14. Fuel Cells

The main advantages of fuel cells are their high efficiency for electricity production of about 60 %, and practically zero emissions if hydrogen is introduced as fuel, in contrast to combustion fuel engines whose efficiency is approximately of 20 % at most and are very polluting. Their principle of operation in hydrogen-based fuel cells is the reverse to the electrolysis process: hydrogen and oxygen (or air) react in the cell producing an electron DC current. In this chapter, we describe the most often employed fuel cell devices, their name being derived from the kind of electrolyte used. The market is dominated by the proton exchange membrane fuel cell (PEMFC), which is probably the best candidate for vehicles and portable applications. They are followed by the phosphoric acid fuel cells (PAFC), which have the advantage of using either hydrogen or natural gas that can be reformed in the cell itself. Other cells studied are the solid-state fuel cells (SOFC), which use a solid oxide electrolyte, the molten carbonate fuel cells (MCFC) that can use CO₂ from natural gas as fuel, etc.