JP2007227126A - Manufacturing method of fuel cell system and catalyst layer of fuel cell, household electric equipment, portable equipment, and transportation equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system in which a durability performance is maintained. <P>SOLUTION: An organic mediator 20 acts as a catalyst and decomposes hydrogen peroxide and hydroxyl radicals which are free radicals and which are a cause of deterioration of an electrolyte film. Because of this, the electrolyte film does not have C-F bond and C-H bond to be cleaved, and the hydroxyl radicals disappear. This system has a conductive catalyst layer, the organic mediator 20 fixed to the catalyst layer, and a base material to fix the organic mediator 20 to the catalyst layer, and this base material is composed of organic polymer particulates 41 modified by a functional group. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system, a method for producing a catalyst layer of a fuel cell, a home appliance, a portable device, and a transportation device.

As a means for solving energy problems, fuel cell technology, particularly polymer electrolyte fuel cell (PEFC) technology, has attracted attention. There are still many technical problems, and an important problem among them is deterioration of the electrolyte membrane and the catalyst layer. The electrolyte membrane serves to divide the fuel electrode (H ₂ electrode) and air electrode (O ₂ electrode) of the fuel cell and send protons (H ⁺ ) reacted at the fuel electrode to the oxygen electrode side.

However, since the electrolyte membrane is composed of a polymer, there are problems that holes are formed due to mechanical or chemical degradation, or that the electrolyte membrane is decomposed. As the chemical degradation mechanism, two mechanisms are considered, namely, H ₂ oxidation at the fuel electrode of the fuel cell and generation of hydrogen peroxide (H ₂ O ₂ ) by H ₂ reduction at the air electrode ( (Refer nonpatent literature 1.). Although this H ₂ O ₂ has a weak oxidizing power, it is stable and has a long life. For example, it is caused by metal ions eluted from the piping of the fuel cell system such as iron ions (Fe ²⁺ ) and copper ions (Cu ⁺ ). The catalytic action causes the following Fenton reaction to generate a highly reactive hydroxy radical (.OH). Hydroxy radicals exist for a short period of 1 millionth of a second, but have strong oxidizing power and are rich in reactions.

Fe ²⁺ + H ₂ O ₂ → Fe ³⁺ + · OH + OH ⁻ Formula (A1)
For this reason, when metal ions eluted from piping or the like are mixed in the electrolyte membrane, hydrogen peroxide is changed to hydroxy radicals by the Fenton reaction in the electrolyte membrane, and the electrolyte membrane may be chemically degraded by the hydroxy radicals. There is.

As a method for suppressing such deterioration of the electrolyte membrane, for example, a method of catalytically decomposing H ₂ O ₂ by dispersing and compounding metal oxides such as manganese oxide and cobalt oxide in the electrolyte membrane, There has been proposed a method for preventing radicalization of H ₂ O ₂ by dispersing and blending a peroxide stabilizer such as a tin compound in an electrolyte membrane (see Patent Document 1).

In addition, for example, a method of blending a compound having a phenolic hydroxyl group into an electrolyte membrane as an antioxidant that traps and inactivates hydroxy radicals has been proposed (see Patent Documents 1 and 2).
JP 2001-118591 A JP 2002-201352 A New Energy and Industrial Technology Development Organization Subcontractor Graduate School of Engineering, Kyoto University <FY 2001 Results Report, Research and Development of Solid Polymer Fuel Cells, Research on Degradation Factors of Solid Polymer Fuel Cells, Basic Research on Degradation Factors (1 ) Electrode catalyst / electrolyte interface degradation factors>

  However, in the example described in Patent Document 1 above, peroxide stabilizers such as metal oxides and tin compounds do not dissolve in water, so even if they are atomized, they are uniformly dispersed in the electrolyte membrane. Is difficult.

Further, when the tin compound is decomposed, the Fenton reaction may occur due to the elution of the metal as a cation in the acidic electrolyte membrane. For example, hydroxy radical (HO.), Hydroperoxyl radical (HOO.) The generation of active oxygen such as hydrogen peroxide (H ₂ O ₂ ) may be accelerated.

  Further, in the examples described in Patent Document 1 and Patent Document 2, compounds that trap and inactivate peroxide radicals such as HO. And HOO. Are not regenerated. The activating compound is consumed and it is difficult to trap radicals over time.

  Moreover, such a compound is hardly soluble in water, and the concentration of the compound in the electrolyte membrane cannot be increased.

  The present invention has been made to solve the above problems, and a fuel cell system according to the present invention includes a conductive first base material, an organic mediator fixed to the first base material, And a second base material that fixes the organic mediator to the first base material, wherein the second base material is organic polymer fine particles modified with a functional group.

  The method for producing a fuel cell catalyst layer according to the present invention comprises mixing a first base material, an organic mediator and organic polymer fine particles in a liquid dispersion medium to form an electrode catalyst ink, and using the electrode catalyst ink as a solid polymer electrolyte membrane Alternatively, the electrode catalyst layer is formed by coating on a gas diffusion layer and drying.

  Household appliances, portable devices, and transportation devices according to the present invention are characterized by using the fuel cell system according to the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell system with which performance was maintained over a long time is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the catalyst layer with which durability performance was maintained is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the household appliances, portable apparatus, and transportation apparatus which can endure a continuous operation for a long time are provided.

  Hereinafter, details of a fuel cell system, a method for producing a catalyst layer of a fuel cell, a home appliance, a portable device, and a transport device according to embodiments of the present invention will be described based on the embodiments. As an example of the embodiment, a solid polymer electrolyte type fuel cell system using a solid polymer electrolyte membrane as an electrolyte membrane is given.

  FIG. 1 is a perspective view showing an external appearance of a fuel cell stack 1 constituting a fuel cell system according to an embodiment of the present invention. FIG. 2 is a main part development view of the fuel cell stack 1.

  A fuel cell stack 1 shown in FIG. 1 has a plurality of unit cells 15 and fuel cell separators 17 that are basic units for generating power by electrochemical reaction, and then end flanges 2 are arranged at both ends. The outer periphery is configured by fastening with fastening bolts 3. The fuel cell stack 1 includes a fuel gas supply line 4 for supplying a fuel gas containing hydrogen such as hydrogen gas to each single cell 15, an air supply line 5 for supplying air as an oxidant gas, and cooling water. A cooling water supply line 6 is provided.

  FIG. 2 is a development view of the main part of the fuel cell stack 1. The MEA (membrane electrode assembly) 15 as a single cell constituting the fuel cell stack 1 and the MEA 15 are separated from other MEAs. The separator 17 is shown. The MEA 15 includes a solid polymer electrolyte membrane 11, and a fuel electrode 14a and an air electrode 14b that sandwich the solid polymer electrolyte membrane 11. Separators 17 are disposed outside the fuel electrode 14a and the air electrode 14b, respectively, and a fuel gas channel 16a and an air channel 16b are defined between the separator 17 and the fuel electrode 14a and the air electrode 14b, respectively.

  The fuel electrode 14a and the air electrode 14b are joined by catalyst layers 12a and 12b made of a conductive base material carrying an electrode catalyst, and gas diffusion layers (also referred to as GDL (abbreviation of Gas Diffusion Layer)) 13a and 13b, respectively. Has been configured. An organic mediator such as NHPI (N-hydroxyphthalimide), which will be described later, is fixed to the catalyst layers 12a and 12b. The organic mediator serves as a reducing agent at a potential lower than the reduction potential at which hydroxy radicals act as an oxidizing agent. It acts as an oxidant at a potential higher than the oxidation potential at which hydrogen peroxide acts as a reducing agent.

  The separator 17 is formed by forming carbon or metal into a plate shape and forming a gas flow path or the like on the surface thereof. The fuel gas channel 16a is formed between the fuel electrode 14a and the separator 17, and supplies hydrogen as a reaction gas to the fuel electrode 14a. The air flow path 16b is formed between the air electrode 14b and the separator 17, and supplies air as a reaction gas to the air electrode 14b. The air flow path 16b also functions as a generated water removal passage.

  In each MEA 15 of the fuel cell configured as described above, when the fuel gas is supplied to the fuel electrode 14a side, the fuel gas is supplied to the gas diffusion layer 13a from the fuel gas flow path 16a of the separator 17 in contact with the fuel electrode 14a. It passes through the layer 13a while diffusing and reaches the catalyst layer 12a. When air is supplied to the air electrode 14b, the air is supplied from the air flow path 16b of the separator 17 in contact with the air electrode 14b to the gas diffusion layer 13b, passes through the gas diffusion layer 13b while diffusing, and passes through the catalyst layer 12b. To. The electrode reaction occurs on the surface of the electrode catalyst included in the catalyst layers 12a and 12b.

Fuel electrode _{^{(anode): H 2 → 2H + +}} 2e - E 0 = 0.00 [V] ... Formula (B1)
Air electrode (positive electrode): O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O E ⁰ = 1.23 [V] (formula (B2))
In the catalyst layer 12a on the fuel electrode 14a side, the reaction of the formula (B1) proceeds and H ⁺ (proton) And e ⁻ (electrons) are generated. H ⁺ moves through the solid polymer electrolyte membrane 11 in a hydrated state and reaches the catalyst layer 12b on the air electrode 14b side. At this time, one H ⁺ ion moves along with 5 to 20 H ₂ O molecules. In the catalyst layer 12b on the air electrode 14b side, the reaction of the formula (B2) proceeds by H ⁺ , e ^−, and oxygen gas in the supplied air to generate water. At this time, electrons generated in the fuel electrode 14a move to the air electrode 14b via an external circuit 18 shown in FIG. 8 described later, so that an electromotive force is obtained, and power generation is possible. E ⁰ is represented by a standard redox potential (NHE).

The solid polymer electrolyte membrane 11 exhibits high hydrogen ion conductivity for the first time in a state swollen with a sufficient amount of water. However, since a large amount of water moves along with the H ⁺ ions moving in the solid polymer electrolyte membrane 11 to the air electrode 14b, it is necessary to always supply water to the solid polymer electrolyte membrane 11. This water is supplied as water vapor (humidified gas) from the gas flow paths 16a and 16b to the gas diffusion layers 13a and 13b, and then supplied to the solid polymer electrolyte membrane 11 through the fuel electrode 14a and the air electrode 14b. Further, of the water generated in the catalyst layer 12b on the air electrode 14b side, excess water that is not required by the solid polymer electrolyte membrane 11 passes from the catalyst layer 12b through the gas diffusion layer 13b to the outside from the air channel 16b. Is discharged.

  The reaction of the entire normal fuel cell system is as shown in equations (B3) and (B4).

2H ₂ + O ₂ → 2H ₂ O Formula (B3)
H ₂ + O ₂ → H ₂ O ₂ Formula (B4)
Formula (B3) is 4-electron reduction of oxygen, and formula (B4) is 2-electron reduction of oxygen. The reactions of formulas (B3) and (B4) proceed simultaneously as a competitive reaction. Here, the formula (B3) is the sum of elementary reactions of the positive electrode main reaction represented by the formula (B2) and the negative electrode reaction represented by the formula (B1). Similarly, the formula (B4) is the sum of elementary reactions of the positive electrode side reaction represented by the formula (B5) and the negative electrode reaction represented by the formula (B2).

O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O ₂ E ⁰ = 0.68 [V] Formula (B5)
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. FIG. 3 shows redox potentials of hydroxy radicals, oxygen, hydrogen peroxide, hydrogen, and NHPI and TEMPO described later. 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. Since the oxidation-reduction potential is affected by pH and temperature, FIG. 3 shows the standard oxidation-reduction potential corrected to the standard hydrogen electrode (NHE). The reaction proceeds when ΔE ^{0 of the} whole system, that is, the difference in redox potential is a positive value.

  The hydrogen peroxide generated in the formula (B4) is considered to disappear by the reactions shown in the formulas (B6) to (B8).

H ₂ O ₂ + H ₂ → 2H ₂ O Formula (B6)
H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O E ⁰ = 1.77 [V] Formula (B7)
2H ₂ O ₂ → 2H ₂ O + O ₂ ... Formula (B8)
Formula (B6) shows a case where, in the air electrode 14b, hydrogen peroxide is reduced to water by H ₂ crossed over from the fuel electrode 14a through the solid polymer electrolyte membrane 11. Formula (B7) shows a case where hydrogen peroxide receives hydrogen ions and electrons at the air electrode 14b and is reduced to water. Formula (B8) 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 formulas (B7) and (B9), hydrogen peroxide acts as a reducing agent for substances having a higher redox potential than hydrogen peroxide, while it has a lower redox potential than hydrogen peroxide. It is known to act as an oxidant for substances.

^{_{H 2 O 2 → O 2 +}} 2H + + 2e - E 0 = 0.68 [V] ··· formula (B9)
Here, the formula (B6) is the sum of the elementary reaction represented by the formula (B7) and the elementary reaction represented by the formula (B4). Formula (B8) is the sum of the elementary reaction represented by formula (B7) and the elementary reaction represented by formula (B9).

Next, consider a case where the fuel cell is contaminated with Fe ²⁺ ions. Hydrogen peroxide generated at the air electrode 14b is converted into a hydroxy radical by the Fenton reaction using Fe ²⁺ as a catalyst.

Fe ²⁺ + H ₂ O ₂ → Fe ³⁺ + OH ⁻ + · OH Formula (B10)
The oxidation-reduction potential of this hydroxy radical is 2.85 [V] and has an extremely high oxidizing power. As shown in the formula (B11), the hydroxy radical disappears by oxidizing the hydrogen ion.

OH + H ⁺ + e ⁻ → H ₂ O E ⁰ = 2.85 [V] (formula (B11))
However, when the supply of hydrogen (hydrogen ions) becomes insufficient due to the start / stop of the fuel cell, etc., since the hydroxyl radical has an extremely high oxidizing power, the C of the solid polymer electrolyte membrane 11 that is not originally oxidized is present. When a -F bond or a CH film is used, the CH bond may be cleaved.

  In the fuel cell system according to the embodiment of the present invention, the catalyst layers 12a and 12b have organic mediators fixed by organic polymer fine particles, and the organic mediator has a potential lower than the reduction potential at which hydroxy radicals act as an oxidizing agent. Since it acts as an oxidant at a potential higher than the oxidation potential at which hydrogen peroxide acts as a reducing agent, the organic mediator acts as a catalyst to decompose hydrogen peroxide and hydroxy radicals, which are active oxygen . For this reason, the hydroxy radical oxidizes the solid polymer electrolyte membrane 11 and disappears by the catalytic action of the organic mediator without breaking the C—F bond or C—H bond of the membrane. In addition, since the organic mediator returns to the original form by the redox cycle of the organic mediator after decomposing active oxygen such as hydroxy radicals, it can be used many times. Moreover, since the organic mediator is fixed, the effective utilization efficiency of the organic mediator is improved. Therefore, the MEA 15 is provided with a fuel cell system in which the durability performance is maintained, and consequently the durability performance is maintained. Further, since the organic polymer fine particle is a soft substrate, when the organic mediator is fixed, the contact with the solid polymer electrolyte membrane 11 is soft and the solid polymer electrolyte membrane 11 is not mechanically damaged.

Here, as an example of the organic mediator, N-hydroxyphthalimide (NHPI20) having a reversible redox cycle is exemplified, and the case where NHPI20 is immobilized on the catalyst layers 12a and 12b is shown. 4 shows phthalimide N-oxyl (PINO21) as a one-electron oxidant of NHPI20 and NHPI20 radicalized by NHPI20 and PINO ⁺ 22, a two-electron oxidant of NHPI20. It represents a mechanism in which hydroxy radicals or hydrogen peroxide disappears over a long period of time when a cycle occurs with an oxyl radical.

NHPI20 acts as a reducing agent for hydroxyl radicals, and PINO21 or two molecules of hydroxyl radicals react to form PINO21, PINO ⁺ 22 and water or hydroxide ions, and PINO21 and PINO ⁺ 22 are peroxidized, respectively. It reacts with hydrogen and returns to NHPI20. At this time, PINO 21 and PINO ⁺ 22 act as an oxidizing agent for hydrogen peroxide and decompose hydrogen peroxide into oxygen. This will be described in more detail. NHPI20 and PINO21 have a redox potential of 1.34 [V].

NHPI → PINO + H ⁺ + e ⁻ E ⁰ = 1.34 [V] (formula (B12))
PINO + H ⁺ + e ⁻ → NHPI E ⁰ = 1.34 [V] (formula (B13))
As shown in Formula (B7), Formula (B11), Formula (B12), and FIG. 3, the redox potential of the hydroxy radical generated by hydrogen peroxide and the Fenton reaction is higher than the redox potential of NHPI20. For this reason, when NHPI 20 is present, hydrogen peroxide or hydroxy radicals are reduced to water by the catalytic action of NHPI 20 as a reducing agent. In this case, as shown in formulas (B14) and (B15), NHPI20 is oxidized to PINO21 by hydroxy radicals or hydrogen peroxide.

OH + NHPI → H ₂ O + PINO Formula (B14)
H ₂ O ₂ + 2NHPI → 2H ₂ O + 2PINO (formula (B15))
Formula (B14) is the sum of the elementary reaction represented by formula (B11) and the elementary reaction represented by formula (B12). Formula (B15) is the sum of the elementary reaction represented by Formula (B7) and the elementary reaction represented by Formula (B13).

  As shown in formulas (B16), (B17), and formula (B13), PINO21, which is an oxidized form of NHPI20, is reduced to NHPI20 by oxidizing hydrogen ions, hydrogen, or hydrogen peroxide as an oxidizing agent. The

2PINO + H ₂ → 2NHPI Formula (B16)
PINO + H ⁺ + e ⁻ → NHPI E ⁰ = 1.34 [V] (formula (B13))
2PINO + H ₂ O ₂ → 2NHPI + O ₂ Formula (B17)
Formula (B16) is the sum of the elementary reaction represented by Formula (B13) and the elementary reaction represented by Formula (B1). Formula (B17) is the sum of the elementary reaction represented by formula (B13) and the elementary reaction represented by formula (B9). The redox potential of PINO22 is 1.34 [V], and is not so high as to thermodynamically break the C—F bond of the solid polymer electrolyte membrane 11 and the C—H bond of the CH-based membrane. For this reason, the solid polymer electrolyte membrane 11 is not oxidized by the PINO 22.

As described above, NHPI 20 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 21 acts as an oxidizing agent for hydrogen peroxide and oxidizes hydrogen peroxide to oxygen. In this way, the oxidation-reduction cycle rotates between NHPI 20 and PINO 21 and PINO ⁺ 22, and at the same time, the hydroxyl radicals and oxygen peroxide are deactivated, and the oxidation of the binder and the electrolyte membrane close to the electrode catalyst of the catalyst layer is performed. Provided is a fuel cell system that prevents and maintains durability performance.

  Here, NHPI is shown as an example of the organic mediator. However, when the purpose is to eliminate only hydroxy radicals, the compound has a standard redox potential in the range of 0.68 [V] to 2.85 [V]. It is preferable. In addition, 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 reduction potential at which hydrogen peroxide acts as an oxidizing agent, and Since it is necessary to act as an oxidizing agent at a potential higher than the oxidation potential acting as a reducing agent, the standard oxidation-reduction potential of this compound is preferably in the range of 0.68 V to 1.77 [V].

  Furthermore, it is more preferable if the oxidized form and reduced form of the organic mediator are relatively stable compounds. Since the actual redox potential (RHE) of each compound varies depending on various conditions such as pH and temperature, it is preferable to use a range in accordance with the conditions. However, considering the poisoning of electrode catalysts such as platinum used for electrodes, the organic mediator must be an organic compound that dissolves in water and consists only of carbon, hydrogen, oxygen, and nitrogen. preferable.

The organic mediator is fixed to the catalyst layers 12a and 12b made of a conductive substrate carrying an electrode catalyst by a second substrate made of organic polymer fine particles. The organic mediator is a low-molecular substance and is hardly soluble in water but dissolves, so that it gradually flows out by H ₂ O in the humidified gas introduced during power generation of the fuel cell. Moreover, since such an organic mediator is hardly soluble in water, the concentration cannot be increased when it is introduced into the fuel cell system. Although depending on the amount of active oxygen generated, it is desirable to dissolve the organic mediator at a high concentration in order to increase the efficiency of inactivating active oxygen. The catalyst layer is composed of an electrode catalyst in which catalyst particles are supported on a conductive carrier and a binder having proton conductivity, and the binder generally uses the same components as the electrolyte membrane. This binder preferably covers a part of the electrode catalyst in order not only to improve proton conductivity but also to stably maintain the electrode structure and enhance electrode performance. Therefore, there is a concern that the hydrogen peroxide generated by the electrode catalyst and the binder are closest to each other, and the metal ions eluted from the piping are mixed into the catalyst layer, so that the frequency of deterioration of the binder adjacent to the electrode catalyst is severe. Is done. In particular, there is a strong concern that the binder portion that coats the electrode catalyst is chemically degraded by hydroxy radicals, leading to a decrease in ion conductivity and instability of the electrode structure.

  In the fuel cell system according to the embodiment of the present invention, the organic mediator is fixed by the organic polymer fine particles modified with the functional group, thereby preventing the organic mediator from flowing out of the catalyst layer or the outflow speed. By reducing the value, the effect can be maintained. Even if the organic mediator is poorly soluble in water, the organic mediator is adsorbed as a single molecule due to the organic mediator being immobilized, so that the organic mediator is uniformly applied to the catalyst layers 12a and 12b. The same effect as the concentration improvement is obtained. Thus, the effective utilization efficiency of an organic mediator improves by the concentration effect more than the saturation density of the organic mediator which is hardly soluble. As a result, the antioxidant effect of the binder and the polymer electrolyte membrane close to the electrode catalyst of the catalyst layer, particularly the HC-based membrane is obtained, the chemical durability is improved, and the durability of the fuel cell is also improved.

  In addition, although the outflow prevention effect of the organic mediator with respect to water can also be considered as follows, the present invention is not limited to such an idea. The organic mediator is adsorbed or chemically bonded to the organic polymer fine particles and immobilized, so that the solvent between the organic mediator and the organic polymer fine particles is larger than the solubility in humidified water or water generated by the reaction on the air electrode side. High immobilization force, that is, adsorption force and chemical bonding force can be expressed. For this reason, it is possible to prevent the organic mediator adsorbed or chemically bonded to the organic polymer fine particles from dissolving or flowing out into water.

  Examples of the method of immobilizing the organic mediator on the catalyst layers 12a and 12b include (1) a method of adsorbing the organic mediator to the organic polymer fine particles, and (2) a method of chemically bonding the organic mediator to the organic polymer fine particles. . That is, if an appropriate amount of a compound obtained by adsorbing or chemically bonding organic mediators to organic polymer fine particles is contained in the catalyst layer, the organic mediator is immobilized on the catalyst layer. In particular, the immobilization method (2) is desirable because it is very excellent in the effect of inhibiting dissolution in water (see Table 1 in the Examples). In the method (1), the outflow can be replenished by continuously supplying the organic mediator aqueous solution from the fuel electrode side.

  As the immobilization method of (1) above, the organic mediator solution is dispersed in the organic polymer fine particles and then adsorbed by removing the solvent. For example, the organic mediator is adsorbed by impregnating the organic polymer fine particles into the organic polymer fine particles. There is a way to make it. However, the method is not limited to these, and various conventionally known methods can be applied as a method for adsorption and immobilization.

  The organic polymer fine particles used for the immobilization of (1) are desirably organic polymers into which a functional group is introduced from the viewpoint of obtaining a high adsorption force by hydrogen bonding, and the functional group includes a carboxyl group, a hydroxyl group, Any one selected from an alkoxyl group, an alkoxycarbonyl group, an acyl group, and a sulfone group can be mentioned, and a carboxyl group is preferable in consideration of oxidation resistance of a functional group.

  The size of the organic polymer fine particles used for the immobilization of (1) is not particularly limited as long as the effect on the electrode reaction of the catalyst layer can be suppressed and the intended purpose can be achieved. . As a general rule, the organic polymer fine particles preferably have an average particle size in the range of 0.1 to 1000 [μm], preferably 10 to 100 [μm].

  The organic polymer material used as the base of the organic polymer fine particles preferably has a functional group that promotes hydrogen bonding with the organic mediator, and is limited as long as it has a carboxyl group such as polyacrylic acid or polyamic acid. Never happen. Polyethylene having no carboxyl group may be oxidized with fuming nitric acid to introduce a carboxyl group.

  The amount of the organic mediator used is preferably 0.001 to 30 [parts by weight], more preferably 0.01 to 10 [parts by weight] based on 100 [parts by weight] of the organic polymer fine particles. preferable. Although it is desirable to adjust so that the total amount of the organic mediator used is adsorbed on the organic polymer fine particles, the total amount of the organic mediator does not necessarily have to be adsorbed on the organic polymer fine particles. That is, depending on the amount of organic mediator used, the adsorption capacity of the organic polymer fine particles may be exceeded. In such a case, a portion of the organic mediator cannot be adsorbed and is simply fixed by adhesion, which is weaker than the adsorption force. May be. Since the organic mediator fixed by adhesion easily dissolves in water and flows out, the amount of adhesion can be easily checked by, for example, a batch shaking test shown in Examples described later. Based on these results, the optimum blending amount can be determined according to the type and size of the organic polymer fine particles, the type of organic mediator, and the like.

  An example of replenishing the spilled organic mediator is shown below. Since the generation of active oxygen continues semipermanently as long as power is generated in the fuel cell stack 1, the organic mediator is supplied to the fuel electrode 14a or the air electrode 14b by the mediator supply means 30 provided outside the fuel cell stack 1. It is more effective to supply continuously as a solution, and it is particularly preferable to supply from the fuel electrode 14a side of the fuel cell stack 1. In this case, even if power generation is continued in the fuel cell stack 1 and active oxygen continues to be generated, the hydroxyl radicals are surely inactivated and erased to prevent deterioration of the solid polymer electrolyte membrane 11. be able to. Even in an environment where the organic mediator is easily oxidized, the efficiency of inactivating the hydroxy radical does not change because the organic mediator is continuously supplied from the outside.

  When the organic mediator is supplied from the fuel electrode 14a side, for example, as shown in FIG. 6, the mediator supply means 30, a mediator solution tank 31 in which the organic mediator solution is sealed, and the mediator solution are supplied to the fuel cell stack 1 A liquid feed pump 32 that supplies the fuel electrode 14a, a mediator solution tank 33 that connects the mediator solution tank 31 and the liquid feed pump 32, and a mediator that connects the liquid feed pump 13 and the fuel gas flow path 16a. And a solution supply pipe 34. As described above, the fuel gas flow path 16a and the air flow path 16b for supplying air and hydrogen as reaction gases are formed on the surface of the separator 17 of the fuel cell stack 1. Each reactive gas passes through the fuel gas passage 16a and the air passage 16b in a state of being humidified by a bubbler (not shown) as shown in the exploded perspective view of the fuel cell stack 1 constituting the fuel cell system shown in FIG. To do. At this time, the mediator solution is supplied from the mediator solution tank 31 to the fuel gas channel 16 a via the mediator solution line 33 and the mediator solution supply line 34 by the driving force of the liquid feed pump 32. The mediator solution supplied to the fuel gas channel 16a diffuses from the fuel electrode 14a side to the solid polymer electrolyte membrane 11 as shown in the explanatory view for explaining the movement of the substance in the membrane electrode assembly 15 shown in FIG. It is uniformly distributed in the air electrode 14b according to the concentration gradient.

  Thus, it is preferable to supply the mediator as a mediator solution from the side of the fuel electrode 14a. The reason why active oxygen such as hydroxy radicals is likely to be generated is near the three-phase interface of the air electrode. . As shown in the schematic diagram showing the three-phase interface in the air electrode shown in FIG. 8, 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 exist and are very easily oxidized. For this reason, when the mediator is introduced from the air electrode, the mediator itself may be oxidized and lost at the three-phase interface of the air electrode regardless of the presence or absence of hydroxy radicals, and the deactivation efficiency of active oxygen is reduced. there's a possibility that.

Further, as described above, the air flow path 16b of the separator 17 also functions as a generated water removal passage. For this reason, mediators that are excessively supplied and become unnecessary, or oxidized mediators that have become inactive by deactivating active oxygen are oxidized by a catalyst on the three-phase interface to produce CO ₂ , H ₂ O, or N _2. Then, it can be discharged from the discharge pipe 35 shown in FIG. For this reason, it is possible to prevent the mediator from becoming unstable radicals or peroxides and causing new oxidation reaction initiators to cause electrolyte membrane deterioration.

  When preparing the mediator solution, it may be difficult to dissolve in the air electrode, but it is important to dissolve in the solvent. In the case of insolubility, the entry and exit of hydrogen radicals becomes impossible, and the effect of inactivating the hydroxy radicals is not sufficiently exhibited. For this reason, it is necessary to select a solvent in which the organic mediator is dissolved, and an aqueous solution, 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, if the organic mediator can be dissolved, an aqueous solution is preferable from the viewpoint of power generation performance.

  As the immobilization method of (2) above, there is a method in which an amino group substituent is introduced into an organic mediator and reacted with a carboxyl group of organic polymer fine particles to cause chemical bonding. Various methods can be applied to bond the organic mediator to the organic polymer fine particles through the surface functional group. As an example, FIG. 9 shows an example of a compound in which the aforementioned NHPI 20 which is a kind of organic mediator is bonded to organic polymer fine particles via an amide bond. In order to obtain this compound, as shown in FIG. 9A, for example, after obtaining a compound 41 in which a carboxyl group is introduced into polyethylene 40 using fuming nitric acid, for example, NHPI 20 having an amino group is mixed with an appropriate solvent ( For example, it is dissolved in benzene.) And subjected to a dehydration condensation reaction with the compound 41 for several tens of hours to obtain organic polymer fine particles 42 chemically bonded with NHPI20. As another example, as shown in FIG. 9B, a copolymer 44 having a carboxyl group and NHPI 20 are reacted in advance to obtain a compound 44. As another example, there is a method in which NHPI 20 is directly reacted with the condensable polymer material 45 and chemically bonded to obtain the compound 46.

  The size of the organic polymer fine particles used for the immobilization in (2) can suppress the influence on the electrode reaction of the catalyst layer and achieve the intended purpose, as in (1) above. There is no particular limitation as long as it is present. As a rough guide, the organic polymer fine particles preferably have an average particle size in the range of 0.1 to 1000 [μm], preferably 10 to 100 [μm].

  The amount of the organic mediator used for the immobilization in (2) is preferably 0.001 to 30 [parts by weight], more preferably 0.01 to 100 parts by weight of the organic polymer fine particles. -10 [parts by weight] is preferably used. Although it is desirable to adjust so that the total amount of organic mediator used is chemically bonded to the organic polymer fine particles, the total amount of organic mediator does not necessarily have to be chemically bonded to the organic polymer fine particles. That is, depending on the amount of the organic mediator used, the number of surface carboxyl groups of the organic polymer fine particles that can chemically bond with the organic mediator may be exceeded. In such a case, the organic polymer fine particles may be fixed not by chemical bonding but by partial adsorption or simply adhesion. Of these, the adsorbed component can obtain the same outflow prevention effect as the immobilization of (1) above. For this reason, a sufficiently high immobilizing force can be obtained only by the above (2), but a higher immobilizing force can be expressed by using the methods (1) and (2). Since the organic mediator fixed by adhesion easily flows out and dissolves in water, the amount of adhesion can be easily examined by, for example, a batch shaking test shown in the examples described later. Based on these results, the optimum blending amount can be determined according to the type and size of the organic polymer fine particles, the type of organic mediator, and the like.

  In the present invention, the immobilization method is not limited to the above, and the organic mediator may be directly immobilized on a conductive carrier such as carbon used in the catalyst layer by chemical bonding or chemical adsorption. In this case, it is necessary to pay sufficient attention to the amount of immobilization so that the catalyst particles such as platinum are dispersed and supported, and the electrode reaction is not hindered.

  The content of the organic mediator in the catalyst layer is not particularly limited as long as it is an amount capable of suppressing the influence of the catalyst layer on the electrode reaction and effectively exhibiting the effects of the present invention. In addition, since it varies depending on the amount of organic mediator used with respect to the organic polymer fine particles, etc., it cannot be defined uniquely. However, as a rough guide, the organic mediators 1 to 50 with respect to 100 [parts by weight] of the total catalyst layer [Parts by weight] is preferably used, more preferably 1 to 10 [parts by weight].

  The polymer used as the base of the organic polymer fine particles is not limited to a thermosetting or thermoplastic polymer, and can be used. Thermosetting resins include those based on phenolic resin (PF), urea resin (UF), melamine resin (MF), unsaturated polyester (UP), epoxy resin (EP), polyimide resin (PI), heat Plastic polymers include polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), acrylic resin (PMMA), polyacetal (POM), polyamide (PA), polycarbonate (PC), PBT Resin (PBT), PET resin (PET), PPS resin (PPS), Polysulfone (PSU), Polyetherether (PEEK), Polyethersulfone (PES), Polyetherimide (PEI), Polyetherketone (PEK) Can be used.

  The functional group possessed by the organic polymer fine particle is a carboxyl group, and the chemical bond with the organic mediator is a bond resulting from the reaction between the hydroxyl group or amino group introduced into the organic mediator and the carboxyl group possessed by the organic polymer fine particle. It is preferable. In this case, the organic polymer fine particles are a copolymer of any one selected from polyethylene, polypropylene, polystyrene, polystyrene and acrylic resin and a polymer having a carboxyl group, for example, a copolymer of acrylic acid. May be. The organic polymer fine particles may be a polymer based on any one selected from polyethylene, polypropylene, polystyrene, polystyrene, and acrylic resin, and having a carboxyl group introduced by oxidation treatment. As a method of introducing a carboxyl group, there is a method of introducing a carboxyl group by oxidizing the base with fuming nitric acid or the like. Further, in order to obtain organic polymer fine particles having a carboxyl group, it may be a reaction intermediate of a condensed polymer in which a carboxyl group remains, which is condensed with a carboxylic acid as a monomer. In addition, a reaction intermediate in which a carboxyl group generated by reacting a monomer having an excess carboxylic acid substituent more than dicarboxylic acid remains, and the reaction intermediate is polyimide resin, polyamide, polycarbonate, PBT resin, PET A polymer reaction intermediate selected from a resin, a PPS resin, and a polyetherimide, for example, a polyamic acid that is a reaction intermediate of polyimide can be used, but is not limited thereto. The organic mediator is immobilized on the organic polymer fine particles by chemical bonds with the functional groups of the organic polymer fine particles.

  In the embodiment of the present invention, as described above, the organic mediator is fixed to the catalyst layers 12a and 12b. However, the organic mediator may be added to or fixed to the solid polymer electrolyte membrane 11. Even if the organic mediator is immobilized, hydrogen radicals can enter and exit, and the catalytic function for eliminating active oxygen is not lost.

The organic mediator is preferably a compound represented by the general formula (I).

However, R1 and R2 represent the same or different arbitrary substituents, and X represents an oxygen atom or a hydroxyl group. In general formula (I), R1 and R2 are more preferably bonded to each other to form a double bond, an aromatic ring, or a non-aromatic ring.

Furthermore, this compound is preferably an imide compound represented by the general formula (II).

However, the ring Y1 represents any one kind of aromatic or non-aromatic 5- to 12-membered rings having a double bond.

  By immobilizing the above-described compounds on the catalyst layers 12a and 12b and coexisting them in the solid polymer electrolyte membrane 11, elementary reactions represented by formulas (B18) and (B19) proceed. Then, only when the hydroxy radical or hydrogen peroxide enters the solid polymer electrolyte membrane 11, the above compound supplies the hydrogen radical, and efficiently reduces the hydroxy radical or hydrogen peroxide to water, resulting in the electrolyte membrane. Suppresses oxidation.

> NOH + OH →> NO · + H ₂ O Formula (B18)
2 (> NOH) + H ₂ O ₂ → 2 (> NO ·) + 2H ₂ O Formula (B19)
Further, the N-oxyl radical (> NO.) Generated by the hydrogen supply draws out hydrogen ions from hydrogen or hydrogen peroxide by the elementary reactions shown in the formulas (B20) to (B22), and the original hydroxyimide (> NOH) ).

2 (> NO ·) + H ₂ → 2 (> NOH) Formula (B20)
> NO ・ + H ⁺ + e ⁻ →> NOH ... Formula (B21)
2 (> NO ·) + H ₂ O ₂ → 2 (> NOH) + O ₂ ... Formula (B22)
As described with reference to FIG. 4, when NHPI is used as a representative example of a compound having a hydroxyimide group, as shown in FIG. 4, NHPI 20 acts as a reducing agent on hydroxy radicals, and PINO 21, Alternatively, two molecules of hydroxyl radicals react to generate PINO21, PINO ⁺ 22 and water or hydroxide ions, and PINO21, PINO ⁺ 22 each react with hydrogen peroxide to return to NHPI20. At this time, PINO 21 and PINO ⁺ 22 act as an oxidizing agent for hydrogen peroxide and decompose hydrogen peroxide into oxygen. Thus, hydrogen peroxide and hydroxy radicals disappear for a long period of time due to the oxidation-reduction cycle between NHPI 20 and PINO 21 and PINO ⁺ 22.

  In addition, organic mediators involve 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 radical, the hydroxy radical disappears even when the hydroxy radical generated during the decomposition of hydrogen peroxide is present at a location away from the organic mediator. FIG. 10 shows this mechanism. As shown in FIG. 10, for example, when NHPI 20 is used as such a compound, a Groththuss Mechanism that exchanges and carries hydrogen radicals between NHPI 20 and water molecules 50 occurs. NHPI 20 reacts with water molecule 50a existing in the vicinity thereof, and exchanges hydrogen radicals between water molecule 50a and water molecule 50b existing in the vicinity thereof. The water molecule 50b exchanges hydrogen radicals with the water molecule 50c existing in the vicinity thereof. The water molecule 50c exchanges the hydroxyl radical 51a and the hydrogen radical existing in the vicinity thereof, and the hydroxy radical 51a disappears by this exchange. Since the reduction reaction proceeds while supplying hydrogen radicals to the water molecules 50 in this way, even when NHPI 20 and the hydroxy radical 51 are separated from each other, a catalytic reaction for eliminating the hydroxy radical 51 proceeds and the hydroxy radical 51 disappears. It becomes possible to do. Moreover, PINO21 which is a radical body of NHPI20 is also involved in the reaction. A radical is exchanged between PINO 21 and 50 g of water molecules present in the vicinity thereof. The water molecule 50g exchanges hydrogen radicals with the water molecule 50h existing in the vicinity thereof. In this way, the radicals are exchanged one after another, reach the hydroxy radical, and the hydroxy radical disappears. As described above, when the fuel cell system according to the present embodiment includes the organic mediator, it is possible to eliminate hydroxy radicals existing in a wide range of the catalyst layer and further the solid polymer electrolyte membrane.

  What is important in selecting a compound (organic mediator) having such a catalytic action is the stability, durability, heat resistance, and solubility in the catalyst layer 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. Further, considering that the steady-state operating temperature of the fuel cell is 80 to 90 [° C.] and the heat resistance of the electrolyte membrane is 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 make this compound contain uniformly in a catalyst layer, although it may be hardly soluble, it is necessary to melt | dissolve with respect to water. If it becomes insoluble in water, it will precipitate in the catalyst layer or the electrolyte membrane, making it impossible for hydrogen radicals to enter and exit, thus losing the effect of eliminating active oxygen, that is, the catalytic function. Therefore, when introducing this compound into the electrolyte membrane in addition to the catalyst layer, it can be said that it is preferable to add it rather than immobilize it.

The compound is preferably an imide compound represented by the general formula (III).

However, 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 an oxygen atom or a hydroxyl group, and n represents an integer of 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.

  Examples of the aryl group include a phenyl group and a naphthyl group. Examples of the cycloalkyl group include a cyclopentyl, cyclohexyl, and cyclooctyl group. Examples of the alkoxy group include about 1 to 10 carbon atoms such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, t-butoxy, pentyloxy, hexyloxy group, and preferably about 1 to 6 carbon atoms. More preferred 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 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 hydrocarbon represented by a 5-norbornene ring. Non-aromatic bridged rings such as rings, aromatic rings such as benzene rings and naphthalene rings. In addition, these rings may have a substituent.

The compound represented by the general formula (III) is preferably a compound represented by the formulas (IVa) to (IVf) particularly from the viewpoint of stability, durability, and solubility of the compound.

Provided that 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, and n is Represents an integer of 1 to 3;

  Among the substituents R3 to R6, the alkyl group includes an alkyl group similar to the alkyl group described above, particularly an alkyl group having about 1 to 6 carbon atoms, and the alkoxy group includes a carbon group selected from the alkoxy groups similar to those described above. Examples of the alkoxycarbonyl group include lower alkoxycarbonyl groups having about 1 to 4 carbon atoms in the alkoxy moiety.

  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.

  As a more preferable form of the imide compound, N-hydroxysuccinimide, N-hydroxymaleimide, N-hydroxyhexahydrophthalimide, N, N from the viewpoint of availability of the compound, ease of synthesis, and cost. '-Dihydroxycyclohexanetetracarboxylic imide, N-hydroxyphthalic imide, N-hydroxytetrabromophthalic imide, N-hydroxytetrachlorophthalic imide, N-hydroxyhetic imide, N-hydroxyhymic imide, N It is preferably at least one imide compound selected from the group consisting of hydroxytrimellitic acid imide, N, N′-dihydroxypyromellitic imide and N, N′-dihydroxynaphthalene tetracarboxylic imide. This compound can be used as a catalyst in the electrolyte membrane.

These imide compounds are obtained by a conventional imidization reaction, for example, by reacting a corresponding acid anhydride with hydroxylamine (NH ₂ OH) to open a ring of acid anhydride, and then ring-closing and imidizing. Can be prepared.

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

However, X represents an oxygen atom or a hydroxyl group. R7 to R12 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 oxycarbonyl group, an acyl group, or an acyloxy group. Moreover, at least two of R7 to R12 may be bonded to each other to form a double bond or an aromatic or non-aromatic ring. At least one of the rings may have an N-substituted cyclic imide group.

In the compound having an N-substituted cyclic imide skeleton, both the 5-membered ring and the 6-membered ring are hydrolyzed as shown in the formulas (B23) and (B24), but the 6-membered ring is more hydrolyzed than the 5-membered ring. Is slow and has high hydrolysis resistance.

For this reason, when the compound having an N-substituted cyclic imide skeleton is a 6-membered cyclic imide, it functions as an organic mediator for a long period of time, so that durability is also improved.

  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.

  Examples of the aryl group include a phenyl group and a naphthyl group. Examples of the cycloalkyl group include a cyclopentyl, cyclohexyl, and cyclooctyl group. Examples of the alkoxy group include about 1 to 10 carbon atoms such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, t-butoxy, pentyloxy, hexyloxy group, and preferably about 1 to 6 carbon atoms. More preferred 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 R7 to R12 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 a compound represented by the general formula (V), R7 to R12 are all hydrogen atoms, and N-hydroxyglutarimide (NHGI60) having a reversible redox cycle is mentioned. The case where it introduces to a battery system is shown. FIG. 11 shows NHGI60, NHGI60 radicalized as one-electron oxidant of NHGI60, glutamic acid N-oxyl (GINO61) and NHGI60 two-electron oxidant, GINO ⁺ 62. NHGI60 hydroxyimide group and GINO61 It represents a mechanism in which hydroxy radicals or hydrogen peroxide disappears over a long period of time when a cycle is cycled between N-oxyl radicals.

NHGI60 is GINO61 acts as a reducing agent to the hydroxy radicals, or react two molecules of hydroxy radicals GINO61, GINO ⁺ 62 and water or generate hydroxide ions,, GINO61, GINO ⁺ 62 respectively peroxide It reacts with hydrogen and returns to NHGI60. At this time, GINO 61 and GINO ⁺ 62 act as an oxidizing agent for hydrogen peroxide and decompose hydrogen peroxide into oxygen. This will be described in more detail. NHGI60 and GINO61 have an oxidation-reduction potential of 1.39 [V].

_{^{NHGI → GINO + H + + e}} - E 0 = 1.39 [V] ··· formula (B25)
GINO + H ⁺ + e ⁻ → NHGI E ₀ = 1.39 [V] (formula (B26))
As shown in the formulas (B7) and (B11), the redox potential of the hydroxy radical generated by the hydrogen peroxide and Fenton reaction is higher than the redox potential of NHGI41. For this reason, when NHGI41 is present, hydrogen peroxide or hydroxy radical is reduced to water by the catalytic action of NHGI41. In this case, as shown in the formulas (B27) and (B28), NHGI41 functions as a reducing agent, and NHGI41 is oxidized to GINO42 by a hydroxyl radical or hydrogen peroxide.

OH + NHGI → H ₂ O + GINO Formula (B27)
H ₂ O ₂ + 2NHGI → 2H ₂ O + 2GINO Formula (B28)
Formula (B27) is the sum of the elementary reaction represented by formula (B11) and the elementary reaction represented by formula (B25). Formula (B28) is the sum of the elementary reaction represented by formula (B7) and the elementary reaction represented by formula (B26).

  As shown in formulas (B29), (B30), and (B26), GINO42, which is an oxidized form of NHGI41, is reduced to NHGI41 by oxidizing hydrogen ions, hydrogen, or hydrogen peroxide as an oxidizing agent. The

2GINO + H ₂ → 2NHGI Formula (B29)
GINO + H ⁺ + e ⁻ → NHGI E ⁰ = 1.39 [V] (formula (B26))
2GINO + H ₂ O ₂ → 2NHGI + O ₂ Formula (B30)
Formula (B29) is the sum of the elementary reaction represented by formula (B26) and the elementary reaction represented by formula (B1). Formula (B30) is the sum of the elementary reaction represented by formula (B26) and the elementary reaction represented by formula (B9). The oxidation-reduction potential of GINO42 is 1.39 [V], and is not so high as to thermodynamically break the C—F bond of the solid polymer electrolyte membrane or the CH bond of the CH-based membrane. For this reason, the electrolyte membrane is not oxidized by GINO42.

As described above, NHGI 60 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 61 acts as an oxidizing agent for hydrogen peroxide and oxidizes hydrogen peroxide to oxygen. In this way, at the same time as the oxidation-reduction cycle rotates between NHGI 60 and GINO 61, GINO ⁺ 62, the hydroxyl radicals and oxygen peroxide are inactivated, and the oxidation of the binder and the electrolyte membrane close to the electrode catalyst of the catalyst layer is performed. Provided is a fuel cell system that prevents and maintains durability performance.

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

However, R13 to R18 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.

  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 an imide compound having at least one 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. This 6-membered cyclic imide, like the 5-membered cyclic imide, coexists in the electrolyte membrane, whereby the elementary reactions shown in the formulas (B31) and (B32) proceed. 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 (B31)
2 (> NOH) + H ₂ O ₂ → 2 (> NO ·) + 2H ₂ O Formula (B32)
Further, the N-oxyl radical (> NO.) Generated by the hydrogen supply draws out hydrogen ions from hydrogen or hydrogen peroxide by the elementary reactions shown in the formulas (B33) to (B35), and the original hydroxyimide (> NOH) ).

2 (> NO ·) + H ₂ → 2 (> NOH) Formula (B33)
> NO ・ + H ⁺ + e ⁻ →> NOH ... Formula (B34)
2 (> NO ·) + H ₂ O ₂ → 2 (> NOH) + O ₂ Formula (B35)
As described with reference to FIG. 11, when NHGI 60 is used as a representative example of a compound having a hydroxyimide group, as shown in FIG. 11, NHGI 60 acts as a reducing agent on hydroxy radicals, thereby causing GINO 61, Alternatively, two molecular hydroxyl radicals react to generate GINO61, GINO ⁺ 62 and water or hydroxide ions, and GINO61, GINO ⁺ 62 each react with hydrogen peroxide to return to NHGI60. At this time, GINO 61 and GINO ⁺ 62 act as an oxidizing agent for hydrogen peroxide and decompose hydrogen peroxide into oxygen. Thus, hydrogen peroxide and hydroxy radicals disappear for a long period of time due to the oxidation-reduction cycle between NHGI 60 and GINO 61 and GINO ⁺ 62.

  In addition, the organic mediator of an imide compound having a 6-membered ring that the fuel cell system according to the present embodiment is concerned with 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 lost even if they are present at locations away from the compound. This mechanism is the same as the mechanism shown in FIG. 10, and a growth mechanism occurs in which hydrogen radicals are exchanged between the imide compound and water molecules. For this reason, even when the imide compound and the hydroxy radical are separated from each other, the catalytic reaction for eliminating the hydroxy radical proceeds, and the hydroxy radical can be lost. For this reason, it becomes possible to lose | dissolve the hydroxy radical which exists in the wide range in a solid polymer electrolyte membrane.

  As described above, when the fuel cell system according to the present embodiment includes the organic mediator, it is possible to eliminate hydroxy radicals existing in a wide range of the catalyst layer and the electrolyte membrane. Furthermore, when the organic mediator 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.

  The organic mediator preferably has a standard redox potential greater than 0.68 [V] (NHE) and less than 1.00 [V] (NHE). 0.68 [V] is a potential at which hydrogen peroxide acts as a reducing agent, and it becomes possible to oxidize hydrogen peroxide when the organic mediator has an oxidation-reduction potential higher than this. On the other hand, the reason why the upper limit of the oxidation-reduction potential is set to 1.00 [V] is to reduce the oxidizing power of the organic mediator. When a fluorine-based membrane is used as the electrolyte membrane, there is no problem even if it is 1.00 [V] or higher. However, when a hydrocarbon-based electrolyte membrane is used, the redox potential of the organic mediator is 1.00 [V] or higher. If present, the film may be oxidized. The potential at which the fluorine-based electrolyte membrane undergoes oxidation is 2.5 [V] or more, and it is not oxidized at all with an oxidizing power of 1.00 [V]. On the other hand, in the case of a hydrocarbon-based electrolyte membrane, when considered by substituting a typical organic compound, 2.00 [V] for benzene, 1.93 [V] for toluene, and 1.58 [x] for xylene. V], and the potential to be oxidized is smaller than that of the fluorine-based one, and is easily oxidized. Thus, when the redox potential of the organic mediator is increased, the hydrocarbon-based electrolyte membrane may be oxidized by the organic mediator. Therefore, by setting the upper limit of the oxidation-reduction potential of the organic mediator to 1.00 [V] or less, application is possible without oxidizing the hydrocarbon film.

The compound represented by the general formula (I) may be a compound represented by the general formula (VII).

However, R19-R21 is an alkyl group or an alkyl group partially substituted with an arbitrary group, and R19-R21 may be chain, cyclic, or branched. R19 to R21 may be bonded to each other to form a ring, and may contain oxygen and nitrogen atoms. When the compound represented by the general formula (VII) is used, the redox potential is low and the oxygen reduction reaction is further promoted. In the compound represented by the general formula (VII), examples of the substituents R19 to R21 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 preferably a compound represented by the general formula (VIII).

However, R19 to R24 are an alkyl group or an alkyl group partially substituted with an arbitrary group, and R19 to R24 may be a chain, a ring, or a branch. R20 and R21, or R23 and R24 may be bonded to each other to form a ring, and may contain oxygen and nitrogen atoms. In the compound represented by the general formula (VII), examples of the substituents R19 to R24 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 preferably a compound represented by the general formula (IX).

In ring Y2, R19 and R22 are bonded to form either a 5-membered ring or a 6-membered ring. Examples of such a ring include 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 carbonization typified by a 5-norbornene ring. Non-aromatic bridged rings such as hydrogen 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 preferably a compound represented by the general formula (X).

However, Z is a kind of substituent 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 hydrogen atom-containing substituent. Show. When Z is an alkyl group, a part of the alkyl group may be substituted with an arbitrary group, a part of the group may be a chain, a ring, or a branch, and oxygen and nitrogen atoms It may be included. When Z is an aryl group, it may be an aryl group partially substituted with an arbitrary group, and may contain oxygen and nitrogen atoms. Since the compound represented by the general formula (X) is difficult to hydrolyze, it can be used for a long time when used as an organic mediator, and the durability is further improved.

  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 naphthyl 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.

  An 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. 12 (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) may be a compound represented by the general formula (XI).

However, Z is a kind of substituent 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 hydrogen atom-containing substituent. To express. When Z is an alkyl group, a part of the alkyl group may be substituted with an arbitrary group, a part of the group may be a chain, a ring, or a branch, and oxygen and nitrogen atoms It may be included. When Z is an aryl group, it may be an aryl group partially substituted with an arbitrary group, and may contain oxygen and nitrogen atoms.

The compound represented by the general formula (IX) may be a compound represented by the general formula (XII).

However, Z is a kind of substituent 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 hydrogen atom-containing substituent. Show. When Z is an alkyl group, a part of the alkyl group may be substituted with an arbitrary group, a part of the group may be a chain, a ring, or a branch, and oxygen and nitrogen atoms It may be included. When Z is an aryl group, it may be an aryl group partially substituted with an arbitrary group, and may contain oxygen and nitrogen atoms. Since these compounds are also difficult to hydrolyze like the compounds represented by the general formula (X), they can be used for a long time when used as a catalyst, and the amount of catalyst used can be further reduced. . 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 compounds represented by general formula (XI) and general formula (XII) are shown in FIGS. Examples of the compounds represented by the general formula (XI) and the general formula (XII) include PROXYL (2,2,5,5-tetramethylpyrrolidine-1-oxyl), DOXYL (4,4-dimethyloxazolidine-3) -Oxyl). These compounds also have a reversible redox cycle similar to TEMPO, and the redox potential is in the range of 0.68 [V] to 1.00 [V]. For this reason, these compounds also act as an oxidizing agent for hydrogen peroxide to oxidize hydrogen peroxide to oxygen, and act as a reducing agent for hydroxy radicals to reduce hydroxy radicals to water.

  FIG. 16 shows a redox mechanism in another example of the antioxidant used in the fuel cell system in the present embodiment. Here, the redox cycle of TEMPO 70 as an organic mediator is shown, and the mechanism of decomposition of hydrogen peroxide and hydroxy radicals by TEMPO 70 is shown.

  As shown in (B36) and formula (B37), hydrogen peroxide acts as a reducing agent for substances having a higher oxidation-reduction potential than hydrogen peroxide, while it becomes a substance having a lower oxidation-reduction potential than hydrogen peroxide. On the other hand, it is known to act as an oxidizing agent.

H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O E ⁰ = 1.77 [V] (formula (B36))
^{_{H 2 O 2 → O 2 +}} 2H + + 2e - E 0 = 0.68 [V] ··· formula (B37)
TEMPO70 is an N-hydroxyimide derivative having a reversible redox cycle, and is redoxed by the elementary reactions shown in formulas (B38) and (B39), and its redox potential is 0.81 [V].

TEMPO ⁺ + e ⁻ → TEMPO E ⁰ = 0.81 [V] (formula (B38))
TEMPO → TEMPO ⁺ + e ⁻ E ⁰ = 0.81 [V] (formula (B39))
The redox potential of TEMPO 70 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 (TEMPO70) of TEMPO, which is a reductant, acts as a reducing agent on the hydroxy radical to supply electrons (e ⁻ ) to the hydroxy radical generated in the electrolyte membrane, thereby generating OH ^−. To reduce.

^{TEMPO + · OH → TEMPO + +} OH - ··· formula (B40)
On the other hand, TEMPO ⁺ 71, which is an oxidant, acts as an oxidizing agent for hydrogen peroxide to extract hydrogen, oxidizes hydrogen peroxide to oxygen, and TEMPO ⁺ 71 recovers to a reduced form (TEMPO 70). . In this reaction, there are two reaction pathways that recover directly to TEMPO70 as shown in formula (B41) and two pathways that recover to TEMPO70 via TEMPO-H72 as shown in formula (B42) and formula (B43). it is conceivable that.

2TEMPO ⁺ + H ₂ O ₂ → 2TEMPO + 2H ⁺ + O ₂ Formula (B41)
TEMPO ⁺ + H ₂ O ₂ → TEMPO-H + H ⁺ + O ₂ Formula (B42)
TEMPO-H + · OH → TEMPO + H ₂ O ... Formula (B43)
TEMPO ⁺ 71 recovers a reduced form, that is, TEMPO 70, and then reduces the hydroxy radical again. In this way, the TEMPO 70 starts a redox cycle between the reductant and the oxidant, and at the same time inactivates the hydroxy radicals and oxygen peroxide to prevent the oxidation of the electrolyte.

Thus, even when TEMPO70 is used as the organic mediator, the oxidation-reduction cycle rotates between TEMPO70, TEMPO ⁺ 71, and TEMPO-H72, and at the same time, the hydroxyl radicals and oxygen peroxide are inactivated, Provided is a fuel cell system which prevents oxidation of a binder and an electrolyte membrane adjacent to an electrode catalyst and maintains durability performance.

  In this embodiment, a fuel cell system of a solid polymer fuel cell using hydrogen as a fuel is taken as an example. However, the fuel cell system according to the embodiment of the present invention is a proton-conducting polymer electrolyte membrane. The fuel cell is not limited to the type of fuel as long as it is a fuel cell, and any fuel cell such as a hydrogen solid polymer fuel cell, a direct methanol solid polymer fuel cell, or a direct hydrocarbon solid polymer fuel cell You may use for. In this case, a fuel cell system whose performance is maintained for a long time is provided.

  Further, the fuel cell system according to the present embodiment can be mounted on a fuel cell vehicle as its application. This fuel cell vehicle can withstand continuous operation for a long time by mounting the fuel cell system according to the present embodiment. The use of this fuel cell system is not limited to fuel cell vehicles, and is applied to fuel cell cogeneration power generation systems, fuel cell home appliances, fuel cell portable devices, stationary fuel cells, and fuel cell transportation devices. It is possible. Even when applied to these, a fuel cell cogeneration power generation system that can withstand continuous operation for a long time is provided.

  Hereinafter, members constituting the fuel cell stack 1 shown in FIGS.

[Solid polymer electrolyte membrane]
The solid polymer electrolyte membrane 11 only needs to have high proton conductivity. As a membrane having high proton conductivity, known materials such as a polymer or copolymer of a monomer having an ion exchange group such as —SO ₃ H group, a polymer of a monomer having an ion exchange group and another monomer, etc. A film made of can be used. For example, a perfluorocarbon sulfonic acid film represented by the formula (C1), an ethylene-tetrafluoroethylene copolymer film, or a fluorine-containing resin film containing trifluorostyrene as a base polymer can be used.

  In the formula (C1), k and m are integers, p is an integer of 0 to 3, q is 0 or 1, n is an integer of 1 to 12, and X is preferably a fluorine atom or a trifluoromethyl group.

  Examples of the membrane made of the above-mentioned polymer of perfluorocarbon sulfonic acid include NAFION (registered trademark) manufactured by DuPont, FLEMION (registered trademark) manufactured by Asahi Glass Co., Ltd., ACIPLEX (registered trademark) manufactured by Asahi Kasei Chemicals Corporation, and The Dow. -DOWEX (registered trademark) manufactured by Chemical Company.

  The thickness of the solid polymer electrolyte membrane can be appropriately determined in consideration of the characteristics of the obtained fuel cell, but the thickness is preferably 5 to 300 [μm], more preferably 10 to 200 [μm]. [mu] m] and particularly preferably 15 to 150 [[mu] m]. When the solid polymer electrolyte film thickness is 5 or more, it is preferable from the viewpoint of strength during film formation and durability during fuel cell operation. When the film thickness is 300 or less, output characteristics during fuel cell operation are preferable. It is preferable from the point.

[Catalyst layer]
The catalyst layers 12a and 12b are composed of an electrode catalyst in which catalyst particles are supported on a conductive carrier and a binder having proton conductivity. Furthermore, in the embodiment of the present invention, the organic mediator fixed in the catalyst layers 12a and 12b is provided, but the description thereof is omitted because it is as described above.

  The electrode catalyst contained in the catalyst layer is made of a conductive carrier carrying catalyst particles. Catalyst particles supported on the conductive carrier include aluminum, silicon, phosphorus, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, germanium, selenium, zirconium, molybdenum, ruthenium, rhodium, palladium, Any one selected from tin, antimony, tellurium, tungsten, rhenium, osmium, iridium, platinum, gold, lead and bismuth, or two or more alloys selected from these can be used. . Among them, platinum, platinum-iron alloy, platinum-cobalt alloy, platinum-nickel alloy, platinum-molybdenum alloy, or platinum-ruthenium in terms of power generation characteristics, durability, poisoning resistance to carbon monoxide and heat resistance, etc. Alloys are preferred.

  The average particle diameter of the catalyst particles is preferably 1 to 30 [nm]. The average particle diameter is preferably 1 [nm] or more from the viewpoint of obtaining catalytic activity corresponding to the specific surface area, and is preferably 30 [nm] or less from the viewpoint of catalytic activity. The average particle diameter of the catalyst can be obtained by calculating the crystallite diameter obtained from the half-value width of the diffraction peak of the catalyst particles in X-ray diffraction or the average value of the particle diameter of the catalyst particles obtained from a transmission electron microscope image. it can.

  The conductive carrier may have any specific surface area for supporting the catalyst in a desired dispersed state and has conductivity that functions as a current collector. Examples of the material of the conductive carrier include carbon black such as ketjen black (registered trademark) or acetylene black, graphite such as activated carbon, coke, natural graphite or artificial graphite, mesocarbon microbeads, glassy carbon powder, and Those whose main component is carbon, such as carbon nanotubes, are preferred. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed.

  The average primary particle diameter of the conductive carrier is preferably 2 [nm] to 1 [μm], more preferably 5 to 200 [nm], and particularly preferably 10 to 100 [nm]. The average primary particle diameter is preferably 2 [nm] or more from the viewpoint of forming an effective conductive network, and is preferably 1 [μm] or less from the viewpoint that the thickness of the catalyst layer can be controlled within an appropriate range.

  The catalyst particles can be supported on the conductive support by a known method. For example, the catalytic metal is dissolved in a first solvent to prepare an aqueous catalytic metal solution. Next, a mixed liquid is prepared by adding a conductive support such as carbon particles, a catalytic metal aqueous solution, and a reducing agent to the second solvent, and reducing and precipitating the catalytic metal to be supported on the conductive support such as carbon particles. Can do. Next, after separating the solid content by filtration, the electrode catalyst can be obtained by drying the solid content.

  When platinum is used as the catalyst metal aqueous solution, a chloroplatinic acid solution or a dinitrodiamine platinum complex solution can be used. As the reducing agent, for example, organic acids having 1 to 6 carbon atoms, alcohols, aldehydes having 1 to 3 carbon atoms, sodium borohydride, hydrazine and the like can be used. Although it does not specifically limit as C1-C6 organic acids, Formic acid, an acetic acid, an oxalic acid, a citric acid, etc. are mention | raise | lifted. Although it does not specifically limit as alcohol, Methanol, ethanol, ethylene glycol, 2-propanol, 1, 3- propanediol etc. are mention | raise | lifted. Although it does not specifically limit as C1-C3 aldehyde, Formaldehyde, acetaldehyde, acrolein, etc. can be used. Water can be used as the second solvent.

  Although the content rate of the catalyst particle with respect to an electroconductive support | carrier is not specifically limited, It is preferable that it is 5-80 [mass%], More preferably, it is 10-75 [mass%], It is 15-70 [mass%]. It is particularly preferred. When the content of the catalyst particles is 5 [% by mass] or more, it is preferable from the viewpoint of maintaining high catalytic activity, and when it is 80 [% by mass], it is preferable from the viewpoint of maintaining high durability. The amount of catalyst particles supported can be determined by inductively coupled plasma emission spectroscopy (ICP).

  The proton conductive binder or polymer electrolyte contained in the catalyst layer preferably covers at least a part of the electrode catalyst. Thereby, not only proton conductivity etc. improve, but an electrode structure can be maintained stably and electrode performance can be improved.

Although it does not specifically limit as said binder, The polymer electrolyte described by the term of the above-mentioned solid polymer electrolyte membrane can be used preferably. That is, a perfluorosulfonic acid polymer proton conductor such as a Nafion (registered trademark) solution, a hydrocarbon polymer compound doped with an inorganic acid such as phosphoric acid, and part of the functional group of the proton conductor. Examples thereof include substituted organic or inorganic hybrid polymers, and ion exchange resins made of proton conductors in which a polymer matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution. Specific examples of perfluorosulfonic acid polymer proton conductors include not only polymers composed of only carbon atoms and fluorine atoms, but also oxygen atoms if all hydrogen atoms are replaced with fluorine atoms. Etc. For example, in the case of the perfluorocarbon sulfonic acid membrane type represented by the above formula (C1), a polymer unit based on CF ₂ = CF ₂ and CF ₂ = CF- (OCF ₂ CFX) _m -O _p- (CF ₂ ) _n- And copolymers containing polymerized units based on SO ₃ H.

  The mass ratio of the binder to the conductive carrier is preferably 0.3: 1 to 1.3: 1 in order, and more preferably 0.5: 1 to 1.1: 1. The mass ratio of the polymer electrolyte as the binder component to the conductive support mass is preferably 0.3 times or more from the viewpoint of good ionic conductivity in the catalyst layer, and if it is 1.3 times or less, the catalyst layer It is preferable in terms of gas diffusion and water discharge.

  The catalyst layer may further contain a water repellent polymer and other various additives. By containing the water-repellent polymer, the water repellency of the resulting catalyst layer can be increased, and water generated during power generation can be quickly discharged. The mixing amount of the water-repellent polymer can be appropriately determined within a range that does not affect the function and effect of the present invention. Examples of the water-repellent polymer include polypropylene, polyethylene, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyhexafluoropropylene, and copolymers of these monomers (for example, tetrafluoroethylene-hexafluoropropylene copolymer). Etc.) can be used.

  A known method can be used as a method for forming the catalyst layer. For example, an electrode catalyst, a binder, and organic polymer fine particles adsorbed or chemically bonded with an organic mediator can be used. Furthermore, if necessary, a water-repellent polymer or other various additives are mixed with a liquid dispersion medium to form an electrode catalyst ink, and a screen printer, bar coater on a substrate, a gas diffusion layer or a polymer electrolyte membrane. It is formed by coating using a die coater, reverse coater, comma coater, gravure coater, spray coater, doctor knife or the like and drying.

  As a liquid dispersion medium used for the electrode catalyst ink, water, alcohol such as ethanol, 1-propanol, 2-propanol, or a mixed solvent thereof can be preferably used. As the substrate, a polytetrafluoroethylene (PTFE) sheet, a polyethylene terephthalate (PET) sheet, or the like can be preferably used. The gas diffusion layer is described in the sections of a gas diffusion layer base material, a carbon particle layer in the gas diffusion layer, and a carbon fiber layer in the gas diffusion layer, which will be described later. Drying is preferably performed at a temperature ranging from room temperature to the boiling point of the solvent used + 10 [° C.], using a device such as an air drying or drying oven for 10 to 300 [min]. When using a device such as a drying oven, it may be performed under reduced pressure.

  When the catalyst layer ink is applied on the substrate or the gas diffusion layer to form the catalyst layer, for example, the catalyst layer and the solid polymer electrolyte membrane can be joined by hot pressing. When the catalyst layer is formed on the base material, use only two base materials on which the catalyst layer is formed, sandwich the solid polymer electrolyte membrane so that the catalyst layers face each other, and perform hot pressing. Can be removed. When the catalyst layer is formed on the gas diffusion layer, two gas diffusion layers on which the catalyst layer is formed may be used, and the solid polymer electrolyte membrane may be sandwiched and hot pressed so that the catalyst layers face each other.

  The hot pressing is preferably performed at a pressing pressure of 110 to 170 [° C.] and 0.1 to 10 [MPa] with respect to the surface on the catalyst layer side. By performing hot pressing in the above-described range, the bondability between the polymer electrolyte membrane and the catalyst layer can be improved.

  The thickness of the catalyst layer in the present invention is not particularly limited, but is preferably 0.1 to 100 [μm], more preferably 1 to 20 [μm]. When the thickness of the catalyst layer is 0.1 [μm] or more, it is preferable in that a desired power generation amount can be obtained, and when it is 100 [μm] or less, it is preferable in that high output can be maintained.

[Gas diffusion layer]
By disposing the gas diffusion layers 13a and 13b so as to be adjacent to the catalyst layers 12a and 12b, the solid polymer electrolyte membrane 11 is uniformly humidified, and exhibits high hydrogen ion conductivity. Further, when the gas diffusion layer 13b is disposed on the air electrode 14b side, the oxidant gas can be continuously supplied, the chemical reaction on the air electrode 14b side can be performed smoothly, and further the chemical reaction It is possible to prevent the decrease in catalytic activity by dispersing water generated by the above. When the gas diffusion layer 13a is disposed on the fuel electrode 14a side, the hydrogen-containing gas can be continuously supplied, and the chemical reaction on the fuel electrode 14a side can be performed smoothly. The gas diffusion layers 13a and 13b may be disposed only on one side of the fuel electrode 14a or the air electrode 14b, or may be disposed on both sides. More preferably, they are arranged on both sides.

  The gas diffusion layers 13a and 13b used in the embodiment of the present invention are composed of a gas diffusion layer base material and may further contain a water repellent polymer or the like. The gas diffusion layer base material is not particularly limited, and examples thereof include a sheet-like material having conductivity and porosity, such as a carbon woven fabric, a paper-like paper body, a felt, and a nonwoven fabric.

  In order to further improve the water repellency of the gas diffusion layer and prevent the flooding phenomenon and the like, it is preferable that the gas diffusion layer substrate contains a water-repellent polymer. The water-repellent polymer is not particularly limited, and any one selected from fluorine-based polymer materials such as polypropylene, polyethylene, PTFE, PVDF, polyhexafluoropropylene, or a copolymer of these monomers. It is preferable to use it. In addition, flooding is a phenomenon in which water accumulates in a gas diffusion channel such as pores in the catalyst layer and hinders gas diffusion.

  As a water repellent treatment method for the gas diffusion layer, a known method can be used. For example, the water-repellent treatment can be performed by impregnating the gas-diffusing layer base material in a dispersion of a water-repellent polymer and then drying the gas-diffusing layer base material by heating. Heat drying is preferably performed using an oven at a temperature of 50 to 150 [° C.] for 10 [minutes] to 5 [hours].

  Although the thickness of a gas diffusion layer is not specifically limited, 50-500 [micrometer] is preferable, More preferably, it is 100-400 [micrometer]. The thickness of the gas diffusion layer is preferably 50 [μm] or more from the viewpoint of gas diffusibility, and is preferably 500 [μm] or less from the viewpoint of reducing electrical resistance.

[Separator]
The separator 17 that holds the MEA 15 is not particularly limited, and a known separator can be used. Specifically, carbon or metal formed into a plate shape and having a gas channel and a cooling water channel formed on the surface thereof can be used. The separator 17 has a function of separating the oxidizing gas and the fuel gas, and a gas supply groove for securing the flow path thereof may be formed. The thickness and size of the separator, the shape of the gas supply groove, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the fuel cell.

  Hereinafter, the fuel cell system according to the present invention will be described more specifically with reference to Examples 1 to 10 and Comparative Examples 1 to 3. However, the scope of the present invention is not limited thereto. These examples are for examining the effectiveness of the present invention, and show examples prepared with different raw materials. In the examples, “%” represents a mass percentage unless otherwise specified.

  Each sample was prepared by the following method.

<Preparation of sample>
Example 1
Polyethylene powder (Ardrich average particle size 45 [μm]) was dissolved in fuming nitric acid, and heated and stirred at 80 [° C.] for 1 [hour]. The obtained powder was washed with water while being filtered to obtain organic polymer fine particles into which carboxyl groups were introduced. Using the obtained organic polymer fine particles 10 [g], a water / ethanol = 1: 1 mixed solvent was added, 0.05 [g] of 1 [%] NHPI was added as an organic mediator, and the mixture was stirred with a homogenizer. Thereafter, drying was performed at 80 [° C.] to obtain NHPI / organic polymer fine particles (sample A) in which NHPI was adsorbed on the organic polymer fine particles.

Example 2
A poly (ethylene-acrylic acid) copolymer (Ardrich 10 [wt%] acrylic acid) was used as the organic polymer fine particles. After the copolymer was dissolved in toluene, it was dropped into a hexane solution and reprecipitated as fine particles of 100 [μm] or less. Water / ethanol = 1: 1 mixed solvent was added to the obtained organic polymer fine particles, 0.05 [g] of 1 [%] NHPI was added as an organic mediator, and the mixture was stirred with a homogenizer. Thereafter, drying was performed at 80 [° C.] to obtain NHPI / organic polymer fine particles (sample B) in which NHPI was adsorbed on the organic polymer fine particles.

Example 3
As the organic polymer fine particles, poly (biphenyltetracarboxylic dianhydride-phenylenediamine) amic acid copolymer (Ardrich) was used. The copolymer was dissolved in dimethylformamide, then dropped into a hexane solution, and reprecipitated as fine particles of 100 [μm] or less were used. Water / ethanol = 1: 1 mixed solvent was added to the obtained organic polymer fine particles, 0.05 [g] of 1 [%] NHPI was added as an organic mediator, and the mixture was stirred with a homogenizer. Thereafter, drying was performed at 80 [° C.] to obtain NHPI / organic polymer fine particles (sample C) in which NHPI was adsorbed on the organic polymer fine particles.

Example 4
Polyethylene powder (Ardrich average particle size 45 [μm]) was dissolved in fuming nitric acid, and heated and stirred at 80 [° C.] for 1 [hour]. The obtained powder was washed with water while being filtered to obtain organic polymer fine particles into which carboxyl groups were introduced. Using the obtained organic polymer fine particles 10 [g], a water / ethanol = 1: 1 mixed solvent was added, 0.05 [g] of 1 [%] TEMPO was added as an organic mediator, and the mixture was stirred with a homogenizer. Thereafter, drying was performed at 80 [° C.] to obtain TEMPO / organic polymer fine particles (sample D) in which TEMPO was adsorbed on the organic polymer fine particles.

Example 5
A poly (ethylene-acrylic acid) copolymer (Ardrich 10 [wt%] acrylic acid) was used as the organic polymer fine particles. After the copolymer was dissolved in toluene, it was dropped into a hexane solution and reprecipitated as fine particles of 100 [μm] or less. Water / ethanol = 1: 1 mixed solvent was added to the obtained organic polymer fine particles, 0.05 [g] of 1 [%] TEMPO was added as an organic mediator, and the mixture was stirred with a homogenizer. Thereafter, drying was performed at 80 [° C.] to obtain TEMPO / organic polymer fine particles (sample E) in which TEMPO was adsorbed on the organic polymer fine particles.

Example 6
As the organic polymer fine particles, poly (biphenyltetracarboxylic dianhydride-phenylenediamine) amic acid copolymer (Ardrich) was used. The copolymer was dissolved in dimethylformamide, then dropped into a hexane solution, and reprecipitated as fine particles of 100 [μm] or less were used. Water / ethanol = 1: 1 mixed solvent was added to the obtained organic polymer fine particles, 0.05 [g] of 1 [%] TEMPO was added as an organic mediator, and the mixture was stirred with a homogenizer. Thereafter, drying was performed at 80 [° C.] to obtain TEMPO / organic polymer fine particles (sample F) in which TEMPO was adsorbed on the organic polymer fine particles.

  Examples 7 to 9 are examples in which organic polymer fine particles having TEMPO immobilized thereon were prepared.

Example 7
It was prepared by the method shown in FIG. Polyethylene powder (Ardrich average particle size 45 [μm]) was dissolved in fuming nitric acid, and heated and stirred at 80 [° C.] for 1 [hour]. The obtained powder was washed with water while being filtered to obtain organic polymer fine particles into which carboxyl groups were introduced. After the obtained organic polymer fine particles 10 [g] are dissolved in chlorobenzene, 4-amino TEMPO and dicyclohexylcarbodiimide (DCC) are added and reacted for 50 [hours] while maintaining 50 [° C.] to obtain the desired TEMPO. Immobilized organic polymer fine particles (sample G) were obtained.

Experimental Example 8
It was prepared by the method shown in FIG. After 10 [g] of a poly (ethylene-acrylic acid) copolymer (Ardrich 10 [wt%] acrylic acid) is dissolved in chlorobenzene, 4-amino TEMPO and dicyclohexylcarbodiimide (DCC) are added to obtain 50 [° C.]. The target TEMPO-immobilized organic polymer fine particles (sample H) were obtained by reacting for 50 hours while maintaining the above.

Example 9
It was prepared by the method shown in FIG. A poly (biphenyltetracarboxylic dianhydride-phenylenediamine) amic acid copolymer (Ardrich) was used. After 10 [g] is dissolved in chlorobenzene, 4-amino TEMPO and dicyclohexylcarbodiimide (DCC) are added and reacted for 50 [hours] while maintaining 50 [° C.], and the desired TEMPO-immobilized organic polymer fine particles ( Sample I) was obtained.

Comparative Example 1
0.05 [g] of 1 [%] NHPI as an organic mediator was mixed with 5 [g] of platinum-supported carbon (TEC10E50E manufactured by Tanaka Kikinzoku) as an electrode catalyst, and the mixture was stirred with a homogenizer. The ink thus prepared was dried in the air for 1 [hour] to obtain Sample J.

Comparative Example 2
0.05 [g] of 1 [%] TEMPO as an organic mediator was mixed with 5 [g] of platinum-supported carbon (TEC10E50E manufactured by Tanaka Kikinzoku) as an electrode catalyst, and the mixture was stirred with a homogenizer. The ink thus prepared was dried in the air for 1 [hour] to obtain Sample K.

  Here, the obtained samples A to J were evaluated by the following evaluation test.

<Evaluation test>
Samples A to K were subjected to a batch shaking test. 0.25 [g] of each sample was obtained and sealed in a glass vial containing pure water 5 [cm ³ ]. The vial was placed in a constant temperature shaking water bath kept at 25 [° C.] and shaken for a predetermined time at a shaking speed of 120 [spm]. After shaking, the aqueous phase solution was sampled and the concentration of the compound eluted from each sample was measured.

Table 1 shows the results of the evaluation test.

  From the results of Table 1, in Comparative Example 1 and Comparative Example 2 in which the organic mediator was not fixed to the electrode catalyst, the organic mediator added in the vial was eluted in pure water. In contrast, in Examples 1 to 9, the amount of elution into pure water was greatly reduced. In particular, in Examples 7 to 9, since the organic mediator is chemically bonded to the organic polymer fine particles, the organic mediator is fixed to the organic polymer fine particles, and the elution amount of the organic mediator in pure water is reduced. It was found that it was significantly reduced.

  From this result, it was found that in the fuel cell system according to the present embodiment, it is possible to prevent the organic mediator from flowing out of the water used for humidification or the water generated by the reaction on the air electrode side. For this reason, the effect of eliminating the hydrogen peroxide generated by the electrode reaction and the hydroxy radical generated from the hydrogen peroxide can be stably maintained for a long time. As a result, the deterioration of the binder and electrolyte membrane of the catalyst layer is prevented, the durability performance of the fuel cell system is maintained, and the durability is improved.

<Measurement of 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. Measurement examples of NHPI, which is an imide-based representative compound, and TEMPO, which is a representative TEMPO-based compound, are as shown in FIGS. In FIG. 17 and FIG. 18, the value obtained to match the redox potential of each substance was corrected to the standard potential E ⁰ (NHE) by the equation shown in equation (D1).

E ⁰ (NHE) = E (SCE) +0.24 [V] (D1)
As shown in FIG. 17, the oxidation-reduction potential of NHPI exists near 1.10 [V] (SCE), and from FIG. 18, the oxidation-reduction potential of TEMPO exists near 0.57 [V] (SCE). Due to this potential, NHPI and TEMPO are larger than the potential 0.68 [V] (NHE) in which hydrogen peroxide becomes a reducing agent, and from the potential 1.77 [V] (NHE) in which hydrogen peroxide acts as an oxidizing agent. It is an organic mediator that reversibly oxidizes and reduces within a small range, and was found to be a compound suitable for this purpose.

<Single cell accelerated durability test>
An open circuit standing test was conducted at a cell temperature of 90 [° C.], and OCV (open circuit voltage) was monitored to examine the durability of the single cell by adding an organic mediator to the electrode catalyst. Hydrogen gas humidified to 30 [%] was supplied to the fuel electrode and oxygen gas humidified to 30 [%] was supplied to the air electrode at a flow rate of 500 [ml / min], and the OCV was measured with the gas flowing. . Single cells were produced by the methods shown in Example 10 and Comparative Example 3 below.

Example 10
TEC10E50E manufactured by Tanaka Kikinzoku as platinum-supported carbon, NHPI-supported polyethylene prepared in Example 1, and 5 wt% Nafion (registered trademark) manufactured by DuPont were used as the electrolyte binder. After the platinum-supporting carbon was sufficiently moistened with water, an electrolyte binder was added, and isopropyl alcohol was added to disperse the platinum-supporting carbon and the electrolyte binder in isopropyl alcohol. Thereafter, the mixture was mixed for 3 hours with a homogenizer and homogenized, and then defoamed to obtain a catalyst ink. Thereafter, two catalyst sheets were applied by applying catalyst ink to a Teflon (registered trademark) sheet so that the platinum amount was 0.4 [mg / cm ³ ] and the NHPI-supporting polyethylene was 0.04 [mg / cm ³ ]. Produced. The catalyst sheet is arranged on the fuel electrode side and the air electrode side of the Nafion (registered trademark) 211 membrane, respectively, and hot pressed at 2 [MPa], 132 [° C.], 10 [minutes] to form the catalyst sheet Nafion (registered trademark). The film was transferred to a 211 membrane to form an electrode catalyst layer, and a CCM (catalyst coated membrane) was obtained. CCM was sandwiched between gas diffusion layers and then sandwiched between a separator and a current collector plate to produce a single cell with a catalyst area of 5 × 5 [cm ² ].

Comparative Example 3
TEC10E50E made by Tanaka Kikinzoku was used as the platinum-supporting carbon, and 5 wt% Nafion (registered trademark) solution made by DuPont was used as the electrolyte binder. After the platinum-supporting carbon was sufficiently moistened with water, an electrolyte binder was added, and isopropyl alcohol was added to disperse the platinum-supporting carbon and the electrolyte binder in isopropyl alcohol. Thereafter, the mixture was mixed for 3 hours with a homogenizer and homogenized, and then defoamed to obtain a catalyst ink. Thereafter, the catalyst ink was applied to a Teflon (registered trademark) sheet so that the amount of platinum was 0.4 [mg / cm ³ ] to produce two catalyst sheets. The catalyst sheet is arranged on the fuel electrode side and the air electrode side of the Nafion (registered trademark) 211 membrane, respectively, and hot pressed at 2 [MPa], 132 [° C.], 10 [minutes] to form the catalyst sheet Nafion (registered trademark). The film was transferred to a 211 film to form an electrode catalyst layer, and CCM was obtained. CCM was sandwiched between gas diffusion layers and then sandwiched between a separator and a current collector plate to produce a single cell with a catalyst area of 5 × 5 [cm ² ].

  FIG. 19 shows the results of the single cell accelerated durability test. In both Example 10 and Comparative Example 3, the OCV was about 0.95 [V] after the start of the test, and the OCV decreased to about 0.9 [V] after 5 hours. In Comparative Example 3 in which no organic mediator was added, the OCV rapidly decreased after 15 hours from the start of the test, the OCV decreased after 20 hours from the start of the test, and power generation became impossible after 40 hours. On the other hand, in Example 10 to which polyethylene fine particles supporting NHPI as an organic mediator were added, OCV was 0.8 [V] or more until 60 hours passed from the start of the test, which is not shown in FIG. Power generation continued until 90 hours passed from the start of the test. Thus, the durability of the single cell was improved by adding polyethylene carrying an organic mediator.

  As described above, it has been found that in the fuel cell system according to the embodiment of the present invention, the performance is maintained for a long time by having the organic mediator fixed to the catalyst layer.

  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.

It is a perspective view which shows the external appearance of the fuel cell stack which comprises the fuel cell system which concerns on embodiment of this invention. It is a principal part expanded view of a fuel cell stack. It is explanatory drawing which shows the oxidation-reduction potential when oxygen, active oxygen, hydrogen, etc. work as an oxidizing agent or a reducing agent. It is explanatory drawing showing the mechanism which lose | disappears active oxygen by NHPI. 1 is a schematic explanatory diagram illustrating an embodiment of a fuel cell system according to the present invention. It is a principal part expanded view of a fuel cell stack. It is explanatory drawing explaining the movement of the substance in a membrane electrode assembly. It is a schematic diagram which shows the three-phase interface in an air electrode. (A) It is a figure explaining the process in which an organic mediator couple | bonds with organic polymer microparticles. (B) It is a figure explaining the process in which an organic mediator couple | bonds with organic polymer microparticles. (C) It is a figure explaining the process in which an organic mediator couple | bonds with organic polymer microparticles. It is explanatory drawing which shows the hydroxyl radical reduction | restoration mechanism by a Gross mechanism. It is explanatory drawing showing the mechanism which lose | disappears active oxygen by NHGI. It is a schematic diagram which shows an example of an organic mediator. It is a schematic diagram which shows an example of an organic mediator. It is a schematic diagram which shows an example of an organic mediator. It is a schematic diagram which shows an example of an organic mediator. It is explanatory drawing showing the mechanism which lose | disappears 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 showing the result of a single cell accelerated durability test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 End flange 3 Fastening bolt 4 Fuel gas supply line 5 Air supply line 11 Solid polymer electrolyte membrane 12a, 12b Catalyst layer 13a, 13b Gas diffusion layer 14a Fuel electrode 14b Air electrode 15 MEA
16a Fuel gas flow path 16b Air flow path 17 Separator 20 Organic mediator 41 Organic polymer fine particle

Claims (49)

A first conductive substrate;
An organic mediator fixed to the first substrate;
A second substrate for fixing the organic mediator to the first substrate;
The fuel cell system, wherein the second base material is organic polymer fine particles modified with a functional group.   2. The fuel cell system according to claim 1, wherein the organic polymer fine particles have an average particle diameter in a range of 0.1 to 1000 [μm].   The fuel cell system according to claim 2, wherein the organic polymer fine particles have an average particle diameter in a range of 10 to 100 [µm].   The fuel cell system according to any one of claims 1 to 3, wherein the organic mediator is fixed to the functional group by a hydrogen bond.   5. The functional group according to claim 1, wherein the functional group is any one selected from a carboxyl group, a hydroxyl group, an alkoxyl group, an alkoxycarbonyl group, an acyl group, and a sulfone group. The fuel cell system described in 1.   The fuel cell system according to claim 5, wherein the functional group is a carboxyl group.   The organic polymer fine particles are based on polymers such as phenol resin, urea resin, melamine resin, unsaturated polyester, epoxy resin, polyimide resin, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylic resin, polyacetal, polyamide, The present invention is one selected from polycarbonate, PBT resin, PET resin, PPS resin, polysulfone, polyether ether, polyether sulfone, polyether imide, and polyether ketone. 7. The fuel cell system according to claim 6.   8. The organic polymer fine particle is based on any one selected from polyethylene, polypropylene, polystyrene, polystyrene, and acrylic resin, and includes a polymer having a carboxyl group introduced by oxidation treatment. The fuel cell system described in 1.   The organic polymer fine particles include a copolymer of any one selected from polyethylene, polypropylene, polystyrene, polystyrene, and acrylic resin, and a polymer having a carboxyl group. Fuel cell system.   8. The fuel cell system according to claim 7, wherein the organic polymer fine particle includes a reaction intermediate of a condensed polymer in which a carboxyl group remains, which is condensed with carboxylic acid as a monomer.   The organic polymer fine particle is a reaction intermediate in which a carboxyl group generated by reacting a monomer having an excess carboxylic acid substituent of dicarboxylic acid or more remains, and the reaction intermediate includes polyimide resin, polyamide, 8. The fuel cell system according to claim 7, comprising a reaction intermediate of a polymer selected from polycarbonate, PBT resin, PET resin, PPS resin, and polyetherimide.   The fuel cell system according to any one of claims 1 to 11, wherein the organic mediator is fixed to the second base material through a chemical bond with the functional group.   The fuel according to claim 12, wherein the functional group is a carboxyl group, and the chemical bond is a bond formed by a reaction between a hydroxyl group or an amino group introduced into the organic mediator and the carboxyl group. Battery system.   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. 14. A fuel cell in which a plurality of single cells are stacked, and a mediator supply means for supplying the organic mediator from the air electrode side or the fuel electrode side of the fuel cell. The fuel cell system according to one item.   The fuel cell system according to claim 14, wherein the organic mediator is continuously supplied to the fuel electrode as a mediator solution.   The fuel cell system according to claim 15, wherein the mediator solution is an aqueous solution.   The mediator supply means includes a mediator solution tank in which the mediator solution is sealed, a liquid feed pump that supplies the mediator solution to the fuel electrode, and a mediator solution pipe that connects the mediator solution tank and the liquid feed pump. 17. The fuel cell system according to claim 15, further comprising: a passage, and a mediator solution supply pipe connecting the liquid feeding pump and the fuel gas flow path.   The fuel cell system according to any one of claims 1 to 17, wherein the organic mediator is a hydrocarbon compound composed of four atoms of carbon, oxygen, nitrogen, and hydrogen. Fuel cell system. In the mediator supply means, the organic mediator is supplied to the fuel electrode, sent to the air electrode using a concentration gradient, and the organic mediator that is no longer needed is oxidized by a catalyst containing the air electrode to produce CO. ₂ the fuel cell system of claim 18, wherein the discharging _as, H 2 _O or N _2.   The fuel cell system according to any one of claims 14 to 19, wherein the first base material is a catalyst layer constituting the fuel electrode or the air electrode.   The organic mediator acts as a reducing agent at a potential lower than the reduction potential at which a hydroxy radical acts as an oxidizing agent, and acts as an oxidizing agent at a potential higher than the oxidation potential at which hydrogen peroxide acts as a reducing agent. The fuel cell system according to any one of claims 1 to 20.   The fuel cell system according to claim 21, wherein the organic mediator has a standard oxidation-reduction potential in a range larger than 0.68 [V] (NHE) and smaller than 2.85 [V] (NHE). .   23. The organic mediator according to claim 22, wherein the standard redox potential has a potential lower than a reduction potential at which hydrogen peroxide acts as an oxidizing agent and higher than an oxidation potential at which hydrogen peroxide acts as a reducing agent. The fuel cell system described.   The fuel cell system according to claim 23, wherein the organic mediator has a standard oxidation-reduction potential in a range larger than 0.68 [V] (NHE) and smaller than 1.77 [V] (NHE). . The organic mediator has the following general formula (I)

25. The fuel cell system according to claim 24, wherein the fuel cell system is a compound represented by the formula: wherein R1 and R2 are the same or different arbitrary substituents, and X represents an oxygen atom or a hydroxyl group.   26. The fuel cell system according to claim 25, wherein R1 and R2 are bonded to each other to form a double bond, an aromatic ring, or a non-aromatic ring. The compound 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). 27. The fuel cell system according to claim 26, characterized in that: The imide 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. Or a hydroxyl group, wherein n represents an integer of 1 to 3.) The fuel cell system according to claim 27.   29. The fuel cell system according to claim 28, wherein R3 and R4 are bonded to each other to form a double bond, an aromatic ring, or a non-aromatic ring.   29. The fuel cell system according to claim 28, wherein R3 and R4 are bonded to each other to form any one of an aromatic or non-aromatic 5- to 12-membered ring.   The R3 and R4 are bonded to each other to form any ring selected from cycloalkane, cycloalkene, a bridged hydrocarbon ring, an aromatic ring, and a substituent thereof. Item 30. The fuel cell system according to Item 28. The imide compound is represented by the following general 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, 32. The fuel cell system according to any one of claims 28 to 31, wherein n is an imide compound represented by an integer of 1 to 3.   The imide compound is N-hydroxysuccinimide, N-hydroxymaleimide, N-hydroxyhexahydrophthalimide, N, N'-dihydroxycyclohexanetetracarboxylic imide, N-hydroxyphthalimide, N-hydroxytetrabromo. Phthalic acid imide, N-hydroxytetrachlorophthalic acid imide, N-hydroxyhetic acid imide, N-hydroxyhymic acid imide, N-hydroxytrimellitic acid imide, N, N'-dihydroxypyromellitic acid imide and N, The fuel cell system according to claim 32, wherein the fuel cell system is an imide compound selected from the group consisting of N'-dihydroxynaphthalenetetracarboxylic imides. The compound represented by the general formula (II) is represented by the following general formula (V):

(Wherein R7 to R12 are the same or different and each represents a hydrogen atom, an alkyl group, an aryl group, a cycloalkyl group, a hydroxyl group, an alkoxy group, a carboxyl group, a substituted oxycarbonyl group, an acyl group or an acyloxy group; At least two of R12 may be bonded to each other to form a double bond or an aromatic or non-aromatic ring, and at least one of the rings has an N-substituted cyclic imide group. The fuel cell system according to claim 27, wherein the compound is a compound represented by: The compound represented by the general formula (V) is represented by the following formula (VIa) or (VIb)

(Wherein R13 to R18 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 fuel cell system according to claim 34, wherein the fuel cell system is a compound.   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 imide, N, N′-dihydroxy-1,8; 4,5-naphthalene tetracarboxylic imide, N, N′-dihydroxy-1,8; 4,5-decalin tetracarboxylic imide and N, N 36. The fuel cell system according to claim 34 or 35, which is an imide compound selected from the group consisting of ', N ″ -trihydroxyisocyanuric acid.   The fuel cell system according to claim 24, wherein the compound has a standard oxidation-reduction potential larger than 0.68 [V] (NHE) and smaller than 1.00 [V] (NHE). The compound represented by the general formula (I) is represented by the following general formula (VII)

(In the formula, R19 to R21 are an alkyl group or an alkyl group partially substituted with an arbitrary group, and R19 to R21 may be chain, cyclic, or branched, and R19 to R21 are bonded to each other. 38. The fuel cell system according to claim 37, wherein the fuel cell system is a compound represented by the following formula: 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)

(In the formula, R19 to R24 are alkyl groups or alkyl groups partially substituted with an arbitrary group, and R19 to R24 may be linear, cyclic, or branched, and R20 and R21, or 39. The fuel cell system according to claim 38, wherein R23 and R24 may be bonded to each other to form a ring and may contain oxygen and nitrogen atoms. 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 R19 and R22 are bonded to form either a 5-membered ring or a 6-membered ring. The fuel cell system described in 1. The compound represented by the general formula (IX) is represented by the following general formula (X)

(In the formula, Z represents a substituent 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 of the groups may be chain, cyclic, or branched, and oxygen and In the case where Z is an aryl group, it may be an aryl group partially substituted with an arbitrary group, and may contain oxygen and nitrogen atoms). 41. The fuel cell system according to claim 40, wherein there is a fuel cell system. 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. When Z is an alkyl group, a part of the alkyl group may be substituted with an arbitrary group, and a part of the group may be chain, cyclic, or branched, Oxygen and nitrogen atoms may be included. When Z is an aryl group, an aryl group partially substituted with an arbitrary group may be included, and oxygen and nitrogen atoms may be included.) 41. The fuel cell system according to claim 40, wherein the fuel cell system is a compound. 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. When Z is an alkyl group, a part of the alkyl group may be substituted with an arbitrary group, and a part of the group may be chain, cyclic, or branched, Oxygen and nitrogen atoms may be included. When Z is an aryl group, an aryl group partially substituted with an arbitrary group may be included, and oxygen and nitrogen atoms may be included.) 41. The fuel cell system according to claim 40, wherein the fuel cell system is a compound.   The fuel cell system according to any one of claims 14 to 43, wherein the fuel cell is any one selected from a hydrogen type, a direct methanol type, and a direct hydrocarbon type. .   By mixing the first substrate, organic mediator and organic polymer fine particles in a liquid dispersion medium to form an electrode catalyst ink, applying the electrode catalyst ink on the solid polymer electrolyte membrane or the gas diffusion layer, and drying A method for producing a catalyst layer for a fuel cell, comprising forming a catalyst layer for an electrode.   The first substrate, organic mediator and organic polymer fine particles were mixed in a liquid dispersion medium to form an electrode catalyst ink, and the electrode catalyst ink was applied to the substrate to form a catalyst layer, whereby the catalyst layer was formed. Two substrates are used to sandwich a solid polymer electrolyte membrane, the solid polymer electrolyte membrane is sandwiched and hot pressed to join the catalyst layer and the solid polymer electrolyte membrane, and after joining, the substrate A method for producing a catalyst layer of a fuel cell, comprising forming a catalyst layer of an electrode by peeling only the material from the solid polymer electrolyte membrane.   45. A home appliance using the fuel cell system according to any one of claims 1 to 44.   45. A portable device using the fuel cell system according to any one of claims 1 to 44.   45. A transportation device using the fuel cell system according to any one of claims 1 to 44.

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