Method for producing carbon support and catalyst composite for fuel cell

Abstract

The invention provides a manufacturing method of a carbon carrier and a catalyst composite for a fuel cell. A method for manufacturing a carbon support having improved porosity and surface hydrophobicity, wherein a carbon support having improved porosity and surface hydrophobicity can be manufactured by activating a carbon support by controlling a pressure factor of an activation gas.

Description

Method for manufacturing carbon support and catalyst composite for fuel cells Technical Field

[0001] This disclosure relates to a method for manufacturing a carbon support having improved porosity and surface hydrophobicity. Furthermore, this disclosure relates to a method for manufacturing a carbon support, wherein, in some embodiments, the carbon support with improved porosity and surface hydrophobicity is manufactured by activating the carbon support by controlling the pressure factor of an activating gas. Background Technology

[0002] The electrode catalyst layer for proton exchange membrane fuel cells (PEMFCs) consists of a carbon support loaded with platinum and other materials, and an ionomer acting as a binder. Notably, platinum and its alloy catalysts immobilized on the carbon support are crucial for the overall performance and durability of the fuel cell. The effectiveness of these catalysts is significantly influenced by the structural properties and characteristics of the catalyst particles and the carbon support. Therefore, optimizing catalyst development is of paramount importance and urgency for enhancing the performance and durability of hydrogen fuel cell vehicles.

[0003] In such fuel cell catalysts, the carbon support acts as an electronic conductor, transferring electrons to the catalyst particles. Furthermore, the carbon support serves as a carrier for distributing small-sized catalyst nanoparticles to enhance catalytic activity. Therefore, the porosity of the carbon support is most directly related to reducing the amount of metal catalyst used to improve fuel cell performance and ensure price competitiveness, as catalysts with dimensions of a few nanometers can be uniformly distributed while reducing mass transfer resistance in the high current density range.

[0004] Activation processes are widely recognized as an effective technique for enhancing the porosity of carbon supports, achieved through the oxidation and etching of the carbon surface at high temperatures. Generally, activation methods are classified into two main types: chemical activation, which involves high-temperature heat treatment in conjunction with chemical reagents, and physical activation, which utilizes high-temperature heat treatment with oxidizing gases such as oxygen, steam, or carbon dioxide. Both methods aim to increase the surface area and porosity of the carbon support, thereby improving its performance in various applications. Chemical activation has the advantage of high activation efficiency, but it presents economic and environmental problems due to low yields and the need for additional washing processes to remove chemical reagents. Conversely, despite its lower activation efficiency, physical activation offers economic advantages because it does not require additional washing processes, and research is underway to improve the activation efficiency of physical activation methods. In particular, physical activation, due to its use of oxidizing gases, offers more controllable reactivity than chemical activation processes (which are existing solid-state reactions), but it still suffers from the following problems: very low yields due to the decreasing forward reaction rate and activation efficiency with increasing product concentration over time, and the tendency for carbon to become over-oxidized, reducing surface durability.

[0005] When developing activation methods for fuel cells, it is essential to simultaneously address surface durability and yield while ensuring sufficient porosity. To advance the development of next-generation carbon supports that effectively balance durability and performance enhancement, innovative synthetic strategies capable of achieving these key properties in a balanced manner are urgently needed. The present invention facilitates the development of carbon supports that not only meet the stringent requirements of fuel cell applications but also exhibit improved performance related to efficiency, porosity, and carbon support durability. Summary of the Invention

[0006] This disclosure addresses challenges in carbon support fabrication, with the primary objective of providing a method for enhancing porosity through controlled pressure cycling. This novel approach aims to significantly improve the performance of electrode catalysts used in fuel cells, thereby contributing to advancements in fuel cell technology. By focusing on optimizing the structural properties of the carbon support, the method disclosed herein overcomes limitations observed in conventional techniques and enhances the overall efficiency and effectiveness of fuel cell systems.

[0007] In some aspects, this disclosure provides a method for manufacturing a carbon support that, compared with existing methods, improves activation efficiency, thereby controlling pore size, improving porosity, and increasing yield.

[0008] In some respects, this disclosure provides a method for manufacturing a carbon support that not only improves cell performance by enhancing the porosity of the carbon support, but also increases durability by improving surface hydrophobicity.

[0009] In some aspects, this disclosure provides a method for manufacturing a carbon support, the method comprising activating the carbon support by reacting it with an activation gas in a pressure-controlled cycle.

[0010] In some embodiments, the carbon support includes any one selected from porous carbon, activated carbon, carbon black, carbon nanotubes, graphene, and any combination thereof.

[0011] In some embodiments, the activating gas includes any one selected from air, oxygen (O2), carbon dioxide (CO2), water vapor (H2O), hydrogen peroxide (H2O2), ozone (O3), and any combination thereof.

[0012] In some implementations, to avoid being bound by theory, the pressure cycle control method means that the pressure of the activation gas supplied to the carbon support cycles between a lower limit pressure and an upper limit pressure. In some implementations, the lower limit pressure can be 0 bar. g Up to 0.1 bar g Within a certain range, and in some implementations, the upper limit pressure can be 0.5 bar. g Up to 1 bar g .

[0013] In some embodiments, the activated carbon support is subjected to a temperature of 800°C to 1200°C for 0.1 to 6 hours.

[0014] In some embodiments, the method includes subjecting the carbon support to an oxidative heat treatment prior to activating the carbon support.

[0015] Therefore, in some embodiments, the oxidative heat treatment includes a process of oxidizing the surface of the carbon support by reacting with an oxidizing gas.

[0016] In some embodiments, the oxidizing gas includes any one selected from air, oxygen (O2), carbon dioxide (CO2), water vapor (H2O), hydrogen peroxide (H2O2), ozone (O3), and any combination thereof.

[0017] In addition, in some embodiments, the oxidative heat treatment is carried out at a temperature of 150°C to 600°C for 0.5 to 5 hours.

[0018] In some embodiments, the method further includes subjecting the activated carbon support to a reducing heat treatment after activation.

[0019] In some embodiments, the reduction heat treatment includes a process of reducing the surface of the activated carbon support by reacting with a reducing gas.

[0020] In some embodiments, the reducing gas includes any one selected from hydrogen (H2), a mixture of hydrogen and an inert gas, ammonia (NH3), and any combination thereof.

[0021] In some embodiments, the reduction heat treatment is carried out at a temperature of 500°C to 1100°C for 0.1 to 6 hours.

[0022] Furthermore, in some embodiments, the reduction heat treatment includes a process of reducing the surface of the activated carbon support by reacting the activated carbon support with a reducing gas in a pressure-cycle controlled manner.

[0023] Here, the pressure circulation control method for the reducing gas can be interpreted as the pressure of the reducing gas supplied to the activated carbon support circulating between a lower limit pressure and an upper limit pressure, where the lower limit pressure can be 0 bar. g Up to 0.1 bar g And the upper limit pressure can be 0.5 bar. g Up to 1 bar g .

[0024] In some aspects, this disclosure provides a method for manufacturing a carbon support, the method comprising subjecting the carbon support to an oxidative heat treatment, activating the pretreated carbon support by reacting it with an activating gas, and subjecting the activated carbon support to a reducing heat treatment, wherein activating the pretreated carbon support comprises activating the carbon support by reacting it with an activating gas in a pressure-cycle controlled manner.

[0025] In some embodiments, hydrophilic groups are formed on the surface of the carbon support by oxidative heat treatment, and in other embodiments, the hydrophilic groups are removed by reduction heat treatment to make the carbon support hydrophobic.

[0026] In some aspects, this disclosure provides a catalyst composite for fuel cells comprising a carbon support manufactured by the methods described above and a catalytic metal supported on the carbon support.

[0027] Details of one or more embodiments of this disclosure are set forth in the following description. Other features or advantages of this disclosure will become apparent from the following drawings, the detailed description of several embodiments, and the appended claims. Details of this disclosure are set forth in the following appended description. Although similar or equivalent methods and materials to those described herein may be used in the practice or testing of this disclosure, illustrative methods and materials are now described. Other features, objects, and advantages of this disclosure will be apparent from the specification and claims. In this specification and the appended claims, the singular form also includes the plural form unless the context clearly requires otherwise. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Attached Figure Description

[0028] Figure 1 shows the activation efficiency of carbon support under the condition that the pressure of the activating gas is kept constant.

[0029] Figure 2 is a graph showing the activation efficiency of the carbon support and the activation gas reaction under controlled pressure conditions in the system where the reaction occurs according to this disclosure.

[0030] Figure 3 illustrates the process of transforming the activated oxidized carbon support surface into a hydrophobic surface through reduction heat treatment.

[0031] Figure 4 shows transmission electron microscope images of the carbon supports according to Comparative Example 1 and Example 5.

[0032] Figure 5 shows transmission electron microscope images of the carbon supports according to Comparative Example 4 and Example 7.

[0033] Figure 6 schematically illustrates the crystal structure of carbon to explain the vertical crystallization size of the carbon support.

[0034] Figure 7 shows the analytical results of gas adsorption on the carbon support according to Comparative Example 1 and Examples 1 to 4.

[0035] Figure 8 shows the desorption curves of the carbon supports according to Comparative Example 1 and Examples 1 to 4.

[0036] Figure 9 shows the analytical results of gas adsorption on the carbon supports according to Comparative Example 4 and Examples 6 and 7.

[0037] Figure 10 shows the desorption curves of the carbon supports according to Comparative Example 4 and Examples 6 and 7.

[0038] Figure 11 shows the analytical results of the water adsorption and desorption capacity of the carbon supports according to Comparative Example 4 and Examples 6 and 7.

[0039] Figure 12 shows the durability test conditions using the membrane electrode assembly of Comparative Example 1 and Example 5.

[0040] Figure 13 shows the results of durability tests conducted on the membrane electrode assemblies of Comparative Example 1 and Example 5 under low temperature, high humidity, and pressurized conditions.

[0041] Figure 14 shows the degradation rate based on the durability test results according to Figure 13.

[0042] Figure 15 shows the results of durability tests conducted on the membrane electrode assemblies of Comparative Example 1 and Example 5 under high temperature, low humidity and pressurized conditions.

[0043] Figure 16 shows the durability degradation rate based on the durability test results according to Figure 15.

[0044] Figure 17 shows the durability test conditions using the membrane electrode assembly of Comparative Example 4 and Example 7.

[0045] Figure 18 shows the results of durability tests conducted on the membrane electrode assemblies of Comparative Example 4 and Example 7 under low temperature, high humidity, and pressurized conditions.

[0046] Figure 19 shows the durability degradation rate based on the durability test results according to Figure 18.

[0047] Figure 20 shows the results of durability tests conducted on the membrane electrode assemblies of Comparative Example 4 and Example 7 under high temperature, low humidity and pressurized conditions.

[0048] Figure 21 shows the durability degradation rate based on the durability test results according to Figure 20. Detailed Implementation

[0049] The above and other objects, features, and advantages of this disclosure will become more clearly understood from the following embodiments, taken in conjunction with the accompanying drawings. However, this disclosure is not limited to the embodiments disclosed herein and can be modified in various forms. These embodiments are provided to thoroughly explain this disclosure and to fully convey the spirit of this disclosure to those skilled in the art.

[0050] Throughout the accompanying drawings, the same reference numerals will indicate the same or similar elements. For clarity of this disclosure, the dimensions of the structures are depicted as larger than their actual dimensions. It will be understood that although terms such as “first” and “second” may be used herein to describe various elements, these elements are not limited by these terms. These terms are used only to distinguish one element from another. For example, a “first” element discussed below may be referred to as a “second” element without departing from the scope of this disclosure. Similarly, a “second” element may also be referred to as a “first” element. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise.

[0051] It will be further understood that when the terms "comprising," "including," "having," etc., are used in this specification, they specify the presence of the stated features, integers, steps, operations, elements, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Furthermore, it will be understood that when an element such as a layer, film, region, or sheet is referred to as being "on" another element, it may be directly on the other element, or there may be intermediate elements therein. Similarly, when an element such as a layer, film, region, or sheet is referred to as being "under" another element, it may be directly under the other element, or there may be intermediate elements therein.

[0052] Unless otherwise specified, all numerical values, specifications, and / or representations used herein to indicate the amounts of components, reaction conditions, polymer compositions, and mixtures should be considered approximate, including various uncertainties affecting the measurement, which inherently occur in obtaining these values, and therefore should in all cases be understood to be modified by the term "about". Furthermore, when numerical ranges are disclosed in this specification, the range is continuous and includes all values ​​from the minimum to the maximum of the range, unless otherwise specified. Additionally, when such ranges involve integer values, all integers from the minimum to the maximum are included, unless otherwise specified.

[0053] In this specification, when describing a range for a variable, it will be understood that the variable includes all values ​​contained within the endpoints described in the stated range. For example, the range “5 to 10” should be understood to include any subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc., as well as the individual values ​​of 5, 6, 7, 8, 9, and 10, and should also be understood to include any values ​​between valid integers within the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, etc. Similarly, the range “10% to 30%” will be understood to include subranges such as 10% to 15%, 12% to 18%, 20% to 30%, etc., as well as all integers, including values ​​up to 30% such as 10%, 11%, 12%, 13%, etc., and will also be understood to include any values ​​between valid integers within the stated range, such as 10.5%, 15.5%, 25.5%, etc.

[0054] In some aspects, this disclosure relates to a method for manufacturing a carbon support, the method comprising activating the carbon support by reacting it with an activation gas in a pressure-cycle controlled manner.

[0055] In some embodiments, the method of manufacturing a carbon support according to the present disclosure may optionally include subjecting the carbon support to an oxidative heat treatment prior to activating the carbon support.

[0056] In some embodiments, the method of manufacturing a carbon support according to the present disclosure may optionally include subjecting the activated carbon support to a reducing heat treatment after activation.

[0057] The steps are described in detail below.

[0058] activation

[0059] Carbon supports are commonly used as supports for catalysts in fuel cells. In some embodiments, the carbon support is activated to increase the efficiency of loading catalytic metals onto the carbon support.

[0060] Activating a carbon support can be a process of oxidizing its surface using an activating gas. During this process, hydrophilic groups such as -OH groups and -COOH groups can form on the surface of the carbon support.

[0061] In one embodiment, the activating gas includes any one selected from air, oxygen (O2), carbon dioxide (CO2), water vapor (H2O), hydrogen peroxide (H2O2), ozone (O3), and any combination thereof. Furthermore, any gas with oxidizing properties and capable of oxidizing the surface of the carbon support can be used without particular limitation.

[0062] When carbon dioxide or water vapor is used as the activating gas, the following reactions may occur on the surface of the carbon support.

[0063] - Scheme 1: C(graphite) + CO2(g) → 2CO(g)

[0064] - Scheme 2: C(graphite) + H₂O(g) → CO(g) + H₂(g)

[0065] Here, based on Le Chatelier's principle (which will be described more specifically using Scheme 1), in a system where an activation reaction occurs, the activation efficiency of the carbon support may be affected by the pressure of the activation gas.

[0066] The reaction index Q of Scheme 1 can be defined as follows.

[0067]

[0068] When the pressure of the activating gas supplied to the carbon support is constant, the denominator [CO2] of the reaction index Q is fixed, and the numerator [CO] of the reaction index is also fixed. 2 The reaction rate increases as the reaction proceeds. Therefore, the reaction exponent Q increases and the difference between it and the equilibrium exponent Kc decreases, thus reducing the forward reaction rate. Therefore, as shown in Figure 1, the activation efficiency may decrease.

[0069] The activated carbon support according to this disclosure may optionally include a process of reacting the carbon support with an activating gas in a pressure-cycle controlled manner. As shown in Figure 2, the pressure-cycle controlled manner means maintaining the amount of activating gas injected into a predetermined space, such as a chamber or tank (where the carbon support and the activating gas react), while controlling its discharge rate, so that the pressure of the activating gas in the system where the reaction occurs repeatedly increases and decreases. Furthermore, the pressure of the activating gas in the system where the reaction occurs can be controlled by pulsed injection of the activating gas into the carbon support.

[0070] Specifically, according to the pressure cycle control method, the pressure of the activating gas supplied to the carbon support can be applied to the system in which the reaction occurs, cycling between a lower limit pressure and an upper limit pressure. More specifically, the pressure of the activating gas can be continuously or discontinuously increased from a level equal to the lower limit pressure to a pressure equal to the upper limit pressure, and then continuously or discontinuously decreased back to a level equal to the lower limit pressure. This process can be repeated during the activation of the carbon support.

[0071] The lower limit pressure can be 0 bar. g Up to 0.1 bar g And the upper limit pressure can be 0.5 bar. g Up to 1 bar g For example, an activating gas can be supplied at a pressure of 0 bar. g Up to 1 bar g Between, preferably at 0.1 barg Up to 0.5 bar g The process repeats itself. If the lower limit pressure of the activating gas is too low, the activation efficiency may be excessively reduced, while if its upper limit pressure is too high, over-oxidation may occur during activation, which reduces activation efficiency and yield.

[0072] As shown in Figure 2, when the amount of injected activating gas is maintained while the pressure of the activating gas is controlled by adjusting the amount of discharged activating gas, the denominator [CO2] of the reaction index Q remains constant, and the numerator [CO] of the reaction index decreases repeatedly as the reaction proceeds. Therefore, the reaction index Q decreases periodically and the difference between it and the equilibrium index Kc remains constant, so the forward reaction may dominate and can improve the activation efficiency.

[0073] In this way, the method for manufacturing carbon support according to the present disclosure can improve porosity by increasing the specific surface area and roughness of the carbon support surface, and can expand the pore size by reacting the carbon support and the activation gas in a pressure-cycle controlled manner.

[0074] In this way, the loading efficiency and mass transfer of metal catalysts are improved due to the carbon support surface with controlled porosity.

[0075] In some embodiments, the carbon support comprises any one selected from porous carbon, activated carbon, carbon black, carbon nanotubes, graphene, and any combination thereof. Furthermore, in some embodiments, the carbon support comprises mesoporous carbon, examples of which include high-porosity mesoporous carbon and highly crystalline mesoporous carbon. Additionally, any conductive carbon material may be used without particular limitation.

[0076] In some embodiments, the activated carbon support is subjected to a temperature of 800°C to 1200°C for 0.1 to 6 hours.

[0077] In some embodiments, the activation of the carbon support is carried out at a temperature of 900°C to 1100°C. If the activation temperature is below 900°C, the activation efficiency may be reduced, while if the activation temperature exceeds 1100°C, the surface of the carbon support may be over-oxidized and the yield may be reduced.

[0078] Furthermore, in some embodiments, the carbon support is activated for 0.5 to 2 hours. If the activation time is less than 0.5 hours, the activation efficiency on the surface of the carbon support may be reduced and the porosity may not be adequately improved, while if the activation time exceeds 2 hours, the surface of the carbon support may be over-oxidized and the yield may be reduced.

[0079] Oxidation heat treatment

[0080] Meanwhile, direct activation on the carbon support without prior oxidative heat treatment results in low activation efficiency on the carbon surface. This low efficiency stems from the high acid resistance associated with reduced reactivity of the carbon surface, which can lead to prolonged activation time and reduced yield. Therefore, optimizing the activation process by incorporating oxidative heat treatment is crucial for enhancing the reactivity of the carbon support, thereby improving activation efficiency and overall yield in the manufacturing process.

[0081] Therefore, in order to improve the activation efficiency of the carbon support, an oxidative heat treatment is performed before activating the carbon support. In some embodiments, the oxidative heat treatment includes a process of oxidizing the surface of the carbon support by reacting with an oxidizing gas.

[0082] Besides oxidizing gases, treatments such as wet acid treatment or dry oxidation methods (including ozone and plasma treatment) are also viable options for enhancing the performance of carbon supports. However, when using gas-phase reactions, there is a tendency for the carbon support surface to undergo uniform oxidation. This uniform oxidation allows for subsequent activation of the carbon support immediately after oxidative heat treatment, thereby significantly improving process efficiency. By integrating these treatment methods, the properties of the carbon support can be optimized, ultimately enhancing its performance in a variety of applications.

[0083] In some embodiments, the oxidizing gas includes any one selected from air, oxygen (O2), carbon dioxide (CO2), water vapor (H2O), hydrogen peroxide (H2O2), ozone (O3), and any combination thereof. Furthermore, any gas with oxidizing properties and capable of oxidizing the surface of the carbon support can be used without particular limitation.

[0084] Oxidative heat treatment can be carried out for 0.5 to 5 hours in a temperature range of 150°C to 600°C.

[0085] In some embodiments, the oxidation heat treatment is performed at a temperature range of 200°C to 400°C. Furthermore, the oxidation heat treatment is preferably performed for 0.5 to 2 hours. If the oxidation heat treatment temperature is less than 150°C, or the oxidation heat treatment time is less than 0.5 hours, inappropriate oxidation may occur on the surface of the carbon support. On the other hand, if the oxidation heat treatment temperature exceeds 600°C, or the oxidation heat treatment time exceeds 5 hours, not only the surface of the carbon support but also the interior of the carbon support may be over-oxidized, which may reduce activation efficiency and yield.

[0086] Reduction heat treatment

[0087] When carbon supports undergo oxidative heat treatment or activation, their surfaces can become oxidized, leading to the formation of hydrophilic functional groups. These modifications can compromise the structural integrity of the carbon support, making it more susceptible to reaction with various external substances. This increased vulnerability can adversely affect the robustness of the carbon support, potentially reducing its overall performance and durability in practical applications. Therefore, carefully balancing the benefits of oxidation with the need to maintain the mechanical stability of the carbon support is crucial.

[0088] Therefore, further heat treatment is performed to improve the surface robustness of the activated carbon support. More specifically, a process is carried out to reduce the surface of the activated carbon support by reacting it with a reducing gas. When the surface of the activated carbon support reacts with the reducing gas, the hydrophilic groups formed on the surface of the carbon support can be removed, and the surface of the carbon support can be transformed into a hydrophobic surface. Thus, excellent robustness and durability are obtained while maintaining the improved porosity of the carbon support.

[0089] In some embodiments, the reducing gas includes any one selected from hydrogen (H2), a mixture of hydrogen and an inert gas (e.g., a gas from Group 18 of the periodic table), ammonia (NH3), and any combination thereof. Furthermore, any gas with reducing properties can be used without particular limitation.

[0090] Furthermore, in some embodiments, the reduction heat treatment includes a process of reducing the surface of the activated carbon support by reacting the activated carbon support with a reducing gas in a pressure-cycle controlled manner.

[0091] Therefore, by using a pressure-cycle control method, the pressure of the reducing gas supplied to the activated carbon support is circulated between a lower limit pressure and an upper limit pressure, where the lower limit pressure can be 0 bar. g Up to 0.1 bar g And the upper limit pressure can be 0.5 bar. g Up to 1 bar g .

[0092] Its detailed description will be omitted because, apart from the gas type, it is essentially the same as that described above in the section on activated carbon support.

[0093] In some embodiments, the reduction heat treatment is carried out for 0.1 hours to 6 hours in a temperature range of 500°C to 1100°C.

[0094] In some implementations, the reduction heat treatment is performed in a temperature range of 700°C to 900°C. If the reduction heat treatment temperature is below 700°C, the reduction efficiency may decrease, while if the reduction heat treatment temperature exceeds 900°C, the pore structure may collapse due to the excessively high temperature.

[0095] Furthermore, in some embodiments, the reduction heat treatment is performed for 0.5 to 2 hours. If the reduction heat treatment time is less than 0.5 hours, the reduction may not occur completely, while if it exceeds 2 hours, the pore structure may collapse.

[0096] Catalyst composites for fuel cells

[0097] Another aspect of this disclosure relates to a catalyst composite for a fuel cell, comprising a carbon support manufactured by the above-described manufacturing method and a catalytic metal supported on the carbon support.

[0098] Catalytic metals can be used without specific limitations, provided they are commonly used in the art to which this disclosure pertains, and, for example, in some embodiments, catalytic metals include at least one selected from platinum (Pt), gold (Au), silver (Ag), rhodium (Rh), nickel (Ni), cobalt (Co), iron (Fe), palladium (Pd), copper (Cu), iridium (Ir), osmium (Os), molybdenum (Mo), vanadium (V), and any combination thereof.

[0099] In some embodiments, the catalytic metal may optionally be included in an amount of 10 to 50 wt% based on the total weight of the catalyst complex. If the amount of catalytic metal is less than 10 wt%, the catalyst density may be insufficient, leading to suboptimal performance. Conversely, when the metal content exceeds 50 wt%, the proximity between catalyst particles becomes too close, resulting in an excess concentration of catalyst material. This excess may hinder the formation of platinum-heterogeneous element bonds, which is crucial for improving catalyst durability. Therefore, it is necessary to carefully optimize the catalytic metal loading within this range to achieve a balance that maximizes catalyst effectiveness and lifetime.

[0100] Any method for loading a catalytic metal onto a carbon support can be used, as long as it is a synthetic method that allows the platinum catalyst or other catalytic metal salt to interact with the surface doped layer of the carbon support, and in some embodiments, typical examples of such catalyst synthesis methods include impregnation, polyol methods, initial wet impregnation, and others.

[0101] Catalyst composites comprising a carbon support and a catalytic metal manufactured according to this disclosure can be applied to the electrodes of fuel cells.

[0102] This disclosure is further illustrated by the following non-limiting examples.

[0103] Example 1

[0104] As a carbon support, carbon substrates with a diameter of approximately 600 to 700 μm were prepared. 2 Specific surface area per g, approximately 1.7 to 1.8 cm² 3 / g total pore volume and approximately 1.00 cm³3 High-porosity mesoporous carbon with a mesoporous volume of / g.

[0105] The carbon support is activated by reacting with carbon dioxide gas. More specifically, the carbon support is placed in a reaction chamber, and carbon dioxide and nitrogen are supplied to the chamber at 200 sccm and 100 sccm, respectively. Therefore, the carbon support is controlled by regulating the amount of carbon dioxide gas discharged, maintaining the carbon dioxide pressure in the reaction chamber at 0.2 bar. g The lower limit pressure and 0.5 bar g The activation is achieved by cycling between the upper limit pressure. Additionally, the activation process is carried out at 900°C for 1 hour.

[0106] The carbon support according to Example 1 is produced by such activation.

[0107] Example 2

[0108] The carbon support according to Example 2 was prepared in the same manner as in Example 1, except that the prepared high-porosity mesoporous carbon was subjected to oxidative heat treatment in air at about 250°C for 1 hour, followed by activation. More specifically, air was supplied at a flow rate of 300 sccm.

[0109] Example 3

[0110] The carbon support according to Example 3 was manufactured in the same manner as in Example 2, except that it was activated for 2 hours.

[0111] Example 4

[0112] The carbon support according to Example 4 was manufactured in the same manner as in Example 2, except that it was activated at about 1000°C.

[0113] Example 5

[0114] After the carbon support was prepared according to Example 4, it was subjected to a reducing heat treatment with a mixed gas of 3% hydrogen (H2) / 97% argon (Ar). More specifically, the mixed gas was supplied at a flow rate of 300 sccm. Thus, the carbon support was controlled by regulating the amount of mixed gas discharged, thereby maintaining the pressure of the mixed gas in the reaction chamber at 0.2 bar. g The lower limit pressure is 0.5 bar. g The carbon support is subjected to reduction heat treatment in a cycle between the upper limit pressure and the lower limit pressure. Furthermore, the reduction heat treatment process is carried out at approximately 900°C for 1 hour. The carbon support according to Example 5 is manufactured through such oxidation heat treatment, activation, and reduction heat treatment.

[0115] Example 6

[0116] As a carbon support, carbon nanotubes with a diameter of approximately 200 to 400 μm were prepared. 2 Specific surface area per g, approximately 1.7 to 1.8 cm² 3 / g total pore volume and approximately 1.00 cm³ 3 Highly crystalline mesoporous carbon with a mesoporous volume of / g.

[0117] The carbon support was subjected to oxidative heat treatment at approximately 250°C in air for 1 hour. Afterward, the pretreated carbon support was activated by reacting with carbon dioxide gas. Therefore, the carbon support was controlled by a pressure-cycle control method, maintaining the carbon dioxide gas pressure in the reaction chamber at 0.2 bar by controlling the amount of emitted carbon dioxide gas. g The lower limit pressure and 0.5 bar g The activation is achieved by cycling between the upper limit pressure. Furthermore, the activation process is carried out at 1000°C for 1 hour.

[0118] The carbon support according to Example 6 is manufactured through such oxidative heat treatment and activation.

[0119] Example 7

[0120] After the carbon support was manufactured according to Example 6, it was subjected to a reducing heat treatment with a mixture of 3% hydrogen (H2) and 97% argon (Ar). Therefore, the carbon support was controlled by regulating the amount of the discharged mixed gas in a pressure-cycle controlled manner to maintain the pressure of the mixed gas in the reaction chamber at 0.2 bar. g The lower limit pressure is 0.5 bar. g The material undergoes a reduction heat treatment cycle between its upper limit pressure and the specified pressure. Furthermore, the reduction heat treatment process is carried out at approximately 900°C for 1 hour.

[0121] The carbon support according to Example 7 is manufactured by such oxidative heat treatment, activation and reduction heat treatment.

[0122] Comparative Example 1

[0123] According to Comparative Example 1, a sample with approximately 600 to 700 μm was prepared. 2 Specific surface area per g, approximately 1.7 to 1.8 cm² 3 / g total pore volume and approximately 1.00 cm³ 3 High-porosity mesoporous carbon with a mesopore volume of / g was used as a carbon support.

[0124] Comparative Example 2

[0125] The carbon support prepared in Comparative Example 1 was activated by reaction with carbon dioxide gas. Therefore, at 0 bar... gThe activation process is carried out at atmospheric pressure. Additionally, the activation process is conducted at 900°C for 1 hour.

[0126] This activation is used to produce the carbon support according to Comparative Example 2.

[0127] Comparative Example 3

[0128] The carbon support prepared in Comparative Example 1 was activated by reacting with carbon dioxide gas. Therefore, at a temperature maintained at 0.5 bar... g The activation process is carried out under gauge pressure. Additionally, the activation process is conducted at 900°C for 1 hour.

[0129] Comparative Example 4

[0130] According to Comparative Example 4, a sample with a diameter of approximately 200 to 400 μm was prepared. 2 Specific surface area per g, approximately 1.7 to 1.8 cm² 3 / g total pore volume and approximately 1.00 cm³ 3 Highly crystalline mesoporous carbon with a mesoporous volume of / g was used as a carbon support.

[0131] Test Example 1 - Surface Composition Analysis Using XPS

[0132] XPS (X-ray photoelectron spectroscopy) was performed to determine the surface composition of the carbon supports according to Examples 1 to 7 and Comparative Examples 1 to 4. The results are shown in Table 1 below.

[0133] [Table 1]

[0134]

[0135] Referring to Table 1, when comparing Comparative Example 1 with Example 4 and Comparative Example 4 with Example 6, which use the same type of carbon support but differ in oxidative heat treatment and activation, surface oxidation occurred after the pore activation process, which confirms that the oxygen content on the surface of the carbon support increased.

[0136] Furthermore, in Examples 5 and 7, in which reduction heat treatment was performed, the oxygen content on the surface of the carbon support was shown to decrease after reduction. In particular, when comparing Comparative Example 1 with Example 5 and Comparative Example 4 with Example 7, the oxygen content on the surface of the carbon support was measured to be similar to the oxygen content before treatment.

[0137] Test Example 2 - Surface Structure Analysis Using TEM

[0138] To analyze the surface structure of the manufactured carbon supports, TEM images were taken of the carbon supports according to Comparative Examples 1 and 5, and Comparative Examples 4 and 7, which are shown in Figures 4 and 5, respectively.

[0139] Referring to Figures 4 and 5, the carbon support of Comparative Example 1 was confirmed to be carbon with a very thin carbon surface layer at the level of about 1 nm to 2 nm. The highly crystalline mesoporous carbon of Comparative Example 4 was confirmed to be carbon with a thick graphite layer at the level of 3 nm or higher.

[0140] Furthermore, when comparing Comparative Example 1 with Example 5 and Comparative Example 4 with Example 7, the structure and porosity were maintained even after oxidative heat treatment, activation and reduction heat treatment.

[0141] Test Example 3 - Lattice Structure Analysis Using XRD

[0142] To analyze the structure of the carbon supports according to Examples 1 to 7 and Comparative Examples 1 to 4, XRD (X-ray diffraction) was performed. Therefore, L c(002) The value (representing the vertical crystallite size as an indicator of carbon support durability) was calculated from the XRD results, as shown in Figure 6, and L c(002) The values ​​were calculated using the Scherrer equation. The results are shown in Table 2 below.

[0143] [Table 2]

[0144] Category L c(002) (nm) Comparative Example 1 1.6 Comparative Example 2 1.5 Comparative Example 3 1.2 Comparative Example 4 4.0 Example 1 1.6 Example 2 1.5 Example 3 1.5 Example 4 1.4 Example 5 1.4 Example 6 3.9 Example 7 3.9 surface

[0145] Referring to Table 2, when comparing Comparative Example 3, in which the carbon support is activated while maintaining a constant carbon dioxide gas pressure, with Example 5, which undergoes oxidative heat treatment, activation, and reduction heat treatment according to this disclosure, Example 5 exhibits a higher L... c(002) The value confirms high durability and effective activation.

[0146] Furthermore, Comparative Example 4, which uses highly crystalline mesoporous carbon, and Examples 6 and 7, which undergo oxidative heat treatment, activation, and / or reduction heat treatment on it, have similar L... c(002) Therefore, regardless of the type of carbon used, the activation efficiency of the carbon support is excellent.

[0147] Test Example 4 - Porosity Analysis Using 77K / N2 Gas Adsorption

[0148] To analyze the surface porosity of the fabricated carbon supports, 77 K / N2 gas adsorption analysis was performed on Examples 1 to 5 and Comparative Examples 1 to 3. Furthermore, the specific surface area (S) was determined using the Brunauer-Emmett-Teller (BET) equation. BET The total pore volume (Vo) was obtained using adsorption curves with relative pressures up to 0.990.tot The mesopore volume (Va) was obtained using the desorption curve obtained by the Barret-Joyner-Halenda (BJH) method. meso Therefore, micropore sizes are obtained by calculating pore volumes of 2 nm or smaller from the pore distribution using the nonlocal density function theory (NLDFT) method. Furthermore, the pore diameter is determined using the pattern of the pore distribution and its weight-average value.

[0149] Depending on the type of carbon support used, the results are described for Comparative Examples 1 to 3 and Examples 1 to 5, and Comparative Examples 4 and Examples 6 and 7, respectively. The results for Comparative Examples 1 to 3 and Examples 1 to 5 are shown in Table 3 and Figures 7 and 8 below, and the results for Comparative Examples 4 and Examples 6 and 7 are shown in Table 4 and Figures 9 and 10 below.

[0150] [Table 3]

[0151]

[0152] Referring to Table 3 and Figures 7 and 8, in carbon supports subjected to at least one of the oxidative heat treatment, activation, or reduction heat treatment according to this disclosure, the efficiency of porosity development, the degree of carbon durability degradation, and the yield are superior compared to Comparative Example 2, which uses carbon dioxide gas for activation treatment without pressure, or Comparative Example 3, which uses activation treatment while maintaining constant pressure. Furthermore, by appropriately controlling the conditions of the oxidative heat treatment, activation, and reduction heat treatment, such as the oxidative heat treatment temperature and time, and the activation temperature, it is possible not only to improve the porosity but also to finely control the pore size.

[0153] [Table 4]

[0154]

[0155]

[0156] Referring to Table 4 and Figures 9 and 10, in Examples 6 and 7, in which at least one of oxidative heat treatment, activation heat treatment, or reduction heat treatment was performed on the highly crystalline mesoporous carbon support according to this disclosure, the porosity was improved compared to Comparative Example 4. Furthermore, the improved porosity was maintained even after the reduction heat treatment.

[0157] Test Example 5 - Analysis of Water Adsorption Capacity

[0158] The water adsorption capacity of Comparative Example 4 and Examples 6 and 7 was analyzed using highly crystalline mesoporous carbon as a carbon support. The results are shown in Table 5 and Figure 11 below. The water adsorption capacity was analyzed by measuring the adsorption capacity simultaneously with the injection of low-pressure H2O (water vapor) at 298 K using a BET apparatus.

[0159] [Table 5]

[0160]

[0161] Referring to Table 5 and Figure 11, in Example 6, in which the activation treatment was performed, the water adsorption capacity was at least doubled compared to Comparative Example 4. This is attributed to the increased hydrophilicity resulting from the introduction of oxygen functional groups onto the surface of the carbon support. Furthermore, in Example 7, in which the reduction heat treatment was performed, the initial water adsorption capacity was reduced compared to Comparative Example 4, confirming that the surface became hydrophobic. This leads to improved durability by suppressing the interaction with water molecules that participate as reactants in the MEA catalyst durability test.

[0162] Test Example 6 - Analysis of Cell Performance and Catalyst Durability of Membrane Electrode Module (MEA)

[0163] After manufacturing a catalyst composite using each of the carbon supports according to Comparative Examples 1 and 5 and the carbon supports according to Comparative Examples 4 and 6 and 7, a membrane electrode assembly comprising the catalyst composite is manufactured.

[0164] Specifically, platinum was loaded onto a carbon support using a known polyol process. Therefore, the amount of platinum was set to 30 wt% based on the total weight of the catalyst complex.

[0165] The preparation process includes a Nafion (DuPont) electrolyte membrane, a positive electrode slurry comprising a catalyst composite manufactured using each of the carbon supports according to Comparative Examples 1 and 5 and the carbon supports according to Comparative Examples 4 and 7, a negative electrode slurry comprising a known Pt / C catalyst composite, carbon paper as a gas diffusion layer, and a separator in which a flow field is formed. A positive electrode is formed by applying the positive electrode slurry to one side of the electrolyte membrane and then drying it, and a negative electrode is formed by applying the negative electrode slurry to the remaining side and then drying it. Subsequently, a membrane electrode assembly (MEA) cell is manufactured by sequentially stacking the gas diffusion layer and the separator in which the flow field is formed on each of the positive and negative electrodes.

[0166] Under the conditions shown in Figure 12, durability tests were conducted on the membrane-electrode assembled cells using the carbon support according to Comparative Example 1 and Example 5 by repeating 10,000 charge-discharge cycles. Therefore, tests were performed under low temperature and high humidity (60°C, RH 50% or higher) and high pressure (1 bar) conditions. aUnder conditions of 80°C or higher and under high temperature and low humidity (RH less than 50%) and pressure (1 bar) conditions, and under high temperature and low humidity (RH less than 50%) and pressure (RH less than 50%) conditions, the following conditions are observed. a Durability tests were conducted under conditions of low temperature and high humidity (or higher). The electrochemical performance and catalyst durability degradation rate before and after durability tests under low temperature and high humidity conditions are shown in Figures 13 and 14, respectively. Furthermore, the electrochemical performance and catalyst durability degradation rate before and after durability tests under high temperature and low humidity conditions are shown in Figures 15 and 16, respectively.

[0167] Based on the evaluation results of the battery performance, in Example 5 where activation was carried out, the initial performance prior to the durability test was further improved. This is attributed to the increased battery performance resulting from improved catalyst distribution and mass transfer (due to improved porosity).

[0168] Furthermore, when comparing the results before and after the accelerated durability test that caused Pt elution, the durability degradation rate of the catalyst (Example 5) that underwent porosity improvement treatment was lower than that of the catalyst using a conventional carbon support (Comparative Example 1).

[0169] In particular, the durability degradation rate was significantly reduced (40 → 15%) under high temperature and low humidity conditions. This is attributed to reduced Pt elution and decreased particle coarsening due to improvements in the specific surface area of ​​the carbon support and the hydrophobicity of the carbon surface.

[0170] Furthermore, under the conditions shown in Figure 17, durability tests were conducted on the membrane electrode assembly cells using the carbon support according to Comparative Example 4 and Examples 6 and 7 by repeating 5000 charge and discharge cycles. Therefore, durability tests were performed under both low-temperature high-humidity and pressurized conditions and high-temperature low-humidity and pressurized conditions as described above.

[0171] Figures 18 and 19 show the electrochemical performance and catalyst durability degradation rate of the membrane electrode assembly cells using Comparative Example 4 and Example 7 before and after durability testing under low temperature and high humidity conditions, respectively. Furthermore, Figures 20 and 21 show the electrochemical performance and catalyst durability degradation rate of the membrane electrode assembly cells using Comparative Example 4 and Example 7 before and after durability testing under high temperature and low humidity conditions, respectively.

[0172] Table 6 below shows the results of Figures 18 to 21, including the results of Example 6.

[0173] [Table 6]

[0174]

[0175] Based on the battery performance evaluation results, the initial performance of the batteries used in Comparative Example 4 and Example 7 before durability testing showed that the activated batteries exhibited better performance. This is attributed to the increased battery performance resulting from improved catalyst distribution and mass transfer (due to improved porosity).

[0176] Moreover, compared with the catalyst used in Comparative Example 4, the durability degradation rate was accelerated in the catalyst using a carbon support on which pores were activated (Example 6).

[0177] This is believed to be due to the carbon surface durability (L) caused by surface oxidation during pore activation. c The carbon surface durability was improved by surface reduction as described in Example 7, and the hydrophobicity was improved by removing the oxygen functional groups, thereby improving the carbon corrosion durability. This is considered to be due to the improved corrosion durability caused by the improved hydrophobicity of the carbon surface.

[0178] As is apparent from the foregoing, the method for manufacturing a carbon support according to this disclosure can control the pore size of the carbon support surface and improve the porosity through the reaction of the carbon support and the activating gas in a pressure-cycle controlled manner. Furthermore, it can provide a hydrophobic carbon support with finely controlled pore size on the carbon support surface.

[0179] In this way, the controlled porosity of the carbon support surface can improve the loading efficiency and mass transfer of the metal catalyst, and the improved hydrophobicity of the carbon support surface can also enhance the catalyst durability.

[0180] The effects of this disclosure are not limited to those described above. It should be understood that the effects of this disclosure include all effects that can be inferred from the description herein.

[0181] As embodiments of this disclosure have been described above, those skilled in the art should understand that various modifications and alterations are possible by modifying, deleting, or adding components without departing from the scope and spirit of this disclosure as described in the appended claims, and such modifications and alterations will also be considered to be included within the scope of this disclosure.

Claims

1. A method for manufacturing a carbon support, comprising activating the carbon support by reacting it with an activation gas in a pressure-controlled cycle.

2. The method according to claim 1, wherein, The carbon support includes any one of the following selected from porous carbon, activated carbon, carbon black, carbon nanotubes, graphene, and any combination thereof.

3. The method according to claim 1, wherein, The activating gas includes any one of the following selected from air, oxygen (O2), carbon dioxide (CO2), water vapor (H2O), hydrogen peroxide (H2O2), ozone (O3), and any combination thereof.

4. The method according to claim 1, wherein, The pressure cycle control method means that the pressure of the activation gas supplied to the carbon support cycles between a lower limit pressure and an upper limit pressure, where the lower limit pressure is 0 bar. g Up to 0.1 bar g The upper limit pressure is 0.5 bar. g Up to 1 bar g .

5. The method according to claim 1, wherein, The carbon support was activated at a temperature of 800°C to 1200°C for 0.1 to 6 hours.

6. The method of claim 1, further comprising subjecting the carbon support to an oxidative heat treatment prior to activating the carbon support.

7. The method according to claim 6, wherein, The oxidative heat treatment includes a process of oxidizing the surface of the carbon support by reacting with an oxidizing gas.

8. The method according to claim 7, wherein, The oxidizing gas includes any one of the following selected from air, oxygen (O2), carbon dioxide (CO2), water vapor (H2O), hydrogen peroxide (H2O2), ozone (O3), and any combination thereof.

9. The method according to claim 6, wherein, The oxidation heat treatment is carried out at a temperature of 150°C to 600°C for 0.5 to 5 hours.

10. The method of claim 1, further comprising subjecting the activated carbon support to a reducing heat treatment after activation.

11. The method according to claim 10, wherein, The reduction heat treatment includes a process of reducing the surface of the activated carbon support by reacting with a reducing gas.

12. The method according to claim 11, wherein, The reducing gas includes any one selected from hydrogen (H2), a mixture of hydrogen and an inert gas, ammonia (NH3), and any combination thereof.

13. The method according to claim 10, wherein, The reduction heat treatment is carried out at a temperature of 500°C to 1100°C for 0.1 to 6 hours.

14. The method according to claim 11, wherein, The reduction heat treatment includes a process of reducing the surface of the activated carbon support by reacting the activated carbon support with the reducing gas in a pressure-cycle controlled manner.

15. The method according to claim 14, wherein, The pressure circulation control method for the reducing gas means that the pressure of the reducing gas supplied to the activated carbon support circulates between a lower limit pressure and an upper limit pressure, wherein the lower limit pressure is 0 bar. g Up to 0.1 bar g And the upper limit pressure is 0.5 bar. g Up to 1 bar g .

16. A method for manufacturing a carbon support, comprising: (i.) subjecting the carbon support to oxidative heat treatment; (ii.) Activation of the pretreated carbon support by reaction with an activating gas; (iii.) subjecting the activated carbon support to a reducing heat treatment, wherein activating the pretreated carbon support comprises activating the carbon support by reacting the carbon support with the activating gas in a pressure-cycle controlled manner.

17. The method according to claim 16, wherein, Hydrophilic groups are formed on the surface of the carbon support by oxidative heat treatment, and the hydrophilic groups are removed by reduction heat treatment to make the carbon support hydrophobic.

18. A catalyst composite for a fuel cell, comprising: (i) a carbon support, manufactured by activating the carbon support by reacting it with an activation gas in a pressure-cycle controlled manner; and (ii) a catalytic metal supported on the carbon support.

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