Boeing has completed test flights of a two-seater airplane powered solely by fuel cells and lithium-ion batteries. During liftoff the plane used both of these power sources. Upon reaching a cruising altitude of 1000 meters, the batteries were disconnected and the plane flew for about 20 minutes at 100 km/h powered only by the fuel cells.

Fuel cells are an intriguing power system and have most commonly been used in space vehicles. They convert hydrogen directly into electricity and heat. Water is the only exhaust product.

We shouldn't expect to see commercially viable electric planes any time soon. Aviation applications will most likely include small unmanned aircraft or auxiliary power systems.