Dehydration of polymer films is studied by TGA and kinetic analysis.

1. Water Loss in Polymer Used as Proton
Exchange Membrane (PEM) in Fuel Cell
Goals of the Project
In the operation of PEMFC, membrane hydration is critical.
It determines proton conductivity, methanol permeability
and electro-osmotic drag. Kinetic analysis of dehydration
shows how strong polymer membrane holds the uptake
water.

2. Free water: freezes at the usual
freezing point.
nonfreezing
bound
water
Freezing
Free water bound Nonfreezing bound water:
water
closely associated with
polymer matrix and does
H20 not freeze at the usual
freezing point.
Freezing bound water:
freezes at a temperature
lower than the usual
freezing point and shows
significantly smaller
enthalpy than that of bulk
water.

3. Methods
Experiment
Thermogravimetry (TG)
Differential Scanning Calorimetry (DSC)
Kinetic Analysis
 qi  E
Coats and Redfern method ln  2
T   const 

  ,i  RT ,i

4. Polymer Systems—Nafion, PPDSA, PBPDSA
and Copolymer
SO3H
* *
n
SO3H
Nafion 115, 117, 212 PBPDSA
poly(biphenylene disulfonic acid)
SO3H
SO3H SO3H
*
n *
* co *
0.2 0.8
SO3H
SO3H SO3H
PPDSA
PBPDSA-co-PPDSA
poly(p-phenylene-2,5-disulfonic acid)

5. Kinetics Analysis of Dehydration
86 o
2 C/min
o
10 C/min
Dehydration in PPDSA
84 o
20 C/min
Mass Fraction /%
82
58
80
78
76 56
Ea / kJ mol -1
74
300 400 500 600 54
T /K
52
0.0 0.2 0.4 0.6 0.8 1.0
58

56
Ea / kJ mol -1
54
52
0.0 0.2 0.4 0.6


6. Dehydration in Nafion 117
o
100 2 C/min
o
10 C/min
o
98 20 C/min 160
Weight Loss /%
96
140
-1
E / kJ mol
94
120
92
90 100
0 50 100 150 200 250
80
T/
oC
0.0 0.2 0.4 0.6 0.8 1.0

Eα of dehydration of Nafion is much
Higher than that of PPDSA
Nafion holds water much better than
PPDSA.

7. Summary
Eα of dehydration of Nafion is much Higher than that
of PPDSA. Nafion holds water much better than
PPDSA.
Kinetic analysis provides important information for
mechanism studies.