Membrane electrode unit, its manufacturing method and its application

Abstract

The present invention relates to a membrane electrode unit (1) having a polymer electrolyte membrane (2) and at least one electrode (3) disposed on the polymer electrolyte membrane (2), wherein the membrane electrode unit (1) has silver and / or a silver-containing compound (4). The present invention also relates to an electrolytic cell, a battery stack, an electrolytic device, a method (100) for manufacturing a membrane electrode unit (1), and the use of the membrane electrode unit (1).

Description

Technical Field

[0001] This invention relates to a membrane electrode unit having a polymer electrolyte membrane (PEM) and at least one electrode disposed on the polymer electrolyte membrane. The invention also relates to an electrolytic cell, a battery stack, an electrolysis apparatus, a method for manufacturing a membrane electrode unit, and the use of the membrane electrode unit. Background Technology

[0002] Hydrogen can be produced by the electrolysis of water, using various techniques. One industrially established technique is polymer electrolyte membrane electrolysis (PEMWE). Here, the core component is a membrane electrode unit with a polymer electrolyte membrane. The polymer electrolyte membrane is primarily used as a proton exchange membrane, i.e., protons are transported through it. Alternatively, the polymer electrolyte membrane can be configured as anion-conductive, allowing hydroxide ions to be transported through it.

[0003] The membrane divides the electrolyzer into two half-cells: an anode side and a cathode side. Electrodes are typically applied to the membrane as catalyst layers, with carbon-supported platinum usually used on the cathode side and metallic iridium or iridium oxide used on the anode side, the metallic iridium being at least partially converted to iridium oxide during electrolysis operation.

[0004] Membrane electrode units are typically manufactured using a so-called transfer process, in which a catalyst layer is applied onto a transfer membrane, and the membrane is arranged between the catalyst layers. Subsequently, the catalyst layers are typically bonded to the membrane by continuous hot pressing. As a result, the catalyst is directly disposed on the membrane, and therefore the membrane can also be called a catalyst-coated membrane.

[0005] The electrodes are electrically contacted via a porous transport layer or a gas diffusion layer. The porous layer is used to transport electrolytes and / or reactants to the electrodes. The proton exchange membrane operates with deionized water. The anion exchange membrane will similarly operate with deionized water in the future. Currently, a dilute alkaline solution of approximately 1 mol / L is used to support ion contact. The material used for the gas diffusion layer is typically graphite nonwoven fabric or carbon paper on the cathode side and a sintered titanium plate or titanium nonwoven fabric reinforced with titanium metal on the anode side.

[0006] In proton exchange membrane electrolysis, on the anode side, water is oxidized into molecular oxygen while releasing protons and electrons. In anion exchange membrane electrolysis, on the anode side, hydroxide ions are oxidized into oxygen. The membrane acts as an electrical insulator between the catalyst layers and can only conduct protons towards the cathode catalyst layer or anions towards the anode. On the cathode side, in proton exchange membrane electrolysis, protons are reduced to molecular hydrogen. In anion exchange membrane electrolysis, hydrogen is formed from water at the cathode. The resulting gaseous hydrogen and oxygen are removed from the electrolytic cell via a gas diffusion layer.

[0007] However, in practice, a membrane that is theoretically impermeable to the generated gases undesirably allows some gas exchange between the anode and cathode sides, a phenomenon known as gas cross-linking. Gas cross-linking leads to a decrease in overall electrolysis efficiency, and also poses safety risks and causes degradation effects.

[0008] For example, if hydrogen contains at least 4% by volume oxygen, oxygen cross-linking can lead to the formation of an explosive hydrogen-oxygen mixture, and vice versa. Oxygen can also cause oxidation of electrolytic cell components, especially iron-containing components. The resulting rust particles can deposit in the electrolytic cell, leading to so-called microfouling. Cations released during such oxidation can also react with electrode or membrane materials, causing an increase in membrane resistance, which negatively impacts electrolysis efficiency. The membrane can also be damaged by free radicals formed by oxygen.

[0009] In addition to these potential damaging effects of oxygen, gas cross-contamination can also lead to the product stream being contaminated by another corresponding gas, which may require purification of the product stream depending on the intended use.

[0010] Therefore, gas cross-contamination should be prevented as much as possible. It is known that platinum, for example, which can be used as an electrode material, also catalyzes the recombination reaction of oxygen and hydrogen into water, and thus can help reduce gas cross-contamination. However, due to its high cost, there is a need to keep the required amount of platinum as low as possible and prevent gas cross-contamination in other ways.

[0011] The use of a silver-containing oxygen-consuming electrode in chlor-alkali electrolysis, operating under strongly alkaline conditions (DE 10 2010 042 729 A1), is known. Here, silver acts as a catalyst in the formation of hydroxide ions from the transported oxygen and water. This prevents the self-protonation of water, thereby avoiding the formation of hydrogen gas. Summary of the Invention

[0012] In this context, the object of the present invention is to provide the possibility of reducing gas cross-contamination through the membrane of the membrane electrode unit at low cost.

[0013] The objective is achieved through the subject matter of the independent claim. The dependent claims relate to design solutions.

[0014] A first aspect of the invention relates to a membrane electrode unit having a polymer electrolyte membrane and at least one electrode disposed on the polymer electrolyte membrane, wherein the membrane electrode unit has silver and / or a silver-containing compound.

[0015] Polymer electrolyte membranes can be configured as proton exchange membranes and have perfluorinated copolymers with ionic groups (e.g., sulfonic acid groups), or are composed of such polymers. The use of fluorine-free polymers is also possible. Alternatively, polymer electrolyte membranes can be configured as anion exchange membranes. The invention is not limited to specific materials for polymer electrolyte membranes. Electrodes can be configured as catalyst layers.

[0016] One or two electrodes are arranged on one or both sides of the polymer electrolyte membrane, which simultaneously serve as electrodes and catalyze the electrolysis reaction. One or more electrodes are preferably in direct contact with or directly disposed on the polymer electrolyte membrane, and are connected to the membrane as a membrane electrode unit by means of a transfer process, for example, as described at the beginning. In particular, there is no gap between the membrane and the electrodes, as is the case in chlor-alkali electrolysis, where a gap exists between the membrane and the electrodes, for example, filled with potassium alkali solution or caustic soda solution.

[0017] The membrane electrode unit can be used to perform electrolysis. Preferably, the membrane electrode unit can be used for the electrolysis of water, for example, for so-called PEM water electrolysis (PEMWE). The membrane electrode unit can be used, for example, as a proton exchange membrane under non-alkaline conditions, especially under neutral conditions, or as an anion exchange membrane under alkaline or neutral conditions.

[0018] The specification states that the membrane electrode unit contains silver and / or a silver-containing compound. This means that the membrane electrode unit contains elemental silver and / or one or more silver-containing compounds.

[0019] The inventors of this invention hypothesize that silver, or silver ions that can be formed from silver and arriving oxygen, primarily functions as an oxygen reduction catalyst, i.e., as a catalyst for the reaction 0.5 O2 + H2O + 2 e-. - → 2 OH - The catalyst. Silver or silver ions catalyze the reaction significantly better than platinum. By catalyzing the conversion of oxygen, the negative effects of oxygen in the product gas hydrogen, as described above, can be reduced or even completely avoided.

[0020] Therefore, the membrane electrode unit preferably contains an amount of silver or a silver-containing compound to achieve sufficient catalytic activity. The mass fraction of silver in the membrane electrode unit can be, for example, between 1% and 50%, preferably between 10% and 30%.

[0021] By introducing silver or silver ions into the membrane electrode unit, particularly between the polymer electrolyte membrane and the electrode, it is possible to reduce unwanted oxygen that has crossed the membrane. This avoids contamination of the actual product gases from electrolysis, thus eliminating the need for, or reducing the need for, product gas purification.

[0022] Problems caused by gas cross-contamination at the beginning can also be reduced. Therefore, it is possible to prevent the formation of explosive gas-hydrogen mixtures by reducing the oxygen content in hydrogen, particularly keeping it below 4% by volume, preferably below 2% by volume. Oxygen-based corrosion, microfouling, and damage to the membrane can also be reduced. Furthermore, the use of silver provides a low-cost feasibility for improving the quality of the product gas.

[0023] Depending on the implementation variant, silver and / or silver-containing compounds can exist at least partially in the form of nanoparticles.

[0024] The term nanoparticle should be understood herein as a particle with a diameter of less than 100 nm in at least one direction of extension. For example, nanoparticles can have a substantially spherical shape, wherein the average particle diameter is less than 100 nm, as determined, for example, by measuring a micrograph.

[0025] By using nanoparticles, the active surface area of ​​silver can be increased while keeping the mass constant, resulting in higher catalytic activity with the least amount of silver.

[0026] According to another implementation variant, the silver-containing compound can be selected from the group consisting of silver oxide (e.g., silver oxide (I)), silver complexes, and silver halides (e.g., silver chloride).

[0027] The aforementioned silver compound provides a low-cost feasibility for introducing silver or silver ions into membrane electrode units. During electrolysis operation, at least partial reduction of the silver in the silver compound is possible, enabling the formation of elemental silver as the active species. Therefore, the catalytic activity does not necessarily depend on the use of silver or a silver-containing compound, nor on the type of silver-containing compound introduced.

[0028] The use of silver-containing compounds, especially silver oxide, also enables the creation of porous structures due to the reduction described during electrolysis, thereby achieving greater catalytic activity at the same mass due to the increased surface area.

[0029] According to another implementation variation, the electrode that can be used as the cathode can have silver and / or silver-containing compounds.

[0030] For example, silver and / or silver-containing compounds can be applied to an electrode that can be used as a cathode.

[0031] In this context, "capable of being used as a cathode" means that the corresponding electrode is used as a cathode during electrolysis, such that, for example, in water electrolysis, hydrogen gas is formed at an electrode provided with silver or a silver-containing compound. In this case, silver or silver ions can induce the reduction of oxygen that is undesirably transmitted across the membrane and generated at the anode, thereby reducing or preventing oxygen contamination of the hydrogen product stream.

[0032] According to another implementation variation, silver and / or silver-containing compounds can be arranged between the polymer electrolyte membrane and the electrode.

[0033] In other words, it is possible to obtain a sequence of polymer electrolyte membrane-silver or silver-containing compound-electrode.

[0034] The arrangement advantageously results in the conversion of gases that undesirably cross the membrane immediately thereafter, i.e., before reaching the electrodes. This allows for particularly effective reduction of gas cross-contamination.

[0035] In particular, silver or silver-containing compounds can be applied as a silver coating to the electrode or catalyst layer, wherein the silver coating is arranged on the side of the electrode facing the membrane in the membrane electrode unit.

[0036] According to another implementation variation, the electrode can have at least one noble metal catalyst.

[0037] Here, the precious metal can be selected from the group consisting of platinum, iridium, palladium, rhodium, gold, and ruthenium. The precious metal catalyst can have one or more precious metals in metallic form or in a suitable chemically bonded form (e.g., as an alloy).

[0038] On the cathode side, a platinum-containing electrode can be arranged in particular, such that, in the presence of silver, silver and platinum can preferably work together on the cathode side.

[0039] On the anode side, electrodes containing iridium and / or iridium oxide can be arranged in particular, such that, in the presence of silver, silver and iridium can preferably work together on the anode side.

[0040] Another aspect of the present invention relates to an electrolytic cell having a membrane electrode unit as described above.

[0041] Another aspect of the invention relates to a battery stack having multiple such electrolytic cells, i.e., comprising multiple such electrolytic cells stacked and electrically connected in series. The electrolytic cells form a battery stack or electrolytic pile that can be scaled up for large electrolysis power.

[0042] Another aspect of the invention relates to an electrolysis apparatus having such a battery stack.

[0043] Current research involves the design schemes, features and / or advantages of membrane electrode units, as well as electrolyzers, battery stacks, electrolysis equipment and / or the entire power-to-X power plant, and vice versa.

[0044] Another aspect of the present invention relates to a method for manufacturing a membrane electrode unit having a polymer electrolyte membrane and at least one electrode disposed on the polymer electrolyte membrane as an electrode, wherein the method includes introducing silver and / or a silver-containing compound into the membrane electrode unit.

[0045] The membrane electrode unit can be constructed in particular according to the foregoing description. Therefore, the description of the membrane electrode unit also serves to illustrate the proposed method. The advantages of the membrane electrode unit are correspondingly related to the method.

[0046] The membrane electrode unit can preferably be manufactured using a transfer method, by means of which one or more electrodes are connected to a membrane to form a membrane electrode unit.

[0047] The step of introducing the silver and / or silver-containing compounds can include applying the silver and / or silver-containing compounds to the electrodes and / or polymer electrolyte membranes.

[0048] In other words, silver or silver-containing compounds can be applied to the membrane and / or the electrode and / or introduced into the electrode.

[0049] Applying silver and / or silver-containing compounds can preferably be carried out by means of methods selected from the group consisting of chemical vapor deposition, physical vapor deposition, spin coating, spray coating, thermal spraying, displacement coating, slot nozzle coating, blade coating, roller coating, powder coating, and printing.

[0050] Particularly preferably, the application of silver and / or silver-containing compounds can be carried out by means of spray coating. For example, silver nanoparticles dispersed in isopropanol or another dispersant can be applied to the electrode by means of spraying (e.g., air brush spray coating).

[0051] Another aspect of the present invention relates to the use of the membrane electrode unit described above for proton exchange membrane electrolysis or anion exchange membrane electrolysis.

[0052] In other words, an electrolysis method is proposed in which a membrane electrode unit is used for electrolysis under non-alkaline or alkaline conditions.

[0053] Another aspect of the present invention relates to the use of the membrane electrode unit according to the foregoing description for water electrolysis.

[0054] In other words, an electrolysis method is proposed in which a membrane electrode unit is used for the electrolysis of water. The electrolysis can be performed under non-alkaline conditions, preferably under neutral conditions. For example, deionized water can be used for electrolysis. Alternatively, water rich in hydroxide ions can be used, allowing the electrolysis to be performed under alkaline conditions.

[0055] The advantages of membrane electrode units are correspondingly linked to the proposed applications. Electrolyzers, battery stacks, and electrolysis equipment can then be used accordingly.

[0056] The expression "and / or" as used herein, when used in a series of two or more elements, means that each of the listed elements can be used alone, or any combination of two or more of the listed elements can be used. Attached Figure Description

[0057] The above-described features, characteristics, and advantages of the present invention, as well as the ways and methods of achieving them, will become clearer and more explicit in conjunction with the following description of the embodiments, which are illustrated in detail with reference to the accompanying drawings, which are shown below:

[0058] Figure 1 A schematic diagram of an exemplary membrane electrode unit is shown;

[0059] Figure 2 A schematic diagram of another exemplary membrane electrode unit is shown;

[0060] Figure 3 A flowchart illustrating an exemplary method for manufacturing a membrane electrode unit;

[0061] Figure 4 The timeline of the oxygen-gas crossover is shown; and

[0062] Figure 5 The voltage time-varying graph is shown. Detailed Implementation

[0063] Figure 1 An embodiment of membrane electrode unit 1 is schematically shown, which is capable of electrolyzing water into hydrogen and oxygen under neutral conditions.

[0064] The membrane electrode unit 1 has a polymer electrolyte membrane 2, which in this embodiment is made of Nafion®. Furthermore, the membrane electrode unit 1 has an electrode 3, which serves as a cathode during electrolysis and is made of platinum. The electrode 3 or cathode is disposed on a gas diffusion layer 5, which in this embodiment is made of graphite nonwoven fabric. Optionally, a bipolar plate 6 is connected to the gas diffusion layer 3, which can also be made of graphite or high-quality steel.

[0065] To prevent oxygen reaching through the polymer electrolyte membrane 2 from contaminating the hydrogen formed at the cathode and causing the other negative effects described at the beginning, a layer containing silver and / or a silver-containing compound 4 is disposed between the polymer electrolyte membrane 2 and the electrode 3. In this embodiment, silver nanoparticles are used for this purpose.

[0066] Alternatively, silver or silver-containing compounds 4 can be arranged in other ways in the membrane electrode unit 1, for example, between the electrode 3 and the gas diffusion layer 5 or as part of the gas diffusion layer 5. In addition to silver nanoparticles, non-nanoparticle forms of silver or compound forms of silver, such as silver oxide, which is reduced under operating conditions, can also be used additionally or alternatively.

[0067] The membrane electrode unit 1 can also be like Figure 2 The structure is symmetrically constructed as shown. This means that electrodes 3a and 3b are arranged on both sides of the polymer electrolyte membrane 2, wherein one electrode 3a serves as the cathode, and the other electrode 3b serves as the anode. The anode can, for example, have iridium and / or iridium oxide or be composed of iridium and / or iridium oxide. Furthermore, reference is made to... Figure 1 The explanation.

[0068] Alternatively or additionally, a layer having silver and / or silver-containing compounds 4 can be arranged on the anode side, for example, between the electrode 3b serving as the anode and the polymer electrolyte membrane 2, to catalyze the recombination of hydrogen reaching through the polymer electrolyte membrane 2 with oxygen formed at the anode. On the side of the anode facing away from the polymer electrolyte membrane 2, similar to the cathode side, a gas diffusion layer 5b can optionally be arranged, for example, in the form of titanium nonwoven fabric or steel nonwoven fabric.

[0069] Figure 2 The membrane electrode unit 1 shown can be, for example, by means of the following reference Figure 3 The method described is 100 for manufacturing. Method 100 is preferably the so-called transfer method.

[0070] In method step S1, an anode and a cathode are provided. For this purpose, a so-called transfer substrate, such as a transfer film, can be coated with a catalyst material of the anode or cathode, such that the anode and cathode are provided as catalyst layers disposed on the transfer substrate.

[0071] In method step S2, silver 4 is applied to the cathode in the form of silver nanoparticles. In this embodiment, this is carried out by spray coating with a dispersion of silver nanoparticles in isopropanol at a mass ratio of 1:40 (silver nanoparticles to isopropanol), wherein the isopropanol is removed by drying after coating.

[0072] Subsequently, the cathode coated with silver nanoparticles, like the anode and polymer electrolyte membrane 2, is stamped to the required size. Optionally, all three components of the membrane electrode unit 1 can also be preheated, for example, to a temperature of 100°C, to facilitate subsequent connections.

[0073] In step S3, the polymer electrolyte membrane 2 is arranged between the anode and the cathode, with the cathode oriented such that the surface of the silver nanoparticles coated on the cathode points toward the polymer electrolyte membrane 2. Furthermore, all three components of the membrane electrode unit 1 are arranged together between polyimide plates.

[0074] In step S4, the anode and cathode are connected to the polymer electrolyte membrane 2 by applying pressure at an elevated temperature. This is done by means of a laminating roller heated to approximately 160°C, which transmits pressure via a polyimide plate. For this purpose, a pressure of 4 bar is applied to the laminating roller itself by means of a pneumatic cylinder. The laminating roller rotates at approximately 0.02 m / s.

[0075] Subsequently, the transfer substrate can be removed, and the membrane electrode unit 1 can be further processed, for example by arranging a gas diffusion layer.

[0076] The mass of the applied silver nanoparticles, relative to the cathode mass applied to the polymer membrane 2 during the fabrication of the membrane electrode unit 1, is between 10% and 50%, preferably between 10% and 30%.

[0077] Figure 4 The oxygen fraction (volume percentage) in the hydrogen product stream, i.e., the oxygen-gas crossover at the cathode side, is shown in time-dependent manner for four different membrane electrode units 1 (denoted by the letters A, B, C, and D). This determination was performed using gas chromatography.

[0078] Membrane electrode units A and B are identically manufactured reference examples, either silver-free or containing silver compounds. Membrane electrode units C and D, however, incorporate silver nanoparticles. These silver nanoparticles are prepared using reference... Figure 3 The described method 100 is manufactured under the same conditions, and according to Figure 2 Composition. To determine the gas crossover, membrane electrode unit 1 was used in an electrolytic cell, and the composition of the product gas stream was analyzed.

[0079] according to Figure 4 It was identified that the oxygen cross-contamination in silver-containing samples C and D was significantly lower, approximately 0.04%, and more stable over time compared to reference samples A and B, where a wide range of oxygen cross-contamination values ​​between 0.06% and 0.09% were observed. Therefore, it can be confirmed that the introduction of silver, particularly in the form of silver nanoparticles, can effectively reduce the oxygen content in the hydrogen product stream by up to 45%, and correspondingly reduce or even eliminate problems associated with gas cross-contamination.

[0080] Figure 5 Shown at 2 A / cm 2Under constant current density, the time-dependent voltage trends of reference sample B and silver-containing samples C and D.

[0081] Similar behavior was observed for all samples. Therefore, it can be concluded that any significant negative impact on overvoltage is not related to the introduction of silver nanoparticles.

[0082] Although the invention has been described and illustrated in more detail through preferred embodiments, the invention is not limited to the disclosed examples, and those skilled in the art can derive other variations therefrom without departing from the scope of protection of the invention.

[0083] This invention relates to a membrane electrode unit 1 having a polymer electrolyte membrane 2 and at least one electrode 3 disposed on the polymer electrolyte membrane 2, wherein the membrane electrode unit 1 has silver and / or a silver-containing compound 4. The invention also relates to an electrolytic cell, a battery stack, an electrolytic apparatus, a method 100 for manufacturing the membrane electrode unit 1, and the use of the membrane electrode unit 1.

[0085] List of reference numerals

[0087] 1 Membrane Electrode Unit

[0088] 2. Polymer electrolyte membrane

[0089] Electrodes 3, 3a, 3b

[0090] 4. Silver / Silver-containing compounds

[0091] 5, 5a, 5b Gas diffusion layers

[0092] 6 bipolar plates

[0093] 100 methods

[0094] S1 provides the anode and cathode.

[0095] S2 applies silver to the cathode.

[0096] S3 arranges the polymer electrolyte membrane between the anode and the cathode. S4 connects the anode and cathode to the polymer electrolyte membrane by means of pressing.

Claims

1. A membrane electrode unit (1), the membrane electrode unit having a polymer electrolyte membrane (2) and at least one electrode (3, 3a, 3b) disposed on the polymer electrolyte membrane (2), wherein, The membrane electrode unit (1) has silver and / or silver-containing compounds (4).

2. The membrane electrode unit (1) according to claim 1, wherein, The silver and / or the silver-containing compound (4) are present at least partially in the form of nanoparticles.

3. The membrane electrode unit (1) according to any one of the preceding claims, wherein, The silver-containing compound (4) is selected from the group consisting of silver oxide, silver complexes and silver halides.

4. A membrane electrode unit (1), wherein, The electrode (3, 3a) that can be used as a cathode has the silver and / or the silver-containing compound (4).

5. The membrane electrode unit (1) according to any one of the preceding claims, wherein, The silver and / or the silver-containing compound (4) are disposed between the polymer electrolyte membrane (2) and the electrode (3).

6. The membrane electrode unit (1) according to any one of the preceding claims, wherein, The electrodes (3, 3a, 3b) have at least one noble metal catalyst.

7. The membrane electrode unit (1) according to claim 6, wherein, The precious metal is selected from the group consisting of platinum, iridium, palladium, rhodium, gold and ruthenium.

8. An electrolytic cell comprising a membrane electrode unit (1) according to any one of claims 1 to 7.

9. A battery stack comprising a plurality of electrolytic cells according to claim 8.

10. An electrolysis apparatus having a battery stack according to claim 9.

11. A method (100) for manufacturing a membrane electrode unit (1), the membrane electrode unit having a polymer electrolyte membrane (2) and at least one electrode (3, 3a, 3b) disposed on the polymer electrolyte membrane (2), wherein, The method (100) includes the step of introducing silver and / or a silver-containing compound (4) into the membrane electrode unit (1).

12. The method (100) according to claim 11, wherein, Introducing the silver and / or the silver-containing compound (4) includes applying the silver and / or the silver-containing compound (4) to the electrodes (3, 3a, 3b) and / or the polymer electrolyte membrane (2).

13. The method (100) according to claim 12, wherein, The application of the silver and / or the silver-containing compound (4) is carried out by means of a method selected from the group consisting of chemical vapor deposition, physical vapor deposition, spin coating, spray coating, thermal spraying, displacement coating, slot nozzle coating, doctor blade coating, roller coating, powder coating and printing.

14. Use of the membrane electrode unit (1) according to any one of claims 1 to 7 for proton exchange membrane electrolysis or anion exchange membrane electrolysis.

15. Use of the membrane electrode unit (1) according to any one of claims 1 to 7 for water electrolysis.

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