Method for producing protective element for chlor-alkali and alkaline water electrolysers

Abstract

The invention relates to an article for an electrolysis cell, in particular a chlor-alkali and alkaline water electrolysis cell, comprising a nickel-based protective element and an electrically conductive pouch wherein the pouch substantially surrounds all sides of the protective element, a batch of two or more such articles, and a process for preparing these batches.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of industrial mass production of protective elements for chlor-alkali and alkaline water electrolyzers. BACKGROUND

[0002] Industrial electrolyzers typically comprise a plurality of adjacent cells, each individual cell containing two opposite electrodes, which can be catalytically coated to promote the desired electrochemical reaction. Depending on the application, the electrode coating composition can contain different percentages of one or more noble metals, such as Ru, Rh, Ir and / or Pt. These materials are scarce and expensive; they strongly influence the cost of the electrode and have an impact on procurement, but they often play a key role in ensuring the economy and performance of the electrolysis system, especially in chlor-alkali (C / A) and alkaline water electrolysis (AWE) applications. In these cases, ruthenium is often preferred for its lower cost and is often used to replace, in whole or in part, other more expensive noble metals in the catalytic coating composition.

[0003] Under nominal operating conditions, the C / A and AWE electrolyzers operate at a certain current density, which remains substantially constant during operation, except for maintenance operations.

[0004] However, unplanned interruption events can occur, thus suddenly interrupting the normal operation of the cell and cutting off the current. These events can have a negative impact on the medium and long-term performance of the cell, thus reducing its performance under standard operating conditions and causing premature breakdown of the coating.

[0005] In fact, unplanned interruption events can cause an undesirable phenomenon known as current reversal. In this case, the reversal current generated during the shutdown event flows through the electrolyzer in the opposite direction to the electrolysis current and can cause cathode deterioration due to elution of the catalyst material, in particular ruthenium, thus severely affecting the performance of the electrolyzer over time.

[0006] Several possible solutions have been developed to solve this problem, a particularly successful method has been described in EP3330409, EP3330410 and EP2615195.

[0007] In these inventions, a protective element, i.e. a body made of a material suitable for absorbing the reversal current, is placed inside the cell, in electrical contact with the cathode itself.

[0008] Suitable protective elements include porous Ni-based compacts, such as sintered nickel sheets.

[0009] In fact, nickel can be oxidized more easily than Ru in alkaline solutions, such as the catholyte used in C / A and AWE tanks. When porous nickel is electrically connected to an activated cathode, the potential of the porous nickel and the cathode can be kept at the same level. When the current flow is reversed, Ni is preferentially oxidized with respect to Ru, thus preserving the catalytic coating of the cathode and the operating parameters of the tank.

[0010] Therefore, the above solutions have proven to be effective in preserving the performance of the electrolyzer over time.

[0011] However, so far the above protective elements are made and handled one by one, which is a time-consuming, tedious and inefficient process when applied at an industrial level.

[0012] In addition, due to the fragility of the reverse current absorbers during operation or during internal handling before shipping and assembly, the reverse current absorbers can break, thus negatively affecting the performance of the tank or the overall cost of the system.

[0013] Therefore, it would be desirable to have an automated or semi-automated process for manufacturing, in batches, protective elements against reverse current in AWE and C / A applications. It would also be desirable that the batch requires a minimum of effort when it comes to installing individual elements within an electrochemical tank. The individual elements thus prepared should exhibit the protective properties expected of their hand-made counterparts and avoid any negative effects in case the reverse current protection material breaks during shipping or during operation. It would also be desirable to have an automatic or semi-automatic machine that implements the process. SUMMARY

[0014] In one aspect, the present invention relates to an article for an electrolysis tank and in particular for AWE and C / A tanks, the article comprising a nickel-based protective element (501) and an electrically conductive pocket, wherein the pocket substantially encloses all sides of the protective element.

[0015] For the purposes of the present invention, electrically conductive pocket means an electrically conductive container comprising a cavity and adapted to house the protective element inside the cavity. The electrically conductive pocket is adapted to protect the protective element from breaking during operation or outside of operation, such as during storage or shipping. The electrically conductive pocket is preferably adapted to ensure that the protective element functions properly even in case of breaking when inside the pocket. The electrically conductive pocket is preferably adapted to prevent the protective element from flying inside the tank in case of breaking.

[0016] Protective element means an element made of materials known in the art, in its final or intermediate stage of preparation, which are able to absorb reverse current during the de-energization and / or shutdown of the electrolyzer in C / A and AWE tanks. These protective elements are typically nickel-based, in their final or intermediate stage of preparation, i.e. they contain nickel metal or nickel in the form of an alloy.

[0017] It has been observed that a protective element that works particularly well when performing the present invention is a heat treated compact body (such as a sheet) comprising nickel. Preferably, the protective element exhibits a nickel content of 45% to 90% by mass and / or has a density of 2.00 g / cm 3 to 6.51 g / cm 3 .

[0018] These materials can be obtained by heat treating a raw material powder consisting of any one of Raney nickel alloy particles containing nickel and an alkali-soluble metal element, metal nickel particles, and a mixture of Raney nickel alloy particles and metal nickel particles. They can be made, for example, with a Ni-Al composition or a Ni-Al alloy. It is understood that the Al or the selected alkali-soluble metal element is removed by leaching, preferably before the protective element is installed in the cell, and during the operation of the element, in order to impart a porous structure to the Ni-based element.

[0019] Generally, one protective element is placed in one individual unit cell, typically corresponding to the cathode.

[0020] In a second aspect, the present invention thus also relates to an electrolyzer comprising one or more articles according to the present invention. Preferably, it is an electrolyzer for chlor-alkali or alkaline water electrolysis.

[0021] When placing the protective element in an electrochemical cell, it can be advantageous to keep the protective element in its pocket: the pocket can be more easily handled and connected to the cathode or other parts of the cell without compromising the function of the protective element. The protective element can be a brittle and porous compact body that is difficult to firmly attach and connect to other elements of the cell by itself.

[0022] The electrically conductive pocket should ensure electrical contact between the protective element and the electrolyte and / or between the protective element and the cathode, if the pocket containing the protective element is welded or connected thereto.

[0023] In a third aspect, the present invention relates to a batch comprising two or more articles according to the present invention, the batch comprising a plurality of protective elements made of a nickel-based material contained within an electrically conductive envelope made of a substance compatible with an alkaline environment and comprising a plurality of pockets, wherein at least two pockets each contain at least one protective element, and each of the at least two pockets encloses all sides of the at least one protective element.

[0024] The electrically conductive envelope is characterized by having a base surface and a lid that are joined together to form an outer casing having an outer periphery and provided with a plurality of pockets.

[0025] The pockets are formed by joining the base surface and the lid of the electrically conductive envelope along one or more paths (joining paths), thereby providing a plurality of containers adapted to contain and enclose one or more protective elements.

[0026] All sides of each bag are essentially closed, meaning that any gaps in the path that joins the bags together are small enough to prevent one or more integral protective elements contained in the bag from spontaneously leaving the bag without being actively cut or torn open as the bag moves around or shakes.

[0027] The joining of the base surface of the envelope and the cap to form its overall shape, as well as the joining path to form a bag within its outer cover, can be achieved by any technique suitable for forming a permanent or semi-permanent joint or coupling between the envelope surfaces. Non-limiting examples of suitable techniques are thermal welding, laser welding, brazing, resistance welding, micro-plasma welding, or mechanical joining (e.g., by folding or wrapping).

[0028] As can be understood below, the fact that multiple protective components constitute a set or batch allows for easier handling and transportation, and reduces their manufacturing time.

[0029] The bags containing the protective elements are designed to be removed from the envelope and separated from each other. Therefore, once ready to install the protective elements in individual slots, the bags can be cut off or otherwise separated from each other and installed individually in the slots. Because the bags surround all sides of the protective elements, if the protective elements break, parts of them remain contained within the bag's container, without compromising the element's protective function or resulting in any substantial loss of material, whether the breakage occurs during transport or within the slot.

[0030] In contrast to processing each component individually, forming a batch of articles including protective components allows certain manufacturing steps of the protective components to be performed in batches.

[0031] For example, a protective element obtained by leaching Al from the Ni-Al composition prior to the preparation of the batch can be used, but it is also possible to leach Al from the Ni-Al protective element later within the batch, thereby completing the preparation of these elements by leaching the entire batch at once. For this purpose, it is sufficient to select a porous structure for the envelope to allow the leaching agent to flow within the bag.

[0032] The use of a porous structure also allows for lighter materials and allows electrolytes to flow within each bag.

[0033] For manufacturing purposes, conductive sheaths or bags with an elongation of >20%, a yield strength of >80 MPa, and a tensile strength of >345 MPa are advantageous. These elastic properties ensure that the sheath can be folded, compressed, or bent, allowing its opposing surfaces to easily adhere to the protective element and / or to each other.

[0034] The electrically conductive envelope or pocket can advantageously be made of nickel, stainless steel or alloys thereof. These materials have been observed to exhibit desirable chemical, electrical and elastic properties and can also be made into meshes, nets or cloths having a porous structure.

[0035] In a preferred embodiment of the application, the electrically conductive envelope or pocket is a nickel fly screen (i.e. a mesh of nickel wires having a diameter > 0.14 mm), a nickel elastic pad, a nickel expanded mesh.

[0036] The electrically conductive envelope can have a substantially planar base surface which can optionally be provided with receptacles adapted to house the protective elements and form pockets.

[0037] In a preferred embodiment of the application, the pockets are substantially coplanar and uniformly distributed within a plane xy. The pockets will be placed at a first fixed distance from each other along a first direction x of this plane and at a second fixed distance from each other along a second direction y of this plane which is perpendicular to the direction x, wherein the first distance and the second distance are equal or different from each other.

[0038] In a fourth aspect, the application relates to a method for manufacturing a batch as described above. The method comprises the following steps:

[0039] (a) placing an upper cover over a plurality of protective elements made of a nickel-based material distributed over a base surface; the upper cover and the base surface being made of an electrically conductive structure;

[0040] (b) forming an electrically conductive envelope by joining the upper cover and the base surface together via joining means so as to form an enclosure containing the plurality of protective elements;

[0041] (c) providing the envelope with at least one joining path obtained via the joining means to form a plurality of pockets contained within the envelope, wherein at least two pockets of the plurality of pockets each comprise at least one protective element.

[0042] It is noted that steps (b) and (c) can be performed sequentially or simultaneously. Since the joining means for steps (b) and (c) can advantageously be selected to be the same, a joining pattern can be designed which simultaneously forms both the envelope and the pockets. The envelope can be formed from a collection comprising the plurality of pockets. Steps (a) to (c) can be performed manually.

[0043] It is understood that step (a) can be preceded by a step (a0) in which a plurality of protective elements made of a nickel-based material are distributed over a base surface which is an electrically conductive structure, manually or using automated means.

[0044] The method according to the present application allows to reduce the labor required for the preparation of a plurality of protective elements, since it conveys these elements in batches, thereby significantly reducing their production time.

[0045] The envelope can be manufactured either by using separate sheets for the base surface and the upper lid, or by using a single manufacturing sheet that is folded upon itself having an overall area A m p <½A m and thus leaving an empty area A e on the manufacturing surface, where A e >A p . Step (a) can then be performed by folding the empty area A e that becomes the upper lid of the envelope onto A p .

[0046] When the protective elements are made of a Ni-Al alloy, the method according to the present application can comprise an additional step (d) that consists in leaching Al from the Ni-Al protective elements, thereby obtaining a plurality of porous nickel-based protective elements. This step can be performed via chemical removal of Al from the batch by impregnating the Al in an alkaline medium to dissolve it. The batch can be impregnated at a temperature comprised between 15°C and 100°C for a time comprised between 1 hour and 48 hours.

[0047] In another aspect, the present application relates to the semi-automatic preparation of a batch of nickel-based protective elements, wherein the machine automatically implements the above mentioned process steps (a) to (c) or (a) to (d). In this instance, the protective elements can be manually placed on the base structure.

[0048] In case step (a0) is also completed using automated means, the present application relates to the automatic preparation of a batch of nickel-based protective elements, wherein the machine automatically implements the process steps (a0) to (c) or (a0) to (d).

[0049] The automatic or semi-automatic machine for the preparation of a batch of protective elements presents considerable time and cost efficiency improvements in the manufacturing of these workpieces, thus offering an attractive alternative to the current state-of-the-art manual one-piece technology.

[0050] ​Several embodiments of the present application are described below with reference to the accompanying drawings, which are intended to illustrate various elements related to the described embodiments of the present application. The drawings are not necessarily to scale. The same reference numbers are used throughout the drawings to indicate the same elements / functions. The coordinate axes x, y, z are always used in the same way in all the drawings. The xy plane is substantially parallel to the main surfaces of the separator and to the other main functional elements of the cell (electrodes, frame, bipolar plate), while z is perpendicular to such a plane and identifies the main longitudinal axis of the electrolyser according to the present application. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 A schematic view of a batch (100) of articles comprising protective elements according to an embodiment of the present application is provided. DETAILED DESCRIPTION

[0052] In particular, Figure 1 a) of Figure 1 provides a top view of a batch (100) provided with 52 protective elements such as (501, 502). The envelope is delimited by the outer perimeter of the batch, the borders of which are joined together, and each protective element is contained within a pocket (not visible). Each pocket is obtained by laser welding the opposite surfaces of the envelope along the joining paths laid between each adjacent protective element. The direction and layout of some of these paths are marked as dotted lines hi, h2, h3 and vi, v2.

[0053] Figure 1 b) of Figure 1 provides a top view of a batch (100) provided with 52 protective elements such as (501, 502). The envelope is delimited by the outer perimeter of the batch, the borders of which are joined together, and each protective element is contained within a pocket (not visible). Each pocket is obtained by laser welding the opposite surfaces of the envelope along the joining paths laid between each adjacent protective element. The direction and layout of some of these paths are marked as dotted lines hi, h2, h3 and vi, v2. Figure 1Fig. 6 is a schematic exploded view of the part of the batch (100) indicated in a) in Fig. 5. At assembly, the upper cover part (300) will be placed over the base surface part (200) with the protection elements (501, 502, 503, 504) distributed over this base surface part. The upper cover and the base surface will be pressed against each other. In a preferred embodiment, they will be made to adhere with the protection elements (when present) and to each other anywhere else. The two opposite surfaces (200, 300) will be laser welded together along specific paths to form pockets, with each pocket enclosing one protection element. For example, the two opposite surfaces (200, 300) can be welded along their outer periphery and along joining paths extending in the hi and vi directions and in other parallel directions extending between the protection elements, so as to form adjacent rectangular shaped pockets each containing one protection element. It can be advantageous not to have pockets containing protection elements adjacent and abutting each other. To this end, additional joining paths can be formed between the surfaces (200) and (300) so as to ensure that no two pockets containing at least one protection element share a joining path. In this way, the protection elements can be recovered by cutting the pockets from the envelope between the joining paths, or along joining paths that do not belong to the periphery of the pockets containing protection elements. In this way, the integrity of the pocket cover is maintained (when the pocket contains a protection element) as the joining paths forming its periphery are not directly subjected to mechanical stresses that separate the pocket from the envelope. This integrity, when the cathode or other structural element is attached to the tank, allows the protection elements to be kept within their pockets, allowing easier and safer assembly and preventing the protection elements from flying inside the tank in case of breakage.

[0054] In the description and claims of the application, the words "comprise" and "contain" and variations such as "comprising" and "comprises" do not exclude the presence of other elements or

[0055] For the purposes of the present application, the term "comprising" or "containing" also includes the term "consisting of" or "consisting essentially of".

[0056] The discussion of documents, certificates, materials, devices, articles or the like is included in the text solely for the purpose of providing context for the present application. It is not to be understood that such material or portions thereof are construed as being prior art to the present application in the field of the application.

Claims

1. An article for use in an electrolytic cell, comprising a nickel-based protective element (501) and a conductive bag, said nickel-based protective element containing nickel in the form of nickel metal or a nickel alloy, wherein said conductive bag is a conductive container including a cavity and adapted to house said protective element within said cavity, and wherein, The bag essentially surrounds all sides of the protective element.

2. The article of claim 1, wherein, The protective element is made of Ni, Ni-Al or their alloys, Ni powder mixed with an alkali-soluble metal, or a Ni alloy containing an alkali-soluble metal.

3. The article of manufacture according to any one of the preceding claims, wherein, The protective element is a sintered dense body containing nickel, preferably with a nickel content of 45% to 90% by mass.

4. The article of manufacture according to any one of the preceding claims, wherein, The protective element is a sintered dense body containing nickel, preferably having a content of 2.00 g / cm³. 3 Up to 6.51 g / cm 3 The density.

5. The article of manufacture according to any one of the preceding claims, wherein, The conductive bag has an elongation percentage of >20%, a yield strength of >80 MPa, and a tensile strength of >345 MPa.

6. The article of manufacture according to any one of the preceding claims, wherein, The conductive bag is made of a porous material.

7. The article of manufacture according to any one of the preceding claims, wherein, The conductive bag is made of nickel, stainless steel, or an alloy thereof.

8. The article of claim 7, wherein, The conductive bag is a nickel fly net, woven net, nickel elastic pad, or nickel extended net.

9. An electrolyzer comprising an article of manufacture according to any one of the preceding claims.

10. A batch (100) comprising two or more articles according to any one of claims 1 to 8, wherein, The batch (100) includes a plurality of said nickel-based protective elements (501, 502, 503, 504) contained within a conductive envelope, the envelope comprising a plurality of said bags, wherein at least two bags each contain at least one protective element, and each of the at least two bags substantially surrounds all sides of said at least one protective element.

11. The batch according to the preceding claim, wherein, The bags are substantially coplanar and uniformly distributed in a plane xy, with the bags placed at a first fixed distance from each other along a first direction x of the plane and at a second fixed distance from each other along a second direction y of the plane perpendicular to the direction x.

12. A method for manufacturing a batch according to claim 10 or 11, comprising the following steps: (a) A top cover (300) is placed over a plurality of protective elements made of a nickel-based material distributed above a base surface (200); the top cover and the base surface are made of a conductive structure; (b) A conductive sheath is formed by joining the top cover and the base surface together via a joining device to form an outer cover containing the plurality of protective elements; (c) Provide the envelope with at least one engagement path obtained via an engagement device to form a plurality of bags contained within the envelope, wherein at least two of the plurality of bags each include at least one protective element.

13. The method according to claim 12, wherein, Steps (b) and (c) are performed simultaneously.

14. The method according to claim 12 or 13, wherein, Perform the following steps before step (a): (a0) Multiple protective elements made of nickel-based material are distributed on the base surface, the base surface being a conductive structure.

15. The method according to any one of claims 12 to 14, wherein: - The base surface and the top cover belong to an integral region A m The same manufacturing surface; - The plurality of protective elements are distributed within the periphery of the manufacturing surface, the periphery defining the base surface and defining region A. p <1 / 2 A m This leaves an empty region A. e >A p ; - By A m Empty region A in e Fold in A p The above will execute step (a).

16. The method according to any one of claims 12 to 15, wherein, The plurality of protective elements are made of Ni-Al or an alloy thereof, and include the following additional steps: (d) Immerse Al from Ni-Al elements to obtain multiple porous nickel-based protective elements.

17. The method according to any one of claims 12 to 16, wherein, The joining device is selected from the following technologies: thermal welding, laser welding, brazing, resistance welding, micro-plasma welding, mechanical joining, and any combination thereof.

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