Control of A Running H2/O2 Fuel Cell With Filled Polymeric Membranes by Impedance Spectroscopy
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S.cm-1 at 250 C), [6]. Filling a moderate capacity polyelectrolyte with H3 reinforces the membrane, avoids an excessive water swelling, while increasing the proton conductivity. Exchange capacity value in between 1.2 and 1.4 meq/g is selected after sulfonation of polysulfone according to [4]. The first generation of H3 filled membranes was prepared with sulfonated polysulfone (SPS) of different cation exchange capacities (cec) : 0.76meq/g., 0.9, 1.1, 1.3 and 1.4 meq/g. Dispersion H3 particles of 10 ýtm grain size was achieved in a SPS solution of a hydrophobic mixture of isopropanol - dichloromethane : the membrane was shaped by casting. During solvent evaporation, H3 aggregates were drive on the upper face of the membrane, leading to an anisotropic material. Some conductivity measurements of a SPS membrane filled with increasing weight of H3 show an optimum value for 8% in H3. (Fig.2) Table I: Conductivity values, cec of pristine SPS and Filled SPS. Sample
cec (meq/g)
I
(40C)(X 10-2) (y (60oC)(x 10-2) (y (80'C)(x 10-2) cecf (S.cm 1 ) (S.cm-1) (S.cm-1)
Of -
SPS 1 SPS1 3,5%H3
0.8 1.
0.001 0.19
0.006 0.35
0.009 0.42
1 1.16
1 >100
SPS2 SPS2 3,5%H SPS2 8%H3 SPS1 12%H3
1.1 1.16 1.28 1.4
0.17 0.9 1.62 1.28
0.21 1.86 1.32
0.24 1.24 1.95 1.6
1 1.1 1.2 1.4
1 5 8 7
SPS3 SPS3 3,5%H3 SPS3 8%H3
1.3 1.34 1.45
0.28 1.8 2.42
0.6 1.86 2,42
0.85 2,5 3,5
1 1,06 1,15
1 3 8
SPS4 SPS4 3,5%H3 SPS4 8%H3
1.4
1.65
2.13
2.5
1
1
1.68
3.45
4.0
5.
1.2
2
£f= filled, p= pristine) Table I provides exchange capacity values of pristine and filled sulfonated polysulfone and the associated conductivity values. The last column compares the ratio between cec of pristine and filled membranes and the associated conductivity values. It clearly appears that a few quantity of H3 improves significantly the conductivity of the membrane, specially for the less sulfonated SPS(c.e.c.=0.9meq/g). Indeed more sulfonated is the polysulfone backbone, less active is the filler. Conductivity improvement of the 1.4 meq/g cec SPS is only 2 whereas for the lowest cec membrane (0.8 meq/g) which does not exhibit significant conduction properties, this factor is 200. 2-Second generation of membranes : submicronic H3 particles dispersed in a hydrophilic SPS solution: Improvements were obtained for the preparation of the composite membrane in using submicronic particles of H3 prepared by high energy grinding and a SPS solution of a hydrophilic solvent: Dimethyl glycolmethoxy ether (DGME), allowing an homogenous dispersion of submicronic particles of H3 to be obtained. After casting XRD diagrams of the upper face of the membrane do no more exhibit any H3 diffraction lines and analysis by
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scanning electron microscope confirms the homogenous dispersion of the filler in the polymeric matrix, [4]. Conductivity measurements of filled-unfilled SPS of different c.e.c were performed 0 under controlled temperature and relative humidity (RH), from 25 C to 80°C with RH going from 50 to 100%. Table II provides the c.e.c and corresponding conductiv
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