Catalyst complex for fuel cells and process for producing an electrode with this catalyst complex

Abstract

Catalyst complex for fuel cells, wherein the catalyst complex is included in an electrode for fuel cells, the catalyst complex for fuel cells comprising: a first catalyst designed to effect a hydrogen oxidation reaction; and a second catalyst designed to effect a water electrolysis reaction with the first catalyst, wherein an outer surface of the first catalyst is coated with a first ionomer binder and an outer surface of the second catalyst is coated with a second ionomer binder, and wherein the equivalent weight (EW) of the second ionomer binder differs from the equivalent weight (EW) of the first ionomer binder, wherein the equivalent weight (EW) of the second ionomer binder is 92% or less of the equivalent weight (EW) of the first ionomer binder, wherein the first catalyst comprises a metal catalyst, and wherein the second catalyst comprises at least metal nanoparticles or a metal oxide.

Description

BACKGROUND(a) Technical field

[0001] The present invention relates to a catalyst complex for fuel cells and a method for producing an electrode comprising this. (b) State of the art

[0002] Most recently, the most commonly used fuel cell for vehicles has been the polymer electrolyte membrane fuel cell (PEMFC). To consistently generate a high output power of at least several tens of kW under varying driving conditions, the polymer electrolyte membrane fuel cell must be able to operate stably across a wide current density range.

[0003] To achieve a desired power level in the fuel cell, it is used in a stacked configuration, where individual cells are assembled into a unit. The unit cell is configured such that gas diffusion layers (GDLs) and seals are stacked on the outer parts of a membrane electrode assembly (MEA), which houses a cathode and an anode. Bipolar plates (or separators) with flow fields for supplying reactant gas (hydrogen as fuel and oxygen or air as oxidizer) and for passing cooling water are located outside the GDLs. Hundreds of these unit cells are stacked, and end plates are then connected to the outermost units to support them.

[0004] In an electrochemical reaction within the fuel cell, expressed in Equation 1 below, hydrogen is supplied to an oxidation electrode (the anode) and separated into protons and electrons via a hydrogen oxidation reaction (HOR). The protons are then moved through the membrane to a reduction electrode (the cathode), while the electrons are transported to the cathode via an external circuit. The protons and electrons react with externally supplied oxygen gas at the cathode via an oxygen reduction reaction (ORR) to generate electricity and heat, as well as water as a byproduct, as expressed in Equation 2 below. H2 → 2H+ + 2e-, E° = 0.000 V (vs. SHE) [Equation 1] 1 / 2O2 + 2H + + 2e - → H2O, E° = 1.229 V (vs. SHE) [Equation 2]

[0005] (Here, E° is a standard electrode potential and SHE is a standard hydrogen electrode).

[0006] In particular, when protons are moved across the membrane from the anode to the cathode, electro-osmotic resistance (EOD) occurs, in which hydronium ions generally bond with water molecules in such a way that the water molecules are carried along. Furthermore, if the amount of water accumulated at the cathode increases, backdiffusion (BD) can occur, in which a certain amount of water is moved in the opposite direction, from the cathode to the anode.If an appropriate amount of water is present, generated, and moved through this fuel cell reaction, it plays a desirable role, serving, for example, to maintain the humidification of the membrane electrode assembly. However, if an excessive amount of water is present and not properly removed, flooding occurs, and this floodwater impedes the supply of reaction gases to the fuel cell, thus increasing voltage drop. Besides flooding the fuel cell with water, various other causes, such as ice formation in winter and anomalies in the reaction gas supply systems, can lead to a reduction in the supply of hydrogen and oxygen.the reaction gases used in the fuel cell, in particular it is known that a lack of hydrogen at the anode has a fatal negative impact on the performance of the fuel cell and greatly reduces the cell voltage.

[0007] In general, hydrogen shortages can be divided into a general hydrogen shortage, where the entire fuel cell is short of hydrogen, and a local hydrogen shortage, where the hydrogen supply to the entire fuel cell is sufficient, but a local hydrogen shortage occurs due to uneven distribution. These hydrogen shortages are particularly noticeable under operating conditions such as uneven supply and distribution of hydrogen gas, sudden increases in the fuel cell's load demand, or fuel cell start-up.A general hydrogen shortage can be detected relatively easily by monitoring a hydrogen supply state or by using a sensor in a balance of operations (BOP). However, a local hydrogen shortage in individual cells can be detected simply by monitoring the corresponding cells of the fuel cell stack using a stack voltage monitoring device. Therefore, detecting a local hydrogen shortage requires considerable effort and a complex control system.

[0008] If no hydrogen gas is present at the anode during operation of the fuel cell, the anode voltage E An increased to such an extent that the protons required for the fuel cell reaction are generated, and then increased further until they are greater than a cathode voltage E Ca is such that the fuel cell reaches a reversal state of cell voltage, in which the cell voltage E Cellless than 0 V (E Cell = E Ca - E An < 0). In this case, carbon, which serves as the catalyst support of the anode, can react with water and thus be oxidized, as expressed in the following equations 3 and 4, but due to the slow reaction rate, it cannot provide sufficient amounts of protons and electrons needed in the cathode, and consequently the anode voltage is rapidly increased. C + 2H2O → CO2 + 4H + + 4e - (0.207 V vs. SHE) [Equation 3] C + H2O → CO + 2H + + 2e - (0.518V vs. SHE) [Equation 4]

[0009] If the vehicle is driven continuously while the increase in anode voltage is ignored, carbon corrosion will be accelerated, and metal catalyst particles carried on the catalyst support will be lost, potentially reducing the fuel cell's performance. If this cell voltage reversal state persists, and the fuel cell thus reaches an excessive voltage reversal state of -2 V or less, an excessive amount of heat will be generated from the fuel cell units, damaging the membrane electrode assembly and the gas diffusion layers. In particular, serious problems such as pinhole formation in the membrane electrode assembly and electrical short circuits in the cells can be caused. This will result in the fuel cell reaching a cell failure state in which the individual units cannot operate normally.Therefore, it is important to develop fuel cell components and a system that exhibit excellent resistance to voltage reversal.

[0010] Furthermore, research is underway to increase the corrosion resistance of a catalyst by supporting a compound to prevent corrosion of the catalyst support on the catalyst support, as described in KR 10 2016 059072 A. However, since a major source for proton generation in an electrode is removed, and thus no protons can be generated, the anode voltage is further increased, which can exacerbate cell damage due to the oxidation of a component located adjacent to a gas diffusion layer and the increased heat generation.

[0011] KR 10 1664627 B1 relates to a polymer electrolyte membrane fuel cell and a method for its manufacture.

[0012] DE 10 2017 215428 A1 discloses a catalytic composition for the production of a fuel cell electrode.

[0013] US 2017 0062835 A1 describes a fuel cell electrode layer containing a catalyst, an electronic conductor, and an ion conductor.

[0014] US 2008 0206616 A1 relates to highly porous catalyst-coated membranes, as well as sprayable inks and methods for manufacturing catalyst-coated membranes. OVERVIEW OF THE INVENTION

[0015] The present invention was developed in an effort to solve the problems described above in connection with the prior art. The object of the present invention is to provide a catalyst complex for fuel cells in which a water-splitting catalyst is coated with a second ionomer binder having a lower equivalent weight (EW) than a first ionomer binder applied to a hydrogen oxidation reaction catalyst.

[0016] Another object of the present invention is the provision of a catalyst complex for fuel cells in which ionomer binders of different equivalent weights are applied to a hydrogen oxidation reaction catalyst and a water splitting catalyst to increase the corrosion resistance of the catalysts and to prevent excessive stress build-up.

[0017] Furthermore, the subject of this disclosure is to provide a catalyst complex for fuel cells in which water can be readily supplied to a water-splitting catalyst present in an electrode upon voltage reversal in order to increase the voltage reversal resistance of a fuel cell stack.

[0018] According to one aspect of the invention, a catalyst complex for fuel cells, which is included in a fuel cell electrode, is provided. The catalyst complex for fuel cells comprises a first catalyst configured to effect a hydrogen oxidation reaction and a second catalyst configured to effect a water electrolysis reaction with the first catalyst. An outer surface of the first catalyst is coated with a first ionomer binder, and an outer surface of the second catalyst is coated with a second ionomer binder, and the equivalent weight (EW) of the second ionomer binder differs from the equivalent weight (EW) of the first ionomer binder.

[0019] According to the invention, the equivalent weight (EW) of the second ionomer binder is 92% or less of the equivalent weight (EW) of the first ionomer binder.

[0020] In another embodiment, the equivalent weight (EW) of the first ionomer binder can be 700 to 1200.

[0021] In yet another embodiment, the first catalyst may comprise a supported-type catalyst in which catalyst particles are carried on a carbon support, and the carbon support may comprise a support selected from the group consisting of carbon black (CB), carbon nanotubes (CNT), carbon nanofibers (CNF), carbon nanowires (CNW), carbon nanohorns (CNH), graphene or combinations thereof.

[0022] According to the invention, the first catalyst comprises a metal catalyst, and the metal catalyst can be selected from the group consisting of platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), gold (Au), silver (Ag), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), yttrium (Y), or combinations thereof. According to the invention, the second catalyst comprises at least metal nanoparticles or a metal oxide. The metal of the second catalyst can be selected from or comprise the group consisting of ruthenium (Ru), iridium (Ir), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), yttrium (Y), or combinations thereof.

[0023] In yet another embodiment, the second catalyst can comprise a supported catalyst in which catalyst particles are applied to a support.

[0024] In another embodiment, the carrier may be selected from or comprise a group consisting of carbon black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanohorns, graphene, titanium oxide, cerium oxide, niobium oxide, tungsten oxide, titanium carbide, titanium nitride or combinations thereof.

[0025] In another embodiment, the content of the second catalyst, based on the weight of the first catalyst, can be 2 wt.% to 80 wt.%.

[0026] According to another aspect, the invention provides a method for producing an electrode for fuel cells, including a catalyst complex. The method comprises producing a first coated catalyst by coating a first catalyst with a first ionomer binder, producing a second coated catalyst by coating a second catalyst with a second ionomer binder having an equivalent weight (EW) that is 92% or less of the equivalent weight (EW) of the first ionomer binder, producing a catalyst ink by mixing the first coated catalyst, the second coated catalyst, and a solvent, and producing the electrode using the catalyst ink, wherein the first catalyst comprises a metal catalyst, and wherein the second catalyst comprises at least metal nanoparticles or a metal oxide.

[0027] In one embodiment, the solvent used to prepare the catalyst ink may comprise at least alcohol or deionized water. The alcohol may comprise or include an alcohol selected from the group consisting of isopropyl alcohol (IPA), n-propyl alcohol (nPA), ethyl alcohol, or combinations thereof.

[0028] In another embodiment, the second catalyst in the catalyst ink can have a content of 2 wt.% to 80 wt.%, based on a weight of the first catalyst.

[0029] In a further embodiment, the production of the first coated catalyst may include the production of a first mixed solution comprising the first catalyst, the first ionomer binder and a first solvent, as well as carrying out drying and heat treatment of the first mixed solution.

[0030] In a further embodiment, the first ionomer binder in the first mixed solution can have a content of 10 wt.% to 50 wt.%, based on the total weight of the first catalyst and the first ionomer binder.

[0031] In yet another embodiment, when carrying out the heat treatment of the first mixed solution, this heat treatment can be carried out within a range from an α-transition temperature of the first ionomer binder to a temperature that is 100 °C higher than the α-transition temperature.

[0032] In another embodiment, when carrying out the heat treatment of the first mixed solution, the heat treatment can be carried out for 10 minutes to 10 hours.

[0033] In another further embodiment, the production of the second coated catalyst may include the production of a second mixed solution comprising the second catalyst, the second ionomer binder and a second solvent, as well as the drying and heat treatment of the second mixed solution.

[0034] In yet another embodiment, the second ionomer binder in the second mixed solution can have a content of 5 wt.% to 40 wt.%, based on the total weight of the second catalyst and the second ionomer binder.

[0035] In a further embodiment, when carrying out the heat treatment of the second mixed solution, the heat treatment can be carried out within a range from an α transition temperature of the second ionomer binder to a temperature that is 100 °C higher than the α transition temperature.

[0036] In yet another embodiment, the heat treatment of the second mixed solution can be carried out for 10 minutes to 10 hours.

[0037] According to another aspect, the present invention provides a method for producing an electrode for fuel cells, including a catalyst complex. The method comprises producing a first mixed solution comprising a first catalyst, a first ionomer binder, and a first solvent; producing a second mixed solution comprising a second catalyst, a second ionomer binder, and a second solvent; producing a second coated catalyst by drying and heat-treating the second mixed solution; producing a catalyst ink by mixing the first mixed solution and the second coated catalyst; and producing the electrode using the catalyst ink, wherein the first catalyst comprises a metal catalyst, and wherein the second catalyst comprises at least metal nanoparticles or a metal oxide.

[0038] Further aspects and embodiments of the invention are discussed below.

[0039] The above and other features of the invention will also be discussed below. BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0040] The above and other features of the invention are described in detail with reference to certain embodiments shown in the accompanying drawings, which are shown below for illustrative purposes only and are therefore not limiting to the present invention, wherein Fig. 1 is a schematic view of a conventional catalyst complex for fuel cells; Fig. Figure 2 is a schematic view of a catalyst complex for fuel cells according to an embodiment of the invention; Fig. Figure 3 is a flowchart that schematically illustrates a process for producing an electrode including a catalyst complex for fuel cells according to an embodiment of the invention; Fig. Figure 4 is a flowchart schematically illustrating a process for producing an electrode including a catalyst complex for fuel cells according to another embodiment of the invention; and Fig. Figure 5 is a flowchart that schematically illustrates a process for producing an electrode including a catalyst complex for fuel cells according to a further embodiment of the invention.

[0041] It is understood that the accompanying drawings are not necessarily to scale and represent a somewhat simplified depiction of various features that illustrate the basic principles of the invention. The specific design features of the invention, as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes, are partly determined by the particular intended application and environment of use.

[0042] In the figures, the reference numerals refer to identical or equivalent parts of the present invention in the different figures of the drawing. DETAILED DESCRIPTION

[0043] The following section refers in detail to various embodiments of the invention, which are illustrated by way of example in the accompanying drawings and described below. In the following description of the embodiments, identical elements are designated by the same reference numerals, even though they are shown in different drawings.

[0044] In the following description of embodiments, terms such as "include," "have," etc., are interpreted as indicating the presence of features, numbers, steps, elements, or parts specified in the description, or combinations thereof, but not as excluding the presence of one or more other features, numbers, steps, elements, parts, or combinations thereof, or the possibility of adding them. Furthermore, terms such as "and / or" can conceptually include any of the specified items and all combinations of one or more of the specified items.

[0045] Furthermore, it is understood that when a part, such as a layer, film, region, or plate, is described as being "on" another part, the part may lie "directly on" the other part, or other parts may be inserted between the two parts. Similarly, it is understood that when a part, such as a layer, film, region, or plate, is described as being "under" another part, the part may be arranged "directly beneath" the other part, or other parts may be inserted between the two parts.

[0046] All numbers, values, and / or expressions representing quantities of components, reaction conditions, polymer compositions, and mixtures used in the description are approximate values ​​reflecting various measurement uncertainties that arise when these values ​​are measured from substantially different things. Therefore, unless otherwise stated, they are understood to be modified by the term "approximately." It is further understood that where a numerical range is specified in the description, such range, unless otherwise stated, encompasses all continuous values ​​from a minimum value to a maximum value of the range. Where such a range refers to integers, the range, unless otherwise stated, encompasses all integers from a minimum integer value to a maximum integer value.

[0047] In the following description of the embodiments, it is understood that when the range of a variable is specified, the variable includes all values ​​within the specified range, including the specified endpoints of the range. For example, a range of "5 to 10" should not only include the values ​​5, 6, 7, 8, 9, and 10, but also arbitrary subranges, such as a subrange of 6 to 10, a subrange of 7 to 10, a subrange of 6 to 9, a subrange of 7 to 9, etc., and arbitrary values ​​between integers that lie within the specified range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, etc. Furthermore, a range of "10% to 30%" should not only include all integers including the values ​​10%, 11%, 12%, 13%, ..., 30%, but also arbitrary subranges, such as...a subrange of 10% to 15%, a subrange of 12% to 18%, a subrange of 20% to 30%, etc., and arbitrary values ​​between integers that lie within the specified range, such as 10.5%, 15.5%, 25.5%, etc.

[0048] The embodiments according to the invention are described in detail below with reference to the accompanying drawing figures.

[0049] Fig. Figure 1 is a schematic representation of a conventional catalyst complex for fuel cells.

[0050] Referring to Fig. 1. The conventional catalyst complex for fuel cells can be contained within an electrode (for example, an anode) of a membrane electrode assembly (MEA) for fuel cells. An electrochemical reaction to generate electricity in a fuel cell can take place in a membrane electrode assembly (MEA) containing an electrolyte membrane and electrodes (an anode and a cathode) based on perfluorinated sulfonic acid (PFSA) and ionomeric electrolytes. An electrode used in a fuel cell electric vehicle can contain a catalyst complex with catalysts that effect a fuel cell reaction or are supported on catalyst carriers, and can include an ionomeric binder that binds the catalysts together or binds the catalysts and the catalyst carriers together.

[0051] As in Fig. As shown in more detail in Figure 1, the catalyst complex contained in the electrode can comprise a supported-type hydrogen oxidation reaction catalyst 100, which includes a hydrogen oxidation reaction catalyst 10 and a carbon support 11 on which the hydrogen oxidation reaction catalyst 10 can be supported, a water-splitting catalyst 20 and an ionomer binder 50, which can be applied to the supported-type hydrogen oxidation reaction catalyst 100 and the water-splitting catalyst 20.

[0052] As a reaction catalyst 10 for hydrogen oxidation, high-priced platinum (Pt) can be used, which can be alloyed with a metallic element such as palladium (Pd), ruthenium (Ru), iridium (Ir), gold (Au), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), yttrium (Y), or similar, in order to reduce the price of a fuel cell stack and prevent catalyst poisoning (e.g., by carbon monoxide), or to improve the catalyst's performance. To increase the reaction surface area of ​​this metal catalyst, nanoscale particles of the metal catalyst can be deposited on a catalyst support with a large specific surface area.A carbon-based material with high electrical conductivity can be used as a support for fuel cell catalysts, such as carbon black, activated carbon, carbon nanotubes, carbon nanofibers, carbon nanospheres, carbon nanowires, graphite, graphene, mesoporous carbon, or the like. Furthermore, an ionomer binder based on perfluorinated sulfonic acid (PFSA) can be used as the electrode 50.

[0053] To prevent the corrosion of a catalyst, the catalyst can be supported on a non-carbon support, such as titanium oxide, cerium oxide, niobium oxide, tungsten oxide, titanium carbide, titanium nitride or the like, which can increase the corrosion resistance of the catalyst.

[0054] Therefore, the water splitting catalyst 20 used by the electrodes splits water upon voltage reversal, as expressed in the following equation 5, and provides protons to prevent an excessive voltage increase of the electrode and to suppress the oxidation of a carbon support, thereby preventing damage to cells. H2O → 1 / 2O2 + 2H + + 2e - (1.229 V vs. SHE) [Equation 5]

[0055] Since, if water present in the electrode or water supplied from outside by humidified gas may not be properly supplied to the water splitting catalyst 20 under a voltage reversal condition, the carbon oxidation reaction may be rapidly increased, resulting in a proton deficiency, and it may be necessary to effectively supply water, i.e. a reactant, to the water splitting catalyst 20.

[0056] Fig. Figure 2 is a schematic representation of a catalyst complex for fuel cells according to an embodiment of the invention.

[0057] Referring to Fig. According to the invention, the catalyst complex for fuel cells comprises a first catalyst 100, which causes a hydrogen oxidation reaction (HOR), and a second catalyst 200, which causes a water electrolysis reaction, i.e., an oxygen evolution reaction (OER), with the first catalyst 100. Furthermore, the outer surface of the first catalyst 100 is coated with a first ionomer binder 110, and the outer surface of the second catalyst 200 is coated with a second ionomer binder 220. In some cases, the equivalent weight (EW) of the second ionomer binder 220 may be lower than the equivalent weight (EW) of the first ionomer binder 110.

[0058] As in Fig. As shown in Figure 2, the first catalyst (i.e., a catalyst for the hydrogen oxidation reaction) 100 can comprise a supported-type catalyst in which the catalyst particles 10 are applied to a carbon support 11. The carbon support 11 can be selected from or include carbon black (CB), carbon nanotubes (CNT), carbon nanofibers (CNF), carbon nanowires (CNW), carbon nanohorns (CNH), graphene, or combinations thereof. The carbon particles 10 can be applied to the carbon support 11.

[0059] Furthermore, the first catalyst 100 includes a metal catalyst. For example, as in Fig. Figure 2 shows that the catalyst particles 10 of the first catalyst are 100 particles of a metal catalyst. The metal catalyst can be selected from or include, for example, a group consisting of platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), gold (Au), silver (Ag), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), yttrium (Y), or combinations thereof.

[0060] Furthermore, the second catalyst 200 comprises at least metal nanoparticles or a metal oxide. This metal of the second catalyst 200 may be selected from or include a metal from a group consisting of ruthenium (Ru), iridium (Ir), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), yttrium (Y), or combinations thereof.

[0061] Furthermore, the second catalyst 200 can, for example, comprise a supported catalyst in which catalyst particles are applied to a support. Therefore, the reaction surface area of ​​the second catalyst 200 can be further increased. The support can, for example, be selected from or include a group consisting of carbon black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanohorns, graphene, titanium oxide, cerium oxide, niobium oxide, tungsten oxide, titanium carbide, titanium nitride, or combinations thereof.

[0062] Furthermore, the catalyst complex for fuel cells can comprise 2 wt% to 80 wt% of the second catalyst 200, relative to the weight of the first catalyst 100 (i.e., the catalyst for the hydrogen oxidation reaction). If the content of the second catalyst 200 is less than 2% of the weight of the first catalyst 100, the proton supply capacity during voltage reversal may be low, making it difficult to suppress the voltage rise at the electrode (i.e., the anode).On the other hand, if the content of the second catalyst 200 exceeds 80% of the weight of the first catalyst 100, the supply of hydrogen gas, which can be a reactant of the hydrogen oxidation reaction, may be hindered under normal operating conditions of the fuel cell, in which no voltage reversal takes place, thereby reducing the power of the fuel cell and thus increasing the material costs due to the use of an excessive amount of the second catalyst 200.

[0063] As in Fig. As shown in Figure 2, the first ionomer binder 110 can be applied to the first catalyst 100, which may be a supported-type hydrogen oxidation reaction catalyst comprising the catalyst particles 10 and the carbon support 11, and can thus bind components of the first catalyst 100 and transfer protons, i.e., a reaction product. The first ionomer binder 110 can be selected from or include a perfluorinated sulfonic acid (PFSA)-based ionomer, a hydrocarbon-based ionomer, or a combination thereof. For example, the first ionomer binder 110 can be a PFSA-based ionomer.

[0064] Furthermore, as in Fig. Figure 2 shows that the second ionomer binder 220 is applied to the second catalyst 200 and thus serves to bind the second catalyst 200, supply water to the second catalyst 200, and transfer protons, i.e., the reaction product. The second ionomer 220 can be an ionomer selected from or including a group consisting of a perfluorinated sulfonic acid (PFSA)-based ionomer, a hydrocarbon-based ionomer, and a combination thereof. For example, the second ionomer 220 can be a PFSA-based ionomer.

[0065] The catalyst complex for fuel cells according to an example of the invention differs from the conventional catalyst complex in that the equivalent weight (EW) of the second ionomer binder 220 can be lower than the equivalent weight (EW) of the first ionomer binder 110. The equivalent weight (EW) of the second ionomer binder 220 is 92% or less of the equivalent weight (EW) of the first ionomer binder 110, i.e., the equivalent weight (EW) of the second ionomer binder 220 can be 8% or more lower than the equivalent weight (EW) of the first ionomer binder 110. This allows water to be readily supplied to the second catalyst 200, which is present in the electrode (e.g., the anode), during voltage reversal of the fuel cell, and consequently, the voltage reversal resistance of the fuel cell stack can be increased.If the equivalent weight (EW) of the second ionomer binder 220 is greater than the equivalent weight (EW) of the first ionomer binder 110 or less than 8% lower than the equivalent weight (EW) of the first ionomer binder 110, it may happen during a voltage reversal that not enough water is supplied to the second catalyst 200 in accordance with the reactant, so that it may be difficult to suppress the increase in voltage of the electrode (i.e. the anode) over a long period of time.

[0066] The equivalent weight (EW) of the first ionomer binder 110 can range from 700 to 1200. Here, the equivalent weight (EW) can represent the dry weight of one ionomer per mole of a sulfonic acid group contained in the ionomer binder. If the equivalent weight (EW) of the first ionomer binder 110 is less than 700, its mechanical stiffness may be reduced, and its water content may be excessively high, potentially leading to water flooding of the electrode during fuel cell operation. Conversely, if the equivalent weight (EW) of the first ionomer binder 110 exceeds 1200, the proton conductivity may be reduced, thus impairing the fuel cell's performance. In some cases, the equivalent weight (EW) of the first ionomer binder 110 may range between 725 and 1100.

[0067] The following describes methods for producing an electrode including a catalyst complex for fuel cells in accordance with several embodiments of the invention. For the sake of simplicity, a detailed description of part of the design and operation of one embodiment, which is essentially the same as that described above with reference to the Fig. 1 and Fig. 2 described agree.

[0068] Firstly, referring to the Fig. 3, a method for producing an electrode for fuel cells comprising a catalyst complex in accordance with an embodiment of the invention, producing a first coated catalyst by coating a first catalyst with a first ionomer binder (step S100), producing a second coated catalyst by coating a second catalyst with a second ionomer binder having an equivalent weight (EW) that is 92% or less of the equivalent weight (EW) of the first ionomer binder 110 (step S200), producing a catalyst ink by mixing the first coated catalyst, the second coated catalyst and a solvent (step S300) and producing the electrode using the catalyst ink (step S400).

[0069] To prepare the first coated catalyst (step S100), for example, the first catalyst, which consists of particles of a hydrogen oxidation reaction catalyst and a carbon support carrying the catalyst particles, can be coated with the first ionomer binder. As described above, in the present invention, the first catalyst is the hydrogen oxidation reaction catalyst. Furthermore, to prepare the second coated catalyst (step S200), for example, the second catalyst, which corresponds to a water-splitting catalyst, can be coated with the second ionomer binder. Although Fig. Figure 3 shows that the catalyst ink is prepared (step S300) by producing the second coated catalyst (step S200) after preparing the first coated catalyst (step S100). The present invention is not limited to this. That is to say, the catalyst ink can be produced (step S300) by simultaneously producing the first coated catalyst (step S100) and the second coated catalyst (step S200), or by producing the first coated catalyst (step S100) after producing the second coated catalyst (step S200).

[0070] In some cases, the solvent used in preparing the catalyst ink (step S300) may include, for example, at least alcohol or deionized water. The alcohol may be selected from or include isopropyl alcohol (IPA), n-propyl alcohol (nPA), ethyl alcohol, or combinations thereof. Therefore, to prepare the catalyst ink (step S300), the catalyst ink (e.g., anode) may be produced by mixing the first catalyst (i.e., the hydrogen oxidation reaction catalyst) coated with the first ionomer binder, the second catalyst (i.e., the water-splitting catalyst) coated with the second ionomer binder, and the solvent.

[0071] Furthermore, as described above, when preparing the catalyst ink (step S300), the prepared catalyst ink can comprise 2 wt.% to 80 wt.% of the second coated catalyst in relation to the weight of the first coated catalyst.

[0072] When manufacturing the electrode (e.g. the anode) (step S400), the electrode can be manufactured using various methods, e.g. a decal transfer method, a spraying method or an inkjet printing method.

[0073] For example, if the decal transfer method is used to manufacture the electrode (step S400), a decal electrode can be produced by applying the catalyst ink to a decal transfer film using a rod applicator and then drying the decal transfer film sufficiently. The loading of the resulting decal electrode with a metal catalyst (e.g., platinum (Pt)) can be adjusted by controlling the concentration or coating thickness of the catalyst ink.Furthermore, since the decal electrode, coated on the decal transfer film, should be easily separable from the electrolyte membrane when transferred to it, and should withstand the conditions of high-temperature heat treatment, the decal transfer film can utilize a heat-resistant polymer. This heat-resistant polymer can, for example, contain one or more polymers selected from or including polytetrafluoroethylene (PTFE), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(trimethylene terephthalate) (PTT), poly(ethylene naphthalate) (PEN), and polyimide (PI). The decal electrode can then be thermocompressed onto the electrolyte membrane, and the decal transfer film can subsequently be removed, thus producing a membrane electrode assembly for fuel cells.

[0074] Next, with reference to Fig. 4. A method for producing an electrode for fuel cells, including a catalyst complex, is described in accordance with another embodiment of the invention. For the sake of simplicity, a detailed description of that part of the design and operation of this embodiment, which is essentially the same as that described above with reference to the Fig. The identical nature of the descriptions in 1-3 is omitted.

[0075] In the process for manufacturing an electrode for fuel cells in accordance with this embodiment of the invention, the production of a first coated catalyst (referring to step S100 of Fig. 3) the preparation of a first mixed solution comprising a first catalyst, a first ionomer binder and a first solvent (step S101), and comprising the preparation of the first coated catalyst by carrying out drying and heat treatment of the first mixed solution (step S110).

[0076] For example, when preparing the first mixed solution (step S101), the first mixed solution can be prepared by adding the first catalyst 100, i.e., a catalyst for the hydrogen oxidation reaction, and the first ionomer binder to the first solvent, stirring the resulting mixture sufficiently at room temperature using a stirrer, and then performing an ultrasonic treatment of the mixture.

[0077] In some cases, when preparing the first mixed solution (step S101), the first mixed solution may contain, for example, 10 wt% to 50 wt% of the first ionomer binder, based on the total weight of the first catalyst (i.e., the hydrogen oxidation reaction catalyst) and the first ionomer binder. If the content of the first ionomer binder, based on the total weight, is less than 10 wt%, it may be difficult to adequately connect and bind the first catalyst (including the hydrogen oxidation reaction catalyst) in a three-dimensional network structure. On the other hand, if the content of the first ionomer binder, based on the total weight, exceeds 50 wt%, an excessive amount of the first ionomer binder may clog the pores in the electrode, and water flooding may occur in the electrode.In some cases, 20 wt.% to 35 wt.% of the first ionomer binder can be used, based on the total weight of the first catalyst and the first ionomer binder.

[0078] Furthermore, the first solvent may include at least alcohol or deionized water, and the alcohol may be selected from or include a group consisting of isopropyl alcohol (IPA), n-propyl alcohol (nPA), ethyl alcohol and combinations thereof.

[0079] When producing the first coated catalyst by performing a drying and heat treatment of the first mixed solution (step S110), the first solvent can be removed by drying the produced first mixed solution, and then the entire surface of the first catalyst can be coated with the first ionomer binder by performing a heat treatment of the obtained cake-like first catalyst (i.e., the hydrogen oxidation reaction catalyst) and the first ionomer binder in a dryer.

[0080] When producing the first coating catalyst by drying and heat treatment of the first mixed solution (step S110), the heat treatment can be carried out, for example, in a range from the α-transition temperature T α of the first ionomer binder up to a temperature that is 100 °C higher than the α-transition temperature T α. Here, the α-transition temperature T can be α This refers to a temperature at which the crystallinity of a polymer suddenly changes. If the temperature of the heat treatment (in step S110) is lower than the α-transition temperature Tα, then the α-transition temperature Tα is αα. α Due to the presence of the first ionomer binder, the binding force between the first catalyst (i.e., the catalyst of the hydrogen oxidation reaction) and the first ionomer binder may be low. Therefore, the first catalyst and the first ionomer binder can separate from each other upon redistribution in the solvent. On the other hand, if the temperature of the heat treatment (in step S110) exceeds the α-transition temperature T1, the ionomer binder may separate. αIf the temperature exceeds 100 °C, the thermal degradation of the first ionomer binder can be accelerated, or the degree of crystallinity of the first ionomer binder can be excessively increased. Therefore, the first ionomer binder may not be redistributed in the solvent due to its decreasing solubility. If the membrane-electrode assembly is subsequently fabricated, the interfacial adhesion between the electrode and the electrolyte membrane may be reduced. In some cases, the temperature of the heat treatment (in step S110) may be within a range of the α-transition temperature Tα. α of the first ionomer binder up to a temperature that is 50 °C higher than the α-transition temperature T α , lie. The α-transition temperature T α The temperature of the first ionomer binder can be, for example, 60°C to 130°C, but is not limited to this range. In other words, the α-transition temperature T αThe first ionomer binder can be varied depending on the type and structure of the ionomer.

[0081] Furthermore, the heat treatment (in step S110) can be carried out for, e.g., 10 minutes to 10 hours. In other words, the heat treatment of the first catalyst (i.e., the hydrogen oxidation reaction catalyst) and the first ionomer binder can be carried out for 10 minutes to 10 hours. In some cases, the heat treatment of the first catalyst (i.e., the hydrogen oxidation reaction catalyst) and the first ionomer binder (in step S110) can be carried out, e.g., in the range of the α-transition temperature T. α of the first ionomer binder up to the temperature which is 100 °C higher than the α-transition temperature T αThe heat treatment can be carried out for 10 minutes to 10 hours. If the heat treatment time is less than 10 minutes, the effects of the heat treatment may be negligible, and if the heat treatment time is more than 10 hours, the thermal degradation of the first ionomer binder may be accelerated or the degree of crystallinity of the first ionomer binder may be excessively increased. This can increase the process cycle time. In some cases, such a heat treatment of the first mixed solution (in step S110) can be carried out for 30 minutes to 5 hours.

[0082] As in Fig. As shown in Figure 4, the production of a second coated catalyst (referring to step S200 of Fig. 3) comprising the preparation of a second mixed solution containing a second catalyst, a second ionomer binder and a second solvent (step S202), and the preparation of the second coated catalyst by drying and heat treatment of the second mixed solution (step S220).

[0083] When preparing the second mixed solution (step S202), for example, the second mixed solution can be prepared by adding the second catalyst (i.e., a water-splitting catalyst) and the second ionomer binder to the second solvent, stirring the resulting mixture sufficiently at room temperature with a stirrer, and then performing an ultrasonic treatment of the mixture.

[0084] When preparing the second mixed solution (step S202), the second mixed solution can contain, for example, 5 wt% to 40 wt% of the second ionomer binder, based on the total weight of the second catalyst and the second ionomer binder. If the content of the second ionomer binder, based on the total weight, is less than 5 wt%, the second ionomer binder may not sufficiently surround the second catalyst (i.e., the water-splitting catalyst), and water, corresponding to a reactant, may not be supplied uniformly to the second catalyst during a voltage reversal, making it difficult to improve the voltage reversal strength of the fuel cell stack. On the other hand, if the content of the second ionomer binder, based on the total weight, exceeds 40 wt%, the second catalyst (i.e.,Water can be readily supplied as a reactant to the water-splitting catalyst during voltage reversal. However, an excessive amount of the second ionomer binder can clog the pores in the electrode, and water flooding can occur in the electrode under normal fuel cell operating conditions where no voltage reversal takes place. In some cases, 15 wt% to 30 wt% of the second ionomer binder can be used, based on the total weight of the second catalyst and the second ionomer binder.

[0085] Furthermore, the second solvent may be a solvent selected from or including, for example, a group containing isopropyl alcohol (IPA), n-propyl alcohol (nPA), ethyl alcohol or combinations thereof.

[0086] When producing the second coated catalyst by drying and heat-treating the second mixed solution (step S220), the second solvent can be removed by drying the produced second mixed solution. Then, the entire surface of the second catalyst can be coated with the second ionomer binder by heat-treating the acquired cake-like second catalyst (e.g., including the water-splitting catalyst) and the second ionomer binder in a dryer.

[0087] When producing the second coated catalyst by drying and heat treatment of the second mixed solution (step S220), the heat treatment can be carried out, for example, in a range from the α-transition temperature T α of the second ionomer binder up to a temperature that is 100°C higher than the α-transition temperature T α .

[0088] Is the temperature of the heat treatment (in step S220) lower than the α-transition temperature T α of the second ionomer binder, the binding force between the second catalyst (including the water-splitting catalyst) and the second ionomer binder can be so low that the second catalyst and the second ionomer binder can be separated from each other when redistributed in the solvent. On the other hand, if the temperature of the heat treatment (in step S220) exceeds the temperature above the α-transition temperature T αIf the temperature is increased by 100 °C, the thermal degradation of the second ionomer binder may be accelerated, or the degree of crystallinity of the second ionomer binder may be excessively increased, preventing redistribution of the second ionomer binder in the solvent due to decreased solubility. Furthermore, if the membrane-electrode assembly is subsequently fabricated, the interfacial adhesion between the electrode and the electrolyte membrane may be reduced. In some cases, the temperature of the heat treatment (in step S220) may be within a range of the α-transition temperature Tα. α of the second ionomer binder up to a temperature that is 50 °C higher than the α-transition temperature T α The α-transition temperature T α The temperature of the second ionomer binder can be, for example, 60 °C to 130 °C, without being limited to this range. That is, the α-transition temperature T αThe composition of the second ionomer binder can be varied depending on the type and structure of the ionomer.

[0089] Furthermore, the heat treatment (in step S220) can be carried out for, e.g., 10 minutes to 10 hours. This means that the heat treatment of the second catalyst (including the water-splitting catalyst) and the second ionomer binder can be carried out for 10 minutes to 10 hours. In some cases, the heat treatment of the second catalyst (including the water-splitting catalyst) and the second ionomer binder (in step S220) can be carried out, e.g., within the range of the α-transition temperature T. α of the second ionomer binder up to a temperature that is 100 °C higher than the α-transition temperature T αThe heat treatment can be carried out for 10 minutes to 10 hours. If the heat treatment time is less than 10 minutes, the effects of the heat treatment may be negligible; if the heat treatment time is more than 10 hours, the thermal degradation of the second ionomer binder may be accelerated, or the degree of crystallinity of the second ionomer binder may be excessively increased. This can increase the process cycle time. Such a heat treatment of the second mixed solution (in operation S220) can take 30 minutes to 5 hours.

[0090] Next, with reference to Fig. 5. A method for producing an electrode for fuel cells, including a catalyst complex, in accordance with a further embodiment of the invention is described. For the sake of simplicity, a detailed description of part of the design and operation of this embodiment, which is essentially the same as described above with reference to the Fig. The identical descriptions in 1-4 have been omitted.

[0091] Referring to the Fig.5 comprises the process for producing an electrode for fuel cells including a catalyst complex according to this embodiment of the invention, the production of a first mixed solution including a first catalyst, a first ionomer binder and a first solvent (step S101), the production of a second mixed solution including a second catalyst, a second ionomer binder and a second solvent (step S202), the production of a second coated catalyst by carrying out drying and heat treatment of the second mixed solution (step S220), the production of a catalyst ink by mixing the first mixed solution and the second coated catalyst (step S350), and the production of the electrode using the catalyst ink (step S400).

[0092] The method according to this embodiment differs from the methods described above according to the first-mentioned embodiments in that, in the production of the catalyst ink (step S350), the catalyst ink (e.g., anode) can be produced by mixing the first mixed solution produced in step S101 with the second coated catalyst produced in step S220. In other words, the method according to this embodiment differs from the methods described above according to the first-mentioned embodiments in that, in the production of the catalyst ink (step S350), the catalyst ink (e.g.,anode) can be produced by mixing the first mixed solution including the first catalyst (including the catalyst of the hydrogen oxidation reaction), the first ionomer binder and the first solvent with the second coated catalyst (including the water-splitting catalyst), produced by coating the second catalyst with the second ionomer binder, without carrying out drying and heat treatment of the first mixed solution.

[0093] This allows the stress reversal strength of the fuel cell stack to be improved through a simpler process and a cost-effective method, thereby achieving an improvement in productivity and marketability as well as a cost reduction of the fuel cell stack in the face of limited resources and energy savings.

[0094] As can be seen from the above description, a catalyst complex for fuel cells and an electrode (e.g. an anode) comprising the same according to some examples according to the invention can effect a uniform supply of water to a water-splitting catalyst and thus suppress an excessive voltage rise of an electrode during voltage reversal.

[0095] Furthermore, the electrode can improve the voltage reversal resistance of a fuel cell stack, thereby improving the driving stability of a vehicle under various driving conditions.

[0096] The electrode, including the catalyst complex, produced according to a method according to the invention, can improve the voltage reversal strength of the fuel cell stack through a simpler and cost-effective process, thereby improving productivity and marketability, reducing the cost of the fuel cell stack with limited resources, and saving energy.

Claims

[1] Catalyst complex for fuel cells, wherein the catalyst complex is included in an electrode for fuel cells, the catalyst complex for fuel cells comprising: a first catalyst designed to effect a hydrogen oxidation reaction; and a second catalyst designed to effect a water electrolysis reaction with the first catalyst, wherein an outer surface of the first catalyst is coated with a first ionomer binder and an outer surface of the second catalyst is coated with a second ionomer binder, and wherein the equivalent weight (EW) of the second ionomer binder differs from the equivalent weight (EW) of the first ionomer binder, wherein the equivalent weight (EW) of the second ionomer binder is 92% or less of the equivalent weight (EW) of the first ionomer binder, wherein the first catalyst comprises a metal catalyst, and wherein the second catalyst comprises at least metal nanoparticles or a metal oxide. [2] Catalyst complex for fuel cells according to claim 1, wherein the equivalent weight (EW) of the first ionomer binder is 700 to 1200. [3] Catalyst complex for fuel cells according to claim 1, wherein the first catalyst comprises a supported-type catalyst in which catalyst particles are carried on a carbon support, and wherein the carbon support is selected from the group consisting of carbon black (CB), carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon nanowires (CNWs), carbon nanohorns (CNHs), graphene or combinations thereof. [4] Catalyst complex for fuel cells according to claim 1, wherein the metal catalyst is selected from a group including platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), gold (Au), silver (Ag), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), yttrium (Y) or combinations thereof, and wherein the metal of the second catalyst is selected from a group including ruthenium (Ru), iridium (Ir), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), yttrium (Y) or combinations thereof. [5] Catalyst complex for fuel cells according to claim 1, wherein the second catalyst comprises a supported catalyst in which catalyst particles are applied to a support. [6] Catalyst complex for fuel cells according to claim 5, wherein the support is selected from the group consisting of carbon black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanohorns, graphene, titanium oxide, cerium oxide, niobium oxide, tungsten oxide, titanium carbide, titanium nitride or combinations thereof. [7] Catalyst complex for fuel cells according to claim 1, wherein the content of the second catalyst, based on the weight of the first catalyst, is 2 wt.% to 80 wt.%. [8] Method for producing an electrode for fuel cells with a catalyst complex, the method comprising: Producing a first coated catalyst by coating a first catalyst with a first ionomer binder; Producing a second coated catalyst by coating a second catalyst with a second ionomer binder having an equivalent weight (EW) that is 92% or less of the equivalent weight (EW) of the first ionomer binder; Producing a catalyst ink by mixing the first coated catalyst, the second coated catalyst and a solvent; and Manufacturing the electrode using the catalyst ink, wherein the first catalyst comprises a metal catalyst, and wherein the second catalyst comprises at least metal nanoparticles or a metal oxide. [9] The method of claim 8, wherein in the preparation of the catalyst ink the solvent comprises at least alcohol or deionized water, and wherein the alcohol is selected from the group consisting of isopropyl alcohol (IPA), n-propyl alcohol (nPA), ethyl alcohol or combinations thereof. [10] Method according to claim 8, wherein the second catalyst in the catalyst ink has a content of 2 wt.% to 80 wt.%, based on the weight of the first catalyst. [11] The method of claim 8, wherein the production of the first coated catalyst comprises: Preparing a first mixed solution comprising the first catalyst, the first ionomer binder, and a first solvent; and Performing drying and heat treatment of the first mixed solution. [12] Method according to claim 11, wherein the first ionomer binder in the first mixed solution has a content of 10 wt.% to 50 wt.%, based on the total weight of the first catalyst and the first ionomer binder. [13] Method according to claim 11, wherein when carrying out the heat treatment of the first mixed solution the heat treatment is carried out within a range from an α-transition temperature of the first ionomer binder to a temperature which is 100 °C higher than the α-transition temperature. [14] Method according to claim 11, wherein when carrying out the heat treatment of the first mixed solution, this heat treatment is carried out for 10 minutes to 10 hours. [15] The method of claim 8, wherein the production of the second coated catalyst comprises: Preparing a second mixed solution comprising the second catalyst, the second ionomer binder, and a second solvent; and Performing drying and heat treatment of the second mixed solution. [16] Method according to claim 15, wherein the second ionomer binder in the second mixed solution has a content of 5 wt.% to 40 wt.%, based on the total weight of the second catalyst and the second ionomer binder. [17] Method according to claim 15, wherein when carrying out the heat treatment of the second mixed solution the heat treatment is carried out within a range from an α-transition temperature of the second ionomer binder to a temperature which is 100 °C higher than the α-transition temperature. [18] Method according to claim 15, wherein when carrying out the heat treatment of the second mixed solution, this heat treatment is carried out for 10 minutes to 10 hours. [19] Method for producing an electrode for fuel cells comprising a catalyst complex, the method comprising: Preparation of a first mixed solution comprising a first catalyst, a first ionomer binder and a first solvent; Preparing a second mixed solution comprising a second catalyst, a second ionomer binder and a second solvent; Producing a second coated catalyst by carrying out drying and heat treatment of the second mixed solution; Producing a catalyst ink by mixing the first mixed solution and the second coated catalyst; and Manufacturing the electrode using the catalyst ink, wherein the first catalyst comprises a metal catalyst, and wherein the second catalyst comprises at least metal nanoparticles or a metal oxide.

Images