Environmental Engineering Reference
In-Depth Information
Chapter 3
Fuel Cells for Automotive Applications
According to the general definition of galvanic cell, any type of fuel cell can be
regarded as a device able to produce DC electricity directly from chemicals. The
same definition could also be applied to batteries during its discharging phase, but
two substantial differences exist between batteries and fuel cells: (i) in a battery the
chemicals providing the electron flow are contained into the same body of the
device, putting a limit to its capacity (specific energy of the battery) while in a fuel
cell they are continuously supplied from external sources, (ii) a battery is able to
give back the DC electricity previously stored in it (during its operation as elec-
trolytic cell, in the recharging phase), and produced elsewhere, while a fuel cell
generates DC electricity by fuel electrochemical oxidation. When a rechargeable
battery receives DC electricity, a chemical reaction is forced to occur, composed by
two semi-reactions on each of the two electrodes, which are involved in the
chemical transformation (electrolysis, see
Sect. 2.1.2
). The electricity stored as
chemical energy into the new materials formed on electrodes is ready to be spon-
taneously released when an electric circuit is closed between the two terminals, with
reinstatement of the original electrode materials. Differently, in a fuel cell the
electrochemical oxidation of an external fuel takes place on electrodes which do not
undergo chemical changes, in particular the fuel is oxidized at the anode, while the
oxygen is reduced at the cathode, producing DC electricity, heat, and other chemical
compounds, whose nature depends on the type of fuel oxidized at the anode. For
applications in the transportation sector, electricity is considered the main product,
while the chemicals produced and heat are byproducts (for stationary applications,
such as co-generation plants, also heat has to be considered as prime product).
A more detailed description of different types of batteries and other electric
energy storage systems for electric vehicles can be found in
Sect. 5.3
, while a
description of the main characteristics and properties of fuel cells for automotive
application is given here, starting from some basic concepts of electrochemistry
and thermodynamic, and focusing the attention on the operative parameters to be
regulated to obtain the best performance in the specific application.
