JP5561250B2 - Support carbon material for catalyst layer for polymer electrolyte fuel cell and polymer electrolyte fuel cell using the same - Google Patents

Description

  The present invention relates to a support carbon material for a catalyst layer for a solid polymer fuel cell, and a solid polymer fuel cell using the same.

  The basic structure of the polymer electrolyte fuel cell according to the present invention is that a catalyst layer serving as an anode and a cathode is disposed with a proton-conducting solid polymer electrolyte membrane interposed therebetween, and a gas diffusion layer is disposed further on the outer side of the catalyst layer. In addition, a separator is disposed on the outer side to constitute a unit cell. Usually, the electrode area of a single cell is determined according to the required current characteristics, and further, the single cells are stacked in series according to the output voltage characteristics, and a practical stack is formed and used as a fuel cell.

In order to take out the current from the fuel cell having such a basic structure, an oxidizing gas such as oxygen or air is supplied to the cathode side from the gas flow path of the separator disposed on both the anode and the cathode, and hydrogen is supplied to the anode side. A reducing gas such as is supplied to the catalyst layer through the gas diffusion layer. For example, when hydrogen gas and oxygen gas are used, H ₂ → 2H ⁺ + 2e ⁻ (E0 = 0 V) that occurs on the catalyst of the anode
And O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O occurring on the cathode catalyst (E0 = 1.23 V)
The current is taken out using the energy difference (potential difference) of the chemical reaction.

Therefore, a gas diffusion path through which oxygen gas or hydrogen gas can move from the gas flow path of the separator to the catalyst inside the catalyst layer, and protons (H ⁺ ) generated on the anode catalyst pass through the proton conductive electrolyte membrane and flow through the cathode. proton conduction paths that can be transmitted to the catalyst, more electrons generated on the anode catalyst (e ^-) is a gas diffusion layer, separator, electron transfer pathway capable of transmitting to the cathode catalyst through an external circuit, continuously without being separated respectively If they are not connected, current cannot be extracted efficiently.

  Inside the catalyst layer, generally, pores that are formed in gaps between the materials and serve as gas diffusion paths, electrolyte materials that serve as proton conduction paths, and conductive materials such as carbon materials and metal materials that serve as electron conduction paths are continuously connected to each other. It is important to form a network.

  In addition, ion exchange resins typified by perfluorosulfonic acid polymers are used as polymer electrolyte materials for proton conducting paths in proton conducting electrolyte membranes and catalyst layers. These generally used polymer electrolyte materials exhibit high proton conductivity for the first time in a wet environment, and the proton conductivity decreases in a dry environment. Therefore, in order to operate the fuel cell efficiently, it is essential that the polymer electrolyte material is in a sufficiently wet state, and it is necessary to always supply water vapor together with the gas supplied to both electrodes.

  In general, in order to supply water vapor, a method of humidifying a gas to be supplied by passing it through water that has been previously kept at a constant temperature is used, and a device for humidification is required in addition to the cell. However, a humidifier that consumes energy to keep warm reduces the energy efficiency of the entire system. Moreover, it is desirable that there is no humidifier for the purpose of reducing the size and weight of the entire system.

  In order to respond to this, it is a problem that the catalyst has 1) high water retention ability and 2) sufficient water vapor release ability in a low humidification region. In order to solve this, various proposals have been conventionally made.

  Patent Document 1 discloses a catalyst material in which hydrophilic fine particles such as zeolite and titania and a hydrophilic catalyst carrier are contained in an anode in order to maintain high battery performance even when the amount of humidification is reduced. Yes. Patent Document 2 contains hydrophilic particles supporting hydrophobic particles such as silica particles supporting Teflon (registered trademark) particles in a catalyst layer for the purpose of providing a fuel cell that can cope with a wide range of humidification conditions. A catalyst material is disclosed.

  However, when the catalyst materials disclosed in Patent Document 1 and Patent Document 2 are used, the water retention capacity is improved. However, since the catalyst layer contains a material that is hydrophilic but does not have conductivity or proton conductivity, Alternatively, the proton transfer path was interrupted, resulting in a new problem of increasing internal resistance.

  In Patent Document 3, as a fuel cell exhibiting excellent startability even in a low-temperature atmosphere, a moisture humectant is contained in the catalyst layer of the anode, and the moisture humectant was hydrophilized as a conductive material subjected to a hydrophilization treatment. Carbon black and the like are disclosed.

  However, according to the study by the inventors, the carbon black that has been subjected to the hydrophilization treatment has been improved in water retention capacity under low humidity conditions, but has not necessarily achieved practically sufficient power generation characteristics.

  Patent Document 4 is made of a carbon material partially containing mesoporous carbon particles for the purpose of providing a fuel cell electrode catalyst having a higher power density than a conventional fuel cell electrode catalyst when used in a fuel cell. An electrode catalyst for a fuel cell having a carrier and catalyst particles carried on the carrier is provided.

  In Patent Document 5, with an object of providing a catalyst layer having high water retention and high battery characteristics even in a low humidity environment, and a polymer electrolyte fuel cell using the catalyst layer, an average pore diameter of 3.0 nm or less, A polymer electrolyte fuel cell using a catalyst having a spherical carbon porous body having a half value of saturated water vapor adsorption amount of 0.15 to 0.5 cc / g as a carrier is disclosed.

JP 2004-342505 A JP 2005-174835 A JP 2006-059634 A JP 2004-071253 A JP 2007-220414 A

  However, the catalyst materials disclosed in Patent Document 4 and Patent Document 5 have the following problems.

  The catalyst material disclosed in Patent Document 4 does not have a function of releasing an amount of water vapor that can sufficiently humidify the catalyst layer at a practically important relative humidity of 50% or less.

  In the catalyst material described in Patent Document 5, since the absolute amount of water vapor that can be contained is small, the moisture retention function of the catalyst layer is not practically sufficient.

  An object of the present invention is to provide a catalyst material for a solid polymer fuel cell that has both a high water retention capacity and a sufficient water vapor release capacity in a low humidification region with a relative humidity of 50% or less.

  The inventors have found the possibility of improving the water retention of the catalyst and improving the low humidification characteristics of the catalyst layer by making the support carbon material carrying the catalyst component porous.

  Furthermore, the desorption characteristics of water vapor adsorption / desorption isotherm of the porous carbon material, the micropore distribution analyzed by the adsorption / desorption isotherm of nitrogen gas, and the oxygen content of the porous carbon material are low in the catalyst layer. It has been found that it is an essential control factor for improving humidification characteristics.

  In addition, in order to improve gas diffusivity, carbon black with a developed structure and high water vapor adsorption amount is mixed with the carrier carbon material. Found to get.

The gist of the present invention is as follows.
(1) moisturizing carbon material and carbon black in a mass ratio of 2: 8-9: a solid polymer fuel catalyst layer carrier carbon material for a battery obtained by mixing in 1, wherein the moisture resistant carbon material, 25 water vapor adsorption amount when you Keru relative water vapor pressure 0.95 desorption curve of water vapor adsorption-desorption isotherm at ° C. (hereinafter, referred to as. "V _0.95") the value _{^{of, 1250cm 3 / g ≦ V 0.95}} ≦ 2500cm ³ / g and a relative water vapor pressure (hereinafter referred to as “P _1/2 ”) showing a water vapor adsorption amount half of V _0.95 satisfies P _1/2 ≦ 0.55, and the carbon black is DBP oil absorption (hereinafter referred to as "O _DBP".) is O a _DBP ≧ 100 mL / 100 g, the carrier for a solid polymer fuel cell catalyst layer V _0.95 is to satisfy the V _0.95 ≧ 100cm ³ / g carbon material.

(2) The moisturizing carbon material further has a specific surface area (hereinafter referred to as “S _BET ”) according to the BET method of nitrogen gas adsorption / desorption isothermal measurement, and S _BET ≧ 2000 m ² / g. The carrier carbon material for a catalyst layer for a polymer electrolyte fuel cell according to (1), wherein the pore volume (hereinafter referred to as “V _micro ”) is V _micro ≧ 0.8 mL / g.

  (3) The oxygen content of the moisturizing carbon material is 3% by mass to 10% by mass, and the catalyst layer for a solid polymer fuel cell according to any one of (1) to (2) Support carbon material.

  (4) A solid polymer fuel cell characterized by using the support carbon material for a catalyst layer for a solid polymer fuel cell according to any one of (1) to (3).

  By using the material for the catalyst layer for the polymer electrolyte fuel cell of the present invention, even in a low humidification environment with a relative humidity of 50% or less, which is a practical operation environment of the polymer electrolyte fuel cell, it is equivalent to the saturated humidification state. There is a remarkable effect of exhibiting performance.

  The gas polymer fuel cell using the catalyst layer material for a solid polymer fuel cell according to the present invention can simplify the mechanism for controlling the humidified state, thereby reducing the cost of the fuel cell system. This brings about a remarkable effect of accelerating the commercial market spread of polymer electrolyte fuel cells.

[First embodiment]
The first embodiment is a support carbon material for a catalyst layer for a polymer electrolyte fuel cell in which a moisture-retaining carbon material and carbon black are mixed at a mass ratio of 2: 8 to 9: 1.

The moisturizing carbon material, water vapor adsorption amount when you Keru relative water vapor pressure 0.95 desorption curve of water vapor adsorption-desorption isotherm at 25 ° C. (hereinafter, referred to as "V _0.95".) The value of, 1250 cm ³ / g ≦ V _0.95 ≦ 2500 cm ³ / g and the relative water vapor pressure (hereinafter referred to as “P _1/2 ”) indicating a water vapor adsorption amount half that of V _0.95 is P _1/2 ≦ 0.55 Meet.

The carbon black, DBP oil absorption (hereinafter referred to as "O _DBP".) Is _{O DBP ≧ 100mL / 100g, V} 0.95 satisfies V _0.95 ≧ 100cm ³ / g.

The moisturizing carbon material further has a specific surface area (hereinafter referred to as “S _BET ”) according to the BET method of nitrogen gas adsorption / desorption isothermal measurement, where S _BET ≧ 2000 m ² / g, and the micropore volume (by SF method) Hereinafter, “V _micro ”) satisfies V _micro ≧ 0.8 mL / g.

  Furthermore, the oxygen content of the moisturizing carbon material is 3% by mass to 10% by mass.

(Moisture retention of moisturizing carbon materials)
The physical property index that defines the amount of moisture that is stored and released by carbon materials is a physical property index that indicates how much water vapor is stored and released when the pressure of water vapor is increased or decreased at a constant temperature, so-called water vapor adsorption. Isothermal characteristics were adopted.

  The evaluation temperature of the water vapor adsorption property was 25 ° C, for which a measurement technique was established for the device.

  The measuring apparatus used was a water vapor adsorption apparatus Bell Soap Aqua (trade name) manufactured by Nippon Bell Co., Ltd. The measured values of Examples and Comparative Examples are measured using this apparatus.

  In general, the surface of a carbon material called graphite or amorphous carbon has a weak polarity, so the interaction with water molecules, which are polar molecules, is weak, and so-called hydrophobicity is exhibited. For this reason, the water vapor adsorption characteristics of carbon materials hardly adsorb or desorb water vapor at low relative pressures of 50% or less (equivalent to a relative water vapor pressure of 0.5), and the amount of adsorption gradually increases from a relative pressure of 0.7 or higher. The amount of adsorption increases greatly in the vicinity of a relative pressure of 1.0 where water condenses, but the amount of adsorption is as low as several percent or less with respect to the mass of the carbon material. That is, in general, carbon materials are inactive against water vapor at a relative pressure of 0.7 or less, and even when a carrier carbon material is used for the catalyst layer, in the practically important region of 50% or less relative humidity, It is considered that the carrier carbon material does not contribute to moisture retention.

Therefore, from the viewpoint of the principle of water vapor adsorption, a carbon material with a special structure absorbs and releases water vapor at a relative pressure of about 0.5 or less, and the adsorption / desorption amount is equivalent to the mass of the carbon material. As an optimum physical property index, when it is applied to a fuel cell catalyst layer, it exhibits an excellent output characteristic equivalent to saturated humidification even in a low humidification operating environment with a relative humidity of 50% or less. _Attention was paid to a water vapor adsorption amount V _0.95 at a relative pressure of 0.95 and a relative water vapor pressure P _1/2 indicating a half water vapor adsorption amount in the adsorption / desorption isothermal measurement.

That is, the moisture retention carrier carbon material specified in the present invention has a water vapor adsorption amount V _0.95 of 1250 cm ³ / g ≦ V at a relative water vapor pressure of 0.95, which is a water vapor adsorption / desorption characteristic at 25 ° C. isothermal. _0.95 ≦ 2500 cm ³ / g, and the relative water vapor pressure (hereinafter referred to as P _1/2 ) indicating a water vapor adsorption amount half of V _0.95 is controlled to 0.55 or less.

If V _0.95 is less than 1250 cm ³ / g, the amount of water released from the catalyst is small, so that the proton conductive resin constituting the catalyst layer cannot be sufficiently moisturized, and as a result, low humidification with a relative humidity of 50% or less. In the environment, the electrical resistance of the catalyst layer increases and the output characteristics deteriorate.

Further, when a catalyst exceeding 2500 cm ³ / g is used for the catalyst layer, the amount of water released from the catalyst is too much, so that flooding occurs at a so-called high current density.

More preferably _{^{1350cm 3 / g ≦ V 0.95 ≦}} 2500cm 3 / g.

If P _1/2 exceeds 0.55, the catalyst layer dries in an operating environment with a relative humidity of 50% or less, so that proton conduction resistance increases and output decreases. More preferably, P _1/2 ≦ 0.50, and still more preferably P _1/2 ≦ 0.45. Particularly preferably, P _1/2 ≦ 0.42.

  The particle size of the moisturizing carrier carbon material defined by the present invention is preferably 10 nm or more and 10 μm or less. If it is less than 10 nm, pores for substantial gas diffusion cannot be secured in the catalyst phase. On the other hand, if the particle diameter exceeds 10 μm, the distribution of catalyst components in the catalyst phase becomes sparse, resulting in a large current density. It becomes difficult to take out. More preferably, it is 50 nm or more and 5 μm or less.

(Method for producing moisturizing carbon material)
As long as the moisture-retaining carbon material satisfies the provisions of the present invention, its production method is not limited, but specific examples include petroleum-based, coal-based pitch, pitch coke, artificial graphite, petroleum, coal. Various carbon materials made from resins of origin, carbon materials made from natural plants, carbon materials made from char, so-called carbon fibers, etc. as raw materials, made porous by so-called activation treatment, Activated carbon produced from natural plants such as bamboo and wood can be applied.

  Examples of the activation treatment method include activation treatment such as oxidation treatment in an oxidizing atmosphere such as air and oxygen, alkali activation, water vapor activation, carbon dioxide gas activation, and zinc chloride activation. After the activation treatment, heat treatment is performed under normal or pressurized conditions in a gas atmosphere in which inert gas, reducing gas, ammonia gas, and oxidizing gas, each of which is a single gas or a mixture of multiple gases. Thus, various functional groups can be selectively imparted and controlled on the surface of the carbon material to control water vapor adsorption characteristics and nitrogen gas adsorption characteristics.

  In addition, porous carbon materials using the so-called template method (template method) (issued by the Japan Society for the Promotion of Science, Carbon Materials 117th Committee (March 2007), new developments in carbon materials, 24-30 contributions, 261 -271) can also be suitably used for the moisturizing carrier carbon material of the present invention. For example, the template method for producing porous carbon is, for example, a mesoporous silica that is a porous material in the mesopore region, a zeolite that is a porous material in the micropore region, and a colloidal that can control various pore sizes. Silica etc. can be mentioned.

  In particular, the presence of so-called micropores is indispensable for exhibiting the water vapor adsorption characteristics defined in the present invention. Water molecules inside the micropores are bound more strongly than those adsorbed on the carbon material surface due to the sum of the Van der Waals forces from the four inner walls even on a hydrophobic surface such as a carbon material. Therefore, water molecules are adsorbed inside the micropores even at a low relative pressure. It is difficult to satisfy the water vapor adsorption characteristics of the present invention simply by the presence of micropores. In order to adsorb a considerable amount of water molecules at a low relative pressure, it is important to increase the pore volume with a diameter of 1 nm or less among the micropores or to increase the hydrophilicity in the micropores. Among the micropores, the volume of ultramicropores (<0.7 nm) can be an important indicator for satisfying the definition of the present invention. This is because if the pore diameter is close to the size of the water molecule, the interaction between the inner wall of the pore and the water molecule due to the Van der Waals force is strengthened, and it is assumed that the adsorption starts from a lower water vapor pressure. .

For the introduction of micropores suitable for the present invention, for example, the following production method can be suitably used. First, in order to increase the absolute value of the water vapor adsorption amount, at least the specific surface area (BET value by nitrogen gas adsorption) is preferably 1500 m ² / g or more, more preferably 2000 m ² / g, more preferably 2500 m ² / g. The above porous carbon is produced. A specific surface area of 2500 m ² / g or more can be obtained by using a commercially available activated carbon of 2000 m ² / g or more for an electric double layer capacitor as a starting material and further applying an activation treatment with carbon dioxide gas and water vapor. Then, in order to further reduce the pore diameter of the micropores, heat treatment is performed at a temperature of 1200 ° C. or higher in an inert atmosphere.
The heat treatment of the carbon material intends to narrow the pores by restructuring the structure of the carbon hexagonal mesh surface constituting the carbon material with heat. The application to the present invention is preferably 1200 ° C. or more and 2000 ° C. or less. This is because when the heat treatment is performed at a high temperature of 2000 ° C. or higher, the crystallinity is increased so that the pores are completely lost. Substantially preferred is 1200 ° C. or higher and 1600 ° C. or lower. Above 1600 ° C, the pores of most carbon materials are crushed. Below 1200 ° C, rearrangement of the carbon network surface does not occur, so the pore structure does not change.

  In order to produce a porous carbon material satisfying the water vapor adsorption characteristics defined in the present invention, it is essential to make the surface of the carbon material hydrophilic in addition to the above-described porous formation (activation treatment) and heat treatment. Specifically, an oxygen-containing functional group having a high polarity is imparted to the surface of the carbon material. For the method, treatment with an oxidizing agent having a strong oxidizing action is preferable. For example, a carbon material is immersed in a solution of a strong oxidizing agent such as fuming nitric acid or fuming sulfuric acid, and an oxidizing treatment while heating is preferred. As other strong oxidation treatments, heat treatment with NOx and heat treatment with a mixture of NOx and oxygen can be suitably used. In particular, heat treatment using a mixed gas of NOx and oxygen can be suitably used in the present invention to increase polarity because nitrogen is introduced in a large amount into the carbon material. In addition, a combination of both and a combination with other oxidation treatments are also effective means. For example, a carbon material is treated by flowing a mixed gas of NO and oxygen at 400 ° C. to 1000 ° C., preferably 400 ° C. to 800 ° C. Further, nitrogen atoms can be introduced into the carbon material by this treatment, and the polarity of the carbon material is further increased, which is suitable for the present invention.

  Furthermore, heat treatment in an inert atmosphere after the oxidation treatment is also preferably used in the present invention. The carbon material is converted into carbon dioxide gas by decomposing oxygen-containing functional groups on the catalyst when the supported catalyst fine particles such as platinum interact with the strongly acidic functional group on the carbon surface and the catalyst is held at a particularly noble potential. Consumes the surface. In order to suppress the consumption of the carbon material, it is effective to perform heat treatment in an inert atmosphere at a temperature of 1000 ° C. or lower. It is possible to selectively remove a strong acidic group such as a carboxyl group which is easily converted to carbon dioxide by heat treatment under an inert atmosphere at 1000 ° C. or lower, preferably 800 ° C. or lower, which is suitable for the present invention.

(Carbon black)
It was found that the amount of DBP oil supply is an important physical property index as an index of the secondary aggregation structure required for carbon black, and the optimum physical property range is 100 mL / 100 g or more.

  The amount of DBP oil supply (dibutyl phthalate: a kind of plasticizer) is an index that has a high positive correlation with the amount of voids in the secondary aggregate structure of carbon black, that is, the degree of structure development. It is based on becoming an important indicator for determining the rate.

  When the DBP oil supply amount is less than 100 mL / 100 g, the porosity required for gas diffusion in the catalyst layer cannot be ensured, resulting in a decrease in power generation characteristics. Although there is no upper limit in the optimum range of DBP oil supply, the upper limit is substantially 1000 mL / g due to the structure of carbon black.

  The DBP oil supply was measured according to JIS K 6217-4.

It has been found that V _0.95 is an important physical property index as a moisturizing index required for the carbon black defined in the present invention, and the optimum physical property range is V _0.95 ≧ 100 cm ³ / g.

More preferably with respect to V _0.95 , V _0.95 ≧ 150 cm ³ / g, more preferably V _0.95 ≧ 200 cm ³ / g.

When V _0.95 is less than 100 cm ³ / g, the low humidification property of the catalyst layer due to the mixing of the catalyst made of the moisture-retaining carrier carbon material and the catalyst made of carbon black becomes insufficient. The upper limit of V _0.95 of the carbon black of the present invention is not particularly limited, but the upper limit is substantially 1000 cm ³ / g due to material restrictions of carbon black.

(Mixing of moisturizing carrier carbon material and carbon black)
Support carbon for catalyst layer for solid polymer fuel cell having “high moisture retention” and “sufficient water vapor releasing ability in low humidification region” by mixing catalyst made of moisture retention carrier carbon material and above-mentioned catalyst made of carbon black Realize the material. The mixing ratio is preferably 2: 8 to 9: 1 by mass ratio, more preferably 3: 7 to 8: 2 by mass ratio.

  If the mass ratio of the moisturizing carrier carbon material is smaller than 2, the moisturizing property cannot be ensured sufficiently, and the low humidification characteristics of the catalyst layer are deteriorated. Further, if the mass ratio of the moisturizing carrier carbon material exceeds 9, the gas diffusibility of the catalyst layer is lowered, which causes a new problem that power generation characteristics are lowered due to the reaction gas supply rate-determining rate.

  The mixed state of the catalyst using the moisturizing carrier carbon material and the catalyst using carbon black may be homogeneously mixed, or each may form an aggregate. The method for mixing the two kinds of catalysts of the present invention is not particularly limited. Illustrative examples include mixing with a mortar or the like, mixing with a ball mill, or the like, and stirring and mixing in a state dispersed in a solvent. Alternatively, the catalyst component can be supported after mixing the carbon materials before supporting the catalyst.

(Specific surface area S _BET / Micro pore volume V _micro )
As a result of intensive studies on the structure of the pore size distribution from the viewpoint that porosity is important for moisture storage characteristics, the specific surface area S _BET by BET analysis in the adsorption and desorption isothermal measurement of nitrogen gas at liquid nitrogen temperature The micro pore volume V _micro by the SF analysis was found to be an important index for improving the low humidification characteristics of the catalyst layer.

That is, when the specific surface area S _BET by the BET analysis of the carbon material is 2000 m ² / g or more and the micropore volume V _micro by the SF method is 0.8 mL / g or more, the carbon material is used as a carrier. It is possible to greatly improve the low humidification characteristics of the catalyst layer using the prepared catalyst.

When S _BET is less than 2000 m ² / g, a sufficient water vapor adsorption amount cannot be ensured, and thus low humidification characteristics of the catalyst layer cannot be ensured. More preferably, S _BET is 2200 m ² / g or more. The upper limit of S _BET is not particularly defined in the present invention, and it is suitably used in the present invention as long as it is 2000 m ² / g or more. However, the present material technology has the largest specific surface area per mass of zeolite template carbon composed only of micropores, and the practical upper limit of S _BET is 5000 m ² / g.

When V _micro is less than 0.8 mL / g, the moisture retention amount of the catalyst layer when operating in a low humidified environment decreases, proton conduction resistance increases, and power generation characteristics deteriorate. Preferably, V _micro is 0.9 mL / g or more, more preferably 1.0 mL / g or more. The upper limit of V _micro is not particularly defined in the present invention, and if it is 0.8 mL / g, it is suitably used in the present invention. However, the actual upper limit of V _micro is 2500 mL / g in the current material technology.

  In order to increase the amount of water vapor adsorption at a low relative pressure, it is important to reduce the average pore diameter of the micropores. The average pore diameter (mode average diameter) according to the SF method analysis in the nitrogen gas adsorption characteristics is preferably 1.5 nm or less, and more preferably 1.3 nm or less.

The smaller the micropore diameter, the greater the amount of water vapor adsorption at a low relative pressure of 0.5 or less.

  In addition, the adsorption isothermal measurement of nitrogen gas in the present invention uses the Autosorb (trade name) of Quantachrome Instruments, and the analysis of the measured value uses software (Autosorb 1 for Windows (registered)) Trademark) 1.24).

The SF analysis method is a theory to analyze the micropore structure based on the gas adsorption isotherm data proposed by A. Saito and HC Foley. Super micropores with a pore diameter of 0.7nm to 2.0nm (specified by IUPAC) The analysis was proposed as an analysis of the classification (Category) and published in the literature “Curvature and Parametric Sensitivity in Models for Adsorption in Micropores”, AIChE Journal, 37, 429-436 (1991). Two methods, the HK method and the SF method, are widely used for the analysis of super-micropores, and the analysis programs for both nitrogen gas adsorption isotherms currently on the market are both included as analysis programs. . The former is an analysis method suitable for slit-type pores, and the latter is suitable for cylindrical pore structures, but the V _micro value used in the present invention is compared with the HK method and SF for various porous materials. The difference between the laws is at most about 5%, and it can be considered that the difference between the two is substantially negligible, and the analysis value according to the HK method can be applied to the provisions of the present invention.

(Oxygen content)
This can be further improved when the oxygen content is 3 mass% or more and 10 mass% or less.

  As a result of intensive studies from the viewpoint of interaction with water molecules on the surface of the moisturizing support carbon material, it was found that the oxygen content contained in the carbon material is an effective index for improving the low humidification characteristics of the catalyst layer. Specified a range. That is, it defines that the oxygen content of the moisturizing carrier carbon material is 3% by mass or more and 10% by mass or less.

  If the oxygen content is less than 3% by mass, the interaction between water molecules and the carbon material surface is small, and the water vapor adsorption amount at a low relative pressure decreases. On the other hand, if the oxygen content exceeds 10% by mass, the oxidative consumption of the carbon material in the operating environment is great and the durability of the catalyst layer is lowered, which is not suitable for the present invention.

  More preferably, the oxygen content is 4% by mass or more and 9% by mass or less, and further preferably 5% by mass or more and 8% by mass or less.

  Control of the oxygen content of the moisturizing carrier carbon material suitable for the present invention is not particularly limited. For example, as a gas phase treatment, heat treatment in an oxygen-containing atmosphere, heating in an ozone-containing atmosphere may be used. Applying a method of heat-treating a carbon material in a generally known oxidizing agent such as nitric acid, sulfuric acid, hydrogen peroxide, etc., as a treatment, (heating) treatment in oxygen plasma, or oxidation treatment in a liquid phase Is possible. After these oxidation treatments, the oxygen content can be controlled by heat treatment in an inert atmosphere or a reducing atmosphere.

  In the measurement of the oxygen content of the present invention, the oxygen content was calculated as the remaining amount from the C, H, N analysis by the so-called combustion method widely used for the elemental analysis of organic substances and the analysis value of S. The oxygen content of the examples was also measured by this method.

[Second Embodiment]
The second embodiment is a polymer electrolyte fuel cell using the support carbon material for the catalyst layer for the polymer electrolyte fuel cell shown as the first embodiment.

(Catalyst component applied to the present invention)
The catalyst layer of the present invention can be applied to both an anode electrode and a cathode electrode of a polymer electrolyte fuel cell. When the catalyst layer of the present invention is applied to the cathode electrode, it is essential to use a catalyst component having oxygen reduction activity as the catalyst component, but the present invention is not particularly limited with respect to the catalyst component.

Examples of catalyst components having oxygen reduction activity include noble metals such as platinum, palladium, ruthenium, gold, rhodium, osmium, iridium, composites and alloys of noble metals obtained by combining two or more of these noble metals, and noble metals and organic compounds. And a complex with an inorganic compound, a transition metal, a complex of a transition metal with an organic compound or an inorganic compound, a metal oxide, and the like. Also, a combination of two or more of these can be used. Further, a non-noble metal-based catalyst having oxygen reduction activity, for example, a porphyrin, an N ₄ -macrocyclic complex of a 3d iron group element typified by phthalocyanine can be applied. Also, a composite of a noble metal-based catalyst component and a non-noble metal-based catalyst component can be applied to the present invention.

  Similarly, in the case of application to the anode electrode, the production method for supporting the catalyst component on the support carbon material is not particularly limited, and a general method for supporting the noble metal fine particles on the carbon support can be applied. For example, after dissolving a noble metal organic complex such as a noble metal chloride, nitrate, lactate or acetylacetone complex in a solvent such as water or an organic solvent, it is reduced with a reducing agent to form fine particles of the catalytically active component. A production method supported on a carbon support is preferred. Examples of the reducing agent include alcohols, phenols, citric acids, ketones, aldehydes, carboxylic acids, ethers, and the like. At that time, sodium hydroxide, hydrochloric acid or the like may be added to adjust the pH, and a surfactant such as polyvinylpyrrolidone may be added to prevent aggregation of particles. The catalyst supported on the carbon support may be further subjected to re-reduction treatment. As the re-reduction treatment method, heat treatment is performed at a temperature of 500 ° C. or lower in a reducing atmosphere or an inert atmosphere. Alternatively, it can be dispersed in distilled water and reduced with a reducing agent selected from alcohols, phenols, citric acids, ketones, aldehydes, carboxylic acids and ethers.

When supporting an N ₄ -macrocyclic complex of a 3d iron group element typified by porphyrin or phthalocyanine, the carrier carbon material is dispersed in a complex solution in which the complex is dissolved in an appropriate solvent, and the solvent is evaporated under reduced pressure and heated. The complex which is a catalyst component can be adsorbed on the surface of the support carbon material and used as it is as a catalyst. In addition, after the carrier carbon material is dispersed in the complex solution, a method of depositing the complex component on the carrier carbon material by introducing a poor solvent of the complex and a solvent compatible with the complex dissolving solvent is also preferably used. However, the method of adsorption of the complex is not limited to the method described above. More preferably, after the complex is adsorbed on the carbon support, heat treatment is performed in an inert atmosphere such as nitrogen, argon, helium, or the like in a nitrogen gas atmosphere, so that the electronic bond with the support carbon material becomes stronger and the catalyst is more concentrated. The activity of the component can be increased, and it can be suitably used in the present invention. As heat processing temperature, 300 to 900 degreeC is preferable.

(Catalyst layer of the present invention and production method thereof)
The catalyst layer of the present invention contains a proton conductive resin as an electrolyte material in addition to the catalyst, but is not limited by the type or form of the proton conductive resin. In addition to the catalyst comprising the carbon support defined by the present invention and the proton conductive resin, there are also added a metal oxide fine particle for improving moisture retention, and a catalyst layer in which a resin such as tetrafluoroethylene for enhancing water repellency is dispersed. It can be suitably used in the present invention. In addition, as electrolyte materials having proton conductivity, fluorine-based polymers introduced with sulfonic acid groups represented by Nafion (registered trademark) manufactured by DuPont, and hydrocarbon-based polymers introduced with phosphoric acid groups, sulfonic acid groups, etc. And a polymer such as polyimide having benzenesulfonic acid introduced therein.

  The method for producing the catalyst layer of the present invention is not particularly limited as long as it contains a catalyst using the carbon support defined by the present invention. However, the catalyst comprising the carbon support of the present invention and the electrolyte having proton conductivity are not limited. An example is a method in which a catalyst layer slurry made of a solvent containing the material is prepared and applied to a polymer material such as a Teflon (registered trademark) sheet, a gas diffusion layer, or an electrolyte membrane and dried. When applied to a polymer material such as a Teflon (registered trademark) sheet, the electrolyte membrane is sandwiched between two polymer materials such as a Teflon (registered trademark) sheet so that the catalyst layer and the electrolyte membrane are in contact with each other. As an example, the catalyst layer can be fixed to the electrolyte membrane in step 1 and then hot-pressed by sandwiching it between two gas diffusion layers to produce a membrane / electrode assembly (Mebrane Electrode Assembly, MEA). . In addition, when applied to the gas diffusion layer, the MEA is applied by sandwiching the electrolyte membrane between the two gas diffusion layers so that the catalyst layer and the electrolyte membrane are in contact, and pressing the catalyst layer to the electrolyte membrane, such as hot pressing. Can be produced. When the catalyst layer is applied to the electrolyte membrane, the MEA can be produced by sandwiching the gas diffusion layer between the two gas diffusion layers so that the catalyst layer and the gas diffusion layer are in contact with each other. it can.

  Examples of the solvent used for the catalyst layer slurry include methanol, ethanol, isopropanol, hexane, toluene, benzene, ethyl acetate, butyl acetate and the like.

  As a function of the gas diffusion layer, a function of uniformly diffusing gas from the gas flow path formed in the separator to the catalyst layer and a function of conducting electrons between the catalyst layer and the separator are required. If it has, it will not specifically limit. As a general example, a carbon material such as carbon cloth or carbon paper is used as a main constituent material.

  On the side of the gas diffusion layer in contact with the catalyst layer, a gas diffusion auxiliary layer called carbon pore having a thickness of several μm to several tens of μm as a main component can be provided. The function of the micropore layer is the same as that of the catalyst layer in order to uniformly supply the gas diffused by the gas diffusion layer having a pore structure of several μm to several tens of μm to the catalyst layer having sub-micron or smaller pores. The gas from the gas diffusion layer is uniformly dispersed in pores of submicron or less by the carbon black structure, and the gas is smoothly supplied to the catalyst layer. The physical properties required for carbon black are water repellency, chemical and electrochemical stability, and pore distribution equivalent to that of the catalyst layer. In order to increase water repellency, it is also effective to increase the crystallinity of carbon black.

(Solid polymer fuel cell using catalyst layer of the present invention and method for producing the same)
A polymer electrolyte fuel cell can be manufactured by sandwiching the MEA having the gas diffusion layers mounted on both electrodes with a separator having a groove for a so-called gas flow path. By controlling the temperature at which the polymer electrolyte fuel cell is operated, the fuel to be supplied (hydrogen gas), the gas flow rate of air (oxygen) as the oxidant, and the amount of water vapor supplied with the gas, it is suitable for the application It is possible to operate a highly efficient polymer electrolyte fuel cell having output characteristics. In particular, by using the catalyst-supported carbon material of the present invention, good output characteristics can be exhibited even under low humidification conditions.

(Preparation of moisturizing carbon material)
Using activated carbon (available from Kuraray Chemical Co., Ltd., nitrogen BET specific surface area nominal 1700 and 2000 m ² / g) as a starting material, activation treatment was performed at 1050 ° C. to 1200 ° C. over 1 hour to 5 hours under the flow of carbon dioxide, The specific surface area was increased, and activated carbon having a density of about 1700-2200 m ² / g was prepared. In order to control the water vapor adsorption amount of these activated carbon materials, in order to increase the polarity of the surface of the carbon material, it is treated at 450 ° C. to 650 ° C. for 1 to 3 hours under a mixed gas flow of nitrogen monoxide and oxygen, Oxygen-containing functional groups were introduced on the carbon surface. In addition, as another oxygen-containing functional group introduction treatment, fuming nitric acid and a carbon material were placed in a beaker and heated on a hot plate for 1 to 3 hours to perform thermal fuming nitric acid treatment. In order to control the amount of oxygen-containing functional groups, these carbon materials were heat-treated at 700 ° C. to 1100 ° C. for several hours under a nitrogen gas atmosphere.

Furthermore, in order to obtain a carbon material having a high water vapor adsorption amount, ZTC (Zeolite Temolated Carbon) consisting only of micropores was prepared by the following method. Y-type zeolite (trade name HZS-320NAA) manufactured by Tosoh Corporation was used as a zeolite as a template. A few grams of zeolite powder and PTFE-coated magnetic stirrer were placed in the flask, vacuum-dried at room temperature for 1 day, and further vacuum-dried at 150 ° C. for 1 day. Next, about 100 mL of furfuryl alcohol (manufactured by Wako Pure Chemical Industries, Ltd.) as a carbon source filled in the pores was added dropwise into the vacuum flask. At this time, the flask was ice-cooled in order to prevent the furfuryl alcohol from being polymerized by the heat generated by the filling. After filling, nitrogen gas was introduced, and the mixture was stirred at room temperature for 1 day in a flow state. Zeolite and furfuryl alcohol are separated by a centrifuge, and the taken-out zeolite is stirred for about 10 minutes with 200 mL of mesitylene (manufactured by Wako Pure Chemical Industries, Ltd.) and then centrifuged to repeat the same operation 5 times. Finally, the zeolite taken out is filtered under reduced pressure with a PTFE immunized lotus filter, placed in a quartz boat and set in a heating furnace, and nitrogen gas is flowed. Heated to 85 ° C over about 1 hour and held for 1 day, then raised to 160 ° C over 2 hours, held for 8 hours and allowed to cool to room temperature, completing the furfuryl alcohol polymerization (polyfurfuryl alcoholization) It was. Polyfurfuryl alcohol-filled zeolite is crushed in a mortar, placed in a quartz boat and set in a heating furnace, and nitrogen gas is circulated. To mix. The concentration of propylene gas was 5 to 10 vol%. After maintaining at 680-720 ° C. for 1-2 hours, the introduction of propylene gas was stopped, only nitrogen gas was circulated again, the temperature was raised to 900 ° C. over 1 hour, maintained for 3 hours, and then allowed to cool to room temperature. The obtained powder was added little by little to 100 mL of hydrofluoric acid and stirred for about 5 hours to dissolve and remove the zeolite. In order to wash hydrofluoric acid, the powder filtered under reduced pressure with a membrane filter was again dispersed in distilled water, stirred and washed. This washing operation was repeated three times and dried under reduced pressure to obtain ZTC.
In order to make the obtained ZTC suitable for water vapor adsorption characteristics suitable for the present invention, fuming nitric acid and a carbon material are placed in a beaker as an oxygen-containing functional group introduction treatment and heated on a hot plate for 1 to 3 hours. Then, a hot fuming nitric acid treatment was performed. Moreover, the same process was performed using fuming sulfuric acid. In order to control the amount of the oxygen-containing functional group, these carbon materials were heat-treated at 400 ° C. to 1100 ° C. for several hours under a nitrogen gas atmosphere circulation to obtain final specimens.

(Evaluation of physical properties of moisturizing carbon materials)
The water vapor adsorption characteristics were measured using a water vapor adsorption device Bell Soap Aqua (trade name) manufactured by Nippon Bell Co., Ltd. After vacuum degassing for 4 hours at 100 ° C., water vapor adsorption / desorption characteristics were measured at 25 ° C. The water vapor adsorption characteristic was measured up to a relative pressure of 0.95, and the water vapor adsorption amount at a relative pressure of 0.95 was V _0.95 . The relative pressure at which the water vapor adsorption amount in the desorption curve shows half of V _0.95 was defined as P1 _{/ 2} .

  Autosorb (trade name) from Quantachrome Instruments is used to evaluate the nitrogen gas adsorption characteristics of carbon materials, and the software (Autosorb 1 for Windows (registered trademark)) supplied with the device is used for analysis of measured values. 1.24). The pretreatment was performed under the same conditions as the water vapor adsorption characteristics.

(Preparation of catalyst)
A chloroplatinic acid aqueous solution and polyvinylpyrrolidone were dissolved in distilled water, and sodium borohydride was dissolved in distilled water while stirring at 60 ° C. to reduce chloroplatinic acid. The catalyst support carbon material was added to the aqueous solution and stirred for 60 minutes, followed by filtration and washing. The obtained solid was vacuum-dried at 90 ° C., pulverized in a mortar, and heat-treated at 250 ° C. for 1 hour in a hydrogen atmosphere to prepare a platinum-supported catalyst. The catalyst was prepared so that the supported amount of platinum was 35% by mass.

(Preparation of catalyst layer and MEA)
Add the catalyst to a 5% Nafion solution (DE521 manufactured by DuPont) in an argon stream so that the mass of Nafion solids is 1.2 times the mass of the catalyst, and after gently stirring, pulverize the catalyst with ultrasound. Then, butyl acetate was added with stirring so that the solid content concentration of the platinum catalyst and Nafion was 2% by mass to prepare each catalyst layer slurry.

The catalyst layer slurry is applied to one side of a Teflon (registered trademark) sheet by a spray method and dried in an argon stream at 80 ° C. for 10 minutes and then in an argon stream at 120 ° C. for 1 hour, for a polymer electrolyte fuel cell A catalyst layer was obtained. In addition, conditions, such as a spray, were set so that each catalyst layer might use platinum usage amount 0.25 mg / cm < ² >. The amount of platinum used was determined by measuring the dry mass of a Teflon (registered trademark) sheet before and after spray coating and calculating the difference.

Further, two pieces of 2.5 cm square are cut out from the obtained catalyst layer for the polymer electrolyte fuel cell, and the electrolyte membrane (Nafion 112 is used with two electrodes of the same type so that the catalyst layer is in contact with the electrolyte membrane. ) And hot pressing was performed at 130 ° C. and 90 kg / cm ² for 10 minutes. After cooling to room temperature, only the Teflon (registered trademark) sheet was carefully peeled off to fix the anode and cathode catalyst layers to the Nafion membrane. Further, two carbon cloths (EC-CC1-060 manufactured by ElectroChem) were cut into 2.5 cm square sizes, and the anode and cathode fixed on the Nafion membrane were sandwiched at 130 ° C. and 50 kg / cm ² . Hot pressing was performed for 10 minutes to produce a membrane / electrode assembly (Mebrane Electrode Assembly, MEA).

(Performance evaluation of catalyst layer by fuel cell)
The produced MEA was incorporated into a cell, and the fuel cell performance was evaluated by a fuel cell measuring device according to the following procedure.

Air was supplied to the cathode, pure hydrogen was supplied to the anode, the amount of gas necessary for power generation of 1000 mA / cm ² was set to 100%, and the utilization was 30% and 60%, respectively, and the gas pressure was 0.1 MPa. . The cell temperature was 80 ° C.

First, the supplied air and pure hydrogen were bubbled and humidified in distilled water kept at 80 ° C., respectively. After supplying a gas to the cell under these conditions, by gradually increasing the load until 300 mA / cm ² to fix the load 300 mA / cm ^2, the inter-cell terminal voltage after the lapse of 60 minutes was saturated humidification output .

Next, the feed gas was bubbled in distilled water kept at 55 ° C. and humidified. After supplying a gas to the cell under these conditions, by gradually increasing the load until 300 mA / cm ² to fix the load 300 mA / cm ^2, and the inter-cell terminal voltage after the lapse of 60 minutes and the low humidification output . A value obtained by subtracting the low humidified output from the saturated humidified output was defined as an “output reduction amount”, which was used as an index for performance evaluation during the low humidified operation in the examples.

Furthermore, as the high load characteristics, the output current density is gradually increased under the same operating conditions after the aforementioned output reduction amount measurement, and the steady value of the output voltage at 1000 mA / cm ² is set as the “high load characteristics”. It was used as an index.

(Example of Embodiment 1)
A catalyst was prepared using template carbon composed of micropores prepared by the above-described method, coke subjected to steam activation treatment, and commercially available activated carbon, and porous carbon further treated with hot nitric acid, hot sulfuric acid, and fuming sulfuric acid as a moisturizing carbon material. Based on commercially available carbon black, oxidized with hot nitric acid and then heat-treated in an inert atmosphere, or activated by heat treatment at 950 to 1150 ° C in a CO2 stream, and further in an inert atmosphere after hot nitric acid oxidation Carbon black having various physical properties was prepared by heat treatment. A catalyst was prepared using this carbon black as a carrier. A catalyst using a moisturizing carbon material as a carrier and a catalyst using carbon black as a carrier were mixed at a predetermined mass ratio, and a catalyst layer was produced according to the above-described method. Table 1 summarizes the composition and various physical property values of the catalyst used in the example of the first embodiment. An MEA was prepared by combining the catalyst layer composed of catalyst No. 6 in Table 1 with the anode and the catalyst layer composed of catalyst Nos. 1 to 26 with the cathode, and the fuel cell characteristics were evaluated. Table 1 summarizes the results of the fuel cell evaluation together with the physical properties of the catalyst.

  A mortar was used for mixing the two kinds of catalysts.

  From Table 1, it was found that the catalyst layer using the carbon support of Embodiment 1 of the present invention exhibits excellent output characteristics when the humidity is low. Catalyst No. In the fuel cell using 24 as the cathode, a so-called flooding phenomenon in which the voltage suddenly drops during high load operation occurred, and a continuous and stable high load characteristic could not be obtained.

(Example of Embodiment 2)
Using the same anode as in the example of Embodiment 1 and using the catalyst shown in Table 2 as the cathode, an MEA was fabricated and the fuel cell characteristics were evaluated. Table 2 summarizes the properties of the cathode catalyst carrier and the fuel cell characteristics.

  It was found that by mixing the catalyst using the moisturizing carrier of Embodiment 2 and the catalyst using the carbon black of Embodiment 1 as a carrier, the output reduction amount and the high load characteristics are greatly improved.

(Example of Embodiment 3)
Template carbon was prepared using zeolite with various crystal structures formed only from steam, activated carbon with different carbon dioxide activation treatment conditions, and micropores as templates. Catalysts were synthesized using these as moisturizing carriers and mixed with the carbon black catalyst used in Embodiment 2 (mass ratio 1: 1) to prepare a catalyst layer. A mortar was used for mixing the two kinds of catalysts. Table 3 summarizes the physical properties of the moisturizing carrier carbon material and carbon black used and the evaluation results of the fuel cell characteristics. The same anode as in Embodiments 1 and 2 was used as the anode.

実施形態３の保湿性炭素を担体に用いた触媒と実施形態２のカーボンブラック触媒とを混合することにより、出力低下量と高負荷特性が大幅に改善することが判った。

It was found that the amount of decrease in output and the high load characteristics are greatly improved by mixing the catalyst using the moisturizing carbon of Embodiment 3 as the carrier and the carbon black catalyst of Embodiment 2.

Claims (4)

A carrier carbon material for a catalyst layer for a polymer electrolyte fuel cell in which a moisture-retaining carbon material and carbon black are mixed at a mass ratio of 2: 8 to 9: 1,
The moisturizing carbon material, water vapor adsorption amount when you Keru relative water vapor pressure 0.95 desorption curve of water vapor adsorption-desorption isotherm at 25 ° C. (hereinafter, referred to as "V _0.95".) The value of,
1250 cm ³ / g ≦ V _0.95 ≦ 2500 cm ³ / g
And a relative water vapor pressure (hereinafter referred to as “P _1/2 ”) indicating a water vapor adsorption amount half that of V _0.95 is P _1/2 ≦ 0.55.
The filling,
The carbon black has a DBP oil supply amount (hereinafter referred to as “O _DBP ”).
O _DBP ≧ 100mL / 100g
And V _0.95 is
V _0.95 ≧ 100 cm ³ / g
A carbon material for a catalyst layer for a solid polymer fuel cell, characterized in that: The moisturizing carbon material further has a specific surface area (hereinafter referred to as “S _BET ”) according to the BET method of nitrogen gas adsorption / desorption isothermal measurement.
S _BET ≧ 2000m ² / g
The micropore volume (hereinafter referred to as “V _micro ”) according to the SF method is
V _micro ≧ 0.8mL / g
The support carbon material for a catalyst layer for a solid polymer fuel cell according to claim 1, wherein   3. The carrier carbon material for a catalyst layer for a polymer electrolyte fuel cell according to claim 1, wherein the oxygen content of the moisturizing carbon material is 3% by mass to 10% by mass.   A solid polymer fuel cell comprising the support carbon material for a catalyst layer for a solid polymer fuel cell according to any one of claims 1 to 3.