Low-Cost Nanomaterials for High-Performance Polymer Electrolyte Fuel Cells (PEMFCs) - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 352

Scheme 1 Three types of
electrochemical energy
conversion and storage
devices and their basic
classification
Fuel cells are electrochemical devices that convert the chemical energy stored
in a fuel directly to electrical energy by sustaining separate redox reactions at the
cathode and anode respectively separated by an electrolyte. The electrode reac-
tions do take place at the three-phase interface (more specifically on the surface of
electrocatalyst), leaving ions to pass through the electrolyte and electrons through
the external circuit. Unlike batteries, fuel cells can operate continuously as long as
the necessary reactant, fuel and oxidant, flows are maintained. By stacking hun-
dreds of such single cells, known as membrane-electrode assemblies (MEAs) in a
modular form, fuel cell power plants can be erected to provide electricity for a
number of applications such as electric vehicles, large grid connected utility power
plants for stationary and portable power applications [ 17 ].
Despite the electrochemical similarities between fuel cells and batteries, bat-
teries have limited space for reactant storage and hence need to get recharged quite
often for practical applications. For example, in fuel cells the reactants are con-
tinuously supplied externally which make them an ideal choice for applications
that require the sustained delivery of power unlike that of batteries. Further, due to
the external supply of fuel cells, filling up (recharging or more correctly replacing
the feed) can be much faster than that of batteries. Also, fuel cells and batteries are
not limited by the Carnot efficiency and hence have higher practical efficiency than
the ICEs. However, many types of batteries have disposal and recyclability issues
and hence special efforts are being made in recent times to make greener batteries.
Fuel cells normally do not have any moving parts which reduce the wear and tear
of their components. The only by-product when pure hydrogen is used as the fuel
is water, thus making them environmental friendly. Due to those above-mentioned
advantages, different types of fuel cells using innovative materials are under
intense research and development for both stationary and transport applications.
4 Polymer Electrolyte Membrane Fuel Cells (PEMFCs)
PEMFCs utilize a solid polymer electrolyte membrane (hence PEM, also meaning
proton exchange membrane) to transport protons from anode to cathode and
restrict electrons from directly going to cathode from anode. PEMFCs operate