Fuel cell is an electrochemical energy conversion device that produces electricity directly from chemical energy, and the by-products are only water and heat. It is seen by many pioneers that fuel cell is the solution to a whole range of environmental challenges, such as global warming and harmful levels of local pollutants. It also provides economic benefits due to the high efficiency and flexibility. The electricity produced can be used to power all sorts of devices, from cars and buses to spacecrafts, and from laptops and cellular phones to provide electricity to a factory. The by-product heat is also used in some applications, for example to keep houses warm. The produced water is required especially in space applications.