Fuel cell is a device that directly generates electrical energy through a chemical reaction.

Fuel cells typically use hydrogen as the most common fuel, reacting with oxygen to produce water and heat.

This reaction generates electricity, which is supplied through an external circuit.

Fuel cells are generally highly efficient and are considered environmentally friendly power sources.

Additionally, they can use various fuels other than hydrogen, such as methanol or ammonia.

Fuel cells are used in various applications including vehicles, ships, backup power systems, and industrial power.

See here for examples of fuel cell vehicles using auxiliary power sources.