Fuel cell electrode, catalyst-coated membrane, fuel cell, and method for producing the fuel cell electrode and catalyst-coated membrane

Abstract

The invention relates to a fuel cell electrode (2, 3) which comprises a metal-containing catalyst (5, 7) and a proton-conductive ionomer (6, 8), wherein the fuel cell electrode (2, 3) has a halide concentration of 50 to 1000 ppm, based on the total mass of the fuel cell electrode (2, 3).

Description

[0001] Fuel cell electrode, catalyst-coated membrane, fuel cell and method for producing the fuel cell electrode and the catalyst-coated membrane

[0002] Description

[0003] The invention relates to a fuel cell electrode, a catalyst-coated membrane, a fuel cell and a method for producing the fuel cell electrode and also a method for producing the catalyst-coated membrane.

[0004] It is known from the prior art that halide ions, and in particular chloride ions, can reduce the functionality or long-term stability of a membrane electrode assembly for fuel cells. Halide ions can be introduced into the membrane electrode assembly via various routes, for example, through the use of halide-containing precursor compounds for the catalysts used in the electrodes of the membrane electrode assembly, such as H2Pt(Cl)e and the like.

[0005] Under real-world operating conditions, MEAs undergo potential cycling, i.e., alternating phases of higher and lower potentials. This results in repeated reduction and oxidation of the catalysts in the fuel cell electrodes, particularly the commonly used platinum on the cathode side of the MEA. This, in turn, leads to repeated dissolution and deposition of the platinum, which can cause individual catalyst particles to agglomerate, a process known as "Ostwald ripening," which reduces the catalyst surface area over the course of operation, thus resulting in a loss of performance.

[0006] Guilminot et al. (J. Electrochem. Soc. 2007, 154 (1), B96-B105) report a

[0007] Poisoning of a platinum-based and carbon-supported (Pt / C) catalyst by halides and a resulting reduction in catalytic activity. It is also noted that adsorbed halides promote the (electro)chemical dissolution of Pt or PtO.

[0008] Halogenated intermediates in the production of perfluorinated polymers, which are used, for example, in fuel cell membranes and as ionomers in fuel cell electrodes, are described in DE102018002337 A1 as a cause of halide contamination. The effect of increased platinum dissolution by chloride or bromide is mentioned in DE102018002337 A1 and in Electrochimica Acta 52(2007): 7444-7552 cited therein, with even a very small amount of approximately 1 ppm being described as negative. A chloride concentration of just 4 ppm is said to lead to a voltage drop of 50 mV. Furthermore, chlorides can lead to increased formation of H2O2, which causes chemical degradation and thus leads to thinning or hole formation in the membrane.DE102018002337 A1 therefore provides a method for improving the long-term stability of an MEA, in which the amount of halide ions is reduced by adding silver carbonate, forming silver halide and then illuminating and thus decomposing the silver halide with release of the halogen.

[0009] Based on the prior art cited above, it is an object of the present invention to provide a fuel cell electrode, a catalyst-coated membrane, and also a fuel cell with improved long-term stability that do not result in any loss of performance when used as intended. Furthermore, it is an object of the present invention to provide methods for producing a long-term stable fuel cell electrode and a long-term stable catalyst-coated membrane, and also a fuel cell, that are simple and cost-effective to implement and improve the long-term stability of the fuel cell electrode, and thus also the long-term stability of the catalyst-coated membrane and the fuel cell, without leading to any loss of performance.

[0010] For this purpose, the fuel cell electrode according to the invention comprises a metal-containing catalyst and a proton-conductive ionomer. The fuel cell electrode can be designed as a cathode or as an anode. Depending on the case, the fuel cell electrode also comprises a corresponding metal-containing catalyst, namely, in the case of a cathode, an oxygen-reducing metal-containing catalyst (this corresponds to the first metal-containing catalyst in the catalyst-coated membrane of the present invention) and, in the case of an anode, a hydrogen-oxidizing metal-containing catalyst (this corresponds to the second metal-containing catalyst in the catalyst-coated membrane of the present invention). The proton-conductive ionomer of the anode and cathode can be the same or different. The fuel cell electrode is characterized by a halide concentration of 50 to 1000 ppm, based on the total mass of the fuel cell electrode.This means that halide ions are actively added to the fuel cell electrode, for example in the form of a halide-containing solution. Any amounts of halide already contained in the individual components of the fuel cell electrode are taken into account in the halide concentration of 50 to 1000 ppm. These can be halide ions, for example, introduced by precursors of the metal-containing catalyst or by the ionomer. However, the amounts of halide concentrations already contained in the individual components of the fuel cell electrode are negligible and are in particular below 20 ppm and especially below 10 ppm. In order to achieve a halide concentration of 50 to 1000 ppm, at least one halide is actively added to the fuel cell electrode.According to the invention, the halide concentration in the fuel cell electrode refers to the halide concentration before the fuel cell electrode is used as intended.

[0011] The halide concentration can be adjusted by adding a single halide or by adding a combination of two or more halides. There are no specific restrictions on the halide type and it is typically introduced into the fuel cell electrode as a dissolved salt. The halides in the fuel cell electrode are determined using ion chromatography. Ion chromatography allows the halides to be differentiated by their retention time (retention times: e.g., F: 6.9 min, CI: 10.4 min, Br: 15.9 min). A mixture of 1.9 L of an aqueous solution of sodium carbonate with a concentration of 3.2 mmol / L, sodium bicarbonate with a concentration of 1.0 mmol / L, and 0.1 L of acetonitrile is used as the mobile phase, resulting in a total of 2.0 L of mobile phase. The measurement is performed using a Metrohm 690 IC (Deutsche METROHM GmbH & Co. KG, Germany). The column model used is Metrosep A Supp7 - 250 / 4.0 mm (Deutsche METROHM GmbH & Co. KG, Germany) is used. The column temperature is set to 40 °C, and the flow rate is 0.7 mL min. -1Depending on the sample preparation, free ions can be measured in ion chromatography. This means that fluorine that is covalently bound, for example, in the polymer, is not detected. For this purpose, the halides are extracted, for example, using water. If the concentration of halides that would otherwise be present in one of the components of the fuel cell electrode is to be determined, the sample can also be ashed and then measured. To determine chloride ions, sample preparation can be carried out using a so-called oxygen pressure digestion. In this method, the sample material is burned under pressure and with the addition of oxygen in a closed system, thus releasing the analytes covalently bound in the material and determining them using ion chromatography.Since chloride ions are not usually present in any of the components in a bound state, the chloride ion concentration of free chloride ions also corresponds to the chloride ion concentration in the entire fuel cell electrode.

[0012] Since the fuel cell electrode is used as intended in a fuel cell, in particular with a second fuel cell electrode and a membrane arranged between the two fuel cell electrodes, it is preferred if only the fuel cell electrode according to the invention comprises an addition of halide(s), so that the halide concentration of this fuel cell electrode is in the range from 150 to 6000 ppm, and no further halides are added to the second fuel cell electrode or the membrane.

[0013] Surprisingly, it has been shown that a halide concentration of 150 to 6000 ppm based on the total mass of the fuel cell electrode improves the long-term stability of the fuel cell electrode and thus prevents degradation of the metal-containing catalyst. The halide concentration does not reduce the performance of the fuel cell electrode when used as intended.

[0014] The subclaims contain advantageous developments and refinements of the invention.

[0015] In light of a balance between long-term stability and performance of the fuel cell electrode, the fuel cell electrode preferably has a halide concentration of 300 to 3000 ppm, based on the total mass of the fuel cell electrode.

[0016] As already disclosed above, the halide used is essentially unlimited. Advantageously, the halide is selected from the group consisting of fluoride, chloride, bromide, iodide, and mixtures thereof, and is preferably chloride due to its excellent availability and processability, as well as its low adverse health effects.

[0017] According to an advantageous development, the metal-containing catalyst comprises a noble metal, or mixtures or alloys of two or more noble metals, or a noble metal-base metal alloy. Base metal alloys are particularly suitable for fuel cell electrodes designed as cathodes, and pure noble metal catalysts are particularly suitable for fuel cell electrodes designed as anodes. It is preferred if the noble metal-base metal alloy comprises a platinum alloy and / or if the noble metal of the metal-containing catalyst comprises platinum and / or palladium.

[0018] Since degradations due to potential cycles of the metal-containing catalysts are particularly evident on the cathode side of a fuel cell, the fuel cell electrode according to the invention is preferably designed as a cathode.

[0019] Furthermore, the invention also describes a catalyst-coated membrane comprising a fuel cell electrode designed as described above. By using the fuel cell electrode according to the invention, the catalyst-coated membrane according to the invention (hereinafter: CCM) is also characterized by very high long-term stability with consistently good performance. Thus, the CCM according to the invention offers the same advantageous effects as described above for the fuel cell electrode according to the invention. These advantageous effects are attributable to the halide concentration of 150 to 6000 ppm in the fuel cell electrode used.

[0020] Furthermore, the invention also describes a method for producing the fuel cell electrode disclosed above. In one process step of the process according to the invention, a halide concentration is added to the fuel cell electrode such that the halide concentration of the fuel cell electrode is 150 to 6000 ppm, and preferably 300 to 3000 ppm, based on the total mass of the fuel cell electrode. Adding a halide concentration here means that the halide is added, in particular, in the form of a soluble salt and is not already introduced with the other fuel cell electrode elements, i.e., in particular, the ionomer and the metal-containing catalyst. The halide(s) are added separately, and thus independently of the other fuel cell electrode elements.

[0021] By adding one or more halides, a fuel cell with high long-term stability can be produced without any loss of performance. The process can be implemented without significant technical or time-consuming effort.

[0022] According to an advantageous development, the addition of the halide concentration is carried out by producing the fuel cell electrode with a solution containing at least one halide. By producing the solution with a halide-containing solution, a very uniform distribution of the halide can be achieved in the fuel cell electrode, so that the fuel cell electrode is evenly well protected against degradation in every catalytically active area, thus preventing any performance losses during intended use.

[0023] The fuel cell electrode can be manufactured as an anode or a cathode. The anode or cathode is typically made from an anode dispersion or cathode dispersion. A halide-containing compound is added to the anode dispersion or cathode dispersion in such a way that the halide weight fraction FA in the anode dispersion satisfies the following formula:

[0024] FA = G4 x B )

[0025] In the above formula, A is 150 to 6000 ppm and preferably 300 to 3000 ppm and B is the solid content of the anode dispersion.

[0026] Alternatively, the halide weight fraction FK in the cathode dispersion satisfies the following formula:

[0027] F K = (A x B ) where A is 150 to 6000 ppm and preferably 300 to 3000 ppm, and B is the solids content of the cathode dispersion.

[0028] As already disclosed above, the halide is preferably selected from the group consisting of fluoride, chloride, bromide, iodide and mixtures thereof, and is preferably chloride due to its very good availability and low harmful effect on health.

[0029] According to an advantageous development, a cation of a halide-containing compound used to generate the required halide concentration is selected from the group of protons, alkali metals, alkaline earth metals, an ammonium ion, or cationic organic compounds. Particularly preferred cations are Na + and K + .

[0030] To further simplify the process, a fuel cell electrode dispersion is prepared for producing the fuel cell electrode by dispersing a metal-containing catalyst and a proton-conductive ionomer, and adding a halide-containing compound to the fuel cell electrode dispersion before, during, or after dispersion. Addition of the halide-containing compound is particularly carried out with further dispersion to achieve a uniform distribution of the halide or halides. The process according to the invention can be used to produce the fuel cell electrode according to the invention. Accordingly, a fuel cell electrode produced according to the process described above is also described, which is characterized by high long-term stability and, at the same time, no loss of performance.

[0031] Furthermore, the invention also describes a catalyst-coated membrane comprising a cathode, an anode and an intermediate proton-conductive membrane, wherein the cathode comprises a first metal-containing catalyst and a proton-conductive ionomer, wherein the anode comprises a second metal-containing catalyst and a proton-conductive ionomer, and wherein the membrane comprises a proton-conductive ionomer.

[0032] According to the invention, a catalyst-coated membrane is understood to mean any arrangement in which an anode and a cathode surround the two sides of a membrane, so that the membrane is arranged between the cathode and the anode. The anode and the cathode can be coated directly onto the membrane and form a composite. In this case, one speaks in particular of a CCM, i.e. a "catalyst-coated membrane." Furthermore, a catalyst-coated membrane is also understood to mean an arrangement for use in a fuel cell in which the anode and the cathode are arranged on two sides of a membrane, and in particular are laminated. In both cases, the two exposed sides of the anode and the cathode can be provided with a gas diffusion layer (GDL). If gas diffusion layers are provided, the overall arrangement is also referred to as a membrane electrode assembly (MEA).According to the present invention, the halide concentration in the case of the catalyst-coated membrane refers to an arrangement as designed above without GDL.

[0033] The catalyst-coated membrane according to the invention has a halide concentration of 50 to 1000 ppm, based on the total mass of the catalyst-coated membrane. The halide concentration is thus the sum of the individual halide concentrations of the anode, the cathode, and the membrane and relates to the total mass of these components. The halide concentration of 50 to 1000 ppm is essentially not introduced by the metal-containing catalyst(s) and the ionomers, but is explicitly added until the desired halide concentration has been established. The halide concentration in the catalyst-coated membrane is determined by ion chromatography, as already described above for the fuel cell electrode. By the selected sample preparation method or by the selection of the halide(s) to be determined, only free halides are determined and not covalently or otherwise (e.g.Complexed halides are detected in the catalyst-coated membrane. Fluorides, which are present, for example, in the ionomer (e.g., when using fluorinated ionomers) or bound in the membrane, are explicitly not detected by aqueous extraction and subsequent measurement using ion chromatography.

[0034] The halide(s) are preferably present primarily in the cathode, as the cathode is particularly susceptible to catalyst degradation. However, since halide ions can partially move through the layers of the catalyst-coated membrane, the desired halide concentration can also be adjusted in the anode or even in the membrane. When the catalyst-coated membrane is used as intended, the effect on the long-term stability of the catalyst-coated membrane results from the halide(s) being evenly distributed throughout the layers, thus providing a uniform stabilizing effect without impairing the performance of the catalyst-coated membrane.

[0035] The halide concentration of 50 to 1000 ppm, which is essential to the invention and relates to the total mass of the catalyst-coated membrane, is present both in an unused (i.e., newly manufactured) catalyst-coated membrane and in a catalyst-coated membrane during or after intended use. This is justified by the fact that the halide(s) can be added to the anode and / or cathode and / or membrane in a desired concentration, so that, in total, based on the total mass of the catalyst-coated membrane, the halide concentration is 50 to 1000 ppm. Even if, for example,When used as intended, halides migrate from their original component to other components of the catalyst-coated membrane (for example from the cathode to the anode or from the anode to the cathode or from the cathode to the membrane and / or the anode or from the anode to the membrane and / or the cathode), the halide concentration based on the total mass of the catalyst-coated membrane always remains the same, namely 50 to 1000 ppm according to the invention.

[0036] This is consistent with the fuel cell electrode according to the invention described above. If this fuel cell electrode according to the invention, which has a halide concentration of 50 to 1000 ppm, is used for the catalyst-coated membrane according to the invention, then, provided the halide concentration in the fuel cell electrode used is at least 50 ppm but below 1000 ppm, one or more halides can also be added to the further fuel cell electrode and / or the membrane, so that in total, based on the total mass of the catalyst-coated membrane, a total halide concentration of the catalyst-coated membrane of 50 ppm to 1000 ppm results. A fuel cell electrode according to the invention with a halide concentration of less than 1000 ppm can also be used with a non-inventive fuel cell electrode, which, for example,a halide concentration of less than 50 ppm, based on the total mass of the fuel cell electrode, can be combined in the catalyst-coated membrane according to the invention, provided that the halide concentration of the catalyst-coated membrane, based on the total mass of the catalyst-coated membrane, is in a range of 50 to 1000 ppm.

[0037] It is also possible to combine two fuel cell electrodes not according to the invention, each of which has, for example, a halide concentration of less than 50 ppm, based on the respective total mass of the corresponding fuel cell electrode, to form a catalyst-coated membrane according to the invention, namely when, based on the total mass of the catalyst-coated membrane, a halide concentration of 50 to 1000 ppm results.

[0038] However, the desired halide concentration of 50 to 1000 ppm, based on the total mass of the catalyst-coated membrane, is preferably introduced via a fuel cell, in particular via the cathode, so that the halide concentration of the fuel cell, which in the fuel cell relates to the total mass of the fuel cell, is reflected in the halide concentration of the catalyst-coated membrane, which relates to the total mass of the catalyst-coated membrane. However, the distribution of the halide(s) in the individual layers of the catalyst-coated membrane can vary during intended use without changing the halide concentration, based on the total mass of the catalyst-coated membrane according to the invention.

[0039] To achieve an improved balance between the effects of improving long-term stability and high performance, the halide concentration in the catalyst-coated membrane is preferably 50 to 500 ppm, based on the total mass of the catalyst-coated membrane.

[0040] As already disclosed above, the halide used is essentially unlimited. However, the halide is advantageously selected from the group consisting of fluoride, chloride, bromide, iodide, and mixtures thereof, and is preferably chloride due to its very good availability and low health impact. According to an advantageous development, the first and second metal-containing catalysts comprise a noble metal, or mixtures or alloys of two or more noble metals, or a noble metal-base metal alloy.

[0041] It is preferred if the noble metal-base metal alloy comprises a platinum alloy and / or if the noble metal of the metal-containing catalyst comprises platinum and / or palladium.

[0042] According to a further preferred development, the anode of the catalyst-coated membrane has a halide weight fraction FA according to the following formula:

[0043] Where A is 50 to 1000 ppm and preferably 50 to 500 ppm, MCCM is the basis weight of the catalyst-coated membrane and MCLA is the basis weight of the anode.

[0044] Furthermore, the cathode of the catalyst-coated membrane preferably has a halide weight fraction FK according to the following formula:

[0045] Here, A is 50 to 1000 ppm and preferably 50 to 500 ppm, MCCM is the basis weight of the catalyst-coated membrane and MCLK is the basis weight of the cathode.

[0046] The above formulas are explained using the following examples, which, however, serve only as illustrations and do not limit the invention. For example, the membrane thickness is 8 to 20 pm, depending on the type, resulting in a basis weight (MCCM) of 1.6 to 4 mg / cm 2 results.

[0047] For a membrane with a membrane thickness of 12 pm, the membrane surface weight MCCM is 2.4 mg / cm 2 .

[0048] The basis weight of the electrodes (MCLA or MCLK) depends on several factors:

[0049] Catalyst loading (e.g. Pt and / or Pd) e.g. platinum content on the catalyst (usually 20 wt.% - 60 wt.%) ionomer content (ie in particular ionomer to carbon ratio - 1:C) Examples:

[0050] Anode with 0.1 mg(Pt) / cm 2 , 20 wt% Pt / C and l:C 0.8:1

[0051] Basis weight (MCLA) = 0.82 mg / cm 2

[0052] Cathode with 0.5 mg(PtCo) / cm 2 , 50 % Pt / C and l:C 1:1

[0053] Basis weight (MCLK) = 1.5 mg / cm 2

[0054] Total basis weight (MCCM) = 4.72 mg / cm 2

[0055] Factor for anode (FA) = 5.76 -> FA = 288 - 5760 ppm

[0056] Factor for cathode (FK) = 3.15 -> FK = 157-3150 ppm

[0057] Furthermore, the invention also describes a fuel cell with very good long-term stability and consistently good performance. The fuel cell according to the invention is characterized in that it comprises the catalyst-coated membrane described above, which also results in the advantageous effects described above for the fuel cell.

[0058] The advantages, advantageous effects and further developments described for the fuel cell electrode according to the invention, the catalyst-coated membrane according to the invention and the fuel cell according to the invention are each mutually applicable.

[0059] Furthermore, the invention also describes a process for producing the catalyst-coated membrane as disclosed above. According to the process, a halide concentration is added to the cathode and / or the anode and / or the proton-conductive membrane such that the halide concentration of the catalyst-coated membrane is 50 to 1000 ppm, preferably 50 to 500 ppm, based on the total mass of the catalyst-coated membrane. The halide concentration is thus composed of the individual halide concentrations of the anode, the cathode, and the membrane and is based on the total mass of these elements / components.

[0060] The desired halide concentration is achieved by adding one or more halides. This concentration is not simply obtained by using a halide-containing catalyst precursor and a halide-containing ionomer, but is explicitly added to the respective element(s) of the catalyst-layered membrane to be produced. A halide concentration of 50 to 1000 ppm, and preferably 50 to 500 ppm, improves the long-term stability of the catalyst-coated membrane without compromising performance. The process is simple to implement without significant technical complexity and is therefore very efficient.

[0061] The process according to the invention for producing a catalyst-coated membrane is suitable for producing the catalyst-coated membrane according to the invention.

[0062] To achieve a particularly uniform halide ion concentration in the catalyst-coated membrane, the catalyst-coated membrane is produced using a solution containing at least one halide. Production using a halide-containing solution can be carried out in one or more or even all layers of the catalyst-coated membrane, provided the desired halide concentration, based on the total weight of the catalyst-coated membrane, is achieved. Producing the catalyst-coated membrane using a halide solution is particularly simple from an industrial perspective, does not require significant technical effort, and enables a particularly uniform distribution of the halide(s) in the corresponding layer.

[0063] According to an advantageous further development, the anode is produced from an anode dispersion and the cathode from a cathode dispersion, wherein a halide-containing compound is added to the anode dispersion and / or the cathode dispersion, wherein the halide weight fraction FA in the anode dispersion satisfies the following formula:

[0064] A is 50 to 1000 ppm and preferably 50 to 500 ppm, B is the solids content of the anode dispersion, MCCM is the basis weight of the catalyst-coated membrane and MCLA is the basis weight of the anode.

[0065] Alternatively or additionally, the halide weight fraction FK in the cathode dispersion satisfies the following formula:

[0066] F K = (A x B x M CCM>

[0067] M CLK '

[0068] Here, A is 50 to 1000 ppm, preferably 50 to 500 ppm, B is the solids content of the cathode dispersion, MCCM is the basis weight of the catalyst-coated membrane, and MCLK is the basis weight of the cathode. The anode dispersion and the cathode dispersion can have different halide weight fractions.

[0069] Also, the halide is essentially not limited and can be selected from fluoride, chloride, bromide or iodide, with chloride being particularly preferred as the halide.

[0070] Due to its good solubility, the cation of a halide-containing compound used to adjust the halide concentration is selected from the groups of protons, alkali metals, alkaline earth metals, an ammonium ion, or cationic organic compounds. Particularly preferred cations are Na + and K + .

[0071] To further simplify the process, the anode dispersion and the cathode dispersion are coated directly onto the membrane or via a decal substrate onto the membrane.

[0072] According to a further advantageous development, a cathode dispersion is prepared for the production of the cathode by dispersing a first metal-containing catalyst and a proton-conductive ionomer. Furthermore, an anode dispersion is advantageously prepared for the production of the anode by dispersing a second metal-containing catalyst and a proton-conductive ionomer. Furthermore, a halide-containing compound is added to the cathode dispersion and / or the anode dispersion before, during, or after dispersion, so that the desired halide ion concentration can be adjusted.

[0073] Dispersing can be carried out using conventional technical aids and is technically simple and can be implemented quickly due to the usually very good solubility of the halide-containing compound.

[0074] The following are exemplary process steps for producing a catalyst-coated membrane according to the invention. Further process steps may be provided.

[0075] Preparation of a catalyst dispersion

[0076] A catalyst dispersion (also called a fuel cell electrode dispersion) is prepared by mixing a metal-containing catalyst in water, solvent, and an ionomer dispersion. The ionomers used in the catalyst layers according to the invention are not specifically limited and can be perfluorinated ionomers (PFSA), partially fluorinated, or hydrocarbon-based (non-fluorinated) ionomers. The catalyst dispersion is milled for approximately 120 minutes in a ball mill (grinding medium: ZrO2 balls). A catalyst layer is produced by applying and drying the catalyst dispersion to an inert substrate, a so-called decal.

[0077] Alternatively, ultrasound or various grinding media mills can be used in dispersion production. Grinding media mills include, for example, ball mills, stirred bead mills, agitator mills, attritors, and specific roller mills.

[0078] To produce a catalyst dispersion according to the invention with a lower chloride concentration, the required amount of a 5% by mass aqueous sodium chloride solution is added to the catalyst ink after the above dispersion process and then stirred on a magnetic stirrer for at least two hours. To achieve higher chloride concentrations, the required amount of a 20% by mass aqueous sodium chloride solution is added to the catalyst ink after the dispersion process and then stirred on a magnetic stirrer for at least two hours.

[0079] Production of the catalyst-coated membrane according to the invention

[0080] Cathode and anode layers made from the correspondingly prepared anode and cathode dispersions can be coated onto an inert film and dried. Common coating technologies such as slot dies, doctor blades, spiral applicators, screen printing, or even spraying devices can be used. The layers are then transferred to the membrane in a lamination process (the so-called decal process). The lamination temperature is typically 150 to 190 °C, and a pressure of 1 to 3 MPa is applied. Lamination can be carried out, for example, in a press or continuously between a pair of rollers. The lamination time in a press in discontinuous operation is approximately one minute and can be as short as a few seconds for a continuous process.

[0081] In an alternative process, the cathode and / or the anode can also be applied directly to the membrane and dried (direct printing process).

[0082] As a further alternative, the cathode and / or the anode can also be applied to a gas diffusion layer (GDL) and dried to obtain a so-called gas diffusion electrode (GDE), which is then brought into contact with the membrane to obtain a membrane electrode assembly (GDE process).

[0083] As a further alternative, a first electrode can be applied to the membrane (via a decal process or a direct printing process) and a second electrode can be applied to a GDL. For the purposes of the invention, the different methods of manufacturing the membrane electrode assembly are considered equivalent.

[0084] The process according to the invention for producing a catalyst-coated membrane can be used to produce the catalyst-coated membrane according to the invention. Accordingly, a catalyst-coated membrane produced according to the process described above is also described, which is characterized by high long-term stability and, at the same time, no loss of performance.

[0085] EXAMPLES

[0086] The present invention is explained in more detail below with reference to the examples and figures.

[0087] It shows:

[0088] Fig. 1 schematic representation of a catalyst-coated membrane according to an embodiment in section,

[0089] Fig. 2 Voltage losses of the examples after 30,000 potential cycles between 0.6 and 0.95 V,

[0090] Fig. 3 Mass activity losses of the examples after 30,000 potential cycles between 0.6 and 0.95 V,

[0091] Fig. 4 EPSA losses (catalyst surface) after 30,000 potential cycles between 0.6 to 0.95 V,

[0092] Fig. 5 Chemical long-term stabilities of a sample without chloride (solid line) and a sample with a measured value of 220 ppm chloride (dashed line) and

[0093] Fig. 6 Cell voltages of the examples at 0.8 A / cm 2 at the beginning of the measurements.

[0094] The figures depict only the essential elements and components of the invention. All other elements and components are omitted for clarity.

[0095] Fig. 1 is a schematic cross-sectional view of a catalyst-coated membrane 1 according to one embodiment. The catalyst-coated membrane 1 comprises a cathode 2, an anode 3, and an intermediate proton-conductive membrane 4, wherein the cathode 2 comprises a first metal-containing catalyst 5 and a proton-conductive ionomer 6, the anode 3 comprises a second metal-containing catalyst 7 and a proton-conductive ionomer 8, and the membrane 4 comprises a proton-conductive ionomer. The catalyst-coated membrane 1 has a halide concentration of 50 to 1000 ppm, based on the total mass of the catalyst-coated membrane 1. The halide 9 is in particular chloride and is explicitly arranged here in the cathode 2. Particularly preferably, the halide 9 is introduced into the cathode 3 in the form of a NaCl solution.

[0096] Due to the halide concentration, the catalyst-coated membrane 1 is characterized by very good long-term stability with no significant loss of performance.

[0097] Potential cycle test

[0098] The potential cycling test is an accelerated stability test that simulates the voltage profile of the cathode during dynamic cycling of a fuel cell, i.e. under normal operating conditions, with power being drawn from the fuel cell.

[0099] The potential cycle test complies with the proposals of the US Department of Energy (DOE) and was carried out as follows:

[0100] The temperature of the single cell (Tzeiie) was 80 °C, and the humidifier temperatures were 80 °C for the anode and 80 °C for the cathode. Hydrogen was applied to the anode and nitrogen at ambient pressure to the cathode. A rectangular voltage was applied to the cell, alternating between a voltage of 0.6 V for 3 s and a voltage of 0.95 V for 3 s. This cycle was repeated 30,000 times.

[0101] Chemical long-term stability test

[0102] The chemical stability test is an accelerated stability test that examines the hydrogen transfer of the catalyst-coated membrane during operation under open clamp voltage.

[0103] The chemical stability test complies with the recommendations of the US Department of Energy (DOE) and was carried out as follows:

[0104] The cell temperature was set at 90 °C, and the humidification was set to 30% RH. Hydrogen was applied to the anode, and air at 1.5 bar was applied to the cathode. No current was applied, so the cell was open-circuited. Hydrogen transfer was measured at regular intervals. Ion chromatography was used to determine the halide content.

[0105] Sample preparation prior to determining the halide content, especially chloride, by ion chromatography was performed using oxygen digestion. The sample material was burned under pressure and with the addition of oxygen in a closed system.

[0106] The halides in the fuel cell electrode were determined using ion chromatography. Ion chromatography allows the halides to be differentiated by their retention time (retention times: e.g., F: 6.9 min, CI: 10.4 min, Br: 15.9 min). A mixture of 1.9 L of an aqueous solution of sodium carbonate with a concentration of 3.2 mmol / L, sodium bicarbonate with a concentration of 1.0 mmol / L, and 0.1 L of acetonitrile was used as the mobile phase, resulting in a total of 2.0 L of mobile phase. The measurement was performed using a Metrohm 690 IC instrument (Deutsche METROHM GmbH & Co. KG, Germany). The column used was a Metrosep A Supp7 - 250 / 4.0 mm column (Deutsche METROHM GmbH & Co. KG, Germany). The column temperature was set to 40 °C, and the flow rate was 0.7 mL min. -1 .

[0107] Example 1

[0108] A catalyst-coated membrane was prepared as described above. The cathode, prepared according to Example 1, comprised a pure platinum catalyst supported on carbon (50 mass% platinum, 50 mass% carbon). The precious metal weight per unit area of ​​the metal-containing catalyst was 0.4 mgpt / cm 2 The cathode also included an ionomer with an equivalent weight (EW) of 790 g / mol (Aquivion® D79-25BS; Solvay Specialty Polymers, Italy). The mass ratio of ionomer to carbonaceous support material was 0.8:1.

[0109] The cathode according to the invention according to Example 1 further comprised sodium chloride in a concentration of 1370 to 1500 ppm chloride, which was determined by ion chromatography as described above.

[0110] The anode prepared according to Example 1 comprised a pure platinum catalyst supported on carbon (20 mass% platinum, 80 mass% carbon). The precious metal area weight of the metal-containing catalyst was 0.1 mgpt / cm 2 The anode also included an ionomer with an equivalent weight (EW) of 790 g / mol (Aquivion® D79-25BS; Solvay Specialty Polymers, Italy). The mass ratio of ionomer to carbonaceous support material was 0.8:1.

[0111] The MEA prepared according to Example 1 was manufactured using the previously described decal process. The anode and cathode were each applied to a glass fiber-reinforced PTFE substrate using a spiral applicator. The wet film thickness was selected to achieve the target loading. The respective catalyst dispersion was then dried in an oven at 100 °C for 5 min. The lamination (decal transfer) of the anode and cathode with the membrane (perfluorinated reinforced sulfonic acid membrane, 15 μm thick) was carried out in a belt laminator at a temperature of 180 °C and a pressure of 1 MPa for 1 min.

[0112] The chloride content of the catalyst-coated membrane was thus 310 to 340 ppm chloride. Examples 2 and 3, Comparative Examples 1 to 3

[0113] Examples 2 and 3 as well as Comparative Examples 1 to 3 were prepared analogously to Example 1, but with the compositions as shown in Table 1 below.

[0114] Table 1 below provides an overview of the tests conducted and the respective test results. Examples and comparative examples are shown, along with their respective chloride contents and losses during the potential cycling test between 0.6 and 0.95 V. (Values ​​at the beginning of the test minus the values ​​after the test.)

[0115] Table 1

[0116] For example, Cabot's Vulcan brand carbons can be used as non-graphitized carbon. "EPSA" stands for effective platinum surface area. The term "geo" refers to the geometrically active area of ​​the catalyst-coated membrane. Thus, EPSA represents the surface area of ​​the platinum [cm 2(Pt)] per area of ​​the catalyst-coated membrane. As shown in Figures 1 to 3, the examples according to the invention, due to the adjusted chloride ion concentration in a range of 50 to 1000 ppm, show much lower voltage losses after 30,000 potential cycles between 0.6 and 0.95 V (see Figure 2), lower mass activity losses after 30,000 potential cycles between 0.6 and 0.95 V (see Figure 3), and lower EPSA losses (effective platinum surface area - platinum surface related to the area of ​​the electrode; ie EPSA indicates the surface area of ​​the platinum [cm 2(Pt)] per area of ​​the catalyst-coated membrane after 30,000 potential cycles between 0.6 and 0.95 V (see Fig. 4) than the comparative examples without the addition of halides. Chloride in the ppm range used leads to a reduction in the potential loss, a reduction in the mass activity loss, and also in the EPSA loss. Furthermore, no negative influence on the long-term chemical stability is observed, which is particularly evident in Fig. 5. An influence of increased H2O2 concentration was not observed.

[0117] Fig. 6 shows that the chloride content has no significant influence on the cell voltage, ie there is no deterioration of the cell voltage.

[0118] In addition to the above written description of the invention, reference is hereby explicitly made to the graphic representation of the invention in Figs. 1 to 6 for its supplementary disclosure.

[0119] List of reference symbols

[0120] 1 catalyst-coated membrane

[0121] 2 Cathode

[0122] 3 Anode 4 Membran

[0123] 5 first metal-containing catalyst

[0124] 6 proton-conductive ionomer

[0125] 7 second metal-containing catalyst

[0126] 8 proton-conductive ionomer 9 halide

Claims

Claims 1. Fuel cell electrode (2, 3) comprising a metal-containing catalyst (5, 7) and a proton-conducting ionomer (6, 8), wherein the fuel cell electrode (2, 3) has a halide concentration of 150 to 6000 ppm, based on the total mass of the fuel cell electrode (2, 3).

2. Fuel cell electrode (2, 3) according to claim 1, wherein the fuel cell electrode (2, 3) has a halide concentration of 300 to 3000 ppm, based on the total mass of the fuel cell electrode (2, 3) and / or wherein the halide is selected from the group consisting of fluoride, chloride, bromide, iodide and mixtures thereof, and preferably is chloride.

3. Fuel cell electrode (2, 3) according to one of the preceding claims, wherein the metal-containing catalyst (5, 7) comprises a precious metal, or mixtures or alloys of two or more precious metals or a precious-non-precious metal alloy, wherein the precious-non-precious metal alloy in particular comprises a platinum alloy and / or wherein in particular the precious metal of the metal-containing catalyst (5, 7) comprises platinum and / or palladium.

4. Fuel cell electrode (2, 3) according to one of the preceding claims, configured as a cathode (2).

5. Catalyst-coated membrane (1) comprising a fuel cell electrode (2, 3) according to one of the preceding claims.

6. Method for producing the fuel cell electrode (2, 3) according to any one of claims 1 to 4, wherein a halide concentration is added to the fuel cell electrode (2, 3) such that the halide concentration of the fuel cell electrode (2, 3) is 150 to 6000 ppm, preferably 300 to 3000 ppm, based on the total mass of the fuel cell electrode (2, 3).

7. Method according to claim 6, wherein the fuel cell electrode (2, 3) is produced with a solution containing at least one halide.

8. Method according to claim 6 or 7, wherein the fuel cell electrode (2, 3) is produced as an anode (3) from an anode dispersion or as a cathode (2) from a cathode dispersion, wherein a halide-containing compound is added to the anode dispersion or the cathode dispersion, where the halide weight fraction FA in the anode dispersion fulfills the following formula: FA = (AXB ) where A is 150 to 6000 ppm and preferably 300 to 3000 ppm, and B is the solid fraction of the anode dispersion or where the halide weight fraction FK in the cathode dispersion satisfies the following formula: F K= (A x B) where A is 150 to 6000 ppm and preferably 300 to 3000 ppm, and B is the solid fraction of the cathode dispersion, wherein the anode dispersion and the cathode dispersion may have different halide weight fractions, and / or wherein a cation of a halide-containing compound is selected from the group consisting of protons, alkali metals, alkaline earth metals, an ammonium ion, or cationic organic compounds, and / or wherein, for the production of the fuel cell electrode (2, 3), a fuel cell electrode dispersion is prepared by dispersing a metal-containing catalyst (5, 7) and a proton-conducting ionomer (6, 8), and adding a halide-containing compound to the fuel cell electrode dispersion before, during, or after dispersion. Catalyst-coated membrane comprising a cathode (2), an anode (3), and an intermediate proton-conducting membrane (4), wherein a.a. the cathode (2) comprises a first metal-containing catalyst (5) and a proton-conducting ionomer (6), b. the anode (3) comprises a second metal-containing catalyst (7) and a proton-conducting ionomer (8), and c. the membrane (4) comprises a proton-conducting ionomer, wherein the catalyst-coated membrane (1) has a halide concentration of 50 to 1000 ppm, based on the total mass of the catalyst-coated membrane (1). Catalyst-coated membrane (1) according to claim 9, wherein the catalyst-coated membrane (1) has a halide concentration of 50 to 500 ppm, based on the total mass of the catalyst-coated membrane (1), and / or wherein the halide is selected from the group consisting of fluoride, chloride, bromide, iodide and mixtures thereof, and preferably is chloride, and / or wherein the first metal-containing catalyst (5) and the second metal-containing catalyst (7) comprise a noble metal, or mixtures or alloys of two or more noble metals or a noble-non-precious metal alloy, wherein in particular the noble-non-precious metal alloy comprises a platinum alloy, and / or wherein in particular the noble metal of the second metal-containing catalyst (7) comprises platinum and / or palladium. Catalyst-coated membrane (1) according to claim 9 or 10, wherein the anode (3) has a halide weight fraction FA according to the following formula: where A is 50 to 1000 ppm and preferably 50 to 500 ppm, and MCCM is the The areal weight of the catalyst-coated membrane (1) and MCLA is the areal weight of the anode (3) or wherein the cathode (2) has a halide weight fraction FK according to the following formula: FK = (AX MCLK ' where A is 50 to 1000 ppm and preferably 50 to 500 ppm, and MCCM the The basis weight of the catalyst-coated membrane (1) and MCLK is the basis weight of the cathode (2). Fuel cell comprising a catalyst-coated membrane according to any one of claims 9 to 11. Method for producing the catalyst-coated membrane (1) according to any one of claims 9 to 11, wherein a halide concentration is added to the cathode (2) and / or the anode (3) and / or the proton-conducting membrane (4) such that the halide concentration of the catalyst-coated membrane (1) is 50–1000 ppm, preferably 50–500 ppm based on the total mass of the catalyst-coated membrane (1). A method according to claim 13, wherein the catalyst-coated membrane (1) is produced with a solution containing at least one halide and / or wherein the anode (3) is produced from an anode dispersion and the cathode (2) from a cathode dispersion, wherein a halide-containing compound is added to the anode dispersion and / or the cathode dispersion, wherein the halide weight fraction FA in the anode dispersion satisfies the following formula: F A = (A x B x MCLA where A is 50 to 1000 ppm and preferably 50 to 500 ppm, B is the solid fraction of the anode dispersion and MCCM is the basis weight of the catalyst-coated membrane (1) and MCLA is the basis weight of the anode (3) and / or where the halide weight fraction FK in the cathode dispersion satisfies the following formula: F K = (A x B x M CCM> M CLK ' wherein A is 50 to 1000 ppm and preferably 50 to 500 ppm, B is the solid fraction of the cathode dispersion, MCCM is the basis weight of the catalyst-coated membrane (1), and MCLK is the basis weight of the cathode (2), wherein the anode dispersion and the cathode dispersion may have different halide weight fractions, and / or wherein a cation of a halide-containing compound is selected from the group consisting of protons, alkali metals, alkaline earth metals, an ammonium ion, or cationic organic compounds, and / or wherein an anode dispersion and a cathode dispersion are coated directly onto the membrane (4) or coated onto the membrane (4) via a decal substrate, and / or wherein to produce the cathode (2) a cathode dispersion is produced by dispersing a first metal-containing catalyst (5) and a proton-conducting ionomer (8), wherein to produce the anode (3) an anode dispersion is produced by dispersing a second metal-containing catalyst (7) and a proton-conducting ionomer (8) and adding a halide-containing compound to the cathode dispersion and / or the anode dispersion before, during or after dispersion.

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