Organic-Inorganic Hybrid Protonic Polymeric Electrolytes Grafted by Sulfonic Acid / Sulfonamide Moieties
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1 12 Laurent Depre , , Christiane Poinsignonr , Michael POPALL LEPMI-ENSEEG BP75 F-38402 St Martin d'H~res Cedex. France 2 Fraunhofer Institut fur Silicatforschung, Neunerplatz 2, D-97082 Wurzburg. Germany 1
ABSTRACT Thin proton conducting membranes of an organic-inorganic polymer electrolyte bearing sulphonamide and sulfonic groups are prepared by sol-gel process. Polycondensation of alkoxysilanes provides the inorganic silicate backbone whereas the organic network is formed from reactive functional groups R'((-CH2)3-SO3H) and [(-CH2)3-SO2 NH2] of alkoxysilanes of R'Si[OR3] type. Proton conductivity measured in the dry and wet state under controlled1 2 1 Temperature and Relative Humidity increases from 10 -4 S.cm- under vacuum to 6 10- S.cmat 70'C and 96% RH. Conductivity dependence on temperature and associated conduction mechanisms are discussed in both states. INTRODUCTION Most part of anhydrous proton conducting polymers were prepared in mixing strong acids with polymers bearing donor centre [oxygen or nitrogen] using similar strategy to the one adopted in the area of polymer electrolytes through the complexation of polyether chains by alkali salts [1]. The acids used have been mainly H2SO4 and H3PO4, which are themselves good proton conductors when pure, due to self ionisation and self solvatation. Proton transfer is ensured by translocation or Grotthus mechanism between complex anions HS04-, H2PO4involved in a reorientation motion around their 4 fold axis. This mechanism was carefully analysed by Lassegues et al [2] in the study of XHSO4 compounds where X was Cs, amines and polyamines, and finally polyethylene imine. Proton Conduction in the dry state occurs by conjugated processes of translocation and transportation : organic polymeric chain of polyethylene oxide (POE) and branched polyethylene imine (BPEI) bearing basic site as
Oxygen or Nitrogen atoms are able to accept the free proton delivered by anhydrous H3PO4 or H2SO4 [3] . Translocation occurs when H+ is able to jump from H2SO4 to a basic atom of the chain : this jump is correlated to segmental diffusion motions of the polymeric chain which
polymer
x
acid/Base
a 300K [Sycm3l]
_____
1
-T53
a373K [S.cml] ____]
POE
0.5
H3PO4
1
H3PO4
BPEI
0.8
H2SO4
5W10-4
Paam Aminosils
1.5 1.5 0.1
H2SO4 H2SO4 HCIO4
6.3 10 -3 1.2 1 0-4 10-6
POE
4
Sulfamide
10-7
PMPEGM
4
Sulfamide
T5 10-5
undoped
10-6
25
imidazole
5 10-6
__4_1_0-4
PVP
Sulfamide Sulfamide
0.05
reference
[eV]
BPEI
_10-5 _
Ea [373K]
3
_
3 10-4
.4 10-T
0.48
2
0.35
4
0.08
8 2 6,7
1.1 1-1 2.2 10-4
0.32
8
10-4
9
11 __
11
Table 1: Characteristics values of several polymers-acid / base blends (x is the number of acid/base molecule for monomer unit). 253 Mat. Res. Soc. Symp. Proc. Vol. 575 © 2000 Materials Research Society
ensures the charge transfer providing POE or BPEI are not in the crystalline phase. That needs those polymers to work in the amorphous phase, above 65°C for POE based electrolytes. A review of all these acidic polymers is given in
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