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Fuel Cells 255

infrastructure. For fuel cells to compete with contemporary power gen-
eration technology, they have to become competitive in terms of the cost
per kilowatt required to purchase and install a power system. A fuel cell
system needs to cost ~$30/kW to be competitive for transportation appli-
cations and for stationary systems; the acceptable price range is
$400–$750/kW for widespread commercial application [9]. Fuel cell tech-
nology needs a few breakthroughs in development to become competi-
tive with other advanced power generation technologies.

9.3 Types of Fuel Cells
Fuel cells are classified primarily on the basis of the electrolyte they use.
The electrolyte is the heart of the fuel cell as it decides the important
operating parameters such as the electrochemical reactions that take
place in the cell, the type of catalysts required, the temperature range of
cell operation, and the fuel (reactants) to be used, and therefore the
applications for which these cells are most suitable. There are several
types of fuel cells currently under development; a few of the most prom-
ising types include

Polymer electrolyte membrane fuel cells (PEMFCs)
Direct methanol fuel cells (DMFCs)
Alkaline electrolyte fuel cells (AFCs)
Phosphoric acid fuel cells (PAFCs)
Molten carbonate fuel cells (MCFCs)
Solid oxide fuel cells (SOFCs)
Biofuel cells

9.3.1 Polymer electrolyte membrane
fuel cells (PEMFCs)
The PEMFC uses a solid polymer membrane as an electrolyte. The main
components of this fuel cell are an electron-conducting anode consist-
ing of a porous gas diffusion layer as an electrode and an anodic cata-
lyst layer; a proton-conducting electrolyte, a hydrated solid membrane;
an electron-conducting cathode consisting of a cathodic catalyst layer
and a porous gas diffusion layer as an electrode; and current collectors
with the reactant gas flow fields (see Fig. 9.3).
In the PEMFC, platinum or platinum alloys in nanometer-size par-
ticles are used as the electrocatalysts with Nafion TM (a DuPont trade-
mark) membranes [3, 10–12]. The polymer electrolyte membranes have
some unusual properties: In a hydrated membrane, the negative ions
are rigidly held within its structure and are not allowed to pass through.