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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. |
