JP4876389B2 - Electrolyte for polymer electrolyte fuel cell, polymer electrolyte fuel cell, polymer electrolyte fuel cell system and fuel cell vehicle - Google Patents

Description

  The present invention relates to an electrolyte for a polymer electrolyte fuel cell, a polymer electrolyte fuel cell, 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. A fuel cell is one in which fuel such as hydrogen, methanol, or other hydrocarbons is electrochemically oxidized in the cell, thereby converting the chemical energy of the fuel directly into electric 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 and automobile.

  There are several types of fuel cells. Among them, the polymer electrolyte fuel cell (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. There are various advantages such as that design is possible, and that (4) a large amount of current can be taken out by controlling the three-phase interface and a high output density can be obtained at the ion exchange membrane / electrode interface.

  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 positive electrode (air electrode) of fuel cells. It has been developed as a membrane resistant to active oxygen. However, in a long-term durability test, it cannot be said that there is still sufficient resistance (see Non-Patent Document 1).

The operating principle of a fuel cell consists of two electrochemical processes: H ₂ oxidation at the negative electrode (fuel electrode) and water generation by 4-electron reduction of molecular oxygen (O ₂ ) at the positive electrode. However, in an actual fuel cell, side reactions occur simultaneously in addition to these reactions. A typical example is the production of hydrogen peroxide (H ₂ O ₂ ) by two-electron reduction of O _{2 at} the positive electrode. 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 (1) and (2). At this time, radicals such as hydroxy radicals and hydroperoxy radical radicals are generated.

H ₂ O ₂ → 2.OH Formula (1)
H ₂ O ₂ → · H + · OOH (2)
The reactions of the formulas (1) and (2) shown here are Haber-Weiss reactions in the presence of metal ions (for example, Fe ²⁺ , Cu ^2+, etc.). In the Harbor Weiss reaction, hydrogen peroxide is converted into hydroxy radicals (.OH) by a catalytic action such as metal ions. 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 the Fenton reaction represented by the following formula (3).

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

Therefore, as a method of preventing radicalization of hydrogen peroxide, a method of catalytically decomposing hydrogen peroxide by dispersing and mixing a metal oxide (for example, manganese oxide, cobalt oxide, etc.) in the electrolyte membrane, or a peroxidation A method of preventing radicalization of hydrogen peroxide by dispersing and blending a physical stabilizer (for example, a tin compound) in an electrolyte membrane has been proposed (see Patent Document 1). In addition, a method of blending an electrolyte membrane with a compound that traps and inactivates peroxide radicals (for example, a compound having a phenolic hydroxyl group) has been proposed (see Patent Document 1 and Patent Document 2). .
JP 2001-118591 A (4th and 5th pages) JP 2000-223135 A (page 3) 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 Research (1) Electrode catalyst / electrolyte interface degradation factors ”, March 2002, p.13, 24

  However, since metal oxides and tin compounds do not dissolve in water, it is difficult to uniformly disperse them in the electrolyte membrane even if the metal oxides or tin compounds are made fine particles. Further, when the tin compound is decomposed, the metal may be eluted as a cation in the acidic electrolyte membrane to cause a Harbor Weiss reaction, which may promote the generation of active oxygen.

  Further, when hydrogen peroxide is decomposed by a catalyst such as a metal oxide, it is based on catalytic decomposition. That is, hydrogen peroxide does not occur unless in the vicinity of the catalyst. For this reason, it is not possible to decompose hydrogen peroxide away from the catalyst.

  Further, when the peroxide radical is trapped and inactivated, a radical inactivating compound equivalent to the molar concentration of the generated radical is required. Since this compound is not regenerated, a radical inactivating compound is required every time a radical is trapped, and it is difficult to consume peroxide for a long period of time.

The present invention has been made to solve the above problems, and the electrolyte for a polymer electrolyte fuel cell according to the first invention functions as a reducing agent at a potential lower than the oxidation-reduction potential of a hydroxy radical, and , hydrogen peroxide and summarized in that a reversible that have a redox cycling compounds which act as oxidizing agent at a potential higher than the redox potential to act as a reducing agent.

  The solid polymer fuel cell according to the second invention is characterized in that at least one of the electrolytes for solid polymer fuel cells according to the first invention is used.

  Furthermore, the solid polymer fuel cell system according to the third invention is characterized by comprising the solid polymer fuel cell according to the second invention.

  According to a fourth aspect of the present invention, there is provided a fuel cell vehicle on which the polymer electrolyte fuel cell system according to the third aspect is mounted.

  According to the first invention, the compound contained in the polymer electrolyte fuel cell electrolyte acts as a catalyst to decompose active oxygen. Moreover, since this compound returns to the original form by the redox cycle of the compound after decomposing active oxygen, it can be used many times. For this reason, it is possible to realize an electrolyte for a polymer electrolyte fuel cell in which durability performance is maintained.

  According to the second invention, it is possible to realize a solid polymer fuel cell in which durability performance is maintained.

  According to the third invention, it is possible to realize a polymer electrolyte fuel cell system whose performance is maintained for a long time.

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

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

  First, an embodiment of an electrolyte for a polymer electrolyte fuel cell according to the present invention will be described. The polymer electrolyte fuel cell electrolyte according to the present embodiment acts as a reducing agent at a potential lower than the oxidation-reduction potential of the hydroxy radical, and at a potential higher than the oxidation-reduction potential at which hydrogen peroxide acts as the reducing agent. It has a compound having a redox cycle that acts as an oxidizing agent.

  The reaction of the entire normal fuel cell system is as shown in the following formulas (4) and (5).

2H ₂ + O ₂ → 2H ₂ O Formula (4)
H ₂ + O ₂ → H ₂ O ₂ Formula (5)
Equation (4) is a four-electron reduction of oxygen, and equation (5) is a two-electron reduction of oxygen. The reactions of formulas (4) and (5) proceed simultaneously as a competitive reaction.

Here, the formula (4) is the sum of elementary reactions of the positive electrode main reaction represented by the following formula (6) and the negative electrode reaction represented by the following formula (7). Note that E ₀ is represented by a normal oxidation-reduction potential (Normal Hydrogen Electrode; NHE).

O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O E ₀ = 1.23 [V] (6)
H ₂ → 2H ⁺ + 2e ⁻ E ₀ = 0.00 [V] (7)
Similarly, the formula (5) is the sum of elementary reactions of the positive electrode side reaction represented by the following formula (8) and the negative electrode reaction represented by the above formula (7).

O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O ₂ E ₀ = 0.68 [V] (8)
Thermodynamically, a substance with a high redox potential acts as an oxidizing agent, and a substance with a low redox potential acts as a reducing agent. The reaction proceeds when ΔE ₀ (redox potential difference) of the entire system is a positive value.

  The hydrogen peroxide generated in the above formula (5) is considered to disappear by the reactions shown in the following formulas (9) to (11).

H ₂ O ₂ + H ₂ → 2H ₂ O (9)
H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O E ₀ = 1.77 [V] (10)
2H ₂ O ₂ → 2H ₂ O + O ₂ ... Formula (11)
Formula (9) shows a case where hydrogen peroxide is reduced to water in the positive electrode by H ₂ crossing over from the negative electrode through the electrolyte membrane. Equation (10) shows a case where hydrogen peroxide receives hydrogen ions and electrons at the positive electrode and is reduced to water. Formula (11) shows a reaction in which two molecules of hydrogen peroxide react, one hydrogen peroxide acts as an oxidizing agent, and the other hydrogen peroxide acts as a reducing agent to generate water and oxygen. . As shown in the above formula (10) and the following formula (12), hydrogen peroxide acts as a reducing agent for a substance having a higher redox potential than hydrogen peroxide, while the redox potential is higher than that of hydrogen peroxide. It is known to act as an oxidant for substances with low levels.

^{_{H 2 O 2 → O 2 +}} 2H + + 2e - E 0 = 0.68 [V] ··· formula (12)
Here, Expression (9) is the sum of the elementary reaction represented by Expression (10) and the elementary reaction represented by Expression (7). Expression (11) is the sum of the elementary reaction represented by Expression (10) and the elementary reaction represented by Expression (12).

Next, consider a case where the fuel cell is contaminated with Fe ²⁺ ions. Hydrogen peroxide generated at the positive electrode is converted into a hydroxyl radical by the Fenton reaction using Fe ²⁺ as a catalyst.

Fe ²⁺ + H ₂ O ₂ → Fe ³⁺ + OH ⁻ + · OH Formula (3)
The oxidation-reduction potential of this hydroxy radical is 2.85 [V] and has an extremely high oxidizing power. The hydroxy radical disappears by oxidizing the hydrogen ion as shown in the following formula (13).

OH + H ⁺ + e ⁻ → H ₂ O E ₀ = 2.85 [V] (13)
However, when hydrogen (hydrogen ion) supply shortage occurs due to the start-stop of the fuel cell, etc., the hydroxyl radical has an extremely high oxidizing power, and therefore, C of the Nafion (registered trademark) membrane that is not oxidized originally. The -F bond may be broken. Therefore, the polymer electrolyte fuel cell electrolyte according to the present embodiment functions as a reducing agent at a potential lower than the oxidation-reduction potential of the hydroxy radical, and higher than the oxidation-reduction potential at which hydrogen peroxide functions as a reducing agent. Since it has a compound having a redox cycle that acts as an oxidant at an electric potential, this compound acts as a catalyst to decompose hydrogen peroxide and hydroxy radicals, which are active oxygen. For this reason, the hydroxy radical disappears by the catalytic action of the compound contained in the electrolyte membrane without oxidizing the electrolyte membrane. In addition, since the compound having the catalytic action returns to the original reduced form by the oxidation-reduction cycle of the compound after decomposing active oxygen, it can be used many times. For this reason, it is possible to realize an electrolyte for a polymer electrolyte fuel cell in which durability performance is maintained.

  Here, as an example of the compound acting as the catalyst, N-hydroxyphthalimide (NHPI) having a reversible redox cycle is shown, and the case where NHPI is introduced into the fuel cell reaction system is shown. When NHPI is oxidized, it becomes PINO (phthalimide-N-oxyl). NHPI and PINO have a redox potential of 1.34 [V].

NHPI → PINO + H ⁺ + e ⁻ E ₀ = 1.34 [V] (14)
PINO + H ⁺ + e ⁻ → NHPI E ₀ = 1.34 [V] (15)
As shown in Formula (10) and Formula (13), the oxidation-reduction potential of the hydroxyl radical generated by the hydrogen peroxide and Fenton reaction is higher than the oxidation-reduction potential of NHPI. For this reason, when NHPI is present, hydrogen peroxide or hydroxy radicals are reduced to water by the catalytic action of NHPI as a reducing agent. In this case, as shown in the following formulas (16) and (17), NHPI is oxidized to PINO by droxy radical or hydrogen peroxide.

OH + NHPI → H ₂ O + PINO Formula (16)
H ₂ O ₂ + 2NHPI → 2H ₂ O + 2PINO (17)
Formula (16) is the sum of the elementary reaction shown by Formula (13) and the elementary reaction shown by Formula (14). Equation (17) is the sum of the elementary reaction represented by equation (10) and the elementary reaction represented by equation (15).

  As shown in the following formulas (18), (19) and (15), PINO, which is an oxidized form of NHPI, is reduced to NHPI by oxidizing hydrogen ions, hydrogen or hydrogen peroxide as an oxidizing agent. Is done.

2PINO + H ₂ → 2NHPI (18)
PINO + H ⁺ + e ⁻ → NHPI E ₀ = 1.34 [V] (15)
2PINO + H ₂ O ₂ → 2NHPI + O ₂ Formula (19)
Equation (18) is the sum of the elementary reaction represented by equation (15) and the elementary reaction represented by equation (7). Equation (19) is the sum of the elementary reaction represented by equation (15) and the elementary reaction represented by equation (12). The redox potential of PINO is 1.34 [V], which is not so high as to thermodynamically break the C—F bond of the Nafion (registered trademark) membrane. For this reason, the electrolyte membrane is not oxidized by PINO.

  Here, FIG. 1 shows redox potentials of hydroxy radicals, oxygen, hydrogen peroxide, hydrogen, NHPI and PINO. The right column of this figure shows the oxidation half reaction formula of the reducing agent, and the left column shows the reduction half reaction formula of the oxidizing agent. The vertical axis represents the oxidation-reduction potential, and the oxidation-reduction potential increases as it goes upward. In other words, the higher the position is, the stronger the oxidizing power is, and it is difficult to oxidize. The lower the position, the weaker the oxidizing power and the easier it is to oxidize. In addition, the numerical value shown in the parenthesis after the half reaction formula is the oxidation-reduction potential of the compound acting as an oxidizing agent or a reducing agent. Moreover, the numerical value in a circle | round | yen shows the number of an above-described formula. Since the oxidation-reduction potential is affected by pH and temperature, FIG. 1 shows the standard oxidation-reduction potential corrected to the standard hydrogen electrode (NHE).

  Thus, in the polymer electrolyte fuel cell electrolyte according to the present embodiment, the redox potential acts as a reducing agent at a potential lower than the redox potential of the hydroxy radical, and the hydrogen peroxide acts as a reducing agent. Since it has a compound having a redox cycle that acts as an oxidizing agent at a high potential, the compound acts as a catalyst and decomposes active oxygen such as hydroxy radicals and hydrogen peroxide. For this reason, the C—F bond of the electrolyte membrane is not broken by hydroxy radicals or hydrogen peroxide, and deterioration of the electrolyte membrane can be prevented. Moreover, since this compound returns to the original reduced form by the redox cycle of the compound after decomposing active oxygen, it can be used many times. For this reason, it is possible to realize an electrolyte for a polymer electrolyte fuel cell in which durability performance is maintained.

  Here, NHPI is shown as an example of a compound that acts as a catalyst. However, when the purpose is to eliminate only hydroxy radicals, the standard redox potential is in the range of 0.68 [V] to 2.85 [V]. It is preferable that the compound has When the purpose is to eliminate both hydroxy radicals and hydrogen peroxide, this compound acts as a reducing agent at a potential lower than the oxidation-reduction potential at which hydrogen peroxide acts as an oxidizing agent. Since it is necessary to act as an oxidizing agent at a potential higher than the redox potential acting as a reducing agent, the standard redox potential of this compound should be in the range of 0.68 [V] to 1.77 [V]. Is preferred.

  Furthermore, it is more preferable if the oxidized form and reduced form of this compound are relatively stable compounds. In addition, since the actual oxidation-reduction potential (Real Hydrogen Electrode; RHE) of each compound changes according to various conditions such as pH and temperature, it is preferable to use those in a range corresponding to the conditions. However, considering the poisoning of platinum used in the electrode, the compound used for the electrolyte for the polymer electrolyte fuel cell according to the present embodiment is an organic compound composed only of carbon, hydrogen, oxygen and nitrogen. It is preferable that

  Thus, the polymer electrolyte fuel cell electrolyte according to the present embodiment can suppress the deterioration of the electrolyte membrane, so that it is possible to realize an electrolyte for a polymer electrolyte fuel cell in which durability performance is maintained. Become.

The above compound has 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 compound has the following general formula (II)

(Wherein ring Y represents a imide compound having a double bond or any one of aromatic or non-aromatic 5- to 12-membered rings).

  By allowing the above-described compound to coexist in the electrolyte membrane, elementary reactions represented by the following formulas (20) and (21) proceed. Only when hydroxy radicals or hydrogen peroxide enters the electrolyte membrane, the above compound supplies N-oxyl radicals (> NO.) And efficiently reduces hydroxy radicals and hydrogen peroxide to water. Suppresses oxidation of the electrolyte membrane.

> NOH + OH →> NO. + H ₂ O (20)
2 (> NOH) + H ₂ O ₂ → 2 (> NO ·) + 2H ₂ O (21)
In addition, the N-oxyl radical generated by the supply of hydrogen extracts hydrogen ions from hydrogen or hydrogen peroxide by the elementary reactions shown in the following formulas (22) to (24) to form the original hydroxyimide (> NOH). Recover.

2 (> NO ·) + H ₂ → 2 (> NOH) (22)
> NO ・ + H ⁺ + e ⁻ →> NOH ... Formula (23)
2 (> NO ·) + H ₂ O ₂ → 2 (> NOH) + O ₂ Formula (24)
FIG. 2 shows N-hydroxyphthalimide (NHPI) as a representative example of a compound having a hydroxyimide group, and phthalic acid imide N-oxyl (PINO) as an oxidized form of NHPI radicalized by NHPI. It represents a mechanism in which hydroxy radicals or hydrogen peroxide disappears over a long period of time by a cycle between the imide group and the N-oxyl radical of PINO. That is, NHPI acts as a reducing agent for hydroxy radicals or hydrogen peroxide, and reduces hydroxy radicals or hydrogen peroxide to water. On the other hand, PINO acts as an oxidizing agent for hydrogen peroxide and oxidizes hydrogen peroxide to oxygen. In this way, a redox cycle occurs between NHPI and PINO, and oxygen peroxide and hydroxy radicals disappear at the same time.

  In addition, the compound included in the polymer electrolyte fuel cell electrolyte according to the present embodiment involves the entry and exit of hydrogen radicals (hydrogen atoms) when hydrogen peroxide is eliminated by reduction and oxidation. Due to the entry and exit of the hydrogen radicals, the hydroxy radicals generated during the decomposition of hydrogen peroxide are eliminated even if they are present at locations away from the compound. FIG. 3 shows this mechanism. As shown in FIG. 3, for example, when NHPI is used as such a compound, a Groththuss Mechanism occurs in which hydrogen radicals are exchanged between NHPI and water molecules. Since the reduction reaction proceeds while supplying hydrogen radicals to water molecules in this way, even when NHPI and hydroxy radicals are separated, a catalytic reaction that eliminates hydroxy radicals proceeds, and hydroxy radicals can be lost. It becomes. For this reason, it is possible to eliminate hydroxy radicals existing in a wide range in the electrolyte membrane.

  What is important in selecting a compound having such a catalytic action is the stability, durability, heat resistance, and solubility in the electrolyte membrane of the compound. In particular, the stability and durability of the compound is most important when the fuel cell is used over a long period of time and in the sense that the active oxygen continues to disappear. 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 electrolyte membrane can sufficiently withstand even at a temperature of about 120 [° C.]. Must have heat resistance. Moreover, in order to dissolve this compound uniformly in the electrolyte membrane, it may be difficult to dissolve, but it is necessary to dissolve in water. If it becomes insoluble in water, it will precipitate in the electrolyte membrane, making it impossible for hydrogen radicals to enter and exit, thus losing the effect (catalytic function) of eliminating active oxygen such as hydroxy radicals and hydrogen peroxide.

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. X represents oxygen. An atom or a hydroxyl group, and n is preferably an imide compound represented by 1 to 3).

  In the compound represented by the general formula (III), examples of the halogen atom among the substituents R3 and R4 include 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. A branched alkyl group can be mentioned. 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. As the alkoxy group, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, t-butoxy, pentyloxy, hexyloxy group, etc., about 1 to 10 carbon atoms, preferably about 1 to 6 carbon atoms, more preferably 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.

  The substituents R3 and R4 may be the same or different. In the compound represented by the general formula (III), R3 and R4 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. May be a heterocyclic ring or a condensed heterocyclic ring, but is preferably a hydrocarbon 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.

Furthermore, the compound represented by the general formula (III) is a compound represented by any of the following formulas (IVa) to (IVf) particularly from the viewpoints of stability, durability, and solubility in the electrolyte membrane.

(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- hydroxyaldehyde trimellitic acid imide, N, to be N'- dihydroxy pyromellitic acid imide, and N, at least one imide compound selected from the group consisting of N'- dihydroxynaphthalene tetracarboxylic acid imide preferably And this compound as a catalyst Te coexist in the electrolyte membrane can be used.

These imide compounds are subjected to a conventional imidation reaction, for example, by reacting a corresponding acid anhydride with hydroxylamine (NH ₂ OH) to open an acid anhydride group, and then ring-closing to imidize. Can be prepared.

Further, 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. At least one of them may have an N-substituted cyclic imide group). In the N-substituted cyclic imide skeleton, the hydrolysis of the 6-membered ring is slower than that of the 5-membered ring, and the hydrolysis resistance is higher. For this reason, when the compound having an N-substituted cyclic imide skeleton is a 6-membered cyclic imide, durability is further maintained.

  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. As the alkoxy group, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, t-butoxy, pentyloxy, hexyloxy group, etc., about 1 to 10 carbon atoms, preferably about 1 to 6 carbon atoms, more preferably 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.

  Here, as an example of the compound represented by the general formula (V), R1 to R6 are all hydrogen atoms, and N-hydroxyglutarimide (NHGI) having a reversible oxidation-reduction cycle is mentioned. The case where it introduce | transduces in a battery reaction system is shown. When NHGI is oxidized, it becomes glutaric imide N-oxyl (GINO). NHGI and GINO have a redox potential of 1.39 [V].

NHGI → GINO + H ⁺ + e ⁻ E ₀ = 1.39 [V] (25)
GINO + H ⁺ + e ⁻ → NHGI E ₀ = 1.39 [V] (26)
As shown in Formula (10) and Formula (13), the redox potential of the hydroxy radical generated by the hydrogen peroxide and Fenton reaction is higher than the redox potential of NHGI. For this reason, in the presence of NHGI, hydrogen peroxide or hydroxy radicals are reduced to water by the catalytic action of NHPI. In this case, as shown in the following formulas (27) and (28), NHGI functions as a reducing agent, and NHGI is oxidized to GINO by a hydroxyl radical or hydrogen peroxide.

OH + NHGI → H ₂ O + GINO Formula (27)
H ₂ O ₂ + 2NHGI → 2H ₂ O + 2GINO Formula (28)
Equation (27) is the sum of the elementary reaction represented by Equation (13) and the elementary reaction represented by Equation (25). Equation (28) is the sum of the elementary reaction represented by equation (10) and the elementary reaction represented by equation (26).

  GINO, which is an oxidized form of NHGI, is reduced to NHGI by oxidizing hydrogen ions, hydrogen, or hydrogen peroxide as an oxidizing agent as shown in the following formulas (29), (30), and (26). Is done.

2GINO + H ₂ → 2NHGI Formula (29)
GINO + H ⁺ + e ⁻ → NHGI E ₀ = 1.39 [V] (26)
2GINO + H ₂ O ₂ → 2NHGI + O ₂ Formula (30)
Equation (29) is the sum of the elementary reaction represented by equation (26) and the elementary reaction represented by equation (7). Equation (30) is the sum of the elementary reaction represented by equation (26) and the elementary reaction represented by equation (12). The redox potential of GINO is 1.39 [V], which is not so high as to cleave the C—F bond of the Nafion (registered trademark) film thermodynamically. For this reason, the electrolyte membrane is not oxidized by GINO.

  Thus, in the polymer electrolyte fuel cell electrolyte according to the present embodiment, the redox potential acts as a reducing agent at a potential lower than the redox potential of the hydroxy radical, and the hydrogen peroxide acts as a reducing agent. Because it has a compound with a 6-membered N-substituted cyclic imide skeleton that has a redox cycle that acts as an oxidizing agent at a high potential, this compound acts as a catalyst to decompose active oxygen such as hydroxy radicals and hydrogen peroxide. To do. For this reason, the C—F bond of the electrolyte membrane is not broken by hydroxy radicals or hydrogen peroxide, and deterioration of the electrolyte membrane can be prevented. Moreover, since this compound returns to the original form by the redox cycle of the compound after decomposing active oxygen, it can be used many times. For this reason, it is possible to realize an electrolyte for a polymer electrolyte fuel cell in which durability performance is maintained.

  Note that NHGI is shown here as an example of a compound that acts as a catalyst. However, the above-described redox mechanism is 0.68 [V] to 2.85 [V] when the purpose is to eliminate only hydroxy radicals. It is preferable that the compound has a standard redox potential in the range of When the purpose is to eliminate both hydroxy radicals and hydrogen peroxide, this compound acts as a reducing agent at a potential lower than the oxidation-reduction potential at which hydrogen peroxide acts as an oxidizing agent. Since it is necessary to act as an oxidizing agent at a potential higher than the redox potential acting as a reducing agent, the standard redox potential of this compound should be in the range of 0.68 [V] to 1.77 [V]. Is preferred.

  Furthermore, it is more preferable if the oxidized form and reduced form of this compound are relatively stable compounds. In addition, since the actual oxidation-reduction potential (Real Hydrogen Electrode; RHE) of each compound changes according to various conditions such as pH and temperature, it is preferable to use those in a range corresponding to the conditions. However, considering the poisoning of platinum used in the electrode, the compound used for the electrolyte for the polymer electrolyte fuel cell according to the present embodiment is an organic compound composed only of carbon, hydrogen, oxygen and nitrogen. It is preferable that

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, durability, and solubility in an electrolyte membrane.

(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.

  Furthermore, the compound represented by the general formula (V), (VIa) or (VIb) is N-hydroxyglutaric acid imide, N-hydroxy-1,8-naphthalenedicarboxylic imide, N-hydroxy-1,8-decalin. Dicarboxylic acid imide, N, N′-dihydroxy-1,8; 4,5-naphthalene tetracarboxylic acid imide, N, N′-dihydroxy-1,8; 4,5-decalin tetracarboxylic acid imide and N, N ′ , N ″ -trihydroxyisocyanuric acid is preferably at least one imide compound (6-membered imide ring) selected from the group consisting of.

A 6-membered cyclic imide is obtained by a conventional imidization reaction, for example, by reacting a corresponding 6-membered ring acid anhydride with hydroxylamine NH ₂ OH to open an acid anhydride group, and then closing the ring to form an imide Can be prepared. Similar to the 5-membered cyclic imide, the 6-membered cyclic imide allows the elementary reactions shown in the formulas (25) and (26) to proceed by coexisting in the electrolyte membrane. Only when hydroxy radicals or hydrogen peroxide enters the electrolyte membrane, the 6-membered imide ring supplies hydrogen radicals and efficiently reduces hydrogen peroxide and suppresses oxidation of the electrolyte membrane.

> NOH + OH →> NO. + H ₂ O Formula (31)
2 (> NOH) + H ₂ O ₂ → 2 (> NO ·) + 2H ₂ O (32)
Further, the N-oxyl radical (> NO.) Generated by the hydrogen supply draws out hydrogen ions from hydrogen or hydrogen peroxide by the elementary reaction shown in the following formulas (33) to (35), and the original hydroxyimide (> NOH).

2 (> NO ·) + H ₂ → 2 (> NOH) (33)
> NO ・ + H ⁺ + e ⁻ →> NOH ... Formula (34)
2 (> NO.) + H ₂ O ₂ → 2 (> NOH) + O ₂ Formula (35)
FIG. 4 shows N-hydroxyglutarimide (NHGI) as a representative example of a compound having a hydroxyimide group, and glutamic acid N-oxyl (GINO) as an oxidized form of NHGI radicalized by NHGI. This represents a mechanism in which hydroxy radicals and hydrogen peroxide disappear over a long period of time by a cycle between the hydroxyimide group of GINO and the N-oxyl radical of GINO. That is, NHGI acts as a reducing agent for hydroxy radicals or hydrogen peroxide, and reduces hydroxy radicals or hydrogen peroxide to water. On the other hand, GINO acts as an oxidizing agent for hydrogen peroxide and oxidizes hydrogen peroxide to oxygen. In this way, the oxidation-reduction cycle starts between NHGI and GINO, and at the same time, oxygen peroxide and hydroxy radicals disappear.

  The imide compound having a 6-membered ring included in the polymer electrolyte fuel cell electrolyte according to the present embodiment involves the entry and exit of hydrogen radicals (hydrogen atoms) when hydrogen peroxide is eliminated by reduction and oxidation. . Due to the entry and exit of the hydrogen radicals, the hydroxy radicals generated during the decomposition of hydrogen peroxide are eliminated even if they are present at locations away from the compound. This mechanism is the same as the mechanism shown in FIG. 3, and a growth mechanism occurs in which hydrogen radicals are exchanged between NHGI and water molecules. For this reason, even if NHGI and the hydroxy radical are separated from each other, a catalytic reaction for eliminating the hydroxy radical proceeds, and the hydroxy radical can be lost. For this reason, it is possible to eliminate hydroxy radicals existing in a wide range in the electrolyte membrane.

  What is important in selecting a compound having such a catalytic action is the stability, durability, heat resistance, and solubility in the electrolyte membrane of the compound. In particular, the stability and durability of the compound is most important when the fuel cell is used over a long period of time and in the sense that the active oxygen continues to disappear. Also, considering that the steady state operating temperature of the fuel cell is 80 to 90 [° C.] and the heat resistance of the electrolyte membrane will be improved in the future, the electrolyte membrane has sufficient heat resistance even at about 120 [° C.]. It is necessary to have. Further, in order to uniformly dissolve the 6-membered ring imide compound in the electrolyte membrane, it may be difficult to dissolve, but it is necessary to dissolve in water. If it becomes insoluble in water, it will precipitate in the electrolyte membrane, making it impossible for hydrogen radicals to enter and exit, thus losing the effect (catalytic function) of eliminating active oxygen such as hydroxy radicals and hydrogen peroxide.

  Thus, in the polymer electrolyte fuel cell electrolyte according to the present embodiment, the redox potential acts as a reducing agent at a potential lower than the redox potential of the hydroxy radical, and the hydrogen peroxide acts as a reducing agent. Since it has a compound having a redox cycle that acts as an oxidant at a high potential, this compound acts as a catalyst and decomposes active oxygen. For this reason, the C—F bond of the electrolyte membrane is not broken by hydroxy radicals or hydrogen peroxide, and deterioration of the electrolyte membrane can be prevented. Moreover, since this compound returns to the original form by the redox cycle of the compound after decomposing active oxygen, it can be used many times. For this reason, it is possible to realize an electrolyte for a polymer electrolyte fuel cell in which durability performance is maintained. Furthermore, when this compound is a 6-membered cyclic imide, the hydrolysis is slower and the hydrolysis resistance is higher than in the case of a 5-membered ring. For this reason, in the case of a 6-membered cyclic imide, more durable performance is maintained.

  Hereinafter, the polymer electrolyte fuel cell electrolyte according to the present invention will be described more specifically with reference to Examples 1 to 22 and Comparative Examples 1 and 2, but the scope of the present invention is limited to these. is not. These examples are investigations of the effectiveness of the polymer electrolyte fuel cell electrolyte according to the present invention, and show examples of polymer electrolyte fuel cell electrolytes prepared with different raw materials. .

<Preparation of sample>
Example 1
A DuPont Nafion (registered trademark) 117 membrane (thickness: 175 [μm]) was cut into 1 [cm] squares and used. 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, after adding 0.5 [mM] NHPI as a catalyst (active oxygen elimination catalyst) in order to make active oxygen disappear in the pretreated Nafion (registered trademark) membrane, 30 [%] hydrogen peroxide solution (Special grade of Wako Pure Chemical Industries, Ltd.) was immersed in 10 [%] hydrogen peroxide 10 [cm ³ ] prepared by diluting with ultrapure water at 80 [° C.] for 12 [hour] and used for evaluation.

(Example 2)
For the purpose of accelerating deterioration in the hydrogen peroxide durability test, a pretreated Nafion (registered trademark) membrane is immersed in a 100 [mM] FeSO ₄ aqueous solution for more than one night, and then ultrasonicated in distilled water for 15 minutes. The Nafion® counterion was exchanged from H ⁺ to Fe ²⁺ by washing and removing ions attached to the membrane. The reagent used was Wako Pure Chemicals special grade FeSO ₄ · 7H ₂ O.

Next, after adding 0.5 [mM] of NHPI as an active oxygen disappearance catalyst to the ion-exchanged Nafion (registered trademark) membrane in the same manner as in Example 1, 30 [%] hydrogen peroxide solution (special grade of Wako Pure Chemical Industries, Ltd.) ) Was diluted with ultrapure water and adjusted for 10 [%] hydrogen peroxide 10 [cm ³ ] at 80 [° C.] for 12 [hours] and used for evaluation.

(Example 3)
As an active oxygen disappearance catalyst, an aqueous solution of 0.5 [mM] N-hydroxymaleimide 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 active oxygen disappearance catalyst, an aqueous solution of 0.5 [mM] N-hydroxymaleimide was used instead of the NHPI aqueous solution, and the same treatment as in Example 2 was carried out as Example 4.

(Example 5)
As an active oxygen disappearance catalyst, a 0.5 [mM] N-hydroxysuccinimide aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 1 was performed as Example 5.

(Example 6)
As an active oxygen disappearing catalyst, a 0.5 [mM] N-hydroxymaleimide aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 2 was carried out as Example 6.

(Example 7)
As an active oxygen disappearance catalyst, an aqueous solution of 0.5 [mM] N-hydroxytrimellitic acid imide was used instead of the NHPI aqueous solution, and the same treatment as in Example 1 was performed as Example 7.

(Example 8)
As an active oxygen disappearance catalyst, an aqueous solution of 0.5 [mM] N-hydroxytrimellitic acid imide was used instead of the NHPI aqueous solution, and the same treatment as that of Example 2 was performed as Example 8.

Example 9
As an active oxygen disappearance catalyst, an aqueous solution of 0.5 [mM] N, N′-dihydroxypyromellitic acid imide was used instead of the NHPI aqueous solution, and the same treatment as in Example 1 was carried out as Example 9.

(Example 10)
As an active oxygen disappearance catalyst, an aqueous solution of 0.5 [mM] N, N′-dihydroxypyromellitic imide was used in place of the NHPI aqueous solution, and the same treatment as in Example 2 was carried out as Example 10.

(Example 11)
As an active oxygen disappearance catalyst, a 0.5 [mM] 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 11.

(Example 12)
As an active oxygen disappearing catalyst, a 0.5 [mM] N-hydroxyglutarimide (NHGI) aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 2 was carried out as Example 12.

(Example 13)
As the active oxygen deactivation catalyst, a 0.5 [mM] N-hydroxy-1,8-naphthalenedicarboxylic imide (NHNDI) aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 1 was performed. Example 13 was used.

(Example 14)
As the active oxygen deactivation catalyst, a 0.5 [mM] N-hydroxy-1,8-naphthalenedicarboxylic imide (NHNDI) aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 2 was performed. Example 14 was adopted.

(Example 15)
As the active oxygen deactivation catalyst, a 0.5 [mM] N-hydroxy-1,8-decalin dicarboxylic imide (NHDI) aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 1 was performed. Example 15 was adopted.

(Example 16)
As the active oxygen deactivation catalyst, a 0.5 [mM] N-hydroxy-1,8-decalin dicarboxylic imide (NHDI) aqueous solution was used instead of the NHPI aqueous solution, and the same treatment as in Example 2 was performed. Example 16 was adopted.

(Example 17)
As an active oxygen deactivation catalyst, 0.5 [mM] N, N′-dihydroxy-1,8; 4,5-naphthalenetetracarboxylic imide (NHNTI) aqueous solution was used instead of NHPI aqueous solution, and Example 1 Example 17 was subjected to the same treatment.

(Example 18)
As an active oxygen deactivation catalyst, 0.5 [mM] N, N′-dihydroxy-1,8; 4,5-naphthalenetetracarboxylic imide (NHNTI) aqueous solution was used instead of NHPI aqueous solution, and Example 2 and Example 18 was subjected to the same treatment.

(Example 19)
As an active oxygen deactivation catalyst, 0.5 [mM] N, N′-dihydroxy-1,8; 4,5-decalintetracarboxylic imide (NHDTI) aqueous solution was used instead of NHPI aqueous solution, and Example 1 Example 19 was subjected to the same treatment.

(Example 20)
As an active oxygen deactivation catalyst, 0.5 [mM] N, N′-dihydroxy-1,8; 4,5-decalintetracarboxylic imide (NHDTI) aqueous solution was used instead of NHPI aqueous solution, and Example 2 Example 20 was subjected to the same treatment.

(Example 21)
As the active oxygen deactivation catalyst, 0.5 [mM] N, N ′, N ″ -trihydroxyisocyanuric acid (THICA) aqueous solution was used instead of NHPI aqueous solution, and the same treatment as in Example 1 was performed. To Example 21.

(Example 22)
As the active oxygen deactivation catalyst, a 0.5 [mM] N, N ′, N ″ -trihydroxyisocyanuric acid (THICA) aqueous solution was used instead of the NHGI aqueous solution, and the same treatment as in Example 1 was performed. This was taken as Example 22.

(Comparative Example 1)
Comparative Example 1 was obtained by adding NHPI to a Nafion (registered trademark) membrane pretreated by the same method as in Example 1.

(Comparative Example 2)
Comparative Example 2 was obtained by adding NHPI to a Nafion (registered trademark) membrane ion-exchanged in the same manner as in Example 2.

  Here, the Nafion (registered trademark) membrane treated by the above method was evaluated by the following method.

<Hydrogen peroxide durability test>
The change in color of the Nafion (registered trademark) film treated by the above method was visually observed.

<Membrane degradation analysis>
The deterioration analysis of the membrane was performed by measuring the fluoride ion concentration generated with the decomposition of the Nafion (registered trademark) membrane. Fluoride ions were detected by diluting the sample solution prepared by the above method 10 times with ultrapure water and measuring the diluted solution with an ion chromatograph. An ion chromatograph manufactured by Dioneck (model name: DX-AQ) was used.

<Stability test of active oxygen elimination catalyst>
The stability test of NHPI and NHGI which are active oxygen disappearance catalysts is carried out by placing NHPI aqueous solution and NHGI aqueous solution adjusted to 1 [mM] in a beaker, keeping them at 80 [° C], and sampling every 24 [hours] to obtain a liquid Chromatographed. And the density | concentration of NHPI and NHGI was measured from the peak area of the obtained chromatogram.

Tables 1 and 2 below show the counterion type, type of catalyst, fluoride ion concentration, and color change of the Nafion (registered trademark) membrane in Examples 1 to 22, Comparative Example 1 and Comparative Example 2.

From the results of Examples 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21 and Comparative Example 1, the H ⁺ type Nafion (registered trademark) film lost active oxygen such as NHPI and NHGI. Regardless of the presence or absence of a catalyst, it was found that even when treated with hydrogen peroxide solution for 12 hours, fluoride ions were hardly detected, and the deterioration of the Nafion (registered trademark) film did not proceed. On the other hand, as shown in Comparative Example 2, in the Fe ²⁺ type Nafion (registered trademark) film, fluoride ions were detected after 12 [hour] treatment, and it was found that the deterioration of the film progressed.
Further, as can be seen from the comparison between Examples 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22 and Comparative Example 2, it is detected by the presence or absence of an active oxygen disappearing catalyst such as NHPI or NHGI. In addition, a difference of 10 times or more was observed in the fluoride ions, and it was found that the decomposition of the Nafion (registered trademark) membrane was suppressed by the presence of the active oxygen disappearing catalyst such as NHPI or NHGI.

Further, although the Fe ²⁺ type Nafion (registered trademark) film is almost transparent, in Comparative Example 2, the film turns brown after being treated with hydrogen peroxide solution for 12 hours, and the counter ion is Fe ²⁺ is Fe ^3+. It was suggested that the Fenton reaction occurred. On the other hand, in Examples 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, and 22 in which active oxygen disappearing catalysts such as NHPI and NHGI are present, even though Fe ²⁺ exists. The color change was not confirmed, and it was found that the Fenton reaction was suppressed.

  Further, during the heat treatment for 12 hours with hydrogen peroxide, the sample bottles of Example 1 and Example 2 containing NHPI were more in comparison with Comparative Example 1 and Comparative Example 2. It was also confirmed by visual observation that the bubbles were generated and the decomposition of hydrogen peroxide was promoted. In addition, from this result, the big difference was not seen in the quantity of the fluoride ion generate | occur | produced with the kind of active oxygen deactivation catalyst.

<Redox potential>
The oxidation-reduction potential of the compounds used in the examples was 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. As a typical example, a cyclic voltammogram of NHPI is shown in FIG. The redox potential of NHPI in this condition (SCE) is in the vicinity of 1.10 [V] (SCE), but in FIG. 1, the claims, and the specification, to match the redox potential of each substance. Is corrected to the standard potential E ⁰ (NHE) by the equation shown in the following equation (36).

E ⁰ (NHE) = E (SCE) +0.24 [V] (36)
With this potential, NHPI is a compound that reversibly functions as an oxidizing agent (hydrogen acceptor) or a reducing agent (hydrogen donor), acts as a reducing agent at a potential lower than the redox potential of the hydroxy radical, and It is shown that the compound has a redox cycle that acts as an oxidant at a potential higher than the redox potential at which hydrogen peroxide acts as a reducing agent, and has a function of eliminating hydrogen peroxide in terms of potential. It has been shown. From the cyclic voltammogram of NHGI, it was found that the oxidation-reduction potential of NHGI exists in the vicinity of 1.15 [V] (SCE).

Next, fuel cells using Examples 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22 and Comparative Example 2 as electrolyte membranes and platinum-supported carbon as electrodes. A single cell was created, and repeated start-stop durability tests were conducted. The surface of the electrolyte membrane obtained was coated with platinum-supporting carbon (20 wt% Pt / Vulcan XC-72 manufactured by Cabot) to 1 [mg / cm ² ] on the surface to be an anode and cathode, and a membrane-electrode assembly ( MEA) was prepared. The produced MEA was incorporated into a single cell and used as a single cell for PEFC for evaluation. The single cell was a 5 [cm ² ] single cell.

  Here, the start / stop repeated experiment was performed by the following method.

<Start / stop repeated endurance test>
70 [° C.] humidified hydrogen gas (atmospheric pressure) as anode gas and 70 [° C.] humidified oxygen gas (atmospheric pressure) as cathode gas are supplied to a single cell maintained at 70 [° C., and 30 [ Min] and then the test was started.

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. In order to accelerate the durability test, all Nafion (registered trademark) films were replaced with Fe ²⁺ type (Examples 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and Comparative Example 2) was used.

FIG. 6 shows a graph of an initial value of a current-voltage curve of a start-stop repeated endurance test of the manufactured fuel cell single cell and a current-voltage curve after endurance. In this graph, the degree of deterioration of the electrolyte membrane after the endurance test was determined using the number of times that the voltage when power was generated at a current density of 1 [mA / cm ³ ] became 0.4 [V] or less. Table 3 below shows the counterion type of Nafion (registered trademark) membrane, the type of catalyst, and the number of repeated starting and stopping in Examples 2, 4, 6, 8, 10 and Comparative Example 2.

As shown in Comparative Example 2, in the case where no active oxygen disappearing catalyst is present, the number of repetitions of starting and stopping is 70, and the voltage when power is generated at a current density of 1 [mA / cm ³ ] is 0.4 [V]. Reduced to: On the other hand, in the case where the active oxygen disappearing catalyst is added, the voltage becomes 0.4 [V] or less when the number of start / stop repetitions is 500 times or more, and the deterioration of the electrolyte membrane is suppressed by adding the active oxygen disappearing catalyst. Turned out to be. Furthermore, in Examples 12, 14, 16, 18, 20, and 22 in which the active oxygen elimination catalyst is a 6-membered ring type, the voltage becomes 0.4 [V] or less after 600 or more start / stop cycles. It was found that the deterioration of the electrolyte membrane was suppressed and the durability was superior to those of Examples 2, 4, 6, 8, and 10 which are member ring types. This is because the 6-membered ring type imide compound has better hydrolysis resistance than the 5-membered ring type and is stable, and thus the number of times of starting and stopping is considered to be increased compared to the 5-membered ring type imide compound. . FIG. 7 shows a graph of the results of the stability test of NHPI and NHGI which are active oxygen elimination catalysts. As shown in FIG. 7, the concentration of NHPI, which is a 5-membered ring type, decreases over time due to hydrolysis shown in the following formula (37), and the concentration of NHPI after 96 hours decreases to about 0.6 [mM]. It was.

On the other hand, the concentration of NHGI, which is a 6-membered ring type, decreases with time due to the hydrolysis shown in the following formula (38) as with NHPI, but the concentration of NHGI after 96 hours was about 0.9 [mM]. It was.

In this way, hydrolysis of the 6-membered ring type imide compound occurs similarly to the 5-membered ring type, but the hydrolysis reaction is slow compared to the 5-membered ring type, and therefore the hydrolysis resistance is good and stable. I understood. In particular, when THICA was used as the active oxygen disappearance catalyst of Example 22, the voltage became 0.4 [V] or less after 850 start-stop repetitions, and it was found that the durability was particularly excellent. Since THICA has a small molecular weight and has three hydroxyimide groups in the molecule, it was considered that the THICA showed good durability because it was more excellent in the catalytic action to lose active oxygen.

  As described above, perfluorosulfonic acid polymers represented by Nafion (registered trademark) membrane, which is the most widely used electrolyte membrane, are sufficiently resistant to active oxygen generated at the positive electrode of the fuel cell. However, the use of an electrolyte membrane containing the above compound as a catalyst makes it possible to repeatedly enter and exit hydrogen radicals, and thus has an effect of eliminating active oxygen over a long period of time. Thus, by using an oxidation catalyst (reactive oxygen elimination catalyst), even if hydrogen peroxide is generated at the positive electrode of the polymer electrolyte fuel cell, the performance of the electrolyte membrane can be maintained over a long period of time, and the electrolyte membrane can be deteriorated. It became possible to suppress, and the durability performance of the fuel cell could be improved.

  The electrolyte for a polymer electrolyte fuel cell according to the present invention can be used as an electrolyte membrane for a polymer electrolyte fuel cell. In this case, the fuel type is not limited as long as it is a fuel cell using a proton conductive polymer electrolyte membrane, and is not limited to a hydrogen type solid polymer fuel cell, a direct methanol type solid polymer fuel cell, a direct hydrocarbon type. It can be used for any fuel cell such as a solid polymer fuel cell.

  The solid polymer fuel cell according to the present invention can be used in a fuel cell system using a proton conducting polymer electrolyte membrane, and its use is not limited to a fuel cell vehicle. It can be applied to a fuel cell cogeneration power generation system, a fuel cell home appliance, a fuel cell portable device, and a fuel cell transport device.

  As mentioned above, although the form of this Embodiment was demonstrated, it should not be understood that the description and drawing which make a part of indication of said Embodiment limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

It is explanatory drawing which shows the oxidation-reduction potential of a hydroxyl radical, oxygen, hydrogen peroxide, hydrogen, NHPI, and PINO. It is explanatory drawing showing the active oxygen disappearance mechanism by NHPI. It is explanatory drawing which shows the hydroxyl radical reduction | restoration mechanism by a Gross mechanism. It is explanatory drawing showing the active oxygen disappearance mechanism by NHGI. It is a cyclic voltammogram in the electrode reaction of NHPI. It is a graph which shows the initial value of the current-voltage curve of the start-stop repetition endurance test of the produced fuel cell single cell, and the current-voltage curve after durability. It is a graph of the result of the stability test of NHPI and NHGI.

Claims (14)

Acts as a reducing agent at a potential lower than the oxidation-reduction potential of the hydroxyl radicals and hydrogen peroxide reversible that of case having a redox cycle acting as an oxidant at a higher potential than the oxidation-reduction potential to act as a reducing agent An electrolyte for a polymer electrolyte fuel cell, comprising: A compound having a redox cycle that acts as a reducing agent at a potential lower than the oxidation-reduction potential of a hydroxy radical, and that acts as an oxidizing agent at a potential higher than the oxidation-reduction potential at which hydrogen peroxide acts as a reducing agent;
The compound is represented by the following general formula (I)

(Wherein, the R1 and R2 identical or different arbitrary substituents, X represents an oxygen atom or a hydroxyl group.) Solid high polymer type fuel cell electrolyte you being a compound represented by. 3. The polymer electrolyte fuel according to claim 2 , wherein in the general formula (I), R1 and R2 are bonded to each other to form a double bond, an aromatic ring, or a non-aromatic ring. Battery electrolyte. The compound represented by the general formula (I) is represented by the following general formula (II):

(Wherein ring Y represents a imide compound having a double bond or any one of aromatic or non-aromatic 5- to 12-membered rings). The electrolyte for a polymer electrolyte fuel cell according to claim 3 . The compound represented by the general formula (II) 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. X represents oxygen. 5. The electrolyte for a polymer electrolyte fuel cell according to claim 4 , which is an imide compound represented by an atom or a hydroxyl group, wherein n represents an integer of 1 to 3. 5. 6. The polymer electrolyte fuel according to claim 5 , 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 electrolyte. 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. 5. The polymer electrolyte fuel cell electrolyte according to 5 . In the above formula (III), bound R3 and R4 together form a cycloalkane, cycloalkene, bridged hydrocarbon rings, aromatic rings, and at least one that is selected from the group consisting of substituents The electrolyte for a polymer electrolyte fuel cell according to claim 5 , wherein the electrolyte is used. The compound represented by the general formula (III) is represented by the following formulas (IVa) to (IVf):

(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 according to any one of claims 5 to 8 , wherein n represents an integer of 1 to 3). Type fuel cell electrolyte. The compound represented by the general formula (III) is N-hydroxysuccinimide, N-hydroxymaleic acid imide, N-hydroxyhexahydrophthalic acid imide, N, N′-dihydroxycyclohexanetetracarboxylic imide, N-hydroxy. phthalimide, N- hydroxy tetrabromophthalic acid imide, N- hydroxy tetrachlorophthalic acid imide, N- hydroxy HET acid imide, N- hydroxy high Mick acid imide, N- hydroxyaldehyde trimellitic acid imide, N, N' dihydroxy pyromellitic acid imide, and N, according to any one of claims 5 to 9, characterized in that at least one imide compound selected from the group consisting of N'- dihydroxynaphthalene tetracarboxylic acid imide Electrolyte for polymer electrolyte fuel cell. 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. 5. An electrolyte for a polymer electrolyte fuel cell according to claim 4 , wherein at least one of them 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). The electrolyte for a polymer electrolyte fuel cell according to claim 11 , 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 acid imide, N, N′-dihydroxy-1,8; 4,5-naphthalene tetracarboxylic acid imide, N, N′-dihydroxy-1,8; 4,5-decalin tetracarboxylic acid imide and N, N ′ The electrolyte for a polymer electrolyte fuel cell according to claim 11 or 12 , which is at least one imide compound selected from the group consisting of N, N ″ -trihydroxyisocyanuric acid. A polymer electrolyte fuel cell comprising the polymer electrolyte fuel cell electrolyte according to any one of claims 1 to 13 .

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