The Principle Behind the Technology
The direct way
A fuel cell is a device that converts chemical energy directly into electricity and heat. Fuel cells can be thought of as batteries that, when provided with fuel and air, will not run down. They are electrochemical devices that convert the chemical energy of the fuel directly into electricity and heat, and do so more efficiently than conventional combustion-based technologies.
Siemens Cylindrical-tube SOFC Technology
The common types of fuel cells are phosphoric acid (PAFC), molten carbonate (MCFC), proton exchange membrane (PEM) and solid oxide (SOFC), all named after their electrolytes. Because of their different materials and operating temperatures, they have varying benefits, applications and challenges, but all share the potential for high electrical efficiency and low emissions. Because they operate at sufficiently low temperatures they produce essentially no NOx, and because they cannot tolerate sulfur and use desulfurized fuel they produce no SOx.
Because they rely on electrochemical reactions instead of combustion, fuel cells need an easily oxidized substance, such as hydrogen. Some fuel cells, such as solid oxide fuel cells (SOFC), can also utilize carbon monoxide (CO). This makes them more fuel flexible and also generally more efficient with available fuels, such as natural gas or propane. Hydrogen and CO can be produced from natural gas and other fuels by steam reforming, for example. Fuel cells like SOFCs that can reform natural gas internally have significant advantages in efficiency and simplicity when using natural gas because they do not need an external reformer.