A fuel cell is an electrochemical
energy conversion device. Fuel cells differ from batteries in that they are designed for continuous replenishment of the reactants
consumed; they produce electricity from an external supply of fuel and oxidant (typically oxygen or air, although chlorine
and chlorine dioxide have also been used among others) as opposed to the limited internal energy storage capacity of a
battery. Additionally, while the electrodes within a battery react and change as they are charged or discharged, a fuel cell's
electrodes are catalytic and relatively stable, therefore unchanging. A fuel cell is a far advanced type of energy production
and device compared to a battery, it is unprecedented in it's ability to produce, replenish, and produce again spontaneously.
Normal reactants used in a fuel cell
are hydrogen on the anode side and oxygen on the cathode side (a hydrogen cell). In most cases, reactants flow in and reaction
products flow out. Though the still electrolyte remains in the cell. Virtually continuous long-term operation is feasible
as long as these flows continue.
the archetypal example of a hydrogen/oxygen proton exchange membrane fuel cell (PEMFC), a proton-conducting polymer membrane,
(the electrolyte), separates the anode and cathode sides.
On the anode side, hydrogen diffuses to the anode catalyst where it dissociates into protons
and electrons. The protons are conducted through the membrane to the cathode, but the electrons are forced to travel in an
external circuit (supplying power) because the membrane is electrically insulating. On the cathode catalyst, oxygen molecules
react with the electrons (which have traveled through the external circuit) and protons to form water. In this example, the
only waste product is water vapor and/or liquid water.
In addition to pure hydrogen, there are hydrocarbon fuels for fuel cells, including diesel, methanol
(direct-methanol fuel cells) and chemical hydrides. The waste products with these types of fuel are carbon dioxide and water.
Unfortunately there are so far few fuel cells that are being produced that can provide energy without the byproduct of carbon
dioxide. Hydrogen fuel cells can produce energy without CO2 but are not yet mass produced and are still in the final stages
of their development.
used in fuel cells differ from each type. The electrode/bipolar plates are usually made of metal, nickel or carbon nano-tubes,
and are coated with a catalyst (like platinum, nano iron powders or palladium) for higher efficiency. Carbon paper separates
them from the electrolyte. The electrolyte of a cell could be ceramic or a membrane in type.
A typical fuel cell produces about 0.86 volts. To create enough
voltage, the cells are layered and combined in series and parallel circuits to form a fuel cell stack. The number of cells
used is usually greater than 45 but varies with design.