Metal body and element for producing the metal body

Abstract

The invention relates to a metal body comprising a substrate (1) made of a metal material. At least one first layer (L1) made of Ni-X-Y is deposited onto the surface of the substrate (1), wherein X is a chemical element which is selected from Al, Zn, Mg, Mn, Sn and / or a plurality of the aforementioned elements and Y is a chemical element which is selected from Mo, Cr, Fe, Cu, Co, Ti, V, Ce and / or a plurality of the aforementioned elements. The at least one first layer (L1) has at least two lamellar regions with different phases in terms of the ternary phase diagram. In order to increase the specific surface area of the at least one first layer (L1), at least one of the lamellar phases which form a region of the at least one first layer (L1) is completely or partially leached.

Description

[0001] FRAUNHOFER SOCIETY...eV, Alantum Europe GmbH

[0002] Metal body and method for producing the metal body

[0003] The present invention relates to a metal body and a method for producing a metal body.

[0004] To conduct alkaline electrolysis, cost-effective and long-term efficient electrodes are required to significantly reduce hydrogen production costs. Electrodes containing precious metals are still generally used for this purpose. If non-precious metal electrodes are used, these are generally Raney nickel or Ni-Mo-

[0005] Electrodes. In the case of Raney electrodes, a Ni-Zn or Ni-Al alloy is used, which is activated by chemical leaching. For example, patent DE 2 926 641 C2 discloses a process for producing a Raney nickel catalyst.

[0006] However, the manufacturing processes usually offer a high degree of process variability, which has a significant influence on the activity of the resulting electrode. However, the manufacturing process is not the primary factor for the precise production of an active electrode; rather, the structure of the electrode and, in particular, the available electrode surface are the main factors for the resulting activity of the Raney Ni electrode.

[0007] The present invention is therefore based on the object of proposing a metal body and a method for its production with which the aforementioned disadvantages are avoided, and with which improved electrode activity can be achieved in an efficient manner.

[0008] This object is achieved according to the invention by a metal body according to the main claim and a method according to the independent claim. Advantageous embodiments and further developments are described in the dependent claims.

[0009] A metal body has a substrate made of a metallic material, wherein at least one first layer of Ni-XY (nickel-XY) is deposited on a surface of the substrate, where X is a chemical element selected from Al (aluminum), Zn (zinc), Mg (magnesium), Mn (manganese), Sn (tin) and / or more of the aforementioned elements (for example in the form of an alloy) and Y is a chemical element selected from Mo (molybdenum), Cr (chromium), Fe (iron), Cu (copper), Co (cobalt), Ti (titanium), V (vanadium), Ce (cerium) and / or more of the aforementioned elements (for example in the form of an alloy). The at least one first layer has at least two lamellar regions with different phases in the sense of the ternary phase diagram.To increase the specific surface area of ​​the at least one first layer, at least one of the lamellar phases forming a region of the at least one first layer is completely or partially leached, i.e., in particular, exposed to an alkali. Typically, at least one chemical element X and / or Y is at least partially removed from the at least one first layer by exposing the at least one first layer to an alkali.

[0010] Leaching results in a structure characterized by firmer, i.e., less leached, and more porous, i.e., more highly leached, lamellae or intermetallic phases, resulting in an overall larger specific and thus catalytically active surface area. This allows for targeted adjustment of manufacturing parameters to provide a highly active electrode (anode and cathode) for alkaline electrolysis and related processes. "Lamellar" refers in particular to an arrangement of (typically superimposed) layers, with the layers arranged similarly and, ideally, parallel. The ternary Ni-XY structure used enables the formation of various alternating ternary lamellar phases in at least one layer, of which at least one lamellar phase is more easily leached than others.

[0011] It can be provided that a non-lamellar intermediate layer made of Ni-XY, Ni-X, Ni-Y or XY is arranged between the substrate and the at least one first layer in order to adjust the properties of the metal body more specifically.

[0012] Alternatively or additionally, at least one second layer of Ni-XY can be arranged on a surface of the at least one first layer facing away from the substrate, in order to also be able to modify the properties more specifically. In this case, the at least one second layer can have at least two lamellar regions with different phases, and preferably at least one of the phases of the at least one second layer differs from the phases of the at least one first layer, for example, in terms of composition.

[0013] Typically, a thickness of the at least one first layer is maintained in the range 1 pm to 50 pm, preferably in the range 10 pm to 30 pm, ie the thickness is 1 pm to 50 pm, preferably in the range 10 pm to 30 pm.

[0014] A thickness of the regions with different phases, ie of the individual lamellae, in the range 100 nm to 10 pm, preferably in the range 1 pm to 7 pm, particularly preferably in the range 3 pm to 5 pm is maintained, ie the thickness of the regions with different phases is 100 nm to 10 pm, preferably 1 pm to 7 pm, particularly preferably in the range 3 pm to 5 pm. Thus, a comparatively thin lamellar structure can be created which nevertheless has a sufficiently large specific surface area.

[0015] The substrate can be designed as an open-pored foam in order to provide a sufficiently large surface to be coated.

[0016] An aqueous potassium hydroxide and potassium / sodium tartrate solution can be used as the leaching solution, but NaOH, KOH, LiOH in pure form or mixtures thereof can also be used.

[0017] An electrode, in particular for alkaline electrolysis, or a catalyst may comprise a metal body with the properties described above.

[0018] In a method for producing a metal body, at least one first layer of Ni-XY is deposited on a surface of a substrate made of a metallic material, where X is a chemical element selected from Al, Zn, Mg, Mn and Sn and / or more of the aforementioned elements, and Y is a chemical element selected from Mo, Cr, Fe, Cu, Co, Ti, V and Ce and / or more of the aforementioned elements. After application, the at least one first layer is subjected to a heat treatment which is stopped before the concentration is completely equalized, so that at least two lamellar regions with different phases are formed in the at least one first layer in the sense of the ternary phase diagram.Subsequently, in order to increase the specific surface area of ​​the at least one first layer, at least one of the lamellar phases forming a region of the at least one first layer is completely or partially leached.

[0019] The formation of at least two phases creates a structure that reacts differently to exposure to lye and is correspondingly altered to varying degrees by the leaching. The formation of two phases is only made possible by stopping the heat treatment before the concentrations have completely equalized.

[0020] The heat treatment typically takes place at a temperature in the range of 600 °C to 850 °C, preferably 600 °C to 700 °C. This heat treatment is also preferably carried out in a nitrogen or inert gas atmosphere. The heat treatment is typically carried out over a period of 1 second to 15 minutes, but preferably a maximum of 60 seconds. Thus, the parameters can be adjusted as desired to enable the formation of the two phases.

[0021] The described process is typically used to produce the metal body described.

[0022] Embodiments of the invention are illustrated in the drawings and are explained below with reference to Figures 1 to 3.

[0023] They show:

[0024] Fig. 1 is a schematic side view of a coated metal body;

[0025] Fig. 2 is a view of the metal body corresponding to Figure 1 with two different layers and

[0026] Fig. 3 is a view corresponding to Figure 1 with an intermediate layer.

[0027] Figure 1 shows a schematic side view of a metal body consisting of a substrate 1 and a lamellar layer LI arranged thereon. In the illustrated embodiment, the substrate 1 is an open-pore nickel foam with a pore size in the selected embodiment of between 100 pm and 5000 pm. The lamellar layer LI is applied to one side of the nickel foam, which can also be done on both sides in further embodiments. The illustrated metal body serves as a catalyst in heterogeneous and electrochemical catalysis. The microstructure realized by this metal body is characterized in that a Ni-Al-Y layer is applied to the substrate 1 as the metallic core, where Y is a chemical element that can be selected from Mo, Cr, Fe, Cu, Co, Ti, V and Ce or several of these elements, e.g. Mo and Cr.This Ni-Al-Y layer can also surround the entire substrate 1 and forms in such a way that two different Ni-Al-Y phases are always present in succession in the sense of the ternary phase diagram in a lamellar structure shown in Figure 1, emanating from the substrate 1, i.e., they are arranged alternately in this layer LI. Lamellae of this lamellar structure generally run parallel to the surface of the substrate 1 or approximately parallel, i.e., at an angle of a maximum of 10°, preferably a maximum of 5°. The thickness of individual lamellae is between 100 nm and 10 pm, while the entire layer LI is between 1 pm and 50 pm thick.

[0028] As shown in Figure 2 in a schematic side view corresponding to Figure 1, in a further exemplary embodiment a further lamellar layer L2 can also be applied to layer LI, or in principle further such layers can also exist. Recurring features are provided with identical reference numerals in this figure as well as in the further figure. Layer L2 also consists of (typically exactly) two different Ni-Al-X phases. The phases of LI and L2 can differ, with the further layer L2 generally having at least one phase different from the first layer LI. However, layer L2 can also have exactly one phase different from layer LI. Layer L2 and further such layers are each between 1 pm and 50 pm thick.Even if aluminum is used in the illustrated embodiments, the first layer LI or the further layer L2 can be formed from Ni-XY, where X is a chemical element selected from Al, Zn, Mg, Mn, Sn or several of these elements.

[0029] An intermediate layer 2 may also be located between the lamellar structures LI and L2 and the substrate 1, as shown in Figure 3 in a schematic side view corresponding to Figures 1 and 2. This intermediate layer 2 is preferably made of Ni2- x X x Al3 and also between 1 pm and 50 pm thick.

[0030] After the application of layers LI, LI, and L2 or the intermediate layer 2 as well as LI, LI, and L2, a leaching step is carried out to selectively leach aluminum (or, if no aluminum is used, the corresponding substitute), which leads to a preferential dissolution of one of the two lamellar-forming phases within the respective layer LI or L2. This results in the formation of a lamellar structure characterized by firmer, i.e., less leached, and more porous, i.e., more strongly leached, lamellae or phases. This results in an overall increased specific surface area, i.e., the catalytically active surface becomes larger.

[0031] The manufacturing process of the metal body can thus be described in a first example as follows: Ni-Mo powder is applied to a Ni foam and then alloyed in a first heat treatment step. This creates a Ni-Mo foam. This Ni-Mo foam is then coated on one side with aluminum by atmospheric plasma spraying and subjected to a second heat treatment step. However, the second heat treatment step is terminated before complete concentration equilibrium can occur, so that lamellar phase regions consisting of the Ni, Mo, and Al components form. This foam is now called Raney Ni-Mo foam. Finally, the aluminum content in the Raney Ni-Mo foam is leached out in an alkaline solution. This leaching takes place in an aqueous solution of potassium hydroxide (1.8 M) and potassium / sodium tartrate (1.5 M) under ambient conditions.The leaching step lasts 24 hours in the illustrated example, but can also take between 18 and 30 hours. The leaching solution is then exchanged and heated to 353 K until gas evolution ceases, which typically takes 2 to 4 hours. One of the two phases is easier to leach than the other, and the more stable lamellae form a structure with a very large internal surface area. The metal bodies thus produced are removed from the leaching solution and thoroughly washed with water. This last leaching step is always the same in the variants discussed below, apart from adjustments to the temperature (which, however, always lies in the range of 330 K to 370 K) and an adjustment to the composition of the leaching solution.

[0032] In a first variant of the first example described, a Ni-Mo powder with the composition Ni7i.2Mo28.9 is used, and the first heat treatment is carried out at 1280 °C and lasts one hour. The aluminum coating is then applied by atmospheric plasma spraying, and the second heat treatment takes place at 670 °C in a nitrogen atmosphere. Typically, this heat treatment, the second in the present embodiment, takes place at a temperature that is at least 10 K and at most 20 K above the melting temperature of the element that was applied as a coating.

[0033] In a second variant, a Ni-Mo powder with the composition Ni7i.2Mo28.9 is again used and subjected to the first heat treatment for one hour. As with the first variant, the aluminum coating is applied by atmospheric plasma spraying, and the second heat treatment takes place at 670 °C, but this time in an argon atmosphere.

[0034] In a third variant, the second heat treatment can also be carried out at a reduced temperature of 660 °C, while the other parameters correspond to the second variant.

[0035] In a fourth variation of the first example, a Ni-Mo powder with the composition Ni7i,2Mo28,9 is again used and subjected to the initial heat treatment at 1280 °C for one hour. The sample to be treated is then sprinkled on one side with aluminum powder until a weight fraction of aluminum powder to foam (mass of aluminum powder mAi-powder / (mass of mesh rri-mesh + mass of aluminum powder mAi-powder)) of 13.9 percent is reached. The final heat treatment takes place, as in the second variation, at 670 °C in an argon atmosphere.

[0036] In a second example, a Ni-Mo-Y mesh (e.g., a Hastelloy C276 mesh) is coated with aluminum and subjected to the first heat treatment, resulting in the formation of lamellar phase regions composed of the Ni, Mo, and Al components, and is now referred to as a Raney Ni-Mo mesh. The aluminum portion is again leached using the aforementioned leaching solution over a period of 24 hours. Subsequently, as in the first example, the leaching solution is replaced with a fresh potassium hydroxide (1.8M) and potassium / sodium tartrate (1.5M) solution and heated to 353 K until gas evolution ceases after 2 to 4 hours. The metal body is thoroughly washed with water as usual. The leaching step is identical for all variants of the second example mentioned below.

[0037] In a first variant of the second example, the mesh as substrate 1 is sprinkled with aluminum powder until an aluminum powder-to-mesh weight ratio of ((mass of aluminum powder mAi-powder / (mass of mesh rriNetz + mass of aluminum powder mAi-powder))) of 13.4 percent is reached. Subsequently, the heat treatment (corresponding to the second heat treatment of the first example) is carried out at 680 °C in a nitrogen atmosphere.

[0038] In a second variant of the second example, the mesh is sprinkled with the aluminum powder until the weight fraction of 33 percent is reached and the described heat treatment is again carried out in a nitrogen atmosphere.

[0039] In a third variant of the second example, a 0.1 mm thick aluminum foil is pressed onto one side of the Ni-Mo-X mesh at 70 MPa and the heat treatment already mentioned is carried out.

[0040] In a fourth variant of the second example, the aluminum foil is pressed onto the mesh on one side at 145 MPa and the described heat treatment is then carried out.

[0041] The process is flexibly adjustable: For example, the more leaching-resistant phase of layer LI may also be present in the plate stack L2, but the less leaching-resistant phase there. Depending on the temperature and time regime, layer structures with specific properties can be generated. The metal body is used as an electrode in electrolysis (e.g., alkaline electrolysis or chlor-alkali electrolysis) or other electrochemical processes such as electroorganic synthesis or electrochemical CCh reduction, as well as in heterogeneous catalysis as a Raney Ni catalyst.

[0042] Only features of the various embodiments disclosed in the exemplary embodiments can be combined with one another and also claimed individually.

Claims

Patent claims 1. A metal body comprising a substrate (1) made of a metallic material, wherein at least one first layer (LI) of Ni-XY is deposited on a surface of the substrate (1), wherein X is a chemical element selected from Al, Zn, Mg, Mn, Sn and / or more of the above elements, and Y is a chemical element selected from Mo, Cr, Fe, Cu, Co, Ti, V, Ce and / or several of the above-mentioned elements, and wherein the at least one first layer (LI) has at least two lamellar regions with different phases in the sense of the ternary phase diagram, wherein in order to enlarge the specific surface area of ​​the at least one first layer (LI), at least one of the lamellar phases forming a region of the at least one first layer (LI) is completely or partially leached out.

2. Metal body according to claim 1, characterized in that a non-lamellar intermediate layer (2) made of Ni-XY, Ni-X, Ni-Y or XY is arranged between the substrate (1) and the at least one first layer (LI).

3. Metal body according to claim 1 or claim 2, characterized in that on a surface of the at least one first layer (LI) facing away from the substrate (1) at least one second layer (L2) of Ni-XY is arranged, wherein the at least one second layer (L2) has at least two lamellar regions with different phases, and preferably at least one of the phases of the at least one second layer (L2) differs from the phases of the at least one first layer (LI).

4. Metal body according to one of the preceding claims, characterized in that a thickness of the at least one first layer (LI) is maintained in the range 1 pm to 50 pm, preferably in the range 10 pm to 30 pm.

5. Metal body according to one of the preceding claims, characterized in that a thickness of the regions with different phases, i.e. of the individual lamellae, is maintained in the range 100 nm to 10 pm, preferably in the range 1 pm to 7 pm, particularly preferably in the range 3 pm to 5 pm.

6. Metal body according to one of the preceding claims, characterized in that the substrate (1) is designed as an open-pore foam.

7. Metal body according to one of the preceding claims, characterized in that the lamellar layer (LI) is formed on both sides of the substrate (1).

8. Metal body according to one of the preceding claims, characterized in that the lamellae in the lamellar layer (LI) are formed at an angle of maximum 10°, preferably maximum 5° to the surface of the substrate (1).

9. An electrode or catalyst comprising a metal body according to any one of claims 1 to 8.

10. A method for producing a metal body, in which at least one first layer (LI) of Ni-XY is deposited on a surface of a substrate (1) made of a metallic material, wherein X is a chemical element selected from Al, Zn, Mg, Mn and Sn and / or several of the above elements, and Y is a chemical element selected from Mo, Cr, Fe, Cu, Co, Ti, V and Ce and / or several of the above-mentioned elements, and the at least one first layer (LI) is subjected to a heat treatment after application, which is terminated before complete concentration equalization, so that in the at least one first layer (LI) at least two lamellar regions with different phases are formed in the sense of the ternary phase diagram, and wherein subsequently, in order to enlarge the specific surface area of ​​the at least one first layer (LI), at least one of the lamellar phases forming a region of the at least one first layer (LI) is completely or partially leached out.

11. The method according to claim 10, characterized in that the heat treatment is carried out at a temperature in the range 600 °C to 850 °C, preferably in the range 600 °C to 700 °C, and also preferably in a nitrogen atmosphere or a noble gas atmosphere.

12. A method according to claim 10 or claim 11, characterized in that the heat treatment is carried out over a period of 1 s to 15 min, but preferably a maximum of 60 s.

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