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Title:
POLYMER COMPOSITES
Document Type and Number:
WIPO Patent Application WO/2007/082350
Kind Code:
A1
Abstract:
A polymer composite comprising at least one inorganic proton conducting polymer functionalised with at least one ionisable group and/or at least one hybrid proton conducting polymer functionalised with at least one ionisable group, and at least one organic polymer capable of forming hydrogen bonds.

Inventors:
DINIZ DA COSTA JOAO CARLOS (AU)
LU GAO QING (AU)
JIN YONGGANG (AU)
MATTHEW LUKE GORDON (AU)
DUKE MIKEL COLIN (AU)
TRAN ANH (NZ)
Application Number:
PCT/AU2007/000052
Publication Date:
July 26, 2007
Filing Date:
January 18, 2007
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
UNIV QUEENSLAND (AU)
DINIZ DA COSTA JOAO CARLOS (AU)
LU GAO QING (AU)
JIN YONGGANG (AU)
MATTHEW LUKE GORDON (AU)
DUKE MIKEL COLIN (AU)
TRAN ANH (NZ)
International Classes:
C08J5/22; C08K3/32; C08K3/34; C08L29/04; C08L31/04; C08L101/12; H01M8/10
Domestic Patent References:
WO2002103834A12002-12-27
WO2003077340A22003-09-18
WO2005105667A12005-11-10
WO2006074098A22006-07-13
Foreign References:
US6953634B22005-10-11
Other References:
PATENT ABSTRACTS OF JAPAN
PATENT ABSTRACTS OF JAPAN
DAE SIK KIM ET AL.: "Proton Conductivity and methanol transport behavior of cross-linked PVA/PAA/silica hybrid membranes", SOLID STATE IONICS, vol. 176, 2005, pages 117 - 126, XP004653312
STANGAR U.L. ET AL.: "Silicotungstic acid/organically modified silane proton-conducting membranes", JOURNAL OF SOLID STATE ELECTROCHEM., vol. 9, 2005, pages 106 - 113, XP019352553
Attorney, Agent or Firm:
CARTER, Chris John et al. (Level 14 255 Elizabeth Stree, Sydney New South Wales 2000, AU)
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Claims:

The Claims:

1. A polymer composite comprising at least one inorganic proton conducting polymer functionalised with at least one ionisable group and/or at least one hybrid proton conducting polymer functionalised with at least one ionisable group, and at least one organic polymer capable of forming hydrogen bonds.

2. A polymer composite according to claim 1 in the form of an electrolyte membrane.

3. A polymer composite according to claim 1 or claim 2 wherein the at least one organic polymer capable of forming hydrogen bonds is a reinforcing polymer.

4. A polymer composite according to any one of claims 1 to 3 wherein the at least one inorganic and/or hybrid proton conducting polymer hydrogen bonds with the at least one organic polymer capable of forming hydrogen bonds.

5. A polymer composite according to any one of claims 1 to 4 wherein the at least one inorganic and/or hybrid proton conducting polymer is at least partially in the form of finely dispersed particles.

6. A polymer composite according to claim 5 wherein the at least one organic polymer capable of forming hydrogen bonds is in the form of a continuous polymer matrix.

7. A polymer composite according to any one of claims 1 to 6 wherein the at least one inorganic proton conducting polymer is chosen from the group including ionically functionalised metallic oxides, a semi-metallic oxides or a metalloids, mixed metal oxides, silicas, zirconias, titanias, aluminas, or caesium derivatives.

8. A polymer composite according to any one of claims 1 to 6 wherein the at least one inorganic proton conducting polymer is chosen from the group including

phosphosilicate pyrophosphate, zirconium phosphate, zirconium phosphate pyrophosphate, sulphated zirconia, silicophosphate-perchlorate, titanium phosphate, sulphonated zirconium phosphate, sulphonated zirconium oxide, sulphonated titanium phosphate, cesium phosphate, and cesium sulphate.

9. A polymer composite according to any one of claims 1 to 8 wherein the at least one organic polymer capable of forming hydrogen bonds is selected from a polyether, polyhydroxylate, polycation, polyanion, basic electrolyte, acidic electrolyte, basic ionomer or acidic ionomer.

10. A polymer composite according to any one of claims 1 to 8 wherein the at least one organic polymer capable of forming hydrogen bonds is selected from one or more hydrogels.

11. A polymer composite according to claim 10 wherein the at least one organic polymer capable of forming hydrogen bonds is selected from the group of hydrogels including: poly(vinyl alcohol) (PVA) including cross-linked poly(vinyl alcohols); naturally occurring carbohydrate polymers such as gums, chitins, chitosans, algal derived polymers such as alginates, mucilages such as tragacanth and xanthan gum, crosslinked derivatives such as polypropylene glycol alginates;

2-hydroxyethyl methacrylate (HEMA); poly(ethylene glycol) diacrylate and dimethacrylate derivatives; poly(ethylene glycol) methyl ether methacrylate (mPEGMA) cross-linked with poly(ethylene glycol) dimethacrylate (PEGDMA); crosslinked poly(ethylene glycol) urethane dimethacrylates; polyacrylamides; poly(vinyl alcohol) - polyacrylamide interpenetrating hydrogels; poly(propylene glycols) and poly(tetramethylene glycols) and crosslinked derivatives thereof; polyvinyl pyrrolidones; carboxyvinyl polymers; polymers of methyl vinyl ether and maleic acid and derivatives; high molecular weight polyethylene glycols and polypropylene glycols; sodium polyacrylates; chitin/chitosan; PVA blends; copolymer hydrogels such as 2-hydroxyethyl methacrylate (HEMA) and 2- aminoethyl methacrylate (AEMA) and ethylene glycol dimethacrylate (EGDMA).

12. A polymer composite according to any one of claims 1 to 6 wherein the at least one hybrid proton conducting polymer is chosen from the group including: mixed metal oxides phosphate such as silicon titanium phosphate, silicon zirconium phosphate, silicon aluminium phosphate; metal oxides doped with heteropolyacids including PWA (H 3 PW 12 O 40 -29H 2 O), PMoA (H 3 PMo 12 O 40 ^H 2 O) and SiWA

(H 3 SiW 12 O 40 -29H 2 O), PWA doped silica, and alumina.

13. A method of preparing an electrolyte membrane, comprising the steps of homogeneously combining particles of at least one ionically functionalised inorganic and/or hybrid proton conducting polymer, with at least one organic polymer capable of forming hydrogen bonds.

14. A method of preparing an electrolyte membrane according to claim 13 wherein the at least one ionically functionalised inorganic and/or hybrid proton conducting polymer is heat treated prior to being combined with the at least one organic polymer capable of forming hydrogen bonds.

15. A method of preparing an electrolyte membrane according to claim 13 or 14 wherein the at least one ionically functionalised inorganic and/or hybrid proton conducting polymer is in particulate powder form and this is dispersed in the organic polymer matrix of the at least one organic polymer capable of forming hydrogen bonds.

16. A method of preparing an electrolyte membrane according to claim 13 or 14 wherein the at least one ionically functionalised inorganic and/or hybrid proton conducting polymer is in the form of a colloidal suspension of particulate inorganic polymer and this is dispersed in the organic polymer matrix of the at least one organic polymer capable of forming hydrogen bonds.

17. An electrolyte membrane according to claim 2 or produced according to any one of claims 13 to 16 for use in fuel cells, hydrogen separation, hydrogen purification,

reforming or partial oxidation of hydrocarbon fuels, contaminant removal, gas sensing (potentionmetric and amperometric gas sensors based on solid state proton conductors), and other processes relevant to energy storage and conversion. Other applications of electrolyte membranes include ion-exchange membranes, extraction of a pre-determined fluid component (such as an ion) from a fluid, acid catalyst in a chemical processing system, other ion conducting applications, or selective ion- transmitting membranes.

Description:

TITLE OF THE INVENTION

"Polymer Composites"

FIELD OF THE INVENTION

This invention relates generally to the field of polymer composites as proton conducting electrolyte membranes. In particular, the invention relates to methods for fabricating electrolyte membranes and to the membranes obtainable by such methods, especially in relation to electrochemical devices like fuel cells requiring an electrolyte membrane.

BACKGROUND OF THE INVENTION

The operation of an electrochemical cell requires both oxidation and reduction reactions which produce or consume electrons. To complete an electrical circuit through the cell, a mechanism must exist for internal charge transfer. This mechanism includes one or more electrolytes, which support charge transfer by ionic conduction. Electrolytes must be poor electronic conductors to prevent internal short circuiting of the cell.

One category of electrolytes particularly suitable for use in conjunction with electrochemical cells are proton exchange membranes (PEM). PEMs usually consist of a polymer matrix to which are attached functional groups capable of exchanging cations or anions. PEMs have application in hydrogen separation, hydrogen purification, reforming or partial oxidation of hydrocarbon fuels, contaminant removal, gas sensing (potentionmetric and amperometric gas sensors based on solid state proton conductors), and as fuel cells and other processes relevant to energy storage and conversion.

Proton exchange membrane fuel cells (PEMFC) have received attention due to their promise in applications such as clean and efficient energy systems. PEMFCs are candidates for clean power generators including transportation, distributed power and portable power systems. PEMFCs are an attractive energy conversion in many industrial applications due to their high-energy efficient and low emission, compared to internal combustion engines and gas turbines.

Up to now, perfluorosulfonic acid (PFSA) membranes such as Nafion (Du Pont) and Dow (Dow chemical) have been the most widely used in both fuel cell research and study. However, these materials possess problems which impede the further development of fuel cells based on these materials such as high methanol crossover rate (or molecular permeability), and a restricted operating temperature range (operable below 8O 0 C). There is also a high cost associated with the preparation of these membranes.

The proton conduction mechanisms of PFSA membranes rely on the presence of water; but because of the unfavourable equilibrium and high evaporation rate at temperatures above the boiling point of water, there is a dramatic decrease of water content, proton conduction and consequently fuel cell performance. The boiling point of water can be increased by increasing the operating pressure, but pressures above 3 Barr (corresponding to a boiling point of about 134 0 C) are undesirable in PEMFC from an efficiency perspective due to the energy penalty associated with compressing the reactant gases.

As alternative candidates, sol-gel derived phosphosilicate gels have been reported as very promising proton conductors due to the high proton conductivity in the low and medium temperature range of the phosphoric-acid functionalised, thermally stable, inorganic silica networks. However, the inherent brittleness of these silica based inorganic materials has prevented their practical application, in particular, because of problematic formability of thin membranes from these materials, and an inherent lack of mechanical strength. Naturally brittle materials, such as ceramics and glasses are known to be difficult to toughen effectively.

Accordingly, there is a need for further electrolyte membranes as alternatives to current membranes.

SUMMARY OF THE INVENTION In one aspect, the invention provides a polymer composite comprising at least one inorganic proton conducting polymer functionalised with at least one ionisable group

and/or at least one hybrid proton conducting polymer functionalised with at least one ionisable group, and at least one organic polymer capable of forming hydrogen bonds.

In one embodiment, the invention provides a polymer composite in the form of an electrolyte membrane.

Li some embodiments, the invention provides an electrolyte membrane wherein at least one of the organic polymers capable of forming hydrogen bonds is a reinforcing polymer.

In some embodiments, the invention provides an electrolyte membrane wherein the at least one inorganic and/or hybrid proton conducting polymer hydrogen bonds with the at least one organic polymer capable of forming hydrogen bonds.

hi another aspect, the present invention provides a method of preparing an electrolyte membrane, comprising the steps of homogeneously combining particles of at least one ionically functionalised inorganic and/or hybrid proton conducting polymer, with at least one ; o i rganic polymer capable of forming hydrogen bonds.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.

FIG.l: TG-DTG curves of the dried gel.

FIG. 2: XRD patterns of the dried gel and the calcined samples at 15O 0 C and 45O 0 C FIG. 3 : FTIR spectra of the dried gel and the calcined samples at 15O 0 C and 45O 0 C

FIG. 4: Proton conductivities for the gels calcined at 15O 0 C and 45O 0 C under various relative humidities at 2O 0 C

FIG. 5: Water adsorption isothermals at 2O 0 C for the gels calcined at 15O 0 C and

45O 0 C

FIG. 6: XRD pattern of the gel calcined at 15O 0 C (i) after the conductivity measurement, (ii) subject to heat-treatment at 15O 0 C for 10 hours after the hydrolysis

FIG. 7: FTIR spectra of the gel calcined at 15O 0 C (i) after the conductivity measurement, (ii) subject to heat-treatment at 15O 0 C for 10 hours after the hydrolysis.

FIG. 8: SEM image of the gel calcined at 15O 0 C. The particle size is around 3-5 μm

FIG. 9: Photograph of the electrolyte membrane (2) (a) and its SEM images presenting the morphology of the surface (b) and cross-section in magnification of

(c) x 500 and (d) x 2000.

FIG. 10: XRD Patterns of the PVA membrane (a), the phosphosilicate gel powder

(b) and the composite membrane (2) (c).

FIG. 11: Proton conductivity of the composite membrane (2) at 2O 0 C and various relative humidities (RH) (a), and their corresponding impedance Nyquist plots (b).

The impedance plots measured at 60%, 70%, 80%, 90% and 100% RH are magnified and shown in the inset of FIG. 1 l(b).

FIG. 12: Temperature dependence on the conductivity of the composite membrane

(2) under 60% and 90% RH. FIG. 13: Methanol permeability of the composite membrane (2) and Nafion 117.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In general, the subject matter of the present invention is a polymer composite comprising at least one organic polymer capable of forming hydrogen bonds, and at least one ionically functionalised inorganic, and/or hybrid proton conducting polymer. Typically, the proton conducting inorganic polymer exists, at least partially, in the form of finely dispersed particles, and the proton conducting organic polymer existing, at least partially, in the form of a continuous polymer matrix.

Polymer composites may span the entire range from fully miscible to completely immiscible. The composite morphology can be affected significantly by many factors

known to those skilled in the art.

Conventionally, the word "polymer" used as a noun is ambiguous; it is commonly employed to refer to both polymer substances and polymer molecules. As used herein, "macromolecule" is used for individual molecules and "polymer" is used to denote a substance composed of macromolecules. The term "polymer" may also be employed unambiguously as an adjective, according to accepted usage, e.g. "polymer composite",

"polymer molecule". As used herein a "macromolecule", is a molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of relatively low molecular mass.

As used herein a "constitutional unit", refers to an atom or group of atoms (with pendant atoms or groups of atoms, if any) comprising a part of the essential structure of a macromolecule, a block or a chain. As used herein a "block", refers to a portion of a macromolecule, comprising many constitutional units, which has at least one feature that is not present in the adjacent portions. As used herein a "chain", refers to the whole or part of a macromolecule or block comprising a linear or branched sequence of constitutional units between two boundary constitutional units, each of which may be either an end- group or a branch point or an otherwise-designated characteristic feature of the macromolecule. As used herein a "constitutional sequence", refers to the whole or part of a chain comprising one or more species of the constitutional unit(s) in a defined sequence.

As used herein the term "linker" refers to a bi-functional chemical moiety attaching a functional group, such as a ligand, to the backbone of a macromolecule.

There is a diverse range of synthetic polymers known to those skilled in the art. The kind and structure of polymer synthesised depends on many factors including the kind and number of monomers used, the polymerisation method, polymerisation conditions, the degree of cross-linking and the various co-factors used at the beginning, during and at the end of the polymerisation process. Illustrative examples of types of polymers include: "homo-polymers" which refers to polymers comprised of macromolecules constructed of

identical monomers; "chain polymers" a kind of homo-polymer which the repetition of units is linear - a chain polymer consists of macromolecular chains with identical bonding linkages to each monomer unit which may be represented as: -[A-A-A-A-A-A]-, wherein "A" represents a monomeric unit; "branched polymers" which are polymers comprised of macromolecules with one or more chemical side chains extending from the main backbone or chain of the macromolecule; "star-branching polymers" which are polymers comprised of branch macromolecules wherein the branches ultimately emanate from a single point; "dendrimers" which are branched macromolecules with a high degree of branching - typically the branches of these molecules have branches themselves; "block polymers" which are polymers comprised of macromolecules composed of two or more connected blocks - in the simplest case, the XY di-block consists of two blocks, X and Y, joined together; "copolymers" which are polymers comprised of macromolecules derived from more than one species of monomer - polymers comprised of macromolecules having monomeric units differing in constitutional or configurational features but derived from a single monomer, are not regarded as copolymers; "graft copolymers" which are polymer comprised of macromolecules with one or more species of block connected to the main chain as side chains. These side chains having constitutional or configurational features that differ from those in the main chain. In a graft copolymer, the distinguishing feature of the macromolecular side chains is constitutional, i.e., the side chains comprise units derived from at least one species of monomer different from those which supply the units of the main chain; "statistical copolymers" which are copolymers comprised of macromolecules in which the sequential distribution of the monomeric units obeys known statistical laws; e.g., the monomer sequence distribution may follow Markovian statistics of zeroth (Bernoullian), first, second, or a higher order; "random copolymers" which are special case of a statistical copolymers - it is a statistical copolymer comprised of macromolecules in which the probability of finding a given monomeric unit at any given site in the chain is independent of the nature of the neighbouring units at that position (Bernoullian distribution); "alternating copolymers" which are copolymers comprised of macromolecules further comprising two species of monomeric units distributed in alternating sequence, for example the arrangement -ABABABAB- or (AB) represents an alternating macromolecule;. "periodic copolymers" which are copolymers comprising

macromolecules where the monomelic units appear in an ordered sequence, for example - [ABC- ABC- ABC]-, wherein "A", "B" and "C" represent different monomeric units.

As used herein, the term "inorganic polymer" refers to a polymeric material that is free of carbon. The term "inorganic polymer" is taken to include materials that are formable by polymerisation and/or sol-gel processes, such as ceramics, mineral polymers and glasses. It is further understood that the term "inorganic proton conducting polymer" refers to a "inorganic polymer" capable of conducting protons.

As used herein, the term "hybrid polymer" refers to an inorganic polymer that has been partially functionalised with organic functional groups or moieties. Accordingly, it is understood that the term "hybrid proton conducting polymer" is a "hybrid polymer" capable of conducting protons.

hi some embodiments, the electrolyte membrane comprises an inorganic proton conducting polymer functionalised with at least one ionisable group and at least one organic polymer capable of forming hydrogen bonds.

As used herein, the term "ionisable group" refers to a chemical moiety capable of partial or full ionisation.

Suitably, the ionisable group is a protogenic functional group.

Non-limiting examples of protogenic functional groups include -COOH, -PO 3 H, -SO 3 H and NH 3 + .

Inorganic proton conducting polymers can be prepared through sol-gel processes. Sol-gel processes are well known to the art and examples of these processes can be found for example in: C. Jeffrey Blinker, George W. Scherer, Sol-Gel Science: The Physic and Chemistry of Sol-Gel Processing; and C. N. R. Rao, Achim Muller, Anthony K. Cheetham (editors), The Chemistry of Nanomaterials: Synthesis, Properties and Applications.

It is known in the art, that as a part of the sol-gel process, different methods, for example, involving high or low gelation and sintering temperatures may be employed to synthesise inorganic polymers as metalloid electrolytes with varying proton conductivities. Similarly, the extent of aging and initial monomer concentration employed during the sol-gel process can be used to modify the properties of the resulting gels. A variety methodologies for preparing proton conducting materials by sol-gel processes have been disclosed see, for example: Alberti G., et al, Adv. Mater., 1996, S, 291; Alberti G, et al, Solid State Ionics, 1999, 125, 91 (zirconium phosphate pyrophosphate); Alberti, G., Solid State Ionics, 2001, 145, 3 - 16. (zirconium phosphates and cesium sulphates); Rodriguez-Castellon, E., et al, Solid State Ionics, 1999, 125, 407-410 (zirconium and titanium phosphates); Tian B., et al, Nature Mater., 2003, 2, 159; Rodriguez-Castellon, E., Adv. Mater., 1988, 10, 812; Stangar, U. L., et al, Solid State Ionics, 2001, 145, 109-118; Tung, T-H., et al, Journal of Membrane Science, 2004, 241, 315-323; Klein, L., C, et al, Polymer, 2005, 4505-4509; and Hitoshi Nakajima et al, Solid State Ionics, 2001, 148, 607-610.

As used herein, the term "sol-gel process" refers the polymerisation of a soluble metal alkoxide. Stable dispersions, or sols, of small particles (typically less than 0.1 micrometre) are formed from precursor chemicals such as metal or metalloid alkoxides, or other metallo-organics. By partial evaporation of the liquid or addition of a suitable initiator, a polymer-like, three-dimensional bonding takes place within the sol to form a gelatinous network, or gel. The gel can then be dehydrated and calcined to obtain a fine, intimately mixed ceramic powder. The polymerisation typically involves a series of hydrolysis and condensation reactions with the generation of alcohol and water as reaction by-products. Non-limiting examples of metal alkoxides used in the preparation of inorganic/hybrid materials are tetraethoxysilane, tetramethoxysilane, tetraisopropoxytitanium (IV), tetrapropoxyzirconium (IV) and tributoxyaluminum.

In some embodiments, the inorganic proton conducting polymer is an ionically functionalised metallic oxide, a semi-metallic oxide or a metalloid, or a mixed metal oxide.

Inorganic proton conducting polymers may be selected from silicas, zirconias, titanias, aluminas, or caesium derivatives.

Non-limiting examples of inorganic proton conducting polymers include: phosphosilicate pyrophosphate, zirconium phosphate, zirconium phosphate pyrophosphate, sulphated zirconia, silicophosphate-perchlorate, titanium phosphate, sulphonated zirconium phosphate, sulphonated zirconium oxide, sulphonated titanium phosphate, cesium phosphate, and cesium sulphate.

Proton exchange membranes (PEM) with high proton conduction (> 0.01 S/cm) but a lower dependence on humidity in the temperature above 100 0 C are important components of the generation of new PEM fuel cells. Such fuel cells, are envisioned to have a higher energy efficiency and higher anode catalyst-tolerance to carbon monoxide (CO) poisoning. CO poisoning occurs when CO is absorbed onto on the Pt anode electrocatalyst, competitively with H 2 . The absolute free energy of absorption of CO on Pt has a larger positive-temperature-dependence than that OfH 2 ; therefore, the CO poisoning effect can be prevented from poisoning the catalyst at temperatures over 100 0 C. Taking into account that the adduct Pt-CO is thermolabile, a higher working temperature for fuel cells could reduce the poisoning and may allow platinum to be replaced by more economical catalysts. In addition, higher temperature operation can improve thermal management, increase reaction rates at both electrodes, and activate catalyst layers.

Fuel cells operating at elevated temperatures are not easy to obtain since the most suitable protonic materials, presently available, work well only in their hydrated form.

Preferably, water in an electrolyte membrane is physically or chemically absorbed water.

Conventional polyfluorosulphonic acids (such as Nafion), have poor proton conductivity at lower humidities and at higher temperatures above (above 8O 0 C), insufficient dimensional stability over different humidities, and high cost. These limitations have stimulated the desire to develop other types of proton conducting membranes.

Proton migration in a polymer system typically happens via two types of mechanisms: (a) vehicular mechanism where the proton is transported by a carrier molecule [H 3 O + or NH 4 + ] to another [NH 3 or H 2 O] or (b) Grotthuss mechanism in which the proton jumps from a donor [e.g. -SO 3 H, -P(OH) 3 to a conveniently placed acceptor [e.g. -SO 3 ' , -P(OH) 2 O " ]. However, there is the also the possibility of mixed mechanisms occurring.

Dipole networks, such as those provided by organic polymers capable of forming hydrogen bonds, may assist in promoting proton transfer.

Thus, in some embodiments, the organic polymer capable of forming hydrogen bonds is selected from a polyether, polyhydroxylate, polycation, polyanion, basic electrolyte, acidic electrolyte, basic ionomer or acidic ionomer.

In some embodiments, the organic polymer is selected from one or more polyether or polyhydroxylated polymers.

As used herein the term "polyhydroxylated polymer" refers to a polymer in which a hydroxyl group is a repeating constituent functionality of the macromolecules or macromolecule of which the polymer is comprised.

Suitably, the polyhydroxylated polymer is selected from a carbohydrate, a vinyl alcohol polymer or a polyphenolic polymer.

In some embodiments, the organic polymer capable of forming hydrogen bonds is selected from one or more hydrogels. As used herein the term "hydrogel" refer to hydrophilic polymers of animal, vegetable, microbial, or synthetic origin that generally contain many hydroxyl groups and may be polyelectrolytes.

Suitably, the polyhydroxylated polymer is a polyalcohol such as a polyvinyl alcohol).

The organic polymer may be a basic polyelectrolyte (poly base), basic ionomer, acidic polyelectrolyte (poly acid), or an acidic ionomer. An example of a basic polyelectrolyte is polybenzimidazole (PBI).

In some embodiments, the organic polymer capable of forming hydrogen bonds is selected from one or more cationic polymers or polycations. As used herein, the term "cationic polymer" or related terms such as "polycation" refer to a polymer composed of positively charged macromolecules.

In some embodiments, the organic polymer capable of forming hydrogen bonds is selected from one or more anionic monomers or polyanions.

As used herein, the term "anionic polymer" or related terms such as "polyanion" refer to a polymer composed of negatively charged macromolecules.

As used herein the term "polyelectrolyte" refers to a polymer composed of macromolecules in which a substantial portion of the constitutional units contain ionic or ionisable groups or both.

The terms "polymer electrolyte" and "polymeric electrolyte" are sometimes used for the term "polyelectrolyte". "Polymer electrolytes" and the like, are distinguished from "electrically conducting polymers". As used herein, the term "electrically conducting polymer" refers to a polymer that exhibits bulk electric conductivity. Unlike, for example, polymer electrolytes in which charges may be transported by ions, the charges in electrically conducting polymers are transported along and between polymer molecules via generated charge carriers.

In some embodiments, the organic polymer capable of forming hydrogen bonds is selected from one or more basic ionomers.

In some embodiments, the organic polymer capable of forming hydrogen bonds is selected from one or more acidic ionomers.

As used herein the term "ionomer" refers to a macromolecule which a small but significant proportion of the constitutional units have ionisable or ionic groups, or both.

Examples of organic polymers capable of forming hydrogen bonds include hydrogels. Hydrogels interact with water reducing its diffusion and stabilising its presence. Generally neutral hydrogels are less soluble whereas polyelectrolytes are more soluble but hydration kinetics depends on many factors. Water may be held by a hydrogel specifically through direct hydrogen bonding or by the structuring of water or within extensive but contained inter- and intra-molecular voids. Interactions between hydrogels and water depend on hydrogen bonding and are therefore dependent on temperature and pressure.

In some embodiments, hydrogen bonding between the components of the electrolyte membrane reduces the aqueous solubility of the membrane.

Suitably, hydrogen bonding between an inorganic proton conducting polymer and an organic polymer capable of forming hydrogen bonds reduces aqueous solubility of the electrolyte membrane.

Hydrogen bonding occurs when an atom of hydrogen is attracted by rather strong forces to two atoms instead of only one, so that it may be considered to be acting as a bond between them. Typically, this occurs where the partially positively charged hydrogen atom lies between partially negatively charged oxygen and nitrogen atoms, but is also found elsewhere.

Depending on their physical environment, hydrogels may exhibit a wide range of conformations if the links along the polymeric chains can rotate relatively freely within valleys in the potential energy landscapes. Large, conformationally stiff hydrogels present essentially static surfaces encouraging extensive structuring in the presence of water. In

particular, hydrogels can provide water for increasing the flexibility (plasticising) in a multi-component system.

Illustrative examples of hydrogels include poly(vinyl alcohol) (PVA) including cross- linked poly(vinyl alcohols); naturally occurring carbohydrate polymers such as gums, chitins, chitosans, algal derived polymers such as alginates, mucilages such as tragacanth and xanthan gum, crosslinked derivatives such as polypropylene glycol alginates; 2- hydroxyethyl methacrylate (HEMA); poly(ethylene glycol) diacrylate and dimethacrylate derivatives; poly(ethylene glycol) methyl ether methacrylate (mPEGMA) cross-linked with poly(ethylene glycol) dimethacrylate (PEGDMA); crosslinked poly(ethylene glycol) urethane dimethacrylates; polyacrylamides; poly(vinyl alcohol) - polyacrylamide interpenetrating hydrogels; poly(propylene glycols) and poly(tetramethylene glycols) and crosslinked derivatives thereof; polyvinyl pyrrolidones; carboxyvinyl polymers; polymers of methyl vinyl ether and maleic acid and derivatives; high molecular weight polyethylene glycols and polypropylene glycols; sodium polyacrylates; chitin/chitosan and PVA blends;

Copolymer hydrogel membranes may be prepared by copolymerisation and crosslinking. For example, 2-hydroxyethyl methacrylate (HEMA) and 2-aminoethyl methacrylate (AEMA) may be copolymerised in the presence of solvent and a crosslinker, for example, ethylene glycol dimethacrylate (EGDMA). By changing the crosslinker content and the ratio of the monomers, series of copolymer hydrogel membranes with different properties may be prepared. Li a further example, chitosan may be crosslinked with glutaraldehyde. By varying the concentration of the crosslinking agent different degrees of crosslinking may be achieved altering the membrane properties.

As such, the properties of hydrogels depend not only on their hydrophilicity, but on numerous other parameters including the chemical composition, presence or absence, types and number of crosslinks, presence or absence of functional groups, quasi-organised water structure, porosity, and the thermodynamic interaction parameters between the components of the membrane.

Hydrophilic polymers (i.e. polymers possessing hydrophilicity) interact with water with greater or comparable strength to water-water interactions whereas hydrophobic solutes (i.e. solutes or structures possessing hydrophobicity) only weakly interact with water with strength far less than water- water interactions.

In some embodiments, the hydrogel is a combination of one or more polyhydroxylated polymers.

The polyhydroxylated polymer may be partially or fully functionalised see, for example: Masanori Yamada, et al, Polymer, 2005, 2986-2992. The polyhydroxylated polymer may be partially or fully functionalised without substantially altering its morphological features such as crystallinity. For example, a poly(vinyl alcohol) film may be surface phosphorylated (Sreenivasan, K., Journal of Applied Polymer Science, 2004, 94, 651-656).

As has been alluded to, it is recognised that many materials with proton conductivities suitable for use in electrolyte membranes, are too brittle to have any utility in that capacity. For example, sol-gel phosphosilicates are materials recognised as potentially promising proton conductors due to the high proton conductivity in the low and medium temperature range. For example, phosphosilicate gels, prepared from H 3 PO 4 and tetraethoxysilane (TEOS), have high proton conductivity above 100 0 C in low humidity, but they are too brittle with little mechanical flexibility to be useful in practical electrical devices. In particular, their application in electrolyte membranes has been prevented because of problematic formability of thin membranes from these materials, and an inherent lack of mechanical strength.

As used herein, a material is "brittle" if it is subject to fracture when stressed. That is, the material has little tendency to deform (or strain) before fracture. This fracture absorbs relatively little energy, even in materials of high strength. When used in materials science the term brittle generally applied to materials that fail in tension rather than shear or when there is no evidence of plastic (ductile) deformation before failure. When a material has reached the limit of its strength, it usually has the option of either deformation or fracture.

A naturally malleable material can be made stronger by impeding the mechanisms of plastic deformation (reducing grain size, dispersion strengthening work hardening etc.), but if this is taken to an extreme, fracture becomes the more likely outcome, and the material can become brittle. Improving material toughness is therefore a balancing act. Naturally brittle materials, such as ceramics and glasses are difficult to toughen effectively.

Organic polymers with mechanical reinforcing properties, in addition to hydrophilic and hydrogen bonding properties, are useful components in the formation of electrolyte membranes.

Thus, in some embodiments, the electrolyte membrane comprises an inorganic proton conducting polymer functionalised with at least one ionisable group and at least one organic reinforcing polymer capable of forming hydrogen bonds.

As used herein the term "reinforce" and like terms such as "reinforced" and "reinforcing" refers to the strengthening or the increasing of structural integrity of a composite material, by the addition of a further component to the composite. Thus, the mechanical stability of a polymer composite may be modified by including a "reinforcing polymer" as a component of the composite.

In an attempt to overcome mechanical problems associated with some inorganic proton conducting materials used in proton conducting membranes, hybrid proton conducting polymers have been prepared: Li, Siwen, et al, Electrochimica Acta, 2005; Teruaka Tezuka, et al, Solid State Ionics, 2005; Di Noto, V., et al, Electrochimica Acta, 2005; Yong-il Parl, et al, Solid State Ionics, 2001, 145, 149-160; Kiyoharu Tadanaga, et al, Solid State Ionics, 2005; I. Honma, et al, Solid State Ionics, 1999, 118, 29 - 36; and I. Honma, Solid State Ionics, 2003, 1162-163, 237-245. Hybrid proton conducting polymers and copolymers can also be prepared through sol-gel processes. Hybrid polymers have demonstrated suitable proton conductivities to be used in fuel cell membranes, although there are still some problems with their application. For example, in an attempt to improve mechanical properties of a proton conducting membrane, a 3-

glycidoxypropyltrimethoxysilane (GPTS) was introduced into silicate-H 3 PO 4 gels to form a hybrid polymer network. However, because the organic chains of GPTS are short and tend to form three-dimensional polymer network, the GPTS-based self-standing membranes do not have enough flexibility for practical application as the electrolyte of PEM fuel cells.

In another embodiment, the electrolyte membrane comprises at least one hybrid proton conducting polymer functionalised with at least one ionisable group, and at least one organic polymer capable of forming hydrogen bonds.

In yet another embodiment, the electrolyte membrane comprises at least one inorganic proton conducting polymer functionalised with at least one ionisable group, at least one hybrid proton conducting polymer functionalised with at least one ionisable group, and at least one organic polymer capable of forming hydrogen bonds.

Inorganic and hybrid proton conducting polymers may be prepared and/or functionalised by methods known to those skilled in the art.

A hybrid copolymer can be formed by copolymerisation of a plurality of monomers one of which is functionalised with an organic chain or group. For example, the precursors can include a plurality of silicon compounds with polymerisation initiated as a sol-gel process.

A first silicon compound can include one or more hydrolysable groups, such as an alkyloxysilyl (or other silyl group) so that the alkyloxysilyl group is at least partially hydrolysed during polymerisation. A second silicon compound may be provided, also with one or more hydrolysable silicon-containing groups and an organic chain, so that the organic chain is incorporated in a hybrid organic-inorganic matrix after hydrolysis occurs.

Through sol-gel processes, for example, acid group functionalised silicon compounds

(such as silane derivatives) can be used in copolymerisation reactions with other monomers to provide acidically functionalised silicates. Examples of acid group containing silicon compounds include PETHS, phosphoryl ethyl trihydroxy silane (and

other alkoxy derivatives), acid substituted trialkyloxysilanes (such as SPS (Si(EtO) 3 -Ph- SO 2 OH)). Acid group containing silicon compounds may further include a functional group, such as a polymerisable group, and/or a group allowing grafting to an organic polymer chain.

The inorganic or hybrid proton conducting polymer may be particulate, such as a nanoparticle, or may be in the form of a film, latex or sheet. The inorganic proton conducting polymer may be heat treated, for example by calcination, and then ground or otherwise refined to afford a desired particle diameter. As used herein the term "particle" or "particulate" refers to a body having finite mass and internal structure but negligible dimensions. Typically a particle is an aggregation of sufficiently many atoms or molecules that it can be assigned macroscopic properties such as volume, density, pressure, and temperature. As defined herein the term "nanoparticle" refers to a particle whose average diameter is typically from 1 — 1000 nanometers.

Of importance to electrolyte membranes is the surface functionalised nature of any polymeric particles comprising the membrane. As used herein the term "surface functionalised" in relation to polymer particles, refers to a polymer particle, the surface of which has pendant functional groups, or has been functionalised to have pendant functional groups. As used herein the term "surface" when applied to a polymer, for example referring to the "polymer surface" or "surface of a polymer", refers to the surface area of a polymeric material including any pores and channels that form a continuous part of the surface area. As used herein the term "functional group" refers to a chemical moiety, such as an atom or group of atoms, in an organic compound that gives the compound some of its characteristic properties. As used herein the term "surface functional groups" refers to the functional groups that are pendant from the polymer surface. As used herein a "pendant group", refers to a chemical offshoot, such as a functional group, that is neither oligomeric nor polymeric from a chain or backbone. As used herein the term "backbone" refers to the main structure of a polymer onto which substituents are attached. As used herein a "substituent" refers to a functional group on a molecule. As used ' herein a "substituent" when used in relation to polymers, refers to a functional group such as a linker or a surface

functional group on a macromolecule. Typically, a substituent, such as a functional group or linker, is substituted in place of an atom on a parent chain.

The type of ionic functionalisation of the inorganic polymeric components of the electrolyte membranes may depend upon the conditions under which the membrane is used. For example, the thermal stability of proton conducting materials containing -SO 3 H groups in not necessarily ensured at temperatures above 19O 0 C inasmuch as there may be loss of SO 3 at temperature higher than 19O 0 C.

Surface functionalised polymers can be prepared in a variety of ways. By way of illustration, a polymer may have an appropriately functionalised surface as a result of the process of polymerisation employed, for example, the addition of an inorganic acid such as a phosphoric acid, during a sol-gel process. Alternatively, a prepared polymer such as polymer (Z) may have its surface suitably functionalised after the polymer has been synthesised. For example, hydroxyl and amino functional groups can be phosphorylated to form phosphonates and phosphonamides respectively, thereby introducing further functionalisation to the polymer through a post-polymerisation surface modification.

As used herein the term "surface functionalisation" when used in relation to a polymer surface, may variously refer to the functionalised surface of the polymer, the process of adding functional groups to the polymer surface, or modifying functional groups present on the polymer surface, in order to obtain desired functional groups on the polymer surface.

Surface functionalisation of particles can result for example, from employing functionalised monomers in the polymerisation process, by adding reagents during the polymerisation process, or by functionalising the polymers resulting from the polymerisation process. By way of example, silica particles surfaces may be phosphorylated as discussed, for example, in US 5,153,166.

Zeolites may be phosphorylated by methods known to the art, for example: Quin D. L., et

al, Heteroatom Chemistry, 1998, Vol. 9, No. 7, 691-698. Similarly, methods for the phosphorylation and sulphation of polymers are known to the art, for example: Kaluzynski, K., et al, Journal of Polymer Science, 2001, 39, 955-963. In addition, it is recognised in the art that many solution phase chemistry techniques can be simply transferred to solid-phase. As such, phosphorylation chemistries, as for example disclosed in Vos, J., N., et al, Bioorganic & Medicinal Chemistry Letters, 1991, 1(3), 143-146, may be applied to the surface functionalisation of solid particles. Further, methods for sulphating functional groups such as hydroxyl groups and amino groups in order to prepare sulphonates and sulphonamides, are well known in the art, for example see Petitou et al., Carbohydr. Res. 1987, 167, 67-75.

As such, it is envisioned that by methods known to the art, that one or more species of ionisable group may be attached through covalent linkages to provide inorganic and hybrid proton conducting polymers functionalised with ionisable groups.

The properties of inorganic proton conducting polymers can be further modified by heating the polymer. Heating at different temperatures may invoke different morphological changes in a material ranging from dehydration of absorbed water, volatisation of chemically absorbed water, to induction of other morphological and functional changes including the induction of a change in a material's crystal structure.

One heating process is calcination. The term "calcination" generally refers to a process in which a material is heated to temperature below which that material undergoes fusing, so that hydrates, carbonates, or other compounds are decomposed and the volatile material is expelled. Typically, calcination is employed to release volatile constituents of a material and may also be used to change a material's crystal structure. As used herein the term "morphology" and variants such as "morphological" when used in relation to a material, refers to the form or structure of that material. As used herein, the term "functional" when used in relation to a material, refers to the properties of a material responsible for the chemical behaviour of that material.

Suitably, the inorganic proton conducting polymer component of an electrolyte membrane, has been pre-treated by heating to a temperature in a range of about 3O 0 C to about 1300 0 C.

Preferably, the inorganic proton conducting polymer has been pre-treated by heating to a temperature in a range of about 4O 0 C to about 500 0 C for about 1 hour to about 7 days

In some embodiments, the inorganic proton conducting polymer has been pre-treated by heating to remove volatile solvents.

In some embodiments, the inorganic proton conducting polymer has been pre-treated by heating to remove hydrogen bonded water.

In some embodiments, the inorganic proton conducting polymer has been pre-treated by heating to induce partial dehydroxylation.

Suitably, the inorganic proton conducting polymer is calcined.

The inorganic proton conducting polymer may be calcined to induce a morphological transformation.

The inorganic proton conducting polymer may be calcined to induce a functional transformation.

hi some embodiments the inorganic proton conducting polymer has been calcined at a temperature in a range of about 100 0 C to 200 0 C.

In some embodiments, the inorganic proton conducting polymer has been calcined at a temperature in a range of about 200 0 C to 300 0 C.

hi some embodiments, the inorganic proton conducting polymer has been calcined at a temperature in a range of about 300 0 C to 400 0 C.

In some embodiments, the inorganic proton conducting polymer has been calcined at a temperature in a range of about 400 0 C to 500 0 C.

In some embodiments, the inorganic proton conducting polymer further comprises pyrophosphate phases induced by heating.

Typically, electrolyte membranes can be prepared by dispersing either (a) a particulate inorganic polymer in powder form or (b) a colloidal suspension of a particulate inorganic polymer, in the organic polymer matrix.

By varying the ratio of the solutions of the composite components, it is possible to obtain membranes of different composition. An essential advantage is that the membrane structure or the membrane properties can be selectively optimised by varying the inorganic/hybrid components and organic polymer components and the mixing ratio. For example, the property profile of the composite membranes can be specifically adapted to the requirements for use in fuel cells by varying the mixing ratio between the inorganic material functionalised with an ionisable group and/or the hybrid proton conducting material functionalised with an ionisable group, and the reinforcing organic polymer capable of forming hydrogen bonds.

Suitably, when preparing membranes, the organic polymer may be partially or completely solvated.

Alternatively, the formation of inorganic or hybrid polymers by a sol-gel process may be initiated in the presence of the organic polymer.

The membrane can be manufactured by casting, knife-coating, or by spreading the composite components, in particular, solutions of the composite components, on the wall of a rotating centrifuge cup and subsequently evaporating the solvent.

After the two component mixture has been formed the resulting solution is poured onto a substrate and levelled to a uniform thickness. Alternatively, the mixture can be cast by doctor blade. The resulting film is dried, removed from the substrate, and cut to size before use. Heating, humidity control, or applying a vacuum to the membrane while drying may also be used to facilitate the rate of evaporation.

m some embodiments, the manufacturing technique for electrolyte membranes is a tape casting method whereby the mixture of components in dispersant is poured onto a level sheet. A doctor blade moving across the gel adjusts the height to the desired thickness ranging from about 0.5 to about 500 μm and preferably from about 20 to about 300 μm. Evaporation of the solvent takes place in a controlled temperature and humidity environment. Afterwards, the membrane is removed from the substrate and conditioned for use as a proton exchange membrane. Although tape casting can be used for producing the membranes disclosed, other methods such as extrusion and tray casting may be employed. For example, a colloidal solution of an inorganic proton conducting material comprising 40%P 2 Os-60%Siθ 2 (molar ratio) can be mixed with a hydrogen bond forming organic polymer, for example a PVA solution, and then a membrane subsequently formed by casting. As this process begins with the colloidal suspension of the inorganic proton conducting material, a high degree and homogenous dispersal of functionalised phosphosilicate gel particles in the organic polymer matrix is achieved, thus avoiding aggregation of solid particles.

Through testing methods known to the art, membranes may be evaluated for their water uptake, proton conductivity, ion-exchange capacity and mechanical properties.

Since the foregoing methods allow intimate mixing of the components in the membrane, a component may be able to confer to the membrane its qualities even when the component is provided in minimal proportions. The methods of fabrication of electrolyte membranes may allow the fabrication of membranes where the proportions of the individual components may vary between approximately 1 wt % and 99 wt %.

Electrolyte membranes may be used in fuel cells, hydrogen separation, hydrogen purification, reforming or partial oxidation of hydrocarbon fuels, contaminant removal, gas sensing (potentionmetric and amperometric gas sensors based on solid state proton conductors), and other processes relevant to energy storage and conversion. Other applications of electrolyte membranes include ion-exchange membranes, extraction of a pre-determined fluid component (such as an ion) from a fluid, acid catalyst in a chemical processing system, other ion conducting applications, or selective ion-transmitting membranes.

Suitably, a fuel cell comprising a electrolyte membrane as described herein includes: a positive electrode, a negative electrode, and a electrolyte membrane constituted and derived as described herein.

The dimensions of the fuel cell can be determined by the configuration of the fuel cell, as is well known in the art. Proton conducting materials can be produced in a form suitable for use as a membrane without further processing, or formed as a tape or sheet that can be cut to a desired shape, or further processed.

In some embodiments, an electrolyte membrane is provided by forming a polymer composite such as described herein, into a membrane having desired dimensions. A fuel cell is provided by further including an electrolyte membrane into a fuel cell configuration, such as a fuel cell configuration known in the art.

In addition to high conductivity, other properties of the electrolyte membrane are of importance in industrial application. For example, in applications such as fabricating sensing devices where durability (ruggedness) may be more useful that high conductivity, the amount if inorganic proton conducting component used in the membrane may be decreased to the minimal proportion capable of producing a continuous network.

Conversely, in applications such as the fabrication of power generation devices, where conductivity may be the more desirable property, the amount of inert polymer may be decreased to the smallest proportion capable of conferring to the composite membrane the

desired structural integrity.

In PEM fuel cells the electrolyte membrane may be exposed to extremely oxidising conditions. Not only one side of the membrane may be exposed to air at elevated temperatures, but the fuel cell reactions themselves may produce trace levels of hydrogen peroxide and peroxyl radicals. Thus, it some instances it is preferable to have membranes with controlled resistance to oxidation.

Some electrolyte membranes undergo a significant change in size (swelling) when the amount or chemical potential of the water in the environment changes. Controlling the shape of composite membranes comprising water-dependent proton conductor may be achieved by including in the membrane a component whose shape does not change with the chemical potential of the water contacting the membrane. Further, methods of preparation of electrolyte membranes may allow the fabrication of membranes where the change in the size of one component may be limited by the presence of another component in the membrane.

Suitably, the electrolyte membrane does not swell substantially in a high humidity environment.

Suitably, the electrolyte membrane does not shrink substantially in a low humidity environment.

Suitably, the electrolyte membrane has a low permeability to methanol.

The invention will now be described with reference to the following examples, which illustrate some preferred aspects of the present invention. However, it is to be understood that the particularity of the following description of the invention is not to supersede the generality of the preceding description of the invention.

EXAMPLES

Example 1 : Preparation of Phosphosilicate Gels

1. Preparation of phosphosilicate gels

A two-step catalysed hydrolysis process was employed to prepare sols using tetraethoxysilane (TEOS), absolute ethanol (EtOH), and distilled water containing nitric acid. TEOS was diluted by EtOH in an ice bath to avoid premature hydrolysis and then H 2 O containing HNO 3 (pH = 2.8) was added at constant stirring. An initial solution with a molar composition of 1.0TEOS:3.8EtOH: LOH 2 O was refluxed under stirring at 6O 0 C for 90 min in a water bath. An appropriate amount of H 3 PO 4 (85% aqueous solution) was added dropwise at room temperature and stirred until a wet gel was formed (about 30 min). The final molar ratio of TEOS: EtOH: H 2 O: H 3 PO 4 was 1:3.8:2:1.33. The wet gel was dried at 5O 0 C for one week in a vessel open to the air to provide gel 1.

Example 2; Characterisation of Phosphosilicate Gels

2. Characterisation of phosphosilicate gel Thermogravimetric (TG) analysis (TGA, Shimadzu TGA 50H) of 1 was performed at a heating-rate of 5°C/min in air atmosphere. X-ray diffraction (XRD) measurements were performed at a speed of 0.02° s "1 by a Rigaku Miniflex XRD machine with Cobalt refractor. BET specific surface area and pore volume of the gel powder was measured by the nitrogen adsorption method (Nova 1200, Quantachrome). Infrared spectra were recorded on a PE2000 Fourier transform infrared (FTIR) spectrophotometer using KBr pellets that contained 1 wt.% of the sample in KBr. Water adsorption isothermal was obtained using a gravimetric adsorption rig.

2.1 Structural characterisation of dried and calcined gels TG analysis was conducted for 1 to examine the thermal behaviour during calcination. The TG Curve and its differential curve (DTG) are shown in FIG.l. A great weight loss

by 17% occurs below 15O 0 C, caused by the evaporation of volatile solvents (e.g. ethanol and physically absorbed water). Another sharp peak was present between 15O 0 C and 22O 0 C on the DTG curve. This corresponded to a weight loss around 10%, which was probably ascribable to the removal of chemically adsorbed water via hydrogen bonding, hydroxyl groups in the structure, as well as the dehydration of phosphoric acid. The following continuous weight loss should be caused by the continuous dehydroxylation. The total weight loss given by the TG curve was 21%. From these results it was determined that water molecules had a good affinity for the phosphosilicate gel (1) matrix, and that water was retained at temperatures up to more than 200 0 C. The hydrogen bonding water/OH in the second stage was considered to play an important role in the proton conductivity of the glass electrolytes. On the basis of the above TGA results, the dried gels were calcined at 15O 0 C in order to avoid too much loss of chemically adsorbed water, and at a higher temperature of 45O 0 C resulting in a fully inorganic gel. As such, the dried gel (1) was ground into a powder and was calcined at 15O 0 C for 4h, at 5°C/min of ramp to provide Ia and 45O 0 C for 4h, at 5°C/min of ramp to provide Ib.

2.2 X-ray diffraction (XRD) measurements

The XRD patterns of the gels 1, 1a and Ib are shown in FIG. 2. It can be seen that the sol- gel synthesis route led to the formation of an amorphous structure in the dried gel. The same diffraction peaks, which are assigned to Si 5 θ(PO 4 ) 6 (JCPDS card 40-0457), were observed for the gels calcined at both temperatures. The above observations suggested that heating induced the crystallisation of phosphorous-rich phases in the amorphous gel. However, sample Ia contained much less crystalline phases than Ib since its XRD pattern had much higher halo basis.

2.3 Fourier Transform Infra-Red (FTIR) Analysis

The structural change of the dried gel after calcination was studied by IR spectroscopy. The FTIR spectra of the dried gel and calcined samples are shown in FIG. 3. On the basis of the comparison with the FTIR spectra of pure silica and phosphoric acid (not shown , here), the bands at 795, 1105 and 1635 cm "1 are assigned to Si-O-Si symmetric stretching, Si-O-Si asymmetric stretching and H-O-H bending of absorbed water, respectively. All

the gels exhibit a broad absorption band in the 3000-3750 cm "1 range, arising from O-H stretches in the hydrogen bonding. The peak near 1010 cm "1 and the shoulder near 1169 cm "1 are due to P-O stretching vibration in P-O-P and P-O-Si units. Compared with the dried gel, the calcined samples have some new peaks appeared at 635, 712 and 1169 cm '1 , which should correspond to the crystallization of Si 5 O(PO 4 ) 6 , in agreement with XRD analysis. Moreover, the intensity of new peaks related to the crystalline phase increase with the calcination temperature. This also indicates that the higher calcination temperature resulted in the higher crystallisation degree. In addition, when the calcination temperature increased, the intensity of band at 1635 cm "1 and O-H band decreased, showing the loss of water and hydroxyl groups.

Example 3: Physical and Chemo-Electric Properties of Gels

3.1 Surface Area and Pore Volume

The BET specific surface area (SSA) and pore volume (PV) for the dried gel and calcined samples are listed in TABLE 1. It can be seen that all phosphosilicate gels had low surface area and were nearly nonporous.

TABLE 1 : BET specific surface area (SSA) and pore volume (PV) of the dried gel and calcined gels at 150 0 C and 450 0 C

Dried gel (1) 150 0 C (Ia) 450 0 C (Ib)

SSA (InV 1 ) 4.58 4.88 6.17

PV (Cm 3 ^ 1 ) 9.194E-03 9.698E-03 1.594E-02

3.2 Proton Conductivity The phosphosilicate gel powders Ia and Ib were separately pressed into pellets of 13mm in diameter and about 1.5-2mm in thickness at 150 kg/cm 2 of pressure. The conductivity of Ia and Ib was determined by the impedance data obtained using an impedance analyser (Solartron SI 1260) in a frequency range of IMHz to IHZ.

FIG. 4 shows proton conductivities under various relative humidities at 2O 0 C for the gels calcined at 15O 0 C and 45O 0 C. Proton conductivities increased with relative humidity. Furthermore, it can be seen that the increase in the calcination temperature led to the decrease in conductivity.

3.3 Water adsorption

The water adsorption isothermals at 2O 0 C for the gels calcined at 15O 0 C (Ia) and 45O 0 C (Ib) are shown in FIG. 5. It is obvious that the gel calcined at lower temperature had much more uptake of water than that calcined at higher temperature.

3.4 Structural evolution of calcined gels after reaction with water

The structural evolution of calcined gels after conductivity measurements exposed to high humid was studied by powder XRD and IR spectroscopy. As ascertained by XRD analysis

(FIG. 6 (i)), the gel calcined at 15O 0 C (Ia) exhibited totally amorphous structure, which suggests that the crystalline phase of Si 5 O(PO 4 ) 6 reacted with water and was completely hydrolysed into amorphous structure during the exposure to the humid atmosphere. When the resulted amorphous sample was reheated at 15O 0 C for 10 hours, as shown in FIG. 6 (ii), re-crystallization occurred. The FTIR spectra corresponded to the above two cases are shown in FIG. 7. It would be seen that absorbance peaks at 635, 712 and 1169 cm '1 assigned to the crystallisation of Si 5 O(PO 4 ) 6 disappear in the hydrolysed sample. As for the reheated sample, low-density peaks at 635 and 712 cm " are present and an advanced shoulder at around 1169 cm '1 appears as well. IR results , are well consistent with the XRD analysis. Moreover, the peak near 1010 cm "1 corresponded to P-O stretching vibration disappears, which may indicate the loss of phosphoric acid.

As for the gel calcined at 45O 0 C, water adsorption during conductivity measurements did not result in the total hydrolysis of the crystalline phase, and the crystalline diffraction peaks were still observed in the XRD pattern, similar to FIG. 6 (ii). This may suggest that

the crystalline phase was harder to totally hydrolyse into amorphous structure in the gel calcined at higher temperature.

Example 4: Preparation of Proton Conductive Membrane

5

4.1 Preparation of Membrane

A two-step catalysed hydrolysis process was employed to prepare phosphosilicate colloidal solution using tetraethoxysilane (TEOS), absolute ethanol (EtOH), and distilled water containing nitric acid. TEOS was diluted by EtOH in an ice bath to avoid premature

10 hydrolysis and then H 2 O containing HNO 3 (pH = 2.8) was added at constant stirring. An initial solution with a molar composition of 1.0TEOS:3.8EtOH: 1.0H 2 O was refluxed under stirring at 60 C for 90 min in a water bath. A solution of H 3 PO 4 (85 wt.%) diluted by EtOH, was added dropwise at room temperature and stirred for 3h. The final molar ratio of TEOS:EtOH:H 2 O:H 3 PO 4 was 1:8:2:1.33. The obtained mixture was mixed with an

15 appropriate amount of 30wt% aqueous solution of PVA and stirred until the homogenous, transparent and viscous slurry was formed. Then it was poured into a Petri-dish and dried under ambient conditions. When visually dry, the membrane (2) was peeled off from the plastic substrate and completely dried at 8O 0 C for 2 days. The mass percentage of PVA in the composite membrane was 40%. The phosphosilicate gel powder was also prepared by

20 keeping the colloidal solution in the 5O 0 C oven for one week to evaporate the solvents and then the stiff gel was grounded into powder. The pure PVA membrane was obtained by casting 30 wt % aqueous solution of PVA.

Table 2 Synthesised composite (phosphosilicate gel) membranes with different amounts of

25 PVA π , λ A n/ Proton conductivity, S/cm ^ 1 ., .,.. PVA, w% (2Q o C; 100% m ' Flexibility

I 25 0.037 Very Brittle

II 40 0.021 Flexible

III 75 0.012 More Flexible

All the characterisation was conducted on the membrane II as it has relatively high conductivity and suitably flexibility

Example 5: Characterisation of Proton Conductive Membrane (2)

5.1 Structural Characterisation and Proton Conductivity measurements

X-ray diffraction (XRD) measurements were performed at a speed of 0.02° s "1 by a Rigaku Miniflex XRD machine with Cobalt refractor. The morphology of the membranes was observed using a scanning electron microscope (SEM) (JEOL FE6400). Proton conductivity of the membranes were determined from the impedance data obtained using an impedance analyzer (Solartron SI 1260) in a frequency range of IMHz to 100Hz.

The synthesised membranes (2) resulted in a flexible film with thickness between 80-200 μm. SEM micrographs show that the phosphosilicate particles were homogeneously dispersed, whilst the PVA crosslinked with the inorganic phase. Based on XRD results, it can be inferred that the hydrogen-bonding interaction between hydroxyl groups in phosphosilicate gel particles and PVA matrix led to an amorphous composite membrane. Unlike the PVA membranes, the composite membranes were insoluble to water, which may also indicate that there may be a strong interaction or crosslinking between the phosphosilicate gel particles and PVA matrix. Proton conductivity increased by several orders of magnitude with increasing humidity, reaching a maximum of 0.021 S/cm at ambient temperature and 100% RH. These results are comparable to those for hydrated Nafion 117 measured at ambient temperature and under the same experimental conditions.

5.2 Methanol Permeability

Methanol permeability of the membranes was determined using a home-made side-by-side diffusion cell. Prior to the experiments, the composite membrane (2) was equilibrated in a methanol aqueous solution (mol/mol = 1:1) for 24 h. Then the composite membrane was clamped between donor and receptor compartments and the permeation of methanol was measured at 25, 50 and 75 0 C with the donor compartment charging with a methanol aqueous solution (mol/mol = 1:1). The concentration of methanol in the receptor

compartment was measured using gas chromatography (Shimadzu GC-17A). As a comparison, Nation 117 membrane was measured at the same conditions.

The composite membrane shows higher resistance to methanol permeation than Nation 117, nearly one order of magnitude permeation reduction was achieved at ambient temperature whilst over 5-fold decrease above 50 0 C. These results suggest that the phosphosilicate particles in the membrane restrict the movement of the PVA polymeric chains, thus restricting the permeation of liquids contrary to the hydrated properties of

Nation membranes. Moreover, the low methanol permeability could be also attributed to alcohol-phobic PVA. This clearly indicates that the methanol crossover can be significantly reduced if the composite phosphosilicate PVA membrane is to be used in

Direct Methanol Fuel Cell (DMFC) systems.

Although several preferred embodiments have been described in detail, it should also be understood that various changes, substitutions, and alterations can be made herein by one ordinarily skilled in the art without departing from the spirit or scope of the present invention.