WO2006132461A1

WO2006132461A1 - Proton exchange membrane comprising compatibilizer and fuel cell comprising the same

Info

Publication number: WO2006132461A1
Application number: PCT/KR2005/003570
Authority: WO
Inventors: Young-Moo Lee; Chang-Hyun Lee; Ho-Bum Park
Original assignee: Industry-University Cooperation Foundation, Hanyang University
Priority date: 2005-06-10
Filing date: 2005-10-26
Publication date: 2006-12-14
Also published as: KR100608482B1

Abstract

The present invention relates to a proton exchange membrane comprising compatibilizer and fuel cell comprising the same, and in particular to polymer electrolyte membrane having compatibilizer containing polyethylene oxide, polypropylene oxide, and their copolymers and fuel cell comprising the same. The polymer electrolyte membranes in the present invention contain compatibilizers such as Pluronics and Tetronic with hydrophilic and hydrophobic properties, which contribute to homogeneous dispersion of hydrophilic and hydrophobic inorganic fillers. Furthermore, the organometallic complexes (compatibilizer and inorganic fillers) reduce the water uptake level around hydrophilic moieties within the membranes, and decrease the swellability of membrane in fabrication of membrane-electrode assemblies, leading to increase of dimensional stability for long term fuel cell operation. Differing from reduction of water uptake level, the organometallic complexes increase bound water content which has a strong interaction with functional groups in the polymeric membranes. As a result, incorporation of the organometallic complexes enhances proton conductivity of the resulting polymers. Simultaneously, addition of compatibilizer or organometallic complexes helps the resulting polymers to have methanol-barrier property and also improved chemical properties including thermal stability, hydrolytic stability, free-radical stability as well as physical properties such as mechanical strength.

Description

PROTON EXCHANGE MEMBRANE COMPRISING COM- PATIBILIZER AND FUEL CELL COMPRISING THE SAME

Technical Field

[1] The polymer electrolyte membranes in the present invention contain polymeric or oligomeric compatibilizers such as Pluronics^Dand Tetronic°with hydrophilic and hydrophobic properties, which contributed to homogeneous dispersion of hydrophilic and hydrophobic inorganic fillers. Furthermore, the organometallic complexes (compatibilizer and inorganic fillers) reduced the water uptake level around hydrophilic moieties within the membranes, and decreased the swellability of membrane in fabrication of membrane-electrode assemblies, leading to increase of dimensional stability for long term fuel cell operation. Differing from reduction of water uptake level, the organometallic complexes increased bound water content which has a strong interaction with functional groups in the polymeric membranes. As a result, incorporation of the organometallic complexes enhanced proton conductivity of the resulting polymers. Simultaneously, addition of compatibilizer or organometallic complexes helped the resulting polymers to have methanol-barrier property and also improved chemical properties including thermal stability, hydrolytic stability, free- radical stability as well as physical properties such as mechanical strength. The present invention relates to a proton exchange membrane comprising compatibilizer with peculiar characteristics mentioned above and fuel cell comprising the same. Background Art

[2] A solid polymer electrolyte was developed in the 1950's for supplying energy to a spacecrafts. In addition to a power sources for a spacecraft, fuel cells have lately attracted considerable attention even in automobiles owing to the following two reasons. Firstly, fuel cells can reduce air pollution derived from an internal combustion engine. It is impossible to prevent all discharge compounds such as nitric oxide, hydrocarbon and acids through a control of an incomplete combustion reaction of an internal combustion engine. Secondly, it is urgently required to develop a vehicle which uses a semi-permanent new fuel instead of fossile fuel such as petroleum and coal.

[3]

[4] As polymer electrolyte fuel cells, there are proton exchange membrane fuel cell

(PEMFC), and direct methanol fuel cell (DMFC) using hydrogen gas and liquid methanol as fuels for anodes, respectively. The supplied hydrogen and methanol are permanent fuels, and generate only water as a by-product through an electochemical reaction.

[5]

[6] FIGURE 1 shows a schematic diagram of an assembly of a fuel cell which generate electrical energy as well as water.

[7]

[8] As shown in FIGURE 1, the proton exchange membrane 1 as a solid polymer electrolyte separates an anode 4 and a cathode 5, where hydrogen or methanol solution 2 is oxidized based on the following reaction using air or oxygen 3 as a fuel. In the case of PEMFC, the reaction formula is 2H 2 → 4H⁺ + 4e , and in the case of DMFC, the reaction formula is CH OH + H O → CO + 6H⁺ + 6e . Oxidizing agents such as

3 2 2 ^{& &} oxygen are reduced at the cathode part 5 and induce production of water 7. In the case of PEMFC, the reaction formula is O + 4H⁺ + 4e^" → 2H O, and in the case of DMFC, the reaction formula is 3/20 2 + 6H⁺ + 6e → CO 2 + 2H 2O.

[9]

[10] The anode and cathode are composed of proton conducting graphite supports containing a metallic particle such as platinum and ruthenium are deposited. Furthermore, a coated layer 8 comprising Nafion thin film with loading of 1-10 mg/cm is incorporated on each surface of the polymer electrolyte membrane to enhance the adhesion property between the polymer electrolyte membrane and each electrode such as cathode and anode, and to improve the proton conductivity derived from the desirable interface formation of the three phase in the electrode.

[H]

[12] The membrane electrode assembly (MEA) has a very thin thickness of the millimeter unit. Fuel gases are supplied through bipolar plates with a serpentine flow path into the each electrode of the MEA.

[13]

[14] Since 1950, many kinds of sulfonated polymer or polymeric materials have been utilized as polymer electrolyte membranes for fuel cells, and their performances have been investigated in relation to chemical structures and membrane morphologies. However, most of sulfonated polymers exhibit proton conduction properties in the hydrated state and consequently show rapid reduction of proton conductivity at high temperature over 90 ⁰C owing to low water retention level within the polymers or thermal degradation of sulfonic acid groups. As a result, there have been a lot of approaches to solve the reduction of proton conductivity in high temperature operation. These include some trials to incorporate inorganic oxides such as SiO , ZrO , tetraethoxysilane (TEOS), and montmorillonite clay into perfluorinated sulfonated ionomer (PFSA) membranes including Nafion (DuPont, USA). Incorporation of inorganic fillers contributes to enhancement of water retention level and then compensate proton conductivity loss to some extent at high temperature over 100 ⁰C. Unfortunately, these incorporation of inorganic oxides have a limitation in their contents considering mechanical properties of the PEMs. The replacement of water molecules with inorganic acids such as phosphoric acid as proton conduction medium has been also tried to reduce the effect of water retention level upon temperature, which is strongly responsible to proton transport in the PFSA membranes.

[15]

[16] In addition to PFSA membranes, non-perfluorinated sulfonated ionomers have been investigated in their application as PEM for high temperature fuel cell. These PEMs have been fabricated via incorporation of sulfonic acid groups for high proton conductivity into thermoplastics such as polysulfones, poly(ether sulfone)s, poly(ether ketone)s, and polyimides. When these PEMs are applied in the high temperature fuel cell, the reduction of their proton conductivities was smaller than those of PFSA membranes. There have been some approaches to increase a water retention level and compensate a reduction of proton conductivity at high temperatures via incorporation of inorganic oxides into thermostable sulfonated polymers, or to incorporate het- eropolyacids (HPAs) as proton conductors and contribute to maintenance or improvement of proton conductivity at high temperature compared to reduced proton conductivity under low humidity condition. In the composite PEMs system, the content of inorganic oxides and leaching-out problem of HPAs from polymer matrix limit their application of PEMs containing inorganic oxides and HPAs, respectively.

[17]

[18] The composite membrane with inorganic fillers is typically fabricated using sol-gel synthetic route where inorganic precursors with constant content are incorporated into polymer matrix and consequently formed hybrid membrane containing inorganic networks. The composite membrane is also fabricated by direct mixing of inorganic fillers. The membrane fabrication using sol-gel method was observed in the hybrid membrane containing porous silica derived from silica precursors such as TEOS via sol-gel method (Journal of membrane science 2002, 109, 356-364), and composite membrane containing water-insoluble zirconium phosphate after immersion of polymer matrix in zirconium chloride and successive phosphoric acid treatment (Journal of membrane science 2004, 237, 145-161). The direct mixing of inorganic fillers was observed in composite membranes fabricated through sonication of inorganic powders in polymer solution for a certain time (Journal of membrane science 2004, 229, 43-51) and HPA-polymer composite membranes fabricated through mechanical stirring for a long time or stirring accompanied by heating (Journal of membrane science 2000, 173, 17-34). In most of cases as described above, the reduction of proton conductivity was compensated, or mechanical strength of polymer matrix was enhanced after incorporation of inorganic fillers. However, most of direct mixing of inorganic fillers without inorganic precursors led to heterogeneous distribution of inorganic fillers. Consequently, resulting composite membranes showed brittleness and low mechanical strength even in low content of inorganic fillers without reproducibility in membrane performances such as proton conductivity, thermal stability, hydrolytic stability. Especially in DMFC application, the resulting composites did not display desirable methanol-barrier property. Disclosure of Invention Technical Problem

[19] It is a ultimate objective of the present invention to develop proton conductive composite membranes with following peculiar characteristics. The polymer electrolyte membranes in the present invention contain polymeric or oligomeric compatibilizers such as Pluronics and Tetronic with hydrophilic and hydrophobic properties, which contributes to homogeneous dispersion of hydrophilic and hydrophobic inorganic fillers. Furthermore, the organometallic complexes (compatibilizer and inorganic fillers) reduce the water uptake level around hydrophilic moieties within the membranes, and decrease the swellability of membrane in fabrication of membrane- electrode assemblies, leading to increase of dimensional stability for long term fuel cell operation. Differing from reduction of water uptake level, the organometallic complexes increase bound water content which has a strong interaction with functional groups in the polymeric membranes. As a result, incorporation of the organometallic complexes enhance proton conductivity of the resulting polymers. Simultaneously, addition of compatibilizer or organometallic complexes helps the resulting polymers to have methanol-barrier property and also improves chemical properties including thermal stability, hydrolytic stability, free-radical stability as well as physical properties such as mechanical strength.

[20] The another objective of the present invention is to develop fuel cells based on a proton exchange membrane comprising compatibilizer. Technical Solution

[21] To achieve the above objectives, the present invention provides polymer electrolyte membrane containing compatibilizers, which includes polyethylene oxide (PEO), polypropylene oxide (PPO), and their copolymers.

[22] The present invention also provides fuel cells based on the proton exchange membranes comprising the compatibilizers.

[23]

[24] The present invention is described in detail.

[25] The inventors perceived that addition of compatibilizers comprising hydrophilic PEO, hydrophobic PPO, and their copolymers led to homogeneous distribution of inorganic fillers, and simultaneously reduced the water uptake level around hydrophilic moieties within the membranes and decreased the swellability of membrane in fabrication of membrane-electrode assemblies, leading to increase of dimensional stability for long term fuel cell operation. The inventors also noticed that the compat- ibilizers increased bound water content which has a strong interaction with functional groups in the polymeric membranes and improved proton conductivity of the resulting polymers. The inventors noticed that addition of compatibilizer or organometallic complexes help the resulting polymers to have methanol-barrier property and also enhanced chemical properties including thermal stability, hydrolytic stability, free- radical stability as well as physical properties such as mechanical strength. Finally, the inventors accomplished the present invention based on overall properties as described above.

[26]

[27] The proton exchange membrane in the present invention contains compatibilizers includes PEO, PPO, and their copolymers.

[28]

[29] The membrane materials in the present invention include conventional polymer materials such as polyimides, polysulfones, poly(arylene ether sulfone)s, poly(arylene ether ketone)s, polybenzimidazoles, polybenzoxazoles, polybenzthiazoles, and polyphosphazenes. Desirably, the membrane materials contain hydrophilic functional groups such as sulfonic acid, carboxylic acid, and phosphoric acid.

[30]

[31] In particular, the compatibilizers in the present invention can be polymers or oligomers having hydrophilic moieties such as PEO and/or hydrophobic moieties such as PPO. Polymeric or oligomeric compatibilizers including Pluronic or Tetronic with both hydrophilic and hydrophilic properties are more desirable.

[32]

[33] The influences of polymeric or oligomeric compatibilizers having hydrophilic PEO moieties and/or hydrophobic PPO moieties in membrane fabrication can be summarized as following:

[34]

[35] 1. Improved distribution of inorganic fillers such as fumed silica.

[36] Pluronic (trade name: Poloxamer), a compatibilizer, is triblock copolymer comprising PEO-PPO-PEO. In the compatibilizer, PEO moieties show hydrophilicity while PPO moieties exhibit hydrophobicity. In case of incorporation of hydrophilic fumed silica into the polymer matrix, for example, interaction of hydrophilic moieties in the polymer-PEO moieties in compatibilizer-hydrophilic fumed silica led to ho- mogeneous distribution of fumed silica nanoparticles via their hydrogen bond (see CHEMICAL FORMULA 1). On the other hand, homogeneous distribution of hydrophobic silica particles was accomplished by interaction of hydrophobic moieties in the polymer-PPO moieties in compatibilizer-hydrophobic fumed silica.

[37] [38] [CHEMICAL FORMULA 1] [39]

mat r ι x

i b i I i zer

Hydroph i I i c f umed s i I i ca

[40]

[41] 2. Reduction of water uptake level in the membrane.

[42] The interaction of polymer-compatibilizer-silica prevented a lot of water molecules from accessing within the resulting composite membranes, and reduced their water uptake level. Large difference in membrane swellability under dry and wet condition causes delamination in MEA, which makes single cell performances low. Therefore, low water uptake level should be needed to achieve a high fuel cell performances.

[43]

[44] 3. Increase of bound water content in the composite membranes

[45] Differing from reduction of water uptake level, bound water content increased from

43 to 87% owing to interaction of hydrophilic moieties in the polymer-hydrophilic moieties in compatibilizer-hydrophilic fumed silica particles with water molecules. Here, the bound water is defined as water molecules showing strong interaction with functional groups in the membrane.

[46]

[47] 4. Improvement of proton conductivity.

[48] High content of bound water significantly affects proton conductivity of resulting composite membranes. That is, it contributed to improvement of proton conductivity at 1) the same measuring temperature and 2) the elevated temperatures. Even in the composite membranes containing only compatibilizers, the proton conductivity increased with high content of hydrophilic moieties in compatibilizers.

[49] [50] 5. Reduction of methanol permeability.

[51] In the composite membranes containing only compatibilizers or organometallic complexes, high methanol-barrier properties caused low methanol permeability.

[52]

[53] 6. Improved mechanical strength in the composite membranes.

[54] The mechanical strength of composite membranes containing compatibilizer or organometallic complexes was more improved than that of pristine polymers.

[55]

[56] 7. Improvement of membrane stability to heat, hydrolysis, and radical attack.

[57] The thermal stability of organic-inorganic composite membrane containing fumed silica was significantly improved as compared with thermal stability of the pristine polymer membrane. In case of sulfonated polyimide membranes with weak hydrolytic stability, addition of fumed silica nanoparticles surprisingly increased their hydrolytic stability. Pristine sulfonated polyimide membrane was easily decomposed after 70 hours. However, sulfonated polyimide- silica nanocomposite membranes showed excellent hydrolytic durability over 5,000 hours after immersion in liquid water at 80 ⁰C owing to condensed polymer structure. The resulting composite membranes also displayed improved resistance to peroxide radical attack using Fenton's reagent (ferrous ammonium salt + H O solution).

[58]

[59] The amount of compatibilizers in the present invention is preferably 0.1 to 10 weight percent per proton conducting polymers. When the amount of compatibilizer is below 0.1 weight percent per proton conducting polymers, the influence of compatibilizer is negligible. When the amount of compatibilizer is over 10 weight percent per proton conducting polymers, membrane performances such as proton conductivity and tensile strength do not increase linearly, which is not economical.

[60]

[61] The compatibilizers in the present invention can be added into the polymer matrix without any inorganic fillers. However, it is preferable that the compatibilizers are incorporated in the organometallic complexes with inorganic oxides such as TiO , SiO ,

2

Al O , ZrO , TEOS, montmorillonite, and mordenite or heteropolyacid including zirconium phosphate(ZrP), phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, silicomolybdic acid. Here, the composite membranes can contain at least one or more inorganic fillers. Although the compatibilizers can be introduced into the polymer matrix, addition of the compatibilizers accompanied by inorganic fillers are most desirable.

[62]

[63] The resulting composite membranes in the present invention can be used in fuel cell, electrolysis, electrodialysis in aqueous or non-aqueous medium, diffusion dialysis, pervaporation, gas separation, dialysis, microfiltration, nanofiltration, and reverse osmosis. Among them, fuel cell application based on the composite membranes is most desirable.

[64]

[65] As described above, the polymer electrolyte membranes in the present invention contain polymeric or oligomeric compatibilizers such as Pluronics and Tetronic with hydrophilic and hydrophobic properties, which contributed to homogeneous dispersion of hydrophilic and hydrophobic inorganic fillers. Furthermore, the organometallic complexes (compatibilizer and inorganic fillers) reduced the water uptake level around hydrophilic moieties within the membranes, decreased the swellability of membrane in fabrication of membrane-electrode assemblies, leading to increase of dimensional stability for long term fuel cell operation. Differing from reduction of water uptake level, the organometallic complexes increased bound water content which has a strong interaction with functional groups in the polymeric membranes. As a result, incorporation of the organometallic complexes enhanced proton conductivity of the resulting polymers. Simultaneously, addition of compatibilizer or organometallic complexes help the resulting polymers to have methanol-barrier property and also improved chemical properties including thermal stability, hydrolytic stability, free- radical stability as well as physical properties such as mechanical strength.

[66]

Advantageous Effects

[67] The polymer electrolyte membranes in the present invention contain polymeric or oligomeric compatibilizers such as Pluronics and Tetronic with hydrophilic and hydrophobic properties, which contributed to homogeneous dispersion of hydrophilic and hydrophobic inorganic fillers. Furthermore, the organometallic complexes (compatibilizer and inorganic fillers) reduced the water uptake level around hydrophilic moieties within the membranes, and decreased the swellability of membrane in fabrication of membrane-electrode assemblies, leading to increase of dimensional stability for long term fuel cell operation. Differing from reduction of water uptake level, the organometallic complexes increased bound water content which has a strong interaction with functional groups in the polymeric membranes. As a result, incorporation of the organometallic complexes enhanced proton conductivity of the resulting polymers. Simultaneously, addition of compatibilizer or organometallic complexes help the resulting polymers to have methanol-barrier property and also improved chemical properties including thermal stability, hydrolytic stability, free- radical stability as well as physical properties such as mechanical strength. [68]

Brief Description of the Drawings

[69] FIGURE 1 shows a schematic diagram of an assembly of a fuel cell which generate electrical energy as well as water. [70]

Mode for the Invention

[71] The desirable examples and comparative examples in the present invention will be described. The following examples are just desirable examples, and the present invention is not limited thereto.

[72]

[73] [EXAMPLE 1]

[74] A 250 ml reactor fitted with a teflon stirring system, an inlet for an inert gas, such as nitrogen, and a sample inlet was installed to carry out condensation reaction of polyimide, and placed in an oil bath to constantly maintain the reaction temperature. The reactor was charged with 0.86 g (2.4 mmol) of 4,4'-diamino diphenyl ether- 2,2'-disulfonic acid (ODADS) and added by m-cresol as a solvent. Moreover, 0.96 g (9.6 mmol) of triethylamine and 0.68 g (5.68 mmol) of benzoic acid were added as reaction catalysts. After complete dissolution, 1.07 g (4 mmol) of 1,4,5,8-Naphthalene tetracarboxylic dianhydride powder was slowly added into the solution. After the reaction was maintained for about 1 h, 0.23 g (1.6 mmol) of 3,5-diaminobenzene was added into the reaction mixture and reacted for 1 h. Then, the mixture was heated at 80 ⁰C for 4 h and 180 ⁰C for 20 h to obtain viscous dark-brown polyimide solution. The polyimide solution was poured into cold acetone to eliminate unreacted monomers or oligomers with low molecular weight. The fiber-like precipitate of sulfonated polyimide (2.3 g) was collected by filtration, washing, and drying in a vacuum oven at 120 ⁰C. The polymer was re-dissolved in 9.2 g of m-cresol. The resulting solution was heated to 150 ⁰C. The pre-treated solution containing 0.023 g of Aerosil 200 (hydrophilic fumed silica) and 0.03 g of Pluronic (Poloxamer 1100, L31) was poured into the resulting polymer solution and reacted for 8 h. The resulting sulfonated polyimide membrane were obtained after casting the solution onto a glass plate, drying at 80 ⁰C for 2 h, and heating at 180 ⁰C for 10 h in a vacuum oven to achieve complete imidization. After vacuum drying at 110 ⁰C for 24 h to remove residual solvent, opaque sulfonated polyimide nanocomposite membrane was obtained with a nominal thickness of 20-40 D. The ion exchange capacity (IEC) was 1.80 meq/g.

[75]

[76] [EXAMPLE 2]

[77] Sulfonated polyimide- silica nanocomposite membrane was fabricated in the same manner as the EXAMPLE 1 except for use of Poloxamer 1900 (L35). [78]

[79] [EXAMPLE 3]

[80] Sulfonated polyimide- silica nanocomposite membrane was fabricated in the same manner as the EXAMPLE 1 except for use of Poloxamer 2900 (L64). [81]

[82] [EXAMPLE 4]

[83] Sulfonated polyimide- silica nanocomposite membrane was fabricated in the same manner as the EXAMPLE 1 except for use of Poloxamer 3500 (L92). [84]

[85] [EXAMPLE 5]

[86] Sulfonated polyimide- silica nanocomposite membrane was fabricated in the same manner as the EXAMPLE 1 except for use of Aerosil 812 (hydrophobic fumed silica). [87]

[88] [EXAMPLE 6]

[89] Sulfonated polyimide- silica nanocomposite membrane was fabricated in the same manner as the EXAMPLE 1 except for use of Poloxamer 1900 (L35) and Aerosil 812

(hydrophobic fumed silica). [90]

[91] [EXAMPLE 7]

[92] Sulfonated polyimide- silica nanocomposite membrane was fabricated in the same manner as the EXAMPLE 1 except for use of Poloxamer 2900 (L64) and Aerosil 812

(hydrophobic fumed silica). [93]

[94] [EXAMPLE 8]

[95] Sulfonated polyimide- silica nanocomposite membrane was fabricated in the same manner as the EXAMPLE 1 except for use of Poloxamer 3500 (L92) and Aerosil 812

(hydrophobic fumed silica). [96]

[97] [EXAMPLE 9]

[98] Sulfonated polyimide- silica nanocomposite membrane was fabricated in the same manner as the EXAMPLE 1 except for use of Poloxamer 2900 (L64) without fumed silica. [99]

[100] [COMPARATIVE EXAMPLE 1]

[101] Sulfonated polyimide membrane was fabricated in the same manner as the

EXAMPLE 1 except for no use of compatibilizer such as Pluronic and inorganic filler [103] [EXPERIMENTS] [104] The proton conductivity at different temperatures (TABLE 1), and at different humidities (TABLE 2), water uptake level (TABLE 3), bound water content (TABLE 4), methanol permeability (TABLE 5), selectivity (TABLE 6), and hydrolytic stability (TABLE 7) of sulfonated polyimide membranes fabricated in EXAMPLE 1 to EXAMPLE 8, and COMPARATIVE EXAMPLE 1 were measured and present in TABLE 1 to TABLE 7.

[105] [106] [EXPERIMENT 1] [107] The ohmic resistance or bluk resistance was measured using four point probe AC impedance spectroscopic method. Then, the proton conductivity was obtained by substitution of the resistance to σ=l/ (RxS). Here, σ(S/cm) is proton conductivity, 1 (cm) is distance between reference electrodes, R (Ω) is ohmic resistance of polymer electrolyte, and S is cross-sectional area where current flows across the membrane. The measurement was performed in the thermo- and hygro-controlled chamber where an electrode system connected with an impedance/gain phase analyzer (Solatron 1260) and an electrochemcial interface (Solatron 1287, Solatron Analytical, Farnborough Hampshire, GU 14, ONR, UK). The ohmic resistance was measured using both Nyquist plot and Bode plot. The measurement was carried out by measuring the voltage drop between inner reference electrodes as constant current (10 mA) flowed across the membrane between outer electrodes. TABLE 1 shows proton conductivity at the elevated temperatures under 95% relative humidity using the measuring apparatus and measurement method.

[108] [109] Table 1 Proton conductivity at different temperatures (S/cm)

[HO]

. D [111] As shown in TABLE 1, the composite membranes fabricated using Pluronic or Poloxamer as compatibilizer showed higher proton conductivities at elevated temperatures and at the constant temperature than pristine polymer membrane owing to increase of bound water content.

[112] [113] [EXPERIMENT 2] [114] TABLE 2 shows proton conductivity at increasing humidities under 60 ⁰C using the measuring apparatus and measurement method.

[115] [116] Table 2 Proton conductivity at different humidities (S/cm)

[117] [118] As shown in TABLE 2, the composite membranes fabricated using Pluronic or Poloxamer^Das compatibilizer also showed more improved proton conductivities at higher relative humidity and at the constant relative humidity than pristine polymer membrane owing to increase of bound water content.

[119] [120] [EXPERIMENT 3] [121] TABLE 3 shows water uptake behavior of each membrane sample. For the measurement, each dry membrane sample was immersed in liquid water at 25 ⁰C for at least 1 day. The water uptake was expressed as follows: W=(Ww-Wd)AVd* 100 where Wd and Ww are the mass of the dry sample and the mass of water-swollen sample.

[122] [123] Table 3 Water uptake level (%)

[124] [125] As shown in TABLE 3, the composite membranes fabricated by incorporation of both compatibilizer and inorganic filler showed reduced water uptake level leading to excellent dimensional stability as compared with pristine polymer.

[126] [127] [EXPERIMENT 4] [128] TABLE 4 shows the state of water in the fully hydrated membranes. The amount of free water was determined using differential scanning calorimetry (DSC). Here, DSC module was purged with nitrogen, quenched down to -50 ⁰C with liquid nitrogen, and then heated up to +50 ⁰C at 5 °C/min. The fraction of free water was approximated using the following equation:

[129] [130] Free water (%) = fusion enthalpy of endothermic peak area from 0 to 10 ⁰C/ [131] endothermic heat of fusion for pure water (334 J/g)*100 [132] Bound water (%) = Total water uptake obtained in TABLE 3 - Free water (%) [133] [134] Table 4 Bound water content (%)

[135] [136] As shown in TABLE 4, the composite membranes fabricated by incorporation of compatibilizer showed higher bound water content than pristine polymer, which contributed to increase of proton conductivity at the elevated temperatures and at a constant temperature.

[137] [138] [EXPERIMENT 5] [139] TABLE 5 shows methanol permeation behavior of each membrane sample. The methanol permeability was determined at 30 ⁰C using a two-chamber diffusion cell method. Prior to the measurement, each membrane coupon was equilibrated in deionized water for at least 1 day, The glass diffusion cell was comprised of two chambers, each with a capacity of 60 ml, separated by a vertical membrane coupon. One chamber of the cell contained a 10 M (34 wt.%) methanol aqueous solution and the other chamber contained deionized water. The methanol permeability was obtained by analyzing the concentration gradient between the two chambers with a gas chromatography (Shimadtzu, GC- 14B, Japan) equipped with a thermal conductivity detector (TCD) at room temperature.

[140] [141] Table 5 Methanol permeability

[142] [143] As shown in TABLE 5, the composite membranes fabricated by incorporation of compatibilizer showed improved methanol-barrier properties. As a result, the methanol permeabilities of the composite membranes were reduced up to 10 times lower than that of pristine polymer

[144] [145] [EXPERIMENT 6] [146] The proton exchange membranes in the present invention should show high proton conductivity and low methanol permeability to apply them to DMFC application. A characteristic factor, selectivity, is required to evaluate both proton conductivity and methanol permeability. Here, selectivity is defined as the ratio of proton conductivity to methanol permeability.

[147] [148] Table 6 Selectivity

[149] [150] As shown in TABLE 6, composite membranes fabricated by incorporation of com- patibilizer showed improved selectivity up to 10 times higher than pristine polymer.

[151] [152] [EXPERIMENT 7] [153] The hydrolytic stability should be needed in the hydrate membrane system where proton is transported in the water medium. The hydrated membranes contain sulfonic acid, carboxylic acid, and phosphoric acid groups in the polymer matrix. The hydrolytic degradation of polymer chains is activated in the acidic water medium. Accordingly, hydrolytic durability is strongly related with reliability of fuel cell performances based on the membranes. The hydrolytic stability in the present invention was defined as the elapsed time that the proton conductivity (measurement condition: 95% RH and 80 ⁰C) was not changed within 5% after aging in liquid water at 80 ⁰C.

[154] [155] Table 7 Hydrolytic stability

[156] [157] As shown in TABLE 7, pristine sulfonated polyimide showed a low hydrolytic stability, which is observed in most of sulfonated polyimide. After incorporation of compatibilizers or organometallic complexes, the hydrolytic stability surprisingly increased in the resulting composite membranes.

[158]

Industrial Applicability

[159] The polymer electrolyte membranes in the present invention contain polymeric or oligomeric compatibilizers such as Pluronics and Tetronic with hydrophilic and hydrophobic properties, which contributed to homogeneous dispersion of hydrophilic and hydrophobic inorganic fillers. Furthermore, the organometallic complexes (compatibilizer and inorganic fillers) reduced the water uptake level around hydrophilic moieties within the membranes, and decreased the swellability of membrane in fabrication of membrane-electrode assemblies, leading to increase of dimensional stability for long term fuel cell operation. Differing from reduction of water uptake level, the organometallic complexes increased bound water content which has a strong interaction with functional groups in the polymeric membranes. As a result, incorporation of the organometallic complexes enhanced proton conductivity of the resulting polymers. Simultaneously, addition of compatibilizer or organometallic complexes help the resulting polymers to have methanol-barrier property and also improved chemical properties including thermal stability, hydrolytic stability, free- radical stability as well as physical properties such as mechanical strength.

[160]

Claims

[1] A proton exchange membrane comprising compatibilizers including polyethylene oxide (PEO), polypropylene oxide (PPO), their copolymers, and their oligomers. [2] A proton exchange membrane of CLAIM 1 comprising triblock- copolymer-typed compatibilizer such as Pluronic or Tetronic containing PEO-

PPO-PEO units. [3] A proton exchange membrane comprising compatibilizer of CLAIM 1, wherein amount of compatibilizer is 0.1 to 40 weight percent per 100 weight percent of the proton exchange membrane. [4] A proton exchange membrane comprising compatibilizer of CLAIM 1, as polymer electrolyte membrane for solid typed fuel cells. [5] A proton exchange membrane comprising compatibilizer of CLAIM 1, wherein at least one inorganic filler is chosen from a group consisting of TiO , SiO , Al O , ZrO , Tetraethoxysilane (TEOS), montmorillonite, mordenite, zirconium phosphate (ZrP), phosphotungstic acid (PWA), silicotungstic acid (SiWA), phos- phomolybdic acid, and silicomolybdic acid. [6] A proton exchange membrane comprising compatibilizer of CLAIM 1, wherein at least one polymeric material is chosen from a group consisting of polyimides, polysulfones, poly(arylene ether sulfone)s, poly(arylene ether ketone)s, polyben- zimidazoles, polybenzoxazoles, polybenzthiazoles, polypyrrolones, and polyphosphazenes . [7] A fuel cell containing proton exchange membranes comprising compatibilizer of

CLAIM 1 to CLAIM 6.