WO2024094888A2

WO2024094888A2 - Cell for forming an electrolyser, electrolyser comprising such cell, method for manufacturing and operating an electrolyser

Info

Publication number: WO2024094888A2
Application number: PCT/EP2023/080787
Authority: WO
Inventors: Albert Bos; Ahmadreza RAHBARI; Ron Folkert VAN DONGEN
Original assignee: Xintc B.V.
Priority date: 2022-11-06
Filing date: 2023-11-06
Publication date: 2024-05-10

Abstract

Cell for forming an electrolyser comprising at least one diaphragm or membrane having a first side and a second side opposite the first side, a first cell plate, arranged on the first side of the diaphragm, provided with a first electrode, provided with an inlet channel for supplying or draining electrolyte to or from the electrode, provided with a first discharge channel for discharging oxygen from the electrode, at least one second cell plate, arranged on the second side of the diaphragm, provided with a second electrode and provided with a second discharge channel for discharging hydrogen from the electrode wherein the at least one first and second cell plate are made of a polymer material.

Description

Cell for forming an electrolyser, electrolyser comprising such cell, method for manufacturing and operating an electrolyser

The present invention relates to a cell for forming an electrolyser, an electrolyser comprising such cell, and a method for manufacturing and operating such electrolyser.

With an increased demand for alternatives for fossil fuels, the demand for hydrogen from renewable energy sources is ever growing, and so is the demand for equipment to generate said hydrogen. Up to now, most hydrogen is made from methane using steam-methane-reforming (SMR). Electrolysers by nature use electricity to split water, and thus are the only option for green hydrogen, as hydrogen made from renewable energy sources is also called.

Alkaline Electrolysers (AEL) are the common device for doing so. These devices comprise a stack formed of diaphragms (membranes) having a first side and a second side opposite the first side, first cell plates arranged on each first side of the diaphragms, provided with a first electrode and with an inlet channel for feeding electrolyte to the electrode and a first discharge channel for discharging oxygen from the electrode, and second cell plates, arranged on the second side of the diaphragms, provided with a second electrode and also with an inlet channel for feeding electrolyte to the electrode and with a second discharge channel for discharging hydrogen from the electrode.

Alternatives to alkaline electrolysers are proton exchange membrane (PEM) electrolysers, and anion exchange electrolysers (AEM). However, their production requires scarce materials, especially metals like platinum, iridium, titanium and stainless steel, which forms a supply bottle neck in today's market. A further constraint is formed by the manufacturing effort due to the complexity of the devices and the steps to compose them. Additionally, scaling up hydrogen plants in which electrolysers are operated under high pressure introduces safety risks, and an increased difficulty to meet all safety standards. It is a goal of the present invention to take away at least some of the disadvantages of prior art solutions and/or to propose a useful alternative for the existing cells and electrolysers equipped therewith. It is a further goal of the present invention to provide a method for less complex manufacturing of an electrolyser, and to provide a method for operating such electrolyser at an industrial scale at a much lower capital and operational expenditures.

For that purpose, the present invention proposes a cell for forming an electrolyser comprising at least one diaphragm ( membrane) having a first side and a second side opposite the first side, a first cell plate, arranged on the first side of the diaphragm and provided with a first electrode and an inlet channel for feeding electrolyte to the electrode as well as a first discharge channel for discharging oxygen from the electrode, at least one second cell plate, arranged on the second side of the diaphragm and provided with a second electrode an inlet channel for feeding electrolyte to the electrode and with a second discharge channel for discharging hydrogen from the electrode wherein the at least one first and second cell plate are made of an electrically non-conducting polymer material.

With respect to the present invention, the term diaphragm (membrane) is used to indicate both a diaphragm (allowing all ions to pass, but blocking gasses) and/or a membrane (only selectively allowing specific ions to pass, depending on the type of membrane that was chosen). The term electrically non conducting polymer material means that the plastics material is not provided with any additions that increase electrical conductivity, especially not electrically conductive particles. Preferably the electrically non-conducting polymer has an infinite electrical resistance.

Polymer materials for the cell plates are available in higher quantities and against lower costs than the usual graphite, titanium or stainless steel. Additionally, they can easier be formed in the right shape of a cell plate, especially with techniques like injection moulding or roll and press forming or resin casting and complex geometries such as Tesla valves and flow restrictors can be included to achieve a better flow distribution. This method of manufacturing not only allows rapid production in high quantities, but also allows very detailed designs of the cell plates and the inlet and outlet channels thereof to be produced and reproduced. A further advantage is that it allows a higher degree of manufacturing automisation, which leads to less labour required and thus reduced costs. When injection moulded, gas-tight plates can be obtained. These need no further processing step like coating in order to be applied. Especially no post-processing is needed in order to make the plates medium tight. A further advantage is that a thus obtained cell plate and an electrolyser formed therewith are light-weight, which makes handling of the device a lot easier and allows to do so by a single person. Finally, the electric insulation properties of plastics are advantageous for the device's overall safety and in reducing shunt currents.

When welding plastics materials and in particular polymer materials, compatible materials, originating from the same polymer-group are preferred.

The use of a polymer material sets boundaries to the operation temperature of the electrolyser. For example, safe operating temperatures for (some) PVC-U polymer are maximised at 60 degrees Celsius, although polymers that can withstand temperatures over 200 Celsius are also generally known. This has to do with the mechanical strength and creep of polymers. Not only those of the cell plates and/or diaphragm, but given that they require a relative low temperature, the remainder of the electrolyser and (part of) its surrounding may also be formed out of polymers. For instance, the invention allows the use of regular PE or PP or PVC (pipes).

Electrolysers according to the state of the art, are normally operated at the highest pressure they mechanically allow. This is because as a next step, the hydrogen is often to be compressed for storage or transportation. The higher the pressure it is delivered at, the more efficient the further compression step takes place. However, a thermoplastic plastic (used for injection moulding) becomes more plastic when its temperature increases. If additionally, when a force is applied at high temperatures, the polymer can start to creep and deform. For this reason, according to the present invention, the electrolyser is operated at a relatively low pressure.

The pressure may therefore be kept below several bars. A maximum operating pressure of 0.5 bar(g) (1.5 bar absolute) provides the benefit that the Pressure Equipment Directive (PED) is not applicable, which allows more freedom in design and parts, and takes away the necessity to demand a Notified Body (NOBO) to issue a certificate, which renders the invention suitable for large scale production and fast roll out.

A second advantage of this low pressure implied by the use of plastics materials is the energy efficiency of an electrolysis process, which is most favourable at low pressure. It then requires less energy (kWh/kg of produced H 2). Also, the crossover of gases is lower (02 diffuses to the H2 side, and vice versa). The diffusion is a function of the partial pressure of the gases on both sides of the membrane/diaphragm. The higher the difference in partial pressure, the more rapid the diffusion process. If at atmospheric pressure the flux of a gas through a diaphragm or membrane is x mol/s.m2, then at 30 bar the flux is roughly 30 times x.

Low pressure results in a lower 02 content in the produced H2 (typically 0.1- 0.4%). Since that 02 may need to be removed further downstream (purification) by allowing the 02 to react catalytically with the H2 produced (a so-called de-oxer unit), the low-pressure operation minimizes this step. In prior art systems, to remove 0.4% 02 in the form of H2O, 0.8% of the H2 produced needs to be sacrificed. This loss of efficiency across the chain is minimized by the present invention.

In a preferred embodiment, the diaphragm for separating both sides is also made of a porous polymer material, and in particular from the same polymer material. This increases the advantages of the cell plates being made from a polymer material, but also allows to weld the cell plates and the diaphragm together, in particular by means of thermal, ultrasonic or vibration welding. Thereto, the cell plates and the diaphragm may be provided with roughened surfaces, at least at those locations where they should adhere to each other. The diaphragm is porous to allow saturation with the electrolyte, which is the carrier of the hydroxide ions (which in turn are the carrier of the electrons). Alternatively, a diaphragm/membrane that is fixed inside a polymer frame of the same polymer type as the cell plate to facilitate welding may be applied.

The saturated diaphragm acts as a barrier which keeps the oxygen and hydrogen gas separate. When the diaphragm is fully saturated with electrolyte, the gasses can only diffuse to the other side through the electrolyte phase, that is by dissolving in the fluid, diffusion through the fluid and evolving to the gas phase on the other side.

Evidently, the electrodes of the cell plates should be of an electrically conductive material, such that a metal, such as nickel, or alloys of nickel including stainless steel types, is the most straight forward. According to the present invention, the cell plates comprise bipolar electrodes. A cell plate then forms a first cell plate for a diaphragm adjacent to its first side and a second cell plate for a diaphragm at its second side, and that it comprises a first discharge channel for discharging oxygen from the unipolar electrode at its first side and a provided with a second discharge channel for discharging hydrogen from the bipolar electrode at its second side.

That also means that an electrode forms a cathode for a cell it forms with a diaphragm at its first side, and an anode for a cell plate it forms with a cell at its second side. The anode is the side that is adjacent to the first side of the diaphragm, the cathode is the side that is arranged at the second side of the diaphragm. Said bipolar electrode may be formed by an electrode material extending from a first side of the cell plate to a second side, the electrode material at least partially covering the cell plate on both sides. In other words, the cell plate is covered on both sides with the electrode material or sandwiched in between the electrode material. The electrode material may in a preferred embodiment be folded around an edge of the cell plate material, or alternatively folded around two opposite edges and having a seam on one side of the cell plate. The latter method reduces the ohmic resistance of transporting current from one side of the cell plate to the other.

The electrodes may be electrochemically enhanced by applying surface catalyst layers. The catalyst layers may be of a different type to specifically enhance the HER (hydrogen evolution reaction) and OER (oxygen evolution reaction).

Alternatively, the bipolar electrode may be of two different metal alloys which are fixed together (electrically conducting) at a point where they are folded around the cell plate.

Furthermore, the electrode material is in a preferred embodiment perforated and the electrode is placed directly against the diaphragm to form a so called zero-gap configuration. These electrolysers are called "zero-gap" because there is virtually no gap between the cathodes, anodes, and the diaphragm (membrane). Herewith, accumulation of hydrogen or oxygen between electrode and diaphragm, blocking the electrolysis process, is avoided due to the porous nature of the electrodes.

However, the electrode material may be ribbed to increase the effective surface area and create channels to guide the drainage of hydrogen and oxygen. It has appeared that these ribbed, or zig-zagged electrodes increase the efficiency of the electrolyser. This is because the effective surface is larger when compared with a flat electrode and the formed channels exhibit a chimney effect thus facilitating the rapid vertical discharge of the formed gases. An additional advantage is that it provides strength to the electrode and/or cell plate. Another advantage is that the ribbed nature compensates for differences in the mechanical temperature expansion coefficients of the polymer and metal (electrode) materials. Yet a further advantage is that the ribbed or zig-zag form ensures constructive integrity during the manufacturing process, and in particular during vibration welding.

In yet a further preferred embodiment, the cell plate is provided with a flow distribution device for distributing the supplied electrolyte more evenly over the width of the cell. Such flow distribution device may comprise a number of channels leading toward the electrode and compensating the difference in path length with an appropriate difference in the channel width. It may also consist of pressure drop inducing elements in the flow path which also result in a more even distribution of the electrolyte flow over the width of the cell. It may also consist of flow directional elements such as Tesla valves. Combined with the chimney effect of the vertical channels in the ribs this ensures an even flow distribution of the total width of the cell with no build-up of gas pockets which may block areas of the electrodes.

Also, the diaphragm may be formed by means of injection moulding, resin casting, machining but alternatively it can be formed from a sintered polymer. With this method, a porous result, as required for the diaphragm is obtained automatically, and it has appeared that its properties with openings of 50 microns down to submicron size can be reproduced very well. Furthermore, it requires less rare compounds than the common diaphragms commercialised as Zirfon.

The invention also relates to an electrolyser comprising a multi-cell assembly composed of the above-described cells, wherein bipolar plates and diaphragms alternate.

The number of cells may be selected such that the total weight, including head and tail plate, is less than 22 kg, which is a maximum weight that may be carried by one man according to (present Dutch) health and safety regulations. This is in particular made possible by using thin wall plastics manufacturing techniques, that allow a reaction zone (the stack of cell plates and membranes) with low weight and therefore enables to house a stack of more elements in the same volume.

Specifically, it has become feasible to manufacture an electrolysis device with a housing that has less than 850 mm length, which allows to place two of them on both sides in a container with at central corridor.

The electrolysis device may comprise a ventilation device for ventilating the exterior of the cells. Preferably, the pressure of the produced hydrogen in the cells is relatively low and comparable with ambient pressure. In case of an accidental leak, when hydrogen escapes from the electrolyser in an uncontrolled manner, its concentration can always be held under the (present Dutch) safety requirement LEL (Lower Explosion Limit) of 4 volume% by ensuring a ventilation flow rate that is always a minimum of 25 times larger than the maximum anticipated hydrogen leak flow rate.

The invention also relates to a method of manufacturing an electrolyser comprising providing a first cell plate on the first side of a diaphragm, a second cell plate on a second side of the diaphragm, wherein the at least one first and second cell plate are made of polymer material, and bonding the first and second cell plates to the diaphragm by thermal, ultrasonic or vibration welding.

The invention further relates to a method for operating a device as claimed in any one of claims 1-10, comprising operating the device under a pressure between 1 and 1,5 bar though higher pressures are possible.

The invention also relates to a method for operating a device according to any one of claims 1-10, comprising operating the device at a temperature between ambient and preferably 60 degrees Celsius, although higher temperatures are possible depending on the choice of polymers.

The invention will now be elucidated into more detail with reference to the following drawings. Herein:

Figure 1 shows a perspective view of a cell plate according to the invention;

Figure 2 shows a cross section of an electrolyser comprising multiple cell plates and diaphragms according to the invention; and Figure 3 shows a schematic medium flow through an electrolyser according to the invention.

Figure 1 shows a perspective view of a cell plate 1 according to the invention comprising a first electrode 2, provided with an inlet channel 3 for supplying or draining electrolyte to or from the electrode and provided with a first discharge channel 4 for discharging oxygen from the electrode, arranged on its first side A. The side A is also referred to as the oxygen side or first side. The cell plate is made of a polymer material, and the electrode 2 is a bipolar electrode as a result of the electrode material extending from a first side A of the cell plate to a second side B, the electrode material 2 at least partially covering the cell plate 1 on both sides, and wherein each cell plate forms a first cell plate for a diaphragm adjacent to its first side and a second cell plate for a diaphragm at its second side. At the second side B, a similar channel for discharging hydrogen from the electrode is provided (not visible), just like an inlet channel for supplying or draining electrolyte to or from the electrode. As visible, the electrode 2 material is ribbed to increase the effective surface area and create channels 5 for the removal of hydrogen and oxygen. These ribs may be of any form, such as triangular, rectangular but preferably sinusoidal. The cell plate is provided with a flow distribution device for distributing the supplied electrolyte.

Figure 2 shows a stack 2 of cells comprising cell plates 1 and diaphragms 6 according to the invention, wherein bipolar plates 1 and diaphragms 6 alternate. The diaphragms 6 are also made of a polymer material, and the cell plates and the diaphragm are welded together by means of thermal, ultrasonic or vibration welding. The electrodes 1 are placed directly against the diaphragms 6 to form a semi zero-gap system.

Figure 3 shows a schematic medium flow 7 through an electrolyser according to the invention. The figure shows that there is a separate electrolyte recirculation flow from the oxygen and the hydrogen gas/liq uid separators 8, 9 as shown schematically in the figure. The oxygen gas/liq uid separator is coupled to the first cell plates of each diaphragm. This gives the lowest crossover of the (dissolved) oxygen and hydrogen gases. However, an imbalance in the electrolyte concentration in both circuits is induced because water disappears on the hydrogen side, which appears from the formula:

4 H2O + 4 e- ^ 2 H2 + 4 OH-

The OH- migrates to the oxygen side to react further there:

So, 4 H2O are consumed on the hydrogen side (cathode side or second cell plate seen from a diaphragm) and 2 H2O are formed on the oxygen side, and that gives 2 H2 on the hydrogen side and 1 02 on the oxygen side (anode side or first cell plate seen from a diaphragm).

In order to bring the electrolyte back into balance in terms of concentration, the electrolyte flows must periodically be mixed 10. With the mixing 10 a larger crossover of gases is obtained because a saturated 02 solution is mixed with a saturated H2 solution. This is therefore to be done as short as possible and the flows are kept separate as long as possible. To accommodate both situations, the stacks of cell plates and diaphragms therefore have separate electrolyte inputs for the 02 and H2 sides of the cells.

The embodiments described above are examples only and do in no way limit the scope of protection of the invention as defined in the following claims.

Claims

1. Cell for forming an electrolyser comprising: at least one diaphragm or membrane having a first side and a second side opposite the first side;

- a first cell plate; o arranged on the first side of the diaphragm; o provided with a first electrode; o provided with an inlet channel for supplying or draining electrolyte to or from the electrode; o provided with a first discharge channel for discharging oxygen from the electrode;

At least one second cell plate, o arranged on the second side of the diaphragm; o provided with a second electrode; o provided with an inlet channel for supplying or draining electrolyte to or from the electrode; o provided with a second discharge channel for discharging hydrogen from the electrode; characterized in that the at least one first and second cell plate are made of an electrically nonconducting polymer material.

2. Cell according to claim 1, wherein the diaphragm is also made of a porous polymer material, wherein the cell plates and the diaphragm are welded together, in particular by means of thermal, ultrasonic or vibration welding, in particular such that an electrochemical and gas-leak tight connection is realized surrounding the opposite inlet and opposite discharge channels.

3. Cell according any of the preceding claims, wherein the cell plates comprise bipolar electrodes formed by an electrode material extending from a first side.

4. Cell according any of the preceding claims, wherein the electrode material is perforated and wherein the electrode is placed directly or very close against the diaphragm to form a semi zero-gap system.

5. Cell according any of the preceding claims, wherein the electrode material is ribbed to increase the effective surface area and create channels for the removal of hydrogen and oxygen.

6. Cell according any of the preceding claims, wherein the cell plate is provided with a flow distribution device for distributing the supplied electrolyte.

7. Cell according any of the preceding claims, manufactured by means of injection moulding or roll and pressforming or resin casting.

8. Cell according any of the preceding claims, wherein the diaphragm is formed from a sintered polymer.

9. An electrolyser comprising a multi-cell assembly according to any preceding claim, wherein bipolar plates and diaphragms alternate.

10. An electrolysis device according to claim 9, wherein the number of cells is selected such that the total weight is less than 22 kg.

11. An electrolysis device according to claim 9 or 10, comprising a ventilation device for ventilating a space surrounding the cells.

12. A method of manufacturing an electrolyser comprising the step of providing a first cell plate on the first side of a diaphragm, a second cell plate on a second side of the diaphragm, wherein the at least one first and second cell plate are made of polymer material and bonding the first and second cell plates to the diaphragm (membrane) by thermal, ultrasonic or vibration welding. A method for operating a device as claimed in any one of claims 1-0, comprising operating the device under a pressure between 1 and 1,5 bar absolute. A method for operating a device according to any one of claims 1-9, comprising operating the device at a temperature between ambient and 132 degrees Celsius and at pressures between 1-30 bar absolute.