It will probably be at least 10 years, though, before you can walk into your local car dealer and drive away in an affordable hydrogen-powered car.
Even then, you will need a place to refuel your hydrogen car. Currently, there are about 25 hydrogen refueling stations nationwide. This is the so-called “chicken and egg” problem that hydrogen developers are working hard to solve. Namely: who will buy hydrogen cars if there are no refueling stations? And who will pay to build a refueling station if there are no cars and customers?
One possible solution is to eliminate refueling stations entirely. Automobile manufacturers have already designed a refrigerator-sized hydrogen generator for your garage that works off electricity. Consumers would simply refill their cars with hydrogen each night while it is parked."
I don't know if the generators mentioned are steam-reformed or electrolysis (both described at the link I posted). Steam-reforming emits a lot of greenhouse gases. Electrolysis emits none. Cars that are fitted to use natural gas can already use hydrogen. I wonder if hydrogen would be feasible for air traffic?
