Catalyst-supporting carbon, membrane electrode assembly for solid polymer fuel cell using same, and solid polymer fuel cell

Abstract

Provided is a catalyst-supporting carbon which has high initial activity and excellent durability. A catalyst-supporting carbon in which catalyst particles comprising platinum or a platinum alloy having a crystallite size of 2.5 nm to 5.0 nm and a catalyst surface area of 40 m < 2 > / g to 80 m < 2 > / g are supported on a carbon carrier having a crystallite size of 3.5 nm to 9 nm, a BET specific surface area of 300 m < 2 > / g to 450 m < 2 > / g, and a pore diameter of 5.0 nm to 20.0 nm.

Description

Technical Field

[0001] The present invention relates to catalyst-supported carbon for use in fuel cells of solid polymer type or the like, water electrolysis devices, and the like. Background Art

[0002] In recent years, in response to societal demands and trends driven by energy and environmental issues, polymer electrolyte fuel cells (PEFCs), which operate at room temperature and achieve high power density, have attracted attention as power sources for electric vehicles and stationary power sources. Water electrolysis devices for hydrogen production are also attracting attention. For example, a characteristic of PFCs is the use of an electrolyte layer composed of a film-like solid polymer membrane.

[0003] A polymer electrolyte fuel cell is typically constructed by stacking multiple single-cell membrane electrode assemblies (MEAs) sandwiched between a pair of separators. An MEA has an electrolyte layer sandwiched between electrode catalyst layers containing a highly dispersed electrode catalyst. These electrode catalyst layers are also called electrodes.

[0004] In the above-mentioned MEA, the electrochemical reaction described below is carried out. First, the hydrogen contained in the fuel gas supplied to the fuel electrode (anode) side is oxidized by the catalyst particles to become protons and electrons. Next, the generated protons pass through the proton conductive electrolyte contained in the electrode catalyst layer and the solid polymer membrane in contact with the electrode catalyst layer to reach the oxygen electrode (cathode) side electrode catalyst layer. In addition, the electrons generated in the anode side electrode catalyst layer pass through the conductive carrier constituting the electrode catalyst layer and the gas diffusion layer, gas separator and external circuit in contact with the side of the electrode catalyst layer other than the solid polymer membrane to reach the cathode side electrode catalyst layer. Then, the protons and electrons reaching the cathode side electrode catalyst layer react with the oxygen contained in the oxidant gas supplied to the cathode side to generate water. In the fuel cell, electricity can be output to the outside through the above-mentioned electrochemical reaction.

[0005] Conventional electrode catalysts used catalyst-supported carbon for both cathodes and anodes. This carbon-based carrier carries catalyst particles such as platinum or a platinum alloy. To achieve highly dispersed support for the micronized catalyst particles, a large amount of carrier carbon with a high specific surface area is used. This increases the electrode reaction area on the catalyst particle surface, allowing for sufficient initial activity with a small catalyst particle loading.

[0006] Polymer electrolyte fuel cells face issues with initial activity and battery life. The battery life is said to be 5,000 hours for automotive use and 40,000 hours for home use, requiring them to maintain high power generation performance over a long period of time.

[0007] However, due to the operating conditions of polymer electrolyte fuel cells, such as long-term continuous operation, startup, shutdown, and storage, when the electrodes are exposed to a noble metal potential environment (approximately 0.8V or above), there is a problem of electrochemical oxidation and corrosion / disappearance of the conductive support or catalyst particles that constitute the electrodes. This reduces the area of ​​the electrodes that function over time, resulting in a decrease in the performance of the polymer electrolyte fuel cell.

[0008] Therefore, various research and development efforts have been made on catalyst-supported carbon having high initial activity and excellent durability, or MEA exhibiting stable power generation performance over a long period of time.

[0009] In the prior art document 1 and the prior art document 2, it is described that the crystallite size of the nanostructured carbon nanotubes is 1.7 nm to 1.9 nm and the crystallite size of the nanostructured carbon nanotubes is 750 nm. 2 / g~1000m 2 Although catalyst-supported carbon is a carbon carrier having a specific surface area of ​​1000 nm / g, further improvement in durability is required.

[0010] In the prior art document 3, it is described that the crystallite size is 3.5 nm or more and 50 nm 2 / g~250m 2 Although the catalyst supports carbon with a specific surface area of ​​1000 nm / g, further improvement of the initial activity is required.

[0011] In the prior art document 4, a high-durability catalyst-supported carbon with a combustion temperature of 350°C or higher is described, but the specific surface area is as low as 250 m 2 / g or less, further improvement of the initial activity is required.

[0012] Prior art literature

[0013] Patent Literature

[0014] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-146305;

[0015] Patent Document 2: Japanese Patent Application Laid-Open No. 2017-73357;

[0016] Patent Document 3: Japanese Patent Application Laid-Open No. 2016-100262;

[0017] Patent Document 4: Japanese Patent Application Laid-Open No. 2005-302527. Summary of the Invention

[0018] Problems to be solved by the invention

[0019] In order to improve the initial activity of catalyst-supported carbon, it is suitable to use a carbon carrier with a high specific surface area and micronized catalyst particles. On the other hand, in order to improve durability, it is suitable to use a carbon carrier with a large crystallite size and catalyst particles with a large particle size that are not micronized. However, large crystallite size and high specific surface area have opposite trends, and there is no example of a carrier that has both characteristics in a high dimension. Therefore, the object of the present invention is to provide catalyst-supported carbon, a membrane electrode assembly for a solid polymer fuel cell using the catalyst-supported carbon, and a solid polymer fuel cell, wherein the catalyst-supported carbon has high initial activity and excellent durability by carrying catalyst particles with a crystallite size within a specific range on a carbon carrier having both large crystallite size and high specific surface area.

[0020] Means for solving problems

[0021] The present inventors adopt a de-componenting process, that is, by contacting a carbon-containing compound (78Mn-22C (mol%)) with molten zinc to selectively dissolve Mn on the molten zinc to obtain a porous carbon material, which can obtain a porous carbon material with a carbon content of 300 to 450 m 2 A carbon support having a specific surface area of ​​1.5 nm / g and a crystallite size of 3.5 nm to 9 nm. Its characteristic structure is a graphitized porous carbon support having both a high surface area and a large crystallite size. It was discovered that by supporting platinum particles or platinum alloy particles having a crystallite size smaller than the mesopore diameter of the carbon support on the carbon support, the above-mentioned problems can be solved, resulting in a catalyst-supported carbon having high initial activity and excellent durability that can be used in solid polymer fuel cells, etc., thus completing the present invention.

[0022] That is, the present invention provides catalyst-supported carbon, a membrane electrode assembly for a polymer electrolyte fuel cell containing the catalyst-supported carbon in an electrode, and a polymer electrolyte fuel cell having the following aspects (1) to (10).

[0023] (1) Catalyst-supported carbon, characterized in that it is a catalyst-supported carbon in which catalyst particles composed of platinum or a platinum alloy are supported on a carbon carrier composed of porous carbon, wherein the carbon carrier of the catalyst-supported carbon has a crystallite size (Lc) of 3.5 nm or more and 9 nm or less based on X-ray diffraction, and a BET specific surface area (SSA) of 300 m 2 / g and above 450m 2 / g or less, a pore diameter of 5.0nm or more and 20.0nm or less, and the catalyst particles composed of platinum or a platinum alloy of the catalyst-supported carbon have a crystallite size of 2.5nm or more and 5.0nm or less based on X-ray diffraction, and a surface area of ​​the catalyst particles measured by CO pulse adsorption measurement of 40m 2 / g~80m 2 / g.

[0024] (2) The catalyst-supported carbon described in (1) above is characterized in that the combustion temperature of the catalyst-supported carbon in an air atmosphere measured by differential thermal analysis is above 400°C, and the half-width of the combustion peak is below 100°C.

[0025] (3) The catalyst-supported carbon described in (1) above is characterized in that the average plane spacing d002 of the (002) plane of the carbon carrier of the catalyst-supported carbon based on X-ray diffraction is less than 0.345 nm.

[0026] (4) The catalyst-supported carbon described in (2) above is characterized in that the average plane spacing d002 of the (002) plane of the carbon carrier of the catalyst-supported carbon based on X-ray diffraction is less than 0.345 nm.

[0027] (5) The catalyst-supported carbon described in (1) above is characterized in that the carbon carrier of the catalyst-supported carbon has a peak intensity ratio (G / D) of the G band to the D band measured by Raman spectroscopy of not less than 0.8, and a peak full width at half maximum (G-FWHM) of the G band of not less than 40 cm -1 Over 60cm -1 the following.

[0028] (6) The catalyst-supported carbon described in (2) above is characterized in that the carbon carrier of the catalyst-supported carbon has a peak intensity ratio (G / D) of the G band to the D band measured by Raman spectroscopy of not less than 0.8, and a peak full width at half maximum (G-FWHM) of the G band of not less than 40 cm -1 Over 60cm -1 the following.

[0029] (7) The catalyst-supported carbon described in (1) above is characterized in that the catalyst-supported carbon is endowed with acidic functional groups as surface functional groups on the carbon carrier.

[0030] (8) The catalyst-supported carbon described in (2) above is characterized in that the catalyst-supported carbon is endowed with acidic functional groups as surface functional groups on the carbon carrier.

[0031] (9) A membrane electrode assembly for a polymer electrolyte fuel cell, characterized in that the catalyst-supported carbon described in (1) above is contained in the electrode.

[0032] (10) A solid polymer fuel cell characterized in that the electrodes of the membrane electrode assembly contain the catalyst-supported carbon described in (1) above.

[0033] Effects of the Invention

[0034] The catalyst-supported carbon of the present invention, by supporting catalyst particles of a specific crystallite size on a carbon support with a high dimensionality and a high specific surface area, exhibits high initial activity and is less susceptible to corrosion and loss of the support, dissolution, or aggregation of the catalyst particles. This provides excellent corrosion resistance even in noble metal potential environments or strongly acidic atmospheres. Consequently, it is possible to provide a catalyst-supported carbon having high initial activity and excellent durability, a membrane electrode assembly for a polymer electrolyte fuel cell, and a polymer electrolyte fuel cell using the catalyst-supported carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] [ Figure 1 ] is a graph showing the relationship between the crystallite size and specific surface area of ​​the carbon carrier of the catalyst-supported carbon obtained in the Examples and Comparative Examples.

[0036] [ Figure 2 ] is a graph showing the relationship between the initial activity and durability of the catalyst-supported carbon obtained in the Examples and Comparative Examples. DETAILED DESCRIPTION

[0037] Next, the present invention will be described based on an embodiment. However, the present invention is not limited to the embodiment described below.

[0038] In the present invention, the carbon support of the catalyst-supporting carbon needs to be the crystallite size (L c ) is 3.5 nm or more and 9 nm or less, and the BET specific surface area (SSA) based on nitrogen adsorption measurement is 300 m 2 / g and above 450m 2 / g or less.

[0039] Figure 1 The crystallite size (L) of the carbon support of the catalyst-supported carbon in the present invention and the prior art is shown in FIG. c ) and BET specific surface area (SSA). The carbon support of the catalyst-supported carbon in the present invention is a carbon support with high dimensionality and crystallite size (L c ) and BET specific surface area (SSA) of carbon supports.

[0040] The carbon support also includes, for example, carbon doped with boron, nitrogen, tungsten, aluminum, titanium, or the like.

[0041] The carbon support can be prepared, for example, as follows. A carbon-containing compound (78Mn-22C (mol%)) is brought into contact with a 600°C molten metal melt to undergo a decomponentation reaction that selectively dissolves Mn from the molten metal. After holding for one hour, the furnace is cooled. The metal component is removed from the composite containing the porous carbon and the metal component in an aqueous nitric acid solution, and the resultant is filtered and dried to obtain the porous carbon. Subsequently, the composite is heated at 2000°C for graphitization.

[0042] The present inventors have found that by contacting a carbon-containing compound (78Mn-22C (mol%)) with molten zinc, selectively dissolving Mn in the molten zinc to obtain a porous carbon material, and then performing a graphitization treatment, a high-dimensional and microcrystalline size (L c ) and BET specific surface area (SSA) of carbon supports, wherein the crystallite size (L c ) is 3.5 nm or more and 9 nm or less and the BET specific surface area (SSA) based on nitrogen adsorption measurement is 300 m 2 / g and above 450m 2 / g or less. The reason for this is not necessarily clear, but the present inventors speculate as follows. That is, during the decomposition process, the porosity is achieved by dissolving Mn from the carbon-containing compound into the molten metal zinc, and the crystal growth is achieved by surface diffusion of carbon in the zinc melt, resulting in both a high specific surface area and a large crystallite size after graphitization at 2000°C.

[0043] By dividing the above crystallite size (L c ) is increased to 3.5nm or more, which can inhibit the degradation of the carbon support and show high durability. c ) represents the size resulting from the stacking of carbon hexagonal meshes, L c The larger the value, the thicker the stacked structure of the carbon hexagonal mesh.

[0044] The corrosion of the carbon support in the electrode catalyst disappears easily starting from the irregular structure of the carbon hexagonal mesh. Therefore, it is preferred to reduce the proportion of the irregular structure of the carbon hexagonal mesh by increasing the stacking of the carbon hexagonal mesh. In addition, because the stacked structure of the carbon support is thick, the electronic conductivity is improved, and it is also possible to expect that the two characteristics of initial activity and durability will be improved. As another solution, the crystallite size can be more than 3.7nm. In addition, as another solution, the crystallite size can be more than 3.9nm.

[0045] On the other hand, if the crystallite size exceeds 9 nm, the BET specific surface area (SSA) described later is reduced, and it is impossible to achieve both the BET specific surface area (SSA) and the crystallite size (L) in a high-dimensional manner. c As another embodiment, the crystallite size may be 8.5 nm or less. In addition, as another embodiment, the crystallite size may be 8.3 nm or less.

[0046] By increasing the BET specific surface area (SSA) to 300 m 2 / g or above, the catalyst particles can be highly dispersed and supported, and high initial activity can be exhibited.

[0047] The BET specific surface area (SSA) indicates the area on which catalyst particles can be supported. A higher BET specific surface area (SSA) means that catalyst particles can be supported with a higher dispersion and a higher supporting density.

[0048] Generally, in catalyst-supported carbon for solid polymer fuel cells, it is required to support catalyst particles on the carbon support at a high loading density of 10% to 70% by mass. 2 / g or more, the catalyst particles can be supported at a desired supporting density, particularly 40% by mass or more, with high dispersion, and can exhibit high initial activity.

[0049] As another option, the BET specific surface area (SSA) can be 320 m 2 / g or more. In addition, as another embodiment, the BET specific surface area (SSA) can be 340m 2 / g or above.

[0050] The corrosion and disappearance of the carbon support in the electrode catalyst are particularly likely to occur at the site where the carbon support contacts the catalyst particles. Therefore, it is found that the electrode catalyst with the catalyst particles highly dispersed in a microparticle form may have poor corrosion resistance. Therefore, it is preferred to adjust the dispersion state of the catalyst particles supported on the carbon support to limit the BET specific surface area (SSA) of the carbon support in the electrode catalyst to an appropriate value. That is, by setting the BET specific surface area (SSA) to 450 m 2 / g or less, the corrosion of the carbon support can be further suppressed.

[0051] In addition, if the BET specific surface area (SSA) is higher than 450 m 2 / g, then the above-mentioned crystallite size (L c ) is reduced, and it is impossible to have both high dimensionality and crystallite size (L c ) and BET specific surface area (SSA). As another embodiment, the BET specific surface area (SSA) can be 430m 2 / g or less. In addition, as another solution, the BET specific surface area can be 410m 2 / g or less.

[0052] The pore diameter of the catalyst-supported carbon of the present invention is preferably 5.0 nm to 20.0 nm, and the crystallite size of the catalyst particles of the catalyst-supported carbon is preferably 2.5 nm to 5.0 nm. By setting the pore diameter of the catalyst-supported carbon and the crystallite size of the catalyst particles of the catalyst-supported carbon within the above ranges, a structure in which the catalyst particles are supported within the pores of the carbon support can be achieved, thereby exhibiting high initial activity.

[0053] By supporting catalyst particles in the pores, especially the mesopores, of the carbon support, the contact area between the catalyst particles and the ionomer can be reduced when forming a catalyst electrode layer for a fuel cell, thereby reducing poisoning of the catalyst particles caused by the sulfonic acid groups of the ionomer, for example.

[0054] The pore diameter of the carbon support of the catalyst-supported carbon of the present invention is measured using a nitrogen adsorption isotherm and calculated by analysis based on the BJH method. Here, "mesopores" refer to pores with a diameter of 2.0 nm to 50.0 nm according to IUPAC. However, in the present invention, mesopores with a pore diameter of 5.0 nm to 20.0 nm are more important.

[0055] When the pore diameter is less than 5.0 nm, the catalyst particles are not loaded in the pores, but are selectively loaded on the surface outside the pores, which makes it impossible to reduce the contact area between the catalyst particles and the ionomer, resulting in a decrease in initial activity. On the other hand, if the pore diameter is greater than 20.0 nm, the ionomer invades the pores, which makes it impossible to reduce the contact area between the catalyst particles and the ionomer, resulting in a decrease in initial activity. That is, the pore diameter of the carbon support is preferably greater than the crystallite size of the catalyst particles, more preferably greater than 125% of the crystallite size of the catalyst particles. As another option, the pore diameter can be greater than 7 nm and less than 18 nm. In addition, as another option, the crystallite size can be greater than 9 nm and less than 16 nm.

[0056] The crystallite size of the catalyst particles contained in the catalyst-supported carbon of the present invention is calculated from the (220) plane of Pt or a Pt alloy. The crystallite size of the (220) plane of Pt or a Pt alloy can be set in the range of 2.5 nm or more and 5.0 nm or less. As another embodiment, the crystallite size of the (220) plane of Pt or a Pt alloy can be 2.7 nm or more and 4.8 nm or less. In addition, as another embodiment, the crystallite size of the (220) plane of Pt or a Pt alloy can be 2.0 nm or more and 4.6 nm or less.

[0057] By making the crystallite size of the (220) surface of the Pt or Pt alloy of the catalyst particles within the above range, it is possible to achieve both initial activity and durability. When the crystallite size of the (220) surface of the Pt or Pt alloy is less than 2.5 nm, the initial activity is expected to increase due to the high metal surface area of ​​the Pt or Pt alloy, but the activity after durability is reduced due to the coarsening caused by the dissolution / reprecipitation of Pt and the movement and aggregation of the catalyst metal particles on the carrier. When the crystallite size of the (220) surface of the Pt or Pt alloy is greater than 5.0 nm, the coarsening caused by the dissolution / reprecipitation of Pt and the movement and aggregation of the catalyst metal particles on the carrier are unlikely to occur, and the durability is expected to increase, but the initial activity is reduced due to the low metal surface area of ​​the Pt or Pt alloy. It should be noted that the "metal surface area" is the "surface area of ​​the catalyst particles" described later.

[0058] Here, the crystallite size of the catalyst particles corresponds to the average particle size calculated from the metal surface area and the catalyst loading, or the average particle size determined from a transmission electron microscope image. The crystallite size of the catalyst represents the particle size of the catalyst. In other words, the particle size of the catalyst is determined by the crystallite size of the catalyst.

[0059] The surface area of ​​the catalyst particles composed of Pt or Pt alloy of the present invention can be set to 40m 2 / g or above and 80m 2 / g or less.

[0060] By setting the surface area of ​​the catalyst particles to the above range, both initial activity and durability can be achieved. 2 / , the initial activity is expected to increase, but the activity after durability decreases due to the coarsening caused by the dissolution / reprecipitation of Pt and the aggregation of catalyst metal particles on the carrier. When the surface area of ​​the catalyst particles composed of Pt or Pt alloy is less than 45m 2 / g, the dissolution / reprecipitation of Pt leading to coarsening and the migration and aggregation of catalyst metal particles on the carrier are unlikely to occur, and durability is expected to be improved. However, the low metal surface area of ​​Pt or Pt alloy leads to a decrease in initial activity. As another option, the surface area of ​​the catalyst particles composed of Pt or Pt alloy can be 43m 2 / g and above 75m 2 / g or less. In addition, as another solution, the surface area of ​​the catalyst particles composed of Pt or Pt alloy can be 46m 2 / g or above and 70m 2 / g or less.

[0061] The catalyst particles contained in the catalyst-supported carbon of the present invention contain platinum (Pt) or a platinum alloy as the catalyst metal. The platinum alloy is generally composed of Pt and one or more other metals. In this case, examples of the one or more other metals forming the platinum alloy include titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), gallium (Ga), yttrium (Y), zirconium (Zr), molybdenum (Mo), lanthanum (La), cerium (Ce), gadolinium (Gd), hafnium (Hf), tantalum (Ta), ruthenium (Ru), iridium (Ir), palladium (Pd), osmium (Os), and rhodium (Rh). When the catalyst particles contained in the catalyst-supported carbon of the present invention contain the above-mentioned catalyst metals, an electrode catalyst having high activity and high durability can be obtained.

[0062] The composition and loading density of the catalyst particles contained in the catalyst-supported carbon can be determined, for example, by dissolving the catalyst metal contained in the catalyst particles from the catalyst-supported carbon using aqua regia and then quantifying the catalyst metal ions in the solution using an inductively coupled plasma (ICP) emission spectrometer.

[0063] The catalyst particles contained in the catalyst-supporting carbon have a loading density of 10% by mass or more and 70% by mass or less, more preferably 20% by mass or more and 50% by mass or less. In the present invention, the loading density of the catalyst particles refers to the percentage of the mass of the catalyst particles relative to the total mass of the catalyst-supporting carbon.

[0064] By setting the supporting density of the catalyst particles within the above range, the thickness of the electrode catalyst layer can be controlled to be suitable for proton transfer, gas diffusion, and discharge of generated water when the electrode catalyst layer is formed.

[0065] The average interplanar spacing d of the (002) plane of the carbon support based on X-ray diffraction is 002 It can be set to 0.345 nm or less. 002 The average interplanar spacing of graphite, i.e., 0.3335 nm, is close to that of graphite. The stacked structure of the carbon hexagonal network becomes stable, and even if the carbon support is exposed to high temperatures in the atmosphere, the structure is not easily destroyed, which can alleviate the oxidative degradation of the carbon support. As another solution, the average interplanar spacing d of the (002) plane based on X-ray diffraction is 0.3335 nm. 002 It can be above 0.3405nm.

[0066] The peak intensity ratio (G / D) of the G band and the D band of the above-mentioned carbon carrier measured by Raman spectroscopy can be 0.8 or more. The peak intensity ratio (G / D) of the G band and the D band represents the existence ratio of the edge portion of the carbon hexagonal mesh surface. The higher the G / D, the smaller the existence ratio of the edge portion. The edge portion of the carbon hexagonal mesh surface is the starting point of the oxidative degradation of the carbon carrier. In order to alleviate the oxidative degradation of the carbon carrier, it is hoped that the edge portion is small, that is, the G / D is high. As another option, the peak intensity ratio (G / D) of the G band and the D band measured by Raman spectroscopy can be 0.84 or more and 2.5 or less. In addition, as another option, the peak intensity ratio (G / D) of the G band and the D band measured by Raman spectroscopy can be 0.9 or more and 2.0 or less.

[0067] The peak full width at half maximum (G-FWHM) of the G band of the carbon support measured by Raman spectroscopy can be 40 cm -1 Over 60cm -1 . G-FWHM represents the ratio of graphite, which is a stacked ordered structure of carbon hexagonal meshes, to a stacked chaotic layer structure of carbon hexagonal meshes. The smaller the G-FWHM, the more the graphitization proceeds, and a structure close to graphite is formed. By performing graphitization, the irregular structure that becomes the starting point of degradation of the carbon support can be reduced, and the structural uniformity can be improved. That is, by promoting graphitization, the oxidative degradation of the carbon support can be alleviated. As another option, the peak half width (G-FWHM) of the G band measured by Raman spectroscopy can be 41 cm -1 Over 59cm -1 In addition, as another embodiment, the full width at half maximum (G-FWHM) of the G band measured by Raman spectroscopy can be 42 cm -1 Over 58cm -1 the following.

[0068] Here, the alleviation of oxidative degradation and structural uniformity can be expressed by the combustion temperature of the carbon support in an atmospheric atmosphere and the half-width of the combustion peak. The combustion temperature is determined by the temperature at which the weight of the carbon support in an atmospheric atmosphere decreases sharply, while the half-width of the combustion peak is determined by the difference between the combustion temperature at which the weight of the carbon support in an atmospheric atmosphere begins to decrease sharply and the combustion starting temperature at which the weight decrease begins.

[0069] The combustion temperature of the catalyst-supported carbon in the present invention may be 400°C or higher, and the half-width of the combustion peak may be 100°C or lower. If the combustion temperature is lower than 400°C or the half-width of the combustion peak is greater than 100°C, sufficient corrosion resistance cannot be ensured, resulting in reduced durability. As another embodiment, the combustion temperature of the catalyst-supported carbon may be 410°C or higher and 550°C or lower. In addition, as another embodiment, the combustion temperature of the catalyst-supported carbon may be 420°C or higher and 500°C or lower. As another embodiment, the half-width of the combustion peak of the catalyst-supported carbon may be 2°C or higher and 40°C or lower. In addition, as another embodiment, the half-width of the combustion peak of the catalyst-supported carbon may be 4°C or higher and 20°C or lower.

[0070] Furthermore, imparting acidic functional groups to the carbon support of the catalyst-supporting carbon can achieve higher activity. While the reason for this is not entirely clear, the present inventors speculate as follows. Specifically, imparting acidic functional groups to the catalyst renders the catalyst surface hydrophilic. This results in improved water retention and, consequently, improved proton conductivity.

[0071] The method for imparting an acidic functional group to a carbon support is not particularly limited, and examples thereof include a method of suspending the carbon support or catalyst-supporting carbon in an acidic solution and heating the suspension.

[0072] The amount of acidic functional groups per unit weight of the carbon support is not particularly limited, but is preferably 1 mmol / g or more.

[0073] Here, the amount of acidic functional groups per unit weight of the carbon support is determined by the following methods: a method of calculating from the amount of carbon monoxide, carbon dioxide, or water desorbed by a temperature programmed reaction (TPR method) under a helium atmosphere, a method of calculating from the peak area of ​​the C-1s peak measured by X-ray photoelectron spectroscopy (XPS), a method of calculating from the titration amount in an acid-base titration method (Boehm method), etc.

[0074] Example

[0075] The present invention will be described in further detail below based on Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0076] (Example 1)

[0077] 1. Modulation of carbon support

[0078] 78Mn-22C (mol%) was placed in contact with molten zinc at 600°C for one hour to undergo a decomponentation reaction, followed by furnace cooling. To remove the metal component from the composite composed of porous carbon and the metal component, the composite was treated with an acid in aqueous nitric acid for 72 hours, filtered, and dried to obtain porous carbon. Subsequently, graphitization was performed at 2000°C.

[0079] 2. Modulation of catalyst-supported carbon

[0080] 1.00 g of the carbon support was suspended in 80.00 g of pure water. 8.33 g of an aqueous solution of dinitrodiamine platinum nitric acid containing 8.0 wt% platinum and 4.80 g of L-ascorbic acid were added to the resulting suspension. After thorough stirring, the suspension was heated at 90°C for 1 hour using a reflux reactor to support the platinum catalyst particles on the carbon support. The suspension was then allowed to cool to room temperature, filtered to remove the resulting catalyst-supported carbon, and dried at 60°C for 12 hours. After drying, the suspension was calcined at 400°C for 1 hour in an atmosphere furnace (HIG B-4060) with a nitrogen flow of 50 L / min to reduce the platinum particles.

[0081] (Example 2)

[0082] Platinum-supported carbon was obtained in the same manner as in Example 1, except that the acid treatment was performed for 24 hours in the carbon support preparation step.

[0083] (Example 3)

[0084] Platinum-supported carbon was obtained in the same manner as in Example 1, except that the carbon support was brought into contact with molten metal zinc for 2 hours in the step of preparing the carbon support.

[0085] (Example 4)

[0086] 1.00 g of the platinum-supported carbon obtained in Example 3 was suspended in 75.00 g of a 0.5 mol / L aqueous nitric acid solution. The resulting suspension was thoroughly stirred and then heated at 80°C for 21 hours in a reflux reactor to adjust the surface functional groups of the platinum-supported carbon. After cooling to room temperature, the resulting platinum-supported carbon was filtered out and dried at 60°C for 12 hours.

[0087] (Example 5)

[0088] Platinum-supported carbon was obtained in the same manner as in Example 4, except that the acid treatment was performed twice in the carbon support preparation step.

[0089] (Example 6)

[0090] Platinum-supported carbon was obtained in the same manner as in Example 5 except that the heating temperature during the adjustment of the surface functional groups in the preparation step of the platinum-supported carbon was set to 90°C.

[0091] (Example 7)

[0092] Platinum-supported carbon was obtained in the same manner as in Example 4, except that the acid treatment was changed from aqueous nitric acid solution to aqueous hydrochloric acid solution in the carbon support preparation step.

[0093] (Example 8)

[0094] Platinum-supported carbon was obtained in the same manner as in Example 4, except that boron and nitrogen were doped into carbon in the carbon support preparation step.

[0095] (Example 9)

[0096] Platinum-supported carbon was obtained in the same manner as in Example 4 except that the temperature of the molten metal zinc in the carbon support preparation step was set to 650°C.

[0097] (Example 10)

[0098] Platinum-supported carbon was obtained in the same manner as in Example 6 except that the temperature of the molten metal zinc in the carbon support preparation step was set to 680°C.

[0099] (Example 11)

[0100] Platinum-supported carbon was obtained in the same manner as in Example 6 except that the firing temperature in the preparation step of the catalyst-supported carbon was set to 250°C.

[0101] (Example 12)

[0102] Platinum-supported carbon was obtained in the same manner as in Example 6 except that the firing temperature in the preparation step of the catalyst-supported carbon was set to 1000°C.

[0103] (Example 13)

[0104] 0.50 g of cobalt nitrate hexahydrate and 1.0 g of pure water were added to the 1.00 g of platinum-supported carbon obtained in Example 6, and the mixture was kneaded to obtain a platinum-cobalt-supported carbon slurry. The obtained slurry was dried at 60 ° C for 12 hours, sintered at 800 ° C for 1 hour under a flow of 4.0% hydrogen / nitrogen 50 L / min, and a platinum-cobalt alloy-supported carbon powder was obtained. The obtained 1.00 g of platinum-cobalt alloy-supported carbon powder was suspended in 15.00 g of 1.0 mol / L nitric acid aqueous solution, and after the obtained suspension was fully stirred, it was heated at 90 ° C for 1 hour using a reflux reaction apparatus to remove the remaining cobalt that was not alloyed with platinum and adjust the surface functional groups of the carbon support. Then, after cooling to room temperature, the obtained platinum-cobalt alloy-supported carbon was filtered out and dried at 60 ° C for 12 hours to obtain a platinum-cobalt alloy-supported carbon.

[0105] Comparative Example (Comparative Example 1)

[0106] Platinum-supported carbon was obtained in the same manner as in Example 1 except that Ketjenblack (EC300J manufactured by Lion) was used as the carbon support.

[0107] (Comparative Example 2)

[0108] Platinum-supported carbon was obtained in the same manner as in Example 1, except that the graphitization treatment temperature in the carbon support preparation step was changed to 2800°C.

[0109] The following physical properties were evaluated for the carbon supports of each catalyst-supported carbon, the catalyst particles of each catalyst-supported carbon, and each catalyst-supported carbon in the Examples and Comparative Examples. The results are shown in Table 1. [Determination of BET Specific Surface Area of ​​Carbon Support of Catalyst-supported Carbon]

[0110] About BET specific surface area (m 2 / g), weighed about 50 mg of the sample (carbon support), and vacuum dried at 300 ° C for 4 hours. For the obtained dried sample, an automatic specific surface area measuring device (3Flex manufactured by Micromeritics) was used to obtain a nitrogen adsorption isotherm by a gas adsorption method using nitrogen, and the specific surface area was determined by a multi-point method based on the BET method.

[0111] [Measurement of Pore Diameter of Carbon Support of Catalyst-Supporting Carbon]

[0112] Regarding the pore diameter (nm), about 50 mg of a sample (carbon support) was weighed and vacuum-dried at 300°C for 4 hours. The dried sample was then subjected to an automatic surface area measurement apparatus (3Flex manufactured by Micromeritics) to obtain a nitrogen adsorption isotherm using nitrogen gas. The pore diameter was determined by a pore distribution analysis method based on the BJH method from the pore diameter with the highest frequency in the pore distribution curve obtained using non-graphite carbon as the standard isotherm.

[0113] [Crystalline size L of the carbon support of the catalyst-supported carbon C Dough interval d 002 Determination of

[0114] About crystallite size Lc and interplanar spacing d 002 The XRD pattern of the carbon support was obtained by using CuKα radiation as a radiation source and an X-ray diffraction device (MiniFlex600 manufactured by Rigaku) ​​under the following measurement conditions. The obtained XRD pattern was analyzed using integrated powder X-ray analysis software (PDXL2 manufactured by Rigaku) ​​to determine the L peak of the C(002) plane near 26°. Cand d 002 .

[0115] XRD measurement conditions

[0116] Radiation source: CuKα (ray focus), wavelength:

[0117] Operating axis: 2θ / θ, measurement method: continuous, counting unit: cps;

[0118] Starting angle: 10.0°, ending angle: 90.0°, cumulative number of times: 1;

[0119] Sampling width: 0.02°, scanning speed: 1° / min;

[0120] Voltage: 40kV, current: 15mA;

[0121] Incident parallel slit: Soller 2.5°, length limiting slit: 10 mm;

[0122] Receiving parallel slit: Soller 2.5°, receiving slit: 13mm;

[0123] Offset angle: 0°;

[0124] Goniometer radius: 150mm, optical system: centralization method;

[0125] Slit: Slit for D / teX Ultra;

[0126] Detector: D / teX Ultra 250;

[0127] Ni-Kβ filter: 0.03mm.

[0128] [Measurement of Crystallite Size of Catalyst-Supported Carbon Catalyst Particles]

[0129] The crystallite size of the catalyst particles was measured using CuKα radiation as a radiation source using an X-ray diffractometer (SmartLab, manufactured by Rigaku) ​​under the following measurement conditions to obtain an XRD pattern of the catalyst-supported carbon. The resulting XRD pattern was analyzed using integrated powder X-ray analysis software (PDXL, manufactured by Rigaku) ​​to determine the crystallite size based on the peak near 67.5° on the Pt (220) plane.

[0130] XRD measurement conditions

[0131] Radiation source: CuKα (ray focus), wavelength:

[0132] Operating axis: 2θ / θ, measurement method: continuous, counting unit: cps;

[0133] Starting angle: 10.0°, ending angle: 90.0°, cumulative number of times: 1;

[0134] Sampling width: 0.01°, scanning speed: 4° / min;

[0135] Voltage: 40kV, current: 30mA;

[0136] Incident parallel slit: Soller 5.0°, length limiting slit: 10 mm;

[0137] Receiving parallel slit: Soller 5.0°, receiving slit: 20mm;

[0138] Offset angle: 0°;

[0139] Goniometer radius: 300mm, optical system: centralization method;

[0140] Slit: Slit for D / teX Ultra;

[0141] Detector: D / teX Ultra 250;

[0142] Ni-Kβ filter: None.

[0143] [Measurement of Surface Area and Particle Size of Catalyst-Supported Carbon Catalyst Particles]

[0144] The surface area of ​​the catalyst particles was measured by weighing approximately 20 mg of a sample (catalyst-supported carbon) and pre-treating it at 130°C under a hydrogen flow for 1 hour. The sample was then measured using a metal dispersion analyzer (BELMETAL3, manufactured by Microtrac BEL) using a pulse method using carbon monoxide gas. The surface area and catalyst particle size were determined from the amount of carbon monoxide adsorbed.

[0145] [Determination of Combustion Temperature and Half Width of Combustion Peak of Catalyst-Supported Carbon]

[0146] The combustion temperature of the catalyst-supported carbon was measured using a differential thermal analyzer (Rigaku Thermoplus EVO2) in an air atmosphere at a temperature increase of 2.0°C / minute to obtain a DTA-TG pattern. The combustion temperature was determined by defining the temperature at which d(TG) / d(T), the temperature derivative of the obtained TG pattern, reached a minimum. Here, TG represents the weight loss rate, and T represents the temperature. Furthermore, the temperature at which d(TG) / d(T) reached 1 / 10 of its minimum value was defined as the combustion onset temperature. The half-width of the combustion peak was calculated as: combustion peak half-width = combustion temperature - combustion onset temperature.

[0147] [Measurement of G / D Ratio of Catalyst-Supported Carbon]

[0148] The peak intensity ratio (G / D ratio) of the G band and the D band of the carbon support of the catalyst-supported carbon and the peak full width at half maximum (G-FWHM) of the G band were obtained using a Raman spectrometer (inVia Raman microscope manufactured by Renishaw). The obtained Raman spectrum was analyzed using analysis software (WiRE4.3 manufactured by Renishaw). The Raman shift of 1570 cm was used to determine the peak intensity ratio (G / D ratio) of the G band and the peak full width at half maximum (G-FWHM) of the G band. -1 The peak intensity and half-peak width of the G band are determined by the peak near 1340 cm -1 The peak intensity of the D band was determined from the peak near the D band, and the G / D ratio was calculated.

[0149] Raman spectroscopy conditions

[0150] Excitation laser wavelength: 532nm;

[0151] Exposure time: 10 seconds;

[0152] Laser power: 0.6mW

[0153] Cumulative number of times: 3 times.

[0154]

[0155] In Examples 1 to 13, no matter which catalyst-supported carbon is used, the BET specific surface area of ​​the carbon support is 300 m 2 / g and above 450m 2 / g or less, and has a pore characteristic of mesopores of 5.0nm or more and 20.0nm or less. In addition, regardless of which catalyst-supported carbon is used, the crystallite size L of the carbon support is c All are above 3.5nm and below 9nm, and show low d 002, high G / D ratio, and low G-FWHM, indicating that all carbon supports have been graphitized and have high structural uniformity. Furthermore, the combustion temperature of the catalyst-supported carbon is above 400°C, and the half-width at half maximum of the combustion peak is below 100°C, which can mitigate oxidative degradation of the carbon support.

[0156] In Comparative Example 1, the BET specific surface area of ​​the carbon support is as high as 300 m 2 / g or more. On the other hand, the crystallite size L of the carbon support c Furthermore, the combustion temperature of the catalyst-supported carbon is as low as 400° C. or less, which cannot alleviate the oxidative degradation of the carbon support.

[0157] In Comparative Example 2, although the carbon support has mesopores, the BET specific surface area is 300 m 2 / g or less. In addition, the crystallite size L of the carbon support is c is 3.5nm or more and shows low d 002 , high G / D ratio, and high G-FWHM, resulting in a graphitized carbon support with high structural uniformity. Furthermore, the catalyst-supported carbon has a combustion temperature of 400°C or higher and a combustion peak half-width of 100°C or lower, which mitigates oxidative degradation of the carbon support.

[0158] Regarding the catalyst-supported carbons of Examples and Comparative Examples, membrane electrode assemblies for evaluating single cells of polymer electrolyte fuel cells were prepared according to the following method.

[0159] 1. Electrode Modulation

[0160] 0.75 g of catalyst-supported carbon, 2.20 g of pure water, 2.20 g of ionomer (Nafion DE2020CS manufactured by Chemours), 2.60 mL of 2-propanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 2.00 mL of 1-propanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 0.50 mL of ethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) of each embodiment and comparative example were mixed and dispersed for 1 hour using a planetary ball mill, and then degassed using a mixer for 5 minutes to prepare a cathode catalyst slurry. The electrode catalyst slurry was applied to one side of a PTFE sheet (manufactured by NICHIAS (NAFLON (registered trademark) sheet, thickness 200 μm) using a spatula and dried at 120° C. under vacuum for 60 minutes to form a cathode catalyst layer on the PTFE sheet.

[0161] 0.75 g of FC-I2 (IFPC40-II manufactured by Ishifuku Metal Industries, Ltd.), a reference catalyst of the Fuel Cell Catalyst Research Group of the Japan Catalyst Association, 5.40 g of pure water, 2.20 g of ionomer (Nafion DE2020CS manufactured by Chemours), 3.50 mL of 2-propanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 2.70 mL of 1-propanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 0.50 mL of ethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed and dispersed in a planetary ball mill for 1 hour, and then degassed in a mixer for 5 minutes to prepare an anode catalyst slurry. The electrode catalyst slurry was applied to one side of a PTFE sheet (NAFLON (registered trademark) sheet manufactured by NICHIAS, with a thickness of 200 μm) using a spatula and dried at 120° C. under vacuum for 60 minutes to form an anode catalyst layer on the PTFE sheet.

[0162] 2. MEA Fabrication

[0163] The solid polymer electrolyte membrane (Nafion NR-211 manufactured by Chemours, 200mm×200mm square) was sandwiched and overlapped so that the electrode catalyst layer-forming side of the two previously prepared PTFE sheets of electrode catalyst layer was on the inner side. A precision heating and pressing device (CYPM manufactured by Shinto Industry) was used to heat press at 130°C for 10 minutes with a pressure of 1.5kN. After cooling, only the PTFE sheet was peeled off, thereby obtaining a joint body with the electrode catalyst layer transferred to the solid polymer electrolyte membrane. At this time, the transfer rate of the electrode catalyst layer from the PTFE sheet to the solid polymer electrolyte was 100%, and the electrode catalyst layer per 1cm on the solid polymer electrolyte membrane was 100%. 2 The weight of platinum per surface of the electrode catalyst layer was 0.30 mg.

[0164] Next, the previously prepared assembly was sandwiched between two gas diffusion layers (GDL 28BC manufactured by SGL, 100 mm x 100 mm square), and sealing material (NAFLON (registered trademark) sheets manufactured by NICHIAS, 150 μm thick and 80 μm thick stacked) was placed on the periphery of the electrode catalyst layer and the gas diffusion layer to form an MEA.

[0165] Thereafter, a gold-plated current collector with gas flow channels was placed on the fabricated MEA, and the collector was sandwiched and fastened with stainless steel end plates to a predetermined surface pressure, thereby obtaining a single cell of a polymer electrolyte fuel cell.

[0166] The following power generation evaluation was performed on MEAs using the catalyst-supported carbons of the Examples and Comparative Examples. The results are shown in Table 2.

[0167] [Measurement of Initial Activity of MEA Using Catalyst-Carbon-Supported Carbon]

[0168] Using a fuel cell power generation evaluation device (manufactured by Chino) and an electron loading device (PLZ164WA manufactured by Kikusui Electronics Co., Ltd.), IV measurements described in the "Battery (Cell) Evaluation and Analysis Procedure (December 2012)" published by the New Energy and Industrial Technology Development Organization (NEDO) were performed. The mass activity was calculated from the current density at 0.85 V and the platinum loading to determine the initial activity.

[0169] [Durability Measurement of MEA Using Catalyst-Carrying Carbon]

[0170] According to the potential cycle (start-stop) test method described in the "Battery (cell, single cell) Evaluation and Analysis Procedure (December 2012)" published by the New Energy / Industrial Technology Development Organization (NEDO), a durability test of accelerated degradation of the carbon carrier of the catalyst-supported carbon was carried out using a fuel cell power generation evaluation device (manufactured by Chino) and a constant potentiostat / constant galvanostat (PGSTAT128N manufactured by Metrohm). The durability was determined by calculating the number of potential cycles at which the electrochemical effective surface area ECSA was 50% of the value before the potential cycle (start-stop) test.

[0171]

[0172] In Examples 1 to 13, the crystallite size (L c ) is 3.5 nm or more and 9 nm or less, and the BET specific surface area (SSA) based on nitrogen adsorption measurement is 300 m 2 / g and above 450m 2 / g or less, it combines both microcrystalline size and BET specific surface area in a high dimensional manner, so it has an initial activity of more than 60A / g by mass activity, and the number of ECSA 50% maintenance cycles is more than three times that of previous technologies, that is, more than 1000 times, which can obtain a membrane electrode assembly with excellent durability.

[0173] In Comparative Example 1, a membrane electrode assembly was obtained, the BET specific surface area (SSA) of which was 300 m 2 / g or more, while the crystallite size is as small as 3.5nm or less, so it has an initial activity as high as 60A / g or more. On the other hand, the ECSA 50% maintenance cycle number is less than 500, and the durability is low.

[0174] In Comparative Example 2, a membrane electrode assembly was obtained in which the crystallite size was as high as 3.5 nm or more, while the BET specific surface area (SSA) measured by nitrogen adsorption was as low as 300 m 2 / g or less, and the ECSA 50% maintenance cycle number is 10,000 or more, indicating excellent durability; however, the mass activity is 50 A / g or less, indicating low initial activity.

[0175] Industrial Applicability

[0176] The catalyst-supported carbon disclosed herein can mitigate oxidative degradation of the carbon support in atmospheric atmosphere, exhibit high initial activity, and exhibit excellent durability. Therefore, the catalyst-supported carbon disclosed herein can be used as an electrode catalyst in membrane electrode assemblies for polymer electrolyte fuel cells.

Claims

1. A catalyst-supported carbon, characterized in that: It is a catalyst-supported carbon in which catalyst particles composed of platinum or a platinum alloy are supported on a carbon support composed of porous carbon. The carbon support of the catalyst-supported carbon has a crystallite size (Lc) of 3.5 nm or more and 9 nm or less as determined by X-ray diffraction, and The BET specific surface area (SSA) measured by nitrogen adsorption was 300 m 2 / g and above 450m 2 / g or less, and a pore diameter of 5.0 nm or more and 20.0 nm or less, The catalyst particles composed of platinum or a platinum alloy of the catalyst-supported carbon have a crystallite size of 2.5 nm or more and 5.0 nm or less based on X-ray diffraction, and The surface area of ​​the catalyst particles was determined to be 40 m 2 / g~80m 2 / g.

2. The catalyst-supported carbon according to claim 1, characterized in that: The combustion temperature of the catalyst-supported carbon in air atmosphere measured by differential thermal analysis is above 400°C, and The half-value width of the combustion peak is 100°C or less.

3. The catalyst-supported carbon according to claim 1, characterized in that: The average interplanar spacing d of the (002) plane of the carbon support of the catalyst-supported carbon is based on X-ray diffraction. 002 It is less than 0.345nm.

4. The catalyst-supported carbon according to claim 2, characterized in that: The average interplanar spacing d of the (002) plane of the carbon support of the catalyst-supported carbon is based on X-ray diffraction. 002 It is less than 0.345nm.

5. The catalyst-supported carbon according to claim 1, characterized in that: The carbon support of the catalyst-supported carbon has a peak intensity ratio (G / D) of the G band to the D band measured by Raman spectroscopy of 0.8 or more, and The full width at half maximum (FWHM) of the G band is 40 cm -1 Over 60cm -1 the following.

6. The catalyst-supported carbon according to claim 2, characterized in that: The carbon support of the catalyst-supported carbon has a peak intensity ratio (G / D) of the G band to the D band measured by Raman spectroscopy of 0.8 or more, and The full width at half maximum (FWHM) of the G band is 40 cm -1 Over 60cm -1 the following.

7. The catalyst-supported carbon according to claim 1, characterized in that: The catalyst-supported carbon has acidic functional groups imparted to the carbon support as surface functional groups.

8. The catalyst-supported carbon according to claim 2, characterized in that: The catalyst-supported carbon has acidic functional groups imparted to the carbon support as surface functional groups.

9. A membrane electrode assembly for a polymer electrolyte fuel cell, characterized in that: The catalyst-supported carbon according to claim 1 is contained in an electrode.

10. A solid polymer fuel cell, characterized in that: The catalyst-supporting carbon according to claim 1 is contained in an electrode of a membrane electrode assembly.

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