Patent Description:
In the technical field of large-scale production of hydrogen and/or chlorine, e.g. in the megawatt range, there are two main design categories of electrolyzers:
The first design category is the so-called filter press design in which the electrolyzer stack comprises two end parts connected to the poles of a power supply, and a multitude of bipolar plates. Adjacent end parts and bipolar plates are separated by a separator being a diaphragm or a membrane, thus forming a multitude of electrolysis cells in series. Each cell is enclosed on the anodic side by one bipolar plate and on the cathodic side by another adjacent bipolar plate and is divided into two half-cells by the separator. The bipolar plate can have any shape that serves to create electrolysis cells. The mechanical integrity and sealing of the cell volumes is provided by means of an external compression device, e.g. a set of tierods, compressing all bipolar plates and separators of the stack at once. Leak-tightness is only achieved in the compressed state. Typically, such electrolyzers for large-scale electrolysis have a cell area of <NUM> to <NUM> square meters and contain between <NUM> and <NUM> electrolysis cells in one electrolysis stack. The total weight of such an electrolyzer is typically several tens of tons, and the sealing force to be supplied by the compression device is about <NUM>-<NUM> MPa. Depending on the sealing area this results in a force of several tens of tons.

Examples of electrolyzers of the filter press design are known e.g. from <CIT> and <CIT>. The filter press design has the disadvantage that replacing such an electrolyzer or exchanging elements thereof is de facto only feasible after opening the electrolyzer on site. Thus, assembly and maintenance of the electrolyzers has usually to be done on site resulting in long downtimes of the involved facilities.

One way to circumvent the above-mentioned problems would be to downsize the electrolyzers and use electrolyzers with a significantly smaller cell area as they are used in smaller scale electrolysis plants, for e.g. hydrogen production or in fuel cells, in the kilowatt range. Due to the reduced size, these electrolyzer stacks are easier to handle, so that they can delivered pre-assembled and replaced as a whole. However, for large-scale production in the megawatt range, in particular in the range of tens to hundreds of megawatt, the downsizing would require a huge number of individual electrolyzers resulting in larger space requirements and increased maintenance costs.

The second known design category is the single element design, as marketed in particular by thyssenkrupp Uhde Chlorine Engineers. In this design, each electrolysis cell comprises two half-shells, namely an anode and a cathode half-shell, that are separated by a membrane or diaphragm as a separator. The two half-shells are connected to each other via a sealing system that isolates the anode and cathode half-shell from each other and prevents leakage of electrolyte and/or gases to the outside. As such, each cell forms a single element that is individually leak-tight and can be safely assembled, handled, and replaced by itself without affecting the whole electrolyzer. The single element cells are suspended in a rack formed by a steel frame and are pressed together to ensure a good electrical conductivity between contacting adjacent single elements. As compared to the filter press design, in which the external compression device has to provide the sealing forces for all cells (and good conductivity), in the single element design the required compression forces to only ensure good conductivity are smaller by orders of magnitude.

An electrolyzer of this type is known e.g. from <CIT>. This design has the disadvantage that it requires a high number of individual components, i.e. two half-shells and a flange frame instead of one bipolar plate, more base materials and more manufacturing steps, resulting in higher manufacturing effort and assembly costs.

From <CIT> an alkaline electrolyzer with a high operating pressure capability of up to <NUM> bar and an active area of the alkaline electrolyzer of <NUM> in<NUM> (= <NUM>,<NUM><NUM>) is known. Tie rod fasteners are used in conjunction with reinforcement bars in order to stiffen the outer half-cell portions against the internal pressures of up to <NUM> bar. Instead of individual tie rods for each cell, a group of six or more cells can be connected into a larger module by extended tie rods. Connectivity between the respective cells is achieved by the installation of spanner tubes connecting opposed sets of banana jack connectors.

In CN <NUM> A a sodium chlorate electrolysis system is described that has <NUM> rows of electrolytic cells, wherein in each row the cells are grouped in four groups of electrolytic cells with <NUM> single cells each. The number of sodium chlorate electrolyzer groups can be flexibly combined according to capacity demand and for maintenance, the electrolyzer groups can be replaced individually.

The object of the invention is to provide an electrolyzer for large-scale electrolytic production of hydrogen and/or chlorine that ensures safe operation and an ease of handling and maintainability, and has reduced requirements for base materials and manufacturing effort at the same time.

This object is achieved by an electrolyzer with the features of claim <NUM>.

Hereby, an electrolyzer is provided, the electrolyzer comprising an electrolysis stack, which contains a plurality of panel-like electrolysis cells being electrically interconnected in series, and means for mechanically securing the electrical interconnection of the electrolysis stack. Each electrolysis cell comprises an anode chamber with an anode arranged therein and a cathode chamber with a cathode arranged therein, wherein the anode chamber and the cathode chamber are separated from one another by a sheet-like separator. According to the invention, the stack contains at least two multi-cell elements, each comprising a plurality of the electrolysis cells and mechanical compression means. The electrolysis cells of each multi-cell element are held together in a sealed manner by the mechanical compression means. The means for mechanically securing the electrical interconnection of the stack are configured to mechanically secure the electrical interconnection of the multi-cell elements.

Thus, according to the invention, the electrolysis stack of the electrolyzer is subdivided into multi-cell elements that are separately sealed by the mechanical compression means. By providing additional compression means for aggregating a plurality of electrolysis cells in a multi-cell element, different means are used to provide the sealing forces and the electrical contact forces, namely the mechanical compression means and the means for mechanically securing the electrical interconnection of the stack, respectively. Thereby the requirements for providing pressure by the means for securing the electrical interconnection are reduced, allowing for a less massive design of the electrolyzer compared to the conventional filter press design. Further, the multi-cell elements can be delivered in a pre-assembled state to the site of the electrolysis plant in which the electrolyzer is to be installed. Hence, it is also possible to make quality and functionality tests on the pre-assembled multi-cell elements before it is delivered.

As compared to a single element design, wherein every single cell has to be encased within two shell parts providing for sufficient mechanical stability to be handled as a single element, in the inventive stack of multi-cell elements only each multi-cell element as a whole needs to exhibit handling stability. Thus, the amount of electrically conductive material, as e.g. nickel or titanium, used to make at least parts of the anode and cathode chambers of the electrolysis cells is reduced. Moreover, since the cells of the multi-cell element do not need to be closed and sealed by individual bolt sets, but can be sealed altogether by the mechanical compression means, the manufacturing effort can be reduced, as well.

Preferably, the multi-cell elements are individually replaceable in a maintenance state of the electrolyzer, in which the means for mechanically securing the electrical interconnection of the stack are in a loosened state, while the mechanical compression means are in a fastened state. Then, it is possible to remove and insert single multi-cell elements without disassembling the electrolyzer completely. Hereby, downtimes of the electrolyzers for maintenance are reduced.

According to the invention, the means for mechanically securing the electrical interconnection of the electrolysis stack are arranged to interact with the outmost electrolysis cells of the stack in order to exert a defined compressive force on the stack. The external compressive force acting on the stack as a whole improves the cell-performance and is also beneficial for alignment of the multi-cell elements in the stack. Alternatively, the means for mechanically securing the electrical interconnection of the electrolysis stack can be attached to at least two, preferably to any two, neighboring multi-cell elements in order to provide a contact pressure for the neighboring multi-cell elements. For example, the contact pressure may be provided between adjacent backwalls and/or between contact tabs of the neighboring multi-cell elements.

In preferred embodiments, the multi-cell elements of the electrolyzer each contain <NUM> to <NUM>, more preferably <NUM> to <NUM>, electrolysis cells. In view of the material requirements, it is preferred to aggregate many electrolysis cells within each multi-cell element. However, for the ease of handling the number of electrolysis cells in each multi-cell element has to be limited. With a number of electrolysis cell in the above range it is ensured that there is a significant positive effect on material and assembly costs, while at the same time the multi-cell elements can still be handled and transported by standard lifting devices, such as gantries or overhead cranes and forklifts.

In principle, it is conceivable that the multi-cell elements end with an open anode or cathode half-cell and are installed in the electrolyzer with interposed additional separators. However, in preferred embodiments the multi-cell elements are equipped with exterior back walls providing, preferably planar, contact surfaces for the electrical connection with an adjacent multi-cell element. Thereby each multi-cell element forms an independent sub-unit of the electrolyzer that can be installed in a plug-and-play manner.

In preferred embodiments the multi-cell elements comprise two end parts, containing the anode chamber and the cathode chamber of the outmost electrolysis cells of the multi-cell element, respectively, a number of middle parts containing the cathode chamber and the anode chamber of adjacent inner electrolysis cells being electrically connected to each other by a shared bipolar partition wall, and the sheet-like separators being interposed between any two adjacent parts of the end and middle parts. By combining the cathode chamber and the anode chamber of adjacent inner electrolysis cells in one middle part of the multi-cell element, the number of individual components and thus the work needed for assembly of the multi-cell elements is further reduced.

Preferably, the anode chamber and/or the cathode chamber of the outmost electrolysis cells of the multi-cell element has a volume that is larger than a volume of each of the cathode chambers and anode chambers of the inner electrolysis cells by a factor in the range of <NUM> to <NUM>. By increasing the volumes of the outmost chambers of the multi-cell element advantages of the conventional filter press design, namely highly efficient electrolysis with small cell volumes, low material and space requirements within the middle part of the multi-cell element are combined with an increased thermostability of the electrolyzer due to the increased heat capacity of the outmost cells. In other words: The larger cell-volumes of the outmost cell chambers of the multi-cell element allow for an improved intermediate cooling of the stack compared to the conventional filter press design. As a result, thermal homogeneity within the stack is improved.

There are several possibilities for the mechanical compression means to hold the electrolysis cells aggregated in a multi-cell element. In particular, the following three possibilities are preferred:
In preferred embodiments the mechanical compression means comprise tie rods extending externally across the electrolysis cells of the multi-cell element, and end components of the multi-cell element, wherein the end components are engaged with the tie rods to exert a compressive sealing force on the electrolysis cells of the multi-cell element. This design is closest to the conventional filter press design, in which, however, the electrolysis stack is subdivided into several multi-cell elements. The electrolysis cells of the multi-cell elements are sealed with respect to the surroundings at their circumferential peripheral region that may also serve to hold the sheet-like separators of the electrolysis cells.

In other preferred embodiments the mechanical compression means comprise at least two shell parts, within which the electrolysis cells of the respective multi-cell element are arranged, wherein the shell parts each comprise a circumferential flange portion, and bolts that are arranged such as to compress the electrolysis cells within the shell parts when the bolts are fastened. Preferably, the mechanical compression means further comprise at least one gasket arranged between the flange portions of the shell parts, wherein the gasket is compressed when the bolts are fastened. Alternatively, the flange portion may be made of or coated with a self-sealing material, such as PTFE. In these embodiments, the shell parts of the mechanical compression means form a casing for the multi-cell module that also seals the module from the surroundings. Thus, the individual electrolysis cells in the module do not need to be perfectly leak-tight, since the module is disposed with a two-stage sealing system. Further it is preferred if the shell parts provide for mechanical stability of the module for handling. In particular, the shell parts can be designed as two half-shells.

In further preferred embodiments, the mechanical compression means comprise circumferential external flange portions that are attached to the end and middle parts of the multi-cell element, and bolts fastening the flange portions of adjacent end and/or middle parts to each other.

All the above-described multi-cell elements can be used with external piping for distribution of electrolyte in or collection of electrolyte and/or product gases from their electrolysis cells. In other embodiments, the multi-cell element contains at least one internal manifold for distribution of electrolyte in or collection of electrolyte and/or product gases from the electrolysis cells of the multi-cell element. In conventional filter press electrolyzers, internal manifolds suffer from large stray currents due to the large number of electrolysis cells and corresponding stack voltages. However, in the inventive multi-cell element internal manifolds are advantageous, as the stray currents become small due to the smaller number of electrolysis cells and individual cell inlets and/or outlets replaced by an internal manifold further reduce manufacturing and maintenance costs.

In preferred embodiments, the electrolyzer further comprises a cell rack, wherein the electrolysis cells of the electrolysis stack and/or the means for mechanically securing the electrical connection of the electrolysis stack are mounted in the cell rack. A cell rack provides a stable frame for the electrolysis stack and allows the multi-cell elements and other parts to be designed in a less massive way. However, it is possible to make use of the invention in a standalone stack without a framing cell rack, as well.

Further advantages of the invention are described in the following with regard to the embodiments shown in the attached drawings.

In the drawings same parts are consistently identified by the same reference signs and are therefore generally described and referred to only once.

In <FIG>, an electrolyzer <NUM> according to the invention is shown. The electrolyzer <NUM> comprises an electrolysis stack <NUM> containing a plurality of panel-like electrolysis cells <NUM> in a side-by-side arrangement being electrically interconnected in series, and means <NUM> for mechanically securing the electrical interconnection of the electrolysis stack <NUM>. Each electrolysis cell <NUM> comprises an anode chamber <NUM> with an anode <NUM> arranged therein and a cathode chamber <NUM> with a cathode <NUM> arranged therein, wherein the anode chamber <NUM> and the cathode chamber <NUM> are separated from one another by a sheet-like separator <NUM> (details not shown in <FIG>, cf. Preferably, the anode and cathode chamber <NUM>, <NUM> are at least partly made from an electrically conductive material. According to the invention, the stack <NUM> contains at least two multi-cell elements <NUM>, each comprising a plurality of the electrolysis cells <NUM> and mechanical compression means <NUM>, wherein the electrolysis cells <NUM> of each multi-cell element <NUM> are held together in a sealed manner by the mechanical compression means <NUM>. The means <NUM> are configured to mechanically secure the electrical interconnection of the multi-cell elements <NUM>.

The stack <NUM> can be connected to an external power supply via endplates <NUM>, <NUM> contacting the outmost electrolysis cells <NUM> of the stack <NUM>.

The electrolyzer of <FIG> further comprises a cell rack <NUM>, wherein the electrolysis cells of the electrolysis stack <NUM> and the means <NUM> for mechanically securing the electrical connection of the electrolysis stack <NUM> are mounted in the cell rack <NUM>. The cell rack <NUM> of the electrolyzer shown in <FIG> comprises two end posts <NUM>, <NUM> carrying a support beam <NUM> on each side. The support beams <NUM> support the electrolysis cells <NUM> in the cell rack <NUM>. The electrolysis cells <NUM> are preferably suspended on the support beams <NUM> on both sides of the rack <NUM>.

As shown in <FIG> the means <NUM> for mechanically securing the electrical connection of the electrolysis stack <NUM> can be arranged to interact with the outmost electrolysis cells <NUM> of the stack in order to exert a defined compressive force on the stack. For example, the means <NUM> for mechanically securing the electrical connection of the electrolysis stack <NUM> shown in <FIG> comprise a pressing plate <NUM> in engagement with the support beams <NUM> that serve as an external tie rod of the means <NUM> in this embodiment. The pressing plate <NUM> is moveable horizontally on the support beams <NUM> in order to compress the multi-cell elements <NUM> of the electrolysis stack <NUM> together with end plates <NUM>, <NUM> providing the power supply. In an operational stage, endplates <NUM>, <NUM> and multi-cell elements <NUM> are in direct contact to each other, so that they are electrically connected in series. To this end, the multi-cell elements <NUM> shown in the drawings are equipped with, preferably flat, exterior back walls <NUM> providing planar contact surfaces for the electrical connection with an adjacent multi-cell element <NUM>.

In alternate embodiments (not shown), the means for mechanically securing the electrical interconnection of the electrolysis stack are attached to at least to, preferably to any two, neighboring multi-cell elements in order to provide a contact pressure for the neighboring multi-cell elements.

In <FIG>, the electrolyzer <NUM> is shown in a maintenance state. In the maintenance state, the means <NUM> for mechanically securing the electrical connection of the electrolysis stack <NUM> are in a loosened state, while the mechanical compression means <NUM> are in a fastened state. As can be seen from <FIG>, the multi-cell elements <NUM> are individually replaceable in the maintenance state, without having to disassemble the electrolyzer <NUM> completely.

As an example, the multi-cell elements <NUM> shown in <FIG> contain four electrolysis cells <NUM>. Preferably, the multi-cell elements <NUM> each contain <NUM> to <NUM>, more preferably <NUM> to <NUM>, electrolysis cells <NUM>. The electrolysis cells <NUM> of the multi-cell element <NUM> are connected electrically in series and in parallel with respect to an electrolyte cycle and product gas stream. Preferably, the electrolysis cells <NUM> of the multi-cell element <NUM> have a cell area in the range of <NUM> to <NUM> square meters. By combining several multi-cell elements <NUM> in one electrolyzer <NUM>, an electrolyzer <NUM> with a nominal capacity in the megawatt range can be provided.

In <FIG>, a first embodiment of a multi-cell element <NUM> to be used in the electrolyzer <NUM> of <FIG> is shown in more detail. The multi-cell-element <NUM> comprises two end parts <NUM>, <NUM>, containing the anode chamber <NUM> and the cathode chamber <NUM> of the outmost electrolysis cells <NUM> of the multi-cell element <NUM>, respectively. The multi-cell element <NUM> further comprises a number of middle parts <NUM> containing the cathode chamber <NUM> and the anode chamber <NUM> of adjacent inner electrolysis cells <NUM> being electrically connected to each other by a shared bipolar partition wall <NUM>. The multi-cell element <NUM> also comprises sheet-like separators <NUM>, being interposed between any two adjacent parts <NUM>, <NUM>, <NUM> of the end parts <NUM>, <NUM> and middle parts <NUM>. The end parts <NUM>, <NUM> and the middle parts <NUM> are preferably sealed with respect to the separators <NUM> by gaskets <NUM> arranged in the respective contact regions of the parts <NUM>, <NUM>, <NUM>.

To better understand the advantages of the invention as compared to the single element design in respect of material requirements and labor costs, the following example is given: A typical electrolyzer of single element design with <NUM> electrolysis cells would contain <NUM> half-shells and <NUM> flange pairs each to be fastened with a set of bolts, which need to be manufactured, handled and assembled. In comparison, an electrolyzer according to the invention with the same number of electrolysis cells and having ten electrolysis cells <NUM> per multi-cell element <NUM> has 2x30 end parts <NUM>,<NUM> and 10x29 middle parts <NUM>, thus a total number of only <NUM> parts <NUM>, <NUM>, <NUM> compared to the <NUM> shell parts of the single element design. Likewise, the number of sets of bolts to be fastened is reduced from <NUM> to <NUM>.

Within the electrolysis cells <NUM> spacers, e.g. in the form of ribs <NUM>, can be provided between the bipolar partition walls <NUM> and the anode <NUM> and/or cathode <NUM>. The spacers serve the purpose to support the electrodes <NUM>, <NUM> within the cell <NUM> at a particularly low distance to the separator <NUM> as to reduce the cell voltage. In particular, the inventive design of the electrolyzer is applicable to zero-gap electrolyzers, in which the electrodes <NUM>, <NUM> are in direct contact with the separator <NUM>. The separator <NUM> may be a membrane or a diaphragm, for example.

As shown in <FIG> the electrolysis cells <NUM> of the multi-cell element <NUM> can be fed with electrolyte by external feed pipes <NUM>, <NUM> with individual inlets to each chamber <NUM>, <NUM> of the electrolysis cells <NUM>. Similarly, an external piping (not shown) may be used to collect electrolyte and/or product gases from the cells <NUM>.

In the embodiment shown in <FIG> the mechanical compression means <NUM> comprise tie rods <NUM> that extend externally across the electrolysis cells <NUM> of the multi-cell element <NUM>. The mechanical compression means <NUM> further comprise end components <NUM> of the multi-cell element <NUM>, wherein the end components <NUM> are engaged with the tie rods <NUM> to exert a compressive sealing force on the electrolysis cells <NUM> of the multi-cell element <NUM>. The end components <NUM> may be formed by the end parts <NUM> being equipped with engagement means, such as perforated protrusions, for the engagement with the tie rods <NUM>. Alternatively, the end components <NUM> may be separate components, as e.g. additional end plates of the multi-cell element <NUM>.

The design of the multi-cell element <NUM> of <FIG> resembles the filter press design electrolyzers, with the differences, that the multi-cell element <NUM> contains a smaller number of individual electrolysis cells <NUM> (preferably in the range <NUM> to <NUM>) and that the mechanical integrity and sealing is already achieved on the level of the multi-cell element <NUM> and not only on the level of the electrolyzers as a whole. Thus, the multi-cell element <NUM> is a self-contained unit that can be exchanged and serviced individually, e.g. in an offsite cell workshop, without affecting the other multi-cell elements <NUM> of the electrolyzer <NUM> at the site of the electrolysis facility.

In <FIG>, a second embodiment of a multi-cell element <NUM> to be used in the electrolyzer <NUM> of <FIG> is shown. In the second embodiment, the mechanical compression means <NUM> comprise two shell parts <NUM>, <NUM>, within which the electrolysis cells <NUM> of the multi-cell element <NUM> are arranged. The shell parts <NUM>, <NUM> each comprise a circumferential flange portion <NUM>, <NUM>. The mechanical compression means <NUM> further comprise a gasket <NUM> arranged between the flange portions <NUM>, <NUM> of the two shell parts <NUM>, <NUM>, and bolts <NUM>. The bolts <NUM> are arranged such as to compress the electrolysis cells <NUM> within the shell parts <NUM>, <NUM> and the gasket <NUM> between the flange portions <NUM>, <NUM> when the bolts <NUM> are fastened. As shown, the shell parts <NUM>, <NUM> may preferably have the form of half-shells.

As compared to the first embodiment of the multi-cell element <NUM>, the multi-cell element <NUM> of <FIG> has a two-stage sealing system. In addition to the single outer gasket <NUM> arranged between the flange portions <NUM>, <NUM> of the two shell parts <NUM>, <NUM>, the electrolysis cells <NUM> are sealed with respect to the separators <NUM> individually, e.g. by inner gaskets <NUM>, arranged in the contact regions of the parts <NUM>, <NUM>, <NUM> of the multi-cell element <NUM>.

The electrolysis cells <NUM> of the multi-cell element <NUM> can be fed with electrolyte by feed pipes <NUM>, <NUM> that are external to the cells <NUM> as in <FIG> but contained within the shell parts <NUM>, <NUM>. A similar piping (not shown) may be used to collect electrolyte and/or product gases from the cells <NUM>. Thereby, the number of inlets and outlets of each multi-cell element <NUM> can be reduced, facilitating the assembly of the electrolyzer <NUM> on site.

Alternatively, the multi-cell element <NUM> shown in <FIG> can be supplied by external piping, distributing to and/or collecting the respective media from each cell <NUM> individually from the outside of the shell parts <NUM>, <NUM>.

In all other respects, the description of the first embodiment shown in <FIG> is applicable to the second embodiment shown in <FIG>, accordingly.

In <FIG>, a third embodiment of a multi-cell element <NUM> to be used in the electrolyzer <NUM> of <FIG> is shown. In this embodiment the mechanical compression means <NUM> comprise circumferential external flange portions <NUM>, <NUM> attached to the end and middle parts <NUM>, <NUM>, <NUM> of the multi-cell element <NUM>, and bolts <NUM> fastening the flange portions <NUM>, <NUM> of adjacent end and/or middle parts <NUM>, <NUM>, <NUM> to each other.

The multi-cell element <NUM> of the third embodiment further contains two internal manifolds <NUM>, <NUM> for distribution of electrolyte to the electrolysis cells <NUM> of the multi-cell element <NUM>. Further internal manifolds could be provided for collection of electrolyte and/or product gases from the cells <NUM>.

In an alternative embodiment not shown the multi-cell element of <FIG> is provided with an external piping as shown in <FIG> instead of the internal manifolds.

In all other respects, the description of the first and second embodiments shown in <FIG> and <FIG> is applicable to the third embodiment shown in <FIG>, accordingly.

In <FIG>, two multi-cell elements according to the embodiment of <FIG> are shown in a side-by-side arrangement. Means <NUM> for mechanically securing the electrical interconnection of the electrolysis stack <NUM> are attached to the two neighboring multi-cell elements <NUM> in order to provide a contact pressure for the neighboring multi-cell elements <NUM>. For example, the means <NUM> can be made of circumferential flanges at both ends of the multi-cell elements <NUM>, wherein the flanges of adjacent multi-cell elements <NUM> are bolted together.

Similar means <NUM> for mechanically securing the electrical interconnection of the electrolysis stack <NUM> may be used in conjunction with all other embodiments of the invention shown in the drawings, as well.

<FIG> shows a variant of the multi-cell element shown in <FIG>, wherein the anode chamber <NUM> and the cathode chamber <NUM> of the outmost electrolysis cells <NUM> of the multi-cell element <NUM>, respectively, have a volume that is larger than the volume of each of the cathode chambers <NUM> and anode chambers <NUM> of the inner electrolysis cells <NUM> by a factor in the range of <NUM> to <NUM>. The enlarged volume of the outmost electrode chambers increases the heat capacity of the stack <NUM> and thus allows for an improved temperature control of the stack.

In all other respects, the description of the embodiment shown in <FIG> is applicable to the variant shown in <FIG>, accordingly.

Claim 1:
Electrolyzer comprising
an electrolysis stack (<NUM>) containing a plurality of panel-like electrolysis cells (<NUM>) in a side-by-side arrangement being electrically interconnected in series,
wherein each electrolysis cell (<NUM>) comprises an anode chamber (<NUM>) with an anode (<NUM>) arranged therein and a cathode chamber (<NUM>) with a cathode (<NUM>) arranged therein, wherein the anode chamber (<NUM>) and the cathode chamber (<NUM>) are separated from one another by a sheet-like separator (<NUM>),
and means (<NUM>) for mechanically securing the electrical interconnection of the electrolysis stack (<NUM>),
characterized in that
the stack (<NUM>) contains at least two multi-cell elements (<NUM>), each comprising a plurality of the electrolysis cells (<NUM>) and mechanical compression means (<NUM>), wherein the electrolysis cells (<NUM>) of each multi-cell element (<NUM>) are held together in a sealed manner by the mechanical compression means (<NUM>), and wherein the means (<NUM>) are configured to mechanically secure the electrical interconnection of the multi-cell elements (<NUM>),
wherein the means (<NUM>) for mechanically securing the electrical interconnection of the electrolysis stack (<NUM>) are arranged to interact with the outmost electrolysis cells (<NUM>) of the stack (<NUM>) in order to exert a defined compressive force on the stack (<NUM>), or
wherein the means (<NUM>) for mechanically securing the electrical interconnection of the electrolysis stack (<NUM>) are attached to at least two neighboring multi-cell elements (<NUM>) in order to provide a contact pressure for the neighboring multi-cell elements (<NUM>).