WO2025119706A1

WO2025119706A1 - Electrolysis assembly

Info

Publication number: WO2025119706A1
Application number: PCT/EP2024/083632
Authority: WO
Inventors: Markus NESSELBERGER; Jean-Philippe Tadiello
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2023-12-08
Filing date: 2024-11-26
Publication date: 2025-06-12
Anticipated expiration: 2026-06-08
Also published as: EP4567156A1

Abstract

An electrolysis assembly for operation with an alkaline electrolysis medium. A first region of the assembly comprises an electrolysis cell stack and is adapted for producing product gases in the respective anode and cathode regions of the assembly from the alkaline electrolysis medium. A second region of the assembly comprises components for discharging electrolysis medium enriched with product gas from the first region, for introducing electrolysis medium depleted in product gas into the first region and for separating the produced product gases from the electrolyte medium. Said components have an inside region for direct contact with the alkaline electrolysis medium, wherein the inside region is at least partially formed from a nickel layer and wherein the nickel layer has a layer thickness of at least 0.1 mm and a nickel content of at least 98% by weight.

Description

ELECTROLYSIS ASSEMBLY

Description

The invention relates to an electrolysis assembly for operation with an alkaline electrolysis medium.

The electrolytic cleavage of water to produce hydrogen is increasingly gaining in importance in the present era of anthropogenic climate change. For the production of electrolytical ly produced hydrogen on a large industrial scale two processes in particular are of exceptional importance, namely proton exchange membrane (PEM) electrolysis and alkaline electrolysis.

In alkaline electrolysis the following half-cell reactions occur on the cathode side and the anode side.

Cathode side: 2 H2O + 2e^_ -> H2 + 2 OH’

Anode side:

The net result is that one mole of water forms half a mole of molecular oxygen and one mole of molecular hydrogen. In order that the reactions can occur in the electrolysis half-cells, hydroxide ions must diffuse from one half-cell into the other through a separator which separates the cathode side and the anode side of the electrolysis cell from one another. Especially in alkaline electrolysis such a separator is referred to as a diaphragm. The diaphragm has the function that the hydroxide ions functioning as charge carriers can diffuse between the half-cell sides and the product gases produced on the cathode and anode side can be mechanically separated from one another.

An electrolysis cell has two electrodes (cathode and anode) which are surrounded by a liquid alkaline electrolysis medium. The electrolysis medium employed is typically concentrated aqueous potassium hydroxide solution or sodium hydroxide solution. An electrolyser on a large industrial scale comprises a multiplicity of electrolysis cells, wherein the individual cells are arranged one above the other in a stack and are combined in a frame or other suitable mechanical apparatus. This design is commonly referred to as an electrolysis stack. In order to increase the efficiency of the cells, electrolysis systems operating with an alkaline electrolysis system are operated at elevated temperature to increase the conductivity of the employed electrolyte and to improve the reaction rate.

The electrolysis system may be fundamentally divided into two regions.

The electrolysis system firstly comprises the electrolysis stack as such. The electrolysis medium and the electric direct current are introduced into the electrolysis stack to produce hydrogen in the cathode spaces and oxygen in the anode spaces of the electrolysis stack. The biphasic mixture of electrolysis medium and product gas (hydrogen or oxygen) is discharged from the electrolysis stack. In addition to the electrodes and the diaphragms the electrolysis stack comprises components such as bipolar plates, cell frames, distributors for liquids and gases, seals and pressure-bearing parts.

The second region comprises the components of the electrolysis system that are primarily fluidically connected or electrically connected to the electrolysis stack. These comprise the circuits for the electrolysis medium enriched with product gases or (largely) product gas-free electrolysis medium, gas-liquid separators, heat exchangers for temperature management of the electrolysis medium, the electrolysis media management system comprising pumps, filters, valves and pipe conduits, the control system comprising sensors (flowmeters, temperature sensors, pressure sensors) and actuators (control valves). Transformers and rectifiers are often also attributed to this region. This second region of the electrolysis system is often referred to as the "balance of stack' region or BOS region for short.

Operation of an electrolysis system requires additional system components that connect the electrolysis system to the particular industrial site or independent process units. These include electrical components such as switchgear and harmonic filters, components for oxygen and hydrogen treatment (purification, conditioning (dehumidifier, autocatalytic recombiner)), cooling units for temperature control (media cooler and heater, coolers for the rectifiers, gas coolers for product gases), a demineralization unit for the water supply and a nitrogen and instrument air supply. These components of the plant are often referred to as "balance of plant' components or BOP components for short. The electrolysis medium used in alkaline electrolysis is typically an aqueous potassium hydroxide (KOH) solution having a concentration of 20% to 30% by weight. The electrolysis medium typically circulates in the electrolysis stack and in the BOS components of the electrolysis system at a temperature of 60°C to 90°C. Alkaline elec- trolysers may be operated at atmospheric pressure and at positive pressure. The latter operating mode is also known as pressure electrolysis. For maintenance of the pressure in such electrolysis systems the BOS components are typically manufactured from metal. The BOS systems that come into contact with the alkaline electrolysis system such as gas-liquid separators, electrolysis media pumps, heat exchangers for temperature control of the electrolysis medium and filters and pipes for circulation of the electrolysis medium are generally produced from steel-based materials (carbon steel and stainless steels). Examples may be found in EP 4001464 A1 and DE 4014778 A1.

In the alkaline electrolysis of an aqueous electrolysis medium the latter typically comes into contact with materials such as steel, in particular carbon steel or stainless steel. The elements present in these steels such as iron, chromium, molybdenum and manganese are leached out by the alkaline electrolysis medium, thus resulting in accumulation of a certain concentration of the ions of these elements in the electrolysis medium.

The aforementioned cations can thus accumulate on the surfaces of the cathodes and anodes of the electrolysis stack and thus lead to accelerated ageing of the catalyst. This especially reduces the electrochemically active surface area of the catalyst. This leads to a continuous degradation of the cell activity and thus of the electrolysis stack once a critically large area is covered with cations. This results in a continuous increase in the consumption of electrical energy at an unchanged amount of product gases formed. This reduction in service life has the result that affected cells correspondingly require earlier replacement. Since the replacement of individual cells of the electrolysis stack is costly and inconvenient, electrodes and electrolysis cells having the longest possible service life are desirable.

Another undesirable process in the deposition of the aforementioned cations is dendrite formation. Dendrite formation is undesirable because it can cause shorts within the cell when the dendrite growth results in a connection of an anode with a cathode. If this phenomenon occurs the affected cell must be replaced immediately. The aforementioned problems are particularly relevant in alkaline electrolysis since the leaching rate increases with increasing temperature and thus the contamination rate of the electrodes also increases with the operating temperature of the electrolysis medium.

Ageing of the electrodes proceeds more quickly when electrodes having a low active surface area are used.

The electrodes of the electrolysis cells have two important characteristic values, geometric surface area and active surface area. In the case of a round electrode the geometric surface area is defined in terms of its diameter. The active surface area defines how much catalytically active surface area of the catalyst is available per unit area (e.g. m² or cm²) of geometric surface area. The active surface area can be many times larger than the geometric surface area, depending on the manner of production of the electrode. At a constant impurity concentration in the electrolysis medium and a constant deposition rate of the ions per unit active electrode surface area, an electrode of smaller active surface area would lose performance faster than an electrode of larger active surface area.

It is an object of the present invention to at least partially overcome the aforementioned disadvantages of the prior art.

It is especially an object of the present invention to avoid or at least limit the accumulation of cations in the electrolyte and thus to avoid or at least limit the ageing of the electrodes in the electrolysis stack due to metal cations. Ageing due to metal cations such as iron, chromium, manganese and molybdenum cations is preferably to be avoided, irrespective of their oxidation state.

The independent claims make a contribution to the at least partial achievement of at least one of the above objects. The dependent claims provide preferred embodiments which contribute to at least partial achievement of at least one of the objects. Preferred embodiments of constituents of one category according to the invention are, where relevant, likewise preferred for identically named or corresponding constituents of a respective other category according to the invention. The terms “having”, “comprising” or “containing” etc. do not preclude the possible presence of further elements, ingredients etc. The indefinite article “a” does not preclude the possible presence of a plurality.

One aspect of the invention proposes an electrolysis assembly for operation with an alkaline electrolysis medium comprising a first region and a second region, wherein

- the first region comprises an electrolysis stack comprising a multiplicity of electrolysis cells, wherein the electrolysis stack is adapted for producing a first product gas in an anode region and for producing a second product gas in a cathode region from the alkaline electrolysis medium;

- the second region is fluidically connected to the first region and the second region comprises a plurality of components, wherein the components of the second region are adapted for discharging electrolysis medium enriched with product gas from the first region, for introducing electrolysis medium depleted in product gas into the first region and for separating the produced product gases from the electrolysis medium, and wherein the components of the second region comprise at least one pipe conduit system and an anode-side and a cathode-side gas-liquid separator, characterized in that the components of the second region have an inside region which is adapted for direct contact with the alkaline electrolysis medium, wherein the inside region is at least partially formed from a nickel layer and wherein the nickel layer has a layer thickness of at least 0.1 mm and a nickel content of at least 98% by weight.

According to the invention the inside region of the second region is at least partially formed from a nickel layer having a layer thickness of at least 0.1 mm and a high nickel content of at least 98% by weight.

It has been found that thinner nickel layers do not achieve the desired technical effect. That is to say, despite the known increase in corrosion resistance brought about by a nickel layer, continuous poisoning of the catalysts of the electrodes by the aforementioned cations is observed. This is attributable to the fact that thinner layers have a higher risk of defects such as pores, holes, cracks, stratifications or inclusions. Such relatively thin layers often have layer thicknesses of less than 50 pm. Such layers are typically obtained by processes such as electroless nickel plating or electroplating.

It was simultaneously found that the nickel layer according to the invention must have a high nickel content of at least 98% by weight. This ensures that the content of nonnickel metals is sufficiently low that any cations of the aforementioned type that are leached out of the nickel layer do not significantly adversely affect the service life of the electrodes and thus of the cells.

Examples of suitable materials for the nickel layer are materials having the identification number EN 2.4066 (UNS N02200) and EN 2.4068 (UNS N02201 ).

Suitable processes for producing the nickel layer include

- lining,

- plating processes such as roller plating, explosive plating and weld plating,

- providing as a solid material with optional subsequent form-fitting, force-fitting or atomic level joining,

- casting,

- subtractive machining of solid material and

- cladding.

The inside region is at least partially formed from the nickel layer. The inside region is the region of the respective component of the second region of the electrolysis assembly which is adapted for direct contact with the alkaline electrolysis medium. That is to say the inside region is in direct contact with the alkaline electrolysis medium during operation of the electrolysis assembly. The inside region may be for example the inside of a pipe conduit, the electrolysis media-contacting surfaces of a recirculation pump or of a valve or the interior surface of a gas-liquid separator. This list is not to be understood as exhaustive.

The inside region defines especially an area which is in direct contact with the alkaline electrolysis medium and which is at least partially formed from the nickel layer. The nickel layer has a nickel content of at least 98% by weight. It is preferable when the nickel layer has a nickel content of at least 98.0% by weight or of at least 98.5% by weight or of at least 99.0% by weight or of at least 99.5% by weight or at least 99.6% by weight or at least 99.7% by weight or at least 99.8% by weight or at least 99.9% by weight or at least 99.95% by weight or at least 99.99% by weight.

It is preferable when the nickel layer has a content of iron of less than 2% by weight or of less than 2.0% by weight or less than 1.0% by weight or less than 0.5% by weight or less than 0.3% by weight or less than 0.2% by weight or less than 0.1 % by weight or less than 500 ppm or less than 100 ppm or less than 50 ppm or less than 25 ppm or less than 10 ppm or less than 5 ppm or less than 1 ppm.

It is preferable when the nickel layer has a content of chromium of less than 2% by weight or of less than 2.0% by weight or less than 1 .0% by weight or less than 0.5% by weight or less than 0.3% by weight or less than 0.2% by weight or less than 0.1 % by weight or less than 500 ppm or less than 100 ppm or less than 50 ppm or less than 25 ppm or less than 10 ppm or less than 5 ppm or less than 1 ppm.

It is preferable when the nickel layer has a content of molybdenum of less than 2% by weight or of less than 2.0% by weight or less than 1.0% by weight or less than 0.5% by weight or less than 0.3% by weight or less than 0.2% by weight or less than 0.1 % by weight or less than 500 ppm or less than 100 ppm or less than 50 ppm or less than 25 ppm or less than 10 ppm or less than 5 ppm or less than 1 ppm.

It is preferable when the nickel layer has a content of manganese of less than 2% by weight or of less than 2.0% by weight or less than 1 .0% by weight or less than 0.5% by weight or less than 0.3% by weight or less than 0.2% by weight or less than 0.1 % by weight or less than 500 ppm or less than 100 ppm or less than 50 ppm or less than 25 ppm or less than 10 ppm or less than 5 ppm or less than 1 ppm.

The first region of the electrolysis assembly comprises an electrolysis stack comprising a multiplicity of electrolysis cells. Electrolysis stacks are well known to those skilled in the art. They are composed of a multiplicity of electrolysis cells arranged in a stack which are secured by a mechanical apparatus.

The electrolysis stack comprises an anode region and a cathode region. The anode region is to be understood as meaning the entirety of the anode spaces of the cells of the electrolysis stack. The cathode region is to be understood as meaning the entirety of the cathode spaces of the cells of the electrolysis stack. The anode region preferably produces oxygen as the product gas. The cathode region preferably produces hydrogen as the product gas.

The second region is fluidically connected to the first region. The fluidic connection between the first and the second region allows circulation of electrolysis medium enriched with product gas and electrolysis medium depleted in product gas between the first region and the second region. Electrolysis medium enriched with product gas is especially to be understood as meaning a biphasic mixture of electrolysis medium and product gas which is produced in the anode region or cathode region of the electrolysis stack. The electrolysis assembly is configured such that this biphasic mixture may be discharged from the first region and introduced into the second region. The electrolysis assembly is further configured such that electrolysis medium depleted in product gas may be discharged from the second region and introduced into the first region. The electrolysis medium depleted in product gas is especially to be understood as meaning an electrolysis medium from which the respective product gas has been separated by gas-liquid separation. It is preferable when the electrolysis medium depleted in product gas comprises only one liquid phase. The electrolysis medium depleted in product gas may nevertheless contain a certain residual amount of dissolved or undissolved product gas.

To fulfil the aforementioned functions the second region comprises a plurality of components. At least the second region comprises the components of a pipe conduit system and an anode-side and a cathode-side gas-liquid separator. The gas-liquid separators are adapted for separating the product gases produced in the first region from the alkaline electrolysis medium. It is preferable when the second region comprises further components, in particular at least one pump, at least one cooler for cooling the electrolysis medium, at least one control valve and at least one sensor. Sensors are especially flowmeters, temperature sensors and pressure sensors. In the context of the invention, transformers and rectifiers are not attributable to the second region since these electronic components are not adapted for contact with the electrolysis medium. The aforementioned components are connected to the electrolysis stack not fluidically via the electrolysis medium but rather electrically.

The electrolysis assembly is preferably configured such that it can be operated at positive pressure. In this context, the term "positive pressure" is to be understood as meaning a pressure above atmospheric pressure. The electrolysis assembly is especially adapted for operation at an absolute pressure of 5 to 40 bar, preferably for an absolute pressure of 15 to 35 bar.

The electrolysis assembly is preferably also configured such that it may be operated at a temperature above room temperature. The electrolysis assembly is especially adapted for operation at a temperature of 40°C to 150°C, preferably for operation at a temperature of 70°C to 120°C, more preferably for operation at a temperature of 70°C to 100°C. The aforementioned maximum temperatures are especially temperatures of the electrolysis medium at an outlet of the electrolysis stack.

In a further aspect of the invention the electrolysis assembly is characterized in that the inside region is partially formed from the nickel layer and partially formed from a metal alloy layer, wherein the metal alloy of the metal alloy layer has an iron content of 10% by weight or less.

In this embodiment a subarea of the inside region is formed from the nickel layer and a subarea of the inside region is formed from a metal alloy layer. The metal alloy of this metal alloy layer has an iron content of 10% by weight or less.

The metal alloy layer preferably has a layer thickness of at least 0.1 mm. It is particularly preferable when the metal alloy layer has the same layer thickness as the nickel layer.

Certain sections of the inside region optionally may not be provided with a nickel layer. A metal alloy having an iron content of 10% by weight or less is preferably employed for these regions. Examples of suitable materials are the materials having the identification numbers UNS N04400, UNS N05500, UNS N06600, UNS N06601 , UNS N06625, and UNS N06022.

It is preferable when the metal alloy layer comprises at least one element from the group of metals

- nickel,

- copper,

- chromium, molybdenum. The metal alloy layer thus preferably comprises a metal alloy comprising or composed of the aforementioned metals and having an iron content of 10% by weight or less.

Suitable processes for producing the metal alloy layer include

- lining,

- plating processes such as roller plating, explosive plating and weld plating,

- casting,

- subtractive machining of solid material and

- cladding.

It is preferable when the metal alloy of the metal alloy layer has an iron content of 10.0% by weight or less or of 8.0% by weight or less or of 6.0% by weight or less or of 5.0% by weight or less or of 4.0% by weight or less or of 3.0% by weight or less or of 2.0% by weight or less or of 1 .0% by weight or less or of 0.5% by weight or less or of 0.25% by weight or less or of 0.10% by weight or less or of 500 ppm or less or of 250 ppm or less or of 100 ppm or less or of 50 ppm or less or of 10 ppm or less.

In a further aspect of the invention the electrolysis assembly is characterized in that the inside region is formed to an extent of at least 50% of its total surface area from the nickel layer.

It is more preferable when the inside region is formed to an extent of at least 60% of its total surface area from the nickel layer or to an extent of at least 70% of its total surface area from the nickel layer or to an extent of at least 80% of its total surface area from the nickel layer or to an extent of at least 90% of its total surface area from the nickel layer.

In a further aspect of the invention the electrolysis assembly is characterized in that the inside region is formed to an extent of at least 50% of its total surface area from the nickel layer and the remaining surface area of the inside region is formed from the metal alloy layer having an iron content of less than 10.0% by weight. It is preferable when the inside region is formed to an extent of at least 60% of its total surface area from the nickel layer or to an extent of at least 70% of its total surface area from the nickel layer or to an extent of at least 80% of its total surface area from the nickel layer or to an extent of at least 90% of its total surface area from the nickel layer and the respective remaining surface area of the inside region is formed from the metal alloy layer having an iron content of less than 10.0% by weight.

In a further aspect of the invention the electrolysis assembly is characterized in that the nickel layer has a layer thickness of at least 0.2 mm, preferably a layer thickness of at least 0.3 mm.

It is further also preferable when the nickel layer has a layer thickness of at least 0.4 mm or of at least 0.5 mm or of at least 0.7 mm or of at least 0.9 mm or of at least 1 .0 cm or of at least 1 .5 cm or of at least 2.0 cm.

In a further aspect of the invention the electrolysis assembly is characterized in that the metal alloy layer has a layer thickness of at least 0.2 mm, preferably a layer thickness of at least 0.3 mm.

It is further also preferable when the metal alloy layer has a layer thickness of at least 0.4 mm or of at least 0.5 mm or of at least 0.7 mm or of at least 0.9 mm or of at least 1 .0 cm or of at least 1 .5 cm or of at least 2.0 cm.

In a further aspect of the invention the electrolysis assembly is characterized in that the nickel layer covers a metallic base layer, wherein the metallic base layer is not adapted for direct contact with the alkaline electrolysis medium.

The nickel layer covers the metallic base layer, i.e. in operation of the electrolysis assembly the nickel layer contacts the alkaline electrolysis medium in the corresponding regions. The metallic base layer is joined to the nickel layer at least by a form-fitting, force-fitting or atomic-level join. The metallic base layer is configured such that it does not contact the alkaline electrolysis medium in operation of the electrolysis assembly.

Having regard to the metallic base layer it is preferable when this is formed from a carbon steel and/or a stainless steel.

Examples of suitable materials are the steels having the material identification number 1.0345, 1.0425, 1.0481 , 1.0473, 1.0487, 1.0488, 1.4404, 1.4462, 1.5415, or 1.0565. In a further aspect of the invention the electrolysis assembly is characterized in that the metal alloy layer having an iron content of 10.0% by weight or less covers a metallic base layer, wherein the metallic base layer is not adapted for direct contact with the alkaline electrolysis medium.

The metal alloy layer having an iron content of 10.0% by weight or less covers the metallic base layer, i.e. in operation of the electrolysis assembly the metal alloy layer contacts the alkaline electrolysis medium in the corresponding areas. The metallic base layer is joined to the metal alloy layer having an iron content of 10.0% by weight or less at least by a form-fitting or force-fitting or atomic-level join. The metallic base layer is configured such that it does not contact the alkaline electrolysis medium in operation of the electrolysis assembly.

It is preferable when the metallic base layer is formed from a carbon steel and/or from a stainless steel.

Examples of suitable materials are the steels having the material identification number 1.0345, 1.0425, 1.0481 , 1.0473, 1.0487, 1.0488, 1.4404, 1.4462, 1.5415, or 1.0565.

In a further aspect of the invention the electrolysis assembly is characterized in that the nickel layer is not produced on the base layer by a chemical or an electrochemical coating process.

The aforementioned methods generally do not achieve sufficient layer thicknesses, i.e. nickels produced therewith typically have a layer thickness of less than 0.1 mm. The use of the aforementioned processes for producing the nickel layer is thus not preferred.

In a further aspect of the invention the electrolysis assembly is characterized in that the electrolysis assembly is adapted for operation with an aqueous electrolysis medium having a hydroxide ion concentration of at least 1 mol per litre of electrolysis medium.

The electrolysis medium is preferably a water-based medium which comprises hydroxide ions and a suitable countercation, in particular sodium and/or potassium.

It is preferable when the aqueous electrolysis medium has a hydroxide ion concentration of at least 2 mol per litre of electrolysis medium or of at least 3 mol per litre of electrolysis medium or of at least 4 mol per litre or of at least 5 mol per litre or of at least 6 mol per litre or of at least 6.5 mol per litre or of at least 6.9 mol per litre.

Aqueous sodium hydroxide solution (NaOH_aq), more preferably aqueous potassium hydroxide solution (KOH_aq) is especially employed as the electrolysis medium.

The invention is explained in more detail below by an exemplary embodiment. The following detailed description makes reference to the attached drawing which illustratively represents a specific embodiment of the invention. The following detailed description is not to be understood in a limiting sense, and the scope of protection of the aforementioned aspects and embodiments of the invention is defined by the accompanying claims.

In the figures:

Figure 1 shows a block flow diagram of an electrolysis assembly 1 according to one example of the invention.

The electrolysis assembly 1 comprises a first region 21 and a second region 22.

The second region 22 comprises two or more components. The components of the second region have an inner side region (not shown) which is adapted for direct contact with a strongly alkaline electrolysis medium, here concentrated aqueous KOH solution. 90 percent of the total surface area of this inside region is formed by a nickel layer (not shown). The nickel layer has a layer thickness of 0.1 mm and a nickel content of more than 98% by weight. The remaining 10 percent of the total surface area of the inside region is formed from a metal alloy layer having an iron content of 10% by weight or less (not shown).

The first region 21 comprises an electrolysis stack 2 having an anode region 3 and a cathode region 4. The first region 21 is fluidically connected to the second region 22 via a pipe conduit 7 and the pipe conduits 10 and 11 . The pipe conduit 7 supplies the electrolysis stack 2 with monophasic electrolysis medium, i.e. with electrolysis medium depleted in product gases. The anode region 3 of the electrolysis stack 2 produces oxygen as the first product gas. The cathode region 4 of electrolysis stack 2 produces hydrogen as the second product gas. Pipe conduit 10 discharges a biphasic mixture of alkaline electrolysis medium and oxygen from the anode region 3. Pipe conduit 11 discharges a biphasic mixture of alkaline electrolysis medium and hydrogen from the cathode region 4.

The second region 22 comprises a unit 6, a cathode-side gas-liquid separator 8 and an anode-side gas-liquid separator 9. The second region further comprises a plurality of pipe conduits, in particular pipe conduits 7, 10, 11 and 23. The latter are attributable to the second region 22 even if otherwise represented in part. Unit 6 comprises at least one cooler and a pump for the alkaline electrolysis medium. Cooled electrolysis medium depleted in product gas is fed to the electrolysis stack 2 via the pipe conduit 7 by means of the unit 6. Pipe conduit 7 is divided into two sections for distribution of the electrolysis medium to the anode region 3 and the cathode region 4 of the electrolysis stack 2.

The components of the second region 22 may also be described as "balance of stack" (BOS) components.

Further components shown that are not attributable to the second region are a rectifier 5, an oxygen cooler 14 and a hydrogen cooler 15. Even if not attributable to the second region 22 here, these components are also often referred to as "balance of stack" (BOS) components.

The gas-liquid separator 8 separates hydrogen from the alkaline electrolysis medium. The electrolysis medium depleted of hydrogen is discharged from the gas-liquid separator 8 by means of pipe conduit 23. The gas-liquid separator 9 separates oxygen from the alkaline electrolysis medium. The electrolysis medium depleted of oxygen is discharged from the gas-liquid separator 9 by means of pipe conduit 23. Pipe conduit 23 combines the cathode-side and anode-side electrolysis media depleted in product gas and supplies them to unit 6.

The first product gas (oxygen) separated in the gas-liquid separator 9 is supplied to the oxygen cooler 14 via an oxygen conduit 12. The oxygen cooler 15 cools and condenses entrained water. The dry oxygen product is discharged via the oxygen conduit 16 and optionally subjected to a further purification and use.

The second product gas (hydrogen) separated in the gas-liquid separator 8 is supplied to the hydrogen cooler 15 via a hydrogen conduit 13. The hydrogen cooler 15 cools and condenses entrained water. The dry hydrogen product is discharged via the hydrogen conduit 17 and subjected to a further purification and use.

The rectifier 5 supplies the electrolysis stack 2 with direct current, i.e. it is electrically connected therewith (see dot-dashed line between elements 2 and 5). The electrolysis arrangement 1 further comprises so-called "balance of plant" components 19, 24 and 25.

The second region 22 is supplied with deionized fresh water via a plant for deionized water 19. This compensates for the amount of water consumed by the electrolysis reaction. The deionized water is supplied to the gas/liquid separator 9 via a conduit 20.

The cooling water system 24 provides for cooling of the separators 8 and 9, the unit 6 and the rectifier 5 via the cooling water conduit system 18.

The transformer 25 converts alternating current from the connected power grid (not shown) into alternating current at a suitable voltage and passes this to the rectifier 5, to which the transformer 25 is electrically connected (see dot-dashed line between elements 25 and 5).

List of reference numerals

1 Electrolysis assembly

2 Electrolysis stack

3 Anode region

4 Cathode region

5 Rectifier

6 Unit with electrolysis media cooler and circulation pump

7 Pipe conduit for monophasic electrolysis medium

8 Cathode-side gas-liquid separator

9 Anode-side gas-liquid separator

10 Pipe conduit for biphasic mixture (anode side)

11 Pipe conduit for biphasic mixture (cathode side)

12, 16 Oxygen conduit

13, 17 Hydrogen conduit

14 Oxygen cooler

15 Hydrogen cooler

18 Cooling water conduit system

19 Plant for production of deionized water

20 Conduit for deionized water

21 First region

22 Second region

23 Pipe conduit for monophasic electrolysis medium

24 Cooling water system

25 Transformer

Claims

1 . Electrolysis assembly (1 ) for operation with an alkaline electrolysis medium comprising a first region (21 ) and a second region (22), wherein

- the first region (21 ) comprises an electrolysis stack (2) comprising a multiplicity of electrolysis cells, wherein the electrolysis stack is adapted for producing a first product gas in an anode region (3) and for producing a second product gas in a cathode region (4) from the alkaline electrolysis medium;

- the second region (22) is fluid ically connected to the first region (21 ) and the second region (22) comprises a plurality of components, wherein the components of the second region (22) are adapted for discharging electrolysis medium enriched with product gas from the first region (21 ), for introducing electrolysis medium depleted in product gas into the first region (21 ) and for separating the produced product gases from the electrolysis medium, and wherein the components of the second region comprise at least one pipe conduit system (7, 10, 11 , 23) and an anode-side and a cathode-side gas-liquid separator (8, 9), characterized in that the components of the second region (22) have an inside region which is adapted for direct contact with the alkaline electrolysis medium, wherein the inside region is at least partially formed from a nickel layer and wherein the nickel layer has a layer thickness of at least 0.1 mm and a nickel content of at least 98% by weight.

2. Electrolysis assembly according to Claim 1 , wherein the inside region is partially formed from the nickel layer and partially formed from a metal alloy layer, wherein the metal alloy of the metal alloy layer has an iron content of

10% by weight or less.

3. Electrolysis assembly according to Claim 1 or 2, wherein the inside region is formed to an extent of at least 50% of its total surface area from the nickel layer.

4. Electrolysis assembly according to either of Claims 2 or 3, wherein the inside region is formed to an extent of at least 50% of its total surface area from the nickel layer and the remaining surface area of the inside region is formed from the metal alloy layer having an iron content of less than 10.0% by weight.

5. Electrolysis assembly according to any of the preceding claims, wherein the nickel layer has a layer thickness of at least 0.2 mm, preferably a layer thickness of at least 0.3 mm.

6. Electrolysis assembly according to any of the preceding claims, wherein the nickel layer covers a metallic base layer, wherein the metallic base layer is not adapted for direct contact with the alkaline electrolysis medium.

7. Electrolysis assembly according to Claim 6, wherein the metallic base layer is formed from a carbon steel and/or from a stainless steel.

8. Electrolysis assembly according to any of Claims 2 to 7, wherein the metal alloy layer having an iron content of 10.0% by weight or less covers a metallic base layer, wherein the metallic base layer is not adapted for direct contact with the alkaline electrolysis medium.

9. Electrolysis assembly according to Claim 8, wherein the metallic base layer is formed from a carbon steel and/or from a stainless steel.

10. Electrolysis assembly according to any of Claims 6 to 9, wherein the nickel layer is not produced on the base layer by a chemical or an electrochemical coating process.

11 . Electrolysis assembly according to any of Claims 1 to 10, wherein the electrolysis assembly is adapted for operation with an aqueous electrolysis medium having a hydroxide ion concentration of at least 1 mol per litre of electrolysis medium.