Electrolysis cell and electrolysis cell stack with improved stray current efficiency

Abstract

The invention at hand relates to an electrolysis cell, a process for the production of hydrogen by electrolysis and a cell stack comprising a multitude of the electrolysis cells, wherein each cell comprises an anode compartment, a cathode compartment and a separator, wherein a sealing member seals the electrolysis cell volume from the surrounding, the electrolysis cell electrolyte feed and / or electrolysis cell electrolyte outlet are located in the cell volume and comprise means for reducing stray currents.

Description

[0001] Electrolysis cell and electrolysis cell stack with improved stray current efficiency

[0002] The invention at hand relates to an electrolysis cell, a process for the production of hydrogen by electrolysis and a cell stack comprising a multitude of the electrolysis cells, wherein each cell comprises an anode compartment, a cathode compartment and a separator, wherein a sealing member seals the electrolysis cell volume from the surrounding, the electrolysis cell electrolyte feed and / or electrolysis cell electrolyte / gas outlet are located in the cell volume and comprise means for reducing stray currents.

[0003] One possible way of decarbonizing energy intensive production processes is the substitution of fossil-based fuels by non-carb on-based energy carriers. In this respect hydrogen is promoted as one of the most promising climate-friendly alternatives, based on the fact that the fundamental principles of hydrogen generation are known for many years and that hydrogen can be provided carbon-neutral in case that green energy is at hand. For instance, alkaline water electrolysers (AWEs) generate hydrogen and oxygen and can be considered the most common type of commercially used water electrolysers. The AWEs usually comprise a multitude of electrochemical cells that are connected in series, forming a so-called electrolyser stack. Two fundamentally different configurations for AWE stacks are described in the literature and used in industry. The configurations mainly differ with respect to the electrolyte feed to and electrolyte and gas removal from the cells. One configuration is known as the bipolar filter-press type, and the other configuration is the single element type. In the bipolar filter-press type the electrolyte is fed via an internal distribution manifold to each cell of the bipolar stack, and oxygen and electrolyte or hydrogen and electrolyte, respectively, are collected via collection manifolds formed by holes and sockets in the electrodes, diaphragms and bipolar plates located in the upper area of the cell. In the single element configuration, the distribution and collection manifolds are located outside the stacks and connected via single hoses to each individual cell. The different flow path of the electrolyte feed in the cells and the overall electrolyte handling in the stack form the basis of certain disadvantages in water electrolysis. One major obstacle for achieving high process efficiencies in stack configurations are stray currents. Stray currents are generated by ionic currents flowing between any two cells in the stack through the electrolytic connections formed via the feed and outlet manifolds. They result in significant efficiency losses, i.e. the achievable molar flow of hydrogen is less than theoretically anticipated without stray currents. Stray currents can result in efficiency losses of typically 2-5% but may reach up to 10% or above in ill- designed AWE stacks, with a large cell number and / or at very low production rates, i.e. at low turn-down. For the bipolar filter press type-configuration with internal manifolds a stray current efficiency of around 90%-95% is standard, whereas designs with individual cell feed / outlets can reach stray current efficiencies of 98% and above. The latter is mainly due to the beneficial length and separate routing of feed and outlet hoses to and from the single cell, nevertheless, this solution is rather expensive, the individualized cell connections are a drawback installation and maintenance, and the multitude of connections and their location outside the cell form possible source of leakages.

[0004] The design of electrolysis cells like AWE-cells and stacks are also discussed in the patent literature.

[0005] DE 19641 125 concerns an electrolysis apparatus for producing halogen gases from an aqueous alkaline halide solution with a plurality of plate-like electrolysis cells which are disposed adjacent one another in a stack, are in electrical contact, and each comprise a housing consisting of two half-shells of electrically conductive material with outer contact strips on at least one housing rear wall. The anode and the cathode are separated from each other by a partition wall, are disposed parallel to one another and are connected in an electrically conductive manner to the respective associated rear wall of the housing by means of metal reinforcements.

[0006] EP 1 766 104 Bl describes an electrolysis cell in the constructive form of single elements, intended for instance for the production of chlorine, hydrogen and / or caustic soda and designed in such a way that the portion of inactive membrane surface is minimised thanks to an optimised flange type so that the ratio between the flange surface of a semi-shell and the active membrane surface can be set to less than 0.045, neither the semi-shells nor the membrane being provided with bores or recesses for accommodating the clamping members. EP 3 696 298 Al, for instance, relates to a cell frame for an electrolysis or fuel cell block, having a receiving opening which is set up to receive an electrolysis or fuel cell membrane, a plurality of collecting channel openings which are set up for supplying and discharging media through the cell frame, a distribution channel structure, which is arranged to supply media from a respective supplying collecting channel opening to an associated half-space adjacent to the receiving opening and to discharge media from this half-space to an associated discharging collecting channel opening, and a sealing structure which is arranged to seal the cell frame to the outside and / or the receiving opening and / or the collecting channel openings, and to an electrolysis block constructed with such cell frames. The distribution channel structure comprises a groove channel structure formed on a first main side of the cell frame and a plurality of through-holes which extend with a directional component parallel to a cell frame plane between the groove channel structure and the associated half-space. The sealing structure is formed on a second main side of the cell frame opposite the first main side.

[0007] Such solutions, known from the prior art, may offer further potential for improvement, especially with regard to the operational safety of the cell design as well as the resulting efficiency in the reduction of stray currents.

[0008] It is therefore the task of the present invention to at least partially overcome the disadvantages known from the prior art. In particular, it is the task of the present invention to disclose an electrolysis cell design with improved electrolyte handling and low current losses based on stray currents. Furthermore, it is the task of the present invention to provide electrolyser cell stacks based on the inventive cells which are easily up-scalable, simple to manufacture and maintain, less prone to leakages and exhibiting a very high current efficiency. In addition, an inventive process is disclosed, based on the usage of the inventive cell and the inventive cell stack for alkaline water electrolysis.

[0009] The task is solved by the features of the independent claims, directed to the electrolysis cell according to the invention, the electrolysis cell stack according to the invention and the process according to the invention. Preferred embodiments of the invention are described in the dependent claims, in the description or in the figures, whereby further features described or shown in the dependent claims or in the description or in the figures may individually or in any combination constitute an object of the invention if the context does not clearly indicate the contrary.

[0010] According to the invention the problem is solved by an electrolysis cell comprising a) an anode compartment comprising an anode electrode contacting an electrically conducting anode support and an anode compartment outlet port; b) a cathode compartment comprising a cathode electrode contacting an electrically conducting cathode support and a cathode compartment outlet port, wherein the anode and / or the cathode compartment comprise an electrolyte compartment inlet port and c) a separator placed in between the anode and the cathode compartment, wherein at least one compartment feed insert is arranged at the electrolyte compartment inlet port, wherein the compartment feed insert comprises a compartment feed channel in fluid connection to the electrolyte compartment inlet port and one or more compartment feed holes in fluid connection to the compartment feed channel and the compartment, and wherein a sealing member is arranged between the electrically conducting anode support and the electrically conducting cathode support, wherein the sealing member is configured for sealing an electrolysis cell volume at least including the anode compartment, the cathode compartment, the separator and the compartment feed insert.

[0011] Surprisingly, it has been found, that the pressure sealing of the electrolysis cell volume to the outside by the cathode and anode support results in an inner electrolysis cell volume free of major pressure gradients resulting from the actively or passively maintained (e.g. by means of a pressure control system) operating pressure in the anode and / or cathode compartment cell volume. The pressure gradient free inner cell volume can be used to integrate in a favourable manner compartment feed inserts, wherein the inserts are able to provide an even electrolyte supply to the cell compartment and efficiently avoid stray or shunt currents. Based on the location of the insert within the pressure gradient free inner cell volume, the mechanical stability and the overall dimensions of the compartment feed insert can be much smaller compared to state-of-the-art solutions, wherein the distribution means have to be designed in order to withstand big pressure gradients between operating pressure and atmospheric pressure. The placing of the insert and the pressure surrounding enables the construction of small, but efficient inserts, requiring only very small overall installation volumes. Such effect and efficiency were not expectable, because prior art attempts, e.g. comprising the distribution inserts in operating pressure bearing cell frames, are voluminous, suggesting major losses in active compartment volume and / or increasing the overall size in the case of a transfer into the cell. The set-up according to the invention results in an even distribution of the electrolyte to each individual cell compartment, an even supply of electrolyte across the width of individual compartment and, at the same time, minimizes stray currents due to its added length. In addition, due to the location within the cell volume there are lower or no side conditions with respect to leakages of the insert. Any leakage will appear in the cell volume itself and will not harm the surrounding of the cell, because the insert and the electrolyte compartment inlet and outlet ports are completely enclosed in the electrolysis cell volume by the sealing member. Therefore, any design, wherein a leakage of the electrolyte at the insert results in a leakage of electrolyte to the surrounding is not within the scope of this invention. The insert can be made from a single, or few, easy to manufacture, assemble, maintain and replaceable plastic part(s) which is / are not a part of the structural design of the cell, wherein the electrolyte distributions suggested by the prior art, and especially in the context of those cells with individual feed / outlet hoses such as the single element type, consists of numerous parts, which can increase both assembly time and cost, as well as complicate maintenance procedures. With respect to a comparison to the bipolar filter press electrolysers, an even electrolyte feed distribution across the complete width of each individual compartment is realized, and stray currents are efficiently reduced. The latter is especially achieved by an increase in the distance between the electrolyte compartment feed port and the compartment volume in contact with the electrode. In addition, the placement of the insert in the pressure gradient free inner cell volume further removes structural and mechanical side conditions for the insert and / or frame. The insert can be flexibly designed in order to provide nearly any channel diameter and length and thus ionic and hydraulic resistance by choosing the number of compartment feed holes or the overall path length and design of the compartment feed channel, resulting in a tailorable stray current reducing effect, which is independent of any mechanical stability or production side conditions caused by bearing a larger pressure gradient.

[0012] The inventive cell is an electrolysis cell. The electrolysis cell can, for instance, be a water electrolysis cell or a chlor-alkali (CA) cell. A water electrolysis cell is able to generate oxygen and hydrogen from water, and a CA cell is able to generate chlorine from aqueous halide salt solutions by the application of a DC electrical power. The water electrolyser can be of the PEM- (Polymer Electrolyte Membrane) or the alkaline-type. PEM electrolysers are able to process pure water as the electrolyte. The electrodes for the PEM-type are made from noble metals, and the separator is a proton-conducting membrane usually made from a perfluorinated sulfonic acid polymer. Preferably the water electrolysis cell is a cell for alkaline electrolysers or AWEs. AWEs use aqueous KOH or NaOH solutions. The chemistry of the reaction allows the use of cheap non-noble electrodes, e.g. based on nickel. The Chlor-alkaline electrolyser cell (CA) can be of the NaCl- or KCl-type, using respective salt solutions. It can also be of the HCl-type, using aqueous hydrochloric acid as electrolyte. Preferably, the electrolysis cell is an AWE or CA cell.

[0013] The electrolysis cell comprises a) an anode compartment comprising an anode electrode contacting an electrically conducting anode support and an anode compartment outlet port. In the anode compartment in the case of an AWE the oxidation of the hydroxide ions in the electrolyte to oxygen and water is performed. The reaction takes place at the anode electrode, which is either directly or indirectly connected to the DC power source. The electrode is in electrical contact to an electrically conducting support, wherein in case of a combination of several cells to a stack the support is called a bipolar plate, because electrodes are present on both sides of the support. At both ends of the stack the cells comprise an end plate. In the case of a single cell, only, one electrode, the anode, is present at the anode support and attached or fixed at one or more positions to the support. The anode electrode can for instance be a nickel -el ectrode. The anode compartment is filled during the reaction with the alkaline aqueous electrolyte. The reaction products e.g. electrolyte (or anolyte) and oxygen leave, at least in part, the anode compartment through the anode compartment outlet port. The anode compartment outlet port is in liquid connection to but does itself not comprise any active electrode surface.

[0014] The electrolysis cell comprises b) a cathode compartment comprising a cathode electrode contacting an electrically conducting cathode support and a cathode compartment outlet port. In the cathode compartment of e.g. an AWE the reduction of the water in the electrolyte to hydrogen and hydroxide ions is performed. The reaction takes place at the cathode electrode, which is either directly or indirectly connected to the DC power source. The cathode is in electrical contact to an electrically conducting support, wherein in case of a combination of several cells to a stack the support is called a bipolar plate, because electrodes are present on both sides of the support. In the case of a single cell, only, one electrode, the cathode, is present at the cathode support and attached or fixed at one or more positions to the support. The cathode electrode can for instance be a nickel-electrode. The cathode compartment is filled during the reaction with the electrolyte. The reaction products hydrogen and electrolyte (catholyte) leave, at least in part, the cathode compartment through the cathode compartment outlet port. The cathode compartment outlet port is in liquid connection to but does itself not comprise any active electrode surface.

[0015] The anode and / or the cathode compartment comprise an electrolyte compartment inlet port. During continuous electrolysis new electrolyte has to be fed into the cell compartments. The cell can either comprise two separated electrolyte compartment inlet ports, wherein one inlet port can supply the anode and the other inlet port can supply the cathode compartment. For an AWE with a porous diaphragm, it is also possible that one inlet port supplies the cell via one compartment, only. In this case the other compartment does not comprise an electrolyte compartment inlet port. The compartment inlet port allows the electrolyte inflow into the compartment volume, being in contact with the electrode. Preferably, the anode and the cathode compartment as defined in a) and b) each comprise an electrolyte compartment inlet port.

[0016] The electrolysis cell comprises c) a separator placed in between the anode and the cathode compartment. The anode and the cathode compartments are physically separated by a separator, wherein the separator is a porous diaphragm or is an ion-selective membrane allowing electrolyte and / or ions, respectively, to pass from the anode to the cathode side or vice versa. At the same time the separator prohibits a cross-over flow of reaction gases like oxygen and hydrogen between the anode and the cathode compartment.

[0017] A sealing member is arranged between the electrically conducting anode support and the electrically conducting cathode support, wherein the sealing member is configured for sealing an electrolysis cell volume at least including the anode compartment, the cathode compartment and the separator. The electrolysis cell volume is formed by the anode compartment, the cathode compartment and the separator. This cell volume is separated with respect to the cell surrounding by a sealing member, e.g. in the form of a gasket. The sealing member is electrically isolating the anode and the cathode in the cell. The sealing member can be a single- or a multipart item. The sealing member may be formed by a gasket between the bipolar plates, by a frame and a gasket between the bipolar plates, or by a frame around at least one support or bipolar plate with gaskets in between. The seal or the gasket can be a polymeric seal or gasket and the seal is in direct or indirect physical contact with the supports or in case of a stack the bipolar plates. The sealing member is arranged in between the supports and prevents any leakage of electrolyte or gas from the cell volume to the surrounding. Preferably, the seal or gasket is arranged at the outer circumference of the support, e.g. 0,5 cm to 2 cm away from the outer circumference of the support or flush with the outer circumference or protruding beyond the outer circumference. This seal forms as such the pressure bearing part or, in combination with a pressure ring, e.g. a metallic hoop, part of the pressure bearing part of the cell in case that the inner cell volume and the outer surrounding of the cell comprise a pressure difference. Usually, AWEs for instance are performed at an operating pressure higher than standard pressure, i.e. the hydrogen and / or oxygen has a gas pressure higher than ambient. Therefore, the sealing member has at least to withstand this inner cell to surrounding pressure difference during operation. Consequently, the cell volume or the anode compartment or the cathode compartment do not comprise any location comprising major pressure differences beyond those resulting from hydrodynamic pressure and static pressure.

[0018] At least one compartment feed insert is arranged at the electrolyte compartment inlet port, wherein the compartment feed insert comprises a compartment feed channel in fluid connection to the electrolyte compartment inlet port. The electrolyte enters the compartment not directly from the electrolyte compartment inlet port. In between the compartment and the electrolyte compartment inlet port there is a compartment feed insert present comprising a compartment feed channel, wherein the compartment feed channel prolongs the path or distance from the electrolyte compartment inlet port to the compartment volume in contact with the electrode. The compartment feed insert is also distributing the electrolyte to the compartment volume. The compartment feed insert can be made from a single piece, i.e. physically including the electrolyte compartment inlet port and the compartment feed channel in a housing. It is also possible, that the insert is physically connected to the compartment inlet port, e.g. by clipping both parts together. In the latter case the feed insert comprises the compartment feed channel and a fluid connection to the inlet port. In case of a cell stack comprising several cells, the combination of all compartment inlet ports forms the stack electrolyte manifold by physically connecting all of the compartment inlet ports. In each case the insert prolongs the electrolyte path to the cell compartment, because the electrolyte must flow from the inlet port through the insert, i.e. the compartment feed channel in the insert, in order to reach the compartment. As a function of the design of the compartment feed channel, the compartment feed channel can be separated into two different parts. One part can include the extra electrolyte flow path from the inlet port to the first fluid connection to the compartment volume. This part can be defined as compartment distribution manifold. The other part of the of the compartment feed channel is extending from the first fluid connection to the compartment volume to possibly present further fluid connections to the compartment volume. This extra path of the compartment feed channel in the insert after the nearest connection to the compartment does not necessarily reduce stray currents. The insert can for instance be produced by injection- or blow-molding. This feed channel lies within the insert and can be tailored with respect to the actual needs to reduce stray or shunt currents by elongation of the electrically isolated electrolyte path from the port to the compartment and / or by minimizing the feed channel diameter. The compartment feed channel can be present in the form of a straight connection, or a bended, angled or meandering channel within the insert. The electrolyte follows the path of the compartment feed channel within the insert. Based on the fact that the insert, the electrolyte compartment port and the compartment are located within the same sealed electrolyte cell volume, the single parts face no pressure difference resulting from the operating pressure. In addition, no severe electrolyte leakage can appear at the interconnection of the parts. The insert part is not bearing the operating pressure and, consequently, there is no need for an extensive mechanical stability of the insert. Therefore, the insert can be very small and only a small fraction of the compartment volume is lost due to the presence of the insert. Preferably the compartment feed channel can exhibit a smaller diameter compared to the inlet port. The latter is especially important in case of an electrolysis stack, in order to obtain an even distribution of electrolyte feed across all cells connected to the stack feed manifold.

[0019] One or more compartment feed holes are in fluid connection to the compartment feed channel and the compartment. The electrolyte from the compartment inlet port enters the insert and passes through the compartment feed channel. At the end of the compartment feed channel the electrolyte leaves the insert via one or more compartment feed holes. The compartment feed holes enable the fluid connection between the compartment and the compartment feed channel. The number and the location of the compartment feed holes can be chosen according to the needs. Preferably, one or more holes can be used to evenly distribute the electrolyte to the compartment and the electrode in the compartment. Preferably, the bore hole size of the compartment feed holes can be smaller compared to the channel diameter of the compartment feed channel. This may help better distributing the electrolyte across the full width of the compartment. The compartment feed channel may also break up into two or more smaller branches to distribute the electrolyte more evenly. Preferably, a ratio between the bore hole size of the compartment feed holes and the compartment feed channel, calculated as cross-sectional area of the feed hole divided by cross-sectional area of the feed channel, may be larger than or equal to 0.005 and smaller than or equal to 2, more preferably larger than 0.008 and smaller than 1.5.

[0020] In a preferred embodiment of the electrolysis cell the anode and the cathode compartment can comprise an electrolyte compartment inlet port and a compartment feed insert. In order to reduce the stray or shunt currents at the anode and the cathode it has been found useful to implement an electrolyte compartment inlet port and a compartment feed insert in the anode and the cathode compartment. This results in a very low contribution of stray currents to the electrical losses in the overall process.

[0021] In a further preferred characteristic of the electrolysis cell the compartment feed insert can comprise at least two compartment feed holes. In order to achieve an optimized distribution of the electrolyte within the compartment it has been found advantageous that at least two compartment feed holes enable the distribution of the electrolyte from the compartment feed insert into the compartment. Preferably, the two or more compartment feed holes can be separated by larger than 5 times of the compartment feed hole diameter. It may further be preferred that the two compartment feed holes can be separated by a distance of larger than 10 times of the compartment feed hole diameter. In a preferred embodiment, a single compartment feed hole diameter can be larger than 1 mm and smaller than 10 mm, further preferred, larger than 2 mm and smaller than 8 mm. In addition, the integral surface of the compartment feed hole diameters can be larger than 3 mm2and smaller than 75 mm2, further preferred, larger than 4 mm2and smaller than 13 mm2. Such dimensions have been found sufficient for adequately reducing stray currents and are able to allow an even electrolyte distribution with acceptable pressure drop. In case that the holes are not circular the corresponding cross-sectional area can fit into the abovedescribed ranges. Preferably, the electrolysis cell is an AWE.

[0022] Within a preferred embodiment of the electrolysis cell a compartment feed channel diameter can be larger than or equal to 3 mm and smaller than or equal to 10 mm. Within this range of compartment feed channel diameters an efficient reduction of stray currents at an acceptable hydrodynamic pressure drop is achieved. Preferably, the compartment feed channel diameter can be larger than or equal to 5 mm and smaller than or equal to 8 mm. In case that the compartment feed channel does not comprise a circular symmetry the largest dimension of the compartment feed channel cross-section is counted.

[0023] Within a preferred embodiment of the electrolysis cell a compartment feed channel cross-sectional area can be larger than or equal to 7 mm2and smaller than or equal to 120 mm2. In case that the compartment feed is performed in non-cylindrical geometries, e.g. in the form of channels comprising a squared or irregular base, the compartment feed channel cross-sectional area can be in above indicated range. Within this range of compartment feed channel cross-sectional area an efficient reduction of stray currents at an acceptable hydrodynamic pressure drop is achieved. Preferably, the compartment feed channel cross-sectional area can be larger than or equal to 10 mm2and smaller than or equal to 100 mm2, preferably larger than or equal to 20 mm2and smaller than or equal to 90 mm2.

[0024] In a further preferred aspect of the electrolysis cell, a ratio of the length of the compartment feed channel and the cross-sectional area of the compartment feed channel, calculated as length of the compartment feed channel divided by the cross-sectional area of the compartment feed channel, can be larger or equal to 1 / mm and smaller or equal to 100 / mm. For an efficient reduction of the stray or shunt currents it has been found useful to enlarge the liquid path of the electrolyte to the cell compartment according to the above-described dimensions. The electrical efficiency of the overall electrolysis is greatly enhanced. These dimensions form a good compromise of a sufficiently enlarged liquid electrolyte path, acceptable hydrodynamic pressure drop and a rather small insert providing the added path length and blocking only a small portion of the compartment volume. Based on the fact that the insert is not bearing the operating pressure, the overall dimensions can be rather small, because the part does not have to provide an extreme mechanical stability. Preferably, the ratio can be larger than 10 / mm and smaller or equal to 75 / mm, even more preferred smaller or equal to 50 / mm.

[0025] For example, in a preferred embodiment the cross-sectional area of the feed channel can be 60 mm2. In this case the length of the compartment feed channel is preferably at least 600 mm, more preferably at least 1500 mm long. Preferably, the feed channel has a maximal length of 6000 mm. Most preferably, the maximum length of the compartment feed channel is 3000 mm. In another preferred embodiment with a cross-sectional area of the compartment feed channel of 28 mm2, the length of the feed channel is preferably at least 280 mm, more preferably at least 700 mm long. These dimensions form a good compromise of a sufficiently enlarged liquid electrolyte path, acceptable hydrodynamic pressure drop and a rather small insert providing the added path length and blocking only a small portion of the compartment volume.

[0026] In a further preferred embodiment, the compartment feed channel may alter the flow direction of electrolyte within the compartment feed insert one or more times larger than or equal to 90°. The prolongation of the travel path of the electrolyte from the inlet port to the compartment volume can efficiently be enhanced by a meandering compartment feed channel. Preferably, the flow direction in the insert can be reversed at least once by 180°. Further preferred, the flow direction in the insert can be reversed at least twice and even more preferred three times by 180° in the compartment feed channel.

[0027] Preferably, the compartment feed channel comprises a maximal length of 5 times of the width of the compartment. Further preferred, the maximum length of the compartment feed channel is 3 times the width of the compartment. Such length of the compartment feed channel enable an efficient reduction of stray currents and small insert dimensions.

[0028] In a further preferred embodiment of the electrolysis cell, a ratio of the area of the compartment feed holes and the cross-section area of the compartment feed channel, calculated as area of the compartment feed holes divided by the cross-section area of the electrolyte compartment feed channel, can be larger than or equal to 0.01 and smaller than or equal to 1. It has been found favourable with respect to the distribution across the width of the compartment to establish a certain relation between the size of the electrolyte compartment feed channel and the area of the compartment feed holes. This relationship may influence the flow resistance of the electrolyte into the cell compartment and in case that the relation is within above defined range a better distribution is achieved. Preferably, the relation can be larger than or equal to 0.05 and smaller than or equal to 0.75, further preferred, the relation can be larger than or equal to 0.1 and smaller than or equal to 0.5.

[0029] In a further preferred embodiment, a cross-sectional area of the compartment feed channel comprising one or more compartment feed holes can be larger than the compartment feed channel. It is further advantageous that the cross-sectional area of this part of the compartment feed channel may be more than one and less than 10 times larger than the cross-sectional area of the feed channel itself. Such dimensions have been found sufficient for adequately distributing electrolyte across the compartment while maintaining low stray currents.

[0030] In a further preferred aspect of the electrolysis cell the compartment feed insert can comprise the electrolyte compartment inlet port. For an easy cell assembly, maintenance and for reducing the possibility of any uncontrolled electrolyte flow paths between the insert and the compartment inlet port it has been found useful to provide the compartment feed insert and the electrolyte compartment inlet port as one piece. In case of a stack, the combined electrolyte compartment inlet ports form the stack electrolyte manifold. The combination of both parts does not result in a combination of both functions. The functional insert will start at that point of the insert forming the compartment feed channel. This part of the insert exhibits a different diameter for the electrolyte compared to the electrolyte compartment inlet port.

[0031] In a preferred characteristics of the electrolysis cell a ratio of the compartment volume and the compartment feed insert volume, calculated as compartment volume divided by compartment feed insert volume, can be larger than or equal to 10 and smaller than or equal to 500. Based on the design that the insert is completely located in the cell, this part is not bearing the operational pressure. This enables the use and construction of very small inserts. This is advantageous, because a smaller fraction of the cell volume is blocked by the insert, but the effect of stray current reduction is efficiently achieved. Advantageously, this ratio can be very small in the case at hand. Preferably, the ratio can be larger than or equal to 20 and smaller than or equal to 250, further preferred, the ratio can be larger than or equal to 50 and smaller than or equal to 150.

[0032] In a preferred embodiment of the electrolysis cell at least one compartment outlet insert can be arranged at one or more compartment outlet port, wherein the compartment outlet insert comprises a compartment outlet channel in fluid connection to or comprising the compartment outlet port and one or more compartment outlet holes in fluid connection to the compartment outlet channel and the compartment. In order to further improve the reduction of stray currents it has been found useful to also place a compartment outlet insert into the compartment. The compartment outlet insert can be placed in the anode compartment, in the cathode compartment or in both. The compartment outlet insert enables a better collection of the electrolyte and the electrolyte / gas and, at the same time, reduces the stray currents generated at the outlets. The overall symmetry of the compartment outlet inserts can be similar to the feed inserts, nevertheless, the flow path of the electrolyte is of course reversed at the outlet inserts. This means, that the electrolyte from the cell compartment first is collected at the compartment outlet holes, passes the compartment outlet channel and is directed to the compartment outlet port. As a function of the prolonged channel set-up the stray currents are further reduced. The outlet channel or the outlet port may further comprise a demister for separating the generated gases from the electrolyte. The outlet insert may also comprise two outlet ports, connecting to two individual outlet manifolds, in fluid connection to the compartment outlet channel. One outlet manifold may preferably conduct electrolyte, while the other outlet manifold may preferably conduct gas.

[0033] Within a preferred aspect of the electrolysis cell, a ratio of the length of the compartment outlet channel and the cross-sectional area of the compartment outlet channel, calculated as length of the compartment outlet channel divided by the cross-sectional area of the compartment outlet channel, is larger or equal to 1 / mm and smaller or equal to 100 / mm. For an efficient reduction of the stray or shunt currents it has been found useful to enlarge the liquid path of the electrolyte from the cell compartment according to the above-described dimensions. The electrical efficiency of the overall electrolysis is greatly enhanced. These dimensions form a good compromise of a sufficiently enlarged liquid electrolyte path, acceptable hydrodynamic pressure drop and a rather small insert providing the added path length and blocking only a small portion of the compartment volume. Based on the fact that the insert is not bearing the operating pressure, the overall dimensions can be rather small, because the part does not have to provide an extreme mechanical stability. Preferably, the ratio can be larger than 10 / mm and smaller or equal to 75 / mm, even more preferred smaller or equal to 50 / mm.

[0034] In a further preferred embodiment of the electrolysis cell, the electrolysis cell may comprise a compartment feed insert and a compartment outlet insert, wherein a ratio of the compartment outlet insert channel length and the compartment feed insert channel length, calculated as compartment outlet insert channel length divided by the compartment feed insert channel length, is larger than or equal to 0.1 and smaller than or equal to 1. For an efficient distribution of the electrolyte to the compartment and for an efficient collection of the spend electrolyte and the gases from the compartment, it has been found favourable that inserts are used, wherein the channel lengths between the inserts at the inlet and the outlet are according to above defined ratio. This relation accounts for distribution of the stray currents at the feed and the outlet. Based on the fact that both, feed and outlet, are located in the cell compartment, a very specific relation of the inserts channel length can be achieved. It is further preferred, that the ratio is larger than or equal to 0.2 and smaller than 1.0, and further preferred, larger than or equal to 0.25 and smaller than or equal to 0.8. The channel length is defined as the added path distance of the electrolyte travelling from the compartment inlet port to the first compartment feed hole.

[0035] In a further preferred embodiment of the electrolysis cell, the compartment feed insert is configured to mechanically fix and stabilize the separator in the cell compartment. It has been found useful to also establish a mechanical connection of the separator and the compartment feed insert. This additional connection can fix the separator within the cell and can ease the overall assembly. Even under high electrolyte volume flows the separator will not change the position and therefore, the individual anode and cathode cell volume remains unchanged during electrolysis.

[0036] In a preferred embodiment of the electrolysis cell, the material of the compartment feed insert and / or the compartment outlet insert comprises polymeric materials selected from the group consisting of polyether ether ketones PEEK, fluorinated plastics; polysulfones; polypropylene copolymers; natural or synthetic rubber; and thermoplastic elastomers such as blends or hybrid compounds of any of the aforementioned thermoplasts and a rubber such as EPDM, and mixtures of at least two members of that group. Such group of materials have been found useful to enable a reliable performance of the insert over long processing times, even in very harsh process conditions. Fluorinated plastics can be selected from the group consisting of PTFE, ETFE, ECTFE, PVDF, PFA or TFM. Polysulfones can be selected from the group consisting of PSU, PPS, PPSU or PESU. Polypropylene copolymers can be selected from the group consisting of polypropylene random copolymers and polypropylene block copolymers. Natural or synthetic rubbers can be a rubber such as EPDM. In addition, the compartment feed insert may consist of one or more of these materials.

[0037] In a further preferred embodiment of the electrolysis cell, wherein the cross-sectional area of the compartment feed channel in the compartment feed insert varies from the electrolyte compartment inlet port to the compartment feed holes, wherein the average cross-sectional area of the compartment feed channel in the region comprising the compartment feed holes is more than 1 and less than 10 times larger in relation to the average cross-sectional area of the compartment feed channel in the region not comprising the compartment feed holes. The cross- sectional area of the compartment feed channel may vary in the insert from the inlet port to the holes distributing the electrolyte into the cell volume. Preferably the cross-sectional area of the compartment feed channel in contact to the compartment feed holes is significantly larger compared to the cross-sectional area of the compartment feed channel guiding the electrolyte from the port to this area. Such set-up allows for an efficient reduction of the stray currents and an acceptable pressure drop. In case that the inlet channel comprises a varying diameter or crosssection, the average cross-sectional area of the two parts is counted. The ratio between the two cross-sectional areas can further be larger or equal to 1.5 and less than or equal to 8, further preferred larger or equal to 2.0 and less than or equal to 7.

[0038] Furthermore, an electrolysis cell stack is according to the invention, wherein the electrolysis cell stack comprises larger than or equal to 2 and smaller than or equal to 800 electrolysis cells according to the invention, wherein the electrolysis cells are in electrical contact by the electrically conducting supports. The electrically conducting support is called a bipolar plate in the case of a stacked arrangement of several electrolytic cells. The inventive electrolysis cell can be used as is or can be used in combination of two or more cells connected in series. In the latter case the cells are physically attached via the conducting supports and the seals. The connection in series includes, that the cell compartments of each cell are not in fluid contact, resulting in hydraulically separated cell compartments. Nevertheless, besides the cell compartments a fluid connection or contact is established outside of the cell compartments via a connection of the inlet and outlet ports, forming the stack manifolds. In the form of a cell stack the stray currents between the cells and, therefore, the overall stack, are very efficiently reduced. The conducting support is arranged in the stack in between two cells and this support forms a bipolar plate, because on one side an anode and on the other side of the plate a cathode is attached. I.e. in the form of a stack two adjacent cells do not comprise at the connection or attachment location two individual supports, but only one. In case that three cells are connected in series the inner cell comprises two bipolar plates comprising an anode and a cathode on each bipolar plate. The outermost cells of the stack comprise one bipolar plate and one support or end plate, respectively. The electrolyte compartment ports and the compartment outlet ports of each cell are connected in series, forming a combined electrolyte stack feed manifold and a combined stack electrolyte and gas outlet manifold. The stack manifolds are formed separately for the anode and the cathode compartments. The stack may comprise separate endplates at both stack ends. The stack may be formed by application of mechanical pressure to each cell by application of pressure to the stack. The mechanical pressure also seals the individual cells, by pressurizing the sealing member in between the electrode supports. Within the stack the electrolyte distribution via the stack manifold and the inserts in the compartments can be considered “pressure less” inserts. Based on the use of the inventive cell design within a stack configuration the stray or shunt currents are dramatically reduced. This results in a big efficiency improvement for filter press type stack designs. Based on the advantageous stray current handling of the individual cells larger stacks can be assembled, comprising more cells. The stray current losses are usually proportional to the number of cells in the stack. Due to inventive design of the single cell, minimizing stray currents, larger stacks can be achieved with the same electrical efficiency. Preferably, the cell stack may comprise larger than or equal to 20 and smaller than or equal to 600 cells, even more preferred the cell stack may comprise larger than or equal to 30 and smaller than or equal to 350 cells. Especially, the latter is preferred, because it would allow 32 cells in one stack, i.e. a good number for cell voltage monitoring, very limited stray currents and it would fall completely out of the low voltage directive, being less than 75 V. In a preferred embodiment of the cell stack the compartment inlet ports of the cells form two or more stack feed manifolds not being in direct hydraulic contact to each other. For an efficient handling of the electrolyte supply it has been found useful to divide the overall electrolyte inlet into the stack. This means, that the inlet ports of all cells are not hydraulically connected to the same manifold. Two or more stack manifolds are present, being formed from the inlet ports of a subgroup of electrolysis cells. For an efficient reduction of the stray currents even for large stacks it has been found useful to alter the stack design by splitting the stack feed manifold into several sections which are individually fed by electrolyte. This may ease the stack assembly, but efficiently reduce the stray or shunt current contribution. Such solution is especially suitable for stacks comprising more than 20, preferably more than 50 individual cells combined in a stack.

[0039] In addition, according to the invention is a process for the production of hydrogen by electrolysis of an aqueous electrolyte, wherein the electrolysis is performed in an inventive electrolysis cell or performed in an electrolysis cell stack according to the invention. The inventive cell and the inventive cell stacks can favourably be used in the electrolysis of water. The overall electrical efficiency is enhanced due to reduction of stray currents, and the process efficiency is optimized. For the further advantages of the process, it is especially referenced to the advantages of the inventive cell and the inventive cell stack as outlined before.

[0040] Within a further preferred aspect of the process, the process can be a chlor-alkali electrolysis or an alkaline water electrolysis. The inventive electrolysis cell and the inventive electrolysis cell stack are very suitable for the electrolysis of aqueous solutions and especially aqueous alkaline solutions. For such electrolysis types stray currents are very efficiently supressed and higher yields with respect to hydrogen and the further process gases like oxygen and halogens are obtainable. In the case of AWE hydrogen and oxygen are generated and in the case of chloralkali electrolysis chlorine and hydrogen are generated as process gases.

[0041] The electrolysis cells and electrolysis cell stacks according to the invention are further described and defined by the following figures. The figures show: Fig. 1 a schematic representation of the structural set-up of an electrolysis cell according to the invention;

[0042] Fig. 2 another schematic representation of the structural set-up of an electrolysis cell according to the invention, wherein the design of the outlet insert is altered;

[0043] Fig. 3 another schematic representation of the structural set-up of an electrolysis cell according to the invention, wherein the design of the outlet insert is altered;

[0044] Fig. 4 a schematic representation of the inlet part of an inventive electrolysis cell according to the invention;

[0045] Fig. 5 a schematic cross-sectional representation of an inventive electrolysis cell according to the invention;

[0046] Fig. 6 a schematic cross-sectional representation of an inventive electrolysis cell stack according to the invention;

[0047] Fig. 7 a schematic representation of an inventive electrolysis cell stack according to the invention.

[0048] Figure 1 shows a schematic representation of the structural set-up of an electrolysis cell 10 according to the invention. Displayed is a half-cell set-up either representing an anode compartment 20 or a cathode compartment 20. The complete cell will be formed by two of such half-cell set-ups in contact to each other, including a membrane, separator 90 or diaphragm in between. The electrolysis cell 10 is enclosed by a support 30, wherein the support 30 is in electrical contact with the electrode thereon (not shown). In a cell stack the support 30 is a bipolar plate, because two different electrodes are in electrical contact to the support 30. Within the compartment 20 the electrolyte is circulating and in contact to the electrode surface. As a function of the half-cell the electrolyte is either the anolyte or the catholyte. The support 30 comprises at the outer circumference a sealing member 40. The sealing member 40 provides a mechanical sealing of the compartment 20 from the outside of the electrolysis cell 10. The sealing member 40 can be a one part or multi -part item. The sealing member 40 prevents any leakage of the electrolyte or produced gases from the compartment to the outside. The sealing member is responsible for bearing the pressure difference from the outside to the electrolysis cell 10. The electrolyte enters the electrolysis cell 10 through one or more compartment inlet ports 60. In this case one compartment inlet port 60 at the lower part of the cell 10 is depicted. The compartment inlet port 60 may comprise any geometry like round, ellipsoidal or square. In this case the compartment inlet port 60 is depicted as a round inlet. Each compartment 20 may comprise one or more compartment inlet ports 60, In addition, for an AWE it is also possible, that only one compartment 20 comprises one or more compartment inlet ports 60. The other compartment 20 may be supplied with electrolyte via the separator 90 (not shown). From the compartment inlet port 60 the electrolyte does not enter the compartment 20 directly. In between the compartment inlet port 60 and the compartment 20 a compartment feed insert 50 is present. The compartment feed insert 50 can for instance be a blow- or injection-moulded plastic part. The compartment feed insert 50 may be an integral part, also including the compartment inlet port 60. In addition, it is possible that the compartment feed insert 50 is attached to a compartment inlet port 60, forming a two piece set-up. The compartment feed insert 50 guides the electrolyte from the compartment inlet port 60 to the compartment 20 and prolongs the electrolyte path from the compartment inlet port 60 to the compartment 20. Based on this extra path stray or shunt currents are reduced, especially for cell stacks comprising two or more cells. The compartment feed insert 50 is located within cell 10 and due to the sealing member 40 the compartment feed insert 50 does not have to also bear the pressure difference to the cell 10 surrounding. The overall mechanical requirements for the compartment feed insert 50 are reduced and the compartment feed insert 50 can be smaller compared to state-of-the-art solutions. In addition, in case of any leakage between the compartment inlet port 60 and the compartment feed insert 50 no electrolyte leakage to the outside occurs, because the sealing member 40 prevents any electrolyte leakage to the outside. The electrolyte enters the compartment feed channel 70. The compartment feed channel 70 allows an effective enhancement of the electrolyte path from the compartment inlet port 60 to the compartment 20. This enhancement efficiently reduces current losses based on stray or shunt currents in combination of two or more electrolytic cells 10. Preferably the diameter or the overall cross section area of the compartment feed channel 70 is smaller compared to the diameter or the overall cross section area of the compartment inlet port 60. The compartment feed channel 70 can be present in the form of a single straight or curved channel or multiple straight or curved channels. Alternatively, the compartment feed channel 70 can also meander through the compartment feed insert 50. After passing through the compartment feed channel 70 the electrolyte enters the compartment 20 via one or more compartment feed holes 80. The compartment feed holes 80 are able to guide the electrolyte into the compartment 20. An even distribution of the electrolyte to the full compartment 20 volume and especially to the electrodes can be achieved. The electrolyte reacts within the compartment at the electrode and reaction products are generated. In the case of an AWE hydrogen and oxygen are generated in the different compartments 20. The electrolyte and reaction gases optionally leave the compartment 20 via a compartment outlet insert 150. At the outlet a similar insert can be realised, also reducing the stray or shunt current contribution at the cell outlet. The compartment outlet insert 150 comprises compartment collection holes 180, responsible for the electrolyte and gas collection from the compartment 20. The electrolyte and the gas pass one or more compartment outlet channels 170 and enter the compartment outlet port 160. One or more compartment outlet ports 160 can be present for each compartment 20. For an AWE at least the anode side and the cathode side each comprise a compartment outlet port 160. In the case of a cell stack several of the connected compartment outlet ports 160 form an outlet manifold. Also, the compartment outlet insert 150 lies within the sealing of the sealing member 40 and, consequently, is “not pressure bearing”.

[0049] Figure 2 depicts another schematic representation of the structural set-up of an electrolysis cell 10 according to the invention, wherein the design of the compartment outlet insert 150 is altered. In this embodiment the compartment outlet insert 150 comprises a different set-up compared to the compartment outlet insert 150 displayed in figure 1. The compartment outlet insert 150 shows a similar design compared to the compartment feed insert 50. The compartment outlet insert 150 collects the generated gases and the electrolyte via the compartment collection holes 180. The gas and the electrolyte are guided through the compartment outlet channel 170, effectively enhancing the electrolyte path and reducing the stray currents. The electrolyte and the gas are collected in the compartment outlet port 160 and may leave the cell or the cell stack. In order to even extend the path further, the compartment outlet channel 170 may meander in the insert compartment outlet insert 150.

[0050] Figure 3 shows another schematic representation of the structural set-up of an electrolysis cell 10 according to the invention, wherein the design of the compartment outlet insert 150 is altered. In this embodiment the compartment outlet channel 170 is meandering from the compartment collection holes 180 to the compartment outlet port 160 within the compartment outlet insert 150. In order to separate the electrolyte from the generated reaction gas a demister is integrated in the insert. The electrolyte is collected in the lower part and leaves the compartment outlet insert 150 through the lower compartment outlet port 160. The recti on gases are collected in the upper part of the demister and leave the compartment outlet insert 150 via the upper compartment outlet port 160.

[0051] Figure 4 shows a schematic representation of the inlet part of an electrolysis cell 10 according to the invention. In this figure the lower electrolysis cell 10 part of one compartment is depicted. The overall designation of the functional parts is the same as in figure 1. The electrolysis cell 10 comprises a compartment 20 and the compartment 20 is supplied with electrolyte via the compartment inlet port 60. The compartment inlet port 60 and the compartment 20 are located within a sealed volume, formed by the sealing member 40 and the supports 30. The encompassed volume includes the anode compartment 20, the cathode compartment 20 and the separator (not shown). The electrolyte passes through the compartment inlet port 60, the compartment feed channel 70 and enters the compartment 20 via the compartment feed holes 80. In addition, the figures show the effective path length in the compartment feed channel 70 (depicted in a different pattern), reducing the stray current contribution at the electrolysis cell inlet. The other section comprising the compartment feed holes 80 can be defined as compartment distribution manifold 71. Furthermore, the variables “a”, “b”, “c” and “d” are defined in this figure. The variable “a” indicates the diameter of the compartment inlet port 60. In case that the symmetry of the compartment inlet port 60 is not cylindrical, this parameter may represent the cross-sectional area. Parameter “b” indicates the diameter of the compartment feed channel 70. In case that the symmetry of the compartment feed channel 70 is not cylindrical, this parameter may represent the cross-sectional area of the compartment feed channel 70. Parameter “c” represents the diameter of the compartment feed holes 80. In case that the symmetry of the compartment feed holes 80 is not cylindrical, this parameter may represent the cross-sectional area of the compartment feed holes 80. Parameter “d” represents the diameter of the compartment distribution manifold 71. In case that the symmetry of the compartment distribution manifold 71 is not cylindrical, this parameter may represent the cross-sectional area of the compartment distribution manifold 71. Preferably, the relation between a, b and c is a > b > c. Preferably, the relation between b, c and d is d > b > c. Preferably, the sum of all cross-sectional areas of c is smaller than the cross-sectional area d.

[0052] Figure 5 shows a schematic cross-sectional representation of an electrolysis cell according to the invention. This figure shows a cross-section of an inventive electrolysis cell 10. The electrolysis cell 10 comprises an anode compartment 20 comprising an anode electrode 91, a cathode compartment 20 comprising a cathode electrode 92 and a separator 90 in between the compartments 20 and the anode electrode 91 and the cathode electrode 92. The compartment 20 are surrounded by two supports 30 on each side. In between the supports 30 is a sealing member 40 arranged. The sealing member 40 physically contacts both supports 30 and provide a liquid-and gas-tight seal to the surrounding. In addition, the sealing member 40 bears the pressure difference between the surrounding and the compartments 20. In this figure the different compartments 20 are explicitly designated as cathode compartment 21 and anode compartment 22. The sealing member 40 can be made from one piece or can be a multi-part sealing. In the cell volume the electrolyte is distributed to the electrolysis cell 10 via the compartment inlet port 60. The cathode compartment 21 comprises a compartment feed insert 50 within the sealed volume of the electrolysis cell 10. The compartment feed insert 50 comprises the compartment inlet port 60 and guides the electrolyte from the compartment inlet port 60 to the compartment 20. The electrolyte is guided through the compartment feed channel 70 and enters the compartment 20 via compartment feed holes 80. The electrolyte passes through the compartment, is electrolyzed and leaves the compartment 20 together with the reaction gases via compartment outlet insert 150 (not shown).

[0053] Figure 6 shows a schematic representation of an electrolysis cell stack 200 according to the invention. This figure depicts a stack of two electrolysis cells 10 according to the invention. The electrolysis cell stack 200 shows the same technical features compared to figure 3. The individual electrolysis cells 10 each comprise compartments 20, supports 30, separator 90, compartment inlet port 60, compartment feed insert 50 and sealing member 40. In the stack configuration between two cells one of the two supports 30 is omitted and the support 30 is a bipolar plate, because an anode and a cathode are present on both sides of the support 20. Therefore, each two adjacent cells 10 share one bipolar plate as support 30. In case of that the electrolysis cell stack 200 comprises 3 cells, at least two bipolar plates are present for the middle cell. In this figure it is also depicted, that the compartment inlet ports 60 of each electrolysis cell 10 are aligned and form together the stack feed manifold 210 as a common electrolyte feed line.

[0054] Figure 7 shows a schematic representation of an electrolysis cell stack according to the invention. The electrolysis cell stack 200 comprises several electrolysis cells 10 hydraulically separated and in electrical contact via supports 30 in the form of bipolar plates. Each electrolysis cell 10 comprises an anode compartment 21 and a cathode compartment 22, separated by a separator 90. The anode compartment 21 comprises an anode electrode 91 and the cathode compartment 22 comprises a cathode electrode 92. The electrolysis cell 10 are connected via manifolds, e.g. in form of the stack feed manifold 210, passing through the complete stack. At the end of the electrolysis cell stack 200 on each side a stack end plate is located. The single cells are each electrically contacted via the supports 30. The reaction gas or reaction gases may be collected in a manifold line and removed from the electrolysis cell stack 200. A stack may preferably comprise at least 20, preferably 50 and more preferably more than 100 individual electrolysis cells 10. The stack feed manifolds 210 and the stack outlet manifolds 160 are in fluid connection to external piping via end plate ports 230, 240 in the endplates 220.

[0055] List of Reference Signs

[0056] 10 Electrolysis cell

[0057] 20 Compartment

[0058] 21 Anode compartment

[0059] 22 Cathode compartment

[0060] 30 Support

[0061] 40 Sealing member

[0062] 50 Compartment feed insert

[0063] 60 Compartment inlet port

[0064] 70 Compartment feed channel

[0065] 71 Compartment distribution manifold

[0066] 80 Compartment feed holes

[0067] 90 Separator

[0068] 91 Anode electrode

[0069] 92 Cathode electrode

[0070] 150 Compartment outlet insert

[0071] 160 Compartment outlet port

[0072] 170 Compartment outlet channel

[0073] 180 Compartment collection holes

[0074] 200 Electrolysis stack

[0075] 210 Stack feed manifold

[0076] 220 Stack end plates

[0077] 230 Stack end plate feed inlet port

[0078] 240 Stack end plate outlet port

Claims

Claims1. Electrolysis cell (10) comprising a) an anode compartment (20, 21) comprising an anode electrode (91) contacting an electrically conducting anode support (30) and at least one anode compartment outlet port (160); b) a cathode compartment (20, 22) comprising a cathode electrode (92) contacting an electrically conducting cathode support (30) and at least one cathode compartment outlet port (160); wherein the anode compartment (20, 21) and / or the cathode compartment (20, 22) comprise at least one electrolyte compartment inlet port (60); and c) a separator (90) placed in between the anode compartment (20, 21) and the cathode compartment (20, 22); characterised in that at least one compartment feed insert (50) is arranged at the at least one electrolyte compartment inlet port (60), wherein the at least one compartment feed insert (50) comprises a compartment feed channel (70) in fluid connection to the at least one electrolyte compartment inlet port (60) and one or more compartment feed holes (80) in fluid connection to the compartment feed channel (70) and to the compartment (20) comprising the at least one electrolyte compartment inlet port (60) at which the at least one compartment feed insert (50) is arranged; and a sealing member (40) is arranged between the electrically conducting anode support (30) and the electrically conducting cathode support (30), wherein the sealing member (40) is configured for sealing an electrolysis cell volume at least including the anode compartment (20, 21), the cathode compartment (20, 22), the separator (90) and the at least one compartment feed insert (50).

2. Electrolysis cell according to claim 1, wherein the at least one compartment feed insert (50) comprises at least two compartment feed holes (80).

3. Electrolysis cell according to any one of the preceding claims, wherein a compartment feed channel (70) cross-sectional area is larger than or equal to 7 mm2and smaller than or equal to 120 mm2.

4. Electrolysis cell according to any one of the preceding claims, wherein a ratio of the length of the compartment feed channel (70) and the cross-sectional area of the compartmentfeed channel (70), calculated as length of the compartment feed channel (70) divided by the cross-sectional area of the compartment feed channel (70), is larger or equal to 1 / mm and smaller or equal to 100 / mm.

5. Electrolysis cell according to any one of the preceding claims, wherein a ratio of the area of the compartment feed holes (80) and the cross-section area of the compartment feed channel (70), calculated as area of the compartment feed holes (80) divided by the cross-section area of the compartment feed channel (70), is larger than or equal to 0.01 and smaller than or equal to 1.

6. Electrolysis cell according to any one of the preceding claims, wherein the at least one compartment feed insert (50) comprises the at least one electrolyte compartment inlet port (60).

7. Electrolysis cell according to any one of the preceding claims, wherein at least one compartment outlet insert (150) is arranged at at least one compartment outlet port (160), wherein the at least one compartment outlet insert (150) comprises a compartment outlet channel (170) in fluid connection to or comprising the at least one compartment outlet port (160) and one or more compartment outlet holes (180) in fluid connection to the compartment outlet channel (170) and to the compartment (20) comprising the at least one compartment outlet port (160) at which the at least one compartment outlet insert (150) is arranged, and wherein the electrolysis cell volume further includes the at least one compartment outlet insert (150).

8. Electrolysis cell according to claim 7, wherein a ratio of the length of the compartment outlet channel (170) and the cross-sectional area of the compartment outlet channel (170), calculated as length of the compartment outlet channel (170) divided by the cross-sectional area of the compartment outlet channel (170), is larger or equal to 1 / mm and smaller or equal to 100 / mm.

9. Electrolysis cell according to claim 7 or 8, wherein the electrolysis cell (10) comprises a compartment feed insert (50) and a compartment outlet insert (150), wherein a ratio of the compartment outlet insert (150) channel length and the compartment feed insert (50) channel length, calculated as compartment outlet insert (150) channel length divided by thecompartment feed insert (50) channel length, is larger than or equal to 0.1 and smaller than or equal to 1.

10. Electrolysis cell according to any one of the preceding claims, wherein the material of the at least one compartment feed insert and / or the at least one compartment outlet insert comprises polymeric materials selected from the group consisting of polyether ether ketones PEEK, fluorinated plastics; polysulfones; polypropylene copolymers; natural or synthetic rubber; and thermoplastic elastomers such as blends or hybrid compounds of any of the aforementioned thermoplasts and a rubber such as EPDM, and mixtures of at least two members of that group.

11. Electrolysis cell according to any one of the preceding claims, wherein the cross-sectional area of the compartment feed channel (70) in the at least one compartment feed insert (50) varies from the at least one electrolyte compartment inlet port (60) to the compartment feed holes (80), wherein the average cross-sectional area of the compartment feed channel (70) in the region comprising the compartment feed holes (80) is more than 1 and less than 10 times larger in relation to the average cross-sectional area of the compartment feed channel (70) in the region not comprising the compartment feed holes (80).

12. Electrolysis cell stack (200) comprising larger than or equal to 2 and smaller than or equal to 800 electrolysis cells (10) according to any one of the preceding claims, wherein the electrolysis cells (10) are in electrical contact by the electrically conducting supports (30).

13. Electrolysis cell stack according to claim 12, wherein the compartment inlet ports (60) of the cells (10) form two or more stack feed manifolds (210) not being in direct hydraulic contact to each other.

14. Process for the production of hydrogen by electrolysis of an aqueous electrolyte, characterized in that, the electrolysis is performed in an electrolysis cell (10) according to any one of claims 1 to 11 or performed in an electrolysis cell stack (200) according to any one of claims 12 or 13.

15. Process according to claim 14, wherein the process is a chlor-alkali electrolysis or an alkaline water electrolysis.

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