Method for producing electrocatalyst

Abstract

The invention relates to a method for producing an electrocatalyst, comprising the following steps: a) electrodepositing or electrochemically plating an alloy comprising nickel and a second metal on a copper, nickel or other metal substrate; and b) electrochemically or chemically dissolving the deposited second metal to obtain a nanoporous structure on a copper, nickel or other metal substrate.

Description

[0001] This application is a divisional application. The international application number of the original application is PCT / EP2018 / 075335, the international application date is September 19, 2018, the Chinese national application number is 201880061421.1, the date of entry into China is March 20, 2020, and the name of the invention is “Method for producing electrocatalysts”. Technical Field

[0002] The present disclosure generally relates to electrocatalysts. In particular, the present invention relates to a method of producing an electrocatalyst and an electrocatalyst. Background Art

[0003] Electrolysis of water is a process in which water molecules break apart to form hydrogen and oxygen. The process occurs due to the flow of electric current between two electrodes immersed in water.

[0004] Electrolytes are often added to water prior to electrolysis to increase the water's electrical conductivity. This ensures a more efficient electrolysis process due to better charge carrying properties. However, the addition of electrolytes may result in the production of undesirable byproducts during the electrolysis process.

[0005] Purified water can be used for electrolysis purposes, essentially eliminating the production of undesirable byproducts. However, it can be more difficult to initiate an efficient electrolysis process in purified water due to its inherent properties (e.g., low electrical conductivity). Summary of the invention

[0006] The purpose of the present disclosure is to improve or at least reduce the problems of the prior art.

[0007] Therefore, according to a first aspect of the present disclosure, a method for producing an electrocatalyst is provided, comprising the following steps: a) electrodepositing or electrochemically plating an alloy comprising nickel and a second metal on a copper, nickel or other metal substrate; b) electrochemically or chemically dissolving the deposited second metal to obtain a nanoporous structure on the copper, nickel or other metal substrate.

[0008] The porous structure increases the surface area of ​​the electrocatalyst, which makes the electrochemical reaction more efficient. For example, if the electrocatalyst is used as an electrode in a water electrolysis application, the active area of ​​the electrode in contact with water increases. Therefore, the contact area with water molecules is increased. Therefore, a more efficient electrolysis reaction and a compact electrolyzer can be obtained.

[0009] Furthermore, where the electrocatalyst forms part of an electrode for electrolysis, the current density in the water to be electrolyzed can be increased. The current density can be increased due to the porous structure of the electrocatalyst, thereby providing a larger surface area for, for example, a copper-based electrode to contact the water.

[0010] In addition, since copper has a low resistivity, the electrical losses during the electrolysis process will be small. Therefore, less heat is generated by the electrolysis device including the electrodes, thereby increasing the efficiency of the entire electrolysis. Less heat also avoids the generation of steam.

[0011] Furthermore, electrocatalysts are very cost-effective and can be produced in large quantities.

[0012] According to one embodiment, a heat treatment step of the copper substrate is provided after step a) but before step b).

[0013] During the heat treatment, the copper substrate having an alloy comprising nickel and a second and / or third metal may be subjected to a temperature of at least 250° C., such as a temperature of at least 275° C., such as a temperature of at least 300° C., such as a temperature of at least 325° C. or at least 350° C. The heat treatment may be provided under normal atmospheric conditions. The heat treatment may be performed, for example, for at least 20 minutes, such as at least 25 minutes, for example at least 30 minutes, before step b).

[0014] The electrochemical or chemical dissolution in step b) may be a dealloying step, such as electrochemical dealloying or chemical dealloying.

[0015] According to one embodiment, the second metal is copper or iron.

[0016] According to one embodiment, the second metal is copper and the method further comprises the step of: c) depositing iron on the porous structure. Step c) may be performed after step b). Electrodepositing iron on a copper electrode with a porous nickel surface increases the current density per square centimeter of the electrode, for example in electrolytic applications.

[0017] In order to electrodeposit iron on the porous structure, 0.86 molar (11% concentration) of ferrous sulfate / iron (II) heptahydrate FeSO4·7H2O and / or ferrous (II) chloride and sodium citrate (Na3C6H5O7) or boric acid (H3BO3) as pH buffers can be used to prepare the electroplating bath solution.

[0018] According to one embodiment, the second metal is iron and the method further comprises the step of: c) depositing copper on the porous structure. Step c) may be performed after step b).

[0019] According to one embodiment, the alloy of step a) also comprises a third metal, such as copper or iron, which is different from the second metal.

[0020] According to one embodiment, the third metal is copper or iron. Thus, if the second metal is copper, the third metal is iron. If the second metal is iron, the third metal is copper. Compared to nickel-copper alloys, alloys including nickel, copper and iron provide greater surface area, improved efficiency and current density of the electrolysis process, and improved stability.

[0021] Different surface morphologies can be obtained by using different electroplating and electrochemical dissolution / dealloying conditions. For example, if copper-iron is dealloyed from a copper-iron-nickel alloy, the surface morphology and current density obtained will be different from the surface morphology and current density obtained from copper dealloyed only from a copper-nickel-copper alloy.

[0022] According to one embodiment, the second metal is copper and in step a) an electroplating solution comprising a copper salt (such as CuSO 4 ) and a nickel salt (such as NiSO 4 ) is used.

[0023] According to one embodiment, an electroplating solution comprising a copper salt such as copper sulfate (CuSO4), a nickel salt such as nickel sulfate (NiSO4) and sodium citrate (Na3C6H5O7) or boric acid (H3BO3) as a pH buffer is used in step a).

[0024] According to one embodiment, the molar ratio of copper to nickel in the electroplating solution is 1:1 to 1:3, such as 1:1.5 to 1:2.5, such as 1:1.8 to 1:2.2.

[0025] According to one embodiment, an electroplating solution including a copper salt such as copper sulfate (CuSO4), a nickel salt such as nickel sulfate (NiSO4), an iron salt such as iron sulfate (FeSO4) and sodium citrate (Na3C6H5O7) or boric acid (H3BO3) as a pH buffer is used in step a).

[0026] According to one embodiment, a plating solution comprising a nickel salt such as nickel sulfate (NiSO4) and an iron salt such as iron sulfate (FeSO4) and sodium citrate (Na3C6H5O7) as a pH buffer or using boric acid (H3BO3) is used in step a).

[0027] The electroplating solution may, for example, be aqueous.

[0028] In one embodiment, the concentration of nickel in the electroplating solution is higher than the concentration of copper. In particular, in a copper-nickel electroplating solution, the concentration of nickel may be higher than the concentration of copper.

[0029] In the iron-nickel electroplating solution and the nickel-copper-iron electroplating solution, the concentration of nickel may be higher than the concentration of iron.

[0030] According to one embodiment, in step a) a voltage of 2V-6V is applied in a two-electrode setup. Thus, in one embodiment, the electrodeposition in step a) is performed by applying a voltage difference in the range of 2V-6V between the copper substrate and the second electrode in a two-electrode setup.

[0031] According to one embodiment, the electrodeposition in step a) involves applying a voltage below -0.5 V relative to saturated calomel electrode (SCE), for example -0.8 V to -0.9 V relative to SCE, such as at least -0.92 V relative to SCE, between the copper substrate and a reference electrode in a three-electrode setup.

[0032] According to one embodiment, a solution comprising sulfate ions, such as a potassium sulfate (K2SO4) solution, an alkaline solution or an acidic solution is used in step b). The solution may, for example, be aqueous. Examples of suitable alkaline solutions are potassium hydroxide and sodium hydroxide. Examples of suitable acidic solutions are hydrochloric acid and sulfuric acid.

[0033] Potassium sulfate is a good dealloying solution / electrolyte / chemical bath for electrochemical dealloying of copper or / and iron in copper-nickel and nickel-copper-iron alloys. It can be anodic dealloying, which means that the copper substrate coated with any of the above alloys treated for electrochemical dealloying is connected to the positive pole of a power supply in a two-electrode setup or as a working electrode in a three-electrode setup.

[0034] According to one embodiment, in step b) a voltage of 1 V-12 V is applied in a two-electrode setup, such as 2 V-3 V. Thus, in one embodiment, the chemical dissolution in step b) is performed by applying a voltage difference in the range of 1 V-12 V between the copper substrate and the second electrode in a two-electrode setup.

[0035] According to one embodiment, a pulse voltage is applied in step b). A higher pulse voltage will produce a larger surface area. In a three-electrode setup, for example, the voltage range can be 1V-4V, such as 1V-3V (relative to SEC). The high pulse voltage parameters can be, for example, [t1=1s, V1=2.5V; t2=5s, V2=0.005V], where t1=2.5V for 1 second, then t2=0.005V for 5 seconds, applied for about 15 minutes.

[0036] By using a higher pulse voltage in step b), more copper or iron or both can be pushed out of the copper-nickel or nickel-copper-iron alloy.

[0037] According to one embodiment, step c) is electrodeposition.

[0038] One embodiment further comprises the step of: d) passivating the deposited iron.

[0039] According to one embodiment, the copper substrate comprises a copper coil. Therefore, the copper coil is subjected to the treatment of steps a)-b). By performing steps a)-b) after the copper coil has been formed from the copper wire, a more uniform coverage of the copper coil can be obtained, compared to the case where the copper coil has been formed after steps a)-b). It has been found that the coil-shaped electrocatalyst provides a particularly efficient electrolysis process.

[0040] According to one embodiment, the other metal is one of iron, cobalt, titanium, zirconium, stainless steel and aluminum.

[0041] According to one embodiment, the copper or nickel substrate is a porous copper or nickel substrate.

[0042] According to a second aspect of the present invention, there is provided an electrocatalyst obtainable by the method of the first aspect.

[0043] According to one embodiment, the second metal is copper or iron.

[0044] The nanoporous structure may include a third metal different from the second metal. The third metal may be, for example, copper or iron. Thus, if the second metal is copper, the third metal is iron. If the second metal is iron, the third metal is copper.

[0045] According to a third aspect of the present disclosure, there is provided an electrode for electrolysis, the electrode comprising the electrocatalyst of the second aspect. The copper substrate comprises a copper coil covered by a nanoporous structure comprising nickel and preferably a second metal, and optionally a third metal.

[0046] In general, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless otherwise explicitly defined herein. Unless otherwise explicitly stated, all references to "a / an / the element, device, component, means, step, etc." should be openly interpreted as referring to at least one instance of an element, device, component, means, step, etc. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. DETAILED DESCRIPTION

[0047] The present disclosure relates to a method of producing an electrocatalyst and an electrocatalyst suitable for oxygen and hydrogen release reactions in alkaline water electrolysis. The electrocatalyst may advantageously form part of an electrode for an electrolysis process.

[0048] The method of producing an electrocatalyst comprises the step of: a) electrodepositing an alloy comprising nickel and a second metal on a copper substrate.

[0049] The step a) of electrodeposition can be, for example, electrochemical deposition or pulsed electrodeposition. If pulsed electrodeposition (i.e., applying a pulsed voltage) is used, a low pulsed voltage can be used compared to the voltage applied during electrochemical dissolution / dealloying. For example, in a three-electrode arrangement, the low pulsed voltage can be -0.92V for 5 seconds, then -0.005V for 1 second. These pulses can be, for example, applied for about 15 minutes to 30 minutes.

[0050] The chemical bath used in step a) (ie in which the copper substrate is immersed) may for example comprise an electroplating solution comprising a copper salt (such as CuSO4) and a nickel salt (such as NiSO4). The electroplating solution may preferably be aqueous.

[0051] In one example, a constant voltage may be applied to the copper substrate during step a) to perform electrodeposition of the alloy on the copper substrate. In a two-electrode setup, the applied voltage may be, for example, in the range of 2V-6V between the copper substrate and the second electrode.

[0052] In one variant, the second metal is copper. In this case, the alloy is a copper-nickel alloy.

[0053] In another variation, the second metal is iron. In this case, the alloy is a nickel-iron alloy.

[0054] In yet another variation, the alloy further comprises a third metal. In this case, the second metal may be, for example, copper, and the third metal may be iron. Thus, in this case, the alloy is a nickel-copper-iron alloy.

[0055] In a variant, the copper substrate with the alloy obtained in step a) is subjected to a heat treatment. This heat treatment is preferably carried out before step b) described below.

[0056] The heat treatment before step b) initiates diffusion mechanisms in the nickel-copper alloy, nickel-copper-iron alloy or nickel-iron alloy on the copper substrate. In the case of electrochemical dealloying using high pulse voltage in step b), the heat treatment after step a) significantly reduces the formation of any nanocracks on the alloy coating. It can also improve the stability and activity of the electrocatalyst. If the copper substrate is heat treated after step a), a more uniform nanoporous surface structure is obtained after step b). If the copper substrate / electrocatalyst is used as an electrode, the heat treatment increases the current density.

[0057] In step b), the copper substrate is subjected to electrochemical dissolution of the deposited second metal to obtain a nanoporous structure on the copper substrate.

[0058] Electrochemical dissolution may involve dealloying. Dealloying may be, for example, electrochemical dealloying or pulse electrochemical dealloying.

[0059] The chemical bath used in step b) may, for example, comprise a dealloying solution comprising sulfate ions (eg a potassium sulfate K2SO4 solution).

[0060] According to one example, in step b), a voltage in the range of 1V-12V, such as 2V-3V, is applied between the copper substrate provided with the deposited alloy and the second electrode in a two-electrode arrangement.

[0061] In one variation, a constant voltage may be used during step b) to perform the electrochemical dissolution of the second metal deposited on the copper substrate. Alternatively, a pulsed voltage may be used during step b) to perform the electrochemical dissolution. In another variation, the constant voltage may be combined with the pulsed voltage; for example, during a portion of the dealloying, a constant voltage may be applied, while during another portion, a pulsed voltage may be applied.

[0062] In the case where the alloy is a copper-nickel alloy, at least a portion of the deposited copper is dissolved electrochemically. Also in this case, in step c), iron is deposited on the porous structure obtained in step b). The deposition in step c) is preferably electrodeposition.

[0063] A variant comprising step c) further comprises a step d) of passivating the deposited iron.

[0064] In the case where the alloy is a nickel-iron alloy, at least a portion of the deposited iron is electrochemically dissolved. In this case, in an optional step c), copper can be deposited on the porous structure obtained in step b). The deposition in step c) is preferably electrodeposition.

[0065] If the alloy is a nickel-copper-iron alloy, in step b) at least a portion of the deposited iron and the deposited copper is electrochemically dissolved.

[0066] Example 1

[0067] Chemicals and Settings

[0068] The following describes an experimental procedure to obtain a high surface area copper wire of about 4 cm long with a diameter of about 1 mm. In this example, the copper wire is a copper substrate to be subjected to steps a) and b). The purity of the copper wire is 99.9%.

[0069] Chemicals: Boric acid (H3BO3, 99.97%), sodium sulfate (Na2SO4, 99.99%), copper sulfate pentahydrate (CuSO4·5H2O, analytical grade 99%-100.5%), nickel sulfate hexahydrate (NiSO4·6H2O, 98%).

[0070] Electrochemical treatment:

[0071] The three-electrode cell was connected to a potentiostat, where a saturated calomel electrode (SCE) was used as a reference electrode and a carbon electrode was used as a counter electrode. A large amount of the plating solution (30 mL) containing nickel and the second metal was selected to ensure complete coverage of the electrodes.

[0072] Note that it is possible to scale down the volumes of the plating and dealloying solutions and still achieve the same results.

[0073] Electrodeposition of an alloy comprising nickel and copper was performed. The deposition of nickel and copper on the copper wire was made from an electroplating solution containing the following ingredients: 0.5M H3BO3, 0.5M NiSO4 and 0.005M CuSO4, resulting in a Cu:Ni ratio of 1:100. Approximately 3 cm-3.5 cm of the copper wire was immersed in the solution. A constant voltage of -0.92 V (relative to SCE) was applied for 15 minutes.

[0074] Then, the copper wire with the nickel-copper layer obtained in the electroplating process was briefly rinsed with deionized water before the electrochemical dissolution step (dealloying step in this embodiment). The dealloying solution consisted of 0.5M H3BO3 and 0.5M Na2SO4, with a total volume of 30mL. The copper wire with the copper-nickel layer was immersed in the dealloying solution and dealloyed by applying a constant voltage of 2.5V (relative to SCE) for 15 minutes.

[0075] Example 2

[0076] Example 2 is similar to Example 1 regarding chemicals and setup. The electrodeposition steps are also the same as in Example 1. However, in the electrochemical dissolution step (here, dealloying), a different voltage profile is applied.

[0077] Instead of a constant voltage, a "low" pulse voltage or a "high" pulse voltage is used. The parameters of the "low" pulse voltage [t1 = 1s, V1 = 0.5V; t2 = 5s, V2 = 0.005V] mean that a voltage of 0.5V is applied for 1 second, then a voltage of 0.005V is applied for 5 seconds, and then the process is repeated for 15 minutes. For the "high" pulse voltage, the parameters are [t1 = 1s, V1 = 2.5V; t2 = 5s, V2 = 0.005V].

[0078] Above the invention has mainly been described with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended claims.

Claims

1. A method for producing an electrocatalyst comprising the following steps: a) electrodepositing or electrochemically plating an alloy comprising nickel, a second metal and a third metal on a copper substrate, a nickel substrate or other metal substrate, wherein the second metal is copper and the third metal is iron, wherein the nickel, copper and iron are provided as an electroplating solution and wherein the concentration of nickel is higher than the concentration of iron; b) electrochemically dissolving or chemically dissolving the deposited second metal to obtain a nanoporous structure on the copper substrate, nickel substrate or other metal substrate; and c) depositing iron on the porous structure; Wherein, the other metal is one of iron, cobalt, titanium, zirconium, stainless steel and aluminum, The method further comprises the step d): passivating the deposited iron, and Wherein, the molar ratio of copper to nickel in the electroplating solution is 1:1 to 1:

3.

2. The method according to claim 1, wherein: The method further comprises a heat treatment step after step a) but before step b), wherein the substrate provided with the alloy comprising nickel and the second metal and the third metal is subjected to a temperature of at least 250°C during the heat treatment.

3. The method according to claim 1, wherein: In step a), an electroplating solution comprising a copper salt and a nickel salt is used.

4. The method according to claim 3, wherein: The copper salt includes CuSO4.

5. The method according to claim 3, wherein: The nickel salt includes NiSO4.

6. The method according to claim 1, wherein: The molar ratio of copper to nickel in the electroplating solution is 1:1.5 to 1:2.

5.

7. The method according to claim 6, wherein: The molar ratio of copper to nickel in the electroplating solution is 1:1.8 to 1:2.

2.

8. The method according to claim 1, wherein: Step c) is electrodeposition.

9. The method according to any one of claims 1 to 8, wherein: In step a), a voltage of 2 V to 6 V is applied in a two-electrode setup.

10. The method according to any one of claims 1 to 8, wherein: In step b), a solution comprising sulfate ions, a basic solution or an acidic solution is used.

11. The method according to claim 10, wherein: The solution containing sulfate ions includes a K2SO4 solution.

12. The method according to any one of claims 1 to 8, wherein: In step b), a voltage of 1 V to 12 V is applied in a two-electrode setup.

13. The method according to claim 12, wherein: In step b), a voltage of 2 V to 3 V is applied in a two-electrode setup.

14. The method according to any one of claims 1 to 8, wherein: In step b), a pulse voltage is applied.

15. The method according to any one of claims 1 to 8, wherein: The copper substrate includes a copper coil.

16. The method according to any one of claims 1 to 8, wherein: The copper substrate or the nickel substrate is a porous copper substrate or a porous nickel substrate.

17. An electrocatalyst obtainable by the method according to any one of claims 1 to 16.