Flow through electrode

Abstract

An electrode (100) for electrolysis, said electrode comprising: a first porous layer (102) permeable to electrolyte and gases produced by the decomposition of electrolyte and a second porous layer (104) permeable to electrolyte and gases produced by the decomposition of electrolyte. The second porous layer is located adjacent to the first porous layer (102), and the first porous layer (102) comprises nickel. Metal swarf may be used as the basis for both porous electrodes through a sintering method. The second porous layer (104) may comprise titanium. The electrode (100) may comprise a flow through electrode for the electrolysis of water.

Description

Description The present disclosure relates to a flow-through electrode for electrolysis of water or ammonia, particularly but not exclusively for the production of hydrogen. The present disclosure further relates to an electrolyser for generating hydrogen for water and a method of manufacturing a flow-through electrode. The process of using electricity to decompose water into oxygen and hydrogen gas is known as electrolysis of water. Hydrogen gas produced in this way can be used in various applications and has become widely known as an energy dense option for fuelling vehicles. In other applications, electrolysis of water may be used as a decentralised storage solution storing electrical energy as chemical energy, particularly electrical energy obtained via renewable power. Other hydrogen production method decompose ammonia into hydrogen and nitrogen by means of electrolysis. In recent years, demand for hydrogen, inter alia, as a fuel for so called hydrogen fuel cells has increased rapidly. Electrolysers can be grouped into proton exchange membrane (PEM) electrolysers, alkaline electrolysers and solid oxide electrolysers. These different types of electrolysers function in slightly different ways depending on the electrolyte material involved. Yet, some of the most prominent drawbacks of most electrolysers include overall inefficiencies and / or failure to supply hydrogen gas at pressures required for further use. In order to maximize the amount of gas (e.g. oxygen / hydrogen) produced with common electrolysers, it is known to arrange a multitude of electrodes parallel to each other in a device known as an "electrode stack". Such electrode stacks include multiple electrolyte chambers, each between neighbouring electrodes, thereby enabling large electrode surface areas to be in contact with the electrolyte solution without requiring large space envelopes. Although electrode stacks are useful to combine a plurality of electrolysers in the smallest possible space, such known stacks are still of significant size, particularly when trying to generate hydrogen for commercial use. Using electrode stacks for domestic purposes is also not currently feasible due to its size and weight. A further issue, particularly in terms of domestic use of hydrogen, is the tank volume required to store hydrogen. One solution is reducing hydrogen volume by means of pressurization or liquefaction. Currently, the vast majority of industrial processes produce hydrogen at atmospheric pressure. Such low-pressure hydrogen gas must then be compressed, e.g. by means of compressor pumps, at considerable cost (and environmental impact). To eliminate the compression step, pressurised hydrogen electrolysis systems have been developed, such as described in GB 2 612 067 A, in the name of the same applicant. Pressurised electrolysis systems are able to produce hydrogen gas at elevated pressures, thereby reducing or eliminating the need for separate post electrolysis hydrogen compressors. Although pressurized electrolysers may significantly reduce the cost for producing pressurized hydrogen, the structure and composition of electrodes employed as the cathode and / or anode within pressurized electrolysers is not only required to optimize the yield of hydrogen and oxygen, but also needs to withstand high pressures and provide desired pressure drop across the electrodes, particularly in flow-through applications. It is an aim of the present disclosure to solve or at least ameliorate one or more of the problems associated with the prior-art. In particular, it is an object of the present invention to provide an improved electrode, which exhibits high yield of process gases and, at the same time, exhibits a long service life. Another object of the present invention is to provide a method of producing an improved electrode in a simple and effective manner. Summary of the invention Aspects and embodiments of the present disclosure provide an electrode, and an electrolysis system for the electrolysis of water, and a method of manufacturing such an electrode as claimed in the appended claims. Further embodiments are disclosed in the appended, dependent claims. According to a first aspect of the present invention, there is provided an electrode for electrolysis of water, said electrode comprising: • a first porous layer permeable to electrolyte and gases produced by the decomposition of electrolyte; • a second porous layer permeable to electrolyte and gases produced by the decomposition of electrolyte, said second porous layer being arranged adjacent to the first porous layer, wherein the first porous layer comprises Nickel. "Electrolyte may refer to any type of process fluid used to generate hydrogen. Typically, this may be water with various known electrolytes. However, in some examples, electrolyte-free water, pure water, or distilled water may be employed too. Further examples of "electrolytes” that may be used in connection with electrodes and electrolysers of the present disclosure include ammonia, which may be decomposed into hydrogen and nitrogen. The present disclosure suggests using two porous layers arranged adjacent to each other, wherein one of the porous layers comprises Nickel. It was found that a Nickel porous layer provides high yield of the process gases, such as hydrogen and / or oxygen and is particularly resistant to corrosion. The second porous layer may act as a support structure for the first porous layer comprising Nickel, allowing the Nickel layer to be particularly thin. Utilizing thin Nickel layers provides the above advantages without increasing costs significantly. In some examples, the first porous layer may consist entirely of Nickel, particularly a Nickel alloy. According to another embodiment, the first porous layer comprises Inconel 625. Inconel alloy 625 is a Nickel-based super alloy that possesses high strength properties and resistance to elevated temperatures. It was found that Inconel 625 is particularly suitable for the first layer of the electrode of the present invention as is protects the electrode against corrosion and oxidation. According to another embodiment, the first porous layer comprises Nickel swarf. Providing Nickel swarf in the first porous layer increases the surface area available for contact between the Nickel layer and the electrolyte penetrating the first porous layer during electrolysis. Moreover, Nickel swarf may be a waste product, e.g., during aerospace manufacturing, and may thus be purchased at low cost. According to another embodiment, the first and second porous layers are made from different materials. According to this embodiment, the second porous layer may be made from a material that is highly abundant and, at the same time, readily processable into the porous structure of the flow-through electrode. In one embodiment, the second porous layer may thus comprise Titanium. The second porous layer may comprise Titanium swarf, e.g., Titanium swarf obtained from aerospace waste. Titanium and particularly Titanium swarf provides for a stable and even porous layer that is highly suitable for supporting the first porous layer made of Nickel. According to another embodiment, the second porous layer is thicker than the first porous layer. The first porous layer may have a thickness of 1mm to 5mm, preferably 3mm. Despite the comparatively low thickness of the first porous layer, the Nickel content will improve corrosion resistance and increase the yield of process gases overall. According to another embodiment, the first and second porous layers are sintered layers. It follows that the first and second porous layers may be permanently connected to each other in a single process, i.e., by sintering the two layers simultaneously. According to another embodiment, the first porous layer comprises a cobalt coating. The second porous layer may comprise a platinum coating. The cobalt coating on the first porous layer acts as a catalyst for the electrolysis process and is particularly suitable for combination with the Nickel layer. Similarly, the platinum coating is a catalyst best applied to the second porous layer made of Titanium. Generally, it should be understood that the material of the catalytic coating of the first and / or second porous layers depends on the electrolyte employed. According to another embodiment, the electrode is a flow-through electrode. In this specification, the term "flow-through electrode" relates to an electrode, which is permeable to electrolyte and the corresponding gases formed at the electrode, when electrolyte is pushed through the porous electrode. In other words, electrolyte, which passes through the flow-through electrode of the present disclosure, will be split into oxygen and / or hydrogen, depending on the polarity of the electrode. In other words, flow-through electrodes are characterized in that electrolyte can be passed through the structure of the electrode from a first surface that is in contact with the cell gap / electrolyte chamber to a drain port / surface. Flow-through electrodes will be penetrated by electrolyte during the electrolysis process, thereby providing a larger surface area within the porous structure of the electrode, as compared to flow-by electrodes. In an alternative example, the electrode may be a flow-by electrode, such that the electrolyte will only contact the first porous layer. When employing a flow-by electrode, the second layer may be porous or non-porous as flow through the second layer is not essential for a flow-by arrangement. According to another aspect of the present invention, there is provided an electrolyser for generating hydrogen from water, said electrolyser comprising: • the above electrode, wherein the first porous layer has a first, preferably flat, surface opposite the second porous layer, • an electrolyte chamber for supplying electrolyte to the electrode, wherein said first surface faces the electrolyte chamber. According to the electrolyser of the present disclosure, the first porous layer of the electrode, which comprises Nickel, is in direct contact with the electrolyte within the electrolyte chamber. Electrolyte penetrating the first porous layer (Nickel layer) may then proceed to penetrate the second porous layer made from a second material, such as Titanium. According to a further embodiment, the electrolyser comprises an electrolyte supply circuit for supplying pressurised electrolyte to the electrolyte chamber. Pressurized electrolyte will be able to penetrate the first porous layer made of Nickel. In this regard, it should be noted that a Nickel layer also exhibits low resistance to the flow of electrolyte, resulting in particularly beneficial pressure drops across the electrode of the present disclosure. By contrast, the second porous layer (e.g. a Titanium layer) has a higher resistance to the flow of electrolyte than the first layer. According to another embodiment, the electrolyser comprises a gas outlet for removing process gases from the electrode, wherein the gas outlet is connected to the second porous layer. According to this embodiment, electrolyte penetrating the electrode of the present disclosure is split into process gases, such as oxygen / nitrogen and hydrogen, whereas the process gases may permeate into the second porous layer and be removed from said second porous layer via the gas outlet. According to another aspect of the present disclosure, there is provided a method of manufacturing a flow-through electrode for electrolysis of water comprising: • providing a mould; • adding Nickel swarf to the mould to create a first layer; • adding Titanium swarf to the mould to create a second layer adjacent to the first layer; and • sintering the first and second layers together inside the mould. According to the present method, the flow-through electrode is sintered in a one-shot sintering process. In a first step, a mould is filled with a layer of Nickel swarf. Titanium swarf is then added to the back surface of the Nickel swarf. During sintering, nanoparticles of the first and second layers diffuse across the boundaries of the particles, fusing the first and second layers together and creating a solid one-piece electrode. Since the sintering process does not have to reach the melting point of the materials of the first and second layers, the Titanium and Nickel swarf will be formed into porous structures with particularly high surface areas, which may later be used to contact the electrolyte during electrolysis. According to another embodiment, the first and second layers are sintered by field assisted sintering. Field assisted sintering also known as Spark Plasma Sintering or Pulsed Electric Current Sintering is based on pulsed or unpulsed DC or AC currents directly passing through the mould, thereby heating the materials within the mould until the required sintering temperatures are achieved. According to another embodiment, the method comprises applying a vacuum during the sintering process. In other words, the first and second layers are preferably sintered by means of vacuum field assisted sintering. According to another embodiment, the method comprises applying a pressure to the first and second layers in the mould, during the sintering process. The pressure and temperature applied during the sintering process will not only affect the porosity of the layers of the electrode but also influence the amount of pressure drop experienced during the pressurized electrolysis process. Accordingly, in one aspect of the present method, the temperature and pressure applied during sintering are chosen to achieve a pre-determined pressure drop during electrolysis. To this end, the sintering process may be guided by a database of empirical data of the relationship between the pressure / temperature of the sintering process and the corresponding pressure drop during electrolysis. According to another embodiment, the method comprises applying a cobalt coating on the first porous layer, preferably by means of Chemical Vapour Deposition. The method may further comprise applying a platinum coating on the second layer, preferably by means of the Chemical Vapour Deposition. Generally, the first and / or the second porous layers may be coated with any suitable catalyst, dependent on the electrolyte to be electrolysed. Brief description of the drawings The aforementioned and other features and advantages of this disclosure, and the manner of attaining them, will become apparent and the disclosure will be better understood by reference to the following description of embodiments of the disclosure taken in conjunction with the accompanying drawings, wherein: FIG. 1 is a schematic view of an electrode according to an embodiment of the present disclosure; FIG. 2 is a schematic representation of an electrolyser according to an embodiment of the present invention; FIG. 3 is a schematic embodiment of the method of the present disclosure; FIG. 4 is a schematic work-flow of the method of the present disclosure; and FIG. 5 is a photograph of an electrode according to another embodiment of the present disclosure. Detailed description FIG. 1 is a schematic representation of an electrode 100 for electrolysis of water according to an embodiment of the present disclosure. The flow-through electrode 100 shown in FIG. 1 comprises a first porous layer 102 and a second porous layer 104. The first and second porous layers 102, 104 are arranged adjacent to each other. In the embodiment of FIG. 1, the electrode 100 is substantially disk-shaped. In particular, the first and second porous layers 102, 104 are disk-shaped and have substantially the same diameter. In principle, any other shape may be employed to produce the electrode of the present disclosure. The first porous layer 102 comprises a first surface 106, which faces away from the second porous electrode 104. A second, opposite surface 108 of the first porous layer is in contact with the second porous layer 104. In particular, the second surface 108 of the first porous layer is mated with a first surface 110 of the second porous layer 104. An opposite, second surface 112 of the second porous layer 104 faces away from the first porous layer 102. When in use, the first surface 106 of the first porous layer 102 faces a first region 10, whereas the second surface 112 of the second porous layer 104 faces a second region 20. In some embodiments, the first region 10 may be an electrolyte supply region, such as a cell gap or electrolyte chamber. The second region 20 may be a gas collection region, in which process gases produced by the electrode 100 and / or overflow electrolyte that has not been split into hydrogen, oxygen, and / or any other gases are collected. As mentioned hereinbefore, the electrode 100 is designed as a porous flow-through electrode, meaning that electrolyte may penetrate the electrode 100 in the direction of arrow 114 shown in FIG. 1. In some examples, the gases produced during electrolysis may be collected at any other surface of the second porous layer. However, it should be noted that the flow-through electrode of the present invention should always be configured in such a way that electrolyte will penetrate both the first and second porous layers and gases produced by the decomposition of the electrolyte will always be removed after passing through parts of the second porous layer 104. In some alternative, non-claimed examples, the electrode shown in FIG. 1 may be used as a flow-by electrode. In such a case, electrolyte will be in contact with the first porous layer only, whereas the second porous layer is exclusively provided as a support structure for the first porous layer. FIG. 2 shows a schematic representation of an electrolyser for generating hydrogen from water according to an embodiment of the present disclosure. The electrolyser 150 of FIG. 2 comprises a first electrode 101 arranged on one side of a cell gap / electrolyte chamber 120 and a second electrode 103 arranged on a second, opposite side of the cell gap / electrolyte chamber 120. The first electrode 101 is an electrode according to the present disclosure, including a first porous layer 102 and a second porous layer 104. The first porous layer comprises Nickel. The first electrode 101 is generally identical to the first electrode 100 discussed in FIG. 1 above. In the embodiment of FIG. 2, the second electrode 103 comprises a single porous layer 130. For example, the porous layer 130 of the second electrode 103 may be made of Titanium swarf, similar to the second porous layer 104 of the first electrode 101. In some embodiments (not shown), the second electrode may be another electrode according to the present invention. In other words, the first and second electrodes 101, 103 may both comprise two porous layers, wherein the first porous layer comprises Nickel. The first electrode 101 is arranged within the electrolyser 150 such that the first surface 106 of the first porous layer (Nickel layer) 102 faces the cell gap / electrolyte chamber 120. The first electrode 101 is exclusively in contact with the cell gap / electrolyte chamber 120 via the first surface 106 of the first porous layer 102. Electrolyte, which is inserted into the electrolyte chamber 120 via electrolyte inlet 121 is pressurized within the walls 122 of the chamber 120, wherein some of the pressurized electrolyte may penetrate the first surface 106 of the first electrode 101 and some the first surface 132 of the second electrode 103. The second electrode 103 comprises a second surface 134, which is arranged opposite to the first surface 132. Electrolyte penetrating the first surface 106, i.e., the Nickel surface of the first porous layer 102, may permeate into the second porous layer 104 (e.g., a Titanium layer). As the electrolyte penetrates the first and second porous layers 102, 104 of the first electrode 101, the electrolyte is split into process gases. In one example, the first electrode 101 is an anode, which acts to produce oxygen within the pores of the first and second layers 102, 104. Oxygen produced within the first electrode 101 may be removed via a gas outlet port 116, which is connected to the second porous layer 104. The second electrode 103 may be a cathode, such that electrolyte penetrating the porous layer 130 of the second electrode 103 will be split into hydrogen. The hydrogen produced by the second electrode 103 may be removed from the porous structure 130 via a second gas outlet 136. Although this is not specifically shown in FIG. 2, electrolyte, which is not split into process gases within the first and / or second electrodes 101, 103 may be drained from their respective electrodes 101, 103 via electrolyte drains, preferably connected to a bottom end of the respective electrodes. Particularly with respect to the anode electrode 101, the first porous layer 102 comprising Nickel will increase the yield of oxygen produced and improve the service life of the electrode 101 due to reduced corrosion. However, it should be noted that Nickel swarf, which is one preferred raw material for the production of the first porous layer 102, is very hard and needs to be supported, e.g. by a lower cost Titanium layer, to form a solid electrode. Nickel swarf cannot form a solid electrode on its own. Turning to FIG. 3, there is shown a diagram of an embodiment of the method of manufacturing a flow-through electrode for electrolysis of water according to an embodiment of the present disclosure. In a first step, Nickel swarf 202 may be inserted into a mould 204. A loose layer 206 of Nickel swarf is thus provided at the bottom of the mould 204 after this first step. The Nickel swarf will be evenly distributed across the surface of the mould to form a layer of appropriate thickness (e.g. around 3mm). During a second step, Titanium swarf 208 is added to the mould 204 on top of the loose first layer 206 of Nickel swarf. A loose second layer 210 is formed adjacent to, that is on top of, the first layer 206. Once both the Nickel swarf and the Titanium swarf have been introduced into the mould 204, a pulsed AC or DC current is applied to terminals 214, 216 in order to increase the temperature of the mould and the swarf within the mould. At the same time, pressure is applied by means of a die 212. The herein described field assisted sintering process may be applied in a vacuum within a sintering machine 218. FIG. 4 shows an exemplary flow-chart of a method according to the present invention. As mentioned above, in a first step, Nickel alloy swarf is introduced into a mould. In a second step S304, Titanium swarf is inserted into the mould. In a third step S306, the Nickel alloy swarf and the Titanium swarf are sintered together to form a one-piece electrode. In an optional fourth step S308, a catalyst may be added to one or both of the porous layers. In some embodiments, the catalysts may be applied by Chemical Vapour Deposition. In another optional step S310, the electrode may be machined to a shape that fits the electrolyser. In some examples, such machining may include waterjet cutting radial or axial holes into the first and / or second porous layers, which may later be used as gas and / or electrolyte collection ports. FIG. 5 shows an image of an electrode according to the present disclosure. The electrode 400 shown in FIG. 5 comprises a first porous layer 402 made of Nickel swarf. The first porous layer 402 is connected to a second porous layer 406 via a back surface 404. An opening 408 is provided axially through the electrode 400. FLOW THROUGH ELECTRODE

Claims

1. An electrode for electrolysis of electrolyte, said electrode comprising:• a first porous layer permeable to electrolyte and gases produced by the decomposition of electrolyte;• a second porous layer permeable to electrolyte and gases produced by the decomposition of electrolyte, said second porous layer being arranged adjacent to the first porous layer,wherein the first porous layer comprises Nickel.

2. The electrode of Claim 1, wherein the first porous layer comprises Nickel Alloy, preferably Inconel 625.

3. The electrode of Claim 1 or 2, wherein the first porous layer comprises Nickel swarf.

4. The electrode of any one of Claims to 3, wherein the first and second porous layers are made from different materials.

5. The electrode of any one of Claims 1 to 4, wherein the second porous layer comprises Titanium.

6. The electrode of any one of Claims 1 to 5, wherein the second porous layer comprises Titanium swarf.

7. The electrode of any one of Claims 1 to 6,wherein the second porous layer is thicker than the first porous layer.

8. The electrode of any one of Claims 1 to 7, wherein the first porous layer has a thickness of 1mm to 5mm, preferably 3mm.

9. The electrode of any one of Claims 1 to 8, wherein the first and second porous layers are sintered layers.

10. The electrode of any one of Claims 1 to 9, wherein the first porous layer comprises a cobalt coating.

11. The electrode of any one of Claims 1 to 10, wherein the second porous layer comprises a platinum coating.

12. The electrode of any one of Claims 1 to 11, wherein the electrode is a flow-through electrode.

13. An electrolyser for generating hydrogen from electrolyte, said electrolyser comprising:an electrode according to any one of Claims 1 to 12, wherein the first porous layer has a first, preferably flat, surface opposite the second porous layers, an electrolyte chamber for supplying electrolyte to the electrode,wherein said first surface faces the electrolyte chamber.

14. The electrolyser of Claim 13, comprising an electrolyte supply circuit for supplying pressurised electrolyte to the electrolyte chamber.

15. The electrolyser of Claim 13 or 14, comprising a gas outlet for removing process gases from the electrode, wherein the gas outlet is connected to the second porous layer.

16. A method of manufacturing a flow-through electrode for electrolysis of water comprising:providing a mould;adding Nickel swarf to the mould to create a first layer;adding Titanium swarf to the mould to create a second layer adjacent to the first layer; and sintering the first and second layers together inside the mould.

17. The method of Claim 16, wherein the first and second layers are sintered by field assisted sintering.

18. The method of Claim 16 or 17, wherein the method comprises applying a vacuum and / or supplying purge gas, such as Nitrogen, during the sintering process.

19. The method of any one of Claims 16 to 18, wherein the method comprises applying a pressure to the first and second layers in the mould, during the sintering process.

20. The method of any one of Claims 16 to 19, comprising applying a catalyst coating, such as cobolt, on the first porous layer, preferably by means of Chemical Vapour Deposition.

21. The method of any one of Claims 16 to 20, comprising applying a catalyst coating, such as platinum, on the second porous layer, preferably by means of Chemical Vapour Deposition.

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