Method for shelf-life maximization of cells in an assembled electrolyser cell stack adapted for electrolysation of water into hydrogen and oxygen

Abstract

Initially an assembled electrolyser cell stack comprising at least alternatingly,  electrodes and bipolar plate assemblies and  diaphragms is provided. Stack internal process and flow volumes, namely catholyte flow volume and process chambers and anolyte flow volume and process chambers adjacent to and on each side of every diaphragm are simultaneously partially or completely flooded through each of stack internal catholyte manifold and stack internal anolyte manifold with a liquid alkaline conservation medium and O2 side electrolyte inlet connection, H2 side electrolyte inlet connection, anolyte and oxygen gas exit connection and catholyte and hydrogen gas exit connection are each sealed off adjacent to an electrolyser endplate after partially or completely flooding the mentioned stack internal volumes with the fluid conservation medium.

Description

[0001] METHOD FOR SHELF-LIFE MAXIMIZATION OF CELLS IN AN ASSEMBLED ELECTROLYSER CELL STACK ADAPTED FOR ELECTROLYSATION OF WATER INTO HYDROGEN AND OXYGEN

[0002] The present disclosure relates to a method for shelf-life maximization of cells in an assembled electrolyser cell stack adapted for electrolyzing water into hydrogen and oxygen, wherein initially an assembled electrolyser cell stack comprising at least alternatingly, a. Electrodes and bipolar plate assemblies and b. Diaphragms is provided in an assembly process.

[0003] Background of the invention

[0004] Various parts of electrolyser cell stacks of the above kind are subject to natural degradation processes if left in an assembled stack over a prolonged period exposed to air or clean water. Further, some kinds of diaphragms will sustain unrecoverable damage from drying out and even in a protected atmosphere, water will tend to evaporate from the diaphragm arranged in a cell stack which is stored for a long time, leaving uppermost parts of the diaphragms prone to damage. Further, when diaphragms are drenched in clean water this water will pick op CO2 from the atmosphere and will easily reach an acidity therefrom which is below pH 7 and hereby pose a danger to nickel elements in the stack, as nickel is vulnerable to acidic water.

[0005] Summary of the invention

[0006] It is therefore an object of the invention to increase the variety of options when it comes to storing finalized electrolyser cell stacks of the filter-press type build. It is further an object of the invention to provide an electrolyser cell stack which when finalized may be easily filled with a conservation fluid to ensure that the elements within the stack may remain un-changed over a long shelf life period and during transport and installation processes and also to ensure long shelf life of an electrolyser cell stack without any external components, such as pumps, pipes and electrical connections and power supply.

[0007] This is achieved by a method as mentioned above, wherein stack internal process and flow volumes, namely a catholyte flow volume and process chamber on one side of each diaphragm and an anolyte flow volume and process chamber adjacent to and on an opposed sided of each of the diaphragms are simultaneously partially or completely flooded through each of stack internal catholyte manifold and stack internal anolyte manifold with a liquid and alkaline conservation medium after the assembly process and whereby 02 side electrolyte (anolyte) inlet connection, H2 side electrolyte (catholyte) inlet connection, anolyte and oxygen gas exit connection and catholyte and hydrogen gas exit connection adjacent to an electrolyser stack endplate are each sealed off after partially or completely flooding the mentioned stack internal volumes with the fluid conservation medium.

[0008] Having performed the above, the electrolyser cell stack may be safely stored for a prolonged time. Hereby is achieved, a combination of improved flexibility as cell stack electrolysers for large scale installations may be produced well in advance of assembly of plants on site. And even during site preparations, some electrolyser cell stacks may be installed and not energized for hydrogen and oxygen production for a protracted period, while remaining parts of the site or recipients of the gasses to be produced are finalized. During all such processes, the stacks filled with the conservation liquid will not undergo any noteworthy changes and may thus safely be utilized after being installed in and connected to a plant having the required electrolyte fluids and electrical power supply.

[0009] In an embodiment, the electrolyser cell stack a. is initially flooded completely with the mentioned conservation medium, b. then subjected to a pressure / and or leak-test with the conservation medium as pressure carrying medium, c. and lastly the conservation medium level inside of the stack is adjusted to a predefined level with respect to inflow and outflow manifold channels of the stack. Adjusting the level of the conservation medium is done simply by tapping some of the conservation medium out of the stack. It is here preferred to reduce the level of conservation medium inside the stack to a level below the two inflow manifolds, which will also ensure that the outflow manifolds are essentially free of conservation medium. An advantage of this embodiment is, that no individual cells are in fluid and thus electrically conductive contact with each other. This may be important, as cells, especially electrodes, left in electrically conductive contact may deteriorate chemically through galvanic cell activity. This is avoided by ensuring that no electric current may pass between cells via the conservation medium filled manifold flow channels. Even if not left submerged in the conservation medium the upper parts of cells will nevertheless have had all surface parts well inundated in the medium and thereby the chances of traces of detrimental components being left on or developing on such surfaces will be diminished.

[0010] In an embodiment of the method, an electrolyser cell stack including the conservation medium is stored between two weeks and eight weeks or is preferably stored between two and sixteen weeks more preferred is stored between two and twenty-six weeks or most preferred is stored between two and fifty-two weeks from its assembly and to its first use in an electrolyser plant.

[0011] Such prolonged storage times would in prior art, require special provisions to ensure that all parts of a cell constructions remain un-affected by such storing, or longer shelf life is simply not an option. This added a further onus on production capacity for the establishment of larger electrolyser facilities, which may not be operational until all parts thereof are installed.

[0012] In an embodiment, the conservation medium is comprised of a KOH water solution.

[0013] In an embodiment, the KOH water solution has a concentration of between 1.0 pM and 100 mM KOH in water

[0014] In an embodiment, the KOH water solution has a concentration of between 10.0 pM 100 pM KOH in water. Concentrations given according to SI units and prefix notation: https: / / da.wikipedia.org / wiki / SI-pr%C3%A6fiks

[0015] It is noted that the water part of the conservation medium should initially be as clean as the water added to the electrolyser unit while in use. This requires the water to have a conductivity at least below 5 pS / cm.

[0016] The sealing of stack inlet and stack outlets will ensure, that the conservation medium stays within the stack also if the stack is overturned during handling thereof. The concentration of the KOH in the conservation medium ensures, that the metal parts and possible coatings on electrodes remain well conserved and protected against corrosion. Also, the diaphragm will stay well soaked in an alkaline solution and protected against drying out. This is achieved without polymer and metal parts being subject to detrimental effects of the conservation medium. It is further to be noted that the conservation medium is not a serious health hazard to the employees, who needs to work with it during filling of the stack and possible pressure / leak testing, or in case the medium is discarded prior to commencement actual use of the stack.

[0017] It is possible to use NaOH as the added alkali component and staying with the same molar concentration as mentioned for KOH would provide a similar alkalinity (pH) of the conservation medium. Some mixing of a NaOH containing conservation medium with the high concentration KOH usually used as electrolyte in alkaline electrolysers will not disturb the operation of a stack or stacks in a plant.

[0018] It is an option to also add a chemical buffer to the KOH or NaOH water solution, such that exposure to atmospheric air or other acidity increasing substances will not cause any notable change in alkalinity of the conservation medium. Preferably, a K2CO3 / KHCO3 containing substance is included in the conservation medium residing in the flow and / or process volumes of the stack.

[0019] In an embodiment of the method, prior to adding the electrolyte to the stack, inlet connection seals are opened and any conservation medium leaving the stack is piped to a drain, while outlet connection seals are opened to allow air to fill the volumes as the conservation medium leaves the stack.

[0020] Any conservation fluid (in case any is present above this level) which resides in the stack at a higher level than the inlet connections may now be drained off, as the outlets connected to the atmosphere allows air to be taken in to thereby supplant the liquid draining out of the catholyte and anolyte flow volume and process chambers of the electrolyser cell stack.

[0021] Alternatively, the inlet connections are both connected to each their supply of electrolyte, while outlet connections are connected to a drain, and by gently pushing in electrolyte through the two inlets, gradually all the conservation fluid will be pushed out of the electrolyser cell stack, and when most or all of the conservation fluid is out of the stack, the outlet connections are connected to the electrolyte circulation system of the plant.

[0022] In an embodiment of the method a rinse and / or flushing operation using clean water such as demineralized water is instigated prior to adding electrolyte to the stack. Here the stack, during at least one rinse and / or flushing operation is filled with clean water, which is subsequently pumped out of the stack along with any traces of conservation medium and buffer substance.

[0023] This leaves the internal flown and process volumes of the stack essentially free of traces of especially buffer chemical, which if residing in an electrolyser plant for producing hydrogen may provoke the formation of solids, such as salts with low solubility in the electrolyte, and any such elements are in risk of causing clogging of flow channels within the stack.

[0024] When no buffer is included, the electrolyte circulation system of a plant is coupled to the in- and outlets, and a concentration of the electrolyte residing in the plant outside of the electrolyser cell stack is initially higher than desired for normal operation. In a step prior to normal operation, the electrolyte in the plant and the conservation medium are now circulated in the entire plant comprising stacks and plant vessels, notably the separator vessels, heat exchangers and pipes, and the two fluids: the conservation fluid and the high concentration electrolyte are mixed, to finally reach the desired concentration of the electrolyte. This is possible as the conservation fluid is in fact a diluted form of the electrolytes used in the plant. When the two fluids are fully mixed, electrolyzation may commence.

[0025] In a further aspect of the invention an electrolyser cell stack adapted to electrolyse water into hydrogen and oxygen comprising at least alternatingly, a. electrode and bipolar plate assemblies and b. diaphragms is provided.

[0026] According to this further aspect, a conservation medium comprising at least an alkaline liquid resides in the stack on each side of the diaphragms in all cells and further the cell stack inlets and outlets or further connections are sealed off from the atmosphere optionally by valves mounted adjacent to an electrolyser cell stack endplate.

[0027] An electrolyser cell stack of this kind will have a very long shelf life, and this allows for important flexibility during production and installation, which is important in cases where a major plant is comprised of a large number of electrolyser cell stacks, which are produced and assembled at a fabrication site, and then transported as one- piece units to the hydrogen and oxygen production site. The sealing off valves, provided adjacent to an endplate may be well known on / off valves. But other means such as simple water lock tubes or one-way diaphragm valves may be used to ensure, that atmospheric gasses are prevented from free access to the interior of the stack.

[0028] In an embodiment of the electrolyser cell stack, the conservation medium comprising a KOH solution.

[0029] In a further embodiment, the KOH solution has a concentration of between 1.0 pM and 100 mM KOH in water. In a further embodiment, the KOH solution has a concentration between 10.0 pM 100 pM KOH in water.

[0030] These concentrations will ensure, that all elements, be they metal based, or polymer based or other shall have a very long shelf life where they are contacted by the conservation medium. And as the stack internal flow volumes have been sealed off from the surroundings there are no noteworthy hazards related to handling the stack with the conservation medium inside.

[0031] In an embodiment of the electrolyser cell stack, the water part of the conservation medium is initially pure water defined by a conductivity at or below 5.0 pS / cm. “Initially” in this connection means that prior to the addition of the alkaline or possible buffer, the water is clean, and at least as clean as the water added to the electrolyser unit while in use. This requires the water to initially have a conductivity at least below 5 pS / cm.

[0032] In case some or all of the conservation medium stays in the electrolyser plant after an installation of the stack with conservation medium therein, it is important that the purity of the water part of the conservation medium is just as good as the purity of the water added to be consumed during electrolysis in the electrolyser plant for the generation of the gases hydrogen and oxygen.

[0033] In an embodiment an electrolyser cell stack is presented, wherein the conservation medium further comprises a buffer substance preferably K2CO3 / KHCO3.

[0034] By having a buffer chemical as part of the conservation medium, an increased safety against formation of acidic components within the stack during prolonged storage is achieved.

[0035] In an embodiment, the electrolyser cell stack comprises: a. an H2 side electrolyte inlet connection which is connected to a stack internal catholyte manifold which manifold connects the H2 side electrolyte inlet connection to each of catholyte flow volume and process chambers at lowermost parts of each catholyte flow volume and process chamber, and an outlet manifold which manifold connects a hydrogen side outlet connection to these same catholyte chambers at an uppermost part of these catholyte flow volume and process chambers, b. an 02 side electrolyte inlet connection which is connected to a stack internal anolyte manifold which manifold connects the 02 side electrolyte inlet connection to each of anolyte flow volume and process chambers at a lowermost part of each anode side analytic flow volume and process chamber, and an outlet manifold connecting an oxygen side outlet to these same anode side analytic flow volume and process chambers at an uppermost part of these side analytic flow volume and process chambers, such that by adding the conservation fluid to the two inlet manifolds simultaneously, all chambers are filled from the lowermost parts thereof and to the uppermost parts thereof, leaving no parts of diaphragms or bipolar plates and electrodes unsubmerged.

[0036] The filling of all flow and process volumes within the electrolyser stack ensures that all stack internal components, at least initially are well submerged in the conservation fluid.

[0037] In an embodiment the electrolyser cell stack has the hydrogen side and oxygen side outlets arranged at a low potential endplate and further, the electrolyser cell stack has the hydrogen and oxygen side electrolyte inlet connections also provided at the low potential endplate.

[0038] The oxygen side and the hydrogen side outlets may in principle be provided at any of the high or low potential endplate, however for the purpose of adding a conservation liquid it is preferable that they are assembled at the one and same endplate. And for the purpose of driving the electrolyser after installation it is further advantageous to have the connections for electrolyte and mixture of electrolyte and gas provided at a low potential endplate.

[0039] It should be emphasized that the term "comprises / comprising / comprised of' when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0040] Brief description of the drawings

[0041] In the following, the invention will be described in greater detail with reference to embodiments shown by the enclosed figures. It should be emphasized that the embodiments shown are used for example purposes only and should not be used to limit the scope of the invention.

[0042] Fig. 1 shows a schematic representation of the flow conduits within the cells 30 in a cell stack 20,

[0043] Fig. 2 shows a schematic representation of an electrolyser cell stack 19, comprising a cell stack 20.

[0044] Detailed description of the embodiments

[0045] It is to be noted that the figures and the above description have shown the example embodiments in a simple and schematic manner. Many of the specific mechanical details have not been shown since the person skilled in the art should be familiar with these details and they would just unnecessarily complicate this description. For example, the specific materials used and the specific method have not been described in detail since it is maintained that the person skilled in the art would be able to find suitable materials and suitable processes to manufacture the stack according to the current invention.

[0046] The individual cells 30 in a cell stack 20 are schematically shown in Fig. 1. An individual cell 30 comprise an anode 45 situated in an anolyte flow volume and process chamber 34, which receives a flow of anolyte through a cell dedicated anolyte flow channel 27. A stack internal anolyte manifold 26 supplies anolyte to all the cell dedicated anolyte flow channels 27 as also indicated in Fig. 1. In Fig. 2, a dashed line representation of the cell dedicated anolyte flow channel 27 is provided on the exterior of the low potential end plate 18, and as seen, the flow channel 27 connects to a lowermost part 40 of anolyte flow volume and process chamber 4034. In Fig. 1 , the low potential endplate 18 is indicated by a dashed vertical line 18, and valves or the like elements 9, 10, 11 , 12 are indicated schematically adjacent to the low potential endplate 18.

[0047] In Fig. 2, Arrows 36 indicates flow in each half-cell moving the electrolyte (catholyte or anolyte) from the lowermost part 41 , 40 to the uppermost parts 15; 16 of the catholyte and anolyte and catholyte flow volume process chambers 33; 34, or simply catholyte and anolyte process chambers 33; 34, or catholyte process chambers, or stack internal process and flow volumes, or stack internal volumes, or cathode / anode side process chambers, process chambers, or chambers. The stack internal anolyte manifold 26 is connected to 02 side electrolyte or anolyte inlet connection 21 at the external side of an endplate 18, usually a low potential endplate 18. In Fig. 1 and 2, cell dedicated anolyte and oxygen evacuation flow channel 24 is shown, and in Fig. 1, the stack internal anolyte and oxygen manifold 14 is also shown. In Fig. 2 the anolyte and oxygen gas exit connection 42, as well as the catholyte and hydrogen gas exit connection 43 are shown adjacent to the low potential end plate 18. Also in Fig. 2, the 02 side electrolyte or anolyte inlet connection 21 and H2 side electrolyte or catholyte inlet connection 22 are shown.

[0048] A cell 30 further comprises a diaphragm 32, which is ion-conducting, but prevents the produced 02 and H2 gas bubbles from being mixed. Opposed to the anolyte flow volume and process chamber 34, the cell comprises a cathode 46 situated in a catholyte flow volume and process chamber 33, which receives a flow of catholyte through a cell dedicated catholyte flow channel 28. A stack internal catholyte manifold 25 supplies catholyte to all of the cell dedicated catholyte flow channels 28 as also indicated in Fig. 1. In Fig. 2 a dashed line representation of the cell dedicated catholyte flow channel 28 is provided on the exterior of the high potential end plate 18, and as seen, the flow channel 28 connects to a lowermost part 41 of catholyte flow volume and process chamber. Arrows 36 indicates flow in each halfcell moving the electrolyte (catholyte or anolyte) from the lowermost part 41 , 40 to the uppermost parts 16, 15 of the anolyte and catholyte process chambers. The stack internal catholyte manifold 25 is connected to H2 side electrolyte or catholyte inlet connection 22 on an external side of an endplate 18, usually a low potential endplate 18. In Fig. 1 and in Fig. 2, cell dedicated catholyte and hydrogen evacuation channel 23 is shown, and in Fig. 1 , the stack internal catholyte and hydrogen manifold 13 is also shown. In Fig. 2 the catholyte and hydrogen gas exit connection 43 is shown adjacent to the low potential end plate 18.

[0049] In Fig. 2 a dashed line indication of outline or circumference 31 of all individual half cells 30 is also provided.

[0050] If a flow of fluid conservation medium is added to both of H2 side electrolyte or catholyte inlet connection 22 and 02 side electrolyte or anolyte inlet connection 21 simultaneously, all of the cells 30 in the stack of cells 20 between the endplates 17, 18 may be filled with the conservation medium, and leaving open the catholyte and hydrogen gas exit connection 43 as well as the anolyte and oxygen gas exit connection 42 during such a filling of the cells 30, will allow a flow of air out of the stack during the filling up of the: i. anolyte and catholyte flow channels 27; 28, ii. anolyte and catholyte flow volume and process chambers 33, 34, and finally, iii. the cell dedicated evacuation channels 23; 24.

[0051] Once this point has been reached, a flow along the two manifolds 13, 14 will commence and a flow out of the two gas exit connections 42; 43 will be observable. And at this point a conclusion of the filling operation may be undertaken by closing valves 11,12 (see Fig. 1) arranged on the two gas exit connections 42; 43 and ending the pumping action with the conservation medium (not shown).

[0052] In Fig. 2, two so-named current injectors 29 are seen, with one current injector at each end of the cells in cell stack 20, and each placed between an endplate 18; 19 and the cell in cell stack 20. The electrical current which drives the electrolyses process in the individual cells as it passes through the cells in the stack, running alternatingly through a bipolar plate and two electrodes and through a diaphragm, is injected into the cells through the sturdy metal current injectors 29 of which only the connection points are visible. Current may travel either way through the stack: from the high potential to the low potential endplate, or vice-versa, depending on whether the high potential endplate the current injector is seated with is a plus pole or minus pole current injector 29. The current injectors 29 are thus always seated in pairs in a stack, and one will effectively serve as a current collector while only the other one of the pair serves as a current injector, however this is not material to the function of the present invention but may serve to better explain the terminology adhered to in the above description and in the claims. Pairs of stacks may have their current injectors 29 at low potential electrically inter-connected, such that electric current passes from a first to a second stack at the low potential current collectors, making the one so named current collector at the low potential endplate of one of such a pair of stacks, functionally a current injector.

[0053] The nature of the conservation fluid is preferably alkaline to ensure internal cell elements against corrosion, and it is preferred to use a weak KOH water solution, such as a KOH water solution between 1.0 pM and 100 mM KOH or more preferred a solution between 10.0 pM and 100 pM KOH in water. A NaOH composition may alternatively be used. During a procedure for emptying out the conservation medium from the stack, some traces of the conservation medium may remain within the stack, such as conservation fluid having soaked the diaphragms or residing as wet surfaces within each cell or in various flow channels. This fluid will become part of the electrolyte composition of the electrolyser unit when a plant is to be used, however a small degree of pollution from NaOH will not disturb the function of the high concentration KOH usually used in alkaline electrolyser plants.

[0054] The use of a buffer as part of the conservation medium composition on order to ensure that the pH level inside the cells stays within predefined limits may be preferred, especially in cases where the stacks are to be stored for a long period of time, (6 months or more). A useful buffer is K2CO3 / KHCO3, which may keep the pH of the conservation fluid around 10 even if some CO2 is inadvertently absorbed in the conservation fluid. Use of a buffer will require a flushing operation of the stack with clean water prior to use of the stack as the buffer may provoke the formation poorly soluble salts during the water electrolysation process in case traces of the buffer remains in the electrolytes during electrolysation, and such salts presents a hazard to the continued functioning of a stack. If a stack is initially filled completely with a conservation medium as explained, a necessary leak and / or pressure test may now be performed using the conservation medium as test medium. The week alkaline concentration will not expose employees to any further health risk and needs to be performed for all stacks. And using the conservation medium as leak / pressure test medium relieves the employees of the task of emptying at least a part of the fluid out of the stack.

[0055] It should be further noticed that in an embodiment of the invention, the stack is left for storage with only a lower part thereof filled with the conservation medium. In Fig. 2 a vertical line 44 is indicated at the low potential endplate 18. The line 44 indicates a level just below the oxygen (02 side) electrolyte inlet connection 21 and the hydrogen (H2 side) inlet connection 22. If the conservation fluid remains under the uppermost filling level 44, none of the four manifold channels will contain a fluid level and it is not possible for electric current to pass through a fluid connection from one cell to another. This further ensures the cells and especially the electrodes against galvanic deterioration during storage with the conservation fluid. If a pressure or leak test is to be performed with the conservation fluid, the stack will have to initially be filled up for the purpose of the test, and then emptied down to the uppermost filling level 44. At the hydrogen production site, where the stack is to be used, electrolyte may be added directly to the stack, provided that the conservation medium holds no buffer chemical. If a buffer chemical is part of the conservation medium, a flush or rinsing procedure will be needed, such as by firstly pumping out the conservation medium, then filling up the stack completely with de-mineralized water, then pump this rinsing medium out of the stack, and optionally repeat this procedure until a satisfactory conductivity of the rinsing water is reached

[0056] It is to be noted that the figures and the above description have shown the example embodiments in a simple and schematic manner. Many of the specific mechanical details have not been shown since the person skilled in the art should be familiar with these details and they would just unnecessarily complicate this description List of parts

[0057] 9 02 side electrolyte inlet valve

[0058] 10 H2 side electrolyte inlet valve

[0059] 11 Anolyte and oxygen exit valve

[0060] 12 Catholyte and hydrogen exit valve

[0061] 13 Stack internal catholyte and hydrogen manifold

[0062] 14 Stack internal anolyte and oxygen manifold

[0063] 15 Uppermost part of anolyte process chamber

[0064] 16 Uppermost part of catholyte process chamber

[0065] 17 High potential endplate

[0066] 18 Low potential endplate

[0067] 19 Electrolyser cell stack

[0068] 20 Cells in cell stack

[0069] 21 02 side electrolyte or anolyte inlet connection

[0070] 22 H2 side electrolyte or catholyte inlet connection

[0071] 23 Cell dedicated catholyte and hydrogen evacuation channel

[0072] 24 Cell dedicated anolyte and oxygen evacuation channel

[0073] 25 Stack internal catholyte manifold

[0074] 26 Stack internal anolyte manifold

[0075] 27 Cell dedicated anolyte flow channel

[0076] 28 Cell dedicated catholyte flow channel

[0077] 29 Current injectors

[0078] 30 Individual cell

[0079] 31 Indication of outline of individual half-cell

[0080] 32 Diaphragm

[0081] 33 Catholyte flow volume and process chamber

[0082] 34 Anolyte flow volume and process chamber

[0083] 35 Bipolar plate

[0084] 36 Arrows indicating flow in each half-cell or process chamber

[0085] 37 First electric current injection electrode

[0086] 38 Second electric current injection electrode

[0087] 40 Lowermost part of anolyte flow volume and process chamber

[0088] 41 Lowermost part of catholyte flow volume and process chamber 42 Anolyte and oxygen gas exit connection

[0089] 43 Catholyte and hydrogen gas exit connection

[0090] 44 Uppermost filling level to keep manifold channels free of conservation fluid

[0091] 45 Anode 46 Cathode

Claims

Claims1 . A method for shelf-life maximization of cells (30) in an assembled electrolyser cell stack (19) adapted for electrolysation of water into hydrogen and oxygen, wherein initially an assembled electrolyser cell stack (19) comprising at least alternatingly, a. electrodes (45; 46) and bipolar plate (35) assemblies and b. diaphragms (32) is provided in an assembly process, wherein stack internal process and flow volumes (33; 34), namely catholyte flow volume and process chambers (33) and anolyte flow volume and process chambers (34) adjacent to and on each side of every diaphragm (32) are simultaneously, and partially or completely flooded through each of stack internal catholyte manifold (25) and stack internal anolyte manifold (26) with a liquid alkaline conservation medium after the assembly process, and wherein- an 02 side electrolyte inlet connection (21),- a H2 side electrolyte inlet connection (22),- an anolyte and oxygen gas exit connection (42), and- a catholyte and hydrogen gas exit connection (43) are each sealed off adjacent to an electrolyser endplate after partially or completely flooding the mentioned stack internal process and flow volumes (33; 34) with the fluid conservation medium.

2. The method according to claim 1 , wherein the electrolyser cell stack (19) flow and process volumes (33, 34) a. are initially flooded completely with the conservation medium, b. then the cell stack (19) is subjected to a pressure / and or leak-test with the conservation medium as pressure carrying medium, and c. lastly the conservation medium level inside of the electrolyser cell stack (19) is adjusted to a predefined level with respect to inflow and outflow manifold channels (25; 26; 13; 14) of the electrolyser cell stack (19).

3. The method according to claim 1 or claim 2, wherein the electrolyser cell stack (19) including the conservation medium is stored between two weeks and eightweeks, or is stored between two and sixteen weeks, or is stored between two and twenty-six weeks, or is stored between two and fifty-two weeks from its assembly and to its first use in an electrolyser plant.

4. The method according to any one of the claims 1-3, wherein the conservation medium comprises a KOH water solution.

5. The method according to claim 4, wherein the KOH water solution, is a solution of between 1.0 pM and 100 mM KOH in water.

6. The method according to claim 5, wherein the KOH water solution, is a solution of between 10.0 pM and 100 pM KOH in water.

7. The method according to any one of the preceding claims, wherein a buffer substance is included in the conservation medium residing in the flow and / or process volumes of the stack.

8. The method according to claim 7, wherein the buffer substance is K2CO3 / KHCO3.

9. the method according to any one of the preceding claims, wherein, prior to adding the electrolyte to the electrolyser cell stack (19), an 02 side electrolyte inlet valve (9) and a H2 side electrolyte inlet valve (10) are opened, and any conservation medium leaving the electrolyser cell stack (10) is piped to a drain, while an anolyte exit valve (11) and a catholyte exit valve (12) are opened to allow air to fil the volumes, as the conservation medium leaves the electrolyser cell stack (19).

10. The method according to any one of the preceding claims, wherein a rinse and / or flushing operation using clean water such as demineralized water is instigated prior to adding electrolyte to the stack, whereby the stack during at least one rinse and / or flushing operation cycle is filled with clean water, which is subsequently pumped out of the stack along with traces of conservation medium and added buffer substance.

11. An electrolyser cell stack (19) configured to electrolyze water into hydrogen and oxygen comprising at least alternatingly, a. electrode (45; 46) and bipolar plate (35) assemblies, and b. diaphragms (32), wherein a catholyte flow volume and process chamber (33), and an anolyte flow volume and process chamber (34) is provided on each side of each diaphragms (32), wherein a conservation medium comprising at least an alkaline liquid resides in the electrolyser cell stack (19) on each side of the diaphragms (32) in all cells (30) and that the electrolyser cell stack inlet connections (21 ; 22) and outlet evacuation channels (23; 24) or further connections are sealed off from the atmosphere by valves (9; 10; 11; 12) mounted adjacent to an electrolyser stack endplate (18).

12. The electrolyser cell stack (19) according to claim 11, wherein the conservation medium comprises a KOH solution13. The electrolyser cell stack (19) according to claim 12, wherein the KOH solution is between 1.0 pM and 100 mM KOH in water14. The electrolyser cell stack (10) according to claim 12 or 13, wherein the conservation medium comprises a KOH solution of between 10.0 pM 100 pM KOH in water.

15. The electrolyser cell stack (10) according to any one of the claims 11-14, wherein the water part of the conservation medium is initially pure water defined by a conductivity at or below 5 pS / cm.

16. The electrolyser cell stack (10) according to any one of the claims 11-15, wherein the conservation medium comprises a buffer substance.17 The electrolyser cell stack (10) according to claim 16 wherein the buffer substance comprises K2CO3 / KHCO3.

18. The electrolyser cell stack (19) according to any one of the claims 11-17, wherein the electrolyser cell stack (19) comprises: a. an H2 side electrolyte inlet connection (22) which is connected to a stack internal catholyte manifold (25) connecting the H2 side electrolyte inlet connection (22) to each of catholyte flow volume and process chambers (33) at a lowermost part (41) of each catholyte chamber and an outlet manifold(13) which manifold connects a hydrogen side outlet connection (43) to these same cathode side process chambers (33) at an uppermost part (16) of these process chambers (33), and b. an 02 side electrolyte inlet connection (21) which is connected to a stack internal anolyte manifold (26) connecting the 02 side electrolyte inlet connection (21) to each of anolyte flow volume and process chambers (34) at a lowermost part of each anode side chamber (40) and an outlet manifold(14) connecting an oxygen side outlet connection (42) to these same anode side process chambers (34) at an uppermost part (15) of these process chambers (34), such that by adding the conservation fluid to the two inlet manifolds (25; 26) simultaneously, all chambers (33; 34) are filled from the lowermost parts (41; 40) thereof and towards the uppermost parts (16, 15) thereof, leaving no parts of diaphragms (32) or bipolar plates (35) and electrodes (45, 46) un-submerged up until at least a liquid level in the stack below the H2 side electrolyte inlet connection (22) and below the 02 side electrolyte inlet connection (21).

19. The electrolyser according to claim 18, wherein the electrolyser cell stack (19) has the hydrogen side and oxygen side outlet connections (43; 42) arranged at a low potential endplate (29), and in that the electrolyser cell stack (19) has the hydrogen and oxygen side electrolyte inlet connections (22; 21) also provided at the low potential endplate (29).

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