JP2006261004A - Fuel cell and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of improving durability while restraining lowering of power generation property, and a fuel cell system equipped with the fuel cell. <P>SOLUTION: The fuel cell 100 is provided with an electrolyte-electrode assembly 10 composed of an electrolyte film 11 and electrodes 12, 13 arranged on both side of the electrolyte film 11. The electrolyte film contains a sulfonic acid group, and ions having a property of decomposing hydrogen peroxide, and an acidic group relatively weak acidic than sulfonic acid and/or inorganic acid are provided to a constituent member out of constituent members 11, 12, 13, 16a, 16b, and/or between the constituent members 11, 12, 13, 16a, 16b. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell and a fuel cell system, and more particularly to a fuel cell and a fuel cell system capable of improving durability while suppressing a decrease in power generation performance.

  A fuel cell is based on an electrochemical reaction in a membrane electrode assembly (hereinafter referred to as “MEA (Membrane Electrode Assembly)”) including an electrolyte and electrodes (cathode and anode) disposed on both sides of the electrolyte. The generated electrical energy is taken out through separators disposed on both sides of the MEA. Among fuel cells, polymer electrolyte fuel cells (hereinafter referred to as “PEFC (Polymer Electrolyte Fuel Cell)”) used in household cogeneration systems, automobiles, etc., operate at low temperatures. This is possible and is typically used at an operating temperature of 80-100 ° C. In addition, PEFC has shown high energy conversion efficiency of 30 to 40%, has a short start-up time, and has a small and lightweight system. Therefore, PEFC has attracted attention as an optimal power source for electric vehicles and portable power sources.

  A unit cell of PEFC includes an electrolyte membrane, a cathode and an anode including at least an electrode layer, and a separator, and has a theoretical electromotive force of 1.23V. However, since such a low electromotive force is insufficient as a power source for an electric vehicle or the like, the stack form is generally configured by disposing end plates or the like at both ends in the stacking direction of a stacked body in which unit cells are stacked in series. A fuel cell is used.

  On the other hand, it is becoming clear that hydrogen peroxide is generated in the unit cell at the time of power generation of the fuel cell, and OH radicals originating from the hydrogen peroxide are the starting point, degrading the polymer electrolyte of MEA. Since such deterioration contributes to a decrease in the power generation performance of the fuel cell, it is desired to reduce the hydrogen peroxide in the MEA to suppress the deterioration and improve the durability and power generation performance of the fuel cell. Yes.

Several techniques for improving the power generation performance of fuel cells have been disclosed so far. For example, Patent Document 1 discloses a technique related to an electrolyte membrane electrode assembly for a polymer electrolyte fuel cell, characterized in that the oxygen electrode is provided with a cerium-containing oxide. It is said that it becomes possible to provide a polymer electrolyte fuel cell with little deterioration in battery performance even when operated for a long time. Patent Document 2 discloses a technique related to a cathode catalyst for a fuel cell, characterized by comprising CeO ₂ supported on a carrier supporting Pt. By using such a catalyst, oxygen at the cathode is disclosed. The reduction reaction rate can be increased. Furthermore, Patent Document 3 discloses a technique related to an electrode catalyst formed by supporting a catalyst, which is a mixture of noble metal fine particles and at least one kind of rare earth oxide fine particles, on a conductive carrier. By using it, the output of the fuel cell can be improved.
JP 2004-327074 A JP 2003-100308 A JP 2004-197130 A

However, even if a cerium-containing oxide is contained in the cathode of the PEFC by the technique disclosed in Patent Document 1, a hydrocarbon-based electrolyte membrane (hereinafter referred to as “HC membrane” in the following) In the case of the above, there is a problem that it is difficult to maintain the performance deterioration suppressing effect for a long time. This is presumably because the HC film is easily damaged by OH radicals caused by hydrogen peroxide, and it is difficult to obtain a sufficient hydrogen peroxide decomposition effect only with the cerium-containing oxide in the cathode. Further, the technique disclosed in Patent Document 2, if it is contaminated with catalyst comprising CeO _2, would also be possible to improve the durability of the fuel cell. However, when a catalyst comprising CeO ₂ is simply mixed into the electrode layer by such a technique, Ce ⁴⁺ dissociated from CeO ₂ forms a salt with the electrolyte component in the electrolyte membrane, so that the proton conduction performance of the electrolyte membrane decreases. There was a problem of fear. Further, even with the technique disclosed in Patent Document 3, there is a problem that it is difficult to improve the durability of the fuel cell while suppressing a decrease in power generation performance.

  Then, this invention makes it a subject to provide a fuel cell which can improve durability, suppressing the fall of electric power generation performance, and a fuel cell system provided with the said fuel cell.

In order to solve the above problems, the present invention takes the following means. That is,
The invention according to claim 1 comprises an electrolyte membrane and an electrolyte / electrode structure comprising an electrode layer disposed on both sides of the electrolyte membrane, the electrolyte membrane comprising a sulfonic acid group and hydrogen peroxide decomposition performance A fuel cell, characterized in that any of the constituent members and / or between the constituent members, and the weakly acidic group and / or the inorganic particles relatively weakly acidic than the sulfonic acid group are provided. Thus, the above problem is solved.

Here, in the present invention, the electrode layer means a layer including a catalyst that contributes to an electrochemical reaction that occurs in the MEA of the fuel cell, specifically, an anode electrode layer that causes an oxidation reaction of hydrogen, and It means a cathode electrode layer that causes a reduction reaction of oxygen. The electrolyte / electrode structure means the MEA. Furthermore, in the present invention, “having a weakly acidic group that is relatively weaker than the sulfonic acid group” means that the weakly acidic group includes H ⁺ and ions (hereinafter referred to as “A ⁻ . which may be described as ") occurring dissociates a _^-, which is a concept including a form in which is provided. That is, for example, when the weakly acidic group is a phosphonic acid group, a sulfonic acid group and a weak acid group and is provided includes a sulfonic acid group, _-PO 3 _{H 2} and / or _-PO ^{3 2-and} is It is meant to be provided. Note that the weakly acidic group is preferably immobilized in the electrolyte membrane from the viewpoint of preventing oxidative degradation of the electrode layer. Here, as a specific example of the method of immobilizing the weakly acidic group, a method of preparing an electrolyte membrane by kneading the polymer having the weakly acidic group immobilized and the electrolyte component can be exemplified.

Furthermore, specific examples of inorganic particles (“inorganic particles having a weakly acidic group” that can be provided in the fuel cell according to the present invention, the same applies hereinafter) include BPO ₄ , Zr (HPO ₄ ) ₂ , C _60. (OH) _{n and the} like can be mentioned. In addition, specific examples of ions having hydrogen peroxide decomposition performance include transition metal ions and rare earth metal ions. Substances that can generate such ions include Sc, Mn, Fe, Pt, Pd, Ni, Cr, Cu, Ce, Rb, Co, Ir, Ag, Au, Rh, Ti, Zr, Al, Hf, Ta, and Nb. , Os, and the like and compounds containing the above elements. Further, in the present invention, the constituent member means a member that is sandwiched via a separator among members constituting the unit cell of the fuel cell. That is, when the unit cell according to the fuel cell of the present invention is provided with a diffusion layer, the electrolyte membrane, the anode electrode layer, the anode diffusion layer, the cathode electrode layer, and the cathode diffusion layer are constituent members. The term “between constituent members” means between the constituent members described above, between the anode diffusion layer and the separator, and between the cathode diffusion layer and the separator.

  The invention according to claim 2 is the fuel cell according to claim 1, wherein the weakly acidic group is a phosphonic acid group and / or a carboxylic acid group.

  The invention according to claim 3 is the fuel cell according to claim 2, wherein when the weakly acidic group is a carboxylic acid group, the carboxylic acid group has a chelating property.

  According to a fourth aspect of the present invention, in the fuel cell according to any one of the first to third aspects, the ion having hydrogen peroxide decomposition performance is a cerium ion.

  The invention according to claim 5 comprises an electrolyte membrane and an electrolyte / electrode structure comprising an electrode layer disposed on both sides of the electrolyte membrane, and the electrolyte membrane is more relative to the sulfonic acid group and the sulfonic acid group. The fuel cell system is characterized in that the above-mentioned problem is provided with a weakly acidic weakly acidic group and / or inorganic particles, and ions having hydrogen peroxide decomposition performance are supplied to the electrolyte / electrode structure. To solve.

  Here, in the present invention, the electrode layer, the electrolyte / electrode structure, and the ions having hydrogen peroxide decomposing performance have the same meaning as in the first aspect of the present invention. In the present invention, as long as ions having hydrogen peroxide decomposition performance are supplied to the electrolyte / electrode structure, the supply form is not particularly limited. Specific examples of the supply form include a form in which the ions are supplied to the electrolyte / electrode structure via a means for supplying ions, and a liquid fuel containing the ions is supplied to the electrolyte / electrode structure. And the like.

  According to the first aspect of the present invention, the electrolyte membrane is provided with weakly acidic groups and / or inorganic particles that are weaker acidic than the sulfonic acid groups. Therefore, a salt composed of an ion having hydrogen peroxide decomposing ability (hereinafter referred to as “decomposed ion”) and the weakly acidic group is formed, and / or the decomposed ion is immobilized by inorganic particles. It becomes possible to reduce the sulfonic acid groups that form salts with such decomposed ions. That is, with the above configuration, it is possible to suppress a decrease in proton conduction performance of the electrolyte membrane. On the other hand, according to the first aspect of the invention, since the decomposition ions are provided, the durability of the fuel cell can be improved. Therefore, according to the first aspect of the present invention, it is possible to provide a fuel cell capable of improving durability while suppressing a decrease in power generation performance.

  According to invention of Claim 2, the phosphonic acid group and / or the carboxylic acid group are provided as a weakly acidic group. These weakly acidic groups are easy to fix in the electrolyte membrane. Therefore, according to the second aspect of the present invention, it is possible to easily provide a fuel cell capable of improving durability while suppressing a decrease in power generation performance.

  According to the invention described in claim 3, the weakly acidic group is a carboxylic acid group having chelating properties. If the weakly acidic group of such a form is provided in the electrolyte membrane, it becomes possible to take in decomposition ions easily. Therefore, according to the third aspect of the present invention, it is easy to improve the durability.

  According to invention of Claim 4, the cerium ion which has hydrogen peroxide decomposition | disassembly performance is provided. Since cerium ions have good hydrogen peroxide decomposition performance, such a configuration makes it possible to provide a fuel cell that can effectively improve durability while suppressing a decrease in power generation performance. become.

  According to the fifth aspect of the present invention, when decomposed ions are supplied to the electrolyte / electrode structure, the decomposed ions hardly form sulfonic acid groups and salts, and form weakly acidic groups and / or inorganic substances. Since the particles are fixed in the electrolyte membrane, it is possible to suppress a decrease in proton conduction performance of the electrolyte membrane. Moreover, since the said decomposition | disassembly ion has hydrogen peroxide decomposition | disassembly performance, it becomes possible to improve the durability of a fuel cell system by setting it as this structure. Furthermore, the decomposition ions are fixed by weakly acidic groups and / or inorganic particles, and elution to the outside of the fuel cell is suppressed. Therefore, according to the fifth aspect of the present invention, it is possible to provide a fuel cell system capable of improving durability while suppressing a decrease in power generation performance.

It is known that hydrogen peroxide is generated in the electrode layer during power generation of the fuel cell, and an electrolyte component (for example, Nafion containing a sulfonic acid group or the like, such as Nafion containing sulfonic acid groups) by OH radicals resulting from the hydrogen peroxide. Is a registered trademark of DuPont, USA). So far, a technology related to a fuel cell having a structure containing a compound (for example, CeO ₂ , CePO _4, etc.) that elutes ions having hydrogen peroxide decomposition performance in the MEA has been disclosed. Applications often remain aimed at improving the reactivity at the cathode. On the other hand, if it is configured to include CeO ₂ , CePO _4, or the like, it is considered that deterioration due to hydrogen peroxide can be suppressed and the durability of the fuel cell can be improved. However, ions eluted from the CeO ₂ or CePO ₄ form a salt with the sulfonic acid group of the electrolyte component, so that there is a possibility that the proton conducting performance of the MEA may be lowered. For this reason, merely by using the CeO ₂ , CePO _4, or the like, the durability of the fuel cell can be improved, but the power generation performance may be reduced.

  The present invention has been made from such a viewpoint, and the gist thereof includes a sulfonic acid group, a weakly acidic group weaker acidic than the sulfonic acid group, and / or inorganic particles. It is in the configuration. By adopting such a configuration, it becomes possible to fix ions having hydrogen peroxide decomposition performance to the electrolyte membrane by the weakly acidic group and / or inorganic particles, and durability while suppressing a decrease in power generation performance. It is possible to provide a fuel cell and a fuel cell system that can improve the fuel efficiency.

  Hereinafter, the fuel cell and the fuel cell system of the present invention will be described more specifically with reference to the drawings.

First, in order to clarify the features of the present invention, an outline of an MEA provided in a conventional fuel cell will be outlined.
FIG. 7 is a schematic view showing a part of an MEA provided in a conventional fuel cell and a conventional fuel cell. 7A and 7B are cross-sectional views schematically showing an enlarged part of the MEA, and FIG. 7C is a cross-sectional view schematically showing a conventional fuel cell. 7A and 7B show the case where the cathode electrode layer is provided with cerium phosphate.

  As shown in FIG. 7A, the MEA 90 provided in the conventional fuel cell includes an electrolyte membrane 91 containing a fluorine-containing ion exchange resin (for example, Nafion) and anodes disposed on both sides of the electrolyte membrane 91. An electrode layer 92 and a cathode electrode layer 93 are provided. The anode diffusion layer 16a, the cathode diffusion layer 16b, and the separators 17 and 17 are further disposed on both sides of the MEA 90, thereby forming a fuel cell 900 (see FIG. 7C). The separators 17 and 17 of the fuel cell 900 have anode reaction gas channels 18a, 18a,... On the surface to be opposed to the anode diffusion layer 16a, and cathode reaction gas channels 18b, 18b on the surface to be opposed to the cathode diffusion layer 16b. Are formed, and further, coolant flow paths 19, 19,... Are formed.

While the cathode reaction gas (hereinafter referred to as “air”) supplied to the cathode electrode layer 93 is humidified, water (water vapor) is generated in the cathode electrode layer 93 by an electrochemical reaction (oxygen reduction reaction). Thus, water may be present in the cathode electrode layer 93. Therefore, cerium phosphate (hereinafter referred to as “CePO ₄ ”) present in the cathode electrode layer 93 can be dissociated into Ce ³⁺ and PO ₄ ³⁻ (see FIG. 7A). On the other hand, the electrolyte membrane 91 is water-containing in order to develop proton conduction performance. The electrolyte membrane 91 is provided with a sulfonic acid group —SO ₃ H, and the sulfonic acid group can be dissociated into H ⁺ and —SO ₃ ^{— in} the presence of water (see FIG. 7A). ). The Ce ³⁺ present in the cathode electrode layer 93 decomposes the hydrogen peroxide generated in the cathode electrode layer 93 and suppresses deterioration (oxidation deterioration) of the electrolyte component, while Ce ³⁺ is present in the presence of water. Since it can be easily moved, it moves to the electrolyte membrane 91. Similarly, the above H ⁺ also moves to the cathode electrode layer 93. Then, when Ce ³⁺ moves to the electrolyte membrane 91 and H ⁺ moves to the electrolyte membrane 91, —SO ₃ ⁻ and Ce ³⁺ contained in the electrolyte membrane 91 form a salt, while moving to the cathode electrode layer 93. The H ⁺ is combined with PO ₄ ³⁻ contained in the cathode electrode layer 93 to generate phosphoric acid (see FIG. 7B).

In this way, when a salt composed of —SO ₃ ^— and Ce ³⁺ is formed, the proton conducting performance of the electrolyte membrane 91 is lowered, and thus the power generation performance of the fuel cell 900 is lowered. That is, according to the conventional technology, there is a problem that the power generation performance of the fuel cell may be deteriorated when decomposition ions such as Ce ³⁺ are introduced in order to improve durability. Further, when phosphoric acid is generated in the cathode electrode layer 93, the phosphoric acid is liquid and thus is easily discharged out of the system. That is, in the conventional fuel cell, phosphoric acid which is an acidic liquid (hereinafter referred to as “acidic waste liquid”) is easily discharged, which is unfavorable for the environment.

  On the other hand, in order to improve such a problem, a weakly acidic group (for example, a phosphonic acid group) that is weaker than the sulfonic acid group is added to the anode electrode layer and / or the cathode electrode layer, and the weakly acidic group and decomposed ions are added. It is also conceivable to reduce decomposition ions capable of forming a salt with a sulfonic acid group by forming a salt consisting of However, simply adding a phosphonic acid group or the like causes the electrode to be poisoned by the phosphonic acid group. Therefore, it is difficult to improve durability while suppressing a decrease in power generation performance even by such means. Therefore, in the present invention, by fixing weakly acidic groups and / or inorganic particles that are weaker than sulfonic acid groups in the electrolyte membrane, it is possible to improve durability while suppressing a decrease in power generation performance. A fuel cell and a fuel cell system are provided.

1. Configuration of fuel cell 1.1. First Embodiment FIG. 1 is a schematic view showing a part of an MEA provided in a fuel cell of the present invention according to a first embodiment and the fuel cell of the present invention. FIG. 1A is a cross-sectional view schematically showing an enlarged part of the MEA, and FIG. 1B is a cross-sectional view schematically showing the fuel cell of the present invention. In the fuel cell according to the first embodiment of the present invention, members having the same configurations as those of the conventional fuel cell are denoted by the same reference numerals as those used in FIG. 7, and description thereof will be omitted as appropriate.

As shown in FIG. 1A, the MEA 10 according to the first embodiment includes an electrolyte membrane 11 including a sulfonic acid group —SO ₃ H and a phosphonic acid cerium group — (PO ₃ ) ₂ Ce, and the electrolyte membrane 11. An anode electrode layer 12 and a cathode electrode layer 13 are provided on both sides. The anode diffusion layer 16a, the cathode diffusion layer 16b, and the separators 17 and 17 are further disposed on both sides of the MEA 10, thereby constituting the fuel cell 100 of the present invention (see FIG. 1B). When the fuel cell 100 is in operation, the humidified reaction gas is supplied to the MEA 10 and water is generated by an electrochemical reaction that occurs in the MEA 10, so water is present in the MEA 10. In this embodiment, the cerium phosphonate group provided in the electrolyte membrane 11 is immobilized on the polymer provided in the electrolyte membrane 11.

Since water is present in the MEA 10 according to the present invention, the sulfonic acid group contained in the electrolyte membrane 11 can be dissociated into —SO ₃ ^— and H ^+, and the phosphonic acid cerium group is represented by — (PO ₃ ^{2 -} ) ^Can dissociate into ₂ and Ce ⁴⁺ . Here, such Ce ⁴⁺ has hydrogen peroxide decomposition performance. Therefore, Ce ⁴⁺ decomposes the hydrogen peroxide generated in the cathode catalyst layer 93 and the like, so that deterioration of the electrolyte component is suppressed, so that the durability of the fuel cell can be improved.

Ce ⁴⁺ provided in the electrolyte membrane 11 can exist in the form of a salt, while the electrolyte membrane 11 is provided with —SO ₃ ⁻ and — (PO ₃ ²⁻ ) _2, and thus Ce ⁴⁺ Can be combined. Here, although such a binding reaction is considered to be an equilibrium reaction, Ce ⁴⁺ selectively binds to — (PO ₃ ²⁻ ) ₂ generated by dissociation from a weakly acidic group. That is, with the above configuration, even when Ce ⁴⁺ is present in the electrolyte membrane 11, it is possible to suppress the formation of a salt by the Ce ⁴⁺ and —SO ₃ ^—. Therefore, it is possible to suppress a decrease in power generation performance due to a decrease in proton conductivity.

  In addition, according to the present invention, since the phosphonic acid groups are immobilized on the polymer or inorganic particles in the electrolyte membrane, it is possible to suppress the discharge of the phosphonic acid groups to the outside of the electrolyte membrane. Therefore, if it is set as this form, it will become possible to suppress generation | occurrence | production of acidic waste liquid, and it will become possible to prevent poisoning of an electrode.

  On the other hand, as described above, the electrolyte membrane 11 according to the present embodiment is provided with a cerium phosphonate group, and this phosphonate cerium group also has heat resistance improving performance. Therefore, by adopting such a configuration, it becomes possible to provide a fuel cell capable of improving heat resistance in addition to the above effects.

1.2. 2nd Embodiment FIG. 2: is schematic which shows a part of MEA with which the fuel cell of this invention concerning 2nd Embodiment is equipped, and the fuel cell of this invention. FIG. 2A is a cross-sectional view schematically showing an enlarged part of the MEA, and FIG. 2B is a cross-sectional view schematically showing the fuel cell of the present invention. In the fuel cell of the present invention according to the second embodiment, parts having the same configuration as the fuel cell according to the first embodiment are given the same reference numerals as those used in FIG. Are omitted as appropriate.

As shown in FIG. 2A, the MEA 20 according to the second embodiment includes an electrolyte membrane 21 having a sulfonic acid group —SO ₃ H and a phosphonic acid group —PO ₃ H ₂ , and both sides of the electrolyte membrane 21. An anode electrode layer 22 and a cathode electrode layer 23 are provided, and the cathode electrode layer 23 is previously provided with cerium phosphonate Ce (PO ₃ ) ₂ . Further, the anode diffusion layer 16a, the cathode diffusion layer 16b, and the separators 17 and 17 are further provided on both sides of the MEA 20 to constitute the fuel cell 200 of the present invention (see FIG. 2B). In the present embodiment, the phosphonic acid group provided in the electrolyte membrane 21 is immobilized on a polymer provided in the electrolyte membrane 21.

As in the case of the first embodiment, since water is present in the MEA 20 according to this embodiment, the sulfonic acid group contained in the electrolyte membrane 21 can be dissociated into —SO ₃ ^— and H ⁺ , The phosphonic acid group can dissociate into — (PO ₃ ²⁻ ) and H ⁺ . On the other hand, in the MEA 20 according to the second embodiment, the cathode electrode layer 23 is provided with cerium phosphonate, and this cerium phosphonate can be dissociated into Ce ⁴⁺ and PO ₃ ^{2− in} the presence of water. Ce ⁴⁺ is generated in the cathode electrode layer 23.

As described above, Ce ⁴⁺ generated in the cathode electrode layer 23 can move to the electrolyte membrane 21, and Ce ⁴⁺ that has moved to the electrolyte membrane 21 is selectively salted with ions − (PO ₃ ²⁻ ). forming a ion -SO ₃ ^- and does not form a little salt. That is, with this configuration, it is possible to maintain the proton conduction performance of the electrolyte membrane. Therefore, according to the second embodiment, it is possible to provide a fuel cell that can suppress a decrease in power generation performance while improving durability.

As mentioned above, in the description concerning 1st Embodiment and 2nd Embodiment, although the form provided with the weak acid group relatively weakly acidic rather than a sulfonic acid group was described for convenience, this invention is limited to the said form. It may be in a form in which inorganic particles are provided. If the inorganic particles are provided, the inorganic particles have weakly acidic groups, and thus, for example, the Ce ⁴⁺ can be immobilized by the inorganic particles. That is, the present invention may be in any form provided with the weakly acidic group, regardless of whether it is in the form of inorganic particles. Therefore, even in such a form, it is possible to provide a fuel cell that can suppress a decrease in power generation performance due to a decrease in proton conductivity.

2. Configuration of Fuel Cell System FIG. 3 is a schematic diagram showing a part of the MEA provided in the fuel cell system of the present invention and an example of the form of the fuel cell provided in the fuel cell system of the present invention. ) Is a cross-sectional view schematically showing an enlarged part of the MEA, and FIG. 3B is a cross-sectional view showing an example of a fuel cell provided in the fuel cell system of the present invention. On the other hand, FIG. 4 is a schematic view showing a part of the fuel cell stack provided in the fuel cell system of the present invention and an example of the form of the fuel cell system of the present invention, and FIG. FIG. 4B is a diagram schematically showing an example of a fuel cell system according to the present invention. 3 and 4, members having the same configuration as that of the fuel cell according to the second embodiment are denoted by the same reference numerals as those used in FIG. 2, and description thereof is omitted as appropriate. Hereinafter, the fuel cell system of the present invention will be described with reference to FIGS. 3 and 4.

As shown in FIG. 3A, the MEA 30 according to this embodiment is provided with an electrolyte membrane 21 having a sulfonic acid group —SO ₃ H and a phosphonic acid group —PO ₃ H ₂ , and both sides of the electrolyte membrane 21. The anode electrode layer 32 and the cathode electrode layer 33 are provided. The anode diffusion layer 16a, the cathode diffusion layer 16b, and the separators 17 and 17 are further disposed on both sides of the MEA 30 to configure the fuel cell 300 according to the present embodiment (see FIG. 3B). ).

On the other hand, as shown in FIG. 4A, the fuel cells 300, 300,... Included in the fuel cell system of the present invention constitute a fuel cell stack 350 by being stacked. As shown in FIG. 4B, the fuel cell system 1000 of the present invention includes a fuel cell stack 350 and a circulation system in which a hydrogen-containing substance (hereinafter referred to as “hydrogen”) is circulated and supplied. The anode line 510 includes a circulation system cathode line 520 to which an oxygen-containing substance (hereinafter referred to as “air”) is supplied, and the anode line 510 includes an ion addition means 590. The ion addition means 590 according to the present embodiment is a pipe constituting a part of the anode line 510 with Ce coating applied to the entire inner peripheral surface. The ion addition means 590 (hereinafter referred to as “pipe 590”). May constitute part of the upstream side of the anode line 510 of the circulation system. Ce coating of the pipe 590 is often applied to a portion located in the lower part of the gravity direction (for example, the lower half of the pipe 590 in the gravity direction), and the acid eluted from the electrolyte membrane in the FC stack during power generation of the fuel cell ( For example, when sulfuric acid or the like comes into contact with the Ce coat applied to the inner peripheral surface of the pipe 590, Ce ⁴⁺ having hydrogen peroxide decomposition performance is eluted. Then, Ce ⁴⁺ eluted from the inner peripheral surface of the pipe 590 is supplied to each MEA 30, 30,... Of the FC stack 350 through the circulation system anode line 510, so that the excess in the MEA 30, 30,. Hydrogen oxide is decomposed to suppress deterioration of the electrolyte membrane. In FIG. 4B, the arrows schematically show the traveling direction of the substances supplied to the MEAs 30, 30,... And the substances discharged from the MEAs 30, 30,.

In the fuel cell system 1000 of the present invention, Ce ⁴⁺ supplied to the MEAs 30, 30,... In the above form reaches the electrolyte membrane 21 having a sulfonic acid group —SO ₃ H and a phosphonic acid group —PO ₃ H _2. . Then, as in the case of the fuel cell according to the second embodiment, Ce ⁴⁺ selectively forms a salt ^with- (PO ₃ ²⁻ ), but hardly forms a salt with -SO ₃ ^−. It is possible to maintain the proton conduction performance of the electrolyte membranes 21, 21,... Provided in each fuel cell 300, 300,. Therefore, according to the present embodiment, it is possible to provide a fuel cell that can suppress a decrease in power generation performance while improving durability.

In the above description according to the third embodiment, a mode in which a weakly acidic group that is relatively weaker than a sulfonic acid group is described. However, the present invention is not limited to this mode, and inorganic particles are used. May be provided. If the inorganic particles are provided, the inorganic particles have weakly acidic groups, and thus, for example, the Ce ⁴⁺ can be immobilized by the inorganic particles. Therefore, even in such a form, it is possible to provide a fuel cell that can suppress a decrease in power generation performance due to a decrease in proton conductivity.

  For convenience, in the description of the fuel cell system of the present invention, the embodiment in which the circulation system anode line and the cathode line are provided has been described. However, the form that the fuel cell system of the present invention can take is not limited to the embodiment. Absent. Examples of other forms include a form in which only one of them is a circulation system, a form in which a non-circulation system anode line and cathode line are provided, and the like. In the above description, the mode in which the ion addition means is provided only on the upstream side of the anode line is described. However, when the ion addition means according to the present invention is provided in the circulation line, the arrangement is It may be on the downstream side of the line, and further, an ion adding means may be provided in the anode line and the cathode line. In addition, when an ion addition means is provided in a non-circulation system line, it is preferable to arrange | position to the upstream of the said line from a viewpoint of enabling supply of decomposition | disassembly ion to MEA effectively.

In addition, in the above description of the fuel cell system of the present invention, the mode in which the ion adding means is a pipe constituting a part of the anode line is described. However, in the present invention, the ion adding means for adding decomposition ions to the MEA Is not limited to this form. As a specific example of the other form, there can be mentioned a form that enables supply of the decomposed ions by injecting a liquid containing decomposed ions into the anode line and / or the cathode line. Further, the ion addition means according to the present invention is not limited to a mode in which the decomposition ions are supplied through the anode lines and / or the cathode lines connected to the fuel cells 300, 300,. Further, the surface of the separators 17 and 17 on the MEA 30 side is coated with Ce, and Ce ^{4+ that} is eluted by contact of the acidic liquid with the Ce coat is supplied to the MEAs 30, 30, etc. good. In the present invention, when cerium ions are supplied to the MEAs 30, 30,..., The valence of the cerium ions is not limited to 4, but Ce ³⁺ having a valence of ³ is supplied. May be.

3. Method for Producing Electrolyte Membrane The electrolyte membrane according to the present invention includes a sulfonic acid group, a weakly acidic group and / or inorganic particles that are weaker acid than the sulfonic acid group, and can further include decomposition ions. Such an electrolyte membrane can be manufactured as follows.

First, an organic solvent composed of a mixture of propanol and water or a polar organic solvent (dimethylacetamide, dimethylsulfoxide, etc.) and the like and an electrolyte component having a sulfonic acid group are mixed to prepare a molten electrolyte component. When the sulfonic acid group and the weakly acidic group are provided in the fuel cell according to the present invention, the molten electrolyte component includes, for example, cerium phosphonate powder and / or a polymer having a phosphonic acid group. It is possible to produce the electrolyte membrane according to the present invention by a method such as dispersion of the electrolyte.
On the other hand, when the sulfonic acid group and the inorganic particles are provided in the fuel cell according to the present invention, the present invention is applied by a method such as dispersing inorganic particles such as BPO _{4 in the} molten electrolyte component. An electrolyte membrane can be manufactured.

  In the above description, for convenience, a form in which a phosphonic acid group is provided as a weakly acidic group weaker than a sulfonic acid group has been described. However, the weakly acidic group according to the present invention is not limited to phosphonic acid, and sulfonic acid Other weakly acidic groups may be used as long as they are weakly acidic than the group and can be immobilized in the electrolyte membrane. Other specific examples of weakly acidic groups that can be provided in the electrolyte membrane according to the present invention include carboxylic acid groups and boronic acid groups. However, the electrolyte membrane according to the present invention has a form including a phosphonic acid group and / or a carboxylic acid group from the viewpoint of easy formation of a salt and easy immobilization in the electrolyte membrane. It is preferable.

  Here, when utilizing a carboxylic acid group as a weakly acidic group concerning this invention, it is preferable that it is a carboxylic acid group which has chelate property from a viewpoint of setting it as an electrolyte membrane which is easy to capture | disassemble a decomposition ion. If the carboxylic acid group has chelating properties, it becomes possible to trap the decomposed ions in a form that sandwiches or holds the decomposed ions, so that the decomposed ions can remain in the electrolyte membrane. The durability improving effect by the decomposed ions can be exhibited over a long period of time.

  In the above description of the fuel cell of the present invention, the form in which the decomposition ions are provided in the electrolyte membrane and the form in which the decomposition ions are provided in the cathode electrode layer are described. It is not limited to the said form, Other forms may be sufficient. Specific examples of the other forms include a form provided in the anode electrode layer, a form provided in the anode diffusion layer, a form provided in the cathode diffusion layer, a form provided between the electrolyte membrane and the anode electrode layer, and an electrolyte membrane. Provided between the cathode electrode layer and the anode diffusion layer, provided between the anode electrode layer and the anode diffusion layer, provided between the cathode electrode layer and the cathode diffusion layer, and between the anode diffusion layer and the separator. , A form provided between the cathode diffusion layer and the separator, a form provided in these two or more portions, and the like.

Furthermore, in the above description, the case where the decomposition ions are Ce ions (Ce ³⁺ , Ce ⁴⁺ ) has been described, but the ions capable of expressing the hydrogen peroxide decomposition performance in the present invention are not limited to these ions. Other ions may also be used. Specific examples of ions having the ability to decompose hydrogen peroxide include transition metal ions and rare earth metal ions, and examples of substances that can generate such ions include Sc, Mn, Fe, Pt, Pd, Ni, and Cr. , Cu, Ce, Rb, Co, Ir, Ag, Au, Rh, Ti, Zr, Al, Hf, Ta, Nb, Os and the like and compounds containing these elements. However, from the viewpoint of effectively expressing the hydrogen peroxide decomposition performance, it is preferable that the fuel cell and the fuel cell system according to the present invention include Ce simple substance, Ce compound, and / or Ce ions.

  In addition, in the above description, a fuel cell in which an electrolyte membrane containing a fluorine-containing ion exchange resin is provided has been described, but the electrolyte membrane provided in the fuel cell according to the present invention is not limited to this, and HC Even a film can be suitably used. According to the present invention, it becomes possible to fix the decomposed ions in the HC film, so that even the fuel cell including the HC film can effectively improve the durability.

  For the sake of convenience, in the above description, the fuel cell including the separator in the form in which the reaction gas supply path is formed on the MEA side is described. However, the separator that can be included in the fuel cell according to the present invention is limited to the form. Instead, for example, a flat separator in which no reaction gas supply path is formed on the MEA side may be used. In the case of such a fuel cell, the layers to be brought into contact with the separator (the anode diffusion layer and the cathode diffusion layer in the fuel cells according to the first and second embodiments) are manufactured by a plating method, a foaming method, or the like. The fuel cell may be formed of a porous material such as a stainless steel, a foam metal such as titanium or nickel, or a sintered metal, and a reaction gas is supplied to the layer.

  Furthermore, in the above description, a fuel cell having an anode diffusion layer and a cathode diffusion layer has been described. However, even when an anode diffusion layer and / or a cathode diffusion layer are not provided, good power generation performance can be obtained. Alternatively, the fuel cell according to the present invention may have a form in which the anode diffusion layer and / or the cathode diffusion layer is not provided.

1. Preparation of test MEA 1.1. Preparation of electrode layer 2.0 g of platinum-supporting carbon having a platinum content of 45% by mass, 0.1 g of cerium oxide (cerium-zirconium composite oxide), 3 g of water, and Nafion containing 10% by mass of a fluorine-containing ion exchange resin The catalyst ink A was prepared by mixing 9 g of the solution and 9 g of ethanol and dispersing with an ultrasonic homogenizer. On the other hand, catalyst ink B not containing cerium oxide (cerium-zirconium composite oxide) was also produced by the same method as described above.

1.2. Preparation of Electrolyte Membrane 10 g of sulfonated polyethersulfone obtained by 50% sulfonation of Udel polyethersulfone was dissolved in 90 g of N-methyl-2-pyrrolidone, and the solution was allowed to stand at 50 ° C. and atmospheric pressure for 3 days. After that, an electrolyte membrane X containing no antioxidant was produced by further vacuum drying for 24 hours.
On the other hand, 10 g of sulfonated polyethersulfone obtained by 50% sulfonation of polyethersulfone manufactured by Udel Co., Ltd. and 90 g of N-methyl-2-pyrrolidone in an amount such that the ratio to the total mass is 10% by mass. After dissolution, the solution was allowed to stand at 50 ° C. and atmospheric pressure for 3 days, and further subjected to vacuum drying for 24 hours to produce an electrolyte membrane Y containing an antioxidant. Note that the phosphorous antioxidant provided in the electrolyte membrane Y contained a phosphonic acid group that was relatively weaker than the sulfonic acid group.

1.3. Preparation of MEA The MEA according to Comparative Example 1 was applied by spraying the catalyst ink B on both surfaces of the electrolyte membrane X, and the MEA according to Comparative Example 2 was applied by spraying the catalyst ink A on both surfaces of the electrolyte membrane X. The MEA according to Comparative Example 3 was produced by spray-coating the catalyst ink B on both surfaces of the electrolyte membrane Y, while the catalyst ink A was spray-coated on both surfaces of the electrolyte membrane Y. An MEA was produced. In each MEA according to the example, comparative example 1, comparative example 2, and comparative example 3, the anode platinum support ratio was 0.2 mg / cm ² and the cathode platinum support ratio was 0.5 mg / cm ^2. It was.

2. Power Generation Performance Evaluation Test Using the MEA according to the above example and the MEA according to Comparative Example 1, a power generation performance evaluation test was performed. The results are shown in FIG. In FIG. 5, the vertical axis represents voltage E (V) and the horizontal axis represents current density I (A / cm ² ).

  From FIG. 5, the power generation performance deterioration mode of the MEA according to Comparative Example 1 (hereinafter described as “Comparative Example 1”) and the MEA according to the example (hereinafter described as “Example”). There was no big difference with the power generation performance degradation form. That is, it was confirmed that if the configuration of the present invention including cerium oxide and an antioxidant is used, it is possible to suppress a decrease in power generation performance due to the addition of these.

3. Leak amount measurement test Prepared by disposing a diffusion layer made of carbon cloth on both sides of each MEA manufactured under the above conditions, and further disposing a calcined carbon separator in a form that sandwiches the diffusion layer. A leak amount measurement test was performed using a single cell. The test conditions are shown in Table 1.

ここで、測定１は拡散によるリーク量の測定を目的とする一方、測定２は拡散と漏れによるリーク量の測定を目的としている。そして、測定１及び測定２のそれぞれの条件下で、０．３Ｖ、０．５Ｖ、０．７Ｖの電圧を単セルに印加した。

Here, measurement 1 aims at measuring the amount of leakage due to diffusion, while measurement 2 aims at measuring the amount of leakage due to diffusion and leakage. And the voltage of 0.3V, 0.5V, and 0.7V was applied to the single cell under each condition of the measurement 1 and the measurement 2.

The process of deriving the leak amount due to leakage from measurement 1 and measurement 2 will be described below.
B is derived in the following relational expression 1 by measuring the current value for each voltage in measurement 1 and measurement 2 and plotting the relationship between the voltage and the current value.
I = aE + b (Formula 1)
Here, it is assumed that I is a current (A), E is a voltage (V), a is a coefficient representing a slope of a straight line, and b is a value (A) generated by a leaked gas.
In this way, b obtained by the measurement 1 and the measurement 2 is derived, and when these are substituted into b in the following equation 2, the leak amount m1 (mol) in the measurement 1 and the leak amount m2 (mol) in the measurement 2 are calculated. Is done.
b * s = m * F * z (Formula 2)
Here, s is time (sec), m is the number of moles of the leaked gas (mol), F is a Faraday constant, z is a valence (z = 2 from H ₂ → 2H ⁺ + 2e ⁻ ), and s = 60 It was.
Then, by substituting m1 and m2 calculated from the above formula 2 into the following formula 3, the leak amount M (mol) is calculated.
M = m2-m1 (Formula 3)

The leak measurement result in the leak amount measurement test using the single cell provided with each MEA is shown in FIG. In FIG. 6, the vertical axis represents the amount of hydrogen leak (nmol / sec / cm ² ), and the horizontal axis represents time (h). The amount of hydrogen leak was calculated by dividing M calculated by the above equation 3 by time (sec) and the area of the electrolyte membrane (cm ² ).

From FIG. 6, since the single cell provided with MEA according to Comparative Example 1 did not contain cerium oxide and phosphonic acid groups, the electrolyte membrane was damaged (oxidized and deteriorated) by hydrogen peroxide generated during the test. The amount of hydrogen leak after 100 hours was 16.8 nmol / sec / cm ² . On the other hand, the unit cell including the MEA according to Comparative Example 2 does not contain a phosphonic acid group, but contains cerium oxide, so that damage to the electrolyte membrane is suppressed. The amount was reduced to 8.9 nmol / sec / cm ² . However, since the single cell including the MEA according to Comparative Example 2 does not include a substance capable of immobilizing cerium oxide, the chemical stability is reduced with consumption of cerium oxide, and the effect of suppressing oxidative degradation is insufficient. there were. On the other hand, the unit cell provided with the MEA according to Comparative Example 3 does not contain cerium oxide, but contains a phosphonic acid group. As a result, the effect of suppressing oxidative degradation of the phosphonic acid group was expressed. The amount of hydrogen leak at the time decreased to 0.18 nmol / sec / cm ² .

On the other hand, since the single cell including the MEA according to the example contained cerium oxide and phosphonic acid groups, the hydrogen leak amount after 330 hours was 0.0011 nmol / sec / cm ² , and 330 hours had elapsed. There was no change compared to the initial leak amount. This is because the cerium oxide added to the electrode layer decomposes hydrogen peroxide produced at the cathode to suppress the production of OH radicals, and the phosphonic acid group was contained in the electrolyte membrane. This is considered to be because elution into the water was suppressed and the hydrogen peroxide decomposition performance was maintained over a long period of time. Here, as described above, the phosphonic acid group contained in the electrolyte membrane of the single cell according to the example has an effect of suppressing oxidative degradation. That is, in the single cell provided with the MEA according to the example, the oxidative deterioration suppressing effect by cerium oxide and the oxidative deterioration suppressing effect of the phosphonic acid group act in a superimposed manner, thereby effectively preventing damage to the electrolyte membrane. It is considered that hydrogen leakage can be reduced.

  Therefore, from the above leak amount measurement test, it was confirmed that according to the present invention, it is possible to provide a fuel cell capable of improving durability over a long period of time by preventing damage to the electrolyte membrane.

  From the power generation performance evaluation test and the leak amount measurement test, according to the present invention, it is possible to provide a fuel cell capable of improving durability while suppressing a decrease in power generation performance. And by setting it as the structure provided with this fuel cell, it becomes possible to provide the fuel cell system which can improve durability, suppressing the fall of electric power generation performance.

It is the schematic which shows a part of MEA with which the fuel cell of this invention concerning 1st Embodiment is equipped, and the fuel cell of this invention. It is the schematic which shows a part of MEA with which the fuel cell of this invention concerning 2nd Embodiment is equipped, and the fuel cell of this invention. It is the schematic which shows a part of MEA with which the fuel cell system of this invention is equipped, and the form example of the fuel cell with which the fuel cell system of this invention is equipped. It is the schematic which shows a part of fuel cell stack with which the fuel cell system of this invention is equipped, and the form example of the fuel cell system of this invention. It is a figure which shows a power generation performance evaluation test result. It is a figure which shows a leak amount measurement test result. It is the schematic which shows a part of MEA with which the conventional fuel cell is equipped, and the conventional fuel cell.

Explanation of symbols

10, 20, 30 Electrolyte / electrode structure (MEA)
11, 21 Electrolyte membrane 12, 22, 32 Electrode layer (anode electrode layer)
13, 23, 33 Electrode layer (cathode electrode layer)
16a Anode diffusion layer 16b Cathode diffusion layer 17 Separator 100, 200, 300 Fuel cell 350 Fuel cell stack 1000 Fuel cell system

Claims (5)

An electrolyte / electrode structure including an electrolyte membrane and electrode layers disposed on both sides of the electrolyte membrane;
The electrolyte membrane includes a sulfonic acid group,
Ions having hydrogen peroxide decomposing performance, and weakly acidic groups and / or inorganic particles that are relatively weaker than the sulfonic acid groups are provided between any of the constituent members and / or the constituent members. A fuel cell is characterized. The fuel cell according to claim 1, wherein the weakly acidic group is a phosphonic acid group and / or a carboxylic acid group. The fuel cell according to claim 2, wherein when the weakly acidic group is a carboxylic acid group, the carboxylic acid group has chelating properties. The fuel cell according to any one of claims 1 to 3, wherein the ion having hydrogen peroxide decomposition performance is cerium ion. An electrolyte / electrode structure including an electrolyte membrane and electrode layers disposed on both sides of the electrolyte membrane;
The electrolyte membrane includes a sulfonic acid group and a weakly acidic group and / or inorganic particles relatively weakly acidic than the sulfonic acid group,
Ions having hydrogen peroxide decomposition performance are supplied to the electrolyte / electrode structure.

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