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A fuel cell is similar to a battery in that an electro-chemical reaction is used to create electric current. The charge carriers can be released through an external circuit via wire connections to anode and cathode plates of the battery or the fuel cell. The major difference between fuel cells and batteries is that batteries carry a limited supply of fuel internally as an electrolytic solution and solid materials (such as the lead acid battery that contains sulfuric acid and lead plates) or as solid dry reactants such as zinc carbon powders found in a flashlight battery. Fuel cells have similar reactions; however, the reactants are gases (hydrogen and oxygen) that are combined in a catalytic process. Since the gas reactants can be fed into the fuel cell and constantly replenished, the unit will never run down like a battery. The fuel (hydrogen) enters the fuel cell, and this fuel is mixed with air, which causes the fuel to be oxidized. As the hydrogen enters the fuel cell, it is broken down into protons and electrons. In the case of proton exchange membrane fuel cells (PEMFC) and phosphoric acid fuel cells (PAFC), positively charged ions move through the electrolyte across a voltage to produce electric power. The protons and electrons are then recombined with oxygen to make water, and as this water is removed, more protons are pulled through the electrolyte to continue driving the reaction and resulting in further power production. In the case of solid oxide fuel cells (SOFC), it is not protons that move through the electrolyte, but oxygen radicals. In molten carbonate fuel cells (MCFC) carbon dioxide is required to combine with the oxygen and electrons to form carbonate ions, which are transmitted through the electrolyte. |
