Water electrolyser stack having a range of half-cells frames

Abstract

Water electrolyser stack having a range of half-cell frames which each circumscribes one of an anolytic or a catholytic process chamber and which half-cell frames are arranged and aligned in an array between a proximal electric current injector / collector plate and a distal electric current injector / collector plate, and where each half-cell frame comprises an embedded furrow flow channel adapted to serve an electrolyte flow from a stack internal inflow manifold channel to a corresponding anolytic or catholytic reaction chamber and an embedded furrow flow channel adapted to serve an electrolyte and gas outflow from a corresponding anolytic or catholytic reaction chamber to a corresponding stack internal manifold channel wherein each of the embedded furrow flow channels comprise at least one fluid and / or gas trap section.

Description

[0001] WATER ELECTROLYSER STACK HAVING A RANGE OF HALF-CELLS FRAMES

[0002] The present invention relates to a water electrolyser stack having a range of halfcells frames.

[0003] Background of the invention

[0004] The prior art design in alkaline electrolyser stacks of the filter press type, of the conduits serving individual half-cells, enables ionic flow through the lye in the conduit, also during periods where lye is stagnant and not circulated such as when pumps are not active. The ionic connection between cathodes and cathodes, anodes and anodes, and cathodes and anodes, allows for a rapid discharge current during periods where the stack is turned off electrically (no applied potential). This drives degradation of the electrodes, shortening the lifetime of the stack.

[0005] Prior art reference: Abdel Haleem, Ashraf, et al. “Effects of Operation and Shutdown Parameters and Electrode Materials on the Reverse Current Phenomenon in Alkaline Water Analyzers.” Journal of Power Sources, vol. 535, July 2022, looks into this issue and quantify the reverse electric currents which are responsible for degradation, with and without the pumps running in a model electrolyzer. Their findings show that if gasses are allowed to stay stagnant in the electrolyzer, the degrading currents are limited.

[0006] The invention seeks to utilize these findings by a re-design of the conduits serving individual half-cells in an electrolyser stack adapted for production of hydrogen and oxygen by alkaline and possibly pressurized electrolyzing of water.

[0007] Summary of the invention

[0008] Water electrolyser stack having a range of half-cells frames which each circumscribes one of an anolytic or a catholytic reaction chamber and which half- cells frames and half-cell reaction chambers are arranged and aligned in an array between a proximal electric current injector / collector plate and a distal electric current injector / collector plate, whereby catholyte and anolyte stack internal inflow manifold channels for the two electrolytes are provided as through-going openings in half-cell frames and wherein further stack internal outflow manifold channels for each one of two electrolytes and respective product gas are provided as through- going openings in half-cell frames, and where each half-cell frame further comprises an embedded furrow flow channel adapted to serve an electrolyte flow from a stack internal inflow manifold channel in a half-cell frame to a corresponding anolytic or catholytic reaction chamber and an embedded furrow flow channel adapted to serve an electrolyte and gas outflow from a corresponding anolytic or catholytic reaction chamber to a corresponding stack internal manifold channel.

[0009] According to the invention, each of the embedded furrow flow channels comprise at least one fluid and / or gas trap section.

[0010] The new design of the conduit traps gasses in the gas trap section between trapped fluids when the pumps are turned off and gas dissolved in the fluid electrolyte form bubbles which rise upwards into the gas trap or traps to form pockets of trapped gasses. As the gasses are trapped, the conductivity of the piece of gas filled conduit drops markedly. This removes or drastically limits the ionic connection between electrodes, which again result in a slower degradation of the electrodes.

[0011] Additionally, the removal of the ionic connection enables the application of protective electrical bias potential that does not produce gasses. With a ionic connection established between half-cells through the liquid filled conduits known from prior art designs, there exists an electrical potential drop over the manifold. Each electrode is positioned in this electrical potential drop, which makes the attempts of protective electrical biases unwarranted, as some of the electrodes will begin to produce hydrogen or oxygen, which will cross the diaphragms and at low or no electrolyte flow through the stack will increase the risk of explosive mixtures of oxygen and hydrogen forming withi the stack. If the electrodes are isolated from the electrical potential drop as will be possible with the design according to the invention, the gas production is eliminated, and protective electrical bias control is made feasible. In an embodiment of the invention, fluid and / or gas trap sections are provided proximal to the through going openings in the half-cell frame. This ensures the longest conduit between the gas trap and the inflow distributor, such that as much gas as possible will be trapped in the embedded furrow flow channel, to thereby maximize the resistance provided by the gas trapped in the gas trap, bearing in mind, that the inner surfaces of the gas filled channel parts will be wet with the electrolyte and thus form an electric current path, however much smaller (with higher resistance) than the electric current path represented by the electrolyte filled channel, known from prior art.

[0012] In an embodiment of the invention, any one of embedded furrow flow channels proximal its connection to stack internal manifold channel comprises at least two generally vertically extending furrow flow sections, which sections are interconnected pairwise by a generally horizontal furrow flow section.

[0013] Each such pair of interconnected furrow flow sections will form either a U-shaped or an inverse U-shaped furrow flow channel, and thus an active gas trap section is ensured whether the furrow flow channel connects a stack internal manifold channel with a higher positioned outflow distributer from a half-cell or connects a stack internal manifold channel with a lower positioned inflow distributer from a half-cell forming an anolyte or catholyte process chamber. Generally vertical means that any released bubbles will travel in a preferred direction from a lower towards a higher position in a given channel when the fluid flow is not active, and generally horizontal means that the bubbles in the fluid, absent fluid flow in any direction, will stay where they are formed, and not travel in either direction in the channel.

[0014] In an embodiment each fluid flow furrow in a cell frame is arranged as an unbranched flow channel.

[0015] This ensures that only one flow path between the manifold channel and a given halfcell process chamber is provided and considerations of short circuits with respect to the trapped gas and / or liquid is not required. It is to be noticed that inflow distributor and outflow collectors provided in the half-cell frames may be shaped as manifold elements themselves, and are not considered parts of the embedded furrow flow channels in each half-cell but considered part of the cell internal flow channels in each cell.

[0016] In an embodiment, the embedded furrow flow channel adapted to serve an electrolyte flow from a stack internal anolyte or catholyte manifold channel to a corresponding half-cell, as well as the embedded furrow flow channel adapted to serve an electrolyte and gas outflow from a half-cell to a stack internal electrolyte and gas manifold channel are provided in the same vertical half plane of a given half-cell frame when the stack is arranged for production.

[0017] By the provision of the two furrow flow channels in one and the same half plane of a half-cell frame, this half-cell frame may be used to serve either an anolytic or a catholytic process chamber with in- and outlet, simply by positioning the half-cell frame, either un-rotated or in a 180 degrees rotational orientation around the cell stack axis during assembly. The use of one and the same cell frame design throughout a cell stack has advantages production wise, however it demands symmetrical designs also in places where it may not benefit flows in and out of the individual process chambers.

[0018] In an embodiment, the embedded furrow flow channel adapted to serve an electrolyte flow from a stack internal anolyte or catholyte manifold channel to a corresponding half-cell and the embedded furrow flow channel adapted to serve an electrolyte and gas outflow from a half-cell to a stack internal electrolyte and gas manifold channel are provided in opposed vertical half planes of any given half-cell frame when the stack is arranged for production.

[0019] This embodiment does not allow the design of a half-cell frame which is shaped to serve a catholyte reaction chamber and to also serve the anolyte reaction chambers with inflow and outflow channels by simple rotation of alternating cell frames in a stack, as the rotation of the half-cell frame cannot shift between connection of anolyte and catholyte manifold channels. However, dedicated half-cell frames adapted to serve as anolytic and catholytic reaction chambers respectively allows the embedded furrow flow channels to be adapted to anolyte and catholyte flows respectively. This also allows for dedicated inflow which are different from the outflow distributers which is advantageous.

[0020] In an embodiment, the at least one fluid and / or gas trap section in a furrow flow channel is of the duck bill type.

[0021] A duck bill type valve is actually a counterflow valve, but at the same time, these valves will cut off direct electrical current connectivity between the reaction chamber and the corresponding manifold inflow cannel feeding catholyte and anolyte respectively to the reaction chambers whenever the electrolyte pumps are turned off, and there is no flow into and out of the half-cells. At the same time the duckbill type valves may serve as gas traps, such that gas will accumulate in front of the duckbill valve, and will not be allowed to leak back into a higher positioned stack internal anolyte or catholyte manifold channel.

[0022] 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.

[0023] Brief description of the drawings

[0024] 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.

[0025] Figure 1 shows a plane view of an embodiment of a cell frame according to the invention, with gas trapped in the flow channels,

[0026] Figure 2 shows the embodiment in Fig. 1 however with electrolyte filled flow channels,

[0027] Figure 3 is a plane view of an embodiment having dedicated anolytic and catholytic chamber half-cell cell frames, Figure 4 shows the embodiment in Fig. 3 with a further secured fluid / gas trap, Figure 5 shows the embodiment in Fig. 4, however with the fluid flows provided in a mirror configuration,

[0028] Figure 6 shows a sectional view in 3D mode of an electrolyser stack,

[0029] Figure 7 is an enlarged view of a part in Fig. 6,

[0030] Figure 8 is a 3D view of a stack, with parts removed to show a prior art cell frame,

[0031] Figure 9 shows a 3D and sectional view of a range of cell frames in a stack, and Figure 10 discloses an enlarged sectional view of a cell frame part of a stack with schematic representation of diaphragm, bipolar plates and electrodes.

[0032] Detailed description of the embodiments

[0033] 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 specific moulding procedures 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 cell frames according to the current invention.

[0034] In order to better understand the background of the invention, an example of a pressurised electrolyser stack is presented here with reference to Figures 6 - 10.

[0035] In Figs. 6 a 3D representation of an electrolyser stack 1 is presented in sectional view. The stack has two end plates 12, 12.1 namely a proximal endplate 12, which also has two inflow channels 20 and two outflow channels 21 and a distal endplate 12.1 without inflow or outflow channels. Inflow and outflow channels may however pass through the proximal or distal endplate according to need. The inflow channels 20 receive catholyte and anolyte respectively from a stack external supply pipe (not shown) and feeds the fluids to the stack internal catholyte manifold channel 27 (seen in Fig. 8) and stack internal anolyte manifold channel 25 (seen in Fig. 8) respectively. The outflow channels 21 delivers a catholyte / hydrogen mix and anolyte / oxygen mix respectively out of the stack and originating from individual halfcell by way of stack internal anolyte and oxygen manifold channel 26 (seen in Fig. 8) and stack internal catholyte and hydrogen manifold channel 28 (seen in Fig. 8). Usually outflow channels 21 are provided above the inflow channels 20, as the gasses produced in the half-cells will have an uplift, and thus upwards flow in the half-cells is preferred.

[0036] It is noted that during the build of a stack 1 , it is customary to place the stack 1 with the stack axis 29 in vertical direction and resting on one endplate 12. During use however, the stack shall rest in the horizontal position shown in Figures 6 and 8 in which position the stack axis 29 shall be horizontal.

[0037] At the rim of each endplate 12, 12.1 , pull rods 30 are arranged to extend through opposed holes in the endplates, and fastened by simple nuts 31 to thereby pull the two endplates 12,12.1 towards one another in order to allow the containment within the stack of pressurised fluids and gasses. Proximal to the two endplates 12, 12.1 , firstly an insulator plate 13 (best seen in Fig. 7) and then distal and proximal electric current injectors / collectors 14, 14.1 are provided respectively, and between the two current injectors / collectors 14, 14.1 the range of individual cells, each comprising two half-cells 2.1 are arranged in a row flat against each other and precisely aligned.

[0038] Each half-cell 2.1 shall comprise an outer so-named individual cell frame 2 which serves at least four distinct and somewhat independent purposes:

[0039] 1. the cell frames 1 serve as pressure maintaining devices,

[0040] 2. they keep in place cell internal elements, namely the diaphragm 35 and the bipolar plates 36 with accompanying electrodes, namely cathode electrode 37 and anode electrode 38 (seen in Fig. 10),

[0041] 3. they ensure that the two different electrolytes with varying amounts of the product gasses hydrogen and oxygen respectively are kept apart and prevented from mixing within the stack 1 and

[0042] 4. they make up the electrolyte and electrolyte / gas distribution networks between stack outflow channels 20 and stack inflow channels 21 for both electrolytes and electrolyte / gas mixtures. With reference to Fig. 9, the pressure carrying properties of the half-cell frames 2 is hereby explained. The half-cell frames 2 are made from injection moulded, electrically insulating polymer, and they need re-enforcement to contain high pressures and followingly, a metal reinforcement ring 33 is supplied to each cell frame 2 at the outermost part thereof. Also, in order to avoid any leakage, an O-ring 34 or similar gasketing means is supplied in a circumferential furrow 32 adapted to receive the O-ring 34, such that when individual half-cell frames 2 are urged against each other between the endplates 12, 12.1, high pressures may be maintained inside of the O-ring 34.

[0043] In Fig. 10 an enlarged sectional view at the cells and half-cell frames 2 is given. The bipolar plates 36 are each electrically connected to a cathode electrode 37 at one side and an anode electrode 38 at the other opposed side and are schematically represented in the figure along with the diaphragms 35. Each electrode 37,38 is customarily adapted to be maintained in a position proximal to a diaphragm 35. The diaphragm 35 serves to keep the gasses produced at the anode electrode 38 (oxygen gas) and at the cathode electrode 37 (hydrogen gas) separated from each other, while allowing ions / electrons to pass through the diaphragm between the two adjacent half-cells. In the space between a bipolar plate 36 and a neighbouring diaphragm 35, an anolytic process chamber 3 or catholytic process chamber 4 is thus defined, which at its circumference is limited by a half-cell frame 2 and limited in the stack axis direction by a diaphragm 35 and the bipolar plate 36.

[0044] As seen in Fig. 8, every process chamber has in inlet at a below part comprising an inflow distributer 15. At an upper part of each process chamber, an outflow collector 16 is provided. The inflow distributers 15 and the outflow collectors 16 are instrumental in ensuring, that the flow is evenly distributed over the area of the halfcells between bipolar plate and diaphragm.

[0045] As seen in Fig. 8, the inflow distributer 15 and outflow collector 16 connects to each their dedicated embedded furrow flow channel 10. As seen in Figs. 9 and 10, the dedicated flow channels 10 are provided as embedded furrows 10 within a first side of each half-cell frame 2. When this furrow is urged against a back-side of the next half-cell frame in a stack, the furrow 10 will have the appearance of a channel which at its one end opens into either the collector 16 or distributer 15 and at its other end opens into one of stack internal manifold channels 25; 26; 27; 28. From anolytic reaction chambers the two dedicated embedded furrow flow channels 10 connect to a stack internal anolyte manifold channel 25 and a stack internal anolyte and oxygen manifold channel 26. Similarly, from the catholytic reaction chambers, the two dedicated furrow flow channels 10 connect with a stack internal catholyte manifold channel 27 and a stack internal catholyte and hydrogen manifold channel 28 respectively. The individual half-cell frame 2, the front part of which is seen in Fig. 8 thus comprises 4 through holes: one being part of the stack internal anolyte manifold channel 25, one being part of the stack internal catholyte manifold channel 27, one being part of the stack internal anolyte and oxygen manifold channel 26 and one being part of the stack internal catholyte and hydrogen manifold channel 28. Usually only one and the same cell frame design is used throughout the assembly of a stack, and the cell frame seen in Fig. 10 will have an identical cell frame placed adjacent thereto, however this adjacent cell frame is rotated 180 degrees around the stack length axis 24, such that alternatingly the stack internal anolyte manifold channel 25 / stack internal anolyte and oxygen manifold channels 26 and the stack internal catholyte manifold channel 27 / stack internal catholyte and hydrogen manifold channels 28 are connected through the respective dedicated embedded furrow flow channels 10 to thereby either serve an anolytic reaction chamber or a catholytic reaction chamber with supply and outflow means.

[0046] Figs. 1 and 2 show a sectional view of a stack 1 comprising half-cells 2.1 according to the invention. In Fig. 1 the stack 1 is in a shut down mode, such that anolyte and catholyte fluid flow pumps (not seen) are not active however, from the electrolyte within the half-cell process chamber 2.1 and in the embedded furrow flow channels 10, some gas 5 will separate from the fluid, and being the lighter of the two components electrolyte and gas, this gas will seep or flow into the higher parts of half-cell and furrow flow channels 10, which parts will then become gas filled. The upper part of the half-cells will always be connected to an outflow embedded furrow flow channel 10, which will have a downward direction, which in itself creates a gas trap, as also seen in Fig. 8, however the inflow embedded furrow flow channel 10 in prior art half-cells will not comprise any such gas trap (lower half of the stack seen in Fig. 8) and any gas released in the inflow embedded furrow flow channel of a prior art half-cell will just flow backword out of the cell through the stack internal anolyte manifold channel 25 or the stack internal catholyte manifold channel 27. However, with the fluid trap in place as disclosed in Figs. 1 and 2, gas released in the inflow embedded furrow flow channel 10 will be trapped due to the downwardly directed parts 17 of the inflow embedded furrow flow channel 10, which creates an upper gas pocket 5. It is noticed, that the anolytic or catholytic process chamber of the half-cell in itself is also a “downward directed part 17” of a flow channel, and that together with the downward directed parts 17 of the corresponding outflow embedded furrow flow channel 10 a gas trap will be present as mentioned above. As also seen in Figs. 1 and 2, there is a multitude of downward directed flow parts 17, such as 3, provided next to each other along the furrow flow channels 10, which along with the half-cell which, as mentioned above, is also a flow channel even if the gas producing reaction also takes place here, such that in effect 4 downward directed flow parts 17 are provided in a side by side manner. If a downward directed flow part 17 and its neighbouring downward directed flow part 17 are interconnected to form an invers u shaped flow channel, one such invers II- shaped flow channel suffice to ensure a gas trap section, which will prevent direct contact between fluid parts within the flow channel at each side of the inverse II- shaped flow channel.

[0047] In the embodiment of the invention seen in Fig. 3, two mirror image designed halfcell frames are needed to serve two consecutive half-cells, as a rotation of the shown frame will not allow the stack internal catholyte and hydrogen manifold channel to gain fluid connection with an inflow distributer at an upper part of a halfcell or catholytic process chamber. Also, in Fig. 3 there is only one inverse II- shaped flow channel part.

[0048] In the embodiment seen in Fig. 4, the downwardly directed part 17 of the inflow channel to each half-cell comprise 3 downward directed flow parts 17 and one inverse U-shaped part filled with gas 5 is disclosed. In Fig. 5 the half-cell frame next to the half-cell frame in Fig. 4 is shown, and this needs to be a mirror representation of the cell frame in Fig. 4 in order to serve the neighbour half-cell with in and outflow connections. Such mirror image half-cell frames will need each their dedicated injection tool for their production. List of parts

[0049] 1 Stack

[0050] 2 Half-cell frame

[0051] 2.1 Half-cell

[0052] 3 Anolytic process chamber

[0053] 4 Catholytic process chamber

[0054] 5 Gas separated from the electrolyte fluid

[0055] 10 Embedded furrow flow channel

[0056] 11 Fluid and / or gas trap section

[0057] 12 Proximal endplate

[0058] 12.1 Distal endplate

[0059] 13 Insulator plate

[0060] 14 Proximal current injector / collector plate

[0061] 14.1 Distal current injector / collector plate

[0062] 15 Inflow distributor

[0063] 16 Outflow collector

[0064] 17 Downwardly directed part of furrow flow channel

[0065] 20 Inflow channel

[0066] 21 Outflow channel

[0067] 25 Stack internal anolyte manifold channel

[0068] 26 Stack internal anolyte and oxygen manifold channel

[0069] 27 Stack internal catholyte manifold channel

[0070] 28 Stack internal catholyte and hydrogen manifold channel

[0071] 29 Stack axis

[0072] 30 Pull rods

[0073] 31 Nuts

[0074] 32 Circumferential furrow

[0075] 33 Metal reinforcement ring 34 O-ring

[0076] 35 Diaphragm

[0077] 36 Bipolar plate

[0078] 37 Cathode electrode 38 Anode electrode

Claims

Claims1. A water electrolyser stack (1) having a range of half cells frames (2) which each circumscribes one of an anolytic (3) or a catholytic(4) process chamber and which half cells frames (2) are arranged and aligned in an array between a proximal electric current injector / collector plate (14) and a distal electric current injector / collector plate (14.1), whereby catholyte and anolyte stack internal inflow manifold channels (25,27) for two electrolytes are provided as through going openings in half cell frames (2) and wherein further stack internal outflow manifold channels (26,28) for each one of two electrolytes and respective product gas are provided as through going openings in half cell frames (2), and where each half cell frame further comprises an embedded furrow flow channel (10) adapted to serve an electrolyte flow from a stack internal inflow manifold channel (25,27) in a half cell frame (2) to a corresponding anolytic or catolytic reaction chamber (3,4) and an embedded furrow flow channel (10) adapted to serve an electrolyte and gas outflow from a corresponding anolytic or catholytic eaction chamber (3,4) to a corresponding stack internal manifold channel (26,28) characterised in that each of the embedded furrow flow channels (10) comprise at least one fluid and / or gas trap section (11).

2. The water electrolyser stack (1) according to claim 1 , wherein fluid and / or gas trap section (11) is provided in embedded furrow flow channel (10) proximal to its corresponding stack internal manifold channel (25,26,27,28) in the half cell frame (2).

3. The water electrolyser stack (1) according to claim 2, wherein any of the embedded furrow flow channels (10) proximal its connection to stack internal manifold channel (25, 26, 27 ,28) comprises at least two generally vertically extending furrow flow sections (17), which sections are interconnected pairwise by a generally horizontal furrow flow section.

4. The water electrolyser stack according to any one of the claims 1-3, wherein each embedded fluid flow furrow (10) in a half-cell frame is arranged as an unbranched flow channel.

5. The water electrolyser stack according to any of the claims 1-4, wherein the embedded furrow flow channel (10) adapted to serve an electrolyte flow from a stack internal anolyte or catholyte manifold channel (25, 27) to a corresponding halfcell as well as the embedded furrow flow channel (10) adapted to serve an electrolyte and gas outflow from a half-cell to a stack internal electrolyte and gas manifold channel (26, 28) are provided in the same vertical half plane of any given half-cell frame when the stack is arranged for production.

6. The water electrolyser stack according to any one of the claims 1 - 4, wherein the embedded furrow flow channel (10) adapted to serve an electrolyte flow from a stack internal anolyte or catholyte manifold channel (25, 27) to a corresponding halfcell and the embedded furrow flow channel (10) adapted to serve an electrolyte and gas outflow from a half-cell to a stack internal electrolyte and gas manifold channel (26, 28) are provided in opposed vertical half planes of any given half-cell frame when the stack is arranged for production.

7. The water electrolyser stack according to claims 5 or 6, wherein the at least one fluid and / or gas trap section (11) in a furrow flow channel (10) is of the duck bill type.

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