JP6672622B2 - Electrode catalyst layer for fuel cell, method for producing the same, and membrane electrode assembly using the catalyst layer, fuel cell, and vehicle - Google Patents

Description

  The present invention relates to an electrode catalyst layer used for a fuel cell (PEFC) and a method for producing the same, and a membrane electrode assembly using the catalyst layer, a fuel cell, and a vehicle.

  A polymer electrolyte fuel cell using a proton-conducting solid polymer membrane operates at a lower temperature than other types of fuel cells, such as a solid oxide fuel cell and a molten carbonate fuel cell. For this reason, polymer electrolyte fuel cells are expected as stationary power sources and power sources for mobile bodies such as automobiles, and their practical use has been started.

  Such a polymer electrolyte fuel cell generally uses an expensive metal catalyst typified by Pt (platinum) or a Pt alloy, which causes a high price of such a fuel cell. . For this reason, there has been a demand for the development of a catalyst manufacturing technique that can reduce the amount of the noble metal catalyst used, reduce the cost of the fuel cell, and have excellent power generation performance.

  For example, Patent Literature 1 discloses a catalyst carrier, an electrode catalyst made of a catalyst metal supported on the catalyst carrier, and an electrode catalyst layer for a fuel cell using the same. The catalyst described in Patent Document 1 has pores having a radius of less than 1 nm and pores having a radius of 1 nm or more, and the pores having a radius of less than 1 nm have a pore volume of 0.3 cc / g carrier or more, and The catalyst metal is supported inside the pores having a radius of 1 nm or more.

International Publication No. 2014/175098

  According to the electrode catalyst using the porous and high specific surface area catalyst carrier described in Patent Document 1, a gas transport path can be secured, and the power generation performance is excellent under high temperature and high humidity and the gas transport resistance is low. A membrane electrode assembly can be obtained. However, the present inventors may not be able to obtain sufficient power generation performance under a low-humidity environment even when a catalyst carrier having a high specific surface area as described in Patent Document 1 is used for an electrode catalyst layer. I found that.

  The present invention has been made in view of the above circumstances. That is, an object of the present invention is to provide an electrode catalyst layer capable of obtaining excellent power generation performance under a low humidity environment (for example, 40% RH).

The present inventors have intensively studied to solve the above problems. As a result, the fuel cell electrode catalyst layer containing a catalyst carrier having a high specific surface area (BET specific surface area exceeding 1000 (m ² / g carrier)) and having a sulfonic acid group density of not less than a predetermined value contains the electrode catalyst. They found that the problem could be solved, and completed the present invention.

ADVANTAGE OF THE INVENTION According to this invention, it contains the electrode catalyst using the catalyst support of high specific surface area (BET specific surface area is more than 1000 (m < ² > / g support)), and has excellent power generation under low humidity environment (for example, 40% RH). An electrode catalyst layer that can obtain performance can be provided. This is considered to be because the proton concentration and hydrophilicity in the catalyst layer are increased and the effective surface area of the electrode catalyst layer at low humidity is improved when the electrode catalyst layer has a high-density sulfonic acid group.

FIG. 1 is a schematic sectional view showing a basic configuration of a polymer electrolyte fuel cell according to one embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional explanatory view showing the shapes and structures of catalysts (a) and (c) according to one embodiment, which are suitably used for an electrode catalyst layer of the present invention. FIG. 2 is a schematic cross-sectional explanatory view showing the shape and structure of a catalyst (b) according to one embodiment, which is suitably used for the electrode catalyst layer of the present invention.

One aspect of the present invention is a fuel cell electrode catalyst layer including a catalyst carrier, a catalyst comprising a catalyst metal supported on the catalyst carrier, and a polymer electrolyte, wherein the catalyst carrier has a BET specific surface area of 1000 (m ² / g carrier), wherein the polymer electrolyte contains sulfonic acid groups and the density of the sulfonic acid groups is 0.26 (mmol / cc catalyst layer) or more. In this specification, the “electrode catalyst layer for fuel cells” is also referred to as an “electrode catalyst layer” or a “catalyst layer”, the “catalyst carrier” is also referred to as a “carrier”, and the “catalyst” is also referred to as an “electrocatalyst”. . “/ G carrier” means “per 1 g of carrier”. “/ Cc catalyst layer” means “per unit volume (1 cm ³ ) of catalyst layer”.

  According to the fuel cell electrode catalyst layer of the present invention, excellent power generation performance can be obtained in a low humidity environment (for example, 40% RH). Although not limiting the technical scope of the present invention, this is presumed to be due to the following mechanism.

  The present inventors have found that in a fuel cell electrode catalyst layer containing a catalyst and a polymer electrolyte (ionomer), even when the catalyst does not come into contact with the electrolyte, the catalyst is made effective by forming a three-phase interface with water. I found that it can be used. Therefore, by using a porous catalyst carrier having a large specific surface area for the electrode catalyst, the catalyst metal is stored in relatively large pores through which the electrolyte cannot enter, and the electrolyte is easily adsorbed on the catalyst surface as compared with a gas such as oxygen. Can be prevented from coming into contact with the catalyst metal. Thus, the present inventors have found that the reaction active area on the catalyst surface is prevented from decreasing, and that the catalyst can be effectively used by forming a three-phase interface with water. Further, in the catalyst described in Patent Document 1, a gas transport path is secured by using a catalyst carrier in which relatively small holes exist in a large volume, and gas transportability is improved. In this specification, pores having a radius of less than 1 nm are also referred to as “micropores”. Further, in this specification, pores having a radius of 1 nm or more are also referred to as “mesopores”.

  On the other hand, even when a catalyst carrier having a large specific surface area as described in Patent Document 1 is used for an electrode catalyst, sufficient power generation performance may not be obtained in a low humidity environment (for example, 40% RH). The present inventors have found that there is a problem. On the other hand, the present inventors have conducted intensive studies and found that the above problem can be solved by setting the sulfonic acid group density of the fuel cell electrode catalyst layer to a predetermined value or more. The present inventors presumed the reason for this as follows. That is, when the catalytic metal is supported inside the mesopores, it is considered that the catalytic reaction proceeds at the three-phase interface of gas (such as oxygen) / water / catalytic metal as described above. However, in a low-humidity environment (for example, 40% RH), the water required for proton transport is insufficient in the three-phase interface reaction, and the catalyst metal supported inside the mesopores is not sufficiently used. It was assumed that the surface area would decrease. However, when the electrode catalyst layer for a battery has a sulfonic acid group at a high density as described above, it is considered that the concentration of protons derived from the sulfonic acid group can be increased even in a low humidity environment. Further, it is considered that the presence of the high-density sulfonic acid group increases the hydrophilicity of the battery electrode catalyst layer, and can improve the water content in the catalyst layer. For the above reasons, by using a battery electrode catalyst layer having a sulfonic acid group density equal to or higher than a predetermined value, sufficient water for the reaction by the catalyst metal in the mesopores to proceed even in a low humidity environment. It is presumed that the three-phase interface reaction proceeds efficiently and high power generation performance is obtained.

  Hereinafter, embodiments of the present invention will be described. Note that the present invention is not limited to only the following embodiments.

  In the present specification, “X to Y” indicating a range means “X or more and Y or less”. Unless otherwise specified, the operation and measurement of physical properties are performed under the conditions of room temperature (20 to 25 ° C.) / Relative humidity of 40 to 50%.

  Hereinafter, an embodiment of a catalyst layer of the present invention, a method for manufacturing the same, and a membrane electrode assembly (MEA), a fuel cell, and a vehicle using the same will be described in detail with reference to the drawings. However, the present invention is not limited to only the following embodiments. Each drawing is exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may be different from the actual one. In addition, in the case where the embodiments of the present invention have been described with reference to the drawings, the same elements will be denoted by the same reference symbols in the description of the drawings, and redundant description will be omitted.

  The fuel cell includes a membrane electrode assembly (MEA), and a pair of separators including an anode-side separator having a fuel gas flow path through which a fuel gas flows and a cathode-side separator having an oxidizing gas flow path through which an oxidizing gas flows. Have. The fuel cell of the present embodiment is excellent in durability and can exhibit high power generation performance.

  FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to one embodiment of the present invention. The PEFC 1 has a solid polymer electrolyte membrane 2 and a pair of catalyst layers (anode catalyst layer 3a and cathode catalyst layer 3c) sandwiching the solid polymer electrolyte membrane 2. The laminate (CCM) of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched by a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). ing. In this manner, the solid polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c) and the pair of gas diffusion layers (4a, 4c) constitute a membrane electrode assembly (MEA) 10 in a stacked state.

  In the PEFC 1, the MEA 10 is further sandwiched by a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5a, 5c) are illustrated as being located at both ends of the MEA 10 illustrated. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used also as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked with the separator interposed therebetween, thereby forming a stack. In an actual fuel cell stack, a gas seal portion is arranged between the separator (5a, 5c) and the solid polymer electrolyte membrane 2 or between the PEFC 1 and another PEFC adjacent thereto. In FIG. 1, these descriptions are omitted.

  The separators (5a, 5c) are obtained, for example, by pressing a thin plate having a thickness of 0.5 mm or less to form an uneven shape as shown in FIG. The protrusions of the separators (5a, 5c) viewed from the MEA side are in contact with the MEA 10. Thereby, an electrical connection with the MEA 10 is ensured. In addition, a concave portion (a space between the separator and the MEA generated due to the uneven shape of the separator) viewed from the MEA side of the separator (5a, 5c) is a gas for flowing gas during operation of the PEFC1. Functions as a flow path. Specifically, a fuel gas (for example, hydrogen) flows through the gas flow path 6a of the anode separator 5a, and an oxidizing gas (for example, air) flows through the gas flow path 6c of the cathode separator 5c.

  On the other hand, the concave portion viewed from the side opposite to the MEA side of the separators (5a, 5c) serves as a refrigerant flow path 7 for flowing a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC1. . Further, the separator is usually provided with a manifold (not shown). This manifold functions as connecting means for connecting the cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

  Note that, in the embodiment shown in FIG. 1, the separators (5a, 5c) are formed in an uneven shape. However, the separator is not limited to only such a concavo-convex form, as long as the function of the gas flow path and the refrigerant flow path can be exhibited, a flat form, an arbitrary form such as a partially concavo-convex shape. Is also good.

  The fuel cell having the MEA of the present invention as described above exhibits excellent power generation performance. Here, the type of the fuel cell is not particularly limited, and in the above description, the polymer electrolyte fuel cell has been described as an example. In addition, an alkaline fuel cell, a direct methanol fuel cell And a micro fuel cell. Among them, a polymer electrolyte fuel cell (PEFC) is preferred because it is compact and can achieve high density and high output. Further, the fuel cell is useful as a stationary power supply in addition to a power supply for a mobile body such as a vehicle having a limited mounting space. Above all, it is particularly preferable to use it as a power source for a mobile body such as an automobile that requires a high output voltage after a relatively long operation stop.

  The fuel used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Among them, hydrogen and methanol are preferably used because high output can be achieved.

  The application of the fuel cell is not particularly limited, but is preferably applied to a vehicle. The electrolyte membrane-electrode assembly of the present invention is excellent in power generation performance and durability, and can be downsized. For this reason, the fuel cell of the present invention is particularly advantageous when the fuel cell is applied to a vehicle from the viewpoint of vehicle mounting.

  Hereinafter, members constituting the fuel cell of the present embodiment will be briefly described, but the technical scope of the present invention is not limited to only the following embodiments.

[Catalyst (electrocatalyst)]
The fuel cell electrode catalyst layer according to the present invention includes a catalyst carrier, a catalyst comprising a catalyst metal supported on the catalyst carrier, and a polymer electrolyte. The catalyst carrier is not particularly limited as long as it has a BET specific surface area of more than 1000 (m ² / g carrier), but preferably has pores (mesopores) having a radius of 1 nm or more as described later. More preferably, the catalyst support has pores (micropores) having a radius of less than 1 nm.

The BET specific surface area of the catalyst (after supporting the catalyst metal) [the BET specific surface area of the catalyst per 1 g of the support (m ² / g support)] is substantially equal to the BET specific surface area of the support. BET specific surface area of the (catalyst after metal loading) catalyst is not particularly limited, preferably 1000 m ² / g carrier greater, more preferably not more than 1000 m ² / g carrier ultra 3000 m ² / g carrier, especially preferably Is 1100 to 1800 m ² / g carrier. With the specific surface area as described above, sufficient mesopores and micropores can be secured, so that more catalysts can be stored in the mesopores while securing sufficient micropores (lower gas transport resistance) for gas transport. The catalyst contains (supports) the metal. Further, with such a catalyst, the electrolyte and the catalyst metal in the catalyst layer can be physically separated (contact between the catalyst metal and the electrolyte can be more effectively suppressed and prevented). Therefore, the activity of the catalyst metal can be used more effectively. In addition, the micropores act as a gas transport path, and the three-phase interface is more significantly formed by water, so that the catalytic activity can be further improved.

In the present specification, the “BET specific surface area (m ² / g carrier)” of the catalyst and the catalyst carrier is measured by a nitrogen adsorption method. Specifically, about 0.04 to 0.07 g of a sample is precisely weighed and sealed in a sample tube. This sample tube is pre-dried at 90 ° C. for several hours in a vacuum dryer to obtain a sample for measurement. An electronic balance (AW220) manufactured by Shimadzu Corporation is used for weighing. In the case of a coated sheet, the net weight of the coated layer obtained by subtracting the Teflon (registered trademark) (base material) weight of the same area from the total weight of the coated sheet is used as the sample weight. . Next, the BET specific surface area is measured under the following measurement conditions. On the adsorption side of the adsorption / desorption isotherm, a BET plot is created from a relative pressure (P / P0) range of about 0.00 to 0.45, and the BET specific surface area is calculated from the slope and intercept.

  The catalyst preferably has an acidic group on the surface of the catalyst particles or on the surface of the pores. In one embodiment of the present invention, there is provided an electrode catalyst layer for a fuel cell, wherein the amount of the acidic group of the catalyst is 0.2 (mmol / g carrier) or more. The acidic group is not particularly limited as long as it is a functional group capable of releasing a proton upon ionization, but preferably contains at least one selected from the group consisting of a hydroxyl group, a lactone group, and a carboxyl group. When the carrier contains carbon, the acidic group preferably contains a hydroxyl group, a lactone group, or a carboxyl group, and when the carrier contains a metal oxide, the acidic group preferably contains a hydroxyl group. Such an acidic group is a hydrophilic group, can make the catalyst surface hydrophilic, and can further improve the water content of the electrode catalyst layer.

  The amount of acidic groups per carrier of the catalyst is preferably 0.25 mmol / g carrier or more, more preferably 0.3 mmol / g carrier or more. The upper limit of the amount of the acidic group is not particularly limited, but is preferably 3.0 mmol / g carrier or less, and more preferably 2.5 mmol / g carrier or less, from the viewpoint of carbon durability.

  The amount of the acidic group can be measured by a titration method using an alkali compound, and specifically, can be measured by the following method.

(Measurement of amount of acidic group)
First, 2.5 g of a catalyst powder having an acidic group is washed with 1 L of warm pure water and dried. After drying, the amount of carbon contained in the catalyst having an acidic group is weighed so as to be 0.25 g, stirred with 55 ml of water for 10 minutes, and then subjected to ultrasonic dispersion for 2 minutes. Next, this catalyst dispersion liquid is moved to a glove box purged with nitrogen gas, and nitrogen gas is bubbled for 10 minutes. Then, an excess of a 0.1 M aqueous base solution is added to the catalyst dispersion, and neutralization titration is performed on the basic solution with 0.1 M hydrochloric acid, and the amount of the functional group is determined from the neutralization point. Here, as the aqueous base solution, three kinds of NaOH, Na ₂ CO ₃ and NaHCO ₃ are used, and a neutralization titration operation is performed for each of them. This is because the types of functional groups to be neutralized are different for each base used. In the case of NaOH, a carboxyl group, a lactone group, and a hydroxyl group are used. In the case of Na ₂ CO ₃ , a carboxyl group, a lactone group, and _{This is because in} the case of _3, a neutralization reaction occurs with the carboxyl group. Then, the amount of the acidic group is calculated from the results of the type and amount of the three bases charged in the titration and the amount of the consumed hydrochloric acid. In order to confirm the neutralization point, a pH meter is used, and the neutralization point is set to pH 7.0 for NaOH, pH 8.5 for Na ₂ CO ₃ , and pH 4.5 for NaHCO ₃ . Thus, the total amount of the carboxyl group, lactone group, and hydroxyl group added to the catalyst is determined.

The catalyst of the electrode catalyst layer for a fuel cell includes the following (a) to (c):
(A) The catalyst has pores with a radius of less than 1 nm and pores with a radius of 1 nm or more, the pore volume of the pores with a radius of less than 1 nm is 0.3 cc / g carrier or more, and the catalyst metal is Carried inside the pores having a radius of 1 nm or more;
(B) The catalyst has pores having a radius of 1 nm or more and less than 5 nm, the pore volume of the pores is 0.8 cc / g carrier or more, and the specific surface area of the catalyst metal is 60 m ² / g carrier or less. is there;
(C) the catalyst has pores with a radius of less than 1 nm and pores with a radius of 1 nm or more, and the mode radius of the pore distribution of the pores with a radius of less than 1 nm is 0.3 nm or more and less than 1 nm; The metal is supported inside the pores having a radius of 1 nm or more.
It is preferable that at least one of the following is satisfied. In this specification, a catalyst satisfying the above (a) is referred to as “catalyst (a)”, a catalyst satisfying the above (b) is referred to as “catalyst (b)”, and a catalyst satisfying the above (c) is referred to as “catalyst ( c) ".

  Hereinafter, the catalysts (a) to (c) which are the preferred embodiments will be described in detail.

(Catalysts (a) and (c))
The catalyst (a) comprises a catalyst carrier and a catalyst metal supported on the catalyst carrier, and satisfies the following structures (a-1) to (a-3):
(A-1) the catalyst has pores with a radius of less than 1 nm (primary pores) and pores with a radius of 1 nm or more (primary pores);
(A-2) the pore volume of the pores having a radius of less than 1 nm is not less than 0.3 cc / g carrier; and (a-3) the catalyst metal is supported inside the pores having a radius of 1 nm or more. ing.

The catalyst (c) comprises a catalyst carrier and a catalyst metal supported on the catalyst carrier, and satisfies the following constitutions (a-1), (c-1) and (a-3):
(A-1) the catalyst has pores with a radius of less than 1 nm and pores with a radius of 1 nm or more;
(C-1) the mode radius of the pore distribution of the pores having a radius of less than 1 nm is 0.3 nm or more and less than 1 nm; and (a-3) the catalyst metal is contained in the pores having a radius of 1 nm or more. It is carried.

  As described above, the present inventors have found that even when the catalyst metal does not contact the electrolyte, the catalyst metal can be effectively used by forming a three-phase interface with water. For this reason, the catalyst activity of the catalysts (a) and (c) can be improved by adopting a configuration in which the catalyst metal (a-3) is supported inside the mesopores into which the electrolyte cannot enter. On the other hand, when the catalyst metal is supported inside the mesopores into which the electrolyte cannot enter, the transport distance of the gas such as oxygen is increased, and the gas transportability is reduced. In such a case, the catalyst performance is reduced. On the other hand, the above (a-2) by securing a sufficient pore volume of the micropores into which the electrolyte or the catalyst metal can hardly enter, or by setting the mode diameter of the (c-1) micropores large, A sufficient gas transport path can be secured. Therefore, a gas such as oxygen can be efficiently transported to the catalytic metal in the mesopores, that is, the gas transport resistance can be reduced. With this configuration, the gas (for example, oxygen) passes through the micropores (gas transportability is improved), and the gas can be efficiently contacted with the catalyst metal. Therefore, when the catalysts (a) and (c) are used for the catalyst layer, since the micropores are present in a large volume, the surface of the catalyst metal present in the mesopores reacts via the micropores (passes). Since gas can be transported, gas transport resistance can be further reduced. Therefore, the catalyst layer containing the catalysts (a) and (c) can exhibit higher catalytic activity, that is, can further promote the catalytic reaction. For this reason, the membrane electrode assembly and the fuel cell having the catalyst layers using the catalysts (a) and (c) can further improve the power generation performance.

  FIG. 2 is a schematic sectional explanatory view showing the shapes and structures of the catalysts (a) and (c). As shown in FIG. 2, the catalysts (a) and (c) 20 are composed of a catalyst metal 22 and a catalyst carrier 23. The catalyst 20 has pores (micropores) 25 with a radius of less than 1 nm and pores (mesopores) 24 with a radius of 1 nm or more. Here, the catalyst metal 22 is supported inside the mesopores 24. Further, the catalyst metal 22 may be at least partially supported inside the mesopores 24, and may be partially supported on the surface of the catalyst carrier 23. However, from the viewpoint of preventing contact between the electrolyte and the catalyst metal in the catalyst layer, it is preferable that substantially all of the catalyst metal 22 be supported inside the mesopores 24. Here, “substantially all catalytic metals” are not particularly limited as long as the catalytic activity can be sufficiently improved. "Substantially all catalytic metals" are present in an amount of preferably at least 50% by weight (upper limit: 100% by weight), more preferably at least 80% by weight (upper limit: 100% by weight), based on all the catalytic metals.

  In the present specification, "the catalytic metal is supported inside the mesopores" can be confirmed using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

  Further, the pore volume of the pores (micropores) having a radius of less than 1 nm (of the catalyst after supporting the catalyst metal) is 0.3 cc / g carrier or more and / or the pore volume of the micropores (of the catalyst after supporting the catalyst metal). The mode radius (most frequent diameter) of the pore distribution is 0.3 nm or more and less than 1 nm. Preferably, the pore volume of the micropores is at least 0.3 cc / g carrier and the mode radius of the pore distribution of the micropores is at least 0.3 nm and less than 1 nm. If the pore volume and / or mode diameter of the micropores are in the above ranges, micropores sufficient for gas transport can be secured, and gas transport resistance is low. For this reason, a sufficient amount of gas can be transported to the surface of the catalytic metal present in the mesopores through the micropores (passes), so that high catalytic activity can be exhibited, that is, the catalytic reaction can be promoted. In addition, an electrolyte (ionomer) or a liquid (for example, water) cannot enter the micropore, and only gas is selectively passed (gas transport resistance can be reduced). In consideration of the effect of improving gas transportability, the pore volume of the micropores is more preferably 0.3 to 2 cc / g carrier, and particularly preferably 0.4 to 1.5 cc / g carrier. More preferably, the mode radius of the pore distribution of the micropores is 0.4 to 1 nm, and particularly preferably 0.4 to 0.8 nm. In this specification, the pore volume of pores having a radius of less than 1 nm is also simply referred to as “micropore pore volume”. Similarly, in the present specification, the mode radius of the pore distribution of the micropores is also simply referred to as “the micropore mode diameter”.

  The pore volume of pores (mesopores) having a radius of 1 nm or more and less than 5 nm in the catalyst (a) or (c) is not particularly limited, but is 0.4 cc / g or more carrier, more preferably 0.4 to 3 cc / g. A carrier, particularly preferably 0.4 to 1.5 cc / g carrier. If the pore volume is within the above range, more catalyst metal can be stored (supported) in the mesopores, and the electrolyte and the catalyst metal in the catalyst layer are physically separated (contact between the catalyst metal and the electrolyte is prevented). It can be more effectively suppressed and prevented). Therefore, the activity of the catalyst metal can be used more effectively. Further, the presence of many mesopores can promote the catalytic reaction more effectively. In addition, the micropores act as a gas transport path, and the three-phase interface is more significantly formed by water, so that the catalytic activity can be further improved. In this specification, the pore volume of pores having a radius of 1 nm or more is simply referred to as “pore volume of mesopores”.

  The mode radius (mode frequency) of the pore distribution of pores (mesopores) having a radius of 1 nm or more in the catalyst (a) or (c) is not particularly limited, but is 1 to 5 nm, and more preferably 1 to 4 nm. Particularly preferably, it is 1 to 3 nm. With the mode diameter of the pore distribution of the mesopores described above, a sufficient amount of the catalyst metal can be stored (supported) in the mesopores, and the electrolyte and the catalyst metal in the catalyst layer are physically separated (catalyst metal The contact between the electrolyte and the electrolyte can be more effectively suppressed or prevented). Therefore, the activity of the catalyst metal can be used more effectively. In addition, the presence of the large volume of mesopores can promote the catalytic reaction more effectively. In addition, the micropores act as a gas transport path, and the three-phase interface is more significantly formed by water, so that the catalytic activity can be further improved. In this specification, the mode radius of the pore distribution of the mesopores is also simply referred to as “mode radius of the mesopores”.

  In the present specification, “pore radius (nm) of micropores” means the radius of pores measured by a nitrogen adsorption method (MP method). Further, “mode radius (nm) of the pore distribution of micropores” means the pore radius of a point having a peak value (maximum frequency) in a differential pore distribution curve obtained by a nitrogen adsorption method (MP method). . Here, the lower limit of the pore radius of the micropore is a lower limit value that can be measured by the nitrogen adsorption method, that is, 0.42 nm or more. Similarly, “the radius of the pores of the mesopores (nm)” means the radius of the pores measured by the nitrogen adsorption method (DH method). The “mode radius of pore distribution of mesopores (nm)” means the pore radius of a point having a peak value (maximum frequency) in a differential pore distribution curve obtained by a nitrogen adsorption method (DH method). . Here, the upper limit of the pore radius of the mesopores is not particularly limited, but is 5 nm or less.

  In the present specification, the “pore volume of micropores” means the total volume of micropores having a radius of less than 1 nm existing in the catalyst, and is represented by a volume per 1 g of carrier (cc / g carrier). The “pore volume of micropores (cc / g carrier)” is calculated as the area (integral value) under the differential pore distribution curve obtained by the nitrogen adsorption method (MP method). Similarly, the “pore volume of mesopores” refers to the total volume of mesopores having a radius of 1 nm or more and less than 5 nm existing in the catalyst, and is represented by a volume per 1 g of carrier (cc / g carrier). The “pore volume of mesopores (cc / g carrier)” is calculated as the area under the differential pore distribution curve (integral value) obtained by the nitrogen adsorption method (DH method).

  In this specification, the “differential pore distribution” is a distribution curve in which the pore diameter is plotted on the horizontal axis and the pore volume corresponding to the pore diameter in the catalyst is plotted on the vertical axis. That is, when the pore volume of the catalyst obtained by the nitrogen adsorption method (MP method for micropores; DH method for mesopores) is V, and the pore diameter is D, the differential pore volume A value (dV / d (logD)) is obtained by dividing dV by the logarithmic difference d (logD) of the pore diameter. Then, a differential pore distribution curve is obtained by plotting this dV / d (logD) against the average pore diameter of each section. The difference pore volume dV refers to an increase in the pore volume between measurement points.

  Here, the method for measuring the radius and the pore volume of the micropores by the nitrogen adsorption method (MP method) is not particularly limited. For example, “Science of adsorption” (Second Edition, Seiichi Kondo, Tatsuo Ishikawa, Ikuo Abe) , Maruzen Co., Ltd.), “Analysis Techniques for Fuel Cells” (edited by Yoshio Takasu, Yu Yoshitake and Tatsumi Ishihara, Chemical Doujin), Sh. Mikhal, S.M. Brunauer, E .; E. FIG. Body J .; Colloid Interface Sci. , 26, 45 (1968). In the present specification, the radius and the pore volume of the micropore by the nitrogen adsorption method (MP method) are described in R.E. Sh. Mikhal, S.M. Brunauer, E .; E. FIG. Body J .; Colloid Interface Sci. , 26, 45 (1968).

  The method for measuring the radius and pore volume of mesopores by the nitrogen adsorption method (DH method) is also not particularly limited. For example, "Science of adsorption" (Second Edition, Seiichi Kondo, Tatsuo Ishikawa, Ikuo Abe) And Maruzen Co., Ltd.) and “Analysis Methods for Fuel Cells” (edited by Yoshio Takasu, Yu Yoshitake and Tatsumi Ishihara, Chemical Doujin), Dollion, G .; R. Heal: J.A. Appl. Chem. , 14, 109 (1964). In this specification, the radius of mesopores and the pore volume according to the nitrogen adsorption method (DH method) are described in D.E. Dollion, G .; R. Heal: J.A. Appl. Chem. , 14, 109 (1964).

  The method for producing a catalyst having a specific pore distribution as described above is not particularly limited, but usually, it is important that the pore distribution (micropores and mesopores) of the carrier be the above-described pore distribution. is there. Specifically, as a method for producing a carrier having micropores and mesopores, and having a pore volume of the micropores of 0.3 cc / g or more, JP-A-2010-208888 (US Patent Application Publication) The methods described in publications such as U.S. Patent No. 2011/318254, hereinafter the same) and WO 2009/75264 (U.S. Patent Application Publication No. 2011/058308, the same hereinafter) are preferably used. Further, as a method for producing a carrier having micropores and mesopores, and having a mode radius of pore distribution of the micropores of 0.3 nm or more and less than 1 nm, Japanese Patent Application Laid-Open No. 2010-208887 and International Publication No. A method described in a gazette such as 75264 is preferably used.

(Catalyst (b))
The catalyst (b) comprises a catalyst carrier and a catalyst metal supported on the catalyst carrier, and satisfies the following structures (b-1) to (b-3):
(B-1) vacancies having a radius of 1 nm or more and less than 5 nm;
(B-2) The pore volume of the pores having a radius of 1 nm or more and less than 5 nm is 0.8 cc / g carrier or more; and (b-3) the specific surface area of the catalytic metal is 60 m ² / g carrier or less.

  According to the catalyst having the above-mentioned constitutions (b-1) to (b-3), particularly in a high-humidity environment, the inside of the pores of the catalyst is prevented from being filled with water, and the reaction gas is transported. Is sufficiently secured. As a result, a catalyst excellent in gas transportability can be provided. In detail, the volume of the mesopores effective for gas transport is sufficiently ensured, and further, by reducing the specific surface area of the catalyst metal, particularly in a high humidity environment, the catalyst metal is held in the mesopores supported. Water can be reduced sufficiently. Therefore, since the filling of the mesopores with water is suppressed, a gas such as oxygen can be more efficiently transported to the catalyst metal in the mesopores. That is, the gas transport resistance of the catalyst can be further reduced. As a result, the catalyst (b) of the present embodiment promotes the catalytic reaction, and can exhibit higher catalytic activity. For this reason, the membrane electrode assembly having the catalyst layer using the catalyst (b) of the present embodiment and the fuel cell can further improve the power generation performance especially in a high humidity environment.

  FIG. 3 is a schematic sectional explanatory view showing the shape and structure of the catalyst (b). As shown in FIG. 3, the catalyst 20 'includes a catalyst metal 22' and a catalyst carrier 23 '. Further, the catalyst 20 'has vacancies (mesopores) 24' having a radius of 1 nm or more and less than 5 nm. Here, the catalyst metal 22 'is mainly supported inside the mesopores 24'. Further, the catalyst metal 22 ′ may be at least partially supported inside the mesopores 24 ′, and may be partially supported on the surface of the catalyst carrier 23 ′. However, from the viewpoint of preventing the contact between the electrolyte (electrolyte polymer, ionomer) and the catalyst metal in the catalyst layer and improving the catalyst activity, substantially all of the catalyst metal 22 'is supported inside the mesopores 24'. Preferably. When the catalytic metal contacts the electrolyte, the area specific activity of the catalytic metal surface decreases. On the other hand, with the above configuration, the electrolyte can be prevented from entering the mesopores 24 'of the catalyst carrier 23', and the catalyst metal 22 'and the electrolyte are physically separated. Then, a three-phase interface can be formed by water, so that the catalytic activity is improved. Here, “substantially all catalytic metals” are not particularly limited as long as the catalytic activity can be sufficiently improved. "Substantially all catalytic metals" are present in an amount of preferably at least 50% by weight (upper limit: 100% by weight), more preferably at least 80% by weight (upper limit: 100% by weight), based on all the catalytic metals.

  The pore volume of pores (mesopores) having a radius of 1 nm or more and less than 5 nm in the catalyst (b) is 0.8 cc / g carrier or more. The pore volume of the mesopores is preferably 0.8 to 3 cc / g carrier, and more preferably 0.9 to 2 cc / g carrier. If the pore volume is in the above range, a large number of pores contributing to the transport of the reaction gas are secured, so that the transport resistance of the reaction gas can be reduced. Therefore, the reaction gas is quickly transported to the surface of the catalyst metal stored in the mesopores, so that the catalyst metal is effectively used. Furthermore, if the volume of the mesopores is in the above range, the catalyst metal can be stored (supported) in the mesopores, and the electrolyte and the catalyst metal in the catalyst layer can be physically separated (the catalyst metal and the electrolyte). Contact can be more effectively suppressed and prevented). In this manner, in the above-described embodiment in which the contact between the catalyst metal in the mesopores and the electrolyte is suppressed, the activity of the catalyst is more effective than when the amount of the catalyst metal supported on the carrier surface is large. Available to

In the catalyst (b), the catalyst metal (catalyst component) has a specific surface area of 60 m ² / g carrier or less. The specific surface area of the catalyst metal is preferably 5 to 60 m ² / g support, more preferably 5 to 50 m ² / g support, further preferably 15 to 50 m ² / g support, and particularly preferably 25 to 50 m ² / g support. 45 m ² / g carrier. The surface of the catalyst metal is hydrophilic, and water is easily retained. If water is excessively retained in the mesopores, the gas transport path becomes narrow, and the diffusion rate of the reaction gas in the water is low, so that the gas transportability decreases. On the other hand, by making the specific surface area of the catalyst metal relatively small as in the above range, it is possible to reduce the amount of water adsorbed on the surface of the catalyst metal particularly in a high humidity environment. Therefore, especially in a high humidity environment, the transport resistance of the reaction gas can be reduced, and the catalytic metal is effectively used. The “specific surface area of the catalytic metal” in the present invention can be measured by, for example, a method described in Journal of Electroanalytical Chemistry 693 (2013) 34-41. In the present specification, the “specific surface area of the catalytic metal” employs a value measured by the following method.

  The specific surface area of the catalyst metal can be reduced by, for example, reducing the amount of the catalyst metal supported on the support surface.

(Method of measuring specific surface area of catalyst metal)
For the cathode catalyst layer, an electrochemically effective surface area (ECA) is determined by cyclic voltammetry. Here, a hydrogen gas humidified so as to be saturated at the measurement temperature is passed through the opposed anode, and this is used as a reference electrode and a counter electrode. Similarly, a humidified nitrogen gas is allowed to flow through the cathode. Immediately before the measurement is started, valves at the cathode inlet and outlet are closed and nitrogen gas is sealed. In this state, measurement is performed under the following conditions using an electrochemical measurement device (manufactured by Hokuto Denko Co., Ltd., model number: HZ-5000).

  The method for producing a catalyst having a specific pore volume as described above is not particularly limited, but it is important that the mesopore volume of the carrier has a pore distribution as described above. Specifically, as a method for producing a carrier having mesopores and a pore volume of the mesopores of 0.8 cc / g or more, Japanese Patent Application Laid-Open No. 2010-208888 (US Patent Application Publication No. 2011/2011) 318254 (hereinafter the same) and WO 2009/75264 (U.S. Patent Application Publication No. 2011/058308, the same applies hereinafter) are preferably used.

The material is not particularly limited as long as the BET specific surface area of the support is more than 1000 m ² / g, but a material having sufficient electron conductivity is preferable. Preferably, the main component is carbon. Specific examples include carbon particles made of carbon black (Ketjen Black (registered trademark), oil furnace black, channel black, lamp black, thermal black, acetylene black, etc.), activated carbon, and the like. "The main component is carbon" means that a carbon atom is included as a main component, and is a concept that includes both of only a carbon atom and substantially consisting of a carbon atom. May be included. The expression "consisting substantially of carbon atoms" means that impurities of about 2 to 3% by weight or less can be mixed.

  More preferably, a carrier manufactured by a method described in JP 2010-20887A or WO 2009/75264 is used because a desired pore region is easily formed inside the carrier. .

  In addition to the above carbon materials, porous metals such as Sn (tin) and Ti (titanium), and conductive metal oxides can also be used as carriers. These carriers may be used in combination.

The BET specific surface area of the support is not particularly limited as long as it exceeds 1000 (m ² / g support). In the case of a catalyst support having a BET specific surface area of 1000 (m ² / g support) or less, it may be difficult to store the catalyst metal in relatively large pores to suppress contact with the electrolyte. The BET specific surface area of the support is preferably more than 1000 (m ² / g support) and 3000 (m ² / g support) or less, more preferably 1100 to 2000 (m ² / g support). If the specific surface area is as described above, sufficient mesopores and micropores can be ensured. Therefore, while ensuring sufficient micropores (lower gas transport resistance) to perform gas transport, more mesopores and The catalyst metal can be stored (supported). Further, the electrolyte and the catalyst metal in the catalyst layer are physically separated from each other (the contact between the catalyst metal and the electrolyte can be more effectively suppressed and prevented). Therefore, the activity of the catalyst metal can be used more effectively. In addition, due to the presence of many micropores and mesopores, the function and effect of the present invention are more remarkably exhibited, and the catalytic reaction can be more effectively promoted. Further, the balance between the dispersibility of the catalyst metal on the catalyst carrier and the effective utilization rate can be appropriately controlled. In addition, the micropores act as a gas transport path, and the three-phase interface is more significantly formed by water, so that the catalytic activity can be further improved.

In the present invention, as long as the BET specific surface area exceeds 1000 (m ² / g carrier), it is not always necessary to use the granular porous carrier as described above.

  That is, examples of the carrier include a non-porous conductive carrier, a nonwoven fabric made of carbon fibers constituting a gas diffusion layer, carbon paper, and carbon cloth. At this time, the catalyst metal may be supported on these non-porous conductive carriers, or may be directly adhered to a nonwoven fabric made of carbon fibers, carbon paper, carbon cloth, etc. constituting the gas diffusion layer of the membrane / electrode assembly. It is possible.

  The catalytic metal that can be used in the present invention has a function of catalyzing an electrochemical reaction. The catalyst metal used for the anode catalyst layer is not particularly limited as long as it has a catalytic action on the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. The catalyst metal used for the cathode catalyst layer is not particularly limited as long as it has a catalytic action on the oxygen reduction reaction, and a known catalyst can be used in the same manner. Specifically, metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, copper, silver, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof Can be selected from

  Among them, those containing at least platinum are preferably used in order to improve catalytic activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. That is, the catalyst metal is preferably platinum or contains platinum and a metal component other than platinum, and more preferably platinum or a platinum-containing alloy. Such a catalytic metal can exhibit high activity. Although the composition of the alloy depends on the type of the metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal to be alloyed with platinum is preferably 10 to 70 atomic%. Note that an alloy is generally a metal element obtained by adding one or more metal elements or non-metal elements, and is a general term for an alloy having metallic properties. The alloy structure includes eutectic alloys, which are so-called mixtures in which the component elements are separate crystals, those in which the component elements are completely dissolved and in solid solution, and those in which the component elements are intermetallic compounds or compounds of metals and nonmetals. Some of them are formed, and any of them may be used in the present application. At this time, the catalyst metal used for the anode catalyst layer and the catalyst metal used for the cathode catalyst layer can be appropriately selected from the above. In this specification, unless otherwise specified, the description of the catalyst metal for the anode catalyst layer and the catalyst metal for the cathode catalyst layer has the same definition for both. However, the catalyst metal of the anode catalyst layer and the catalyst metal of the cathode catalyst layer do not need to be the same, and can be appropriately selected so as to exert the above-described desired action.

  The shape and size of the catalyst metal (catalyst component) are not particularly limited, and the same shape and size as those of known catalyst components can be adopted. As the shape, for example, a granular shape, a scale-like shape, a layered shape and the like can be used, but a granular shape is preferable. At this time, the average particle diameter (diameter) of the catalyst metal (catalyst metal particles) is not particularly limited, but is preferably more than 2.5 nm, more preferably 3 to 30 nm, particularly preferably more than 3 nm and 10 nm or less. When the average particle size of the catalyst metal is 3 nm or more, the catalyst metal is relatively firmly supported in the mesopores, and the contact with the electrolyte in the catalyst layer is more effectively suppressed or prevented. In addition, the micropores remain without being blocked by the catalyst metal, and the gas transport path is better secured, so that the gas transport resistance can be further reduced. In addition, elution due to a potential change can be prevented, and a decrease in performance over time can be suppressed. Therefore, the catalytic activity can be further improved, that is, the catalytic reaction can be more efficiently promoted. On the other hand, when the average particle diameter of the catalyst metal particles is 30 nm or less, the catalyst metal can be supported inside the mesopores of the carrier by a simple method, and the electrolyte coverage of the catalyst metal can be reduced. The “average particle size of the catalytic metal particles” in the present invention refers to the crystallite diameter determined from the half width of the diffraction peak of the catalytic metal component in X-ray diffraction, or the catalytic metal particles determined by a transmission electron microscope (TEM). Can be measured as the average value of the particle diameters.

  The amount of the catalyst metal carried on the carrier (sometimes referred to as the carrying ratio) is preferably 10 to 80% by weight, more preferably 20 to 70% by weight, based on the total amount of the catalyst (that is, the carrier and the catalyst metal). Good to do. It is preferable that the loading amount is in the above-mentioned range since sufficient dispersibility of the catalyst metal on the carrier, improvement in power generation performance, economic advantages, and catalytic activity per unit weight can be achieved.

In the fuel cell electrode catalyst layer, the catalyst metal content per unit catalyst application area (mg / cm ² ) (the “content per unit catalyst application area” of the catalyst metal is also referred to as “basis weight”) is as follows: There is no particular limitation as long as a sufficient degree of dispersion of the catalyst on the carrier and power generation performance can be obtained. The basis weight is, for example, 0.01 to 1 mg / cm ² . However, when the catalyst contains platinum or a platinum-containing alloy, the platinum content per unit catalyst application area is preferably 0.5 mg / cm ² or less. The use of expensive noble metal catalysts typified by platinum (Pt) and platinum alloys has become a factor of high cost of fuel cells. Therefore, it is preferable to reduce the amount of expensive platinum used (platinum content) to the above range to reduce costs. The lower limit is not particularly limited as long as power generation performance is obtained, and is, for example, 0.01 mg / cm ² or more. More preferably, the platinum content is 0.02 to 0.4 mg / cm ² , even more preferably 0.02 to 0.3 mg / cm ² . The fuel cell electrode catalyst layer according to the present invention has a high activity per weight of the catalyst, and the amount of expensive catalyst used can be reduced.

In addition, in the present specification, inductively coupled plasma emission spectroscopy (ICP) is used for measurement (confirmation) of the “catalyst metal (platinum) content per unit catalyst application area (mg / cm ² )”. A person skilled in the art can easily adjust the desired “content of catalyst metal (platinum) per unit catalyst application area (mg / cm ² )”. For example, the composition of the slurry (catalyst concentration) and the application amount Can be adjusted to control the amount.

[Catalyst layer]
The fuel cell electrode catalyst layer (catalyst layer) of the present invention may be present in either the cathode catalyst layer or the anode catalyst layer, but is preferably used in the cathode catalyst layer. As described above, the fuel cell electrode catalyst layer of the present invention can effectively utilize the catalyst by forming a three-phase interface with water without contact with the electrolyte. It is because it forms.

  The fuel cell electrode catalyst layer of the present invention contains an ion-conductive polymer electrolyte. The polymer electrolyte plays a role of transmitting protons generated around the catalyst active material on the fuel electrode side, and is therefore also called a proton conductive polymer. Further, the polymer electrolyte used for the fuel cell electrode catalyst layer of the present invention contains a sulfonic acid group as an ion exchange group. It is considered that the sulfonic acid group contained in the polymer electrolyte increases the hydrophilicity of the battery electrode catalyst layer, and can improve the water content. Further, it is considered that the proton concentration derived from the sulfonic acid group can be increased by setting the sulfonic acid group equivalent (unit density of the sulfonic acid group) per unit volume of the fuel cell electrode catalyst layer to a predetermined value or more.

  Polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes depending on the type of ion exchange resin that is a constituent material.

  Examples of the ion exchange resin constituting the fluorinated polymer electrolyte containing a sulfonic acid group include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, Asahi Glass Co., Ltd.) Perfluorocarbon sulfonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, polyvinylidene fluoride-perfluorocarbon sulfonic acid polymer, and the like. From the viewpoint of excellent heat resistance, chemical stability, durability and mechanical strength, these fluorine-based polymer electrolytes are preferably used, and particularly preferably a fluorine-based polymer electrolyte composed of a perfluorocarbonsulfonic acid-based polymer. Is used.

  Specific examples of the hydrocarbon-based electrolyte containing a sulfonic acid group include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated polyetherether. Ketone (S-PEEK), sulfonated polyphenylene (S-PPP) and the like can be mentioned. From the viewpoint of production that the raw materials are inexpensive, the production process is simple, and the selectivity of the material is high, these hydrocarbon-based polymer electrolytes are preferably used.

  In addition, only one kind of the above-mentioned ion exchange resins may be used alone, or two or more kinds may be used in combination. Further, the present invention is not limited to only the above-described materials, and other materials may be used.

  In addition, the fuel cell electrode catalyst layer is used in combination with a polymer electrolyte containing a sulfonic acid group, and a polymer electrolyte containing no sulfonic acid group at an arbitrary ratio within a range that does not impair the effects of the present invention. May be used. Examples of the polymer electrolyte containing no sulfonic acid group include a perfluorocarbon phosphonic acid-based polymer, an ethylene-tetrafluoroethylene copolymer, and a phosphonated polybenzimidazole alkyl. When a polymer electrolyte containing no sulfonic acid group is used in combination, the ratio of the polymer electrolyte containing no sulfonic acid group to the entire polymer electrolyte contained in the electrode catalyst layer for a fuel cell is, for example, more than 0 to 20%. % By weight (dry weight).

  In a polymer electrolyte responsible for proton transmission, proton conductivity is important. Here, if the EW of the polymer electrolyte is too large, the ionic conductivity of the entire catalyst layer decreases. Therefore, the catalyst layer of the present embodiment preferably contains a polymer electrolyte having a low EW. Specifically, the catalyst layer of the present embodiment preferably contains a polymer electrolyte having an EW of less than 1000 g / mol, more preferably contains a polymer electrolyte of less than 900 g / mol, and particularly preferably has a high EW of 800 g / mol or less. Contains molecular electrolyte.

  On the other hand, if the EW is too small, the hydrophilicity is too high, and it is difficult to smoothly move water. From such a viewpoint, the EW of the polymer electrolyte is preferably 400 g / mol or more, more preferably 500 g / mol or more. In addition, EW (Equivalent Weight) represents the equivalent weight of an exchange group having proton conductivity. The equivalent weight is a dry weight of the ion exchange membrane per equivalent of the ion exchange group, and is expressed in units of “g / mol”.

  In the fuel cell electrode catalyst layer of the present invention, two or more types of polymer electrolytes having different EWs may be used. In this case, it is preferable that the EW of the polymer electrolyte as a whole is within the above numerical range.

  When a polymer electrolyte containing no sulfonic acid group is used in combination with a polymer electrolyte containing a sulfonic acid group, the value of EW is the equivalent weight of the sulfonic acid group in the proton-conductive exchange group. When a polymer electrolyte containing no sulfonic acid group is used in combination with a polymer electrolyte containing a sulfonic acid group, the EW value used in Formula 1 described below is also used as the sulfonic acid group in the proton-conductive exchange group. Is the equivalent weight for

  When a plurality of polymer electrolytes having different EWs are used, or when a polymer electrolyte containing no sulfonic acid group is used in combination with a polymer electrolyte containing a sulfonic acid group, the value of EW used in the following formula 1 is as follows: It is calculated as follows. That is, it is calculated as the dry weight of the entire polymer electrolyte contained in the fuel cell electrode catalyst layer per sulfonic acid group equivalent. For example, when 2 parts by weight of the polymer electrolyte (2) having the EW = 1000 is used in combination with 1 part by weight of the polymer electrolyte (1) having the EW = 700, The value is (700 × １ ／) + (1000 × ２) = 900.

  Further, the catalyst layer includes two or more types of polymer electrolytes having different EWs in the power generation surface. At this time, the polymer electrolyte having the lowest EW among the polymer electrolytes has a relative humidity of the gas in the flow passage of 90% or less. Region may be used. By adopting such a material arrangement, the resistance value is reduced irrespective of the current density region, and the battery performance can be improved.

  Further, it is desirable to use the polymer electrolyte having the lowest EW in a region higher than the average temperature of the inlet and outlet of the cooling water. Thereby, the resistance value is reduced regardless of the current density region, and the battery performance can be further improved.

  Furthermore, from the viewpoint of reducing the resistance value of the fuel cell system, the polymer electrolyte having the lowest EW is within 3/5 of the flow path length from at least one of the gas supply ports of the fuel gas and the oxidizing gas. It is desirable to use it in the area of the range.

  The catalyst layer of the present embodiment may include, between the catalyst and the polymer electrolyte, a liquid proton conductive material capable of connecting the catalyst and the polymer electrolyte in a state capable of conducting protons. The introduction of the liquid proton conducting material ensures a proton transport path between the catalyst and the polymer electrolyte via the liquid proton conducting material, and efficiently transports protons required for power generation to the catalyst surface. Becomes possible. As a result, the utilization efficiency of the catalyst is improved, so that the usage amount of the catalyst can be reduced while maintaining the power generation performance. The liquid proton conductive material only needs to be interposed between the catalyst and the polymer electrolyte. The pores between the porous carriers in the catalyst layer (secondary pores) and the pores in the porous carrier (micropores) Alternatively, they can be arranged in mesopores (primary pores).

  The liquid proton conductive material is not particularly limited as long as it has ion conductivity and can exhibit a function of forming a proton transport path between the catalyst and the polymer electrolyte. Specific examples include water, protic ionic liquid, aqueous perchloric acid, aqueous nitric acid, aqueous formic acid, and aqueous acetic acid.

  If water is used as the liquid proton conducting material, introduce water as the liquid proton conducting material into the catalyst layer by wetting the catalyst layer with a small amount of liquid water or humidified gas before starting power generation. Can be. Further, water generated by an electrochemical reaction during the operation of the fuel cell can be used as a liquid proton conductive material. Therefore, it is not always necessary to hold the liquid proton conductive material when the fuel cell starts operating. For example, it is desirable that the surface distance between the catalyst and the electrolyte be 0.28 nm or more, which is the diameter of oxygen ions constituting water molecules. By maintaining such a distance, water (liquid proton conductive material) is interposed between the catalyst and the polymer electrolyte (liquid conductive material holding portion) while maintaining the non-contact state between the catalyst and the polymer electrolyte. Thus, a proton transport path by water between the two can be secured.

  When using a substance other than water, such as an ionic liquid, as the liquid proton conductive material, it is desirable to disperse the ionic liquid, the polymer electrolyte, and the catalyst in the solution when preparing the catalyst ink. An ionic liquid may be added when applying to the layer substrate.

  It is preferable that the total area of the catalyst in contact with the polymer electrolyte is smaller than the total area of the catalyst exposed to the liquid conductive material holding portion.

  These areas are compared, for example, when the liquid conductive material holding part is filled with the liquid proton conductive material, and the capacity of the electric double layer formed at the catalyst-polymer electrolyte interface and the catalyst-liquid proton conductive material interface is larger or smaller. This can be done by asking for a relationship. That is, since the electric double layer capacity is proportional to the area of the electrochemically effective interface, the electric double layer capacity formed at the catalyst-electrolyte interface is changed to the electric double layer capacity formed at the catalyst-liquid proton conductive material interface. If it is smaller, the contact area of the catalyst with the electrolyte is smaller than the exposed area of the liquid conductive material holding portion.

  Here, a method of measuring the electric double layer capacity formed at each of the catalyst-electrolyte interface and the catalyst-liquid proton conductive material interface, in other words, the size relationship between the contact areas between the catalyst and the electrolyte and between the catalyst and the liquid proton conductive material ( A method of determining the magnitude relationship between the contact area of the catalyst with the electrolyte and the exposed area of the liquid conductive material holding portion) will be described.

That is, in the catalyst layer of the present embodiment,
(1) Catalyst-polymer electrolyte (CS)
(2) Catalyst-liquid proton conductive material (CL)
(3) Porous carrier-polymer electrolyte (Cr-S)
(4) Porous carrier-liquid proton conductive material (Cr-L)
Can contribute as electric double layer capacitance (Cdl).

Electric double layer capacitor, as described above, since that is directly proportional to the area of the electrochemically active surface, Cdl C-S _(catalytic - electric double layer capacity of the polymer electrolyte interface) and Cdl _{C-L (catalytic} - The electric double layer capacity at the liquid proton conductive material interface may be determined. The contribution of the above four types of interfaces to the electric double layer capacitance (Cdl) can be separated as follows.

  First, the electric double layer capacity is measured under high humidification conditions such as 100% RH and low humidification conditions such as 10% RH or less. In addition, as a measuring method of the electric double layer capacitance, cyclic voltammetry, electrochemical impedance spectroscopy, and the like can be given. From these comparisons, the contribution of the liquid proton conducting material (in this case, “water”), that is, the above (2) and (4) can be separated.

  Further, when the catalyst is deactivated, for example, when Pt is used as the catalyst, the electric energy is reduced by deactivating the catalyst by supplying CO gas to the electrode to be measured and adsorbing CO on the Pt surface. The contribution to the overlay capacitance can be separated. In such a state, the electric double layer capacity under the high humidification and low humidification conditions is measured by the same method as described above, and the contribution of the catalyst, that is, the above (1) and (2) are separated from these comparisons. be able to.

  As described above, all the contributions of the above (1) to (4) can be separated, and the capacity of the electric double layer formed at the interface between the catalyst, the polymer electrolyte, and the liquid proton conductive material can be obtained.

  That is, the measured value (A) in the high humidification state is the electric double layer capacity formed at all the interfaces (1) to (4), and the measurement value (B) in the low humidification state is (1) and (3). Becomes the electric double layer capacitance formed at the interface of. The measured value (C) in the catalyst deactivated / high humidified state is the electric double layer capacity formed at the interface between (3) and (4), and the measured value (D) in the catalyst deactivated / low humidified state is The electric double layer capacitance formed at the interface of (3).

  Therefore, the difference between A and C is the electric double layer capacitance formed at the interface of (1) and (2), and the difference between B and D is the electric double layer capacitance formed at the interface of (1). Then, by calculating the difference between these values, (AC)-(BD), the electric double layer capacitance formed at the interface of (2) can be obtained. The contact area of the catalyst with the polymer electrolyte and the exposed area of the conductive material holding portion can be determined by, for example, TEM (transmission electron microscope) tomography in addition to the above.

  If necessary, a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene, a tetrafluoroethylene-hexafluoropropylene copolymer, a dispersant such as a surfactant, glycerin, ethylene glycol (EG) ), Polyvinyl alcohol (PVA), propylene glycol (PG), and other thickening agents, and additives such as pore-forming agents.

  The thickness (dry film thickness) of the catalyst layer is preferably 0.05 to 30 μm, more preferably 1 to 15 μm, and still more preferably 3 μm or more and less than 10 μm. The above thickness is applied to both the cathode catalyst layer and the anode catalyst layer. However, the thicknesses of the cathode catalyst layer and the anode catalyst layer may be the same or different.

  The electrode catalyst layer for a fuel cell according to the present invention has a sulfonic acid group equivalent (density of sulfonic acid group) per unit volume of the catalyst layer of 0.26 (mmol / cc catalyst layer) or more. By using such an electrode catalyst layer having a high sulfonic acid group density for an electrode assembly for a fuel cell, even when a catalyst carrier having a high specific surface area is used, the catalyst can be used in a low humidity environment (for example, 40% RH). In this case, excellent power generation performance can be obtained.

  In this specification, the sulfonic acid group density of the fuel cell electrode catalyst layer is a value calculated by the following equation.

  As shown in the above formula 1, the sulfonic acid group density of the electrode catalyst layer for a fuel cell includes a catalyst metal weight, a catalyst metal loading, a polymer electrolyte / catalyst carrier weight ratio (IC), a catalyst layer thickness, It can be controlled by arbitrarily setting the EW of the polymer electrolyte. For example, in order to increase the sulfonic acid group density of the fuel cell electrode catalyst layer, the ratio of the polymer electrolyte in the polymer electrolyte / catalyst carrier weight ratio (IC) is increased, or the polymer electrolyte having a low EW is used. It may be used for preparing an electrode catalyst layer for a fuel cell. By increasing the proportion of the polymer electrolyte in the polymer electrolyte / catalyst carrier weight ratio (IC) or by using a polymer electrolyte with a low EW, the catalyst metal weight per unit area is reduced and the amount of expensive noble metal used , And excellent power generation performance can be obtained in a low humidity environment.

  From the viewpoint of power generation performance under a low humidity environment (for example, 40% RH), the sulfonic acid group density of the fuel cell electrode catalyst layer preferably exceeds 0.30 (mmol / cc catalyst layer). More preferably, the sulfonic acid group density is at least 0.35 (mmol / cc catalyst layer), even more preferably at least 0.4 (mmol / cc catalyst layer). Although the upper limit of the sulfonic acid group density is not particularly limited, it is, for example, 0.75 (mmol / cc catalyst layer) or less from the viewpoint of power generation performance in a high humidity environment.

  The sulfonic acid group density of the fuel cell electrode catalyst layer can be analyzed by elemental analysis. Examples of the elemental analysis method include ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy, Inductively Coupled Plasma Emission Spectroscopy), Fluorine NMR (Nuclear Magnetic Resonance, Nuclear Magnetic Resonance) and the like. Regarding the sulfonic acid group density of the fuel cell electrode catalyst layer, when there is an error between the value calculated by the above formula 1 and the analysis value, the value calculated by the formula 1 is adopted as the sulfonic acid group density in the present invention. .

(Method for producing catalyst layer)
The electrode catalyst layer for a fuel cell of the present invention is preferably produced by using a catalyst ink containing a polymer electrolyte having an EW of less than 900 g / mol in a weight ratio of 0.9 or more to a catalyst carrier. That is, according to one aspect of the present invention, there is provided a method for producing a catalyst carrier and a catalyst comprising a catalyst metal supported on the catalyst carrier, and a fuel cell electrode catalyst layer including a polymer electrolyte, wherein A step of preparing a catalyst ink containing the catalyst and the polymer electrolyte in such a ratio that the weight ratio of the molecular electrolyte is 0.9 or more, wherein the BET specific surface area of the catalyst carrier exceeds 1000 (m ² / g carrier) Wherein the polymer electrolyte has an EW (Equivalent Weight) of less than 900 g / mol. However, the method for producing the fuel cell electrode catalyst layer according to the present invention is not limited to the above-described method. Hereinafter, preferred embodiments for producing a catalyst layer will be described, but the technical scope of the present invention is not limited to only the following embodiments. In addition, since various conditions such as the material of each component of the catalyst layer are as described above, the description is omitted here.

First, a catalyst support having a BET specific surface area of more than 1000 (m ² / g support) (also referred to as “porous support” in this specification) is prepared.

Next, a catalyst metal is supported on the porous carrier to obtain a catalyst powder. The catalytic metal can be supported on the porous carrier by a known method. For example, known methods such as an impregnation method, a liquid phase reduction supporting method, an evaporation to dryness method, a colloid adsorption method, a spray pyrolysis method, and a reverse micelle (microemulsion method) can be used. In order to keep the average particle size of the catalyst metal in a desired range, after the catalyst metal is supported on a carrier, heat treatment may be performed in a reducing atmosphere. At this time, the heat treatment temperature is preferably in the range of 300 to 1200 ° C, more preferably in the range of 500 to 1150 ° C, and particularly preferably in the range of 700 to 1000 ° C. Further, the reducing atmosphere is not particularly limited as long as it contributes to the grain growth of the catalytic metal, but it is preferable to perform the reducing atmosphere in a mixed atmosphere of a reducing gas and an inert gas. The reducing gas is not particularly limited, but is preferably a hydrogen (H ₂ ) gas. The inert gas is not particularly limited, but helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), nitrogen (N ₂ ), and the like can be used. The inert gas may be used alone or in the form of a mixture of two or more gases. Further, the heat treatment time is preferably from 0.1 to 2 hours, more preferably from 0.5 to 1.5 hours.

  The catalyst powder may be treated with an oxidizing solution to provide acidic groups. By treating with an oxidizing solution, an acidic group can be imparted to the support and the hydrophilicity of the support can be increased. That is, one embodiment of the present invention provides a catalyst support and a catalyst metal supported on the catalyst support. Treating the catalyst with an oxidizing solution to give an acidic group to the catalyst.

  The oxidizing solution used is preferably an aqueous solution of sulfuric acid, nitric acid, phosphorous acid, potassium permanganate, hydrogen peroxide, hydrochloric acid, chloric acid, hypochlorous acid, chromic acid, or the like. This oxidizing solution treatment is performed by bringing the catalyst into contact with the oxidizing solution at least once. When performing the oxidizing solution treatment a plurality of times, the type of the solution may be changed for each treatment. As the conditions for the oxidizing solution treatment, an aqueous solution containing the oxidizing agent in an amount of 0.1 to 10.0 mol / L is preferable, and it is preferable to immerse the catalyst in the solution. The immersion time is preferably 1 to 10 hours, and the treatment temperature is preferably 50 to 90 ° C. The volume ratio of the amount of water vapor adsorbed to the amount of nitrogen adsorbed or the amount of acidic group of the carrier can be controlled by adjusting the BET specific surface area of the catalyst, the type of oxidizing solution, the concentration, the treatment time, and the treatment temperature.

  A catalyst ink containing the obtained catalyst powder, polymer electrolyte and solvent is prepared. The solvent is not particularly limited, and a common solvent used for forming a catalyst layer can be used in the same manner. Specifically, tap water, pure water, ion-exchanged water, water such as distilled water, cyclohexanol, methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, tert-butanol, etc. And lower alcohols having 1 to 4 carbon atoms, propylene glycol, benzene, toluene, xylene and the like. Besides these, butyl acetate, dimethyl ether, ethylene glycol, and the like may be used as the solvent. These solvents may be used alone or in a mixture of two or more. Preferably, from the viewpoint of the dispersibility of the polymer electrolyte, an aqueous solution containing the lower alcohol having 1 to 4 carbon atoms at a concentration of 5 to 45% by weight is used as the solvent. In the catalyst ink, the catalyst powder and the polymer electrolyte may be dissolved in the solvent, but may not be dissolved.

  From the viewpoint of the sulfonic acid group density of the catalyst layer, the catalyst ink preferably contains the polymer electrolyte at a ratio of 0.9 or more to the catalyst carrier in the catalyst powder. More preferably, the weight ratio of the polymer electrolyte to the catalyst carrier is 1.0 or more, and still more preferably 1.1 or more. The upper limit of the weight ratio of the polymer electrolyte to the catalyst carrier is not particularly limited, but is, for example, 2.0 or less from the viewpoint of power generation performance in a high humidity environment.

  The amount of the solvent constituting the catalyst ink is not particularly limited as long as the solvent can completely dissolve the electrolyte. Specifically, the concentration of components other than the solvent such as the catalyst powder and the polymer electrolyte is preferably 1 to 50% by weight, and more preferably about 5 to 30% by weight in the electrode catalyst ink.

  When additives such as a water repellent, a dispersant, a thickener, and a pore former are used, these additives may be added to the catalyst ink. At this time, the amount of the additive to be added is not particularly limited as long as the amount does not hinder the effect of the present invention. For example, the amount of each additive is preferably 5 to 20% by weight based on the total weight of the electrode catalyst ink.

  Next, a catalyst ink is applied to the surface of the substrate. The method of coating the substrate is not particularly limited, and a known method can be used. Specifically, it can be performed using a known method such as a spray (spray coating) method, a gulliver printing method, a die coater method, a screen printing method, a doctor blade method, and the like.

  The catalyst ink is applied so that the thickness of the catalyst layer after drying is preferably 0.05 to 30 μm, more preferably 1 to 15 μm, and still more preferably 3 μm or more and less than 10 μm. The above thickness is applied to both the cathode catalyst layer and the anode catalyst layer. However, the thicknesses of the cathode catalyst layer and the anode catalyst layer may be the same or different.

  At this time, a solid polymer electrolyte membrane (electrolyte layer) or a gas diffusion substrate (gas diffusion layer) can be used as a substrate on which the catalyst ink is applied. In such a case, after forming a catalyst layer on the surface of a solid polymer electrolyte membrane (electrolyte layer) or a gas diffusion substrate (gas diffusion layer), the obtained laminate is directly used for production of a membrane electrode assembly. Can be used. Alternatively, a peelable substrate such as a polytetrafluoroethylene (PTFE) [Teflon (registered trademark)] sheet is used as a substrate, and after forming a catalyst layer on the substrate, the catalyst layer portion is peeled from the substrate. Thereby, a catalyst layer may be obtained.

  Finally, the coating layer (film) of the catalyst ink is dried at room temperature to 150 ° C. for 1 to 60 minutes under an air atmosphere or an inert gas atmosphere. Thereby, a catalyst layer is formed.

[Membrane electrode assembly, fuel cell, vehicle]
According to a further embodiment of the present invention, there is provided a fuel cell membrane electrode assembly including the fuel cell electrode catalyst layer. That is, the solid polymer electrolyte membrane 2, the cathode catalyst layer arranged on one side of the electrolyte membrane, the anode catalyst layer arranged on the other side of the electrolyte membrane, the electrolyte membrane 2 and the anode catalyst layer There is provided a membrane electrode assembly for a fuel cell, comprising a pair of gas diffusion layers (4a, 4c) sandwiching the cathode catalyst layer 3c. In this membrane electrode assembly, at least one of the cathode catalyst layer and the anode catalyst layer is the catalyst layer of the embodiment described above.

However, considering the necessity of improving the proton conductivity and the transport characteristics (gas diffusivity) of the reaction gas (particularly O ₂ ), at least the cathode catalyst layer may be the catalyst layer of the embodiment described above. preferable. However, the catalyst layer according to the above embodiment is not particularly limited, and may be used as an anode catalyst layer or as both a cathode catalyst layer and an anode catalyst layer.

  According to a further embodiment of the present invention, there is provided a fuel cell including the membrane electrode assembly according to the above aspect. That is, one embodiment of the present invention is a fuel cell having a pair of an anode separator and a cathode separator sandwiching the membrane electrode assembly of the above-described embodiment.

  Hereinafter, the components of the PEFC 1 using the catalyst layer of the above embodiment will be described with reference to FIG. However, the present invention is characterized by the catalyst layer. Therefore, specific configurations of members other than the catalyst layer constituting the fuel cell can be appropriately modified with reference to conventionally known knowledge.

(Electrolyte membrane)
The electrolyte membrane is composed of, for example, a solid polymer electrolyte membrane 2 as shown in FIG. The solid polymer electrolyte membrane 2 has a function of selectively transmitting protons generated in the anode catalyst layer 3a to the cathode catalyst layer 3c along the thickness direction during the operation of the PEFC 1. Further, the solid polymer electrolyte membrane 2 also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidizing gas supplied to the cathode side from being mixed.

  The electrolyte material constituting the solid polymer electrolyte membrane 2 is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, the fluorine-based polymer electrolyte or the hydrocarbon-based polymer electrolyte described above as the polymer electrolyte can be used. At this time, it is not always necessary to use the same polymer electrolyte as that used for the catalyst layer.

(Gas diffusion layer)
The gas diffusion layers (anode gas diffusion layer 4a, cathode gas diffusion layer 4c) are formed of catalyst layers (3a, 3c) of gas (fuel gas or oxidizing gas) supplied through gas flow paths (6a, 6c) of the separator. ) And a function as an electron conduction path.

  The material constituting the base material of the gas diffusion layers (4a, 4c) is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, a conductive and porous sheet material such as a carbon woven fabric, a paper-like paper body, a felt, and a nonwoven fabric may be used. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, and may be about 30 to 500 μm. When the thickness of the base material is within such a range, the balance between mechanical strength and diffusibility of gas, water, and the like can be appropriately controlled.

  The gas diffusion layer preferably contains a water repellent for the purpose of further increasing the water repellency and preventing the flooding phenomenon and the like. Examples of the water repellent include, but are not particularly limited to, fluorine-based high-molecular compounds such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples include a molecular material, polypropylene, and polyethylene.

  In order to further improve the water repellency, the gas diffusion layer is provided with a carbon particle layer (microporous layer; MPL, not shown) made of an aggregate of carbon particles containing a water repellent on the catalyst layer side of the substrate. You may have.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately used. Among them, carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black can be preferably used because of their excellent electron conductivity and large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. As a result, a high drainage property can be obtained by the capillary force, and the contact with the catalyst layer can be improved.

  Examples of the water repellent used in the carbon particle layer include the same water repellents as described above. Among them, a fluorine-based polymer material can be preferably used because it is excellent in water repellency, corrosion resistance during an electrode reaction, and the like.

  The mixing ratio between the carbon particles and the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) by weight in consideration of the balance between water repellency and electron conductivity. Is good. The thickness of the carbon particle layer is not particularly limited, and may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer.

(Method of manufacturing membrane electrode assembly)
The method for producing the membrane / electrode assembly is not particularly limited, and a conventionally known method can be used. For example, a catalyst layer is transferred or applied to a solid polymer electrolyte membrane by a hot press and dried, and then a gas diffusion layer is bonded to the solid polymer electrolyte membrane. If it is not contained, two gas diffusion electrodes (GDE) are prepared by applying a catalyst layer on one side of the substrate layer in advance and drying, and hot-pressing the gas diffusion electrodes on both sides of the solid polymer electrolyte membrane. The application and bonding conditions such as hot pressing may be appropriately determined depending on the type of polymer electrolyte (perfluorosulfonic acid or hydrocarbon) in the solid polymer electrolyte membrane or the catalyst layer. Adjust it.

(Separator)
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. Further, the separator also has a function as a partition for separating the fuel gas, the oxidizing gas, and the coolant from each other. In order to secure these flow paths, as described above, it is preferable that each of the separators is provided with a gas flow path and a cooling flow path. As a material for forming the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately used without any limitation. The thickness and size of the separator, the shape and size of each flow path provided, and the like are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

  The method for manufacturing the fuel cell is not particularly limited, and conventionally known knowledge in the field of the fuel cell can be appropriately referred to.

  Further, a fuel cell stack having a structure in which a plurality of membrane electrode assemblies are stacked via a separator and connected in series may be formed so that the fuel cell can exhibit a desired voltage. The shape and the like of the fuel cell are not particularly limited, and may be appropriately determined so as to obtain desired cell characteristics such as a desired voltage.

  The above-mentioned PEFC and the membrane electrode assembly use a catalyst layer excellent in power generation performance and durability. Therefore, the PEFC and the membrane electrode assembly are excellent in power generation performance and durability.

  The PEFC of this embodiment and the fuel cell stack using the same can be mounted, for example, as a drive power source in a vehicle. According to one embodiment of the present invention, there is provided a vehicle including the above fuel cell.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

(Comparative Example 1)
Ketjen Black (registered trademark) EC300J (manufactured by Ketjen Black International) (support A) having a BET specific surface area of 720 m ² / g carrier was prepared.

  Using a carrier A, platinum (Pt) having an average particle size (diameter) of 2.5 nm as a catalyst metal was carried thereon so that the carrying ratio became 50% by weight, to obtain a catalyst powder A. That is, 46 g of the carrier A was immersed in 1000 g (platinum content: 46 g) of a dinitrodiammineplatinum nitric acid solution having a platinum concentration of 4.6% by mass and stirred, and then 100 ml of 100% ethanol as a reducing agent was added. This solution was stirred and mixed at the boiling point for 7 hours, and platinum was supported on the carrier A. Then, by filtering and drying, a catalyst powder A having a loading of 50% by weight was obtained.

For the catalyst powder A thus obtained, the pore volume of micropores and mesopores, the mode radius of micropores and mesopores, the BET specific surface area, and the amount of acidic groups were measured. As a result, the pore volume of the micropores was 0.23 cc / g carrier; the pore volume of the mesopores was 0.30 cc / g carrier; the BET specific surface area was 720 m ² / g carrier; and the amount of acidic group was 0.42 mmol / g. g carrier. In catalyst powder A, mesopore or micropore mode radii were not clearly detected.

  A fluorine-based polymer electrolyte (Nafion (registered trademark) D2020, EW = 1100 g / mol, manufactured by DuPont) and a catalyst powder A as a polymer electrolyte, and the weight ratio of the polymer electrolyte to the catalyst carrier was 1.0. And mixed. Further, a 40% by weight normal propyl alcohol solution was added as a solvent so that the solid content ratio (Pt + carbon carrier + ionomer) became 15% by weight to prepare a cathode catalyst ink.

  Ketjen Black (registered trademark) (particle size: 30 to 60 nm) is used as a carrier, and platinum (Pt) having an average particle size of 2.5 nm is supported thereon as a catalyst metal so that the loading ratio is 50% by weight. Thus, a catalyst powder was obtained. This catalyst powder and an ionomer dispersion liquid (Nafion (registered trademark) D2020, EW = 1100 g / mol, manufactured by DuPont) as a polymer electrolyte were mixed so that the weight ratio of the carbon carrier to the ionomer was 1.3. Further, a normal propyl alcohol solution (50% by weight) was added as a solvent so that the solid content (Pt + carbon carrier + ionomer) was 5% by weight to prepare an anode catalyst ink.

Next, a gasket (Teonex, Teijin, Teijin Dupont, thickness: 25 μm (adhesive layer: 10 μm)) was arranged around both sides of the polymer electrolyte membrane (NAFION NR211, thickness: 25 μm, manufactured by Dupont). An anode catalyst ink was applied to one surface of the electrolyte membrane by a spray coating method. The anode catalyst ink was dried by maintaining the stage for performing the spray coating at 60 ° C. for 1 minute to form an anode catalyst layer. Separately, a cathode catalyst ink was applied to a transfer base material (PTFE) to a size of 5 cm × 2 cm by screen printing. Thereafter, the cathode catalyst ink was dried at 80 ° C. for 15 minutes, and transferred to an exposed portion of one surface of the polymer electrolyte membrane by hot pressing (transfer conditions: 150 ° C., 0.8 MPa, 10 minutes), and the electrode catalyst layer ( A cathode catalyst layer) was formed (catalyst layer thickness: 11 μm). Thus, a membrane / catalyst layer assembly (1) (CCM (1)) was obtained. The platinum basis weight of the cathode catalyst layer was 0.35 mg / cm ² , and the sulfonic acid group density was 0.29 mmol / cc catalyst layer.

(Comparative Example 2)
A membrane catalyst layer assembly (2) (CCM (2)) was obtained in the same manner as in Comparative Example 1, except that the weight ratio between the polymer electrolyte and the catalyst carrier in the cathode catalyst ink was changed to 1.2. The platinum basis weight of the cathode catalyst layer in the membrane catalyst layer assembly (2) is 0.35 mg / cm ² , and the sulfonic acid group density is 0.35 mmol / cc catalyst layer.

(Comparative Example 3)
The carbon material 1 was produced by the method described in WO 2009/75264. The obtained carbon material 1 was heated at 1800 ° C. for 5 minutes in an atmosphere of argon gas to prepare a carrier B.

The BET specific surface area of the carrier B thus obtained was 1200 m ² / g carrier.

  Using a support B, platinum (Pt) having an average particle diameter (diameter) of 3.2 nm was supported as a catalyst metal on the support B such that the loading ratio was 30% by weight, to obtain a catalyst powder B-1. That is, 46 g of the carrier A was immersed in 429 g (platinum content: 19.7 g) of a dinitrodiammineplatinic nitric acid solution having a platinum concentration of 4.6% by mass, stirred, and then 100 ml of 100% ethanol as a reducing agent was added. This solution was stirred and mixed at the boiling point for 7 hours, and platinum was supported on the carrier A. Then, by filtering and drying, a catalyst powder having a loading of 30% by weight was obtained. Thereafter, the temperature was kept at 900 ° C. for 1 hour in a hydrogen atmosphere to obtain a catalyst powder B-1.

For the catalyst powder B-1 thus obtained, the pore volume of micropores and mesopores, the mode radius of micropores and mesopores, the BET specific surface area, and the amount of acidic groups were measured. As a result, the pore volume of the micropores was 0.69 cc / g carrier; the pore volume of the mesopores was 0.80 cc / g carrier; the mode radius of the micropores was 0.75 nm; and the mode radius of the mesopores was 1.66 nm. A carrier having a BET specific surface area of 1230 m ² / g; and the amount of acidic groups was below the detection limit. It was confirmed with an electron microscope that the catalyst metal was supported inside the mesopores in the catalyst powder B-1.

Comparative Example 1 except that the catalyst powder B was used instead of the catalyst powder A, the weight ratio between the polymer electrolyte and the catalyst carrier of the cathode catalyst ink was changed to 0.9, and the thickness of the cathode catalyst layer was changed to 15 μm. Similarly, a membrane catalyst layer assembly (3) (CCM (3)) was obtained. The platinum basis weight of the cathode catalyst layer in the membrane catalyst layer assembly (3) is 0.15 mg / cm ² , and the sulfonic acid group density is 0.19 mmol / cc catalyst layer.

(Comparative Example 4)
A membrane catalyst layer assembly (4) (CCM (4)) was obtained in the same manner as in Comparative Example 3, except that the weight ratio between the polymer electrolyte and the catalyst carrier in the cathode catalyst ink was changed to 0.6. In the membrane catalyst layer assembly (4), the cathode catalyst layer had a platinum basis weight of 0.15 mg / cm ² and a sulfonic acid group density of 0.13 mmol / cc catalyst layer.

(Comparative Example 5)
A membrane catalyst layer assembly (5) (CCM (5)) was obtained in the same manner as in Comparative Example 4, except that the polymer electrolyte in the cathode catalyst ink was changed to a fluorine-based polymer electrolyte (EW = 700 g / mol). Was. The cathode catalyst layer in the membrane catalyst layer assembly (5) has a platinum basis weight of 0.15 mg / cm ² and a sulfonic acid group density of 0.20 mmol / cc catalyst layer.

(Example 1)
A membrane catalyst layer assembly (6) (CCM (6)) was obtained in the same manner as in Comparative Example 5, except that the weight ratio between the polymer electrolyte and the catalyst carrier in the cathode catalyst ink was changed to 0.9. The cathode catalyst layer in the membrane / catalyst layer assembly (6) had a platinum basis weight of 0.15 mg / cm ² and a sulfonic acid group density of 0.30 mmol / cc catalyst layer.

(Example 2)
Using a carrier B, platinum (Pt) having an average particle diameter (diameter) of 3.2 nm as a catalyst metal was supported on the carrier B such that the loading ratio became 50% by weight, to obtain a catalyst powder B-2. That is, 46 g of the carrier A was immersed in 1000 g (platinum content: 46 g) of a dinitrodiammineplatinum nitric acid solution having a platinum concentration of 4.6% by mass, stirred, and then 100 ml of 100% ethanol as a reducing agent was added. This solution was stirred and mixed at the boiling point for 7 hours, and platinum was supported on the carrier A. Then, by filtering and drying, a catalyst powder having a loading rate of 50% by weight was obtained. Thereafter, the temperature was maintained at 900 ° C. for 1 hour in a hydrogen atmosphere to obtain catalyst powder B-2.

For the catalyst powder B-2 thus obtained, the pore volume of micropores and mesopores, the mode radius of micropores and mesopores, the BET specific surface area, and the amount of acidic groups were measured. As a result, the pore volume of the micropore was 0.71 cc / g carrier; the pore volume of the mesopore was 0.91 cc / g carrier; the mode radius of the micropore was 0.75 nm; and the mode radius of the mesopore was 1.64 nm. A carrier having a BET specific surface area of 1190 m ² / g; and an amount of acidic group was below the detection limit. In the catalyst powder B-2, it was confirmed by an electron microscope that the catalyst metal was supported inside the mesopores.

The catalyst powder B-2 was used in place of the catalyst powder B-1, a 10% by weight aqueous solution of isopropanol was used as a solvent for the preparation of the cathode catalyst ink, and the weight ratio of the polymer electrolyte to the catalyst carrier of the cathode catalyst ink was 1.3. Then, a membrane catalyst layer assembly (7) (CCM (7)) was obtained in the same manner as in Example 1 except that the thickness of the cathode catalyst layer was changed to 8 μm. The cathode catalyst layer in the membrane / catalyst layer assembly (7) had a basis weight of platinum of 0.20 mg / cm ² and a sulfonic acid group density of 0.46 mmol / cc catalyst layer.

(Example 3)
The catalyst powder B-2 was subjected to an oxidizing solution treatment for adding an acidic group. The catalyst powder B-2 was immersed in a 3.0 mol / L aqueous nitric acid solution at 80 ° C. for 6 hours, and then filtered and dried to obtain a catalyst powder B-3 having an acidic group.

For the catalyst powder B-3 thus obtained, the pore volume of micropores and mesopores, the mode radius of micropores and mesopores, the BET specific surface area, and the amount of acidic groups were measured. As a result, the pore volume of the micropores was 0.80 cc / g carrier; the pore volume of the mesopores was 1.10 cc / g carrier; the mode radius of the micropores was 0.75 nm; and the mode radius of the mesopores was 1.64 nm. A BET specific surface area of 1260 m ² / g carrier; and an acidic group content of 0.32 mmol / g carrier.

The catalyst powder B-3 was used in place of the catalyst powder B-2, a 40% by weight aqueous solution of isopropanol was used as a solvent for preparing the cathode catalyst ink, and the weight ratio between the polymer electrolyte and the catalyst carrier of the cathode catalyst ink was 1.2. Was obtained in the same manner as in Example 2 except that the membrane catalyst layer assembly (8) (CCM (8)) was obtained. The cathode catalyst layer in the membrane / catalyst layer assembly (8) had a platinum basis weight of 0.20 mg / cm ² and a sulfonic acid group density of 0.43 mmol / cc catalyst layer.

Experiment 1: Evaluation of power generation performance For the membrane catalyst layer assemblies (1) to (8), the current density (mA / cm ² Pt) when the voltage after IR correction was 0.9 V was measured under the following evaluation conditions. Then, the power generation performance was evaluated. The results are shown in Table 1 below.

  Table 1 shows that the CCM using the electrode catalyst layer of the present invention has excellent power generation performance. Also, from the comparison of Comparative Example 4, Comparative Example 5, and Example 1, it was found that the weight ratio of the polymer electrolyte to the catalyst carrier was 0.9 or more, and the polymer electrolyte having an EW of less than 900 g / mol was used. It turns out that an acid group density becomes high. In addition, it can be seen that an electrode catalyst layer having excellent power generation performance can be manufactured even in a low humidity environment.

1: Solid polymer fuel cell (PEFC),
2. Solid polymer electrolyte membrane,
3 ... catalyst layer,
3a: anode catalyst layer,
3c: cathode catalyst layer,
4a: anode gas diffusion layer,
4c: cathode gas diffusion layer,
5. Separator,
5a: anode separator,
5c: cathode separator,
6a: anode gas flow path,
6c: cathode gas flow path,
7 ... refrigerant channel,
10 ... membrane electrode assembly (MEA),
20, 20 '... catalyst,
22, 22 ': catalytic metal,
23, 23 '... carrier (catalyst carrier),
24, 24 '... mesopore,
25 ... Micropore.

Claims (11)

A catalyst comprising a catalyst carrier and a catalyst metal supported on the catalyst carrier, and a fuel cell electrode catalyst layer containing a polymer electrolyte,
The catalyst support having a BET specific surface area of more than 1000 (m ² / g support);
The polymer electrolyte contains a sulfonic acid group,
The density of the sulfonic acid group is 0.26 (mmol / cc catalyst layer) or more;
An electrode catalyst layer for a fuel cell, wherein the catalyst satisfies the following (b):
(B) The catalyst has pores having a radius of 1 nm or more and less than 5 nm, the pore volume of the pores is 0.8 (cc / g carrier) or more, and the specific surface area of the catalyst metal is 60 ( m ² / g carrier) or less (excluding 30 (m ² / g carrier) or less) . The specific surface area of the catalyst metal, 40 to 60 is ^(m 2 / g carrier), a fuel cell electrode catalyst layer according to claim 1. The specific surface area of the catalyst metal, 30 is an ultra ~45 (m ² / g carrier), a fuel cell electrode catalyst layer according to claim 1. The electrode catalyst layer for a fuel cell according to any one of claims 1 to 3, wherein the density of the sulfonic acid group is 0.30 to 0.75 (mmol / cc catalyst layer). The fuel cell electrode catalyst layer according to any one of claims 1 to 4 , wherein the density of the sulfonic acid group is 0.35 to 0.75 (mmol / cc catalyst layer). The electrode catalyst layer for a fuel cell according to any one of claims 1 to 5 , wherein the amount of the acidic group of the catalyst is 0.2 (mmol / g carrier) or more. The fuel cell electrode catalyst layer according to any one of claims 1 to 6 , wherein the catalyst satisfies at least one of the following (a) or (c):
(A) the catalyst has pores having a radius of less than 1 nm and pores having a radius of 1 nm or more, and the pores having a radius of less than 1 nm have a pore volume of 0.3 (cc / g carrier) or more; And the catalyst metal is supported inside the pores having a radius of 1 nm or more;
(C) the catalyst has pores with a radius of less than 1 nm and pores with a radius of 1 nm or more; the mode radius of the pore distribution of the pores with a radius of less than 1 nm is 0.3 nm or more and less than 1 nm; The catalyst metal is supported inside the pores having a radius of 1 nm or more. A membrane electrode assembly for a fuel cell, comprising the electrode catalyst layer for a fuel cell according to any one of claims 1 to 7 . A fuel cell comprising the fuel cell membrane electrode assembly according to claim 8 . A vehicle comprising the fuel cell according to claim 9 . A catalyst comprising a catalyst carrier and a catalyst metal supported on the catalyst carrier, and a method for producing a fuel cell electrode catalyst layer comprising a polymer electrolyte,
Preparing a catalyst ink containing the catalyst and the polymer electrolyte at a ratio where the weight ratio of the polymer electrolyte to the catalyst carrier is 0.9 or more,
The catalyst support having a BET specific surface area of more than 1000 (m ² / g support);
The catalyst metal weight is 0.01 to 1 mg / cm ² ,
The catalyst metal loading is 10 to 80% by weight based on the total amount of the catalyst,
The polymer electrolyte / catalyst support weight ratio (IC) is 0.9 or more;
The thickness of the catalyst layer is 0.05 to 30 μm,
The polymer electrolyte has an EW (Equivalent Weight) of less than 900 g / mol,
A method for producing a fuel cell electrode catalyst layer, wherein the catalyst satisfies the following (b):
(B) The catalyst has pores having a radius of 1 nm or more and less than 5 nm, the pore volume of the pores is 0.8 (cc / g carrier) or more, and the specific surface area of the catalyst metal is 60 ( m ² / g carrier) or less (excluding 30 (m ² / g carrier) or less) .