EP4698698A1

EP4698698A1 - Process for the manufacturing of protective elements for chlor-alkali and alkaline water electrolysis cells

Info

Publication number: EP4698698A1
Application number: EP24737484.6A
Authority: EP
Inventors: Emanuele VIGO; Leonello Carrettin; Giorgio MAGGIO; Alessandro FIORUCCI
Original assignee: Industrie de Nora SpA
Current assignee: Industrie de Nora SpA
Priority date: 2023-07-07
Filing date: 2024-07-05
Publication date: 2026-02-25
Also published as: KR20260036438A; AU2024297549A1; CL2025004171A1; IL325386A; WO2025012153A1; IT202300014220A1; CN121399295A; TW202513889A

Abstract

The present invention relates to an article for electrolytic cells, especially Chlor-Alkali and Alkaline Water Electrolysis cells, comprising a nickel-based protective element and an electrically conductive pocket, wherein said pocket substantially encloses said protective element on all sides, a batch of two or more such articles and a process for the preparation of these batches.

Description

PROCESS FOR THE MANUFACTURING OF PROTECTIVE ELEMENTS FOR CHLORALKALI AND ALKALINE WATER ELECTROLYSIS CELLS

FIELD OF THE INVENTION

The present invention relates to the field of industrialized batch production of protective elements for chlor-alkali and alkaline water electrolysis cells.

BACKGROUND OF THE INVENTION

Industrial electrolysers typically comprise a plurality of adjacent cells, each individual cell hosting two opposite electrodes that may be catalytically coated to foster the desired electrochemical reaction. Depending on the application, the electrode coating compositions may comprise one or more noble metals such as Ru, Rh, Ir and/or Pt, in varying percentages. These materials are scarce and expensive; they strongly affect the cost of the electrodes and have an impact on procurement, but they often play a pivotal role in ensuring the economics and performance of electrolytic systems, especially in Chlor-Alkali (C/A) and Alkaline Water Electrolysis (AWE) applications. In these scenarios, ruthenium is often preferred for its lower cost and is typically substituted, in toto or in part, to the other more expensive noble metals in the catalytic coating compositions.

During nominal operating conditions, and with the exception of maintenance operations, C/A and AWE electrolysers operate with a certain current density, which is kept substantially constant during operation.

However, nonscheduled interruption events may occur, thus abruptly discontinuing the functioning of the cells and cutting off the current. These events may negatively affect the medium- and long-term performance of the cells, reducing their performance at the standard operative conditions and causing the premature breakdown of the coating.

SUBSTITUTE SHEET (RULE 26) Indeed, nonscheduled interruption events may cause an undesired phenomenon, which is known as current reversal. In this case, reverse currents generated during shut down events flow through the electrolyser in a direction opposite to the electrolytic current and may cause cathode degradation by elution of the catalyst material, especially ruthenium, and thus severely affect the electrolyser performance over time.

While several possible solutions have been developed to address this issue, a particularly successful approach has been described in EP3330409, EP3330410 and EP2615195.

In these inventions, a protective element, i.e. a body made of a material suitable to absorb reverse current, is placed within the cell, in electrical contact with the cathode itself.

Suitable protective elements include porous Ni-based compact bodies, such as sintered nickel tablets.

Indeed, nickel can be more easily oxidized compared to Ru in alkaline solutions like the catholytes used in C/A and AWE cells. 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 reverse current flows, Ni oxidizes preferentially with respect to Ru, thereby preserving the catalytic coating of the cathode and the operation parameters of the cell.

Therefore, the above solution has proven to be effective in preserving the electrolyser performance over time.

However, to this day, the above-described protective elements are handmade and handled one by one, which is a time consuming, cumbersome, and ineffective process when applied at industrial level.

Additionally, the reverse current absorption body may break because of its brittleness either under operation or during transport and in-house operations before assembly, thereby negatively impacting either the performance of the cell or the overall costs of the system. It is therefore desirable to have an automated or semi-automated process for batch manufacturing of protective elements against reverse currents in AWE and C/A applications. It is also desirable for said batches to require the least amount of work when it comes to the installation of the individual elements within an electrochemical cell. The individual elements thus prepared should exhibit the desired protective properties of the individually handmade counterpart and avoid any negative impact in case the current reversal protective material breaks in transit or during operation. It is also desirable to have an automatic or semiautomatic machine implementing said process.

DETAILED DESCRIPTION

Under one aspect, the present invention relates to an article for electrolytic cells, and particularly for AWE and C/A cells, comprising a nickel-based protective element (501 ) and an electrically conductive pocket, wherein said pocket substantially encloses said protective element on all sides.

For the purpose of the present invention, the 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 breakage during or outside the operation, such as during storage or transportation. The electrically conductive pocket is preferably adapted to ensure that the protective element functions while it is inside the pocket and even in the case of breakage. The electrically conductive pocket is preferably adapted to prevent the protective element from scattering within the cell in case of breakage.

By protective element it is meant an element, in its final or intermediate preparation stage, that is made of materials known in the art for their ability to absorb current reversal during electrolyser power outages and/or shutdowns in C/A and AWE cells. These protective elements, in both their final or intermediate preparation stage, are typically nickel-based, i.e. they contain nickel in the form of nickel metal or alloys.

Protective elements that have been observed to work particularly well in the execution of the invention are thermally treated compact bodies, such as tablets, containing nickel. Preferably the protective elements exhibit a nickel content of 45 - 90% by mass and/or have a density of 2.00 - 6.51 g/cm³

These materials can be obtained by thermally treating a raw material powder composed of any one of Raney nickel alloy particles containing nickel and an alkali-soluble metal element, metallic nickel particles, and a mixture of Raney nickel alloy particles and metallic nickel particles. They can be made for instance with a Ni-AI composition or a Ni- Al alloy. It is understood that Al, or the alkali-soluble metal element of choice, is preferably removed by leaching prior to installation of the protective element within the cell, as well as during the element operation, so as to impart a porous structure to the Ni-based element.

Typically, one protective element is placed within one individual elementary cell, often in correspondence with the cathode.

Under a second aspect, the present invention thus also relates to an electrolyzer comprising one or more article according to the present invention. Preferably an electrolyzer for chlor-alkali or alkaline water electrolysis.

It may be advantageous to keep the protective element within its pocket when placing it in the electrochemical cell: the pocket may be more easily handled and connected to the cathode or other parts of the cell without detriment to the functionality of the protective element. The latter may be a brittle and porous compact body difficult to attach and connect securely to other elements of a cell on its own.

The conductive pocket shall ensure electrical contact between the protective element and the electrolyte and/or the protective element and the cathode if the pocket containing the protective element is welded or connected thereto. Under a third aspect, the present invention relates to a batch of two or more articles according to the present invention comprising a plurality of protective elements made of a nickel-based material contained within an electrically conductive envelope, said envelope being made of a substance compatible with an alkaline environment and comprising a plurality of pockets, wherein at least 2 pockets contain at least one protective element each, and each of said at least 2 pockets encloses said at least one protective element on all sides.

The conductive envelope is characterized by having a base surface and a cover that are joined together to form an enclosure having an outer perimeter and provided with a plurality of pockets.

The pockets are created by joining together the base surface and the cover of the conductive envelope along one or more paths (joining paths), thereby providing a plurality of receptacles suitable to host and enclose one or more protective elements.

Each pocket is substantially closed on all sides, by which it is meant that any gaps in the path joining the pocket together are small enough to prevent one or more integer protective elements contained therein to spontaneously exit the pocket when the latter is moved around or shaken, without actively cutting or ripping it.

The joining of the envelope base surface and cover to form its overall shape, as well as the joining paths forming pockets within its enclosure, may be obtained by any technique suitable to create a permanent or semipermanent joint or coupling between the envelope surfaces. Non limiting examples of suitable techniques are thermal welding, laser welding, soldering, resistance welding, micro-plasma welding, or mechanical joining (for example by folding or wrapping)

The fact that the plurality of protective elements constitutes an ensemble, or batch, allows for easier handling and shipping, and reduces their manufacturing time, as may be appreciated in the following. The pockets containing the protective elements are suitable to be detached from the envelope and to be separated from one another. Therefore, once the protective elements are ready to be installed in the individual cells, the pockets may be cut or otherwise detached from one another and individually installed within a cell. Since the pocket encloses the protective element on all sides, if the latter breaks its parts remain confined within the pocket’s receptacle, without detriment to the protective function of the element and without substantial loss of material, regardless of whether the breakage occurs during in transport or within the cell.

The batch of articles comprising protective elements allows to perform certain manufacturing steps of the protective elements in batches, as opposed to processing each element individually.

For instance, it is possible to employ protective elements which have been obtained by leaching Al from a Ni-AI composition before preparing the batch, but it is also possible to leach Al from Ni-AI protective elements after they are within the batch, thereby finalizing the preparation of these elements by leaching the entire batch at once. It is sufficient for this purpose that the envelope is chosen as a foraminous structure, to allow the flow of leaching agents within the pockets.

The use of a foraminous structure also allows for a more lightweight material and allows the flow of the electrolyte within each pocket.

It is advantageous, for manufacturing purposes, that the electrically conductive envelope or the pocket has a percent elongation > 20%, a yield strength > 80 MPa and a tensile strength > 345 MPa. These elastic properties ensure that the envelope can be folded, pressed, or bent so that it can its opposite surfaces can be easily made to adhere to the protective element and/or with each other.

The electrically conductive envelope or the pocket may be advantageously made of nickel, stainless steel, or alloys thereof. These materials have been observed to exhibit the desired chemical, electrical and elastic properties, and may be also manufactured in meshes, nets or cloths with a foram inous structure.

Under a preferred embodiment of the present invention, the electrically conductive envelope or the pocket is a nickel flynet (i.e. a net of nickel wires having a diameter >0.14 mm), nickel elastic mattress, nickel expanded meshes.

The electrically conductive envelope may have a substantially planar base surface which may be optionally provided with receptacles suited to host the protective elements and form the pockets.

Under a preferred embodiment of the present invention, the pockets are substantially coplanar and evenly distributed within a plane xy. The pockets will be placed at a first fixed distance between each other along a first direction x of the plane, and at a second fixed distance between each other along a second direction y of the plane perpendicular to direction x, with the first and second distance equal or different from each other.

Under a fourth aspect, the present invention relates to a process for manufacturing the batch hereinbefore described. The process comprises the following steps:

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

(b) forming an electrically conductive envelope by joining said upper cover and said base surface together via joining means, so as to create an enclosure containing said plurality of protective elements;

(c) providing said envelope with at least one joining path obtained via joining means to form a plurality of pockets contained within said envelope, with at least two pockets of said plurality of pockets comprising at least one protective element each.

It is noted that step (b) and (c) can be performed in sequence or simultaneously. Because the joining means used for step (b) and (c) may be advantageously chosen as the same, its is possible to devise a joining pattern that creates both the envelope and the pockets at the same time. The envelope may form from the ensemble comprising the plurality of pockets. Steps (a)-(c) may be performed by hand.

It is understood that step (a) may be preceded by a step (ao), in which a plurality of protective elements made of a nickel-based material is distributed, by hand or using automated means, on a base surface which is an electrically conductive structure.

The process according to the present invention allows to reduce the effort required in the preparation of a plurality of protective elements, because of it delivers these elements in batches, thereby cutting down significantly their production time.

The envelope may be manufactured either by using separate sheets for the base surface and the upper cover, or by using one manufacturing sheet having an overall area A_m folded on itself. In this latter case the process according to the invention may be performed by distributing the plurality of protective elements on the manufacturing surface within a perimeter that defines the base surface and delimits an area A_p < A_m, and thus leaving an empty area A_e on the manufacturing surface, with A_e > A_p. Step (a) may then be carried out by folding the empty area A_e, which becomes the upper cover of the envelope, over A_p.

When the protective elements are made of Ni-AI alloys, the process according to the present invention may comprise an additional step (d), which consists of leaching Al from the Ni-AI protective elements thereby obtaining a plurality of porous nickel based protective elements. This step may be performed via the chemical removal of Al from the batch by dissolution in an alkali media by immersion. The batch may be immersed for time 1 to 48 hours at a temperature of 15°C to 100°C.

Under another aspect, the present invention relates to a semi-automatic preparation of batches of nickel-based protective elements wherein said machine automatically implements the process steps (a)-(c) or (a) to (d) described above. In this instance, the protective elements can be placed manually on the base structure.

In case also step (ao) is done using automated means, the present invention relates to an automatic preparation of batches of nickel-based protective elements wherein said machine automatically implements the process steps (ao)-(c) or (ao) to (d) .

The automatic or semiautomatic machine for the preparation of batches of protective elements represents a considerable time and cost-effective improvement in the manufacturing of these pieces and therefore offer an appealing alternative to current state of the art manual, one-piece techniques.

A few embodiments of the invention are described by way of example below with reference to the appended drawings, the purpose of which is solely to illustrate the mutual arrangement of the various elements relating to said embodiments of the invention. The drawings are not to scale. Identical numbers are used to indicate features having the same purpose/effect. The coordinate axis x, y, z, are used in the same fashion throughout all figures. The xy plane is substantially parallel to the major surface of the separators and the other main functional elements of the cell (electrodes, frames, bipolar plates), whereas z is perpendicular to such plane and identifies the main longitudinal axis of the electrolyser according to the invention.

DESCRIPTION OF THE DRAWINGS

Fig. 1 provides a schematic view of a batch (100) of articles comprising protective elements according to an embodiment of the present invention.

Specifically, Fig. 1.a) provides a top view of the batch (100) provided with 52 protective elements such as (501 , 502). The envelope is delimited by the outer perimeter of the batch, with its border joined together, and each protective element is contained within one pocket (not visible). Each pocket is obtained by laser welding the opposite surfaces of the envelope along joining paths placed between every adjacent protective element. The direction and placement of a few of these paths have been marked as dash-dotted lines hi , h2, h3 and v1 , v2.

Fig.1 . b) provides a schematic exploded view of the section of the batch (100) indicated in Fig. 1 .a). On assembly, the upper cover section (300) is to be placed over the base surface section (200), where the protective elements (501 , 502, 503, 504) are distributed. 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 protective element, where present, and with each other everywhere else. The two opposite surfaces (200, 300) will be laser welded together along specific paths to create pockets, with each pocket enclosing one protective element. For instance, the two opposite surfaces (200, 300) may be welded along their outer perimeter and along joining paths running in the direction of hi and v1 , and the other parallel directions running between the protective elements, in order to create adjacent rectangular shaped pockets containing one protective element each. It may be advantageous not to have the pockets containing the protective elements to be adjacent and contiguous to each other. To this effect, additional joining paths between surfaces (200) and (300) may be formed in order to ensure that no two pockets containing at least one protective element share a joining path. In this way, the protective elements may be recovered by cutting the pockets from the envelope between joining paths, or along a joining path that does not belong to the perimeter of a pocket containing a protective element. In this way, the integrity of the pocket enclosure (when the pocket contains a protective element) is maintained, since the joining path forming its perimeter is not directly subject to mechanical stress to separate the pocket from the envelope. This integrity allows to keep the protective element within its pocket when attached to the cathode or other structural elements of the cell, which allows for an easier and more secure assembly and keeps the protective element from scattering within the cell in case of breakage.

In the description and the claims in this application the words "comprise" and its variations such as "comprising" and "comprises" do not rule out the presence of other additional elements, components, or stages.

For the purposes of the present invention the term "to comprise" or "to include" also comprises the term "to consist in" or "essentially consisting of".

The discussion of documents, deeds, materials, apparatus, articles and the like is included in the text solely for the purpose of providing context for this invention; it should not however be understood that this material or part thereof constitutes general knowledge in the field relating to the invention prior to the priority date of each of the claims appended to this application.

Claims

1 . An article for electrolytic cells comprising a nickel-based protective element (501 ) and an electrically conductive pocket, wherein said pocket substantially encloses said protective element on all sides.

2. The article according to claim 1 , wherein said protective element is made of Ni, Ni- Al or alloys thereof, Ni powders mixed with an alkali-soluble metal, or Ni alloys with an alkali soluble metal.

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

4. The article according to any one of the preceding claims, wherein said protective element is a sintered compact body containing nickel, preferably with a density of 2.00 - 6.51 g/cm³

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

6. The article according to any one of the preceding claims, wherein the electrically conductive pocket is made of a foraminous material.

7. The article according to any one of the preceding claims, wherein the electrically conductive pocket is made of nickel, stainless steel, or alloys thereof.

8. The article according to claim 7 wherein the electrically conductive pocket is a nickel flynet, a woven mesh, a nickel elastic mattress, or a nickel expanded mesh.

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

10. A batch (100) of two or more articles according to any one of the preceding claims

1 to 8, wherein the batch (100) comprises a plurality of said nickel-based protective elements (501 , 502, 503, 504) contained within an electrically conductive envelope, said envelope comprising a plurality of said pockets, wherein at least 2 pockets contain at least one protective element each, and each of said at least 2 pockets substantially encloses said at least one protective element on all sides.

11 . The batch according to the preceding claim, wherein said pockets are substantially coplanar and evenly distributed within a plane xy, said pockets being placed at a first fixed distance between each other along a first direction x of the plane, and at a second fixed distance between each other along a second direction y of the plane perpendicular to direction x.

12. A process for manufacturing the batch according to claim 10 or 11 comprising the following steps:

(a) placing an upper cover (300) over a plurality of protective elements made of a nickel-based material distributed over a base surface (200); said upper cover and said base surface being made of an electrically conductive structure;

13. The process according to claim 12 wherein step (b) and (c) are performed simultaneously.

14. The process according to claim 12 or 13 wherein step (a) is preceded by the following step:

(ao) distributing a plurality of protective elements made of a nickel-based material on a base surface, said base surface being an electrically conductive structure.

15. The process according to any one of claims 12-14 where:

- the base surface and the upper cover belong to one same manufacturing surface having an overall area A_m;

- the plurality of protective elements is distributed on the manufacturing surface within a perimeter that defines the base surface and delimits an area A_p < A_m, thus leaving an empty area A_e > A_p;

- step (a) is carried out by folding the empty area A_e of A_m over A_p.

16. The process according to any one of claims 12-15 wherein the plurality of protective elements is made of Ni-AI or alloys thereof and comprises the following additional step:

(d) Leaching Al from the Ni-AI elements thereby obtaining a plurality of porous nickel based protective elements.

17. The process according any one of claims 12-16 wherein the joining means are chosen among the following techniques: thermal welding, laser welding, soldering, resistance welding, micro-plasma welding, mechanical joining, and any combination thereof.