WO2016152506A1 - Carbon powder for fuel cell, catalyst using said carbon powder for fuel cell, electrode catalyst layer, membrane electrode assembly, and fuel cell - Google Patents

Abstract

The present invention provides: a carbon powder with which it is possible to provide a catalyst having excellent durability; and a catalyst. This carbon powder for a fuel cell is a carbon powder having carbon as a main component, wherein the BET specific surface area according to nitrogen adsorption is 800 m²/g or more, and when the area of a peak 0 at a position where 2θ=22.5-25° as observed by XRD analysis is termed A and the area of a peak 1 at a position where 2θ=26° as observed by XRD analysis is termed B, the ratio (B/A) of the area B of peak 1 to the area A of peak 0 is 0.06 or more.

Description

Carbon powder for fuel cell and catalyst, electrode catalyst layer, membrane electrode assembly and fuel cell using carbon powder for fuel cell

The present invention relates to a carbon powder for a fuel cell, particularly a carbon powder for a fuel cell catalyst, and a catalyst, an electrode catalyst layer, a membrane electrode assembly, and a fuel cell using the carbon powder for a fuel cell.

A polymer electrolyte fuel cell (PEFC) using a proton-conducting polymer electrolyte membrane is lower in temperature than other types of fuel cells such as a solid oxide fuel cell and a molten carbonate fuel cell. Operate. For this reason, the polymer electrolyte fuel cell is expected as a stationary power source or a power source for a moving body such as an automobile, and its practical use has been started.

In such a polymer electrolyte fuel cell, generally, an expensive metal catalyst represented by Pt (platinum) or a Pt alloy is used. Further, as the carrier for supporting the metal catalyst, a carrier having a large specific surface area is used in order to highly support and disperse the metal catalyst. For example, in Patent Document 1, nano-sized platinum or platinum-containing alloy particles are supported on a support having a specific surface area of 1200 m ² / g or more in a platinum amount ranging from 56 to 90% by weight with respect to the total weight of the electrode catalyst. A catalyst is described. In Patent Document 1, the surface area of platinum particles that can contribute to the reaction on the support (support) is increased by highly supporting and highly dispersing the catalyst particles on the support having a large surface area, and the maximum of the catalytic reaction active region is maximized. It is described that it can be realized (improvement of fuel cell performance).

Special table 2008-517426 (US 2006/0134506 A1)

Although the catalyst described in Patent Document 1 is excellent in performance, it has a problem that it is inferior in durability.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a carbon powder for a fuel cell capable of improving durability.

Another object of the present invention is to provide a carbon powder for a fuel cell that can exhibit high catalytic activity when a catalytic metal is supported.

Another object of the present invention is to provide a catalyst, an electrode catalyst layer, a membrane electrode assembly and a fuel cell which are excellent in durability and power generation performance.

As a result of intensive studies to solve the above problems, the present inventors have solved the above problems by using carbon powder for fuel cells having a specific specific surface area and crystallinity as a support. The headline and the present invention were completed.

It is a schematic sectional drawing which shows the basic composition of the polymer electrolyte fuel cell which concerns on one Embodiment of this invention. In FIG. 1, 1 is a polymer electrolyte fuel cell (PEFC); 2 is a solid polymer electrolyte membrane; 3a is an anode catalyst layer; 3c is a cathode catalyst layer; 4a is an anode gas diffusion layer; Cathode gas diffusion layer; 5a anode separator; 5c cathode separator; 6a anode gas channel; 6c cathode gas channel; 7 refrigerant channel; and 10 membrane electrode assembly (MEA) ) Respectively.

The carbon powder for fuel cells of the present invention (in the present specification, simply referred to as “carbon powder” or “carbon powder of the present invention”) contains carbon as a main component. Here, “mainly composed of carbon” is a concept including both carbon and substantially carbon, and elements other than carbon may be included. “Substantially consists of carbon” means that 98% by weight or more, preferably 99.5% by weight or more (upper limit: less than 100% by weight) of the whole is composed of carbon.

Moreover, the carbon powder for fuel cells of the present invention satisfies the following configurations (a) and (b):
(A) the BET specific surface area per weight by nitrogen adsorption is 800 m ² / g or more; and (b) the area of peak 0 existing at a position of 2θ = 22.5 ° to 25 ° observed by XRD analysis. A, where B is the area of peak 1 existing at 2θ = 26 ° observed by XRD analysis, the ratio of area B of peak 1 to area A of peak 0 (B / A) is 0.06 or more It is. Since the carbon powder for fuel cells satisfying this configuration has a large specific surface area and high crystallinity, it has a large electric double capacity and excellent corrosion resistance. Therefore, a catalyst having excellent durability and catalytic activity can be provided by using the carbon powder for fuel cells of the present invention as a carrier.

In this specification, the BET specific surface area per weight by nitrogen adsorption is also simply referred to as “BET specific surface area”. Further, in this specification, the peak 0 existing at the position of 2θ = 22.5 ° to 25 ° observed by XRD analysis is simply “peak 0”, and the area of the peak 0 is simply “area A”. Also called. Similarly, in this specification, the peak 1 existing at the position of 2θ = 26 ° observed by the XRD analysis is simply referred to as “peak 1”, and the area of the peak 1 is also simply referred to as “area B”. In this specification, the ratio of the area B to the area A is also referred to as “B / A” or “B / A ratio”.

The support (carrier) described in Patent Document 1 has a large specific surface area. For this reason, the catalyst using such a support (support) can improve the performance because the effective surface area of the platinum or platinum-containing alloy particles is increased. However, on the other hand, since the carbon corrosion deterioration is proportional to the specific surface area of the support, the support having a large specific surface area has low carbon corrosion durability. For this reason, the durability of the electrode catalyst using such a support, and further the membrane electrode assembly (MEA) is lowered.

On the other hand, the carbon powder according to the present invention satisfies the above (a). Since the carbon powder for fuel cells having the configuration (a) has a large specific surface area, the electric double layer capacity is large. Further, when the catalyst metal is supported on the carbon powder, the catalyst metal can be highly dispersed on the carbon powder by suppressing aggregation of the catalyst metal. For this reason, the catalyst formed by supporting the catalytic metal on the carbon powder of the present invention can exhibit high catalytic activity. The carbon powder according to the present invention satisfies the above (b). The carbon powder for fuel cells having the above-described configuration (b) has high crystallinity, and therefore has excellent electrochemical corrosion resistance (not easily corroded). For this reason, the catalyst which carries | supports a catalyst metal on the carbon powder of this invention is excellent in durability.

Therefore, the carbon powder for a fuel cell of the present invention is excellent in durability, and can exhibit high catalytic activity when the catalytic metal is supported and can maintain the activity. Further, by using the carbon powder of the present invention as a carrier, a catalyst having excellent catalytic activity and durability, and an electrochemical device (for example, MEA, capacitor) having high performance and high durability can be provided. For this reason, the carbon powder for fuel cells of the present invention can be suitably used as a support for a catalyst, particularly a catalyst for a fuel cell. That is, the present invention includes a fuel cell catalyst in which a catalyst metal is supported on the fuel cell carbon powder of the present invention. The carbon powder (support) for a fuel cell of the present invention has a high specific surface area. Therefore, according to the fuel cell catalyst of the present invention, the dispersibility of the catalyst can be improved, and the electric double layer capacity (electrochemical reaction area) can be increased, that is, the power generation performance can be improved. In addition, the carbon powder (support) for a fuel cell of the present invention has high crystallinity (small amount of carbon edge). For this reason, according to the fuel cell catalyst of the present invention, it is possible to suppress / prevent performance degradation due to carbon corrosion, that is, to improve durability. The fuel cell catalyst in which the catalyst metal is supported on the fuel cell carbon powder of the present invention is excellent in durability, can exhibit high catalytic activity (can promote catalytic reaction), and can maintain the activity. For this reason, the membrane electrode assembly and fuel cell which have a catalyst layer using such a catalyst are excellent in power generation performance and durability. Accordingly, the present invention provides a fuel cell electrode catalyst layer containing the catalyst and electrolyte, a fuel cell membrane electrode assembly including the fuel cell electrode catalyst layer, and a fuel cell including the fuel cell membrane electrode assembly. I will provide a.

Hereinafter, an embodiment of the catalyst of the present invention, and an embodiment of a catalyst layer, a membrane electrode assembly (MEA) and a fuel cell using the same will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited only to 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. Further, in the case where the embodiment of the present invention is described with reference to the drawings, the same reference numerals are given to the same elements in the description of the drawings, and redundant description is omitted.

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

[Fuel cell]
A fuel cell includes a membrane electrode assembly (MEA), a pair of separators including an anode side separator having a fuel gas flow path through which fuel gas flows and a cathode side separator having an oxidant gas flow path through which oxidant gas flows. Have. The fuel cell of this 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 an embodiment of the present invention. The PEFC 1 first has a solid polymer electrolyte membrane 2 and a pair of catalyst layers (an anode catalyst layer 3a and a cathode catalyst layer 3c) that sandwich the membrane. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched between a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). Thus, the 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 PEFC1, MEA 10 is further sandwiched between a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5 a, 5 c) are illustrated so as to be located at both ends of the illustrated MEA 10. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form a stack. In an actual fuel cell stack, a gas seal portion is disposed between the separator (5a, 5c) and the solid polymer electrolyte membrane 2 or between PEFC 1 and another adjacent PEFC. These descriptions are omitted in FIG.

The separators (5a, 5c) are obtained, for example, by forming a concavo-convex shape as shown in FIG. 1 by subjecting a thin plate having a thickness of 0.5 mm or less to a press treatment. The convex part seen from the MEA side of the separator (5a, 5c) is in contact with MEA 10. Thereby, the electrical connection with MEA 10 is ensured. In addition, a recess (space between the separator and the MEA generated due to the uneven shape of the separator) seen from the MEA side of the separator (5a, 5c) is used for circulating gas during operation of PEFC 1. Functions as a gas flow path. Specifically, a fuel gas (for example, hydrogen) is circulated through the gas flow path 6a of the anode separator 5a, and an oxidant gas (for example, air) is circulated through the gas flow path 6c of the cathode separator 5c.

On the other hand, the recess viewed from the side opposite to the MEA side of the separator (5a, 5c) is a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC 1. The Further, the separator is usually provided with a manifold (not shown). This manifold functions as a connection means for connecting cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

In the embodiment shown in FIG. 1, the separators (5a, 5c) are formed in an uneven shape. However, the separator is not limited to such a concavo-convex shape, and may be any form such as a flat plate shape and a partially concavo-convex shape as long as the functions of the gas flow path and the refrigerant flow path can be exhibited. Also good.

The fuel cell having the MEA of the present invention as described above exhibits excellent power generation performance and durability. Here, the type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell has been described as an example. However, in addition to the above, an alkaline fuel cell and a direct methanol fuel cell are used. And a micro fuel cell. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is small and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. Among them, it is particularly preferable to use as a power source for a mobile body such as an automobile that requires a high output voltage after a relatively long time of 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. Of these, hydrogen and methanol are preferably used in that high output is possible.

Further, the application application of the fuel cell is not particularly limited, but it 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 this invention is especially advantageous when this fuel cell is applied to a vehicle from the point of in-vehicle property.

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

[Carbon powder (carrier)]
The carbon powder (carrier) satisfies the following (a) and (b):
(A) the BET specific surface area per weight by nitrogen adsorption is 800 m ² / g or more; and (b) the area of peak 0 existing at a position of 2θ = 22.5 ° to 25 ° observed by XRD analysis. A, where B is the area of peak 1 existing at 2θ = 26 ° observed by XRD analysis, the ratio of area B of peak 1 to area A of peak 0 (B / A) is 0.06 or more It is.

According to the above (a), since the carbon powder has a sufficient specific surface area, a large electric double layer capacity can be achieved. For this reason, the catalyst which carries | supports a catalyst metal on the carbon powder which satisfy | fills said (a) can exhibit high activity. On the other hand, when the BET specific surface area per weight of the carbon powder is less than 800 m ² / g, the specific surface area is small, so that it is difficult to carry out high dispersion (high loading) when loading the catalyst metal. For this reason, activity will fall. Further, when an electrode catalyst layer is formed using a catalyst in which a catalyst metal is supported on such carbon powder, the catalyst coverage by the electrolyte is increased. For this reason, the gas transport property of an electrode catalyst layer falls, and activity will fall further. Considering further improvement of electric double layer capacity, the BET specific surface area of the carbon powder is preferably 800 to 3000 m ² / g, more preferably 850 to 1800 m ² / g, and 900 to 1500 m ² / g. It is particularly preferred that

In the present specification, “BET specific surface area (m ² / g)” or “BET specific surface area (m ² / g carrier)” is measured by a nitrogen adsorption method. First, after a sample (carbon powder or carrier) was placed in a sealed glass cell for adsorption measurement, the sample was evacuated and subjected to deaeration treatment at 300 ° C. for 2 hours. Nitrogen adsorption isotherm was determined by measuring at 77k (-196 ° C) using nitrogen gas as the adsorption gas. For this measurement, an automatic gas / vapor adsorption measuring device BELSORP-18 manufactured by Nippon Bell Co., Ltd. is used. The BET specific surface area is calculated from measurement points in the range of relative pressure (P / P0) = 0.05 to 0.20.

In addition, according to the above (b), since the carbon powder has sufficient crystallinity, the edge amount of carbon (graphene) that becomes the starting point of electrochemical corrosion can be sufficiently reduced. For this reason, by using such a carbon powder as a catalyst, carbon corrosion can be suppressed, durability can be improved, and a decrease in catalytic activity when a catalytic metal is supported can be effectively suppressed / prevented. On the other hand, when the B / A ratio of the carbon powder is less than 0.06, the crystallinity of the carbon powder is lowered and the durability is lowered. In consideration of further improvement in durability, the ratio of the area B of the peak 2 to the area A of the peak 1 of the carbon powder (B / A ratio) is preferably 0.06 to 0.40, preferably 0.07 to More preferably, it is 0.35.

Here, peak 0 is a broad peak present at a position of 2θ = 22.5 ° to 25 ° observed by XRD analysis. Peak 0 is attributed to a carbon structure with low crystallinity. Further, peak 1 is a sharp peak existing at a position of 2θ = 26 ° observed by XRD analysis, and peak 2 is a sharp peak existing at a position of 2θ = 26.5 ° observed by XRD analysis. . Peak 1 and peak 2 are peaks derived from the (002) plane of carbon, and are attributed to a highly crystalline carbon structure. For this reason, the large area B of peak 1 means that the crystallinity of carbon is high (the edge amount of carbon that is the starting point of electrochemical corrosion is small). Therefore, by setting the B / A ratio high, it is possible to improve the durability of the carbon powder, and therefore it is possible to effectively suppress / prevent a decrease in the activity of the catalyst when used as a carrier.

Areas A and B are present at the positions of 2θ = 22.5 ° to 25 ° (peak 0) and 2θ = 26 ° as measured by X-ray diffractometer (XRD) according to the following method. It is determined based on the peak (Peak 1) and the peak (Peak 2) existing at the position of 2θ = 26.5 °.

[Measurement method of areas A and B]
X-ray diffraction measurement is performed by placing a sample (carbon powder) on a silicon non-reflective plate and using an X-ray diffractometer RINT-TTRIII manufactured by Rigaku Corporation to obtain an XRD pattern. In the X-ray diffraction measurement, CuKα rays are used as a radiation source.

In the obtained XRD pattern, fitting is performed using a Voigt function (forked function), and peaks existing at positions of 2θ = 22.5 ° to 25 °, 26 °, and 26.5 ° (peak 0, peak 1, and peak), respectively. Each area of 2) is calculated. Next, the area (B) of the peak 1 calculated above is divided by the area (A) of the peak 0 to obtain the ratio (B / A) of the area B of the peak 1 to the area A of the peak 0.

The method for producing the carbon powder of the present invention is not particularly limited. Hereinafter, although the preferable form of the manufacturing method of the carbon powder of this invention is demonstrated, this invention is not limited to the following form. That is, (i) an organic material is mixed with a magnesium compound or an alkaline earth metal compound (step (i)), (ii) the mixture obtained in (i) above is heated to produce a carbon material, and then the magnesium compound Alternatively, the alkaline earth metal compound is removed (step (ii)), and (iii) the carbon material obtained in the above (ii) is heat-treated (step (iii)). The steps (i) and (ii) are known methods such as those described in JP-A-2006-062954, JP-A-2012-082134, JP-A-2012-122158, and JP-A 2012-218999. A method using a thermoplastic resin in the method can be applied in the same manner or appropriately modified.

(Process (i))
In this step, an organic material is mixed with a magnesium compound or an alkaline earth metal compound to prepare a mixture.

Here, the organic material used as the raw material of the carbon powder is not particularly limited, but organic acids such as acetic acid and citric acid or thermoplastic resins can be preferably used. By using these as raw materials, carbon wall stacking (stacking) can be formed even at a relatively low temperature, and the (002) plane can be grown (the B / A ratio can be increased).

Examples of thermoplastic resins include, but are not limited to, polyvinyl alcohol, polyester resins (aliphatic and aromatic polyester resins), polyolefin resins, acrylic resins, styrene resins, polyamide resins, polyacrylonitrile resins, polybutadiene and polyisoprene. Main elastomers, natural rubber, petroleum resins and the like can be mentioned. Among these, polyvinyl alcohol, a polyester resin, a styrene resin, and a petroleum resin that are substantially composed of only carbon atoms, hydrogen atoms, and oxygen atoms are preferable. In particular, when polyvinyl alcohol is used as a raw material for carbon powder, the carbon powder has micropores in addition to mesopores. Further, when polyethylene terephthalate or hydroxypropylene glycol is used as a raw material for carbon powder, the carbon powder has relatively large mesopores.

Further, the organic material may be mixed with the magnesium compound or the alkaline earth metal compound in any form. Specifically, it can be used in a solid form such as a powder, a pellet, or a lump, or in the form of a solution or dispersion dissolved or dispersed in an appropriate solvent.

The magnesium compound or alkaline earth metal compound mixed with the organic material is not particularly limited as long as it acts as a template during carbonization of the organic material. Specifically, examples of the alkaline earth metal include calcium, strontium, and barium. Among these, it is preferable to mix a magnesium compound and a calcium compound with an organic material.

The magnesium compound or alkaline earth metal compound may be in any form of magnesium or alkaline earth metal. Specifically, magnesium compounds or alkaline earth metal compounds include magnesium, alkaline earth metal oxides, hydroxides and carbonates, and acetates, oxalates, citrates, acrylates, and the like. Preferred are organic acid salts such as methacrylate. Among these, an oxide is preferable because it can promote the formation of a porous carbide without deteriorating the heat treatment furnace or generating a polluting gas in the firing step of the next step (ii).

The magnesium compound and alkaline earth metal compound may be used alone or in the form of a mixture of two or more. Alternatively, the magnesium compound and the alkaline earth metal compound may be used in appropriate combination.

Further, the mixed form of the magnesium compound or alkaline earth metal compound is not particularly limited, and examples thereof include powder, pellets, granules, and pastes. Of these, powder and granule are preferable from the viewpoint of uniform mixing with an organic material and making the carbide porous.

The size of the magnesium compound or alkaline earth metal compound is not particularly limited. The pore diameter (especially mesopores) of the carbon material obtained by the next step (ii) can be adjusted by the crystallite size of the magnesium compound or alkaline earth metal compound. That is, when the produced magnesium oxide or alkaline earth metal oxide (crystallite) is eluted with an acid, pores corresponding to the crystallite size of the oxide are produced in the carbon material. For this reason, it is preferable that the average crystallite size is selected according to the desired pore size (particularly mesopores) of the carbon powder. Specifically, the average crystallite size is preferably 5 to 150 nm. With such a crystallite size, the pore size and pore distribution of the obtained carbon material (and hence the carbon powder of the present invention) can be adjusted to an appropriate range. Here, “crystallite” refers to the largest group that can be regarded as a single crystal. The “average crystallite size” employs an average of values measured by X-ray diffraction for statistically significant numbers (for example, 300) unless otherwise specified. The “crystallite size (diameter)” means the maximum distance among the distances between any two points passing through the center of the crystallite and on the contour line of the particle.

The mixing ratio of the organic material and the magnesium compound or alkaline earth metal compound is not particularly limited. The organic material is preferably mixed at a ratio of 40 to 700 parts by weight, more preferably 100 to 300 parts by weight, with respect to 100 parts by weight of the magnesium compound or alkaline earth metal compound. With such a mixing ratio, the carbon material can be made sufficiently porous to produce a carbon material having the desired pore size and pore distribution (and hence the carbon powder of the present invention) more efficiently.

(Step (ii))
In this step, the magnesium compound or alkaline earth metal compound is removed after the mixture obtained in (i) above is heated (fired) to produce a carbon material. By this process, the organic material is carbonized and made porous, and a carbon material having a desired pore size and pore distribution is obtained.

Here, the heating (firing) conditions of the mixture are not particularly limited, and can be performed in an air atmosphere or in an inert gas atmosphere such as argon gas or nitrogen gas. Preferably, heating (baking) is performed in an inert gas atmosphere. More specifically, the mixture is charged into a heating apparatus such as an electric furnace, and the inside is replaced with an inert gas such as argon gas or nitrogen gas, and then heated while blowing a non-oxidizing gas into the apparatus. . By this operation, the organic material is thermally decomposed (carbonized). Thus, carbides and magnesium oxide or alkaline earth metal oxides remain after heating.

The heating (firing) conditions are not particularly limited. Specifically, the heating (firing) temperature is preferably 500 to 1500 ° C., more preferably 700 to 1200 ° C. The heating (firing) time is preferably about 0.5 to 5 hours, more preferably about 1 to 2 hours. Under such conditions, the magnesium compound or the alkaline earth metal compound acts sufficiently effectively on the organic material to promote the carbonization and porosity of the organic material more effectively, and further increase the specific surface area of the carbon material. Can be big. Note that magnesium oxide or alkaline earth metal oxide is thermally stable, and hydroxide, carbonate, and organic acid salt are thermally decomposed during heat treatment to be converted into stable oxides. For this reason, the heat treatment can be performed safely without the deterioration of the lining refractory of the heating furnace or the generation of harmful gas causing environmental pollution even in the heat treatment of the next step (iii).

As described above, the carbon material obtained after this step coexists with magnesium oxide or alkaline earth metal oxide. For this reason, a carbon material is isolate | separated by processing the product of this process (ii) with an acid aqueous solution. Here, the acid used in the acid aqueous solution is not particularly limited as long as it elutes magnesium oxide or alkaline earth metal oxide. Specific examples include mineral acids such as sulfuric acid, nitric acid, and hydrochloric acid, and organic acids such as acetic acid and oxalic acid. The concentration of the aqueous acid solution is not particularly limited as long as it can dissolve magnesium oxide or alkaline earth metal oxide, and can be appropriately selected. In addition, after the treatment with the acid aqueous solution, the treated product is preferably filtered and washed with water to remove the acid and then dried. By this step, a carbon material substantially free of impurities is obtained.

(Process (iii))
In this step, the carbon material obtained in the above (ii) is heat-treated. By the said process, the carbon powder of this invention is obtained.

Here, the heat treatment condition of the carbon material is not particularly limited as long as it can achieve the above configurations (a) and (b) or the above configurations (a), (b) and (c). Specifically, when the organic material is a thermoplastic resin, the heat treatment temperature is preferably less than 2000 ° C., more preferably more than 1300 ° C., 1900 ° C., still more preferably 1400-1850 ° C., Particularly preferred is 1500-1800 ° C. The temperature increase rate in the heat treatment is preferably 100 to 1000 ° C./hour, particularly preferably 300 to 800 ° C./hour. The heat treatment time (holding time at a predetermined heat treatment temperature) is not particularly limited, but is particularly preferably 1 minute or more and 60 minutes or less. Note that the heat treatment is performed in an inert gas atmosphere such as argon gas or nitrogen gas. If it is such conditions, the carbon powder which satisfy | fills the said structure (a) and (b) or the said structure (a), (b) and (c) will be obtained simply. In addition, when heat processing conditions are less than the said minimum (heat processing conditions are too gentle), B / A ratio of carbon powder may become too small. On the other hand, when the heat treatment condition exceeds the above upper limit (the heat treatment condition is too severe), graphitization proceeds too much and the BET specific surface area of the carbon powder may be too small.

[Catalyst (Electrocatalyst)]
The catalyst (electrode catalyst) is composed of the carbon powder (support) and a catalytic metal supported on the carbon powder.

Catalyst metal has a function of catalyzing an electrochemical reaction. The catalyst metal used in the anode catalyst layer is not particularly limited as long as it has a catalytic action in the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. The catalyst metal used in the cathode catalyst layer is not particularly limited as long as it has a catalytic action for 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.

Among these, those containing at least platinum are preferably used in order to improve catalytic activity, poisoning resistance to carbon monoxide, heat resistance, and the like. That is, the catalyst metal is preferably platinum or contains a metal component other than platinum and platinum, and more preferably platinum or a platinum-containing alloy. Such a catalytic metal can exhibit high activity. In particular, when the catalyst metal is platinum, platinum having a small particle diameter can be dispersed on the surface of the carbon powder (support), so that the platinum surface area per weight can be maintained even if the amount of platinum used is reduced. Moreover, when a catalyst metal contains metal components other than platinum and platinum, since the usage-amount of expensive platinum can be reduced, it is preferable from a viewpoint of cost. Although the composition of the alloy depends on the type of 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%. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any 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 the present specification, unless otherwise specified, the description of the catalyst metal for the anode catalyst layer and the cathode catalyst layer has the same definition for both. However, the catalyst metals of the anode catalyst layer and the cathode catalyst layer do not have to be the same, and can be appropriately selected so as to exhibit the desired action as described above.

The shape and size of the catalyst metal (catalyst component) are not particularly limited, and the same shape and size as known catalyst components can be adopted. As the shape, for example, a granular shape, a scale 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 3 nm or more, more preferably more than 3 nm and not more than 30 nm, particularly preferably more than 3 nm and not more than 10 nm. If the average particle diameter of the catalyst metal is 3 nm or more, the catalyst metal is more firmly supported on the carbon powder (for example, in the mesopores of the carbon powder) and more effectively suppresses contact with the electrolyte in the catalyst layer.・ Prevented. Further, when the carbon powder has micropores, the micropores remain without being clogged with the catalytic metal, and a gas transport path can be secured better, and the gas transport resistance can be further reduced. In addition, elution due to potential change can be prevented, and deterioration in performance over time can be suppressed. For this reason, the catalytic activity can be further improved, that is, the catalytic reaction can be promoted more efficiently. On the other hand, if the average particle diameter of the catalyst metal particles is 30 nm or less, the catalyst metal can be supported on the carbon powder (for example, inside the mesopores of the carbon powder) by a simple method, and the electrolyte coverage of the catalyst metal is reduced. can do. The “average particle diameter of the catalytic metal particles” in the present invention is the crystallite diameter determined from the half-value width of the diffraction peak of the catalytic metal component in X-ray diffraction, or the catalytic metal particles examined by a transmission electron microscope (TEM). It can be measured as the average value of the particle diameters.

In this embodiment, the content (mg / cm ² ) of the catalyst metal per unit catalyst coating area is not particularly limited as long as sufficient degree of dispersion of the catalyst on the carrier and power generation performance can be obtained. ˜1 mg / cm ² . However, when the catalyst contains platinum or a platinum-containing alloy, the platinum content per unit catalyst coating 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 high cost factor for fuel cells. Therefore, it is preferable to reduce the amount of expensive platinum used (platinum content) to the above range and reduce the cost. 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 . In this embodiment, since the activity per catalyst weight can be improved by controlling the pore structure of the carrier, the amount of expensive catalyst used can be reduced.

In this specification, inductively coupled plasma emission spectroscopy (ICP) is used for measurement (confirmation) of “catalyst (platinum) content per unit catalyst application area (mg / cm ² )”. A person skilled in the art can easily carry out a method of making the desired “catalyst (platinum) content per unit catalyst coating area (mg / cm ² )”, and control the slurry composition (catalyst concentration) and coating amount. You can adjust the amount.

The amount of the catalyst supported on the carrier (sometimes referred to as the loading ratio) is preferably 10 to 80% by weight, more preferably 20 to 70% by weight, based on the total amount of the catalyst carrier (that is, the carrier and the catalyst). % Is good. If the loading is within the above range, it is preferable because a sufficient degree of dispersion of the catalyst components on the carrier, improvement in power generation performance, economic advantages, and catalytic activity per unit weight can be achieved.

The structure of the catalyst is not particularly limited as long as the carbon powder satisfies the above (a) and (b). That is, the catalyst can have the same structure as the conventional one except that the carbon powder of the present invention is used as a support.

Further, the method for producing the catalyst (method for supporting the catalytic metal on the carbon powder) is not particularly limited. Preferably, a method of increasing the particle size of the catalyst metal by performing a heat treatment after depositing the catalyst metal on the surface of the catalyst carrier is preferable. In the above method, the heat treatment is performed after the precipitation to increase the particle shape of the catalyst metal. For this reason, a catalyst metal having a large particle diameter can be supported inside the pores (particularly mesopores) of the catalyst carrier. That is, the present invention includes (i) a step of depositing a catalyst metal on the surface of the catalyst support (precipitation step), and (ii) a step of performing a heat treatment after the deposition step to increase the particle size of the catalyst metal (heat treatment). And a process for producing the catalyst of the present invention. Hereinafter, although the said method is demonstrated, this invention is not limited to the following form.

Hereinafter, although the preferable form of the manufacturing method of the said catalyst is demonstrated, this invention is not limited to the following form.

(I) Deposition step In this step, a catalyst metal is deposited on the surface of the catalyst carrier. This step is a known method. For example, a method in which the catalyst support is immersed in a catalyst metal precursor solution and then reduced is preferably used.

Here, the precursor of the catalyst metal is not particularly limited and is appropriately selected depending on the type of the catalyst metal used. Specific examples include chlorides, nitrates, sulfates, chlorides, acetates and amine compounds of catalyst metals such as platinum. More specifically, platinum chloride (hexachloroplatinic acid hexahydrate), palladium chloride, rhodium chloride, ruthenium chloride, cobalt chloride and other nitrates, palladium nitrate, rhodium nitrate, iridium nitrate and other nitrates, palladium sulfate, sulfuric acid Preferred examples include sulfates such as rhodium, acetates such as rhodium acetate, and ammine compounds such as dinitrodiammine platinum and dinitrodiammine palladium. The solvent used for the preparation of the catalyst metal precursor solution is not particularly limited as long as it can dissolve the catalyst metal precursor, and is appropriately selected depending on the type of the catalyst metal precursor used. Specifically, water, an acid, an alkali, an organic solvent, etc. are mentioned. The concentration of the catalyst metal precursor in the catalyst metal precursor solution is not particularly limited, but is preferably 0.1 to 50% by weight, more preferably 0.5 to 20% by weight in terms of metal. .

Examples of the reducing agent include hydrogen, hydrazine, sodium borohydride, sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, formaldehyde, methanol, ethanol, ethylene, carbon monoxide and the like. . Note that a gaseous substance at room temperature such as hydrogen can be supplied by bubbling. The amount of the reducing agent is not particularly limited as long as the catalyst metal precursor can be reduced to the catalyst metal, and known amounts can be similarly applied.

The deposition conditions are not particularly limited as long as the catalyst metal can be deposited on the catalyst support. For example, the precipitation temperature is preferably near the boiling point of the solvent, more preferably from room temperature to 100 ° C. The deposition time is preferably 1 to 10 hours, more preferably 2 to 8 hours. In addition, you may perform the said precipitation process, stirring and mixing if necessary.

Thereby, the precursor of the catalyst metal is reduced to the catalyst metal, and the catalyst metal is deposited (supported) on the catalyst carrier.

(Ii) Heat treatment step In this step, heat treatment is performed after the deposition step (i) to increase the particle size of the catalyst metal.

The heat treatment conditions are not particularly limited as long as the particle diameter of the catalyst metal can be increased. For example, the heat treatment temperature is preferably 300 to 1200 ° C., more preferably 500 to 1150 ° C., and particularly preferably 700 to 1000 ° C. The heat treatment time is preferably 0.02 to 3 hours, more preferably 0.1 to 2 hours, and particularly preferably 0.2 to 1.5 hours. Note that the heat treatment step may be performed in a hydrogen atmosphere.

This causes the catalyst metal to increase in particle size at the catalyst support (especially within the mesopores of the catalyst support). For this reason, it becomes difficult for catalyst metal particles to be detached from the system (from the catalyst carrier). In addition, if there are micropores present near the catalyst support surface than the catalyst metal, it is possible to more effectively suppress / prevent the larger catalyst metal particles from detaching from the catalyst support even under mechanical stress. Therefore, the catalyst can be used more effectively.

[Catalyst layer]
As described above, the catalyst of the present invention can reduce gas transport resistance and exhibit high catalytic activity, that is, promote catalytic reaction. Therefore, the catalyst of the present invention can be suitably used for an electrode catalyst layer for a fuel cell. That is, the present invention also provides a fuel cell electrode catalyst layer comprising the electrode catalyst of the present invention and an electrolyte. The electrode catalyst layer for a fuel cell of the present invention can exhibit high performance and durability.

The fuel cell electrode catalyst layer of the present invention can be used in the same manner as in the prior art or appropriately modified except that the carbon powder of the present invention is used as a carrier. For this reason, although the preferable form of a catalyst layer is demonstrated below, this invention is not limited to the following form.

In the catalyst layer, the catalyst is coated with the electrolyte, but the electrolyte does not enter the mesopores (and also the micropores) of the catalyst (particularly the support). For this reason, the catalyst metal on the surface of the carrier comes into contact with the electrolyte, but the catalyst metal supported in the mesopores is not in contact with the electrolyte. The catalytic metal in the mesopores forms a three-phase interface between oxygen gas and water in a non-contact state with the electrolyte, thereby ensuring a reaction active area of the catalytic metal.

The catalyst 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 catalyst of the present invention can effectively use the catalyst by forming a three-phase interface with water without contacting the electrolyte, but water is formed in the cathode catalyst layer. .

The electrolyte is not particularly limited, but is preferably an ion conductive polymer electrolyte. Since the polymer electrolyte plays a role of transmitting protons generated around the catalyst active material on the fuel electrode side, it is also called a proton conductive polymer.

The polymer electrolyte is not particularly limited, and conventionally known knowledge can be appropriately referred to. 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 ion exchange resins constituting the fluorine-based polymer electrolyte include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-per Examples thereof include fluorocarbon sulfonic acid polymers. From the viewpoint of excellent heat resistance, chemical stability, durability, and mechanical strength, these fluorine-based polymer electrolytes are preferably used, and particularly preferably fluorine-based polymer electrolytes composed of perfluorocarbon sulfonic acid polymers. Is used.

Specific examples of the hydrocarbon electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, sulfonated poly Examples include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon polymer electrolytes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the selectivity of the material is high. In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is not restricted only to the material mentioned above, Other materials may be used.

Proton conductivity is important in polymer electrolytes responsible for proton transmission. Here, when the EW of the polymer electrolyte is too large, the ionic conductivity in the entire catalyst layer is lowered. Therefore, it is preferable that the catalyst layer of this embodiment contains a polymer electrolyte having a small EW. Specifically, the catalyst layer of this embodiment preferably has an EW of 1500 g / eq. The following polymer electrolyte is contained, More preferably, it is 1200 g / eq. The following polymer electrolyte is included, and particularly preferably 1000 g / eq. The following polymer electrolytes are included.

On the other hand, if the EW is too small, the hydrophilicity is too high and it becomes difficult to smoothly move water. From such a viewpoint, the EW of the polymer electrolyte is preferably 600 or more. Note that EW (Equivalent Weight) represents an equivalent weight of an exchange group having proton conductivity. The equivalent weight is the dry weight of the ion exchange membrane per equivalent of ion exchange group, and is expressed in units of “g / eq”.

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 90% or less of the gas in the flow path. It is preferable to use in the region. By adopting such a material arrangement, the resistance value becomes small regardless of the current density region, and the battery performance can be improved. The EW of the polymer electrolyte used in the region where the relative humidity of the gas in the flow channel is 90% or less, that is, the polymer electrolyte having the lowest EW is 900 g / eq. The following is desirable. Thereby, the above-mentioned effect becomes more reliable and remarkable.

Furthermore, it is desirable to use a polymer electrolyte with the lowest EW in a region higher than the average temperature of the cooling water inlet and outlet. As a result, 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 from the gas supply port of at least one of the fuel gas and the oxidant gas with respect to the flow path length. It is desirable to use it in the range area.

For the catalyst layer, a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, a dispersing agent such as a surfactant, glycerin, ethylene glycol (EG), as necessary. ), A thickener such as polyvinyl alcohol (PVA) and propylene glycol (PG), and an additive such as a pore-forming agent may be contained.

The thickness of the catalyst layer (dry film thickness) is preferably 0.05 to 30 μm, more preferably 1 to 20 μm, still more preferably 2 to 15 μm. The above applies to both the cathode catalyst layer and the anode catalyst layer. However, the thickness of the cathode catalyst layer and the anode catalyst layer may be the same or different.

(Method for producing catalyst layer)
Hereinafter, although preferable embodiment for manufacturing a catalyst layer is described, the technical scope of this invention is not limited only to the following form. Further, since various conditions such as the material of each component of the catalyst layer are as described above, description thereof is omitted here.

First, carbon powder (also referred to as “porous support” or “conductive porous support” in this specification) as a support is prepared. Specifically, as described in the method for producing carbon powder, it may be produced.

Next, the catalyst is supported on the porous carrier to obtain catalyst powder. The catalyst can be supported on the porous carrier by a known method. For example, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used.

Subsequently, a catalyst ink containing catalyst powder, polymer electrolyte, and solvent is prepared. The solvent is not particularly limited, and ordinary solvents used for forming the catalyst layer can be used in the same manner. Specifically, water such as tap water, pure water, ion exchange water, 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 alcohol, dimethyl ether, ethylene glycol, and the like may be used as a solvent. These solvents may be used alone or in the form of a mixture of two or more.

The amount of the solvent constituting the catalyst ink is not particularly limited as long as it is an amount capable of completely dissolving the electrolyte. Specifically, the solid content concentration of the catalyst powder and the polymer electrolyte is preferably 1 to 50% by weight, more preferably about 5 to 30% by weight in the electrode catalyst ink.

In addition, when additives such as a water repellent, a dispersant, a thickener, and a pore-forming agent are used, these additives may be added to the catalyst ink. At this time, the amount of the additive added is not particularly limited as long as it is an amount that does not interfere with the effects of the present invention. For example, the amount of additive added is preferably 5 to 20% by weight with respect to the total weight of the electrode catalyst ink.

Next, a catalyst ink is applied to the surface of the substrate. The application method to 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 gravure printing method, a die coater method, a screen printing method, or a doctor blade method.

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

(Membrane electrode assembly / fuel cell)
According to a further embodiment of the present invention, a fuel cell membrane electrode assembly including the fuel cell electrode catalyst layer and a fuel cell including the fuel cell membrane electrode assembly are provided. That is, the solid polymer electrolyte membrane 2, the cathode catalyst layer disposed on one side of the electrolyte membrane, the anode catalyst layer disposed on the other side of the electrolyte membrane, the electrolyte membrane 2 and the anode catalyst layer There is provided a fuel cell membrane electrode assembly having 3a and 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, in consideration of the necessity for improvement of proton conductivity and improvement of transport characteristics (gas diffusibility) of the reaction gas (especially 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 may be used as an anode catalyst layer, or may be used as both a cathode catalyst layer and an anode catalyst layer, and is not particularly limited.

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

Hereinafter, the components of 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, the specific form of the 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 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 during the operation of the PEFC 1 to the cathode catalyst layer 3c along the film thickness direction. 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 oxidant 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 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 used for the catalyst layer.

The thickness of the electrolyte layer may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte layer is usually about 5 to 300 μm. When the thickness of the electrolyte layer is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

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

The material which comprises the base material of a gas diffusion layer (4a, 4c) is not specifically limited, A conventionally well-known knowledge can be referred suitably. For example, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric can be used. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

The gas diffusion layer preferably contains a water repellent for the purpose of further improving water repellency and preventing flooding. The water repellent is not particularly limited, but fluorine-based high repellents such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples thereof include molecular materials, polypropylene, and polyethylene.

In order to further improve the water repellency, the gas diffusion layer has a carbon particle layer (microporous layer; MPL, not shown) made of an aggregate of carbon particles containing a water repellent agent 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 employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

Examples of the water repellent used for the carbon particle layer include the same water repellents as described above. Among these, fluorine-based polymer materials can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like.

The mixing ratio of the carbon particles to 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 electronic conductivity. It is good. In addition, there is no restriction | limiting in particular also about the thickness of a carbon particle layer, What is necessary is just to determine suitably in consideration of the water repellency of the gas diffusion layer obtained.

(Method for producing membrane electrode assembly)
A 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 hot pressing, and this is dried, and a gas diffusion layer is bonded to the gas diffusion layer, or a microporous layer side (a microporous layer is attached to the gas diffusion layer). When not included, two gas diffusion electrodes (GDE) are prepared by applying a catalyst layer on one side of the base material layer in advance and drying, and hot pressing the gas diffusion electrodes on both sides of the solid polymer electrolyte membrane. The application and joining conditions such as hot press are appropriately determined depending on the type of polymer electrolyte in the solid polymer electrolyte membrane or catalyst layer (perfluorosulfonic acid type or hydrocarbon type). 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. The separator also functions as a partition that separates the fuel gas, the oxidant gas, and the coolant from each other. In order to secure these flow paths, as described above, each of the separators is preferably provided with a gas flow path and a cooling flow path. As a material constituting 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 employed without limitation. The thickness and size of the separator and the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

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

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

The above-mentioned PEFC and membrane electrode assembly use a catalyst layer having excellent 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 on a vehicle as a driving power source, for example.

The effect 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.

Example 1
Carrier A was prepared as follows.

Specifically, citric acid powder and magnesium oxide powder were mixed at a weight ratio of 3: 1, and then the mixture was heat-treated at 900 ° C. for 1 hour in a nitrogen atmosphere. The mixed powder obtained by the heat treatment was put into a dilute sulfuric acid aqueous solution, sufficiently stirred at room temperature (25 ° C.), filtered, sufficiently washed with water, and dried to produce a carbon material A.

Next, the carbon material A was heated to 1500 ° C. in a nitrogen atmosphere, and then heat-treated at 1500 ° C. for 1 hour, thereby preparing a carrier A. For the carrier A thus obtained, the BET specific surface area was measured. As a result, the BET specific surface area of the carrier A was 1460 m ² / g. The ratio of the area B of the peak 1 to the area A of the peak 0 (B / A) of the carrier A thus obtained was 0.06. The area (area A) was calculated with the peak observed at 2θ = 23.92 ° as the peak 0.

Example 2
In Example 1, Support B was produced in the same manner as in Example 1 except that the carbon material A was heat-treated at 1800 ° C. for 1 hour in a nitrogen atmosphere. For the carrier B thus obtained, the BET specific surface area was measured. As a result, the BET specific surface area of the carrier B was 950 m ² / g. The ratio of the area B of peak 1 to the area A of peak 0 (B / A) of the carrier B thus obtained was 0.16. The area (area A) was calculated with the peak observed at 2θ = 24.32 ° as the peak 0.

Comparative Example 1
A carrier C was produced in the same manner as in Example 1 except that the carbon material A was not heat-treated in Example 1. With respect to the carrier C thus obtained, the BET specific surface area was measured. As a result, the BET specific surface area of the carrier C was 1550 m ² / g. Further, the ratio of the area B of the peak 1 to the area A of the peak 0 (B / A) of the carrier C thus obtained was 0. The area (area A) was calculated with the peak observed at 2θ = 22.70 ° as the peak 0.

Example 3
Using the carrier A prepared in Example 1 above, platinum (Pt) having an average particle size of more than 3 nm and not more than 5 nm as a catalyst metal was loaded so that the loading ratio was 30% by weight to obtain catalyst powder A. . That is, 46 g of carrier A was immersed in 1000 g (platinum content: 46 g) of a dinitrodiammine platinum nitric acid solution having a platinum concentration of 4.6% by weight, and 100 ml of 100% ethanol was added as a reducing agent. This solution was stirred and mixed at the boiling point for 7 hours, and platinum was supported on the carrier A. The catalyst powder having a loading rate of 30% by weight was obtained by filtration and drying. Thereafter, in a hydrogen atmosphere, the temperature was maintained at 900 ° C. for 1 hour to obtain catalyst powder A.

Example 4
In Example 3, catalyst powder B was obtained in the same manner as in Example 3 except that the carrier B prepared in Example 2 was used instead of the carrier A.

Comparative Example 2
In Example 3, catalyst powder C was obtained in the same manner as in Example 3 except that the carrier C prepared in Comparative Example 1 was used instead of the carrier A.

Experiment 1: Evaluation of durability The durability of the catalyst powders A and B prepared in Examples 3 to 4 and the catalyst powder C prepared in Comparative Example 2 were evaluated according to the following method. The results are shown in Table 1 below.

That is, a three-electrode electrochemical cell was used, and Hokuto Denko's electrochemical system HZ-5000 + HR301 was used as a potentiostat. Using a glassy carbon rotating electrode (GC-RDE) (φ (diameter) = 5 mm) as a working electrode, each catalyst powder produced in Examples and Comparative Examples was dispersed in water and 1-propanol mixed solvent as a dispersion medium. An electrode was used that was coated with dried ink to a dry film thickness of 1 μm and dried. Carbon was used as the counter electrode, and a reversible hydrogen electrode (RHE) was used as the reference electrode. The electrolyte was saturated with O ₂ using 0.1M perchloric acid. The measurement was performed at 60 ° C. (liquid temperature).

The calculation of the effective catalyst surface area (ECA) was performed by cyclic voltammetry (CV). Prior to the measurement, a potential scan was performed at a potential of 1.0 V for 30 seconds. Thereafter, the potential range of 1.0 to 1.5 V was increased (1 second) and decreased (1 second) at a potential sweep rate of 0.5 V / s, and this was defined as 1 cycle (2 seconds / cycle). When this potential cycle is repeated, the peak potential of the quinone-hydroquinone reduction current near 0.6 V measured by the cyclic voltammetry method shifts to the lower potential side as the potential cycle increases. The state of carbon was estimated from the change in the reduction current. Specifically, the number of cycles that could be repeated until the potential of the reduction current became 0.5 V or less was used as an index of durability.

From the results shown in Table 1, the catalyst powders of Examples 3 and 4 have a larger number of cycles in which the reduction current decreases compared to the catalyst powder of Comparative Example 2 in which the BET specific surface area and / or B / A ratio deviates from the present invention. Is shown. From this, it is considered that the catalyst using the carbon powder of the present invention has a small decrease in electric double layer capacity and can maintain a significantly high activity (excellent in durability).

This application is based on Japanese Patent Application No. 2015-059040 filed on March 23, 2015, the disclosure content of which is referenced and incorporated as a whole.

1 ... Polymer electrolyte fuel cell (PEFC),
2 ... Solid polymer electrolyte membrane,
3a ... anode catalyst layer,
3c ... cathode catalyst layer,
4a ... anode gas diffusion layer,
4c ... cathode gas diffusion layer,
5a ... anode separator,
5c ... cathode separator,
6a ... anode gas flow path,
6c ... cathode gas flow path,
7: Refrigerant flow path,
10: Membrane electrode assembly (MEA).

Claims (6)

1. A carbon powder mainly composed of carbon,
   The BET specific surface area by nitrogen adsorption is 800 m ² / g or more, and the area of peak 0 existing at a position of 2θ = 22.5 ° to 25 ° observed by XRD analysis is A, 2θ observed by XRD analysis = The carbon powder for a fuel cell, wherein the ratio of the area B of the peak 1 to the area A of the peak 0 (B / A) is 0.06 or more when the area of the peak 1 existing at the position of 26 ° is B.
2. A fuel cell catalyst comprising a catalytic metal supported on the fuel cell carbon powder according to claim 1.
3. The fuel cell catalyst according to claim 2, wherein the catalyst metal is platinum or contains a metal component other than platinum and platinum.
4. A fuel cell electrode catalyst layer comprising the fuel cell catalyst according to claim 2 or 3 and an electrolyte.
5. A fuel cell membrane electrode assembly comprising the fuel cell electrode catalyst layer according to claim 4.
6. A fuel cell comprising the fuel cell membrane electrode assembly according to claim 5.

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