http://www.ck12.org Chapter 23. Electrochemistry
Fuel Cells
The burning of fossil fuels to generate electricity is an inherently inefficient process; it is harmful to the environment
as well. The upper limit for a power plant is to convert about 40% of the chemical energy into electricity. Fuel cells
offer an alternative approach to extracting chemical energy in a useful form. Afuel cellisan electrochemical cell
that requires a continuous supply of reactants to keep functioning. A diagram for a hydrogen-oxygen fuel cell is
shown below (Figure23.4).
FIGURE 23.4
A hydrogen-oxygen fuel cell is a clean
source of power that generates only water
as a product.A typical hydrogen-oxygen fuel cell uses an electrolyte solution containing hot, concentrated potassium hydroxide.
The inert electrodes are made of porous carbon. Hydrogen gas is fed into the anode compartment while oxygen gas
is fed into the cathode compartment. The gases slowly diffuse through the electrodes, and the following reactions
take place.
Anode (oxidation): 2H 2 (g)+4OH−(aq)→4H 2 O(l)+4e−
Cathode (reduction): O 2 (g)+2H 2 O(l)+4e−→4OH−(aq)
Overall: 2H 2 (g)+O 2 (g)→2H 2 O(l)The standard voltage from a hydrogen-oxygen fuel cell is 1.23 V.
A number of other fuels have been developed for fuel cells, including methane, propane, and ammonia. Fuel cells
are more efficient than other engines and have been used for many years on space missions. Another advantage to
fuel cells is that they produce fewer pollutants, particularly in the case of the hydrogen-oxygen fuel cell, where the
only product of the reaction is water. The primary drawback to current fuel cell technology is that fuel cells are very
expensive to build and maintain.