Carbon material for catalyst carriers for solid polymer fuel cell, catalyst layer for solid polymer fuel cells, and fuel cell

Abstract

To provide a carbon material for catalyst carriers for a solid polymer fuel cell which is improved in durability further together with a power generation performance, a catalyst layer for solid polymer fuel cells utilizing the same, and a fuel cell.SOLUTION: Disclosed are: a carbon material for catalyst carriers for a solid polymer fuel cell consisting of porous active carbon black satisfying the following requirements (A1) and (B1); a catalyst layer for solid polymer fuel cells utilizing the same; and a fuel cell. (A1) A ratio (S1fin / Sini) of a BET specific surface area S1fin after performing heat treatment upon the porous active carbon black at 2000°C for 1 hour and a BET specific surface area Sini before the heat treatment is 0.9 or more. (B1) The BET specific surface area Sini before the heat treatment is 600 m2 / g or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a carbon material for a catalyst support of a polymer electrolyte fuel cell, a catalyst layer for a polymer electrolyte fuel cell, and a fuel cell. [Background technology]

[0002] A polymer electrolyte fuel cell, a type of fuel cell, comprises a pair of catalyst layers disposed on both sides of a solid polymer electrolyte membrane, gas diffusion layers disposed on the outer side of each catalyst layer, and separators disposed on the outer side of each gas diffusion layer. One of the pair of catalyst layers serves as the anode of the polymer electrolyte fuel cell, and the other serves as the cathode of the polymer electrolyte fuel cell. In a typical polymer electrolyte fuel cell, multiple unit cells each having the above components are stacked to obtain the desired output.

[0003] A fuel gas such as hydrogen is introduced into the separator on the anode side. The fuel is diffused into the gas diffusion layer on the anode side before being introduced into the anode. The anode contains a catalyst component, a catalyst support that supports a fuel cell catalyst, and an electrolyte material with proton conductivity. Hereinafter, the catalyst component that promotes the power generation reaction (oxidation reaction or reduction reaction described below) in the fuel cell will also be referred to as the "fuel cell catalyst." The catalyst support is often made of a porous carbon material. An oxidation reaction of the fuel gas occurs on the fuel cell catalyst, producing protons and electrons. For example, when the fuel gas becomes hydrogen gas, the following oxidation reaction occurs: H2→2H + +2e - (E0=0V)

[0004] Protons produced in this oxidation reaction pass through the electrolyte material in the anode and the solid polymer electrolyte membrane to be introduced to the cathode. Electrons pass through the catalyst support, gas diffusion layer, and separator to be introduced to the external circuit. After performing work in the external circuit, these electrons are introduced to the separator on the cathode side. These electrons then pass through the separator on the cathode side and the gas diffusion layer on the cathode side to be introduced to the cathode.

[0005] The solid polymer electrolyte membrane is made of a proton-conductive electrolyte material and introduces the protons generated in the oxidation reaction to the cathode.

[0006] An oxidizing gas, such as oxygen gas or air, is introduced into the cathode-side separator. The oxidizing gas is diffused into the cathode-side gas diffusion layer and then introduced into the cathode. The cathode includes a fuel cell catalyst, a catalyst support that supports the fuel cell catalyst, and a proton-conductive electrolyte material. The catalyst support is often made of a porous carbon material. A reduction reaction of the oxidizing gas occurs on the fuel cell catalyst, producing water. For example, when the oxidizing gas becomes oxygen gas or air, the following reduction reaction occurs: O2+4H + +4e - →2H2O (E0=1.23V)

[0007] The water produced by the reduction reaction is discharged outside the fuel cell along with the unreacted oxidizing gas. In this way, solid polymer fuel cells generate electricity by utilizing the free energy difference (potential difference) generated by the oxidation reaction of the fuel gas. In other words, the free energy generated by the oxidation reaction is converted into work performed by electrons in an external circuit.

[0008] Meanwhile, porous carbon materials to be used as catalyst carriers for polymer electrolyte fuel cells have been studied and various proposals have been made.

[0009] For example, Patent Document 1 proposes "porous carbon having mesopores and carbonaceous walls that form the outer peripheries of the mesopores, characterized in that the carbonaceous walls have portions that form a layered structure." Furthermore, Patent Document 2 proposes "a method for increasing the surface area of ​​carbon black, the method comprising contacting a carbon black starting material having a first BET nitrogen surface area with an oxidizing agent in a fluidized bed under conditions effective to produce a carbon black product having a second BET nitrogen surface area greater than the first BET nitrogen surface area." [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-188309 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-052967 Summary of the Invention [Problem to be solved by the invention]

[0011] Catalyst supports for polymer electrolyte fuel cells (hereinafter also simply referred to as "fuel cells") are required to have durability (that is, resistance to oxidation and wear) in addition to power generation performance. In particular, in recent years, devices that use fuel cells have been required to operate for even longer periods of time. For example, in the automotive field, large vehicles such as large trucks and large buses are required to be transported over long distances, so there is an increasing demand for improvements not only in power generation performance (i.e., fuel efficiency) but also in the durability of fuel cells (i.e., oxidation and wear resistance of catalyst carriers). To date, the only generally recognized improvement in the durability (i.e., resistance to oxidation consumption) of porous carbon materials that constitute catalyst supports in fuel cells is the improvement of the crystallinity of the porous carbon material. However, no further improvement guidelines have been recognized for improving the durability of porous carbon materials.

[0012] Therefore, an object of the present invention is to provide a carbon material for a catalyst support of a polymer electrolyte fuel cell that has excellent durability in addition to power generation performance, and a catalyst layer for a polymer electrolyte fuel cell and a fuel cell that utilize the same. [Means for solving the problem]

[0013] The means for solving the above problems include the following aspects. <1> A carbon material for a catalyst support in a polymer electrolyte fuel cell, comprising porous activated carbon black, which satisfies the following requirements (A1) and (B1): (A1) The BET specific surface area S1 of the porous activated carbon black after heat treatment at 2000°C for 1 hour fin and the BET specific surface area S before the heat treatment ini and the ratio (S1 fin / S ini ) is 0.9 or greater. (B1) BET specific surface area S before the heat treatment ini But 600m 2 / g or more. <2> Satisfy requirement (A2) instead of requirement (A1) <1> 2. The carbon material for a catalyst support of a polymer electrolyte fuel cell according to claim 1. (A2) The BET specific surface area S2 of the porous activated carbon black after heat treatment at 2200°C for 1 hour fin and the BET specific surface area S before the heat treatment ini and the ratio (S2 fin / S ini ) is 0.8 or more. <3> Satisfy the following requirement (B2) instead of the requirement (B1) above. <1> or <2> 2. The carbon material for a catalyst support of a polymer electrolyte fuel cell according to claim 1. (B2) BET specific surface area S before the heat treatment ini But 700m 2 / g or more. <4> <1> ~ <3> 1. A catalyst layer for a polymer electrolyte fuel cell, comprising the carbon material for a catalyst support of a polymer electrolyte fuel cell according to any one of claims 1 to 9. <5> <4> A fuel cell comprising the catalyst layer for a polymer electrolyte fuel cell according to claim 1. <6> The catalyst layer for a polymer electrolyte fuel cell is a catalyst layer on the cathode side. <5> The fuel cell according to claim 1. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a carbon material for a catalyst support of a polymer electrolyte fuel cell that has excellent durability in addition to power generation performance, as well as a catalyst layer for a polymer electrolyte fuel cell and a fuel cell that utilizes the same. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing a general configuration of a fuel cell according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment that is an example of the present disclosure will be described. In this specification, when a numerical range is expressed using "to" without the addition of "greater than" or "less than" before or after the numerical value, it means a range that includes these numerical values ​​as the lower and upper limits. When the numerical value is added with "greater than" or "less than" before or after the numerical value, it means a range that does not include these numerical values ​​as the lower or upper limit. In the present specification, the upper limit of a numerical range may be replaced by the upper limit of another numerical range, or may be replaced by a value shown in an example. The lower limit of a numerical range may be replaced by the lower limit of another numerical range, or may be replaced by a value shown in an example. In this specification, components having substantially the same functions are denoted by the same reference numerals throughout the drawings, and redundant explanations may be omitted. In this specification, the "electrolyte material having proton conductivity" used in the catalyst layer of a fuel cell is also referred to as an "ionomer."

[0017] <Carbon materials for catalyst supports in polymer electrolyte fuel cells> The carbon material for a catalyst support of a polymer electrolyte fuel cell according to this embodiment (hereinafter also referred to as "catalyst support") is made of porous carbon black and satisfies the requirements (A1) and (B) described below. That is, the carbon material for a catalyst support according to this embodiment is made of porous activated carbon black that satisfies the requirements (A1) and (B) described below. Here, the porous activated carbon black is carbon black that has been made porous or has an increased degree of porosity through activation.

[0018] Due to the above-described structure, the carbon material for a catalyst support according to this embodiment is a carbon material that is excellent in durability as well as power generation performance. The carbon material for a catalyst support according to this embodiment was discovered based on the following findings.

[0019] In a fuel cell, catalytic metal particles of a few nanometers in size (for example, catalytic metal particles mainly composed of Pt) are adsorbed (i.e., supported) on a catalyst carrier carbon material made of porous activated carbon black. This powder is then mixed with ionomer resin (a resin with proton conductivity) to form an ink. The ink is then coated on both sides of a proton conductive membrane to form a three-layer structure (Membrane Electrode Assembly: MEA), which is the heart of power generation. In a fuel cell, in order to secure a reaction surface area with a small amount of catalytic metal, the catalytic metal must be as small as possible and must be uniformly dispersed and supported on the catalyst support.

[0020] Therefore, the porous activated carbon black used in the catalyst carrier is required to have the following physical properties in order to improve the power generation efficiency and durability of the fuel cell. 1) The catalyst should be made of a carbon material with a large surface area, since densely loaded catalyst metals result in higher catalyst metal utilization and improved power generation efficiency. 2) The catalyst is made of porous activated carbon black with mesopores, because supporting the catalyst metal inside increases the utilization rate of the catalyst metal and improves power generation efficiency. 3) To enhance durability when used as a catalyst support for the cathode catalyst layer, the material must be made of a carbon material that is resistant to oxidation and consumption at high potentials (for example, high potentials of 1.2 V or higher).

[0021] Therefore, the inventors have investigated the activation treatment of various raw carbon blacks, and as a result, have obtained the following findings.

[0022] As activation treatment intensifies, the surface area increases in direct proportion to the mass loss. Next, beyond the region where the surface area increases, the mass decreases, but at least the surface area saturates and remains constant. In the region where the surface area remains saturated at a constant value, the mass loss is mainly due to the loss of carbon from the surface, and the carbon material becomes smaller and its bulk decreases significantly, as can be observed visually. Note that in such a region of strong activation, the yield of the carbon material decreases and the original shape of the carbon material is damaged, so it is common to stop the activation treatment before this occurs.

[0023] However, the inventors have found that the pores of the porous raw carbon black produced by the activation treatment are controlled by two factors. Specifically, they are as follows: The ease with which raw carbon black is activated is strongly correlated with the degree of crystallinity of the raw carbon black. When the crystallinity of a carbon material is low, the rate of pore formation from the surface to the interior tends to be higher than the thinning of the outer surface, which does not lead to pore formation.

[0024] The reaction rate of the surface thinning of raw carbon black and the formation of pores inside the carbon material due to activation is such that, when the temperature is increased (i.e., the activation conditions are strengthened), the degree of surface thinning of raw carbon black increases and the formation of pores inside the raw carbon black decreases. As a result, the development of pores is suppressed and the final surface area decreases. On the other hand, if the temperature is lowered, only the flammable parts react selectively, which makes it easier for pores to develop inward. Although such low-temperature reactions inevitably require a longer reaction time, they are effective conditions for pore formation, and the pores that are formed tend to first develop into small micropores, which then widen and develop into larger pores.

[0025] In such low-temperature activation, controlling the reaction pressure in addition to the temperature increases the degree of pore development and shortens the reaction time, even under low-temperature conditions. Specifically, setting the temperature at a few atmospheres increases the reaction gas concentration at the pore tip, thereby increasing the selectivity of pore formation inward. As a result, it becomes possible to promote pore development while suppressing shape changes.

[0026] Then, by performing a deep activation treatment on raw material carbon black that has a large thermal weight loss rate in thermogravimetric analysis and a specific surface area within a predetermined range at a low temperature under a pressurized environment, porous raw material carbon black with developed pores that do not collapse can be obtained. In addition, by subjecting the porous raw material carbon black, which has developed pores through deep activation treatment, to graphitization treatment, the crystallinity is greatly increased, improving oxidation and wear resistance.

[0027] From these findings, it was found that it is possible to obtain porous carbon black whose pores do not collapse when heated to 2000°C, i.e., porous carbon black that maintains a high specific surface area while having high crystallinity on the same level as that obtained by graphitization at 2000°C, that is, porous carbon black (i.e., a carbon material for a catalyst support) that satisfies the requirements (A1) and (B1) described below.

[0028] From the above findings, the inventors have discovered a carbon material for a catalyst support according to this embodiment that is excellent in durability as well as power generation performance.

[0029] Hereinafter, the carbon material for a catalyst support according to this embodiment (that is, the porous activated carbon black) will be described in detail.

[0030] (Porous activated carbon black) The carbon material for a catalyst support according to this embodiment is made of porous activated carbon black. The catalyst layer of a polymer electrolyte fuel cell must have passages for gas diffusion within the catalyst layer. Carbon black has a three-dimensional structure called an aggregate, in which primary particles of 10 to 100 nm in size are connected three-dimensionally. Therefore, when carbon black is used as a catalyst support, it becomes possible to form uniform, interconnected passages of a size suitable for gas diffusion in the catalyst layer. Therefore, when porous activated carbon black, which is carbon black made porous by a so-called activation treatment, is used as the carbon material for a catalyst support according to this embodiment, it becomes possible to realize a polymer electrolyte fuel cell with excellent power generation performance.

[0031] (Requirement (A)) The carbon material for a catalyst support according to this embodiment (that is, the porous activated carbon black) satisfies the following requirement (A1). (A1) BET specific surface area S1 of porous activated carbon black (i.e., carbon material for catalyst support) after heat treatment at 2000 ° C for 1 hour fni and the BET specific surface area S before the heat treatment ini and the ratio (S1 fin / S ini ) is 0.9 or greater. Here, the heat treatment is carried out under normal pressure (0.1 MPa).

[0032] ratio(S1 fin / S ini ) of 0.9 or more is equivalent to maintaining high crystallinity equivalent to that of a 2000°C treatment, i.e., it corresponds to a level at which the normally required durability, specifically, resistance to oxidation and depletion, can be fully achieved. In other words, even if the fuel cell is repeatedly started and stopped, the porous carbon material is less susceptible to oxidation and depletion, and durability is improved. Here, the ratio (S1 fin / S ini If the value of ) is less than 0.9, oxidation consumption is likely to proceed during heat treatment, causing pores to collapse and reducing durability.

[0033] ratio(S1 fin / S ini ) is preferably 0.92 or more, more preferably 0.94 or more, from the viewpoint of improving durability. However, the ratio (S1 fin / S ini ) is ideally 1.0, but may be, for example, 0.99 or less.

[0034] The carbon material according to this embodiment (that is, the porous activated carbon black) preferably satisfies the following requirement (A2) from the viewpoint of improving oxidation consumption resistance. (A2) BET specific surface area S2 of porous activated carbon black after heat treatment at 2200°C for 1 hour fni and the BET specific surface area S before the heat treatment ini and the ratio (S2 fin / S ini) is 0.8 or more. Here, the heat treatment is carried out under normal pressure (0.1 MPa).

[0035] ratio(S2 fin / S ini ) of 0.8 or more is equivalent to maintaining extremely high crystallinity equivalent to that of 2200°C treatment, that is, equivalent to a level at which the highest required durability can be fully achieved. That is, even if the fuel cell is repeatedly started and stopped, the porous carbon material is less susceptible to oxidative consumption, and durability is improved. That is, even if the fuel cell is repeatedly started and stopped, the porous carbon material is even more resistant to oxidative consumption, and durability is further improved.

[0036] ratio(S2 fin / S ini ) is preferably 0.85 or more, more preferably 0.90 or more, from the viewpoint of improving durability. However, the ratio (S2 fin / S ini ) is ideally 1.0, but may be, for example, 0.99 or less.

[0037] Each BET specific surface area is a specific surface area determined by BET analysis of a nitrogen adsorption isotherm, and is a value measured by the measurement method described in the examples below.

[0038] (Requirement (B)) The carbon material according to this embodiment (that is, the porous activated carbon black) preferably satisfies the following requirement (B1), and more preferably satisfies the following requirement (2). (B1) BET specific surface area S before heat treatment (i.e., before heat treatment at 2000 ° C or 2200 ° C for 1 hour under normal pressure (0.1 MPa)) ini But 600m 2 / g or more. (B2) BET specific surface area S before heat treatment (i.e., before heat treatment at 2000 ° C or 2200 ° C for 1 hour under normal pressure (0.1 MPa)) ini But 700m 2 / g or more.

[0039] BET specific surface area S iniis 600m 2 When the pore density is 1 / g or more, the pores of the porous carbon material are developed and a larger amount of catalytic metal can be supported, thereby improving the power generation performance. Here, the BET specific surface area is 600m 2 If the amount is less than 1 / g, the catalyst metal loading capacity decreases, which may result in a decrease in power generation performance.

[0040] BET specific surface area S ini From the viewpoint of improving power generation performance, 2 / g or more is preferable, and 700m 2 / g or more is more preferable. However, the BET specific surface area S ini The upper limit of the porous carbon material is 1500 m from the viewpoint of balancing power generation performance with the physical strength (i.e., mechanical strength) and durability (i.e., oxidation resistance) of the porous carbon material. 2 / g or less is preferable, and 1300m 2 / g or less is more preferable.

[0041] Each BET specific surface area is a specific surface area determined by BET analysis of a nitrogen adsorption isotherm, and is a value measured by the measurement method described in the examples below.

[0042] (Method for producing carbon material for catalyst support of polymer electrolyte fuel cells) An example of a method for producing a carbon material for a catalyst support (that is, porous activated carbon black) for a polymer electrolyte fuel cell according to this embodiment will be described below. An example of a method for producing a carbon material for a catalyst carrier (i.e., porous carbon black) for a polymer electrolyte fuel cell according to this embodiment includes an activation treatment step of subjecting commercially available non-porous raw carbon black or commercially available raw carbon black that has already been made porous to an activation treatment, and a graphitization treatment step of subjecting the activated porous raw carbon black to a graphitization treatment.

[0043] (raw carbon black) The raw carbon black for obtaining the carbon material for catalyst supports (porous activated carbon black) preferably has a primary particle diameter of 20 nm to 80 nm. A primary particle diameter of 20 nm or more ensures sufficient mechanical strength against pressure applied to the catalyst layer even after activation. A primary particle diameter of 80 nm or less allows for a well-developed aggregate structure to be realized, and activation allows for the formation of sufficient voids in the catalyst layer for gas diffusion. A more preferred range for the primary particle diameter of the raw carbon black is 25 nm to 70 nm. The aggregate structure of raw carbon black, which corresponds to the three-dimensional structure, can be quantitatively expressed by the DBP oil absorption according to the JIS standard. The DBP oil absorption is preferably 70 to 200 mL / 100 g. When the DBP oil absorption is 70 mL / 100 g or more, sufficient voids for gas diffusion can be formed in the catalyst layer by activation. When the DBP oil absorption is 200 mL / 100 g or less, the catalyst layer will have sufficient mechanical strength against pressure applied thereto, even after activation.

[0044] (Activation treatment process) In the activation treatment step, commercially available raw carbon black is activated under a gas flow of, for example, CO gas or water vapor, either alone or in combination, at a pressure exceeding atmospheric pressure (0.1 MPa) but not exceeding 0.5 MPa, at 750°C to 1050°C, and for 1 hour to 100 hours, with the conditions appropriately selected to form pores within the carbon black. Whether the commercially available raw carbon black used as the raw material is already porous or not, optimizing the conditions can further develop the internal pores and increase the BET specific surface area. Specifically, by varying the type of raw carbon black, the type of gas used for activation, the activation temperature, activation time, and activation pressure, it is possible to prepare an appropriately porous carbon black. Specifically, the raw carbon black is selected based on the degree of porosity of the raw carbon black, i.e., the surface area of ​​the carbon black.

[0045] To obtain porous activated carbon black that simultaneously satisfies requirements (A) and (B), it is important to perform uniform and deep activation deep into the carbon black. The most appropriate indicator of the degree of deep activation is the almost complete disappearance of the 002 diffraction peak in X-ray diffraction. The almost complete disappearance of the 002 diffraction peak corresponds to the average number of stacked crystallites constituting the carbon black being two or less. If the average number of stacked crystallites is two or less, the spacing between the crystallites increases, suppressing the increase in the number of stacked crystallites and the thermal fusion between the crystallites due to the thermal energy of the graphitization treatment at 1800°C or higher. This reduces the likelihood of pore collapse, i.e., reduces the reduction in surface area. In other words, it becomes easier to obtain porous activated carbon black that simultaneously satisfies requirements (A) and (B). To achieve a high rate of wall thinning during activation, deep activation, and uniform pore formation, it is important to slow the reaction rate of the oxidation reaction that causes activation and to activate under high pressure. Gases such as CO2 and steam are preferred as activation media, and in the case of gas activation, low activation temperatures and high activation gas pressures are effective. Pressurized activation treatment, which uses an activating gas containing water vapor and / or carbon dioxide as an oxidizing gas, i.e., a pressurized activation process, is an activation method for uniforming the pores formed in the center of the primary particles of raw carbon black with the pores formed near the surface. When activating raw carbon black, the pores formed in the interior of the raw carbon black have a lower concentration of activating gas as they move toward the interior of the raw carbon black compared to the surface. As a result, pore development slows and the interconnectivity of pores decreases toward the interior of the raw carbon black. However, by applying pressure, the absolute pressure, i.e., the activating gas concentration, is increased, thereby reducing the relative difference in activating gas concentration between the surface and the interior. This effect does not improve even if the absolute pressure during gas activation of raw carbon black is increased above 0.5 MPa. Furthermore, if the raw carbon black is porous, this effect is saturated at 0.2 MPa. Therefore, for example, activation should be performed at a gauge pressure of approximately 0.5 MPa for non-porous raw carbon black and approximately 0.2 MPa for porous raw carbon black.

[0046] In the activation treatment step, the activation treatment may be either a gas activation treatment or a chemical activation treatment. However, from the viewpoint of uniformly reducing the thickness of the raw material carbon black, making the pores less likely to collapse, and obtaining a porous carbonized material having a high specific surface area, gas activation treatment is preferred. The gas activation treatment may be either a gas activation treatment using water vapor, carbon dioxide gas, etc., or a gas activation treatment using oxygen, air, etc. Here, the gas activation treatment is preferably carried out in an atmosphere with an activation gas concentration of 5 to 100% by volume relative to the total volume of the atmospheric gas. The activation gas concentration is preferably 10 to 100% by volume.

[0047] The gas activation treatment may be carried out by supporting an activation catalyst, which promotes the activation reaction of the porous carbon raw material, in the pores of the porous carbon raw material. The activation catalyst may be any catalyst that promotes the activation reaction of the porous carbon material. Here, the activation reaction refers to a reaction that reduces (in other words, consumes) the carbon layer that constitutes the porous carbon material by oxidation. The activation catalyst promotes the activation reaction of the carbon raw material present around the activation catalyst. Examples of the activation catalyst include particles containing at least one of 3d elements (fourth period transition elements such as Ni, Fe, Co, and Ti) and noble metal elements (Ru, Cu, Ag, Pt, Pd, etc.). Of these, particles containing at least one of Ni, Fe, Co, and Pt are preferred. The activation catalyst may be particles consisting of these elements alone or alloy particles with other metals. For example, alloy particles of a 3d element and Pt may be used as the activation catalyst. The activation catalyst remaining in the porous carbon after activation treatment with the activation catalyst is subjected to a removal method appropriate for the metal species, such as aqua regia treatment, to remove the catalytic metal species, and then applied to the graphitization treatment step.

[0048] In the activation treatment step, it is preferable to perform the activation treatment on the raw carbon black until the thickness reduction rate reaches 70 to 95%. This allows the production of porous activated carbon black with a high BET specific surface area. In other words, it becomes easier to obtain a carbon material for a catalyst support (porous activated carbon black) that satisfies requirement (B). The specific surface area of ​​the activated raw carbon black is 1300 m 2 / g or more 2100m 2 / g or less. After activation, the specific surface area of ​​the raw material carbon black is preferably 1300 m 2 If the specific surface area of ​​the activated raw carbon black is less than 2100 m / g, the degree of activation is low, and the pores are significantly crushed by heat treatment at 1800°C or higher, making it impossible to support a sufficient amount of catalyst in the pores. As a result, it is difficult to obtain porous activated carbon black with a high BET specific surface area, resulting in a decrease in power generation performance. On the other hand, if the specific surface area of ​​the activated raw carbon black is 2100 m / g, 2 If the carbon content exceeds 1 / g, the carbon walls for forming the pores become too thin, causing significant oxidative wear after heat treatment, which reduces the durability of the fuel cell.

[0049] (Graphitization process) In the graphitization treatment step, for example, the activated porous raw carbon black is graphitized under normal pressure (i.e., 1 atmosphere) in an inert gas atmosphere at 1800 to 2200°C for 1 to 10 hours, with the conditions appropriately selected.

[0050] In the graphitization step, the activated porous raw carbon black is graphitized, thereby increasing the crystallinity of the porous raw carbon black. More specifically, by subjecting the porous raw carbon black, which has been activated under the above-described strong activation conditions and has a BET specific surface area, to graphitization under the above-described conditions, the crystallinity of the porous raw carbon black can be increased while maintaining the pores. In other words, a carbon material for a catalyst support (porous activated carbon black) that satisfies requirements (A1) and (B1) can be produced.

[0051] The graphitization step is not particularly limited as long as it is a step that can heat the porous raw carbon black under the above conditions. Examples of the heating method include resistance heating, microwave heating, high-frequency heating, and furnace-type heating methods. The furnace type is not limited, and may be a graphitization furnace, batch furnace, tunnel furnace, or the like, as long as it can achieve normal pressure and an inert gas atmosphere.

[0052] Through the above steps, the carbon material for a catalyst support (porous activated carbon black) according to this embodiment can be obtained. In order to obtain the carbon material for a catalyst support (porous activated carbon black) according to this embodiment, the activation treatment conditions and the graphitization treatment conditions affect each other. Therefore, it is preferable to produce the carbon material for a catalyst support (porous activated carbon black) according to this embodiment under the following conditions. For example, when non-porous raw material carbon black is activated at a pressure of 0.5 MPa, the activation time is preferably 40 hours or more and less than 80 hours when the activation temperature is 800°C or more and 850°C or less; the activation time is preferably 20 hours or more and less than 60 hours when the activation temperature is more than 850°C and less than 900°C; and the activation time is preferably 10 hours or more and 30 hours or less when the activation temperature is 900°C or more and 950°C or less. When the porous raw material carbon black is activated at a pressure of 0.2 MPa, the activation time is preferably 15 hours or more and less than 30 hours when the activation temperature is 800°C or more and less than 850°C, preferably 10 hours or more and less than 20 hours when the activation temperature is 850°C or more and less than 900°C, and preferably 8 hours or more and less than 15 hours when the activation temperature is 900°C or more and less than 950°C.

[0053] <Catalyst layer for polymer electrolyte fuel cells / Polymer electrolyte fuel cells> The catalyst layer for a polymer electrolyte fuel cell according to this embodiment contains the carbon material for a catalyst support according to this embodiment. The polymer electrolyte fuel cell according to this embodiment includes the catalyst layer for a polymer electrolyte fuel cell according to this embodiment. Here, the catalyst layer for a polymer electrolyte fuel cell is preferably a catalyst layer on the cathode side.

[0054] Specifically, the catalyst support carbon material according to this embodiment can be applied to, for example, a polymer electrolyte fuel cell 100 shown in Fig. 4. The polymer electrolyte fuel cell 100 includes separators 110 and 120, gas diffusion layers 130 and 140, catalyst layers 150 and 160, and an electrolyte membrane 170.

[0055] Separator 110 is an anode-side separator that introduces a fuel gas such as hydrogen into gas diffusion layer 130. Separator 120 is a cathode-side separator that introduces an oxidizing gas such as oxygen gas or air into the gas diffusion condensation layer. There is no particular restriction on the type of separators 110 and 120, and they may be any separators used in conventional fuel cells, such as solid polymer fuel cells.

[0056] The gas diffusion layer 130 is an anode-side gas diffusion layer that diffuses the fuel gas supplied from the separator 110 and then supplies it to the catalyst layer 150. The gas diffusion layer 140 is a cathode-side gas diffusion layer that diffuses the oxidizing gas supplied from the separator 120 and then supplies it to the catalyst layer 160. There is no particular restriction on the type of gas diffusion layers 130 and 40, as long as they are gas diffusion layers used in conventional fuel cells, such as solid polymer fuel cells. Examples of gas diffusion layers 130 and 40 include porous carbon materials (carbon cloth, carbon paper, etc.), porous metal materials (metal mesh, metal wool, etc.), etc. A preferred example of the gas diffusion layers 130 and 140 is a two-layer gas diffusion layer in which the layer on the separator side of the gas diffusion layer is a gas diffusion fiber layer mainly composed of a fibrous carbon material, and the layer on the catalyst layer side is a micropore layer mainly composed of carbon black.

[0057] The catalyst layer 150 is a so-called anode. An oxidation reaction of the fuel gas occurs in the catalyst layer 150, producing protons and electrons. For example, when the fuel gas becomes hydrogen gas, the following oxidation reaction occurs. H2→2H + +2e - (E0=0V)

[0058] Protons produced by the oxidation reaction pass through catalyst layer 150 and electrolyte membrane 170 to reach catalyst layer 160. Electrons produced by the oxidation reaction pass through catalyst layer 150, gas diffusion layer 130, and separator 110 to reach the external circuit. After performing work in the external circuit, the electrons are introduced into separator 120. The electrons then pass through separator 120 and gas diffusion layer 140 to reach catalyst layer 160.

[0059] The configuration of the catalyst layer 150 that serves as the anode is not particularly limited. That is, the configuration of the catalyst layer 150 may be the same as that of a conventional anode, may be the same as that of the catalyst layer 160, or may be more hydrophilic than the catalyst layer 160.

[0060] The catalyst layer 160 is a so-called cathode. Within the catalyst layer 160, a reduction reaction of the oxidizing gas occurs, producing water. For example, when the oxidizing gas becomes oxygen gas or air, the following reduction reaction occurs: The water produced by the oxidation reaction is discharged to the outside of the polymer electrolyte fuel cell 100 together with the unreacted oxidizing gas. O2+4H + +4e - →2H2O (E0=1.23V)

[0061] In this way, the energy difference (potential difference) between the oxidation reaction and the reduction reaction is utilized to generate electricity in the polymer electrolyte fuel cell 100. In other words, the electrons generated in the oxidation reaction perform work in an external circuit.

[0062] The catalyst layer 160 preferably contains the catalyst support carbon material according to this embodiment. That is, the catalyst layer 160 contains the catalyst support carbon material according to this embodiment, an electrolyte material, and a fuel cell catalyst. This can improve the power generation performance and durability in the catalyst layer 160. As a result, the power generation performance and durability of the polymer electrolyte fuel cell 100 can be improved.

[0063] The fuel cell catalyst loading rate in the catalyst layer 160 is not particularly limited, but is preferably 30% by mass or more and less than 80% by mass. The fuel cell catalyst loading rate is preferably the mass % of the fuel cell catalyst relative to the total mass of the catalyst-loaded particles (particles in which the fuel cell catalyst is loaded on a catalyst-supporting carbon material). In this case, power generation performance and durability are further improved. If the fuel cell catalyst loading rate is less than 30% by mass, it may be necessary to thicken the catalyst layer 160 to make the polymer electrolyte fuel cell 100 practical. On the other hand, if the fuel cell catalyst loading rate is 80% by mass or more, catalyst aggregation is likely to occur. Furthermore, if the catalyst layer 160 becomes too thin, flooding may occur.

[0064] The mass ratio I / C of the mass I (g) of the electrolyte material in the catalyst layer 160 to the mass C (g) of the catalyst support carbon material is not particularly limited, but is preferably greater than 0.5 and less than 5.0. In this case, both the pore network and the electrolyte material network can be achieved, resulting in high power generation performance and durability. On the other hand, if the mass ratio I / C is 0.5 or less, the electrolyte material network tends to be weak and the proton conduction resistance tends to increase. If the mass ratio I / C is 5.0 or more, the pore network may be disrupted by the electrolyte material. In either case, power generation performance and durability may be reduced.

[0065] Furthermore, the thickness of the catalyst layer 160 is not particularly limited, but is preferably more than 5 μm and less than 20 μm. In this case, oxidizing gas is more likely to diffuse within the catalyst layer 160, and flooding is less likely to occur. If the thickness of the catalyst layer 160 is 5 μm or less, flooding is more likely to occur. If the thickness of the catalyst layer 160 is 20 μm or more, oxidizing gas is less likely to diffuse within the catalyst layer 160, and the fuel cell catalyst near the electrolyte membrane 170 becomes less effective. In other words, power generation performance and durability may be reduced.

[0066] The electrolyte membrane 170 is made of a proton-conductive electrolyte material. The electrolyte membrane 170 introduces protons generated in the oxidation reaction to the catalyst layer 160, which serves as the cathode. The type of electrolyte material is not particularly limited, and any electrolyte material used in conventional fuel cells, such as polymer electrolyte fuel cells, may be used. A suitable example is an electrolyte material used in polymer electrolyte fuel cells, i.e., an electrolyte resin. Examples of the electrolyte resin include polymers with introduced phosphate groups, sulfonic acid groups, etc. (e.g., perfluorosulfonic acid polymers or polymers with introduced benzenesulfonic acid). Of course, the electrolyte material according to this embodiment may also be of another type. Examples of such electrolyte materials include inorganic and inorganic-organic hybrid electrolyte materials. The polymer electrolyte fuel cell 100 may be a fuel cell that operates within a temperature range from room temperature to 150°C.

[0067] <Method of manufacturing a polymer electrolyte fuel cell> The method for manufacturing the polymer electrolyte fuel cell according to this embodiment is not particularly limited, and may be the same as a conventional manufacturing method. However, it is preferable to use the carbon material for a catalyst support according to this embodiment for the catalyst support on the cathode side. [Example]

[0068] Examples of the present invention will be described below, but the present invention is not limited to these examples. <Measuring methods for each parameter> (Method for measuring nitrogen adsorption / desorption isotherm) Approximately 30 mg of sample was weighed out and vacuum dried for 2 hours at 120°C. The sample was then placed in an automatic specific surface area measuring device (MicrotrackBell, BELSORP MAX) and the nitrogen adsorption / desorption isotherm was measured at a measurement temperature of 77 K using nitrogen gas as the adsorbate. In measuring the nitrogen adsorption / desorption isotherm, the measurement interval of the relative pressure P / P0 was set smaller than in general measurements (specifically, the measurement interval of P / P0 was set to take fixed points in increments of 0.005). In other words, the measurement accuracy of the relative pressure P / P0 in the measurement was set to 0.005.

[0069] (BET specific surface area) The BET specific surface area was calculated by BET analysis of a nitrogen adsorption isotherm in the relative pressure P / P0 range of 0.05 to 0.15.

[0070] <Carbon black used as raw material> The raw carbon black used for activation was commercially available Ketjenblack EC600JD, which is already porous and manufactured by Lion Corporation, and also commercially available non-porous Ketjenblack EC200L, manufactured by Lion Corporation. These are shown as EC200L and EC600JD in Table 1, respectively.

[0071] <Example> The above-mentioned raw carbon black was activated and then graphitized by the following method. (Activation treatment) A quartz tube was used as the furnace core in a vertical tubular electric furnace, with quartz wool packed in the center of the quartz tube, and the raw carbon black to be treated placed on top of it. CO2 gas was flowed from bottom to top. The flow rate was linearly between 0.5 cm / sec and 3 cm / sec, and the pressure was adjusted to 0.5 MPa or 0.2 MPa using a pressure relief valve. The activation treatment was performed at the activation temperature and for the activation time shown in Table 1.

[0072] (Heat treatment) Heat treatment to improve durability was performed in a graphitization furnace under argon flow at the temperatures shown in Table 1 for 1 hour.

[0073] The obtained carbon material (porous activated carbon black) was examined for the following properties. BET specific surface area S1 after heat treatment at 2000°C for 1 hour fin BET specific surface area S2 after heat treatment at 2200°C for 1 hour fin BET specific surface area S before heat treatment ini

[0074] <Catalyst preparation, catalyst layer fabrication, MEA fabrication, fuel cell assembly, and cell performance evaluation> Using the obtained carbon material (porous activated carbon black), a catalyst for a polymer electrolyte fuel cell carrying a catalytic metal was prepared as follows: a catalyst layer ink solution was prepared using the obtained catalyst; a catalyst layer was then formed using this catalyst layer ink solution; a membrane electrode assembly (MEA) was fabricated using the formed catalyst layer; the fabricated MEA was incorporated into a fuel cell; and a power generation test was performed using a fuel cell measuring device. The preparation of each component and cell evaluation through the power generation test are described in detail below.

[0075] (1) Preparation of catalysts (platinum-supported carbon materials) for polymer electrolyte fuel cells The resulting porous carbon material was dispersed in distilled water, and formaldehyde was added to the dispersion. The dispersion was then placed in a water bath set at 40°C. Once the temperature of the dispersion reached the same 40°C as the bath, an aqueous solution of dinitrodiamine platinum complex nitric acid was slowly poured into the dispersion while stirring. Stirring was continued for approximately two hours, followed by filtration and washing of the resulting solid. The resulting solid was vacuum dried at 90°C, crushed in a mortar, and then heat-treated for one hour at 200°C in an argon atmosphere containing 5% hydrogen by volume to produce a platinum catalyst particle-supported carbon material. The amount of platinum carried in this platinum-supported carbon material was adjusted to 40 mass % relative to the total mass of the porous carbon material and platinum particles, and was confirmed by measurement using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0076] (2) Preparation of the catalyst layer Using the platinum-supported carbon material (Pt catalyst) prepared as described above, and Nafion (registered trademark: Nafion; a persulfonic acid-based ion exchange resin) manufactured by DuPont as the electrolyte resin, the Pt catalyst and Nafion were mixed under an Ar atmosphere in a ratio of 1.0 times the mass of the Nafion solids relative to the mass of the platinum catalyst particle-supported carbon material, and 0.5 times the mass of the non-porous carbon. After light stirring, the Pt catalyst was crushed using ultrasound, and ethanol was added so that the total solid concentration of the Pt catalyst and electrolyte resin combined was adjusted to 1.0 mass %, thereby preparing a catalyst layer ink liquid in which the Pt catalyst and electrolyte resin were mixed.

[0077] Ethanol was further added to each catalyst layer ink liquid thus prepared, each having a solids concentration of 1.0% by mass, to prepare a catalyst layer ink liquid for spray application with a platinum concentration of 0.5% by mass. The spray conditions were adjusted so that the mass of platinum per unit area of ​​the catalyst layer (hereinafter referred to as "platinum coverage") was 0.2 mg / cm2. The catalyst layer ink for spray application was sprayed onto a Teflon (registered trademark) sheet, which was then dried in argon at 120°C for 60 minutes to prepare a catalyst layer.

[0078] (3) Preparation of MEA Using the catalyst layer prepared as above, an MEA (membrane electrode assembly) was prepared by the following method. A square electrolyte membrane with sides of 6 cm was cut out from a Nafion membrane (NR211 manufactured by DuPont). The anode and cathode catalyst layers coated on Teflon (registered trademark) sheets were each cut into a square with sides of 2.5 cm using a cutter knife. The electrolyte membrane was sandwiched between the anode and cathode catalyst layers cut out in this way so that the catalyst layers were in contact with each other with the center of the electrolyte membrane sandwiched between them and no misalignment was observed between them. 2 After cooling to room temperature, the Teflon sheets were carefully peeled off from both the anode and cathode to prepare a catalyst layer-electrolyte membrane assembly in which the anode and cathode catalyst layers were fixed to the electrolyte membrane.

[0079] Next, a pair of square carbon paper sheets, each 2.5 cm on a side, was cut out from carbon paper (35BC manufactured by SGL Carbon Co., Ltd.) to form a gas diffusion layer. The catalyst layer-electrolyte membrane assembly was sandwiched between these carbon papers so that the anode and cathode catalyst layers were aligned with each other without any misalignment. The assembly was then heated at 120°C and 50 kg / cm 2 The mixture was pressed at 100°C for 10 minutes to prepare an MEA. The basis weight of each component of the catalytic metal component, carbon material, and electrolyte material in each MEA produced was calculated from the mass of the catalyst layer fixed to the Nafion membrane (electrolyte membrane) obtained from the difference between the mass of the Teflon sheet with the catalyst layer before pressing and the mass of the Teflon sheet peeled off after pressing, and then calculated from the mass ratio of the composition of the catalyst layer.

[0080] (4) Evaluation of fuel cell power generation characteristics (Pre-durability evaluation: Evaluation of power generation performance) The MEAs prepared in each test example and fabricated using the prepared porous carbon materials for catalyst supports were each incorporated into a cell, which was then set in a fuel cell measuring device, and the performance of the fuel cell was evaluated according to the following procedure. The reactant gases were supplied at a back pressure of 0.04 MPa, with air supplied to the cathode side and pure hydrogen supplied to the anode side, with the pressure adjusted by a back pressure valve installed downstream of the cell under atmospheric pressure so that the utilization rates were 40% and 70%, respectively. The cell temperature was set to 80°C, and the reactant gas supplied to both the cathode and anode was bubbled with distilled water kept at 80°C in a humidifier, and humidified gas at 80°C was supplied to the cell at 80°C to evaluate power generation.

[0081] Under these conditions, the reaction gas was supplied to the cell, and the load was gradually increased until the current density reached 100 mA / cm. 2 The voltage between the cell terminals at this time was recorded as the output voltage, and the power generation performance of the fuel cell was evaluated using the following pass / fail ranking criteria. The results are shown in Table 1. [Passing rank] ◎: 100mA / cm 2 The output voltage is 0.880V or more. ○: 100mA / cm 2 The output voltage is 0.870V or more. [Failure rank] ×:100mA / cm 2 The output voltage is 0.850V or more and less than 0.870V.

[0082] (Post-durability evaluation: durability evaluation) The cell was left with the anode in place, and argon gas was passed through the cathode under the same humidified conditions as above. One cycle consisted of a cell voltage of 0.9 V, held for 4 seconds, and then a cell voltage of 1.3 V, held for 4 seconds (repeated square-wave voltage fluctuation). After 1,000 cycles of this square-wave voltage fluctuation, durability was evaluated in the same manner as in the evaluation of power generation performance described above. Evaluation was based on the following pass / fail ranking criteria. The results are shown in Table 1. [Passing rank] ◎: 100mA / cm 2 The output voltage at the end of the test is 85% or more of the value before endurance. ○: 100mA / cm 2 The output voltage at the end of the test is 75% or more of the value before endurance. [Failure rank] ×:100mA / cm 2 The output voltage at the end of the test is less than 75% of the value before endurance.

[0083] [Table 1-1]

[0084] [Table 1-2]

[0085] [Table 1-3]

[0086] From the above results, it can be seen that the porous carbon material (catalyst support) of this example has higher power generation performance and improved durability compared to the porous carbon material (catalyst support) of the comparative example. [Explanation of symbols]

[0087] 100 Polymer electrolyte fuel cell 110, 120 separator 130, 140 Gas diffusion layer 150, 160 catalyst layer 170 Electrolyte membrane

Claims

1. A carbon material for a catalyst support of a polymer electrolyte fuel cell, comprising porous activated carbon black, which satisfies the following requirements (A1) and (B1): (A1) BET specific surface area S1 of the porous activated carbon black after heat treatment at 2000°C for 1 hour ｆｉｎ and the BET specific surface area S before the heat treatment ｉｎｉ and the ratio (S1 ｆｉｎ / S ｉｎｉ ) is 0.9 or more. (B1) BET specific surface area S before the heat treatment ｉｎｉ But 600m ２ / g or more.

2. 2. The carbon material for a catalyst support of a polymer electrolyte fuel cell according to claim 1, which satisfies requirement (A2) instead of requirement (A1). (A2) The BET specific surface area S2 of the porous activated carbon black after heat treatment at 2200°C for 1 hour ｆｉｎ and the BET specific surface area S before the heat treatment ｉｎｉ and the ratio (S2 ｆｉｎ / S ｉｎｉ ) is 0.8 or more.

3. 2. The carbon material for a catalyst support of a polymer electrolyte fuel cell according to claim 1, which satisfies the following requirement (B2) instead of the requirement (B1): (B2) BET specific surface area S before the heat treatment ｉｎｉ But 700m ２ / g or more.

4. A catalyst layer for a polymer electrolyte fuel cell, comprising the carbon material for a catalyst support of a polymer electrolyte fuel cell according to any one of claims 1 to 3.

5. A fuel cell comprising the catalyst layer for a polymer electrolyte fuel cell according to claim 4.

6. 6. The fuel cell according to claim 5, wherein the catalyst layer for a polymer electrolyte fuel cell is a catalyst layer on the cathode side.

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