HIGH TEMPERATURE POLYMER FUEL CELLS
QINGFENG LI , JENS OLUF JENSEN, CHAO PAN, ANDREAS VESTBØ and NIELS J. BJERRUM
Materials Science Group, Department of Chemistry, Technical University of Denmark
Building 207, DK-2800 Lyngby
High temperature proton exchange membrane fuel cell
(PEMFC) is the focus of recent development. Compared
with the technology based on perfluorosulfonic acid
(PFSA, e.g. Nafion®) membranes, the new PEMFC
using acid doped polybenzimidazole (PBI) membranes
can operate at temperatures up to 200°C. At higher
temperatures, the kinetics for electrode reactions is
enhanced. Over its boiling point, the water management
is easier. In fact the acid doped PBI membranes can
operate at very low atmospheric humidity. Tolerance to
fuel impurities e.g. CO is dramatically enhanced, which
in turn will decisively simplify the fuel processing
system. The thermal management, i.e. cooling will be
simple due to the increased temperature gradient. The
heat from the fuel cell stack can be recovered in several
way so that the overall system efficiency will be
increased. The following is an illustration of these
1 kW high temperature PEMFC stack, consisting of 40 cell stack with
technical features.
electrode area of 256 cm². Constructed in the AMFC project (EUFP5)
Water management - system construction and operation
Water is a necessity for FC
operation, i.e. both fuel and
oxidant need to be carefully
humidified by the water condensed
from the exhaust. A cooling loop is
normally integrated.
HT-PEMFC does not need the
water management.
CO tolerance and the fuel processing system
Fuel
vaporizer
Fuel
stoarge
Steam
Water
reformer
-gas
Selective
oxidizer
shift
PEMFC
80°C Air
Catalytic burner
Heating
80-200°C
11.3 kJ
1.6%
Ref.
200°C
3H2
200°C
840 kJ
115.7%
80°C
FC
80°C
0.6V
Fuel
stoarge
Steam
PEMFC
reformer
200°C
Catalytic burner
Heat utilization in systems with the fuel cell at 80 and 200°C
El, 303 kJ
41.7%
Heat, 441 kJ
60.7%
Heat
loss
397 kJ
54.6%
For FC at 80°C with a methanol
reformer or with a hydrogen
storage tank at 200°C, the heat
for reforming or desorption is
from burning of fresh fuel.
H2
25°C
286 kJ
100%
NaAlH4
200°C
H2
200°C
280 kJ
98.0%
H2
200°C
245 kJ
85.8%
Heat for
desorption
35 kJ
12.3%
Burner
Cooler.
Evaporation
CH3OH
35 kJ
4.9%
Reforming
57 kJ
7.8%
H2 used for
heating
and reforming
109 kJ
15.0%
Cooler.
200°C
80°C
Evaporation
H2O
40.6 kJ
5.6%
Heater, evap.
Heating
to 80°
8.6 kJ
1.1%
Heater, evap.
1MeOH
1H2O
25°C
726 kJ
100%
Burner
The FC tolerance to CO at
80°C is 10-100 ppm while at
200°C is 30,000 ppm. High
CO tolerance make it
possible to use reformate
hydrogen directly from a
reformer or even possible to
integrate the reformer and
FC stack.
FC
80°C
0.6V
El, 99 kJ
34.7%
Heat, 144 kJ
50.5%
Air