JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

1-31
Preparation of Anion-Exchange Membranes for
Fuel Cell Applications by -ray Pre-Irradiation Grafting
H. Koshikawa, T. Yamaki, M. Asano and Y. Maekawa
Environment and Industrial Materials Research Division, QuBS, JAEA
Fuel cells are considered as large sources of clean
energy because they do not emit any toxic substances and
carbon dioxide. However, their widespread
commercialization has been hindered by economic
problems associated with the extensive use of platinum as
well as by many restrictions due to much additional
infrastructure and insufficient hydrogen storage capacity.
In order to overcome such difficulties, worldwide
researchers have recently been developing anion-exchange
membrane fuel cells (AEMFCs), which do not need
expensive platinum catalysts in the electrodes. We report
here the preparation of new membranes for applications to
“hydrazine-fueled” AEMFCs 1) by the -ray pre-irradiation
2, 3)
grafting method .
Our membrane preparation involved the grafting of
chloromethylstyrene (CMS) into poly(ethylene-cotetrafluoroethylene)
(ETFE) films and subsequent
2)
quaternization (Fig. 1) . A 50 μm-thick ETFE film was
pre-irradiated at room temperature in an Ar atmosphere
with a 60 Co γ-ray at doses of 10, 20, 30 and 50 kGy. Graft
polymerization was performed by immersing the irradiated
ETFE film in the CMS/xylene 50/50 vol% solution in a N2 atmosphere at 60 ºC for 1-24 h. The ETFE-g-CMS film
was then quaternized in a 30% trimethylamine (TMA)
solution at room temperature for 24 h. After the
membrane was washed several times in water and in a
1 mol/dm 3 HCl solution for 24 h (to remove residual TMA),
the chloride form of the membrane was converted to the
alkaline form in a 1 mol/dm 3 aqueous KOH solution for 12 h.
CH CH CF CF 2 2 y CF CF 2 2 y n
ETFE (50 m) m)
CH 2 CH y CF 2 CF 2 y n
m
ETFE-g-CMS
CH 2 Cl
CH 2 CH y CF 2 CF 2 y n
-ray -ray
(CH3 ) 3 Cl
m
Quaternized membrane (Cl - (CH3 ) 3 Cl
m
Quaternized membrane (Cl form) -form) N +
N +
10-50 kGy
CH 2 CH y CF 2 CF 2 y n
CMS /xylene
60ºC 1-8h
30% TMA 1 mol/L
solution HCl
water
1mol/L
KOH water
(CH3 ) 3OH m
anion-exchange membrane (OH- (CH3 ) 3OH m
anion-exchange membrane (OH form) -form) N +
N +
Fig. 1 The scheme for the preparation of
anion-exchange membranes.
JAEA-Review 2010-065
- 35 -
Figure 2 shows the degree of grafting vs. time curves for
CMS grafting into ETFE films pre-irradiated with the γ-ray
at the different doses. The degree of grafting was
calculated as (Wg − W0)/W0 × 100, where W0 and Wg are
the film weights before and after the grafting, respectively.
The degree of grafting increased during the course of
reaction for up to 8 h. We obtained higher degree of
grafting as the pre-irradiation dose became higher. The
highest degree of grafting reached 101% at a dose of
50 kGy for 8 h.
The ratio of chloride-to-alkaline conversion, related to
the ion exchange capacity of the resulting anion-exchange
membrane, was estimated from a weight change between
before and after the treatment with the KOH aqueous
solution and by the titration technique. The conversion
ratios were approximately 60 and 50% for the
above-mentioned grafted film, respectively although the
reason for such low conversion efficiency has not yet been
given. The hydroxide ion conductivity was 0.044 S/cm at
room temperature and a relative humidity of 100%. This
value is higher than or comparable to that of the previous
4)
radiation-grafted anion-exchange membranes (0.027 S/cm) .
Degree of grafting (%)
120
100
80
60
40
20
50 kGy
30 kGy
20 kGy
10 kGy
0
0 2 4 6 8
Time (hours)
Fig. 2 The degree of grafting vs. time curves for CMS
grafting into ETFE films irradiated with γ-rays at
doses of 10, 20, 30, and 50 kGy.
References
1) K. Asazawa et al., J. Electrochem. Soc. 156 (2009)
B509.
2) H. Koshikawa et al., 59th SPSJ Ann. Meet. (2010)
1239.
3) T. Yamaki, J. Power Sources, in press.
4) J.R. Varcoe et al., Chem. Mater. 19 (2007) 2686.