Sulfonated poly (styrene-co-maleic anhydride)-poly (ethylene glycol

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					                                      Abstract no PCNT-PO-110

  Sulfonated Poly(styrene-co-maleic anhydride)-poly(ethylene glycol)-silica
   Nanocomposite Membranes for Direct Methanol Fuel Cell Applications
                 Bijay P. Tripathi, Arunima Saxena, Mahendra Kumar, Vinod K. Shahi
    Electro-Membrane Processes Division, Central Salt and Marine Chemicals Research Institute, Bhavnagar,
                                               Gujarat, India


Recently, there is considerable interest for the development of polyelectrolyte membranes as a key component in
the most promising electrochemical devices for convenient and efficient power generation such as polymer
membrane fuel cells.1,2 Among both types of fuel cells, DMFC offers reasonably high fuel energy density, readily
stored and available liquid fuel, ease of refueling and direct and complete electro-oxidation of methanol at
moderate temperatures. Nafion®, perflurosulfonic acid copolymers are state-of-art membranes for DMFC and
hydrogen/air fuel cells due to their high conductivity, good mechanical and chemical stability. However, there is
much interest in alternative polyelectrolyte membranes because of Nafion’s reduced performance above 80 oC,
high methanol crossover and cost. Fluorine-free materials with properties comparable to Nafion is one of the
directions in the development of cheaper polyelectrolytes.

Organic-inorganic nanostructured composites constitute an emerging research field, which has opened the
possibility of tailoring new materials because they combine in a single solid both the attractive properties of a
mechanically and thermally stable inorganic backbone and the specific chemical reactivity and flexibility of the
organo functional groups.2,3 To develop polyelectrolyte membranes, several investigators reported the material,
where functional groups were either introduced on the organic part or by doping polyelectrolytes in the host matrix.
Problem with these types of composite materials associated either excessive swelling of the organic part due to its
functionalization or leaching out proton carriers on prolonged use at elevated temperature. Additionally, less effort
has been given to study the effect of spacing between inorganic segments covalently bound with organic segment.

A method for the preparation of highly conductive and stable organic-inorganic nanocomposite polyelectrolyte
membranes with controlled spacing between inorganic segment and covalently bound sulfonic acid functional
groups has been established. These polyelectrolyte membranes were prepared by condensation polymerization of
the silica precursor (tetraethylorthosilicate) in dimethylacetamide in the presence of poly(ethylene glycol) (PEG) of
desired molecular weight and sulfonated poly (styrene-co-maleic anhydride) was attached to the polymeric
backbone by hydrogen bonding. Molecular weight of PEG has been systematically changed to control the
nanostructure of the developed polymer matrix for studying effects of molecular structure on the thermal as well as
conductive properties. These polyelectrolyte membranes were extensively characterized by studying their thermo-
gravimetric analysis (TGA), ion-exchange capacity (IEC), water content, conductivity, methanol permeability and
current-voltage polarization curves under direct methanol fuel cell (DMFC) operating conditions as a function of
silica content and molecular weight of PEG used for membrane preparation. Moreover, from these studies and
estimation of selectivity parameter among all synthesized membranes, 30% silica content and 400 Dalton
molecular weight of PEG resulted best nanocomposite polyelectrolyte membranes, which exhibited comparable
performance to Nafion 117 membrane for DMFC applications.

1. V.K. Shahi, Solid State Ionics, 177 (2007) 3395
2. V.V. Binsu, R.K. Nagarale, V.K. Shahi, J. Mater. Chem., 15 (2005) 4823
3. R.K. Nagarale, G.S. Gohil, V.K. Shahi, R. Rangarajan, Macromolecules, 37(2004) 10023