Page 48 - Introduction to Transfer Phenomena in PEM Fuel Cells

Introduction to Hydrogen Technology 37
On the contrary, it is important to note that a fuel cell module, to operate,
must be associated with ancillary equipment that supplies reagents
(hydrogen and air), their conditioning (pressure, hygrometry and flow rate)
and the control of the reaction products (water, heat, electricity). These
ancillaries can represent up to 60% in mass and volume of the system and an
energy expenditure of around 20%. Fuel storage is the main technological
hurdle, because it determines, for certain applications, the autonomy of the
system.
Most car manufacturers have been developing fuel cell models over the
last decade and they have produced at least one prototype. The best reason
for developing fuel cell vehicles is their efficiency, as well as their very low
polluting or zero emissions.

Fuel cell vehicles have at least one of these advantages:

– the fuel cell produces all the energy required to operate the vehicle;
– a battery can be used for start-up;

– a fuel cell performs best at constant power, therefore for accelerations
or for power peaks, devices such as batteries or ultracapacitor batteries are
used in addition;
– in certain vehicle models, the primary source of energy may be
batteries, in which case the fuel cell becomes the secondary source whose
task is to recharge the batteries;

– the fuel cell can supply energy to all or part of the vehicle.

The operating temperature of a car fuel cell varies from 50 to 80°C; a
temperature above 100°C would improve heat transfer and simplify the
cooling of the battery, but most vehicles use proton-exchange membrane fuel
cell (PEMFC) or direct methanol fuel cell (DMFC), whose operating
temperature cannot reach 100°C, to facilitate water circulation inside the cell
[HOR 09].

1.3.1. The basic structure of the PEMFC

A PEMFC cell is an electrochemical device that converts chemical
energy of a reaction directly into electrical energy while releasing heat and
producing water.