This invention relates to inorganic-organic hybrid
membranes with low methanol permeability characteristics
for possible direct methanol fuel cell (DMFC), architected,
formulated and fabricated through blending of polyvinyl
alcohol (PVA) - polyacrylamide (PAM) followed by cross-
linking with glutaraldehyde (Glu). Cesium salts of
heteropolyacids such as phosphomolybdic acid (PMA),
phosphotungstic acid (PWA) and silicotungstic acid (SWA)
were incorporated into the polymer network to form
corresponding hybrid membrane materials namely PVA-
PAM-CsPMA-Glu, PVA-PAM-CsPWA-Glu and PVA-PAM-
CsSWA-Glu respectively. All the three fabricated hybrid
polymer membranes exhibited excellent swelling, thermal,
oxidative and additive stability properties with desired proton
conductivity. A dense network formation has been achieved
through blending of PVA-PAM and crosslinking with Glu
which led to an order of magnitude decrease in methanol
permeability compared to the state of the art commercial
Nafion 115 membrane. The hybrid membrane containing
cesium salt of SWA exhibited very low methanol permeability
(1.4 x 10'^ cm^s"'') compared to other membranes containing
cesium salt of heteropolyacids such as PMA and PWA. The
results illustrate the attractive features and suitability of the

fabricated hybrid membranes as electrolyte for direct methanol fuel cell (DMFC) applications.
Direct methanol fuel cell (DMFC) technology is considered as an alternative energy source for portable applications owing to its high energy density, low temperature operation, system simplicity and for the ease of handling liquid fuel methanol. A reliable and successful performance of DMFC depends critically on the role played by the membrane, one of the main components of a fuel cell. Hence membranes having high proton conductivity, low methanol permeability along with good electrochemical and dimensional stability have been the targets for DMFC application. Extensive efforts have been made to reduce the methanol permeability in the polymer electrolyte membranes through various approaches, for example, i) reducing the proton transport channels by Incorporating various ceramic fillers (ii) modifying the surface of the membrane by applying plasma, ion or electron beam thereby affecting the transport properties of the membrane or iii) designing inorganic-organic hybrid membranes. The later approach has attracted attention because such hybrids may show controllable thermal and mechanical properties by virtue of

the combination of the properties of organic polymers and inorganic compounds such as hygroscopic oxides or solid inorganic proton conductors.
In the present invention, we report the formulation and fabrication of a new class of hybrid membranes containing cesium salt of different heteropolyacids such as phosphomolybdic acid (PMA), phosphotungstic acid (PWA) and silicotungstic acid (SWA) incorporated into the polyvinyl alcohol (PVA)-polyacrylamide (PAM) blend. A simple fabrication route was adopted in the preparation of these hybrid materials. These membranes have passed through various physico-chemical tests, morphological studies and permeability experiments. The suitability of these membranes for direct methanol fuel cell application has been explored by carefully investigating various required key characteristics of the membrane such as proton conductivity, water uptake and ion-exchange property. The membranes exhibited desired properties for DMFC application such as low methanol crossover, optimum swelling with desired proton conductivity, excellent additive and oxidative stability. These membranes have the additional advantage of cost

effectiveness compared to present commercial Nafion membranes.
EXAMPLE
Cesium salts of various heteropolyacids such as phosphomolybdic acid (PMA), phosphotungstic acid (PWA) and sllicotungstic acid (SWA) were synthesized at room temperature by neutralization of respective acid solution with appropriate amount of 0.1 M cesium carbonate solution. Attempts were made to control the number of protons substituted as two by controlling the stoichiometry of the added cesium carbonate solution. The crystals were dried at room temperature and kept under constant humidity of air until constant mass was attained.
The hybrid membranes were fabricated through a solution-cast method. A 10.0 wt % of PVA {MW: 125,000, SRL Chemicals, India) solution in water was prepared under vigorous stirring at 70 "C. To this solution, a mixture of 10.0 wt % of PAM (l\AW\ 5,000,000, Otto Kemi. India) dissolved in water and required quantity of one of the cesium salt of heteropolyacids such as phosphomolybdic acid (PMA),

phosphotungstic acid (PWA) or silicotungstic acid (SWA) were added and stirred for 6 h, to obtain a homogenous solution. The weight percent of PAM and heteropolyacids in the hybrid membrane was maintained as 10.0 each. The homogeneous solution was spread uniformly on a clean glass plate and leveled perfectly. Water was removed slowly by keeping the glass plate at room temperature and the dried membrane was detached from the glass plate. The obtained dry membrane was immersed into crosslinking bath containing glutaraldehyde, acetone and hydrochloric acid for 30 min at room temperature.
The Fourier transformed infrared (FTIR) spectroscopic measurements (Nicolet 6700 FT-IR interfaced with Omnic software) for the hybrid membranes were made in the wave number range 600-4000 cm"'' at room temperature (RT). X-ray diffraction (XRD) patterns were collected with a Rigaku D/max 2400 powder diffractometer using CUKQ as a radiation source. The thermogravi metric analysis (TGA) was performed on a Perkin-Elmer TG/DTA (Diamond) instrument at a heating rate of 20 K min"^ under air atmosphere. iViorphological characteristics of the hybrid membrane materials were examined by using a scanning electron

microscope (SEM) (FEI, Model:Quanta 200) to observe the microstructures. All of the images were taken in secondary electron mode. The oxidative stability of the fabricated membranes was tested by immersing the membrane sample (90-100 mg) into 50 ml of Fenton's reagent (3% H2O2 containing 2 ppm FeS04) at room temperature. The membrane samples were intermittently taken out of the oxidative solution and weighed after removing the surface attached water. Oxidative stability of the fabricated hybrid membranes was evaluated from the weight change of the membrane stripe. Proton conductivity studies of the fabricated membranes were done by employing an alternate current (ac) impedance technique (PARSTAT 2263) using four electrode probe method, in which the ac frequency was scanned from 1 MHz to 1 Hz at an amplitude of 5 mV. Fully hydrated membranes were sandwiched in a Teflon conductivity cell equipped with Pt foil contacts and the impedance was measured by placing the cell in a temperature-controlled chamber under a temperature range of 303-353 K. Constant relative humidity (RH) was maintained at 50 % RH by using saturated magnesium nitrate [Mg(N03)2] and It was sensed by a hygrometer which was calibrated prior to the experiments. Cyclic voltammetric

technique (Bioanalytical Systems (BAS), USA) was used to estimate the amount of crossed-over methanol. For this experiment, a two compartment glass cell was employed by mounting the membrane under examination at the middle by separating the two houses. These experiments were repeated three times to confirm the reproducibility of the results obtained. The variation in the obtained results was found to be less than 2 %.
After the physico-chemical characterization and morphological studies, the prepared hybrid materials were examined for their suitability to function as a membrane material for direct methanol fuel cells.
The membranes proposed herein have an interpenetrating network formed by the blending of PVA with PAM and this leads to an order of decrease in methanol crossover and swelling compared to state of the art Nation® 115 membrane employed for DMFC applications.

We Claim:
1. Inorganic-organic hybrid membranes comprising a blend of polyvinyl alcohol (PVA) - polyacrylamlde (PAM) cross-linked with glutaraldehyde (Gtu) to form a polymer network; cesium salts of heteropolyacids incorporated into the polymer network to form corresponding hybrid membrane materials namely PVA-PAM-CsPMA-Glu, PVA-PAM-CsPWA-Glu and PVA-PAM-CsSWA-Glu respectively.
2. Inorganic-hybrid membranes as claimed in Claim 1 wherein the heteropolyacids consist of phosphomolybdic acid (PMA), phosphotungstic acid (PWA) and silicotungstic acid (SWA).
3. Inorganic-organic hybrid membranes substantially as herein described with reference to, and as Illustrated by the Example.
4. A process of manufacture of inorganic-organic hybrid members as claimed in any one of the preceding Claims wherein cesium salts of heteropolyacids such as phosphomolybdic acid (PMA), phosphotungstic acid (PWA) and silicotungstic acid (SWA) were synthesized at room

temperature by neutralization of respective acid solution with appropriate amount of 0.1 M cesium carbonate solution, the crystals being dried at room temperature and kept under constant humidity of air until constant mass was attained.
5. A process as claimed in Claim 4. wherein the hybrid membranes are fabricated through a solution-cast method.
6. A process as claimed in Claim 4 or Claim 5 wherein a 10.0 wt % of PVA solution in water was prepared under vigorous stirring at 70 "C, to this solution, a mixture of 10.0 wt % of PAM dissolved in water and required quantity of one of the cesium salt of heteropolyacids such as phosphomolybdic acid (PMA), phosphotungstic acid (PWA) or silicotungstic acid (SWA) being added and stirred for 6 h. to obtain a homogenous solution, the weight percent of PAM and heteropolyacids in the hybrid membrane being maintained as 10.0 each, the homogeneous solution being spread uniformly on a clean glass plate and leveled perfectly, the water being removed slowly by keeping the glass plate at room temperature and the dried membrane detached from the glass plate, the obtained dry membrane being immersed

into a crosslinking bath containing glutaraldehyde, acetone and hydrochloric acid for 30 min at room temperature.
7. A process as claimed in any one of the Claims 4 to 6 substantially as herein described and illustrated with reference to the Example.