Environmental Engineering Reference
In-Depth Information
out the electrochemical reaction. At present, rapid unassisted cold start of PEMFC
stacks is still hardly feasible, especially when room temperatures reach values
lower than -20C[
51
]. The warm-up of the stack starting from subfreezing tem-
peratures implies that stack temperature must be raised above 0C before the ice
completely covers the cathode surface, blocking the reaction progress. Managing
buildup of ice is the key to realize an effective start-up, and recent modeling studies
suggest that it is useful to operate the stack near short-circuit conditions [
51
], as
''ohmic heat'' (Eq.
4.7
) is the largest heating source at low cell voltages [
52
].
4.6.3 FCS Costs
A discussion on manufactured costs of fuel cell vehicles, with particular emphasis
to PEMFC stacks and BOP components, is useful to assess the present limits for
the commercialization with high production volumes. Recent evaluations evi-
denced that the estimated costs related to PEMFC and integrated FCSs results too
high, at least four to five times higher than conventional engines [
15
,
53
,
54
]. At
this regard PEMFC stack materials and the relative complexity of FCS play an
important role in determining the overall expected cost. A drastic reduction of the
costs is then crucial for a realistic application in automotive field.
Projected costs for an high pressure plant of about 80 kWe realized by Argonne
Laboratories in 2005 have been fully estimated [
15
], considering the existent
technology but also including some conceptual future possibilities for improved
materials and related FCS management strategies. In the Table
4.2
a breakdown of
the most significant costs for FCS components, expressed as percentage ratio
between the individual component and actual reference FCS cost, is summarized. It
can be noted that the stack is largely the most expensive device in H
2
FCS (63%), but
future developments could strongly reduce its impact on overall cost (about 30%).
The electrodes represent, in stack manufacture, the main outlay (77%), while
membranes (6%), gas diffusion layers (5%), and bipolar plats (5%) follow spaced
out. Electrode costs are strictly related to the very expensive Pt content. Thus,
Table 4.2 Projected costs for stack and BOP components
FCS component
Projected actual
cost (%)
Projected future
cost (%)
Stack
63
30
Air management system
13
12
Water management system (humidifiers)
7
3
Fuel supply system (blowers and ejectors)
4
4
Coolant pumps and fans
4
3
Miscellaneous and assembly
9
9
Total
Overall FCS cost
100
61
Adapted from ref. [
15
]
