JP5870495B2 - POLYMER ELECTROLYTE, MEMBRANE ELECTRODE ASSEMBLY USING THE POLYMER ELECTROLYTE, AND FUEL CELL - Google Patents

Description

  The present invention relates to a polymer electrolyte, a membrane electrode assembly using the polymer electrolyte, and a fuel cell. More specifically, the present invention relates to a polymer electrolyte that exhibits high proton conductivity under low humidification conditions and is excellent in water resistance, a membrane electrode assembly using the polymer electrolyte, and a fuel cell.

  In recent years, the use of fuel cells has attracted attention as an effective solution to environmental and energy problems. A fuel cell is a cell that oxidizes a fuel such as hydrogen using an oxidant gas such as oxygen and converts chemical energy associated with the oxidation into electrical energy.

  Fuel cells are classified into alkaline, phosphoric acid, solid polymer, molten carbonate, solid oxide, etc., depending on the type of electrolyte. The polymer electrolyte fuel cell (PEFC) is characterized by low-temperature operation and high output density, and can be reduced in size and weight. Therefore, it can be used as a portable power source, a household power source, and an in-vehicle power source. Expected.

  As a PEFC electrolyte, a perfluoro electrolyte represented by Nafion (registered trademark of Nafion, DuPont, which has practical stability) having practical stability is used. However, these electrolytes exhibit high proton conductivity but have a problem of high cost.

  In order to solve this problem, inexpensive hydrocarbon electrolytes are being studied. For example, Patent Documents 1 and 2 disclose sulfonated engineering plastics as inexpensive hydrocarbon electrolytes. However, the electrolytes described in Patent Documents 1 and 2 exhibit high proton conductivity under high humidity conditions, but have a problem that proton conductivity decreases under low humidity conditions. Therefore, as a method of showing high proton conductivity even under low humidity conditions, a method of increasing the concentration of proton acid groups has been tried, but increasing the concentration of proton acid groups reduces the water resistance of the electrolyte membrane, There is a problem that the mechanical strength that can withstand practical use cannot be obtained.

  On the other hand, in order to improve the durability, water resistance and mechanical strength of the hydrocarbon electrolyte membrane, a method of crosslinking the electrolyte has been proposed (Patent Document 3). However, in the crosslinked electrolyte described in Patent Document 3, the crosslinking reaction proceeds via a protonic acid group bonded to the proton conducting polymer. Therefore, when the crosslinking density is improved, there is a problem that the hydrogen ion exchange capacity of the crosslinked electrolyte is lowered and the proton conductivity is lowered. Moreover, in the crosslinked electrolyte proposed in Patent Document 4, it is necessary to introduce a crosslinking group into the electrolyte, and there is a problem that the crosslinked electrolyte cannot be easily obtained.

Japanese Patent Laid-Open No. 11-116679 JP 2007-329120 A JP 2007-70563 A Japanese Patent Application Laid-Open No. 2004-10777

  The present invention has been made in view of such a conventional problem. The electrolyte is cross-linked without lowering the ion exchange capacity, exhibits high proton conductivity in a low humidified condition, and has an excellent water resistance. An object of the present invention is to provide a membrane electrode assembly using a molecular electrolyte and a fuel cell at low cost.

（一般式（１）中、Ａは−（ＣＨ₂）_m−、−Ｏ−（ＣＨ₂）_m−、−Ｓ−（ＣＨ₂）_m−、−ＮＨ−（ＣＨ₂）_m−から選択される連結基であり、ｍは３または４であり、Ｙはスルホン酸基、ホスホン酸基、ヒドロキシル基、カルボキシル基から選択されるプロトン酸基であり、ｋは１〜４の整数である） The polymer electrolyte of the present invention is a crosslinked polymer electrolyte formed mainly of a crosslinked polymer obtained by crosslinking a proton conducting polymer and a crosslinking agent via a portion other than a proton acid group. The proton conductive polymer has a structural unit represented by the following general formula (1).

(In the formula (1), A is _{- (CH 2) m -,} - O- (CH 2) m -, - S- (CH 2) m -, - NH- (CH 2) m - is selected from M is 3 or 4, Y is a protonic acid group selected from a sulfonic acid group, a phosphonic acid group, a hydroxyl group, and a carboxyl group, and k is an integer of 1 to 4)

  By having such a configuration, the present invention crosslinks an electrolyte without reducing the ion exchange capacity, exhibits high proton conductivity under low humidification conditions, and has excellent water resistance and a membrane using the polymer electrolyte An electrode assembly and a fuel cell can be provided at low cost. In addition, since the electrolyte and the cross-linking material are chemically bonded via a portion other than the proton acid group, the cross-linking can be performed without reducing the hydrogen ion exchange capacity, and a decrease in proton conductivity is suppressed.

The proton conductive polymer preferably has a hydrogen ion exchange capacity of 1 meq / g or more and 6 meq / g or less. By having such a configuration, high proton conductivity is exhibited, and the internal resistance of the fuel cell can be reduced to obtain a high output density.

  The crosslinking agent preferably has at least two methylol groups in the molecule. By having such a configuration, the reaction proceeds without going through the protonic acid group contained in the proton conductive polymer, and therefore, it is possible to achieve a further remarkable effect that the proton conductivity is not impaired by the reaction.

  It is preferable that the proton conductive polymer and the crosslinking agent are chemically bonded by heating. By having such a configuration, since the reaction can be easily advanced by heating, the apparatus and the process are simplified, and a further remarkable effect that the reaction can be easily performed economically can be achieved. .

  The heating temperature is preferably 60 ° C. or higher and 250 ° C. or lower. By using the child having such a configuration, it is possible to obtain a further remarkable effect that the reaction can be easily advanced while suppressing the separation and decomposition reaction of the proton acid group contained in the proton conductive polymer.

  Moreover, this invention is a membrane electrode assembly using the said polymer electrolyte. By having such a configuration, the present invention can suppress the deterioration of the electrolyte, and can achieve remarkable effects that high power generation characteristics and power generation stability can be ensured during long-time operation of the fuel cell and reliability can be improved.

  Furthermore, the present invention is a fuel cell using the above polymer electrolyte. By having such a configuration, the present invention can suppress the deterioration of the electrolyte, and can achieve a remarkable effect that high power generation characteristics and power generation stability can be ensured during long-time operation of the fuel cell and reliability can be improved. .

  According to the polymer electrolyte of the present invention, the membrane electrode assembly using the polymer electrolyte, and the fuel cell, the electrolyte is cross-linked without decreasing the ion exchange capacity, exhibits high proton conductivity under low humidification conditions, It is possible to provide an electrolyte excellent in performance, a membrane electrode assembly using the polymer electrolyte, and a fuel cell at low cost.

Sectional drawing of the membrane electrode assembly which formed the electrode catalyst layer on both surfaces of the polymer electrolyte membrane concerning one Embodiment of this invention Sectional drawing which shows the structure of the single cell of the fuel cell equipped with the membrane electrode assembly concerning one Embodiment of this invention.

  Hereinafter, the present invention will be described in detail.

（一般式（１）中、Ａは−（ＣＨ₂）_m−、−Ｏ−（ＣＨ₂）_m−、−Ｓ−（ＣＨ₂）_m−、−ＮＨ−（ＣＨ₂）_m−から選択される連結基であり、ｍは３または４であり、Ｙはスルホン酸基、ホスホン酸基、ヒドロキシル基、カルボキシル基から選択されるプロトン酸基であり、ｋは１〜４の整数である） The polymer electrolyte of the present invention is a crosslinked polymer electrolyte formed mainly of a crosslinked polymer obtained by crosslinking a proton conducting polymer and a crosslinking agent via a portion other than a proton acid group. The proton conductive polymer has a structural unit represented by the following general formula (1).

(In the formula (1), A is _{- (CH 2) m -,} - O- (CH 2) m -, - S- (CH 2) m -, - NH- (CH 2) m - is selected from M is 3 or 4, Y is a protonic acid group selected from a sulfonic acid group, a phosphonic acid group, a hydroxyl group, and a carboxyl group, and k is an integer of 1 to 4)

  The proton conductive polymer having the structural unit represented by the general formula (1) is not particularly problematic even if it is a copolymer with another aromatic ring or the like. Examples of the other aromatic rings include aromatic rings having high electron density and high reactivity with the crosslinking agent in the present invention, such as benzene rings, naphthalene rings, fluorene rings, and thiophene rings, and derivatives thereof. it can. Moreover, it does not specifically limit as a polymerization method for obtaining the polymer electrolyte concerning this invention, For example, well-known polymerization methods, such as random copolymerization, alternating copolymerization, and block copolymerization, are employable.

  The type of proton acid group in the proton conductive polymer is not particularly limited, and examples thereof include a sulfonic acid group, a phosphonic acid group, a hydroxyl group, and a carboxyl group. Among these, a sulfonic acid group is preferable from the viewpoints of dissociation constant, stability to water, and the like.

  The hydrogen ion exchange capacity of the proton conductive polymer having proton conductivity used in the present invention is preferably 1 meq / g or more and 6 meq / g or less from the viewpoint of ion conductivity. When the hydrogen ion exchange capacity is less than 1 meq / g, the proton conductivity is inferior, and when used in a fuel cell, the internal resistance tends to be large and the output density tends to decrease. On the other hand, when it exceeds 6 meq / g, the water resistance of the proton conducting polymer membrane tends to be impaired.

  The proton conductive polymer of the present invention is preferably used in combination with other polymers in order to improve mechanical strength and water resistance. Specific examples of other polymers include, for example, aromatic polyethers, aromatic polyether ketones, aromatic polyether ether ketones, aromatic polyether sulfones, aromatic polysulfones, aromatic polyether nitriles, aromatic polyethers. Examples thereof include pyridine, aromatic polyimide, aromatic polyamide, aromatic polyamideimide, aromatic polyazole, aromatic polyester, and aromatic polycarbonate. These polymers may be sulfonated or not sulfonated.

The crosslinking agent used in the present invention can cause the reaction to proceed at a portion other than the proton acid group without passing through the proton acid group of the proton conductive polymer. The crosslinking agent is not particularly limited as long as it does not change the proton conductivity of the proton conductive material before and after the reaction. Among them, a crosslinking agent having a structure in which a methylol group represented by —CH ₂ OH is bonded to an aromatic ring (hereinafter also referred to as “crosslinking agent having a methylol group”) can easily react with a proton conductive material by heating. It is preferable because it proceeds and chemically bonds.

  Among the cross-linking agents having a methylol group, a compound having at least two aromatic rings having a methylol group in the molecule proceeds without involving a protonic acid group contained in the proton-conducting polymer. Proton conductivity is not impaired, and it can be suitably used in that the reaction proceeds easily by heating.

  As the reaction method, a light irradiation method, a heating method, a pH adjustment method, and the like can be used. However, since the proton conductive polymer solution used in the present invention is acidic, a pH adjustment method that reacts under acidic conditions is used. preferable.

  FIG. 1 is a cross-sectional view of a membrane electrode assembly in which an electrode catalyst layer (air electrode side) 2 and an electrode catalyst layer (fuel electrode side) 3 are formed on both surfaces of a polymer electrolyte membrane 12 according to an embodiment of the present invention. is there.

  As shown in FIG. 1, an electrode catalyst layer 2 (air electrode side) and an electrode catalyst layer 3 (fuel electrode side) are bonded and laminated on both surfaces of a polymer electrolyte membrane 1 by a conventional method to form a membrane electrode assembly 12. Is formed. The electrode catalyst layer 2 and the electrode catalyst layer 3 respectively react with the carbon black particles as a conductive agent, a reaction catalyst, the proton conductive polymer, or the proton conductive polymer and a crosslinking agent to react with the proton conductive material. And a polymer electrolyte obtained by chemical bonding through a portion other than the protonic acid group of the polymer. The air electrode and the fuel electrode described above refer to an electrode for supplying an oxidant gas and an electrode for supplying a fuel gas, respectively, and are shown as an air electrode 6 and a fuel electrode 7 in FIG.

  As reaction catalysts, platinum, palladium, ruthenium, iridium, rhodium, osmium, platinum group elements, metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, or these metals An alloy, an oxide, a double oxide, or the like can be used. Moreover, since the activity of a catalyst will fall when the particle size of these reaction catalysts is too large, and there exists a tendency for the stability of a catalyst to fall when too small, about 0.5-20 nm is preferable, About 1-5 nm More preferably.

  Generally, carbon particles are used as the conductive agent supporting these reaction catalysts. The type of carbon particles is not particularly limited as long as it is in the form of fine particles and has conductivity and is not affected by the catalyst. For example, carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotube, fullerene, etc. are used. be able to. If the particle size of the carbon particles is too small, it becomes difficult to form an electron conduction path. If the particle size is too large, the gas diffusibility of the electrode catalyst layer tends to decrease or the utilization factor of the catalyst tends to decrease. About -1000 nm is preferable and it is more preferable that it is about 10-100 nm.

  FIG. 2 is a cross-sectional view showing the configuration of a single cell of a fuel cell equipped with the membrane electrode assembly 12 according to one embodiment of the present invention. As shown in FIG. 2, the electrode catalyst of the membrane electrode assembly 12 is shown. Gas diffusion layer 4 (air) having a structure in which a mixture of carbon black and polytetrafluoroethylene (PTFE) is applied to carbon paper, facing layer 2 (air electrode side) and electrode catalyst layer 3 (fuel electrode side). (Electrode side) and gas diffusion layer 5 (fuel electrode side) are arranged. Thereby, the air electrode 6 and the fuel electrode 7 are comprised, respectively.

  As shown in FIG. 2, the separator 10 includes a gas flow path 8 for reaction gas distribution facing the gas diffusion layer 4 (air electrode side) and the gas diffusion layer 5 (fuel electrode side). A cooling water flow path 9 for circulating cooling water is provided on the surface, and it is made of a material that is electrically conductive and impermeable to gas. The single cell 11 has a configuration in which a membrane electrode assembly 12 is sandwiched between a pair of the separators 10. In the single cell 11, an oxidant gas such as air or oxygen is supplied from the air electrode 6, and a fuel gas containing hydrogen or an organic fuel is supplied from the fuel electrode 7.

  The manufacturing method of the membrane electrode assembly 12 of this invention is demonstrated. First, on the gas diffusion layer 4 and the gas diffusion layer 5 made of the conductive porous body for uniformly supplying the fuel gas to the electrode catalyst layer 2 and the electrode catalyst layer 3, the reaction catalyst, the conductive agent, The catalyst electrode layer 2 and the catalyst electrode layer 3 are laminated | stacked by apply | coating with the ink which consists of a proton conductive polymer which has a proton acid group, and drying after that. Thereafter, the polymer electrolyte membrane 1 is sandwiched between the catalyst electrode layer 2 and the catalyst electrode layer 3 and joined by thermocompression bonding to produce a membrane electrode assembly 12. The method for applying the ink on the gas diffusion layer 4 and the gas diffusion layer 5 is not particularly limited, and for example, a doctor blade method, a screen printing method, a spray method, or the like can be employed.

  The membrane electrode assembly 12 is produced by producing the catalyst electrode layer 2 and the catalyst electrode layer 3 on both surfaces of the polymer electrolyte membrane 1 by transfer or spray spraying, and then the gas diffusion layer 4 and the gas diffusion layer. Alternatively, a method of holding at 5 may be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited at all by these Examples.

Example 1
First, 1 g of a proton conductive polymer represented by the following general formula (2) and 0.20 g of 1,4-benzenedimethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) as a crosslinking agent were mixed in an organic solvent.

Next, the produced solution is formed on a polyimide base material by a casting method, dried, and then the obtained film is heated and pressed to advance the reaction so that the proton conductive polymer according to Example 1 is used. An electrolyte membrane was obtained. The heating press conditions were a press temperature of 120 ° C., a press time of 3 hours, and a press pressure of 60 kgf / cm ² . When the obtained polymer electrolyte membrane was immersed in water, dimethyl sulfoxide (DMSO), and dimethylformamide (DMF), none of them was dissolved, so that the polymer electrolyte membrane was confirmed to be crosslinked. The proton conductivity of the obtained polymer electrolyte membrane was measured. The results are shown in Table 1.

(Measurement of proton conductivity)
The AC resistance of the electrolyte membrane is obtained from the measurement of AC impedance between platinum wires by pressing a platinum wire against the surface of a 10 mm-wide strip-shaped proton conducting membrane sample, holding the sample in a constant temperature and humidity device. Impedance is measured in an environment of temperature 80 ° C., relative humidity 95% and 60%. The proton conductivity values of the polymer electrolyte membrane and Nafion obtained in Example 1 at the respective humidity are measured.

  It was found that the polymer electrolyte membrane obtained in Example 1 exhibited a proton conductivity almost equal to or higher than that of Nafion in an environment of a temperature of 80 ° C., a relative humidity of 95% and 60%.

(Comparative Example 1)
A polymer electrolyte was prepared in the same manner as in Example 1 except that no crosslinking agent was added. When the obtained polymer electrolyte was immersed in the above-mentioned solvent, it was confirmed that it was not crosslinked because it was dissolved.

  The polymer electrolyte according to the present invention, the membrane electrode assembly using the polymer electrolyte, and the fuel cell crosslink the electrolyte without lowering the ion exchange capacity, exhibit high proton conductivity under low humidification conditions, For example, it can be suitably used in the field of fuel cells and the like.

DESCRIPTION OF SYMBOLS 1 Polymer electrolyte 2, 3 Electrode catalyst layer 4, 5 Gas diffusion layer 6 Air electrode 7 Fuel electrode 8 Gas flow path 9 Cooling water flow path 10 Separator 11 Single cell 12 Membrane electrode assembly

Claims (8)

In a crosslinked polymer electrolyte mainly composed of a crosslinked polymer in which an aromatic ring of a proton conductive polymer having an aromatic ring is crosslinked by a crosslinking agent ,
The proton conductive polymer has a structural unit represented by the following general formula (1).

(In General Formula (1), A is a linking group selected from — (CH ₂ ) _m —, —S— (CH ₂ ) _m —, and —NH— (CH ₂ ) _m —, and m is 3 or is 4, Y is a protonic acid group selected from a phosphonic acid group, mosquitoes carboxyl group, k is an integer from 1 to 4) In a crosslinked polymer electrolyte mainly composed of a crosslinked polymer in which an aromatic ring of a proton conductive polymer having an aromatic ring is crosslinked by a crosslinking agent ,
The proton conductive polymer has a structural unit represented by the following general formula (2).

  The polymer electrolyte according to claim 1 or 2, wherein the proton-conductive polymer has a hydrogen ion exchange capacity of 1 meq / g or more and 6 meq / g or less.   The polymer electrolyte according to any one of claims 1 to 3, wherein the crosslinking agent has at least two methylol groups in the molecule. The polymer electrolyte according to any one of claims 1 to 4, wherein the proton conductive polymer and the cross-linking agent have a property of being chemically bonded by heating.   6. The polymer electrolyte according to claim 5, wherein the heating temperature is 60 ° C. or higher and 250 ° C. or lower.   The membrane electrode assembly using the polymer electrolyte of any one of Claims 1-6.   The fuel cell using the polymer electrolyte of any one of Claims 1-6.

Images