JP2006100251A - Solid polymer fuel cell system and fuel cell vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell system which certainly inactivates the active oxygen and is superior in durability. <P>SOLUTION: The solid fuel cell system comprises a solid polyelectrolyte fuel cell 1 in which a plurality of unit cells 2 are laminated that have a membrane electrode assembly 3 having an air pole 5 on one side of the solid polyelectrolyte membrane 4 and a fuel pole 6 on the other side, an air pole side separator 7 which is arranged on the air pole 5 side of this membrane electrode assembly 3 and forms an air passage 8 between the membrane electrode assembly 3, and a fuel pole side separator 9 which is arranged on the fuel pole 6 side of the membrane electrode assembly 3 and forms a fuel gas passage 10 between the membrane electrode assembly 3, and an anti-oxidant supply means 11 which supplies an anti-oxidant for inactivating the active oxygen from the air pole 5 side or fuel pole 6 side of the solid polyelectrolyte fuel cell 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polymer electrolyte fuel cell system and a fuel cell vehicle.

Fuel cell technology is attracting attention as a means of solving the recent energy resource problems and global warming problems associated with CO ₂ emissions. In a fuel cell, fuel such as hydrogen, methanol, or other hydrocarbons is electrochemically oxidized in the cell, thereby converting the chemical energy of the fuel directly into electrical energy and taking it out. For this reason, the fuel cell has been attracting attention as a clean electric energy source without generating NO _X or SO _X due to fuel combustion in an internal combustion engine such as thermal power generation or automobile.

  There are several types of fuel cells. Among them, the polymer electrolyte fuel cell (hereinafter referred to as PEFC) has attracted the most attention and is being developed. PEFC is (1) easy to start and stop due to low temperature operation, (2) high theoretical voltage and high conversion efficiency, and (3) flexible cell structure such as vertical because there is no liquid phase in the electrolyte. (4) At the ion exchange membrane / electrode interface, there are various advantages such as that a large current can be taken out by securing a three-phase interface as a reaction field and a high output density can be obtained. .

  However, even though PEFC has received the most attention, there are still many problems. Among them, polymer electrolyte membrane technology is one of the most important issues. At present, perfluorosulfonic acid polymers represented by Nafion (registered trademark) membranes, which are the most widely used electrolyte membranes and are commercially available from DuPont, USA, are generated at the air electrode (positive electrode) of fuel cells. It has been developed as a membrane resistant to active oxygen. However, according to the results of a long-term durability test, it cannot be said that there is sufficient resistance yet.

The operating principle of the fuel cell is that there are _two electrochemical processes: H ₂ oxidation at the fuel electrode (negative electrode) and water generation by 4-electron reduction of molecular oxygen (O ₂ ) at the air electrode shown in the following formula (1). It consists of a process.

O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (1)
In practice, however, side reactions occur simultaneously. A typical example is the production of hydrogen peroxide (H ₂ O ₂ ) by two-electron reduction of O _{2 at} the air electrode shown in the following formula (2).

O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O ₂ Formula (2)
Hydrogen peroxide has a weak oxidizing power but is stable and has a long life. Hydrogen peroxide is decomposed according to the following reaction formulas (3) and (4), and radicals such as hydroxy radicals (.OH) and hydroperoxy radicals (.OOH) are generated upon decomposition. These radicals, especially hydroxy radicals, have a strong oxidizing power, and even perfluorosulfonated polymers used as electrolyte membranes can be decomposed by long-term use.

H ₂ O ₂ → 2.OH Formula (3)
H ₂ O ₂ → · H + · OOH (4)
In addition, when low-valence ions of transition metals such as Fe ²⁺ , Ti ³⁺ , and Cu ⁺ exist, Harbor Weiss (Haber −) in which hydrogen peroxide is reduced one electron by these metal ions to generate a hydroxy radical. Weiss) reaction occurs. Hydroxyl radicals are known to be most reactive among active oxygens and have very strong oxidizing power. When the metal ion is an iron ion, the Harbor Weiss reaction is known as a Fenton reaction represented by the following formula (5).

Fe ²⁺ + H ₂ O ₂ → Fe ³⁺ + OH ⁻ + · OH Formula (5)
As described above, when metal ions are mixed in the electrolyte membrane, hydrogen peroxide is changed into hydroxy radicals in the electrolyte membrane by the Harbor Weiss reaction, and the electrolyte membrane may be deteriorated by the hydroxy radicals (Non-Patent Document). 1).

Thus, as a method for preventing oxidation of the electrolyte membrane by hydroxy radicals, for example, a method has been proposed in which a compound having a phenolic hydroxyl group is blended in the electrolyte membrane, and peroxide radicals are trapped and inactivated (patent) Reference 1). In addition, a method of eliminating generated radicals by blending an electrolyte membrane with a phenol compound, an amine compound, a sulfur compound, a phosphorus compound or the like as an antioxidant has been proposed (see Patent Document 2). Furthermore, a molecule having a binding energy smaller than that of the carbon-fluorine bond is contained in a catalyst layer disposed adjacent to the electrolyte membrane, and this molecule preferentially reacts with a hydroxyl radical to protect the electrolyte membrane. A method has been proposed (see Patent Document 3).
JP 2000-223135 A JP 2004-134269 A JP 2003-109623 A New Energy and Industrial Technology Development Organization Subcontractor, Graduate School of Engineering, Kyoto University, “2001 Results Report, Research and Development of Solid Polymer Fuel Cells, Research on Degradation Factors of Polymer Electrolyte Fuel Cells, Basics on Degradation Factors Study (1) Electrode catalyst / electrolyte interface degradation factors ", March 2002, p.13, 24, 27

  However, since oxygen and platinum as the electrocatalyst exist in the vicinity of the three-phase interface of the air electrode where there is a high possibility of generating hydroxy radicals, the environment in which the compound is likely to be oxidized oxidizes the electrolyte membrane as described above. In the method in which only the compound to be prevented is contained, the compound may be oxidized and lost regardless of the presence or absence of the hydroxy radical, and the efficiency is poor. In addition, the compound may become unstable radicals or peroxides by reaction with hydroxy radicals and become a new oxidation initiator, which may cause electrolyte membrane deterioration.

  The present invention has been made to solve the above-mentioned problems. The solid polymer fuel cell system according to the first aspect of the present invention includes an air electrode on one surface of a solid polymer electrolyte membrane and a fuel on the other surface. A membrane electrode assembly having an electrode, an air electrode side separator disposed on the air electrode side of the membrane electrode assembly and forming an air flow path between the membrane electrode assembly, and a fuel electrode side of the membrane electrode assembly A solid polymer electrolyte fuel cell in which a plurality of single cells having a fuel electrode side separator disposed on the surface and forming a fuel gas flow path between the membrane electrode assembly and the active oxygen are inactivated And an antioxidant supply means for supplying the antioxidant from the air electrode side or the fuel electrode side of the solid polymer electrolyte fuel cell.

  The gist of the fuel cell vehicle according to the second invention is that the solid polymer fuel cell system according to the first invention is mounted.

  According to the first invention, hydrogen acting as a fuel from the outside of the fuel cell, or an antioxidant that does not participate in the fuel cell reaction is supplied separately from the hydrogen ions, so that the active oxygen is reliably converted into inert water or oxygen. It is possible to realize a polymer electrolyte fuel cell system that is decomposed into two and has excellent durability.

  According to the second aspect of the invention, a fuel cell vehicle that can withstand continuous operation for a long time can be realized.

  Hereinafter, the details of a polymer electrolyte fuel cell system and a fuel cell vehicle according to the present invention will be described based on embodiments.

  FIG. 1 is a schematic explanatory view illustrating an embodiment of a polymer electrolyte fuel cell system according to the present invention. As shown in FIG. 1, the polymer electrolyte fuel cell system according to the present embodiment is disposed outside the polymer electrolyte fuel cell 1 and the polymer electrolyte fuel cell 1, and this solid It is generally composed of an antioxidant supply means 11 for supplying an antioxidant that inactivates active oxygen to the polymer electrolyte fuel cell 1.

  As shown in FIG. 1, a solid polymer electrolyte fuel cell 1 constituting the solid polymer fuel cell system according to the present embodiment includes a plurality of single cells 2 that are basic units for generating power by an electrochemical reaction. It includes a fuel cell stack (not shown) configured by disposing end flanges (not shown) at both ends after stacking and fastening the outer periphery with fastening bolts (not shown). The single cell 2 is disposed on the air electrode 5 side of the membrane electrode assembly 3 having the air electrode 5 on one surface of the solid polymer electrolyte membrane 4 and the fuel electrode 6 on the other surface. A fuel gas is disposed between the air electrode side separator 7 that forms the air flow path 8 between the membrane electrode assembly 3 and the fuel electrode 6 side surface of the membrane electrode assembly 3, and between the membrane electrode assembly 3. And a fuel electrode side separator 9 that forms a flow path 10.

  As the solid polymer electrolyte membrane 4 used for the unit cell 2, a perfluorocarbon polymer membrane having a sulfonic acid group (trade name; Nafion (registered trademark) 112, DuPont, USA) and the like can be used. The membrane electrode assembly 3 is formed by joining a platinum catalyst-supporting carbon catalyst layer as an air electrode 5 on one surface of the solid polymer electrolyte membrane 4 and a fuel electrode 6 on the other surface.

  The air electrode side separator 7 and the fuel electrode side separator 9 are formed by forming carbon or metal into a plate shape and forming a gas channel and a cooling water channel on the surface thereof. The air flow path 8 is formed between the air electrode 5 and the air electrode side separator 7, and supplies air as a reaction gas to the air electrode 5. The fuel gas channel 10 is formed between the fuel electrode 6 and the fuel electrode side separator 9, and supplies hydrogen as a reaction gas to the fuel electrode 6. The fuel gas channel 10 functions as a moisture replenishment passage by humidifying the fuel gas, and the air channel 8 also functions as a generated water removal passage. A gas diffusion layer formed of carbon paper or carbon nonwoven fabric is appropriately disposed between the separators 7 and 9 and the electrodes 5 and 6.

  In each single cell 2 of the solid polymer electrolyte fuel cell 1 having the above-described configuration, when air and hydrogen gas are respectively supplied to the air flow path 8 and the fuel gas flow path 10, the air and hydrogen gas are respectively supplied to the air electrode 5 and the air electrode 5. Supplied to the fuel electrode 6 side, the following reactions (6) and (7) occur.

Fuel electrode side: H ₂ → 2H ⁺ + 2e ⁻ Expression (6)
Air electrode side: (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (7)
As shown in FIG. 3, when hydrogen gas is supplied to the fuel electrode 6 side, the reaction of the formula (6) proceeds and H ⁺ (proton) And e ⁻ (electrons) are generated. H ⁺ moves in the solid polymer electrolyte membrane 4 in a hydrated state and flows to the air electrode 5 side. On the air electrode 5 side, H ⁺ , e ⁻ and oxygen gas in the supplied air represent the formula ( The reaction of 7) proceeds to produce water. At this time, an electromotive force is obtained by electrons generated at the fuel electrode 6 moving to the air electrode 5 via the external circuit 17 shown in FIG.

Thus, the reaction at the air electrode 5 is generation of water by four-electron reduction of molecular oxygen (O ₂ ). In addition to this 4-electron reduction of oxygen, side reactions occur simultaneously, superoxide (O ₂ ⁻ ), which is a one-electron reductant of oxygen, hydroperoxy radical (· OOH), a conjugate acid of superoxide, and a two-electron reductant. Active oxygen such as hydrogen peroxide (H ₂ O ₂ ), a three-electron reduced form, or a hydroxy radical (.OH) is generated. The generation mechanism of each active oxygen is presumed to be a complex reaction through a plurality of elementary reaction processes represented by the following formulas (8) to (12).

O ₂ + e ⁻ → O ₂ ⁻ (8)
O ₂ ⁻ + H ⁺ → · OOH Formula (9)
O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O ₂ Formula (10)
H ₂ O ₂ + H ⁺ + e ⁻ → H ₂ O + · OH Formula (11)
H ₂ O ₂ → 2.OH Formula (12)
The generated active oxygen is presumed to be finally reduced to water through the elementary reaction processes of the following formulas (13) to (15). Note that E ₀ is represented by a normal oxidation-reduction potential (Normal Hydrogen Electrode; NHE).

OOH + H ⁺ + e ⁻ → H ₂ O ₂ E ₀ = 1.50 [V] (13)
H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O E ₀ = 1.77 [V] (14)
OH + H ⁺ + e ⁻ → H ₂ O E ₀ = 2.85 [V] (15)
The problem here is a hydroxy radical having a high oxidation-reduction potential of 2.85 [V] and a strong oxidizing power. Hydroxyl radicals are the most reactive of active oxygen and have a very short lifetime of one millionth of a second. It also has strong oxidizing power. For this reason, hydroxyl radicals react with other molecules unless they are reduced quickly. It is speculated that most of the oxidative degradation that is a problem in fuel cells is caused by this hydroxy radical. This hydroxy radical continues to be generated via the above formulas (8) to (12) while the fuel cell is generating power. On the other hand, hydroperoxy radicals and hydrogen peroxide are less oxidative than hydroxy radicals, but may pass through hydroxyl radicals in the process of being reduced to water. Thus, the generation of hydroxy radicals continues semipermanently as long as power is generated by the solid polymer electrolyte fuel cell. For this reason, unless the compound that inactivates the hydroxy radical is continuously supplied to the solid polymer electrolyte fuel cell, the solid polymer electrolyte membrane may be deteriorated by the hydroxy radical that continues to be generated. In the polymer electrolyte fuel cell system according to the present embodiment, the antioxidant is supplied to the polymer electrolyte fuel cell 1 by the antioxidant supply means 11 provided outside the polymer electrolyte fuel cell 1. Even when the solid polymer fuel cell 1 continues to generate power and active oxygen continues to be generated, it does not participate in the fuel cell reaction separately from hydrogen or hydrogen ions acting as fuel from the outside of the fuel cell. Since the active oxygen can be reliably inactivated and erased by the oxidant, the solid polymer electrolyte membrane can be prevented from being deteriorated. Further, even in an environment where the antioxidant is easily oxidized, the efficiency of inactivating active oxygen is not lowered because the antioxidant is supplied from the outside.

  Since the generation of active oxygen continues semipermanently as long as power is generated by the solid polymer electrolyte fuel cell, it is more effective to continuously supply the antioxidant as an antioxidant solution from the air electrode or the fuel electrode. Is. Desirably, the polymer electrolyte fuel cell 1 is preferably supplied from the fuel electrode 9 side. When the antioxidant is supplied from the fuel electrode 9 side, for example, as shown in FIG. 1, an antioxidant supply means 11 is connected to an antioxidant solution tank 12 in which an antioxidant solution is sealed, and an anti-oxidant solution. A liquid feed pump 13 for supplying an oxidant solution to the fuel electrode 6 side of the solid polymer electrolyte fuel cell 1, an antioxidant solution line 14 connecting the antioxidant solution tank 12 and the liquid feed pump 13, The liquid supply pump 13 and the fuel gas flow path 10 are connected to each other, and the antioxidant supply pipe 15 is connected. As described above, on the surfaces of the air electrode side separator 7 and the fuel electrode side separator 9 of the polymer electrolyte fuel cell 1, the air flow path 8 and the fuel gas flow for supplying air or hydrogen as the reaction gas are provided. Each path 10 is formed. Each reaction gas is air-flowed in a state of being humidified by a bubbler (not shown) as shown in an exploded perspective view of a single cell of the solid polymer electrolyte fuel cell constituting the solid polymer fuel cell system shown in FIG. 8 and the fuel gas flow path 10. At this time, the antioxidant solution is supplied from the antioxidant solution tank 12 to the fuel gas passage 10 through the antioxidant solution pipe 14 and the solution supply pipe 15 by the driving force of the liquid feed pump 13. The antioxidant solution supplied to the fuel gas channel 10 is a solid polymer electrolyte from the fuel electrode 6 side as shown in the explanatory view for explaining the movement of substances in the membrane electrode assembly constituting the single cell shown in FIG. It diffuses in the membrane 4 and moves to the air electrode 5 side. The antioxidant is uniformly dispersed in the air electrode 5 according to the concentration gradient.

  As described above, the reason why it is preferable to supply the antioxidant from the fuel electrode 6 side as an antioxidant solution is that active oxygen such as hydroxy radicals is likely to be generated near the three-phase interface of the air electrode. There is something. As shown in the schematic diagram showing the three-phase interface in the air electrode shown in FIG. 4, the vicinity of the three-phase interface of the air electrode is an environment where oxygen in the air and platinum as an electrode catalyst are present and are easily oxidized. For this reason, when an antioxidant is introduced from the air electrode, the antioxidant itself may be oxidized and disappeared at the three-phase interface of the air electrode regardless of the presence or absence of hydroxy radicals. Efficiency may be reduced.

Further, as described above, the air flow path 8 of the air electrode side separator 7 also functions as a generated water removal passage. For this reason, an antioxidant that is supplied excessively and becomes unnecessary, or an antioxidant that has become an oxidant by inactivating active oxygen is oxidized by a catalyst on the three-phase interface to produce CO ₂ , H ₂ O or N after _two such, generated water and can be discharged from the discharge pipe 16 shown in FIG. 1 at the same time. For this reason, it can be prevented that the antioxidant becomes an oxidant, unstable radical or peroxide due to the reaction with active oxygen, and becomes a new oxidation reaction initiator to cause deterioration of the electrolyte membrane.

  When preparing the antioxidant solution, it may be difficult to dissolve in the air electrode, but it is important to dissolve in the solvent. If insoluble, hydrogen radicals cannot enter and exit, and the effect of inactivating active oxygen is not sufficiently exhibited. For this reason, it is necessary to select a solvent in which the antioxidant is dissolved, and an organic solvent alone or a mixed solvent of an organic solvent and water is used as necessary. And when using an organic solvent, it is necessary to confirm beforehand that it does not affect a power generation performance. For this reason, it is preferable from the point of power generation performance to use aqueous solution if the antioxidant can be dissolved.

The antioxidant is preferably a hydrocarbon compound composed of four atoms of carbon, oxygen, nitrogen and hydrogen. Atoms other than carbon, oxygen, nitrogen, and hydrogen can poison the platinum in the electrode and hinder the power generation performance of the fuel cell. Further, in the case of a base metal atom, there is a possibility of promoting the generation of hydroxy radicals. Furthermore, in consideration of the case where the antioxidant is oxidized and discharged at the air electrode, it is composed of only four atoms of carbon, oxygen, nitrogen and hydrogen, and is a hydrocarbon system that is decomposed into CO ₂ , H ₂ O and N ₂ A compound is preferred. Since the oxidation-reduction potential of the hydroxy radical is very high, most of the hydrocarbon compounds composed of the four atoms are considered to act thermodynamically as a reducing agent for the hydroxy radical. Each compound is considered to have a difference in reducing ability in terms of kinetics. And considering the high reactivity of the hydroxy radical, the inactivation reaction of the antioxidant is preferably kinetically fast. In addition, the stability of an oxidant obtained by oxidizing an antioxidant, that is, a compound obtained by oxidation with active oxygen is also important. This is because if the oxidant of the antioxidant is unstable, the oxidized substance becomes an initiator of a new side reaction and may promote deterioration of the electrolyte membrane. Therefore, secondary alcohol compounds having a hydroxyl group such as isopropanol, 2-butanol, cyclohexanol, phenols, phenol, cresol, picrine, etc., which are relatively kinetically fast and chemically stable in oxidant. Aromatic compounds having hydroxyl groups such as acid, naphthol and hydroquinone, ether compounds such as dioxane, tetrahydrofuran and benzylmethyl ether, nitrogen-containing compounds such as propylamine, diethylamine, acetamide, aniline and N-hydroxy compounds, and the above Examples thereof include compounds having a plurality of the substituents shown.

  What is important in selecting such a compound is the stability, durability and heat resistance of the compound. In particular, the stability and durability of the compound is of utmost importance in the sense that the active oxygen will continue to be inactivated and the fuel cell will be used for a long time. Moreover, it is more preferable that the hydrolyzate obtained by hydrolyzing the oxidized oxidant of the antioxidant is also chemically stable. As for the stability of the antioxidant, it is possible to obtain an effect of inactivating active oxygen if it is stable while the antioxidant is supplied to the fuel electrode and discharged from the air electrode. On the other hand, considering that the active oxygen is deactivated as described above and is discharged at the same time as the generated water, the antioxidant hydrolyzate is stable without generating radicals. Is preferable for operating the system for a long period of time. Considering that the steady-state operating temperature of the fuel cell is 80 to 90 [° C.] and that the heat resistance of the electrolyte membrane will be improved in the future, the antioxidant has a heat resistance that is stable up to a temperature of about 120 [° C.]. It is necessary to have.

  The compound that inactivates active oxygen is preferably a compound having an oxidation potential of 2.85 [V] or less that is oxidized at least promptly by a hydroxyl radical, but more preferably it is not only oxidized but also oxidized. Those exhibiting redox reversibility having a redox cycle that returns to its original form when the oxidized form is reduced are preferred. The oxidation-reduction potential is preferably larger than 0.68 [V] (NHE) and smaller than 1.00 [V] (NHE). 0.68 [V] (NHE) is a potential at which hydrogen peroxide acts as a reducing agent, and when this potential is exceeded, the oxidant of the compound oxidizes hydrogen peroxide and the compound returns to its original form. On the other hand, 1.77 [V] (NHE) is a potential at which hydrogen peroxide acts as an oxidant. When the oxidation potential is higher than this, an oxidant of the compound acts as a new oxidant, and the electrolyte membrane Etc. may be oxidized.

  In some cases, the redox potential is more preferably 1.00 [V] or less in order to reduce the oxidizing power of the compound. When a fluorine-based membrane is used as the electrolyte membrane, the potential at which the fluorine-based electrolyte membrane undergoes oxidation is 2.5 [V] or higher, and therefore the electrolyte membrane is not oxidized with an oxidizing power of 1.00 [V]. Absent. On the other hand, when a hydrocarbon-based electrolyte membrane is used as the electrolyte membrane, the hydrocarbon-based electrolyte membrane may be oxidized if the oxidation-reduction potential of the compound to be added becomes higher than 1.00 [V]. Substituting a representative organic compound, benzene is oxidized at 2.00 [V], toluene is 1.93 [V], and xylene is oxidized at 1.58 [V], which is compared with a fluorine electrolyte membrane. Then, it is oxidized at a low redox potential. For this reason, by setting the oxidation-reduction potential to 1.00 [V] or less, even when a hydrocarbon film is used, the electrolyte film is not oxidized and can be used for a long time. In addition, since an actual oxidation-reduction potential (Real Hydrogen Electrode; RHE) changes depending on various conditions such as pH and temperature, it is preferable to use a voltage in a range corresponding to the conditions.

  Having redox reversibility is important for the following reasons. When performing oxidation prevention while generating power with a fuel cell, electrolytic oxidation must also be considered. When a compound that reduces active oxygen to water is supplied as an antioxidant from the electrode side to the electrolyte, the antioxidant is electrolytically oxidized at the electrode and may enter the electrolyte in an oxidized state. In particular, a compound having a theoretical voltage of 1.23 [V] (NHE) or less, which is a theoretical voltage of a polymer electrolyte fuel cell, is very likely to be electrolytically oxidized before entering an electrolyte. In the case of a compound that does not exhibit a reversible redox ability, the function as an antioxidant is lost when this compound is electrolytically oxidized. When the compound exhibits a reversible oxidation-reduction ability, it is regenerated using hydrogen peroxide or the like as a reducing agent to form a reductant, and again has a function as an antioxidant. Also from this viewpoint, when the compound supplied as the antioxidant has a reversible redox ability, the supply amount of the antioxidant can be reduced. In addition, if the antioxidant has reversible oxidation-reduction ability, a method to inactivate hydrogen peroxide without passing through hydroxyl radicals by positive electrolytic oxidation has been established, making active oxygen more effective. May be inactivated.

In addition, the antioxidant is represented by the following general formula (I)

(Wherein R1 and R2 represent the same or different arbitrary substituents, X represents an oxygen atom or a hydroxyl group), and R1 and R2 are preferably bonded to each other to form It is preferable to form a heavy bond, an aromatic ring, or a non-aromatic ring.

Further, this antioxidant has the following general formula (II)

(In the formula, ring Y1 represents an imide compound represented by any one of aromatic or non-aromatic 5- to 12-membered rings having a double bond).

  When the above-mentioned compound is supplied as an antioxidant to the polymer electrolyte fuel cell, hydroxy radicals are efficiently reduced to water by the elementary reaction shown in the following formula (16) to suppress oxidation of the electrolyte membrane.

> NOH + OH →> NO. + H ₂ O (16)
Further, the N-oxyl radical (> NO.) Generated by the hydrogen supply draws out the hydrogen radical from hydrogen peroxide and recovers to the original hydroxyimide (> NOH) form.

2 (> NO ·) + H ₂ O ₂ → 2 (> NOH) + O ₂ Formula (17)
FIG. 5 shows N-hydroxyphthalimide (NHPI) as a representative example of a compound having a hydroxyimide group, and phthalimide N-oxyl (PINO) as an oxidant of NHPI radicalized by NHPI. Describes the mechanism for inactivating radicals and hydrogen peroxide. As shown in FIG. 5, NHPI acts as a reducing agent on hydroxy radicals to produce PINO and water, and PINO reacts with hydrogen peroxide to return to NHPI. At this time, PINO acts as an oxidizing agent for hydrogen peroxide to inactivate the hydrogen peroxide to oxygen. As described above, since the redox cycle between NHPI and PINO can be used as many times as an antioxidant, it is possible to inactivate active oxygen over a long period of time, and durability performance is improved. A maintained electrolyte system for a polymer electrolyte fuel cell can be realized. Furthermore, since the oxidation-reduction cycle rotates, the antioxidant does not become an initiator that causes a new side reaction after the hydroxy radical is reduced.

Further, the above compound has the following general formula (III)

(Wherein R3 and R4 are the same or different and each represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a cycloalkyl group, a hydroxyl group, an alkoxyl group, a carboxyl group, an alkoxycarbonyl group or an acyl group, and X is an oxygen atom. Alternatively, the hydroxyl group is preferably an imide compound represented by n represents an integer of 1 to 3.

  In the compound represented by the general formula (III), the halogen atom in the substituents R3 and R4 includes iodine, bromine, chlorine and fluorine. Examples of the alkyl group include straight chain having about 1 to 10 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, octyl and decyl groups. Branched alkyl groups are included. Preferred is a lower alkyl group having about 1 to 6 carbon atoms, more preferably about 1 to 4 carbon atoms.

  In addition, the aryl group includes a phenyl group, a naphthyl group, and the like, and the cycloalkyl group includes a cyclopentyl, cyclohexyl, cyclooctyl group, and the like. Examples of the alkoxy group include about 1 to 10 carbon atoms, preferably about 1 to 6 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, t-butoxy, pentyloxy, and hexyloxy groups, and more preferably about 1 to 6 carbon atoms. Includes a lower alkoxy group having about 1 to 4 carbon atoms.

  As the alkoxycarbonyl group, for example, the carbon number of the alkoxy moiety such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, isobutoxycarbonyl, t-butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl group and the like is 1 About 10 to 10 alkoxycarbonyl groups are included. A lower alkoxycarbonyl group having preferably about 1 to 6 carbon atoms, more preferably about 1 to 4 carbon atoms, is preferable.

  Examples of the acyl group include acyl groups having about 1 to 6 carbon atoms such as formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl, isovaleryl, and pivaloyl groups.

  The substituents R3 and R4 may be the same or different. In the compound represented by the general formula (III), R3 and R4 are bonded to each other, and R3 and R4 are bonded to each other to form a double bond, an aromatic ring, or a non-aromatic ring. Also good. Among them, the aromatic ring or the non-aromatic ring preferably forms any one of 5 to 12-membered rings, more preferably about 6 to 10-membered rings. Alternatively, it may be a condensed heterocyclic ring, but is preferably a hydrocarbon ring.

  Examples of such rings include non-aromatic hydrocarbon rings such as cycloalkane rings such as cyclohexane rings, non-aromatic hydrocarbon rings such as cycloalkene rings such as cyclohexene rings, and non-aromatics such as bridged hydrocarbon rings such as 5-norbornene rings. Aromatic rings such as sex bridged rings, benzene rings and naphthalene rings are included. In addition, these rings may have a substituent.

  In addition, in the compound represented by the general formula (III), particularly from the viewpoint of stability, durability, and solubility in the electrolyte membrane, more preferable compounds R3 and R4 are bonded to each other to form an aromatic or non-aromatic compound. A 5-membered or 12-membered ring or a group in which R3 and R4 are bonded to each other and have a substituent, a cycloalkane ring, a substituent, a cycloalkene ring, or a substituent It is possible to use a bridged hydrocarbon ring or one having a substituent.

Furthermore, the compound represented by the general formula (III) is a compound represented by the following formulas (3a) to (3f) particularly from the viewpoint of the stability, durability, and solubility in the electrolyte membrane of the compound.

(Wherein R3 to R6 are the same or different and each represents a hydrogen atom, a halogen atom, an alkyl group, a hydroxyl group, an alkoxyl group, a carboxyl group, an alkoxycarbonyl group, an acyl group, a nitro group, a cyano group or an amino group, n represents an integer of 1 to 3).

  In the substituents R3 to R6, the alkyl group includes an alkyl group having about 1 to 6 carbon atoms among the same alkyl groups as the above-described alkyl group, and the alkoxy group particularly includes the same alkoxy groups as the previous method. A lower alkoxy group having about 1 to 4 carbon atoms is included, and the alkoxycarbonyl group includes a lower alkoxycarbonyl group having about 1 to 4 carbon atoms in the alkoxy moiety among the alkoxycarbonyl groups similar to the previous method.

  Examples of the acyl group include acyl groups having about 1 to 6 carbon atoms among the same acyl groups as described above. Examples of the halogen atom include fluorine, chlorine and bromine atoms. The substituents R3 to R6 are usually a hydrogen atom, a lower alkyl group having about 1 to 4 carbon atoms, a carboxyl group, a nitro group, or a halogen atom in many cases.

Furthermore, as a more preferable form of the imide compound, N-hydroxysuccinimide, N-hydroxymaleimide, N-hydroxyhexahydrophthalimide, N from the viewpoint of availability of the compound, ease of synthesis, and cost. , N'-dihydroxycyclohexanetetracarboxylic imide, N-hydroxyphthalic imide, N-hydroxytetrabromophthalic imide, N-hydroxytetrachlorophthalic imide, N-hydroxyhetic imide, N-hydroxyhymic imide N-hydroxytrimellitic imide, N, N′-dihydroxypyromellitic imide and N, N′-dihydroxynaphthalene tetracarboxylic imide are preferably at least one imide compound, Using this compound as a catalyst It can be used to coexist in the electrolyte membrane. These imide compounds are obtained by a conventional imidization reaction, for example, by reacting the corresponding acid anhydride with hydroxylamine NH ₂ OH to open the acid anhydride group and then ring-closing and imidizing. Can be prepared.

The compound represented by the general formula (II) has the following general formula (V) having a 6-membered N-substituted cyclic imide skeleton.

(In the formula, X represents an oxygen atom or a hydroxyl group. R1 to R6 are the same or different and each represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a cycloalkyl group, a hydroxyl group, an alkoxy group, a carboxyl group, a substituted oxy group) Represents a carbonyl group, an acyl group or an acyloxy group, and at least two of R1 to R6 may be bonded to each other to form a double bond or an aromatic or non-aromatic ring. Of these, at least one of them may have an N-substituted cyclic imide group. In the N-substituted cyclic imide skeleton, both the 5-membered ring and the 6-membered ring are hydrolyzed as shown in the following formula (18) and the following formula (19), but the 6-membered ring is more hydrolyzed than the 5-membered ring. Slow and highly resistant to hydrolysis.

For this reason, when the compound having an N-substituted cyclic imide skeleton is a 6-membered cyclic imide, it can be used many times as a redox catalyst, so that the amount of catalyst used can be further reduced.

  The alkyl group includes, for example, a straight chain having about 1 to 10 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, octyl and decyl groups. And a branched alkyl group. Preferred is a lower alkyl group having about 1 to 6 carbon atoms, more preferably about 1 to 4 carbon atoms.

  In addition, examples of the aryl group include a phenyl group and a naphthyl group, and examples of the cycloalkyl group include a cyclopentyl, cyclohexyl, and cyclooctyl groups. Examples of the alkoxy group include about 1 to 10 carbon atoms, preferably about 1 to 6 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, t-butoxy, pentyloxy, and hexyloxy groups, and more preferably about 1 to 6 carbon atoms. Is a lower alkoxy group having about 1 to 4 carbon atoms.

  As the alkoxycarbonyl group, for example, the carbon number of the alkoxy moiety such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, isobutoxycarbonyl, t-butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl group and the like is 1 About 10 to 10 alkoxycarbonyl groups. A lower alkoxycarbonyl group having preferably about 1 to 6 carbon atoms, more preferably about 1 to 4 carbon atoms, is preferable.

  Examples of the acyl group include acyl groups having about 1 to 6 carbon atoms such as formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl, isovaleryl, and pivaloyl groups.

  In the compound represented by the general formula (V), at least two of R1 to R6 may be bonded to each other to form a double bond, an aromatic ring, or a non-aromatic ring. Among them, the aromatic ring or the non-aromatic ring preferably forms any one of 5 to 12-membered rings, more preferably about 6 to 10-membered rings. It may be a heterocycle or a fused heterocycle. Examples of such a ring include a non-aromatic hydrocarbon ring such as a cycloalkane ring typified by a cyclohexane ring, a cycloalkene ring such as a cyclohexene ring, and a bridged hydrocarbon ring typified by a 5-norbornene ring. And aromatic rings such as non-aromatic bridged rings, benzene rings, and naphthalene rings. In addition, these rings may have a substituent.

In addition, the compound represented by the general formula (V) is preferably represented by the following general formula (VIa) or (VIb) from the viewpoints of stability and durability of the compound.

(Wherein R7 to R12 are the same or different and each represents a hydrogen atom, an alkyl group, a hydroxyl group, an alkoxyl group, a carboxyl group, an alkoxycarbonyl group, an acyl group, a nitro group, a cyano group, or an amino group). A compound is preferred.

The compound represented by the general formula (V), (VIa), or (VIb) is N-hydroxyglutaric acid imide, N-hydroxy-1,8-naphthalenedicarboxylic acid imide, N-hydroxy-1,8-decalin dicarboxylic acid. Acid imide, N, N′-dihydroxy-1,8; 4,5-naphthalene tetracarboxylic imide, N, N′-dihydroxy-1,8; 4,5-decalin tetracarboxylic imide and N, N ′, It is preferably at least one imide compound selected from the group consisting of N ″ -trihydroxyisocyanuric acid. Regardless of the 5-membered ring or 6-membered ring, the imide compound is a conventional imidation reaction, for example, by reacting a corresponding acid anhydride with hydroxylamine (NH ₂ OH) to open the acid anhydride group. Thereafter, it can be prepared by ring closure and imidization.

The compound represented by the general formula (I) is represented by the following general formula (VII)

(Wherein R13 and R14 are an alkyl group or an alkyl group partially substituted with an arbitrary group, and R13 and R14 may be chain, cyclic or branched. R13 and R14 are bonded to each other. It may form a ring and may contain oxygen and nitrogen atoms). By continuously supplying the compound represented by the general formula (VII), the continuously generated active oxygen is inactivated and the oxidation of the electrolyte membrane is suppressed. In the compound represented by the general formula (VII), examples of the substituents R13 and R14 include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, Examples thereof include a linear or branched alkyl group having about 1 to 10 carbon atoms such as a decyl group. Preferred is a lower alkyl group having about 1 to 6 carbon atoms, more preferably about 1 to 4 carbon atoms.

The compound represented by the general formula (VII) is represented by the following general formula (VIII)

(Wherein R13 to R16 are an alkyl group or an alkyl group partially substituted with an arbitrary group, and R13 to R16 may be a chain, a ring, or a branch. Also, R13 and R14 Or R15 and R16 may be bonded to each other to form a ring, which may contain oxygen and nitrogen atoms). In the compound represented by the general formula (VII), examples of the substituents R13 to R16 include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, Examples thereof include a linear or branched alkyl group having about 1 to 10 carbon atoms such as a decyl group. Preferred is a lower alkyl group having about 1 to 6 carbon atoms, more preferably about 1 to 4 carbon atoms.

The compound represented by the general formula (VIII) is represented by the following general formula (IX)

In the formula, ring Y2 is preferably a compound represented by R13 and R14 which are bonded to form either a 5-membered ring or a 6-membered ring. Examples of such a ring include, for example, a non-aromatic hydrocarbon ring such as a cycloalkane ring typified by a cyclohexane ring, a cycloalkene ring typified by a cyclohexene ring, and a bridged type typified by a 5-norbornene ring. Non-aromatic bridged rings such as hydrocarbon rings, aromatic rings such as benzene rings and naphthalene rings are included. In addition, these rings may have a substituent.

The compound represented by the general formula (IX) is represented by the following general formula (X)

(Wherein, Z is a kind of substitution selected from the group consisting of an alkyl group, an aryl group, an alkoxy group, a carboxyl group, an alkoxycarbonyl group, a cyano group, a hydroxyl group, a nitro group, an amino group, and a substituent containing a hydrogen atom. In the case where Z is an alkyl group, the alkyl group may be partially substituted with an arbitrary group, and some groups may be chain, cyclic, or branched, And may contain oxygen and nitrogen atoms, and when Z is an aryl group, it may be an aryl group partially substituted with any group, and may contain oxygen and nitrogen atoms). It is preferable that Since the compound represented by the general formula (X) is difficult to hydrolyze, it is possible to inactivate continuously generated active oxygen and suppress oxidation of the electrolyte membrane by continuously supplying this compound. Become.

  In the substituent Z, the alkyl group includes an alkyl group having about 1 to 6 carbon atoms among the same alkyl groups as those described above, and examples of the aryl group include a phenyl group and a naltyl group. As the alkoxy group, an alkoxy group having about 1 to 6 carbon atoms is particularly included among the same alkoxy groups as the above alkyl group, and examples of the carboxyl group include a carboxyl group having about 1 to 4 carbon atoms. As the alkoxycarbonyl group, for example, the carbon number of the alkoxy moiety such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, isobutoxycarbonyl, t-butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl group and the like is 1 About 10 to 10 alkoxycarbonyl groups. A lower alkoxycarbonyl group having preferably about 1 to 6 carbon atoms, more preferably about 1 to 4 carbon atoms, is preferable.

  One example of the compound represented by the general formula (X) is TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl). Examples of compounds represented by TEMPO and general formula (X) are shown in FIG. TEMPO shown in FIG. 6 (i) is an N-hydroxyimide derivative having a reversible redox cycle, and ultimately reduces oxygen to water.

The compound represented by the general formula (IX) is represented by the following general formula (XI)

(Wherein, Z is a kind of substitution selected from the group consisting of an alkyl group, an aryl group, an alkoxy group, a carboxyl group, an alkoxycarbonyl group, a cyano group, a hydroxyl group, a nitro group, an amino group, and a substituent containing a hydrogen atom. In the case where Z is an alkyl group, the alkyl group may be partially substituted with an arbitrary group, and some groups may be chain, cyclic, or branched, And may contain oxygen and nitrogen atoms, and when Z is an aryl group, it may be an aryl group partially substituted with any group, and may contain oxygen and nitrogen atoms). The compound represented by the general formula (IX) may be represented by the following general formula (XII):

(Wherein, Z is a kind of substitution selected from the group consisting of an alkyl group, an aryl group, an alkoxy group, a carboxyl group, an alkoxycarbonyl group, a cyano group, a hydroxyl group, a nitro group, an amino group, and a substituent containing a hydrogen atom. In the case where Z is an alkyl group, the alkyl group may be partially substituted with an arbitrary group, and some groups may be chain, cyclic, or branched, And may contain oxygen and nitrogen atoms, and when Z is an aryl group, it may be an aryl group partially substituted with any group, and may contain oxygen and nitrogen atoms). It may be. Since these compounds are also difficult to hydrolyze like the compounds represented by the general formula (X), continuous supply of this compound inactivates active oxygen generated continuously, and oxidizes the electrolyte membrane. It becomes possible to suppress. When the compound is represented by general formula (XI) or general formula (XII), the same substituents as those of the compound represented by general formula (X) can be used.

  Examples of the compounds represented by general formula (XI) and general formula (XII) are shown in FIGS. Examples of the compound represented by the general formula (XI) and the general formula (XII) include PROXYL (2,2,5,5-tetramethylpyrrolidine-1-oxyl) and DOXYL (4,4-dimethyloxazolidine-3- Oxyl). These compounds also have a reversible redox cycle similar to TEMPO and reduce oxygen to water.

  FIG. 10 shows a redox mechanism in another example of the compound used in the polymer electrolyte fuel cell system in the present embodiment. Here, as a representative example of the above compound, a redox cycle of TEMPO is shown, and a mechanism of inactivation of hydrogen peroxide and hydroxy radical by TEMPO is shown.

  As shown in the above formula (14) and the following formula (20), hydrogen peroxide acts as a reducing agent for substances having a higher redox potential than hydrogen peroxide, while it has a redox potential higher than that of hydrogen peroxide. It is known to act as an oxidant for low substances.

^{_{H 2 O 2 → O 2 +}} 2H + + 2e - E 0 = 0.68 [V] ··· formula (20)
TEMPO is an N-hydroxyimide derivative having a reversible redox cycle, and is redoxed by the elementary reactions shown in the following formulas (21) and (22), and its redox potential is 0.81 [V]. .

TEMPO ⁺ + e ⁻ → TEMPO E ₀ = 0.81 [V] (21)
TEMPO → TEMPO ⁺ + e ⁻ E ₀ = 0.81 [V] (formula 22)
The redox potential of TEMPO is higher than the redox potential of hydrogen peroxide and lower than the redox potential of hydroxy radicals. For this reason, the N-oxyl radical form of TEMPO, which is a reductant, acts as a reducing agent on the hydroxy radical, supplies electrons (e ⁻ ) to the hydroxy radical generated in the electrolyte membrane, and reduces it to OH ⁻ .

TEMPO + · OH → TEMPO ⁺ + OH ⁻ (23)
On the other hand, hydrogen abstraction acts as an oxidizing agent to hydrogen peroxide acts as an oxidizing agent to TEMPO ⁺ Hydrogen peroxide is the oxidant, to oxidize the hydrogen peroxide into oxygen TEMPO ⁺ is It recovers to a reduced form.

2TEMPO ⁺ + H ₂ O ₂ → 2TEMPO + 2H ⁺ + O ₂ Formula (24)
TEMPO reduces hydroxy radicals again after recovering to a reduced form. In this way, TEMPO rotates the redox cycle between the reductant and the oxidant, and at the same time, deactivates hydroxy radicals and oxygen peroxide and prevents oxidation of the electrolyte.

When TEMPO is supplied from the fuel electrode of the fuel cell, a part of the TEMPO may undergo electrolytic oxidation represented by the formula (22) on the fuel electrode catalyst, and may be diffused into the electrolyte as oxidant TEMPO ^+. . Even in this case, TEMPO having a reversible oxidation-reduction cycle has a function as an oxidizing agent that can recover hydrogen radicals to the original reduced form TEMPO using hydrogen peroxide as a reducing agent and reduce hydroxy radicals again. Become. In the case of a compound that does not have a reversible redox cycle, the antioxidant function is lost when the hydroxy radical is reduced, and it no longer functions as an oxidizing agent. Can maintain the function as an antioxidant to some extent by having a reversible redox cycle.

  Thus, the polymer electrolyte fuel cell system according to the present embodiment includes a membrane electrode assembly having an air electrode on one surface and a fuel electrode on the other surface of the polymer electrolyte membrane, and a membrane electrode assembly. Between the air electrode side separator that is arranged on the air electrode side of the membrane and forms an air flow path between the membrane electrode assembly and the fuel electrode side surface of the membrane electrode assembly, and between the membrane electrode assembly A solid polymer electrolyte fuel cell in which a plurality of single cells each including a fuel electrode side separator that forms a fuel gas flow path are stacked, and an antioxidant that inactivates active oxygen. And an antioxidant supply means for supplying from the air electrode side or the fuel electrode side, hydrogen acting as fuel from the outside of the fuel cell, or a new antioxidant that does not participate in the fuel cell reaction apart from hydrogen ions By supplying, it is possible to ensure active oxygen It is possible to realize a polymer electrolyte fuel cell system can be erased activated.

  Hereinafter, the polymer electrolyte fuel cell system according to the present invention will be described more specifically with reference to Examples 1 to 12 and Comparative Examples 1 to 2, but the scope of the present invention is not limited thereto. Absent. These examples are for examining the effectiveness of the polymer electrolyte fuel cell system according to the present invention, and show examples of polymer electrolyte fuel cell systems using different antioxidants.

<Preparation of sample>
Example 1
A Nafion (registered trademark) 117 membrane (thickness: 175 [μm]) manufactured by DuPont was used as a solid polymer electrolyte membrane cut into 1 [cm] squares. The Nafion (registered trademark) membrane is pretreated according to NEDO PEFC R & D project standard treatment, boiled in 3% hydrogen peroxide water for 1 hour, then boiled in distilled water for 1 hour. M] The solution was boiled in an aqueous solution of sulfuric acid for 1 hour, and finally boiled in distilled water for 1 hour.

Next, in order to facilitate the determination of deterioration prevention in an endurance test, the Nafion (registered trademark) membrane was subjected to ion exchange treatment after pretreatment. In the ion exchange treatment, a pretreated Nafion (registered trademark) membrane was immersed in a 100 [mM] FeSO ₄ aqueous solution for one night or more, and then adhered to the membrane using ultrasonic cleaning for 15 [minutes] in distilled water. The Nafion® counter ion was exchanged from H ⁺ to Fe ²⁺ by removing the ions. The reagent used was Wako Pure Chemicals special grade FeSO ₄ · 7H ₂ O.

Next, a platinum-supported carbon (20 wt% Pt / Vulcan XC-72 manufactured by Cabot) was applied to both surfaces of the ion exchange treatment electrolyte membrane so as to be 1 [mg / cm ² ], and a membrane-electrode assembly (MEA). Was made. The produced MEA was incorporated into a single cell to obtain a single cell for PEFC. The single cell was a 5 [cm ² ] single cell. Then, 70 [° C.] humidified hydrogen gas (atmospheric pressure) as fuel electrode side gas and 70 [° C.] humidified oxygen gas (atmospheric pressure) as air electrode gas are supplied to a single cell maintained at 70 [° C.] via a bubbler. did. Further, 1 [mM] NHPI aqueous solution as an antioxidant that inactivates active oxygen was fed to the fuel gas flow path at a flow rate of 1 [cm ³ / min] using a liquid feed pump. The single cell was controlled to maintain 70 [° C.].

(Example 2)
As an antioxidant, an N-hydroxymaleimide (NHMI) aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 1 was carried out as Example 2.

(Example 3)
As an antioxidant, an N-hydroxysuccinimide (NHSI) aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 1 was performed as Example 3.

Example 4
As an antioxidant, an N-hydroxyglutarimide (NHGI) aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 1 was carried out as Example 4.

(Example 5)
As an antioxidant, an N, N ′, N ″ -trihydroxyisocyanuric acid (THICA) aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 1 was carried out as Example 5.

(Comparative Example 1)
In Example 1, the case where no aqueous antioxidant solution was passed was designated as Comparative Example 1.

  In Examples 6 to 11, a sulfonated polyethersulfone (S-PES) membrane was used as the polymer solid electrolyte membrane. Regarding S-PES membranes, New Energy and Industrial Technology Development Organization FY 2002 Results Report “Solid Polymer Fuel Cell System Technology Development Business Solid Polymer Fuel Cell Element Technology Development Business, etc. An equivalent product described in “Research and development of highly durable hydrocarbon-based electrolyte membrane” P31 was obtained and used.

(Example 6)
An S-PES film (thickness 170 [μm]) is cut into 1 [cm] squares, and platinum-supported carbon (20 wt% Pt / Vulcan XC-72 manufactured by Cabot) is 1 [mg / cm] on both sides of the S-PES film. ² ] to prepare a membrane-electrode assembly (MEA). The produced MEA was incorporated into a single cell to obtain a single cell for PEFC. The single cell was a 5 [cm ² ] single cell. Then, 70 [° C.] humidified hydrogen gas (atmospheric pressure) as fuel electrode side gas and 70 [° C.] humidified oxygen gas (atmospheric pressure) as air electrode gas are supplied to a single cell maintained at 70 [° C.] via a bubbler. did. In addition, a 1 [mM] TEMPO-OH aqueous solution as an antioxidant that inactivates active oxygen was fed to the fuel gas channel at a flow rate of 1 [cm ³ / min] using a feed pump. The single cell was controlled to maintain 70 [° C.].

(Example 7)
As an antioxidant, a TEMPO-COOH (Aldrich) aqueous solution was used in place of the TEMPO-OH aqueous solution, and the same treatment as in Example 6 was carried out as Example 7.

(Example 8)
As an antioxidant, a TEMPO (Aldrich) aqueous solution was used instead of the TEMPO-OH aqueous solution, and the same treatment as in Example 6 was performed, and Example 8 was designated.

Example 9
As an antioxidant, a PROXYL-CONH ₂ (Aldrich) aqueous solution was used instead of the TEMPO-OH aqueous solution, and the same treatment as in Example 6 was carried out as Example 9.

(Example 10)
As an antioxidant, Example 10 was obtained by using a PROXYL-COOH (Aldrich) aqueous solution in place of the TEMPO-OH aqueous solution and performing the same treatment as in Example 6.

(Example 11)
As an antioxidant, a 3-carbamoyl-2,2,5,5-tetramethylpyrrolin-1-yloxy (Aldrich) aqueous solution was used instead of the TEMPO-OH aqueous solution, and the same treatment as in Example 6 was performed. Was taken as Example 11.

(Example 12)
As an antioxidant, a di-t-butyl nitroxide (DTBN: Aldrich) aqueous solution was used instead of the TEMPO-OH aqueous solution, and the same treatment as in Example 6 was carried out as Example 12.

(Comparative Example 2)
In Example 6, the case where no antioxidant aqueous solution was passed was designated as Comparative Example 2.

  Here, the sample obtained by the said method was evaluated by the method shown below.

<Measurement of redox potential>
The oxidation-reduction potentials of the compounds used in the examples were measured using glassy carbon as the working electrode, platinum as the counter electrode, a saturated calomel electrode (SCE) as the reference electrode, and 1 [M] sulfuric acid as the electrolyte. Measurement examples of NHPI, which is a typical imide compound, and TEMPO, which is a typical TEMPO compound, are shown in FIGS. 11 and 12, respectively. In FIG. 11 and FIG. 12, in order to match the redox potential of each substance, the standard potential E ⁰ (NHE) is corrected and displayed according to the equation (25).

E ⁰ (NHE) = E (SCE) +0.24 [V] Expression (25)
As shown in FIG. 11, the oxidation-reduction potential of NHPI exists near 1.10 [V], and from FIG. 12, the oxidation-reduction potential of TEMPO exists near 0.57 [V]. This potential indicates that NHPI and TEMPO are compounds that function as reducing agents for hydroxy radicals and compounds that function as oxidizing agents for hydrogen peroxide, and are suitable for this purpose. It turns out that it is.

<Start / stop repeated endurance test>
The test was started after holding the fuel electrode side in an open circuit state for 30 minutes. In the test, gas was flowed through a single cell at a flow rate of 300 [dm ³ / min], the current density was increased from the discharge open circuit state, and discharge was performed until the terminal voltage became 0.3 [V] or less. Then, after the terminal voltage became 0.3 [V] or less, the circuit was held again for 5 [min] as an open circuit state. This operation was repeated, and the durability performance was compared with the number of times that the voltage when the power was generated at a current density of 1 [mA / cm ³ ] became 0.4 [V] or less. FIG. 13 shows, as an example, an initial value of a current-voltage curve of a start-stop repeated endurance test of the single fuel cell produced in Example 1, and a graph of the current-voltage curve after endurance. In this graph, the number of times that the voltage is 0.4 [V] or less when the power is generated at a current density of 1 [mA / cm ³ ] is the number of start / stop repetitions.

<Analysis of substances generated at the air electrode>
Degradation analysis of the membrane was performed by measuring the fluoride ion concentration and the sulfate ion concentration generated with the decomposition of the Nafion (registered trademark) membrane, and the sulfate ion concentration generated with the decomposition of the S-PES membrane. . For detection of eluted ions, the liquid discharged from the air electrode was collected and measured by ion chromatography. An ion chromatograph manufactured by Dioneck (model name CX-120) was used. As a specific test method, in each of the examples and comparative examples, the liquid discharged from the air electrode at the end of 100 times was collected and compared in the start-stop test. Further, gas generated at the air electrode was measured with a gas chromatograph mass spectrometer. A gas chromatograph mass spectrometer manufactured by Shimadzu Corporation (GCMS-QP5050) was used.

In Tables 1 and 2, the types of electrolyte membranes in Examples 1 to 12 and Comparative Examples 1 to 2, the antioxidant used, the oxidation-reduction potential of the antioxidant, the number of repetitions of start and stop, fluoride ions, Indicates whether or not sulfate ions and carbon dioxide are generated at the air electrode.

  The oxidation-reduction potentials of the compounds used in Examples 1 to 12 were 0.68 [V] (NHE) at which hydrogen peroxide serves as a reducing agent, and 1.77 [potential at which hydrogen peroxide serves as an oxidizing agent. V] (NHE), which proved to be a suitable compound for this purpose.

As a result of the start / stop repeated endurance test, in Comparative Example 1 in which no antioxidant was supplied, the number of start / stop repetitions was 120, and the voltage when power was generated at a current density of 1 [mA / cm ³ ] was 0.4. [V] Decreased below. On the other hand, in Examples 1 to 5 in which the antioxidant was supplied, the voltage became 0.4 [V] or less at about 1200 start / stop repetitions, and the solid polymer was added by adding the antioxidant. It was confirmed that the deterioration of the electrolyte membrane was suppressed and the durability was improved. In Examples 6 to 12, the voltage became 0.4 [V] or less when the number of start / stop repetitions was 600 times or more, and it was confirmed that durability was improved by suppressing deterioration of the electrolyte membrane.

Moreover, from the analysis result in the ion chromatograph, in Comparative Example 1, fluoride ions and sulfate ions were detected, and in Comparative Example 2, sulfate ions were detected, and it was confirmed that the electrolyte membrane was deteriorated due to decomposition. In contrast, the fluoride ions and sulfate ions generated in Examples 1 to 5 were below the detection limit, and it was confirmed that the decomposition of the Nafion (registered trademark) membrane was suppressed by introducing the antioxidant. It was done. Moreover, the sulfate ion generated in Example 6 to Example 12 was below the detection limit, and it was confirmed that the decomposition of the S-PES film was suppressed by introducing the antioxidant. Looking at the results of the gas chromatograph mass spectrometer, in Examples 1 to 12 in which the antioxidant was introduced, CO ₂ was detected, and after the antioxidant introduced from the fuel electrode inactivated the active oxygen, It was confirmed that it was oxidized at the pole and discharged as CO ₂ .

  As described above, perfluorosulfonic acid polymers represented by Nafion (registered trademark) membranes, which are the most widely used electrolyte membranes, and hydrocarbon polymers shown in S-PES are the fuel cell air. Although it could not be said that the active oxygen generated at the electrode is sufficiently resistant, by supplying the above compound as an antioxidant, the active oxygen generated continuously is deactivated and the electrolyte membrane deteriorates. As a result, the durability of the fuel cell can be improved.

  In the polymer electrolyte fuel cell system according to the present embodiment, the polymer electrolyte fuel cell can be any of hydrogen type, direct methanol type, and direct hydrocarbon type.

  Moreover, the polymer electrolyte fuel cell system according to the present embodiment can be mounted on a fuel cell vehicle as its application. By mounting the polymer electrolyte fuel cell system according to the present embodiment, the fuel cell vehicle according to the present embodiment can withstand continuous operation for a long time.

  The polymer electrolyte fuel cell system according to the embodiment of the present invention is not limited to a fuel cell vehicle as its application, but is a fuel cell cogeneration power generation system, a fuel cell home appliance, a fuel cell portable device, and a fuel cell. It can be applied to transportation equipment.

  Although the embodiment of the present invention has been described above, it should not be understood that the description and the drawings, which form part of the disclosure of the above-described embodiment, limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

1 is a schematic explanatory view illustrating an embodiment of a polymer electrolyte fuel cell system according to the present invention. 1 is an exploded perspective view showing a single cell of a solid polymer electrolyte fuel cell constituting a solid polymer fuel cell system according to the present invention. FIG. It is explanatory drawing explaining the movement of the substance in the membrane electrode assembly which comprises a single cell. It is a schematic diagram which shows the three-phase interface in an air electrode. It is explanatory drawing showing the mechanism which inactivates active oxygen by NHPI. It is an example of an antioxidant. It is another example of an antioxidant. It is a further example of an antioxidant. It is another example of an antioxidant. It is explanatory drawing showing the mechanism which inactivates active oxygen by TEMPO. It is a cyclic voltammogram in the electrode reaction of NHPI. It is a cyclic voltammogram in the electrode reaction of TEMPO. It is a graph which shows the initial value of the current-voltage curve of the start-stop repetition endurance test of the fuel cell single cell produced in Example 1, and the current-voltage curve after durability.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte type fuel cell 2 Single cell 3 Membrane electrode assembly 4 Solid polymer electrolyte membrane 5 Air electrode 6 Fuel electrode 7 Air electrode side separator 8 Air flow path 9 Fuel electrode side separator 10 Fuel gas flow path 11 Antioxidation Agent supply means

Claims (30)

A membrane electrode assembly having an air electrode on one surface of the solid polymer electrolyte membrane and a fuel electrode on the other surface, and an air flow between the membrane electrode assembly disposed on the air electrode side of the membrane electrode assembly An air electrode side separator that forms a passage; and a fuel electrode side separator that is disposed on a fuel electrode side surface of the membrane electrode assembly and forms a fuel gas flow path between the membrane electrode assembly and the air electrode side separator. A solid polymer electrolyte fuel cell in which a plurality of single cells are stacked;
An antioxidant supply means for supplying an antioxidant for inactivating active oxygen from the air electrode side or the fuel electrode side of the solid polymer electrolyte fuel cell;
A solid polymer fuel cell system comprising:   2. The polymer electrolyte fuel cell system according to claim 1, wherein the antioxidant is continuously supplied to the fuel electrode as an antioxidant solution.   The solid polymer fuel cell system according to claim 2, wherein the antioxidant solution is an aqueous solution.   The antioxidant supply means includes an antioxidant solution tank in which the antioxidant solution is sealed, a liquid feed pump that supplies the antioxidant solution to the fuel electrode, the antioxidant solution tank, and the The anti-oxidant solution line for connecting the liquid feed pump and the anti-oxidant solution line for connecting the liquid feed pump and the fuel gas flow path are provided. Item 4. The polymer electrolyte fuel cell system according to Item 3.   5. The solid polymer according to claim 1, wherein the antioxidant is a hydrocarbon compound composed of four atoms of carbon, oxygen, nitrogen, and hydrogen. Type fuel cell system.   6. The polymer electrolyte fuel cell system according to claim 1, wherein the hydrolyzate obtained by hydrolyzing the oxidized oxidant is chemically stable. Mu.   7. The antioxidant according to claim 1, wherein the antioxidant has a reversible redox ability, and the oxidized form of the antioxidant is chemically stable. 8. Solid polymer fuel cell system. The waste antioxidant or the oxidized form of the antioxidant is oxidized by a catalyst contained in the air electrode and discharged as CO ₂ , H ₂ O or N _2. The polymer electrolyte fuel cell system according to claim 7.   9. The solid according to claim 1, wherein a standard oxidation-reduction potential of the antioxidant is larger than 0.68 [V] and smaller than 1.77 [V]. Polymer fuel cell system. The antioxidant is represented by the following general formula (I)

(Wherein R1 and R2 represent the same or different arbitrary substituents, and X represents an oxygen atom or a hydroxyl group). The polymer electrolyte fuel cell system described in the item.   11. The polymer electrolyte fuel according to claim 10, wherein, in the general formula (I), R 1 and R 2 are bonded to each other to form a double bond, an aromatic ring, or a non-aromatic ring. Battery system. The antioxidant is represented by the following general formula (II)

(In the formula, ring Y1 represents a single bond of aromatic or non-aromatic 5- to 12-membered rings having a double bond). The polymer electrolyte fuel cell system according to claim 10 or 11. The antioxidant is represented by the following general formula (III)

(Wherein R3 and R4 are the same or different and each represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a cycloalkyl group, a hydroxyl group, an alkoxyl group, a carboxyl group, an alkoxycarbonyl group or an acyl group, and X is an oxygen atom. Or a hydroxyl group, wherein n represents an integer of 1 to 3.) The polymer electrolyte fuel cell system according to claim 12, wherein the polymer is an imide compound.   14. The polymer electrolyte fuel according to claim 13, wherein in the general formula (III), R3 and R4 are bonded to each other to form a double bond, an aromatic ring, or a non-aromatic ring. Battery system.   In the general formula (III), R3 and R4 are bonded to each other to form any one of aromatic or non-aromatic 5- to 12-membered rings. 14. The polymer electrolyte fuel cell system according to 13.   In the general formula (III), R3 and R4 are bonded to each other to form at least one selected from the group consisting of a cycloalkane, a cycloalkene, a bridged hydrocarbon ring, an aromatic ring, and a substituent thereof. The polymer electrolyte fuel cell system according to claim 13, wherein The imide compound represented by the general formula (III) is represented by the following formulas (3a) to (3f):

(Wherein R3 to R6 are the same or different and each represents a hydrogen atom, a halogen atom, an alkyl group, a hydroxyl group, an alkoxyl group, a carboxyl group, an alkoxycarbonyl group, an acyl group, a nitro group, a cyano group or an amino group, The solid polymer fuel cell system according to any one of claims 13 to 16, wherein n represents an imide compound represented by 1).   The imide compound represented by the general formula (III) is N-hydroxysuccinimide, N-hydroxymaleimide, N-hydroxyhexahydrophthalimide, N, N'-dihydroxycyclohexanetetracarboxylic imide, N- Hydroxyphthalimide, N-hydroxytetrabromophthalimide, N-hydroxytetrachlorophthalimide, N-hydroxyheptimide, N-hydroxyhymic imide, N-hydroxytrimellitic imide, N, N'- 18. The polymer electrolyte fuel cell system according to claim 17, which is at least one imide compound selected from the group consisting of dihydroxypyromellitic imide and N, N′-dihydroxynaphthalenetetracarboxylic imide. The compound represented by the general formula (II) is represented by the following general formula (V):

(In the formula, X represents an oxygen atom or a hydroxyl group. R1 to R6 are the same or different and each represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a cycloalkyl group, a hydroxyl group, an alkoxy group, a carboxyl group, a substituted oxy group) Represents a carbonyl group, an acyl group or an acyloxy group, and at least two of R1 to R6 may be bonded to each other to form a double bond or an aromatic or non-aromatic ring. 13. The polymer electrolyte fuel cell system according to claim 12, wherein at least one of the compounds may have an N-substituted cyclic imide group. The compound represented by the general formula (V) is represented by the following formula (VIa) or (VIb)

(Wherein R7 to R12 are the same or different and each represents a hydrogen atom, an alkyl group, a hydroxyl group, an alkoxyl group, a carboxyl group, an alkoxycarbonyl group, an acyl group, a nitro group, a cyano group, or an amino group). 20. The polymer electrolyte fuel cell system according to claim 19, which is a compound.   The compound represented by the general formula (V), (VIa), or (VIb) is N-hydroxyglutarimide, N-hydroxy-1,8-naphthalenedicarboxylic imide, N-hydroxy-1,8-decalin. Dicarboxylic imide, N, N′-dihydroxy-1,8; 4,5-naphthalene tetracarboxylic imide, N, N′-dihydroxy-1,8; 4,5-decalin tetracarboxylic imide and N, N ′ 21. The polymer electrolyte fuel cell system according to claim 19 or 20, which is at least one imide compound selected from the group consisting of N, N ″ -trihydroxyisocyanuric acid.   22. The solid according to claim 1, wherein a standard redox potential of the antioxidant is greater than 0.68 [V] and less than 1.00 [V]. Polymer fuel cell system. The compound represented by the general formula (I) is represented by the following general formula (VII)

(Wherein R13 and R14 are an alkyl group or an alkyl group partially substituted with an arbitrary group, and R13 and R14 may be chain, cyclic or branched. R13 and R14 are bonded to each other. 11. The polymer electrolyte fuel cell system according to claim 10, which may form a ring and may contain oxygen and nitrogen atoms. The compound represented by the general formula (VII) is represented by the following general formula (VIII)

(Wherein R13 to R16 are an alkyl group or an alkyl group partially substituted with an arbitrary group, and R13 to R16 may be a chain, a ring, or a branch. Also, R13 and R14 Or a solid polymer according to claim 23, wherein R15 and R16 may be bonded to each other to form a ring and may contain oxygen and nitrogen atoms). Type fuel cell system. The compound represented by the general formula (VIII) is represented by the following general formula (IX)

The ring Y2 is a compound represented by the formula: wherein R13 and R14 are bonded to form either a 5-membered ring or a 6-membered ring. Solid polymer fuel cell system. The compound represented by the general formula (IX) is represented by the following general formula (X):

(Wherein, Z is a kind of substitution selected from the group consisting of an alkyl group, an aryl group, an alkoxy group, a carboxyl group, an alkoxycarbonyl group, a cyano group, a hydroxyl group, a nitro group, an amino group, and a substituent containing a hydrogen atom. In the case where Z is an alkyl group, the alkyl group may be partially substituted with an arbitrary group, and some groups may be chain, cyclic, or branched, And may contain oxygen and nitrogen atoms, and when Z is an aryl group, it may be an aryl group partially substituted with any group, and may contain oxygen and nitrogen atoms). 26. The polymer electrolyte fuel cell system according to claim 25. The compound represented by the general formula (IX) is represented by the following general formula (XI)

(Wherein, Z is a kind of substitution selected from the group consisting of an alkyl group, an aryl group, an alkoxy group, a carboxyl group, an alkoxycarbonyl group, a cyano group, a hydroxyl group, a nitro group, an amino group, and a substituent containing a hydrogen atom. In the case where Z is an alkyl group, the alkyl group may be partially substituted with an arbitrary group, and some groups may be chain, cyclic, or branched, And may contain oxygen and nitrogen atoms, and when Z is an aryl group, it may be an aryl group partially substituted with any group, and may contain oxygen and nitrogen atoms). 26. The polymer electrolyte fuel cell system according to claim 25. The compound represented by the general formula (IX) is represented by the following general formula (XII)

(Wherein, Z is a kind of substitution selected from the group consisting of an alkyl group, an aryl group, an alkoxy group, a carboxyl group, an alkoxycarbonyl group, a cyano group, a hydroxyl group, a nitro group, an amino group, and a substituent containing a hydrogen atom. In the case where Z is an alkyl group, the alkyl group may be partially substituted with an arbitrary group, and some groups may be chain, cyclic, or branched, And may contain oxygen and nitrogen atoms, and when Z is an aryl group, it may be an aryl group partially substituted with any group, and may contain oxygen and nitrogen atoms). 26. The polymer electrolyte fuel cell system according to claim 25.   29. The solid polymer electrolyte fuel cell according to any one of claims 1 to 28, wherein the solid polymer electrolyte fuel cell is any one selected from a hydrogen type, a direct methanol type, and a direct hydrocarbon type. The described polymer electrolyte fuel cell system.   30. A fuel cell vehicle on which the polymer electrolyte fuel cell system according to any one of claims 1 to 29 is mounted.

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