Page 269 - Alternative Energy Systems in Building Design

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FUEL CELL TECHNOLOGY

Fuel cells are energy-conversion devices that produce electricity through the chemical
oxidation of a reactant, or fuel, and an oxidant. The oxidation reaction takes place in
the presence of electrolytes, which act as catalysts and strip electrons from atoms of
the fuel, promoting the circulation of electrons, or electric current, through an external
conduction path. In general, the fuel, or reactant, flows in, and reaction products flow
out, whereas the electrolytes remain in the cell. Fuel cells can use numerous types of
reactants and oxidants and can operate virtually continuously as long as the necessary
flow is maintained.
A few examples of fuel cells include combinations of reactants and oxidants such
as, hydrogen and oxygen, a hydrocarbon and alcohol, air and chlorine, and many
more. Fuel cells differ from conventional batteries in that they consume the reactant,
which must be replenished continuously, whereas batteries store electrical energy
chemically in a closed system. Another difference is that the electrodes within a battery
change and become depleted during the charging and discharging cycle, whereas fuel
cell electrodes are catalytic and relatively stable.

Fuel Cell Design

As mentioned earlier, fuel cells operate by a catalytic process that involves the sepa-
ration of the component electrons and protons from the reactant fuel, resulting in a
flow of electrons that circulates through an electronic circuit that gives rise to electric
power. Typical catalysts include platinum and a group of metal alloys. In some
instances, the catalytic process involves the circulation and recombination of electrons
with protons and produces waste products such as water and carbon dioxide.
In a typical hydrogen-oxygen proton-exchange-membrane fuel cell (PEMFC), a proton-
conducting polymer membrane, or electrolyte, separates the anode and the cathode sides
and produces water as a waste product. It should be noted that the PEMFC acronym
applies equally to polymer-electrolyte-membrane and proton-exchange-membrane fuel
cell.

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