Computers at the First National Bank of Omaha get energy from them. Some of Chicago's public transit buses use them. They are fuel cells.
Fuel cells are electrochemical devices that produce electrical power without combustion.
They generate electricity chemically, much in the manner that batteries do. But the chemicals that fuel cells use are elemental hydrogen and oxygen, and the product of the chemical reaction is water. Inputs such as natural gas can also be used, though, of course, hydrocarbon fuels would generate some level of carbon dioxide emissions. Because fuel cells can be made highly efficient and clean, they hold great promise as an environmentally sound energy source that could help reduce greenhouse gas emissions and other pollution. The main obstacle to widespread use of fuel cells is their high cost relative to other devices for generating electricity or powering vehicles.