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What are Fuel Cells?
Fuel cells are energy conversion devices that continuously transform the chemical energy of
a fuel and an oxidant into electrical energy. This energy conversion process is accomplished
by means of an electrochemical reaction whereby the reactants are consumed,
by-products are expelled, and heat may be released or consumed. Fuel cells will continue
to generate electricity as long as both fuel and oxidant are available. Pure hydrogen,
hydrocarbons, alcohols, and hydrazine are common fuels while pure oxygen and air are
conventional oxidants. For space
applications, pure hydrogen and oxygen function exclusively as the fuel and oxidant,
respectively, while water and heat are the sole reaction products.
How a Fuel Cell Works
![[Fuel Cell Diagram Thumbnail]](../images/fuel_cellsm.jpg)
Figure 1. Simplified Diagram of the H2 - 02 Proton Exchange
Membrane Fuel Cell Operating Principals
A simplified description of a H2-02 Proton Exchange Membrane (PEM) Fuel
cell will illustrate, in general, how a fuel cell works. The fuel cell consists of a negative
electrode (the anode), a positive electrode (the cathode), and an electrolyte. Fuel gas (in
this case pure hydrogen) is transported through the anode towards the anode-electrolyte interface
where the following (simplified) oxidation reaction occurs:
H2(g) = 2H+ + 2e-
The liberated electrons migrate out of the anode and through the external circuit where work is performed, then finally, into the cathode. On the other hand, the positive hydrogen ions (H+) migrate across the electrolyte, towards the cathode, where they ultimately react with oxygen gas and electrons to form water according to:
2H+ + 1/2 02 (g) + 2e- = H20
The overall fuel cell reaction then is simply:
H2 + 1/2 02 = H20
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