JP4520815B2 - Gas diffusion layer for fuel cell, gas diffusion electrode for fuel cell, and fuel cell - Google Patents

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell that operates under conditions where water easily aggregates in a catalyst layer, such as a polymer electrolyte fuel cell.

  The basic structure of the fuel cell according to the present invention is, for example, a structure of a general polymer electrolyte fuel cell, and a catalyst layer serving as an anode and a cathode is disposed with a proton conductive electrolyte membrane interposed therebetween. Thus, a gas diffusion layer is further arranged on the outer side, and a separator is further arranged on the outer side to constitute a unit cell. Normally, these are stacked according to the required output and used as a fuel cell.

  In order to extract 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 at both electrodes, and a reducing property such as hydrogen is supplied to the anode side. Gas is supplied to the catalyst layer through the gas diffusion layer.

For example, when hydrogen gas and oxygen gas are used, a chemical reaction of H ₂ → 2H ⁺ + 2e ⁻ (E ₀ = 0V) occurring on the anode catalyst and O ₂ + 4H ⁺ + 4e ⁻ → 2H occurring on the cathode catalyst. _The current is taken out by utilizing the energy difference of the chemical reaction of ₂ O (E ₀ = 1.23 V).

  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 a proton conduction path through which protons generated on the anode catalyst can be transmitted to the cathode catalyst through the proton conductive electrolyte membrane. Furthermore, if the electron transfer paths through which the electrons generated on the anode catalyst can be transmitted to the cathode catalyst through the gas diffusion layer, the separator, and the external circuit are not disconnected, the current cannot be efficiently extracted. .

  Inside the catalyst layer, generally, pores formed in the material gaps as gas diffusion paths, electrolyte materials as proton conduction paths, and conductive materials such as carbon materials and metal materials as electron conduction paths form their respective networks. is doing.

  In particular, an ion exchange resin typified by a perfluorosulfonic acid polymer is used as a polymer electrolyte material in the proton conduction path. These generally used ion exchange resins exhibit high proton conductivity for the first time in a wet environment, and the proton conductivity decreases in a dry environment. This is thought to be due to the interposition and accompanying of water molecules for proton transfer.

  Therefore, in order to operate the fuel cell efficiently, it is essential that the electrolyte material is always in a wet state, and it is necessary to always supply water vapor together with the gas supplied to both electrodes.

  In general, for the purpose of supplying water to the electrolyte material, a method of humidifying the gas supplied to the cell and operating the cell at a temperature near the dew point is employed. According to this method, the water vapor supplied into the cell partially aggregates to form droplets of aggregated water. On the other hand, when current is taken out by the cathode reaction described above, water is generated on the cathode catalyst. Although depending on the operating conditions of the cell, the generated water aggregates when the water vapor in the catalyst layer becomes supersaturated, and forms aggregated water droplets.

  The droplets formed by the water vapor supplied to humidify agglomerate in the gas diffusion layer or the catalyst layer or the water produced by the reaction agglomerate block the gas diffusion path. This phenomenon is called flooding, and is remarkable in the cathode in which a large amount of water is generated during a large current discharge, leading to insufficient supply of gas and causing an extreme voltage drop.

  Therefore, in order to stably operate the fuel cell, it is necessary to satisfy the conflicting requirement that the condensed water is quickly discharged out of the system while sufficiently humidifying the inside of the catalyst layer.

  For this reason, the present inventors have been able to maintain a suitable moist environment and express extremely efficient battery performance without dividing the mass transfer path in the catalyst layer of the fuel cell according to Patent Document 1 so far. A catalyst layer has been proposed.

  On the other hand, the gas diffusion layer disposed outside the catalyst layer of both electrodes has 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. Various techniques have been conventionally proposed in order to efficiently operate a fuel cell.

  Among them, the technique of dividing the gas diffusion layer into a two-layer structure has succeeded in expressing a certain performance. Usually, the separator side has a first layer having a relatively large pore size with an emphasis on gas diffusivity, and the second layer on the catalyst layer side has a rough first layer and a microstructure. This is a technique for functioning as an intermediate layer for ensuring electronic conductivity and uniformity with the catalyst layer.

  For example, Patent Document 2 proposes a water-repellent gas diffusion layer mainly composed of carbon particles or fibers and a fluororesin, and a preferred embodiment proposes a two-layer structure having different porosity and pore diameter. Further, Patent Document 3 proposes a two-layer structure in which a layer mainly composed of fluororesin and carbon black is formed on the surface of a carbon fiber woven fabric as a structure of the gas diffusion layer.

  Further, Patent Document 4 proposes an intermediate layer having at least two pore size distribution centers between the electrode substrate and the catalyst layer, and as a preferred embodiment, two or more types of carbon particles having different particle size distributions are proposed. It has been proposed to have as the main component.

JP 2003-109643 A US Pat. No. 5,620,807 JP-A-10-261421 JP-A-2001-57215

  In Patent Document 2, although a preferable range of the porosity and the pore diameter is defined, there is no definition relating to the carbon particles or fibers to be used, and a method for controlling the pore diameter of the microporous layer in contact with the catalyst layer is one of the main components. Depending on the amount and molecular weight of the polymer material, it is difficult to control the pore size, which is not common.

  Patent Document 3 proposes a laminated structure of a gas diffusion layer having a two-layer structure. However, as in Patent Document 2, there is no provision regarding a preferable type or structure of carbon black, and all the performance of the catalyst layer is extracted. However, it is difficult only with the proposed content. In particular, these Patent Documents 2 and 3 both rely on a water-repellent polymer material as a means for securing a gas diffusion path with water, and in order to improve gas diffusivity, high insulation properties are required. It is necessary to increase the content of the molecular material, which tends to impair the conductivity.

  Furthermore, Patent Document 4 proposes to use a mixture of large-diameter carbon particles and small-diameter carbon particles as the main component of the gas diffusion layer in contact with the catalyst layer, and refers to the structure of the carbon material itself used. However, depending on the combination of particle diameters, there are cases where the gas diffusion path is interrupted, and when holes formed in different particle gaps between large and small diameter carbon particles are used as the gas diffusion path, In some cases, the particles move due to the fastening pressure of the cell and the pores are blocked, or the arrangement of the particles changes due to long-term use, and the pore diameter may change from the optimum state, which is not a sufficient proposal.

  Therefore, with the content that has been proposed in the past, particularly when a catalyst layer having high performance as proposed in Patent Document 1 is connected, a certain level of performance appears, but the maximum that the catalyst layer has. It was difficult to bring out the performance.

  Therefore, the present invention solves the above-mentioned problems, and while sufficiently humidifying the inside of the catalyst layer, the condensed water is quickly discharged out of the system, and does not cause flooding even during a large current discharge, and exhibits stable battery performance. An object of the present invention is to propose a gas diffusion layer for a fuel cell, a gas diffusion electrode, and a fuel cell using the same.

  In order to solve the above problems, as a result of repeated studies on the gas diffusion layer, in order to sufficiently bring out the performance of the high performance catalyst layer proposed in Patent Document 1, a micropore layer adjacent to the catalyst layer is used. In addition, the material itself has a structure that can form pores of an appropriate size in order to use carbon black with an appropriate surface property for water as a main component and to secure a gas movement path or a water movement path. And found that is effective.

  Furthermore, in order to select materials with these characteristics accurately, quantitative indicators were found. In other words, a micropore layer mainly composed of carbon black having an appropriate water vapor adsorption amount is disposed adjacent to the catalyst layer, and an appropriate amount is obtained using the DBP oil absorption amount and the specific surface area obtained by nitrogen adsorption. It was found that selecting carbon black having a structure and using it for the micropore layer was effective.

  Moreover, it has been found that such a gas diffusion layer is also useful for a general catalyst layer, and has led to the present invention.

  That is, the gist of the present invention is as follows.

(1) A gas diffusion layer for a fuel cell having a two-layer structure having a micropore layer using carbon black on one side of a gas diffusion fiber layer using a fibrous carbon material, and having 25 of the carbon black of the micropore layer A gas diffusion layer for a fuel cell, wherein an adsorption amount of water vapor at 100 ° C. and a relative humidity of 90% is 100 mL / g or less.

(2) The ratio X / Y of the DBP oil absorption amount X (mL / 100 g) and the nitrogen adsorption specific surface area Y (m ² / g) of the carbon black used for the micropore layer is 1 or more. The gas diffusion layer for a fuel cell according to (1) above.

(3) A catalyst layer using a catalyst component, a carbon material, and an electrolyte material is disposed in contact with the micropore layer of the fuel cell gas diffusion layer according to (1) or (2). A gas diffusion electrode for a fuel cell having a three-layer structure.

  (4) The carbon material of the catalyst layer is composed of a catalyst carrier carbon material carrying a catalyst component and a gas diffusion carbon material not carrying a catalyst component, and water vapor at 25 ° C. and a relative humidity of 90% of the gas diffusion carbon material. Adsorption amount is 100 mL / g or less, The gas diffusion electrode for fuel cells as described in said (3) characterized by the above-mentioned.

  (5) A fuel cell including a pair of electrodes sandwiching a proton conductive electrolyte membrane, wherein at least one of the electrodes is the gas diffusion electrode for a fuel cell according to (3) or (4). A fuel cell.

  (6) A fuel cell including a pair of electrodes sandwiching a proton conductive electrolyte membrane, wherein the fuel cell gas diffusion layer according to (1) or (2) is contained in at least one of the electrodes. A fuel cell.

  The fuel cell gas diffusion layer, the fuel cell gas diffusion electrode, and the fuel cell using the fuel cell according to the present invention have adequate characteristics of the carbon black used for the gas diffusion layer, so that the catalyst layer is sufficiently humidified. However, it is difficult for the gas diffusion path to be blocked by the generated water droplets and the like, and more efficient battery performance can be exhibited.

  The gas diffusion layer of the present invention has a two-layer structure, the separator side layer is a gas diffusion fiber layer mainly composed of a fibrous carbon material, and the catalyst layer side layer is a micropore mainly composed of carbon black. Composed of layers.

  The reason why the gas diffusion fiber layer mainly composed of the fibrous carbon material is selected on the separator side is that the gas permeability and the electron conductivity are both aimed. A fibrous carbon material is a suitable material as a material that can have a good electron conductivity while forming a large pore diameter that facilitates gas diffusion. Although it does not specifically limit, if a preferable example is shown, the carbon cloth and carbon paper comprised with the carbon fiber can be mentioned.

  In the present invention, the fibrous carbon material is the main component of the gas diffusion fiber layer, and for the purpose of increasing mechanical strength, it is reinforced with a binder such as a polymer material or further carbonized. The second and third components may be combined.

  Furthermore, the fibrous carbon material can be used with increased water repellency by coating the surface of the fibrous carbon material with a fluororesin, a surfactant, a silane coupling agent, or the like. Alternatively, the fibrous carbon material can be heat-treated in an inert atmosphere to improve water repellency.

  Coating methods include a method in which a liquid in which a fluororesin emulsion or a pulverized fluororesin is dispersed or a liquid containing a silane coupling agent is applied to the gas diffusion fiber layer by contact, dipping, spraying, etc., and then dried. Is mentioned. In the case of a fluororesin, the coating can be made uniform by raising the temperature to the melting point or higher after drying and melting or softening.

  Since the gas diffusion fiber layer of the present invention has a large pore diameter and thus has a rough structure, in a structure that directly contacts a catalyst layer having a micro structure, when the cell is assembled, the gas diffusion fiber layer and the catalyst layer There are few contact parts in between, and a rough distribution is generated in the surface pressure applied to the catalyst layer. These lead to, for example, distribution of electron conduction resistance, gas diffusivity, and reactivity in the catalyst layer, and as a result, the performance as a battery is not sufficiently exhibited.

  In order to prevent such a problem, a micropore layer is provided between the gas diffusion fiber layer and the catalyst layer. If it can be connected to the catalyst layer by canceling the roughness of the structure of the gas diffusion fiber layer with a material that does not impair the gas diffusibility and electronic conductivity while having a more micro structure, preferably the same structural scale as the catalyst layer, Reaction distribution in the catalyst layer can be suppressed, and battery performance can be sufficiently exhibited.

  Carbon black is used as a main component in the micropore layer of the present invention. The primary reason carbon black is used is that it has the same structural scale as the catalyst layer, has excellent electronic conductivity, and has appropriate surface characteristics depending on the type, so that the gas diffusion path is blocked by water. This is because it can be effectively prevented.

  Such carbon black can be selected using the water vapor adsorption amount as an index. Specifically, if the water vapor adsorption amount of carbon black at 25 ° C. and relative humidity 90% is 100 mL / g or less, for example, it is possible to suppress clogging of the gas diffusion path due to water generated during large current discharge on the cathode side, A current can be taken out with a stable voltage. If it exceeds 100 mL / g, the condensed water stays in the micropore layer during current discharge, the gas diffusion path is blocked, and the voltage behavior becomes unstable.

  In order to obtain a higher effect, carbon black having a water vapor adsorption amount of 1 mL / g to 50 mL / g at 25 ° C. and a relative humidity of 90% is selected.

  When the water vapor adsorption amount is within the above range, the electrolyte material in the cathode can be prevented from being dried and maintained in a suitable wet state even during a small current discharge with a small amount of water generated inside the cathode. Even during discharge, water generated inside the catalyst layer can be efficiently discharged out of the electrode, and a gas diffusion path can be secured, so an efficient battery can be obtained over the entire range regardless of load conditions from low load to high load. Can do.

  Moreover, if the carbon material has a water vapor adsorption amount of 1 mL / g or more and 50 mL / g or less at 25 ° C. and a relative humidity of 90%, two or more kinds of carbon materials may be mixed and used as a gas diffusion carbon material. it can. When the water vapor adsorption amount at 25 ° C. and relative humidity 90% is less than 1 mL / g, it becomes difficult to obtain the effect of humidifying from the outside of the cell, and it becomes difficult to maintain a suitable wet state especially in the electrolyte material at the time of start-up. , Proton conductivity may be reduced.

  When the water vapor adsorption amount at 25 ° C. and 90% relative humidity exceeds 50 mL / g, the water generated inside the catalyst layer cannot catch up when a large current is continuously taken out, and the gas diffusion path is blocked. There is a risk.

  Here, the water vapor adsorption amount at 25 ° C. and 90% relative humidity, which is an index in the present invention, is shown by converting the water vapor amount adsorbed per 1 g of the carbon material placed in the environment of 25 ° C. into the water vapor volume in the standard state. It was. The water vapor adsorption amount at 25 ° C. and relative humidity 90% can be measured using a commercially available water vapor adsorption amount measuring device. Alternatively, dry carbon black having a known mass can be allowed to stand for a sufficient time in a constant temperature and humidity chamber at 25 ° C. and a relative humidity of 90%, and measurement can be performed from the mass change.

  The carbon black used for the micropore layer of the present invention can be selected from the generally existing carbon black using the water vapor adsorption amount as an index. Or even if it is carbon black which has the water vapor | steam adsorption amount which deviated from the suitable range, it can adjust to a suitable range by processing.

  For example, when the amount of water vapor adsorption is too large, the amount of fluorine resin or the like is generally increased to impart water repellency, but it may satisfy electron conductivity, gas diffusibility, etc. Control is difficult and undesirable. A method of firing carbon black in an inert atmosphere and reducing the water vapor adsorption amount to a suitable range is preferable. For example, the amount of water vapor adsorption can be reduced by heat treatment in an atmosphere such as argon, nitrogen, helium, or vacuum.

Also, if the amount of water vapor adsorption is too small, the water vapor adsorption amount should be increased to a suitable range by treating the surface of the carbon material with an acid or base or exposing it to an oxidizing atmosphere environment. Can do. Without limitation, for example, treatment in warm concentrated nitric acid, immersion in an aqueous hydrogen peroxide solution, heat treatment in an ammonia stream, immersion in a heated aqueous sodium hydroxide solution The amount of water vapor adsorption can be increased by heat treatment in dilute oxygen, dilute NO or NO ₂ .

  The second reason why carbon black is used for the micropore layer of the present invention is the three-dimensional structure of carbon black. In carbon black, a plurality of primary particles are fused to form a secondary structure called a structure. Depending on the type, this structure has developed, and the network of primary particles has a structure that encloses space. In the micropore layer, a gas diffusion path surrounded by a network of primary particles can be formed by connecting such spaces.

  The gas diffusion path formed in this way is not easily broken even when the cell is strongly fastened, and it is easy to maintain the hole diameter when the micropore layer is formed over a long period of time. Further, if the type of carbon black is determined using the structure as an index, the hole diameter of the gas diffusion path formed in the micropore layer is determined, so there is an advantage that control is easy.

  In the micropore layer of the present invention, carbon black having a higher structure is preferably used as a main component. This is because if the structure is low, formation of a gas diffusion path by the structure cannot be expected. The degree of the structure can be determined by observing with an electron microscope, but can be determined by the relationship between the DBP oil absorption and the specific surface area.

  The DBP oil absorption amount is the amount of dibutyl phthalate absorbed by carbon black when unitary carbon black is brought into contact with carbon black, and is mainly absorbed in the gaps between primary particles. When the structure is developed, the DBP oil absorption amount becomes large, and when the structure is not so developed, the DBP oil absorption amount tends to be small.

  However, DBP is absorbed not only by the gaps between the primary particles but also by the fine pores formed inside the primary particles, so that the DBP oil absorption amount does not always represent the degree of the structure. This is because as the specific surface area as measured by the nitrogen adsorption amount increases, the DBP absorbed in the micropores increases, and the overall DBP oil absorption amount also increases.

  Therefore, in the high structure carbon black, the DBP oil absorption amount is large for the nitrogen adsorption amount, and conversely, in the low structure carbon black, the DBP oil absorption amount is small for the nitrogen adsorption amount.

Preferably, when carbon black having a ratio X / Y of DBP oil absorption X (mL / 100 g) and nitrogen adsorption specific surface area Y (m ² / g) of 1 or more is used, a micropore layer having a preferable gas diffusion path Can be formed. This is because when the X / Y ratio is 1 or more, the structure is large and a gas diffusion path can be expected to be formed by the structure.

  When the X / Y ratio is less than 1, formation of a gas diffusion path due to the structure cannot be expected, and the gap between the secondary particles of carbon black mainly forms a gas diffusion path. The hole diameter cannot be secured, and the holes are easily broken when the cells are fastened, so that it is difficult to control and it is difficult to stably extract the performance of the catalyst layer.

  More preferably, the X / Y ratio is 1.5 or more. If it is 1.5 or more, the network of gas diffusion paths due to the structure is sufficiently developed, and flooding becomes difficult even when a high current is taken out. With such a structure, gas easily diffuses, and it is difficult to block the gas diffusion path by water, so that the original performance of the catalyst layer is easily extracted.

  The carbon black that can be used in the micropore of the present invention can be selected, for example, by examining the amount of water vapor adsorption and the ratio of the DBP oil absorption amount and the nitrogen adsorption specific surface area of commercially available carbon black. Alternatively, the ratio of the DBP oil absorption amount and the nitrogen adsorption specific surface area satisfies the preferred range, but when the water vapor adsorption amount is outside the preferred range, the water vapor adsorption amount is artificially changed by the above-described method, and the optimum Can be used.

  The type of carbon black is not particularly limited as long as it has electron conductivity that is generally present, but it may cause a chemical reaction other than the originally required reaction, or may be a carbon material by contact with condensed water. A material from which the substance constituting the substance is eluted is not preferable, and a chemically stable material is preferable.

  In the micropore layer, carbon black as described above can be used as a main component, but other materials can be combined as an auxiliary component for enhancing the function. For example, the carbon black may be fixed with a small amount of a polymer material such as a fluororesin for the purpose of increasing the mechanical strength without impairing the surface characteristics and structure of the carbon black of the micropore layer.

  The blending amount of such a polymer material is preferably 40% by mass or less with respect to the total mass of the micropore layer. If it exceeds 40% by mass, the pores that become the gas diffusion path are filled with a polymer material, or the majority of pores formed by the aggregation of the polymer material and carbon black become large, and the pore diameter is limited only to the structure of carbon black. It becomes difficult to make it depend.

  More preferably, it is 20 mass% or less. If it is 20% or less, the influence of the polymer material is small, and the pores formed by the structure can be utilized in the micropore layer, so a gas diffusion path that is easy to control and difficult to change over a long period is formed in the micropore layer. Can be made.

  The catalyst layer used in the present invention is not particularly limited as long as it is composed of a mixture containing a catalyst component, a carbon material, and an electrolyte material. Since the gas diffusion layer is excellent, the performance of the catalyst layer can be sufficiently extracted.

  The type of carbon material used in the catalyst layer of the present invention is not particularly limited as long as it is a carbon material having an electron conductivity that is generally present, but it causes a chemical reaction other than the originally required reaction. In addition, a material from which a substance constituting the carbon material is eluted by contact with the condensed water is not preferable, and a chemically stable carbon material is preferable.

  Further, the primary particle diameter of the carbon material is preferably 1 μm or less, and a carbon material larger than this can be pulverized and used. When the primary particle diameter is more than 1 μm, there is a high possibility that the gas diffusion path and the proton conduction path are divided, and the distribution of the carbon material in the catalyst layer tends to be uneven, which is not preferable.

  As a preferred carbon material, carbon black is the most common, but in addition, graphite, carbon fiber, activated carbon, etc., pulverized products thereof, carbon compounds such as carbon nanofiber, carbon nanotube, and the like can be used. Moreover, these two or more types can be mixed and used.

  The carbon material contained in the catalyst layer of the present invention is more preferably divided into a catalyst carrier carbon material and a gas diffusion carbon material.

  By including a carbon material in which the catalyst component is not supported, that is, a gas diffusion carbon material in the catalyst layer, a path through which the gas can diffuse in the catalyst layer can be developed. In the case of a mixed gas or cathode mainly composed of oxygen, oxygen or air easily diffuses into the catalyst layer and can come into contact with many catalyst surfaces. Therefore, the reaction in the catalyst layer is efficiently advanced, and high battery performance is obtained.

  The catalyst support carbon material used in the catalyst layer of the present invention can carry a catalyst component effective for the type of gas to be supplied, and if it is a carbon material with good electron conductivity, the catalyst component and carbon The kind of material is not limited. Examples of catalyst components include noble metals such as platinum, palladium, ruthenium, gold, rhodium, osmium, and iridium, composites and alloys of noble metals obtained by compounding two or more of these noble metals, noble metals and organic compounds and inorganic compounds. A complex, a transition metal, a complex of a transition metal and an organic compound or an inorganic compound, a metal oxide, and the like can be given. Moreover, what compounded these 2 or more types can also be used.

  As an example of the catalyst support carbon material, carbon black is the most common, but in addition, graphite, carbon fiber, activated carbon, etc., pulverized products thereof, carbon compounds such as carbon nanofiber, carbon nanotube, etc. can be used. . Moreover, these two or more types can be mixed and used.

  The preferable content of the catalyst support carbon material in the catalyst layer is affected by the type and content of the catalyst support carbon material and the gas diffusion carbon material, the type of catalyst component and the support rate, and thus cannot be specified. If it is the range of 5 mass% or more and 80 mass% or less, a fuel cell will function at least and the effect of this invention can be acquired.

  If a more preferable range is illustrated, it is 10 mass% or more and 60 mass% or less. If it is out of this range, the balance with other main components is deteriorated, and an efficient fuel cell cannot be obtained. For example, if it is less than 5% by mass, the amount of the catalyst component supported on the catalyst support carbon material becomes too small. For example, if it exceeds 80% by mass, the amount of the electrolyte material becomes too small and the proton transmission path becomes poor, so that an efficient battery cannot be obtained.

  Furthermore, when the catalyst support carbon material has a water vapor adsorption amount of 50 mL / g or more at 25 ° C. and a relative humidity of 90%, the electrolyte in the vicinity of the catalyst component is kept in a suitable wet state, and the proton conductivity is lowered. Therefore, the proton conduction resistance does not increase even during a low current discharge in which water is not generated so much on the catalyst component of the cathode, and a favorable state as a fuel cell can be maintained.

  Moreover, on such a catalyst-supporting carbon material, the catalyst component generally supported is easy to be miniaturized, and the reaction surface area can be increased even with a small amount of the catalyst component, which is preferable.

  Therefore, the catalyst-supporting carbon material is better as it is easily wetted with water, and the upper limit value of the preferable range of the water vapor adsorption amount at 25 ° C. and relative humidity of 90% cannot be limited.

  However, as long as the carbon material is used as a catalyst carrier, there is a limit to the amount of water vapor that can be adsorbed. Therefore, if a substantial upper limit value of the amount of water vapor adsorption at 25 ° C. and 90% relative humidity is illustrated as an example. And about 1500 mL / g obtained with activated carbon having a high specific surface area.

  When the water vapor adsorption amount at a relative humidity of 90% is lower than 50 mL / g, the electrolyte in the vicinity of the catalyst component tends to dry and proton conductivity tends to decrease, which is not preferable. In addition, the particle size of the supported catalyst component generally tends to be large, and a large amount of the catalyst component is required to exhibit sufficient battery performance, which is not preferable.

  The content of the gas diffusion carbon material used in the catalyst layer of the present invention in the catalyst layer is more preferably in the range of 5% by mass to 50% by mass. If it is less than 5% by mass, the gas diffusion path cannot be sufficiently expanded, and the effect of including the gas diffusion carbon material becomes unclear. If it exceeds 50% by mass, the proton conduction path becomes poor and the IR drop becomes large, so that the battery performance is lowered.

  Although depending on the type and form of the carbon material to be used, it is most preferably 10% by mass or more and 35% by mass or less. Within this range, the gas diffusion path can be developed without impairing the proton conduction path and the electron conduction path.

  In particular, this effect is significant when the amount of water vapor adsorption at 25 ° C. and 90% relative humidity of the gas diffusion carbon material is 100 mL / g or less.

  If the water vapor adsorption amount at 25 ° C. and relative humidity 90% of the gas diffusion carbon material is 100 mL / g or less, it is possible to further suppress the blockage of the gas diffusion path due to water generated during large current discharge, and to take out the current with a stable voltage. be able to. If it exceeds 100 mL / g, the condensed water is stagnated in the catalyst layer during current discharge, the gas diffusion path is likely to be blocked, and the voltage behavior tends to become unstable.

  In order to obtain a higher effect, a gas diffusion carbon material having surface characteristics with respect to water in an appropriate range is used. Specifically, a carbon material having a water vapor adsorption amount of 1 mL / g or more and 50 mL / g or less at 25 ° C. and a relative humidity of 90% is selected as the gas diffusion carbon material.

  Within this range, it is possible to prevent the electrolyte material in the cathode from being dried and maintain a suitable wet state even during a small current discharge with a small amount of water generated inside the cathode. Since water generated inside the bed can be efficiently discharged out of the catalyst bed and a gas diffusion path can be secured, an efficient battery can be obtained over the entire region regardless of load conditions from low load to high load.

  Moreover, if the carbon material has a water vapor adsorption amount of 1 mL / g or more and 50 mL / g or less at 25 ° C. and a relative humidity of 90%, two or more kinds of carbon materials may be mixed and used as a gas diffusion carbon material. it can.

  When the water vapor adsorption amount at 25 ° C. and relative humidity 90% is less than 1 mL / g, the electrolyte material coexisting in the catalyst layer is difficult to maintain a suitable wet state, particularly during low current discharge, and proton conductivity is reduced. Since there exists a possibility that it may fall, the effect of adding a gas diffusion carbon material may become low.

  When the amount of water vapor adsorption at 25 ° C and 90% relative humidity exceeds 50 mL / g, when a large current is continuously taken out, the water generated inside the catalyst layer cannot catch up, blocking the gas diffusion path. Therefore, the effect of adding the gas diffusion carbon material may be reduced.

  Control of the hydratability of the gas diffusion carbon material and catalyst support carbon material of the present invention can be achieved by selecting the water vapor adsorption amount as an index from the carbon materials generally present. Alternatively, even in the case of a carbon material having a water vapor adsorption amount less than the preferred range, the water vapor adsorption amount can be reduced by treating the carbon material surface with an acid, a base, or the like, or exposing the carbon material to an oxidizing atmosphere environment. It can be increased to a suitable range.

Without limitation, for example, treatment in warm concentrated nitric acid, immersion in an aqueous hydrogen peroxide solution, heat treatment in an ammonia stream, immersion in a heated aqueous sodium hydroxide solution The amount of water vapor adsorption can be increased by heat treatment in dilute oxygen, dilute NO or NO ₂ .

  On the other hand, when the amount of water vapor adsorption is too large, the water vapor adsorption amount can be reduced to a suitable range by firing in an inert atmosphere. Although not limited, the amount of water vapor adsorption can be reduced by heat treatment in an atmosphere of argon, nitrogen, helium, vacuum, or the like.

  The catalyst layer used in the present invention exhibits an effect regardless of the type and form of the electrolyte membrane and electrolyte material used, and is not particularly limited thereto.

  The fuel cell in which the catalyst layer included in the fuel cell of the present invention is most effective is used in a fuel cell that operates under conditions where water easily aggregates in the catalyst layer, such as a polymer electrolyte fuel cell. However, the effect of the catalyst layer of the present invention is not dependent on the type, form, operating temperature, etc. of the electrolyte.

  The electrolyte material used in the electrolyte membrane or catalyst layer used in the present invention is a polymer in which a phosphoric acid group, a sulfonic acid group or the like is introduced, such as a polymer in which perfluorosulfonic acid polymer or benzenesulfonic acid is introduced. However, the present invention is not limited to polymers, and may be used for fuel cells using electrolyte membranes such as inorganic and inorganic-organic hybrids. If a particularly preferable operating temperature range is exemplified, a fuel cell that operates within a range of room temperature to 150 ° C. is preferable.

  The mass ratio of the catalyst carrier carbon material and the electrolyte material in the catalyst layer is preferably 1/5 to 5/1. If the catalyst support carbon material is less than 1/5, the surface of the catalyst is excessively covered with the electrolyte material, and the area where the reaction gas can come into contact with the catalyst component is reduced. When the material is contained, the network of the electrolyte material becomes poor and the proton conductivity is lowered, which is not preferable.

  The functions of the gas diffusion layer and gas diffusion electrode and fuel cell of the present invention are not limited by the production method.

  An example of a generally possible method is as follows. For example, carbon paper or carbon cloth is immersed in a Teflon dispersion as necessary, dried and fired to make it water repellent, and then mixed with carbon black and Teflon emulsion as necessary to create a dispersion. Is coated with spray, dried and heat-treated to form a micropore layer, and the gas diffusion layer of the present invention is obtained.

  Thereafter, the ink for forming the catalyst layer is sprayed and dried on the micropore layer side to obtain the gas diffusion electrode of the present invention. When used as a battery, an electrolyte membrane is sandwiched between two produced gas diffusion electrodes of the present invention, and is crimped by a hot press to be incorporated into a separator to form a battery.

  In the above steps, for example, for the purpose of increasing the mechanical strength of the gas diffusion layer, hot pressing may be performed when the gas diffusion layer is formed, and then the catalyst layer may be coated. In addition, in the coating of the micropore layer and the catalyst layer, the coating method uses powder coating, electrophoresis, etc. if the micropore layer can be formed on the gas diffusion fiber layer or the catalyst layer can be formed on the micropore layer. It doesn't matter. Alternatively, it is also possible to take a technique such as forming the micropore layer and the catalyst layer independently in a film shape, laminating them, and pressing them with a hot press.

<Measurement of physical properties of carbon black>
In order to show examples of the gas diffusion layer or gas diffusion electrode and fuel cell of the present invention, nine types of carbon blacks A to I were prepared. Table 1 shows the water vapor adsorption amount, DBP oil absorption amount X (mL / 100 g), nitrogen adsorption specific surface area Y (m ² / g), and X / Y of various carbon blacks.

  The water vapor adsorption amount was measured using a constant capacity water vapor adsorption device (BELSORP18, manufactured by Nippon Bell Co., Ltd.). The water vapor was gradually supplied from the vacuum state to the saturated vapor pressure of water vapor at 25 ° C., the relative humidity was changed stepwise, and the water vapor adsorption amount was measured.

  An adsorption isotherm was drawn from the obtained measurement results, and the water vapor adsorption amount at a relative humidity of 90% was read from the figure. In Table 1, the read water vapor amount is shown in terms of the water vapor volume in the standard state adsorbed per 1 g of the sample.

  Nitrogen adsorption specific surface area is measured with nitrogen gas using an automatic specific surface area measuring device (BELSORP36 manufactured by Nippon Bell Co., Ltd.) after vacuum drying at 120 ° C, and the specific surface area is determined by a one-point method based on the BET method. did.

  The DBP oil absorption amount was determined by converting the DBP addition amount at 70% of the maximum torque into the DBP oil absorption amount per 100 g of the sample using an absorber meter (manufactured by Brabender).

<Production of gas diffusion layer>
Commercially available carbon paper (Toray TGP-H-060) and carbon cloth (ElectroChem EC-CC1-060) were prepared, dipped in a Teflon dispersion diluted to 5%, dried, and further The temperature was raised to 340 ° C. in an argon stream to produce a gas diffusion fiber layer. Further, 99 g of ethanol was added to 1 g of each of the carbon blacks A to I, and the carbon black was pulverized with a ball mill to prepare a primary dispersion.

  Thereafter, while stirring the primary dispersion, 0.833 g of 30% Teflon dispersion was dropped little by little to prepare a micropore layer slurry. This slurry is applied to one side of the previously produced gas diffusion fiber layer using a spray, dried at 80 ° C. in an argon stream, heated to 340 ° C., and the gas diffusion fiber layer and the micropore layer are laminated. A gas diffusion layer was prepared.

  As a comparison, two types of gas diffusion layers of carbon paper and carbon cloth without a micropore layer were also prepared. Table 2 summarizes the types of gas diffusion layers produced in total, together with the materials used.

Example 1
A commercially available platinum catalyst (EC-20-PTC manufactured by ElectroChem, platinum loading rate: 20 wt%) is placed in a container, and 5% Nafion solution (manufactured by Aldrich) is added to the mass of the platinum catalyst in an argon stream. After adding lightly, the catalyst is pulverized with ultrasound, and ethanol is added while stirring so that the solid content concentration of Pt catalyst and Nafion is 6% by mass. Thus, a catalyst layer ink was prepared.

This catalyst layer ink was applied to the surface of the 20 types of gas diffusion layers shown in Table 2 on the micropore layer side by spraying and dried in an argon stream at 80 ° C. for 1 hour to obtain 20 types of gas diffusion electrodes. In addition, conditions, such as spraying, were set so that the amount of platinum used might be 0.10 mg / cm < ² > for each electrode. The amount of platinum used was determined by measuring the dry mass of the electrode before and after spray coating and calculating the difference.

  Further, two pieces of 2.5 cm square are cut from the obtained gas diffusion electrode, and the electrolyte membrane (Nafion 112) is sandwiched between two electrodes of the same type, and hot for 3 minutes at 130 ° C. and a total weight of 0.625 t. Press was performed to produce 20 types of MEA.

  The obtained 20 types of MEA were each incorporated in a fuel cell measurement device, and the cell performance was measured. In battery performance measurement, the voltage between the cell terminals is changed stepwise from the open voltage (usually about 0.9 to 1.0 V) to 0.2 V, and flows when the voltage between the cell terminals is 0.8 V and 0.5 V. Each current density was measured.

The gas is supplied at a constant flow rate so that the utilization rate is 30% and 50%, respectively, when the current density is 1 A / cm ² , and air is supplied to the cathode and pure hydrogen to the anode. The pressure was adjusted to 0.1 MPa with a back pressure valve provided downstream. The cell temperature was set to 80 ° C., and the supplied air and pure hydrogen were bubbled in distilled water kept at 80 ° C. and 90 ° C., respectively, and humidified.

  Table 3 shows the obtained MEA 20 types and battery performance results. As shown in Table 3, the MEAs 1 to 6, 9 to 15 and 18 using the gas diffusion layers of the present invention had the same catalyst layer, but the MEAs of Comparative Examples 7, 8, 16, 17, and 19 were used. , 20, the current density at the same cell voltage was high, and good performance was exhibited.

  In particular, MEAs 1 to 5 and 10 to 14 using carbon black having an X / Y value of 1 or more in Table 1 for the micropore layer have a large current density when the cell voltage is 0.8V and 0.5V. Excellent properties were shown.

(Example 2)
A commercially available platinum catalyst (EC-20-PTC manufactured by ElectroChem, with a platinum loading rate of 20 wt%) is placed in a container, and a 5% Nafion solution (manufactured by Aldrich) is added to the mass of the platinum catalyst in an argon stream. Add the mass so that it doubles, lightly stir, pulverize the catalyst with ultrasonic waves, add butyl acetate while stirring so that the solid content concentration of Pt catalyst and Nafion is 6% by mass, A catalyst slurry was prepared.

  In a separate container, each of the four types of carbon black B, D, E, and G shown in Table 1 is taken, butyl acetate is added so that the carbon black is 6% by mass, and the carbon black is pulverized with ultrasonic waves. Four types of carbon black slurry were prepared. The previously prepared catalyst slurry and the carbon black slurry were mixed at a mass ratio of 8: 2 and sufficiently stirred to prepare 4 types of catalyst layer slurries.

Each of the four catalyst layer slurries was sprayed onto the surface of the gas diffusion layer CC-D shown in Table 2 on the micropore layer side, and dried in an argon stream at 80 ° C. for 1 hour to obtain a gas diffusion carbon material. Four types of gas diffusion electrodes containing carbon black B, D, E, and G in the catalyst layer were obtained. In addition, conditions, such as a spray, were set so that each electrode might use platinum usage amount to 0.10 mg / cm < ² >.

  Further, the obtained gas diffusion electrode was hot-pressed under the same conditions as in Example 1 to produce 4 types of MEA.

  The obtained MEA 4 types were subjected to battery performance measurement under the same conditions as in Example 1.

  Table 4 shows the obtained MEA 4 types and battery performance results. As shown in Table 4, the MEAs 21 to 24 of the present invention all showed excellent characteristics as compared with the MEA 13 that does not contain a gas diffusion carbon material in the catalyst layer.

  In particular, the MEA 21 to 23 of the present invention containing carbon black having a water vapor adsorption amount of 100 mL / g or less at 25 ° C. and a relative humidity of 90% as a gas diffusion carbon material in the catalyst layer also uses the same gas diffusion layer. Regardless, the current density at the same cell voltage is high and good compared to MEA22 which contains carbon black having a water vapor adsorption amount of more than 100 mL / g at 25 ° C. and 90% relative humidity as a gas diffusion carbon material. Performance was demonstrated.

  Among them, MEA 21 and 22 containing a gas diffusion carbon material having a gas diffusion carbon material with a water vapor adsorption amount of 50 mL / g or less at 25 ° C. and a relative humidity of 90% of the gas diffusion carbon material exhibit particularly excellent performance during high current discharge. did.

(Example 3)
Carbon blacks B, D, E, and G of Table 1 were dispersed as catalyst support carbon materials in an aqueous chloroplatinic acid solution, respectively, kept at 50 ° C., added with hydrogen peroxide while stirring, and then Na. ₂ S ₂ O ₄ aqueous solution was added to obtain a catalyst precursor. The catalyst precursor was filtered, washed with water and dried, and then subjected to a reduction treatment in a 100% H ₂ stream at 300 ° C. for 3 hours to prepare 4 types of Pt catalysts in which 20% by mass of Pt was supported on the catalyst support carbon material. .

  Take these 4 types in a container, add a 5% Nafion solution (manufactured by Aldrich) in an argon stream so that the mass of Nafion solids is 2 times the mass of the platinum catalyst, and after gently stirring, The catalyst was pulverized, and butyl acetate was added with stirring so that the solid content concentration of the Pt catalyst and Nafion was 6% by mass to prepare 4 types of catalyst slurry.

  In a separate container, the carbon black D shown in Table 1 was taken, butyl acetate was added so that the carbon black was 6% by mass, and the carbon black was pulverized with ultrasonic waves to prepare a carbon black slurry. Each of the four types of catalyst slurry prepared earlier and the carbon black slurry were mixed at a mass ratio of 8: 2, and sufficiently stirred to prepare four types of catalyst layer slurry.

  Each of the four catalyst layer slurries was spray-coated on the surface of the gas diffusion layer CC-D shown in Table 2 on the micropore layer side and dried in an argon stream at 80 ° C. for 1 hour to obtain carbon as a catalyst-supporting carbon material. Four types of gas diffusion electrodes of the present invention containing black B, D, E, G as a gas diffusion carbon material and carbon black D in the catalyst layer were obtained.

Further, as a comparison, a gas diffusion electrode containing carbon cloth and carbon paper not coated with a micropore layer as a gas diffusion layer, carbon black G as a catalyst-carrying carbon material, and carbon black D as a gas diffusion carbon material in the catalyst layer Two types were also obtained as comparative examples. In addition, conditions, such as spraying, were set so that the amount of platinum used might be 0.10 mg / cm < ² > for each electrode.

  Further, the obtained gas diffusion electrode was hot pressed under the same conditions as in Example 1 to produce MEA 6 species.

  The obtained 6 MEAs were subjected to battery performance measurement under the same conditions as in Example 1.

  Table 5 shows the obtained MEA types and battery performance results. As shown in Table 5, the characteristics of the MEA 25 to 28 of the present invention exhibited superior characteristics as compared with the MEAs 29 and 30 of the comparative examples. Among them, MEA 27, 28 containing carbon black having a water vapor adsorption amount of 50 mL / g or more at 25 ° C. and a relative humidity of 90% as a catalyst carbon material and carbon black of 100 mL / g or less as a gas diffusion carbon material in the catalyst layer. Has excellent characteristics of 0.8V.

  In particular, MEA 28 containing a catalyst-supporting carbon material having a water vapor adsorption amount of 100 mL / g or more at 25 ° C. and 90% relative humidity in the catalyst layer exhibited extremely excellent performance.

  As described above, according to the present invention, a fuel cell that exhibits more efficient battery performance can be provided. Therefore, the present invention has great industrial applicability.

Claims (6)

A gas diffusion layer for a fuel cell having a two-layer structure having a micropore layer using carbon black on one side of a gas diffusion fiber layer using a fibrous carbon material, wherein the carbon black of the micropore layer has a relative temperature of 25 ° C. A gas diffusion layer for a fuel cell, wherein a water vapor adsorption amount at a humidity of 90% is 100 mL / g or less. The ratio X / Y of DBP oil absorption X (mL / 100 g) and nitrogen adsorption specific surface area Y (m ² / g) of carbon black used for the micropore layer is 1 or more. A gas diffusion layer for a fuel cell according to 1. A catalyst layer using a catalyst component, a carbon material, and an electrolyte material is disposed in contact with the micropore layer of the gas diffusion layer for a fuel cell according to claim 1 or 2. Gas diffusion electrode for fuel cell with layer structure.   The carbon material of the catalyst layer is composed of a catalyst carrier carbon material carrying a catalyst component and a gas diffusion carbon material not carrying a catalyst component. The gas diffusion carbon material has a water vapor adsorption amount at 25 ° C. and a relative humidity of 90%. The gas diffusion electrode for a fuel cell according to claim 3, wherein the gas diffusion electrode is 100 mL / g or less.   5. A fuel cell comprising a pair of electrodes sandwiching a proton conductive electrolyte membrane, wherein at least one of the electrodes is the gas diffusion electrode for a fuel cell according to claim 3 or 4.   A fuel cell comprising a pair of electrodes sandwiching a proton conductive electrolyte membrane, wherein the fuel cell gas diffusion layer according to claim 1 or 2 is contained in at least one of the electrodes. .