Page 29 - Introduction to Transfer Phenomena in PEM Fuel Cells

18 Introduction to Transfer Phenomena in PEM Fuel Cells
1.2.1.3.1. Operating characteristics
Table 1.4 summarizes the characteristics and performance of AFC
[BOU 07].
Characteristics and performance
Operating temperature 60 to 90°C
Operating pressure 1 to 5 bars
Electrical efficiency > 60% (with pure hydrogen)
Actual voltage 0.7 to 1.0 V
Current density 100–200 m A/cm²
Start-up time Several minutes
Response time to a rapid variation in demand Relatively quick
Lifetime 5,000 hours (value in 2006)

Table 1.4. Characteristics and performances of an AFC

1.2.1.3.2. Advantages and disadvantages

Alkaline fuel cells have the advantage of allowing the use of non-
precious catalysts based on nickel for the anode and activated carbon for the
cathode.

They may also have the following advantages [BOU 07]:
– operation at atmospheric pressure and at low temperature;

– low costs of the electrolyte and catalysts;
– response time and fast start time;
– high electrical efficiency;

– operates at low temperature (below 0°C).

The main disadvantage posed by this type of battery is their sensitivity to
carbon dioxide (CO 2) which, remember, is present in the air. This sensitivity
implies a thorough purification of hydrogen (total elimination of CO 2) when it
is obtained by reforming a hydrocarbon fuel. For this reason, the AFC battery
has been abandoned for transport applications. Another reason for this is due
to the liquid and corrosive state of the electrolyte which, subject to the
transport constraints (vibrations, accelerations, etc.), can leak from the battery.