GB2629128A

GB2629128A - Electrolyser

Info

Publication number: GB2629128A
Application number: GB2219459.1A
Authority: GB
Inventors: Leuchtenberg Katya
Original assignee: Kp2m Ltd
Current assignee: Kp2m Ltd
Priority date: 2022-12-21
Filing date: 2022-12-21
Publication date: 2024-10-23
Also published as: WO2024134203A1; GB202219459D0

Abstract

An electrolyser 10 for the electrolysis of seawater, which comprises a housing for containing electrolyte in use, an anode 13a, 13b and a cathode 12 and an ultrasound generator 15a-d. A body 14 for the transmission of at least a part of incidental ultrasonic energy is also present. The body 14 comprises a peripheral support for an inboard portion, the inboard portion comprising a first portion comprising membrane (figure 3, 31) for the transmission of ions and a second portion for the transmission of ultrasonic energy (figure 3, 33), the second portion having a higher propensity for the transmission of ultrasonic energy than the first portion. A membrane unit 14 may be provided which supports porous membrane material (figure 3, 31) and is constructed as such to allow ultrasonic energy from the ultrasonic generators 15a-d travel through the membrane unit 14 to reach the central cathode 12 to mitigate passivation by removing the double layer.

Description

ELECTROLYSER

This invention relates generally to an electrolyser suitable for removing carbon dioxide from water, e.g. seawater. More specifically, although not exclusively, this invention relates to an electrolyser and a body comprising a membrane for use in said electrolyser.

Human activities such as burning fossil fuels release more carbon dioxide into the atmosphere than natural processes can remove, which causes the amount of carbon dioxide in the atmosphere to increase each year. The ocean acts as a carbon "sink" by dissolving carbon dioxide from the atmosphere into seawater to form carbonic acid (H2CO3).

The ability of the ocean to capture and store carbon has helped to slow the accumulation of atmospheric carbon dioxide. However, the dissolution of CO2 in sea water leads to ocean acidification. Since the start of the Industrial Revolution, the pH of the ocean's surface waters has dropped from 8.21 to 8.10. Ocean acidification has a negative impact on, for is example, marine life that have calcium carbonate shells or skeletons, because acidic conditions can cause dissolution of solid carbonates. The removal of small animals at or toward the base of a food chain can be deleterious for animals (including humans) further up the food chain. Therefore, there is a desire or need to reduce the amount of carbon dioxide dissolved in seawater.

One approach to remove carbon dioxide from seawater is to use electrochemistry. Seawater contains cations including magnesium and calcium, as well as carbonate ions from the dissolved carbon dioxide gas. The electrolysis of seawater causes the generation of hydroxide ions at the cathode. The electrochemical cell may contain a porous membrane located between the anode and cathode. The purpose of the membrane is to slow down the migration of ions in the electrolyte, which enables the pH at the cathode to become, and remain, strongly alkaline (and the pH at the anode to become, and remain, strongly acidic). This promotes the precipitation of magnesium and calcium carbonate salts (e.g. Mg(OH)2 and MgCa(CO3)2), which are insoluble in alkaline conditions, and as such can be recovered as a solid from the electrochemical process. Consequently, this process enables carbon dioxide (as presented in its dissolved, carbonic acid form) to be removed from seawater, and hence the ocean.

A problem that has been encountered with this process is cathode fouling, wherein the cathode surface becomes coated with a passivation layer originating from the metal ions in the seawater.

It is known in other electrochemical systems to use ultrasound to prevent the build-up of a passivation layer at an electrode. Ultrasonication (typically 15 -200 kHz or 20 to 200 kHz frequency) generates alternating low pressure and high pressure waves in fluids, leading to the formation and violent collapse of small vacuum bubbles. This phenomenon is termed cavitation and causes high speed impinging liquid jets and strong hydrodynamic shear-forces. These effects cause the destruction of the Helmholtz double layer or the Stern boundary layer surrounding the electrodes, which inhibits or prohibits the development of, or removes, the passivation layer from an electrode, for example the cathode. Our earlier patent application, W02016146986, describes the use of ultrasound generators mounted lo to the exterior of the grounded electrode of an electrochemical fluid treatment unit.

There is a concern that the use of ultrasonics as explained in our previous patent application may cause damage to the membranes used in water splitting electrolysis.

is It is therefore a first non-exclusive object of the invention to provide a means for effectively generating acidic and alkali conditions in an electrolyser.

It is a further object of the invention to provide means for effectively generating the electrochemical conditions for the removal of carbon dioxide from a fluid, for example sea 20 water.

It is a further object of the invention to effectively use ultrasound within an electrolyser to at least inhibit passivation of an electrode.

Accordingly, a first aspect of the invention provides an electrolyser comprising a housing for containing electrolyte in use, an anode and a cathode, an ultrasound generator, and a body for the transmission of at least a part of incidental ultrasonic energy, the body comprising a peripheral support for an inboard portion, the inboard portion comprising a first portion comprising membrane for the transmission of ions and a second portion for the transmission of ultrasonic energy, the second portion having a higher propensity for the transmission of ultrasonic energy than the first portion.

In a process for electrolysing seawater to remove carbon dioxide, we have been found although ultrasound does not damage the membrane, it does appear that the membrane reflects (or at least mitigates transmission of) ultrasound energy, which at least partially inhibits the passage of ultrasonic energy to the cathode to destroy (or at least disrupt) the passivation layer thereon.

By providing, in the body, a membrane portion (the first portion) and a non-membrane portion (the second portion) a balance can be struck between the transmission or passage of ions from one electrode to another (or from one side of the membrane to the other side of the membrane) with the passage of ultrasound waves which can help to at least partially inhibit the passivation of an electrode.

io We have found this to be particularly useful in a system where the tank comprises, or is provided as, a ground electrode (cathode) and a further electrode array of anode, cathode, anode is provided.

Such a system, when used as an electrolyser, might be described as C-M-A-M-C-M-A-M-is C (or perhaps, more accurately, Cl-M1-Al-M2-C2-M3-A2-M4-C3, where in each case M represents a body comprising a membrane. With the ultrasound generators mounted to the exterior surface of the tank (e.g. to the exterior of one of Cl and C3, and preferably both), ultrasound can be transmitted to effectively inhibit passivation of the central cathode (e.g. C2) even though it has to pass through a cathode, and anode, two bodies comprising membranes and the electrolytic solution being treated.

The bodies of the invention and the apparatus may also comprise a tank comprising or providing a ground electrode (cathode) and a central anode. Such a system, when used as an electrolyser, might be describes as C-M-A-M-C (or perhaps, more accurately, Cl-M1-Al-M2-C2, where in each case M represents a body comprising a membrane. The ultrasound generators are mounted to the exterior surface of the tank (e.g. to the exterior of one of Cl and C2, and preferably both). In such a system passivation of either side of the anode Al is inhibited by transmission of the ultrasound waves.

For reasons of throughput and efficiency, it is preferable to have a central cathode and two internal anodes over a single internal anode.

As will be appreciated, different systems with plural inboard cathodes may be used (e.g. Cl-M1-Al-M2-C2...Mm-Am-Mn-Cn-An...M3-A2-M4-C3 to further increase throughput.

In embodiments, the electrolyser may be suitable for use in a process to remove dissolved carbon dioxide (e.g. carbonate ions) from water, e.g. seawater. In embodiments, the electrolyte may be seawater. In embodiments, the removal of dissolved carbon dioxide may be in the form of crystalised magnesium and/or calcium carbonate salts.

A further aspect of the invention provides a body for the transmission of at least a part of incidental ultrasonic energy, the body comprising a peripheral support for an inboard portion, the inboard portion comprising a first portion comprising membrane for the transmission of ions and a second portion for the transmission of ultrasonic energy, the io second portion having a higher propensity for the transmission of ultrasonic energy than the first portion.

Advantageously, the body according to the invention allows ultrasound energy to travel through the second portion to reach the cathode to prevent passivation, whilst allowing ions is to travel through the first portion such that the membrane can perform its function of slowing down the migration of ions in the electrolyte to increase the efficiency of the electrochemical reaction. Thus, the body minimises losses of ultrasound energy caused by the membrane whilst allowing the membrane to function for reaction efficiency.

In embodiments, the transmission coefficient of ultrasound energy relative to water through the second portion of the body may be greater than 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or 0.99.

In embodiments, the transmission coefficient of ultrasound energy relative to water through the first portion of the body may be less than 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01.

In embodiments, the surface area of the first portion, e.g. the membrane of the first portion, of the body may be greater than 30% of the total surface area of the body, e.g. greater than 35%, or greater than 40%, or greater than 45%, or greater than 50%, or greater than 55%, or greater than 60%, or greater than 65%, or greater than 70%, or greater than 75%, or greater than 80% of the total surface area of the body.

Advantageously, we have found that a surface area of greater than 30% (surface area of first portion) of the total surface area of the body provides an effective balance between the ultrasound energy reaching the internal electrode, e.g. an internal cathode to prevent passivation, and the slowing down of the migration of ions for reaction efficiency.

In embodiments, the peripheral support may be provided by a frame. In embodiments, the second portion of the body may be provided as an extension of the frame, for example, the frame (or peripheral support) may be formed (e.g. moulded) as a single piece with the second portion.

In embodiments, the membrane of the first portion of the body may comprise a main body and one or more aperture(s). In embodiments, the one or more apertures of the membrane may comprise cut-out portion(s) which are not fully surrounded by the main body of the membrane. In embodiments, the cut-out portion(s) may be located at an edge, e.g. a first is and/or second edge, of the main body of the membrane. In embodiments, the one or more apertures may be located within the main body of the membrane.

In embodiments, the one or more aperture(s) of the membrane of the first portion of the body, and the second portion of the body, e.g. an extension of the frame, may be in registry, and/or may align with one another. In embodiments, the second portion of the body, e.g. an extension of the frame, may completely cover the one or more aperture(s) of the membrane of the first portion of the body.

Advantageously, the alignment of the one or more aperture(s) of the membrane and the second portion allows ultrasound energy to travel therethrough to reach the cathode to prevent passivation, whilst supporting the porous membrane located between the anode and cathode such that it can perform its function of slowing down the migration of ions in the electrolyte.

In embodiments, the membrane may comprise more than one aperture, e.g. two, three, four, five, six, or more, or plural apertures. In embodiments, the second portion aligns with, and fully covers, the more than one, e.g. plural, apertures.

In embodiments, the membrane may be a porous membrane. In embodiments, the porous membrane may comprise pores having a diameter of from 0.01 to 1.0 pm, for example, from 0.10 to 0.90 pm, or from 0.11 to 0.80 pm, or from 0.12 to 0.70 pm, or from 0.13 to 0.60 pm, or from 0.14 to 0.50 pm, or from 0.15 to 0.40 pm, or from 0.20 to 0.30 pm, e.g. 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, or 0.29 pm. In embodiments, the porous membrane may comprise pores having a density of between 50 to 100%, e.g. from 60 to 90%, or from 70 to 80%.

In embodiments, the membrane, e.g. the porous membrane, may have a thickness of from 50 to 500 pm, e.g. from 60 pm to 400 pm, or from 70 to 300 pm, or from 80 to 200 pm, e.g. 100 pm.

In embodiments, at least part of, or all of, the membrane, e.g. the porous membrane, may be fabricated from polytetrafluoroethylene (PTFE). In embodiments, at least part of, or all of, the membrane, e.g. the porous membrane, may be fabricated from polyvinylidene fluoride (PVDF). In embodiments, at least part of, or all of, the membrane, e.g. the porous is membrane, may be fabricated from one or more of polypropylene and/or polysulfonone.

In embodiments, the frame may have a thickness of 1 to 5mm, e.g. from 2 to 4mm.

In embodiment, the frame may be formed as a unitary component.

In embodiments, at least part of, or all of, the frame, e.g. a solid portion of the frame, may be fabricated from a polymer, e.g. polyvinylchloride (PVC), polytetrafluoroethylene (PTFE), or polyamide (e.g. Nylon). For example, at least part of, or all of, the frame may be fabricated from unplasticized PVC (uPVC). Advantageously, u-PVC is compatible with the strongly acidic and basic conditions that surround the anode and cathode of the electrolyser.

In embodiments, the electrolyser may further comprise a support member for location adjacent the membrane. In embodiments, the support member may comprise at least one, e.g. two, three, four, five, six, or more, or plural apertures. In embodiments, the at least one, e.g. plural, aperture(s) of the support member may align with, or be in registry with, the at least one, e.g. plural, aperture(s) of the membrane. In embodiments, the second portion, e.g. provided by the frame, may align with, and fully cover, the more than one, e.g. plural, apertures of the support member and/or membrane.

In embodiments, at least part of, or all of, the support member is fabricated from a mesh. In embodiments, at least part of, or all of, the support member is fabricated from polypropylene, e.g. polypropylene mesh. In embodiments, the support member has a thickness of between 100 to 1000 pm, e.g. from 200 to 800 pm, or from 300 to 600 pm, e.g. s 400 pm.

In embodiments, the membrane and the support member have a combined thickness of between 0.1 to 1.0 pm, e.g. from 0.2 to 0.8 pm, or from 0.3 to 0.7 pm, or from 0.4 to 0.6 pm, e.g. 0.5 pm.

In embodiments, the membrane, e.g. the porous membrane, may have a thickness of 100pm, and the support member may have a thickness of 400 pm.

In embodiments, the membrane, e.g. the porous membrane, is coated onto the support is member.

In embodiments, the membrane, the frame, and the support member may form a membrane unit. The membrane unit may comprise or provide the body according to the invention. The electrolyser may comprise one, two, three, four, or more, or plural membrane units.

In embodiments, the cathode may comprise an outer cathode. In embodiments, the cathode may comprise a further, e.g. central, cathode. In embodiments, the cathode may comprise an outer cathode and a central cathode. In embodiments, the outer cathode may form at least part of the housing of the electrolyser. In embodiments, the outer cathode may be a grounded electrode. In embodiments, the central cathode is located substantially centrally in the housing, e.g. the outer cathode, of the electrolyser. In embodiments, the central cathode is a flat plate electrode comprising a first major surface and a second major surface.

In embodiments, the anode may comprise a first anode and a second anode. In embodiments, the first anode and/or the second anode is a flat plate electrode comprising a first major surface and a second major surface.

In embodiments, the electrolyser may comprise more than one, e.g. two, three, four, or more, or plural treatment zones, wherein a treatment zone is defined as the volume between a major surface of an anode and a major surface of a cathode.

s In embodiments, the electrolyser comprises more than one body comprising a membrane, e.g. membrane unit. In embodiments, each body comprising a membrane, e.g. membrane unit, is located between a major surface of a cathode and a major surface of an anode. In embodiments, the electrolyser may comprise a body comprising a membrane, e.g. membrane unit, in each treatment zone.

In embodiments, the electrolyser comprises an outer cathode, a central cathode, and a first and second anode, wherein the first anode is located between the outer cathode and a first major surface of the central cathode, the second anode is located between the outer cathode and the second major surface of the central cathode, wherein a body comprising is a membrane, e.g. membrane unit, is located between each of the outer cathode and the first anode, the first anode and the central cathode, the central cathode and the second anode, and the second anode and the outer cathode.

In embodiments, the electrolyser may comprise more than one ultrasound generator, e.g. two, three, four, or more, or plural ultrasound generators.

In embodiments, one or more or all of the ultrasound generators may be piezoelectric transducers.

In embodiments, one or more or all of the ultrasound generators may generate ultrasound energy having a frequency of 20 to 50 kHz, for example 30 to 40 kHz.

In embodiments, the one or more ultrasound generators may be located on, e.g. fixed or mounted to, the housing, e.g. the outer cathode, of the electrolyser. In embodiments, one or more or each of the ultrasound generators may be configured to provide ultrasound energy in a direction towards the central cathode through the body, e.g. through the second portion, for example provided by the frame, and the one or more apertures of the membrane and/or support member.

Advantageously, location of the ultrasound generators in this manner provides ultrasound energy which is able to travel though the one or more apertures of the membrane and/or support member, and is also able to travel through the second portion to reach the central cathode and mitigate passivation. More advantageously, location of the ultrasound s generators in this manner provides does not increase the transfer of ions through the membrane, such that it is able to effectively perform its function of slowing down the migration of ions.

In embodiments, the electrolyser may comprise an inlet for electrolyte, e.g. seawater, to be io received into the housing, e.g. into the outer cathode. In embodiments, the electrolyser may comprise an outlet for treated fluid, e.g. treated seawater, to be removed from the housing, e.g. the outer cathode.

A further aspect of the invention provides a method of treating seawater to remove is dissolved carbon dioxide using the electrolyser of the invention, the method comprising providing the electrolyser of the invention, introducing seawater into the housing, applying a voltage across the anode and cathode to produce an electrolytic current, and providing power to the ultrasound generator.

A yet further aspect of the invention provides a method of removing carbonic acid from water (e.g. sea water) using an electrolyser, the method comprising continuously feeding water into a tank of the electrolyser, the electrolyser comprising at least one cathode and at least one anode and a membrane unit provided therebetween, the method further comprising allowing or causing ions to pass through first portion of the membrane unit comprising a membrane whilst passing ultrasound through a second portion of the membrane unit comprising a solid portion.

The ultrasound being useful to at least partially inhibit passivation of at least one of the anode and cathode.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. For the avoidance of doubt, the terms "may", "and/or", "e.g.", "for example" and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, s whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

io Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is an electrolyser according to the prior art; Figure 2 is an electrolyser according to an embodiment of the invention; is Figure 3A is a membrane unit for use in the electrolyser of Figure 2; Figure 3B is an exploded view of the membrane unit of Figure 3A; Figure 4A is a membrane unit for use in the electrolyser of Figure 2 according to a further embodiment of the invention; Figure 4B is an exploded view of the membrane unit of Figure 4A; Figure 5A is a membrane unit for use in the electrolyser of Figure 2 according to a further embodiment of the invention; Figure 5B is an exploded view of the membrane unit of Figure 5A;.

Figure 6A and 6B are photographs of experimental results.

Referring now to Figure 1, there is shown an electrolyser 1 according to the prior art. The electrolyser 1 is suitable for use in a process to remove dissolved carbon dioxide (e.g. carbonate ions) from water, e.g. seawater. The electrolyser 1 comprises an anode 2, a cathode 3, a porous membrane 4, and electrolyte 5. The electrolyte 5 is seawater, which contains a mixture of ions including sodium (Na'), chloride (Cr), sulphate (S043-), magnesium (Mg2+), potassium (IC), calcium (Ca2+), and other minor constituents. The dissolved gaseous carbon dioxide is present in the form of carbonate (C032-) ions.

In use, a current is applied across the anode 2 and cathode 3, which causes the following water splitting reactions to occur: At the anode: 2H20 -> 02 + 4H+ +4e At the cathode: 2H20 + 2e-H2 + 20H-Therefore, protons are generated at the anode 2 resulting in acidic conditions, and hydroxide ions are generated at the cathode 3 resulting in basic conditions.

The porous membrane 4 is located between the anode 2 and cathode 3. The porous membrane 4 is a microfiltration membrane which is freely permeable to the passage of water molecules and ions dissolved therein. The purpose of the porous membrane 4 is to o slow down the passage of the protons and the hydroxide ions generated at the anode 2 and cathode 3 respectively, which generates a more acidic environment at the anode 2 (pH -2) and a more basic environment at the cathode 3 (pH -12).

In strongly alkaline conditions (pH -12) at the cathode 3, the magnesium (Mg2+) and calcium is (Ca2+) ions in the electrolyte may combine with the carbonate ions (C032-) to form insoluble salts (e.g. magnesium hydroxide and calcium carbonate), which co-precipitate out of the solution at pH 12. In this way, carbon dioxide is removed from the seawater.

A problem encountered in this process is that the cathode 3 is fouled by becoming coated with a crystalline passivation layer originating from the metal ion content of the seawater.

The inventors have found that the use of sonochemistry is effective in removing this passivation layer. Ultrasound generators may be positioned on the exterior surface of the grounded electrode in a similar manner to that described in the previous patent application W02016146986. However, the porous membrane 4 reflects the ultrasound energy, which at least partially blocks the passage of the ultrasound energy to the cathode 3 to destroy the passivation layer surrounding the cathode 3.

Referring now to Figure 2, there is shown an electrolyser 10 according to a first embodiment of the invention. The electrolyser 10 is suitable for use in a process to remove dissolved carbon dioxide (e.g. carbonate ions) from water, e.g. seawater.

The electrolyser 10 comprises an outer cathode 11, a central cathode 12, a first anode 13a, a second anode 13b, four membrane units 14a to 14d, and four ultrasonic generators 15a to 15d. In this embodiment, the ultrasonic generators 15a to 15d are piezoelectric 35 transducers.

The central cathode 12 comprises a first major surface 12a and a second major surface 12b The electrolyser 10 further comprises a lid 16, an inlet 17 for incoming flow of electrolyte (e.g. seawater), a gas extraction duct 18, a distribution manifold 19, and an outlet manifold 20.

The outer cathode 11 provides a reaction chamber for the electrolyser 10, which contains io the seawater electrolyte in use. The central cathode 12, the first and second anodes 13a, 13b, and the four membrane units 14a to 14d each have a flat plate structure. The central cathode 12, the first and second anodes 13a, 13b, and the four membrane units 14a to 14d are located within the outer cathode 11. The central cathode 12 is provided substantially centrally within the outer cathode 11. The first anode 13a is located between the outer is cathode 11 and the first major surface 12a of the central cathode 12. The second anode 13b is located between the outer cathode 11 and the second major surface 12b of the central cathode 12.

There is a membrane unit, e.g. one of 14a to 14d, provided between each anode 13a, 13b and cathode major surface 12a, 12b. The structure of the membrane units 14a to 14d is described further in Figures 3A and 3B. The first membrane unit 14a is located between the outer cathode 11 and the first anode 13a. The second membrane unit 14b is located between the first anode 13a and the central cathode 12. The third membrane unit 14c is located between the central cathode 12 and the second anode 13b. The fourth membrane unit 14d is located between the second anode 13b and the outer cathode 11.

The four ultrasonic generators 15a to 15d are located on, and fixed to, the exterior surface of the outer cathode 11.

In this embodiment, the outer cathode 11 and the central cathode 12 are fabricated from stainless steel. The first and second anodes 13a, 13b are fabricated from platinised titanium. Advantageously, platinised titanium minimises chlorine evolution, which is known to form during the electrolysis of seawater. The plate structure of each of the first and second anodes 13a, 13b, and the central cathode 12, is 3mm thick.

Referring now to Figure 3A, there is shown a membrane unit 14, e.g. any one of 14a to 14d for use in the electrolyser 10 shown in Figure 2, according to an embodiment of the invention. Referring also to Figure 3B, there is shown an exploded view of the membrane unit 14. The membrane unit 14 comprises a porous membrane material 31, a support s member 32, and a frame 33.

The porous membrane material 31 comprises plural openings 31a to 31d and a solid portion A. The support member 32 also comprises plural openings 32a to 32d and a main aperture B. The frame 33 is shaped to comprise plural solid portions 33a to 33d and a cut-out portion C. The plural openings 31a to 31d of the porous membrane material 31 align with the plural openings 32a to 32d of the support member 32 and the plural solid portions 33a to 33d of the frame 33 when the membrane unit 14 is assembled. The plural openings 31a to 31d of is the porous membrane material 31 need not be exactly the same shape as the plural openings 32a to 32d support member 32.

The main aperture B of the support member 32 and the cut-out portion C of the frame 33 algin with the solid portion A of the porous membrane material 31 when the membrane unit 14 is assembled.

In this embodiment, the porous membrane material 31 is fabricated from PTFE, the support member 32 is polypropylene mesh, and the frame 33 is fabricated from a non-conductive polymeric material, e.g. u-PVC. The porous membrane material 31 is pre-coated onto the support member 32. Advantageously, u-PVC is compatible with the strongly acidic and basic conditions that surround the anodes 13a, 13b, and cathodes 11, 12 of the electrolyser 10. These layers are laminated together to provide a membrane having 0.22 pm pore size and a thickness of 0.5 mm.

The particular shape and configuration of the components in this membrane unit 14 provide an exposed surface area of the porous membrane material 31 of 56%.

It has been found that the porous membrane material 31 and the support member 32 at least partially block the passage of ultrasound energy therethrough, and instead reflect the ultrasonic sound waves. It has been surprisingly found that the material from which the frame 33 is fabricated allows most of the ultrasound energy to pass therethrough.

The membrane unit 14 is usable in the electrolyser 10 of Figure 2. The membrane unit 14, s e.g. 14a, 14b, 14c, 14d, may be located within the outer cathode 11 of the electrolyser 10 using guide railings (not shown).

The plural openings 31a to 31d in the porous membrane material 31 and the plural openings 32a to 32d of the support member 32 align with the position of the ultrasonic generators 15a to 15d on the external surface of the outer cathode 11.

The following table shows the transmission coefficient and reflection coefficient of suitable materials for the fabrication of the frame 33. The frame 33 must be made of a material of a similar acoustic impedance to water. This can be calculated from the impedance of a is material. The closer the transmission coefficient is to 1, the greater the penetration of ultrasound energy through the material. Additionally, the table shows how the porous membrane material 31 does not allow ultrasound energy through.

The transmission coefficient was calculated as follows: a T 4Z1 Z2 (Zi ±Z2) 2 The reflection coefficient was calculated as follows: (Z2 -Zi) 2 Z1 +Z2 Water-u-PVC Water -PTFE Water-Nylon Water-porous Water-porous PP PTFE i.e. i.e. membrane membrane 31 Transmission coefficient 0.89 0.96 0.94 0.11 0.20 Reflection 0.11 0.04 0.06 0.94 0.86 coefficient aR In use, the electrolyser 10 of Figure 2 functions to remove dissolved carbon dioxide (e.g. carbonate ions) from water, e.g. seawater. The seawater is fed through the inlet 17 and enters the reaction chamber provided by the outer cathode 11. A current is applied across the outer cathode 11, the central cathode 12, and the first and second anodes 13a, 13b to enable the water splitting reaction to occur, as described in respect of Figure 1. The power used in this embodiment is up to 400 amps per reactor module. During the electrolysis s reaction, the central cathode 12 becomes passivated with a layer of metal ions. The ultrasonic generators 15a to 15d are used to generate ultrasound energy, which travels through the seawater electrolyte, through the frame 33, to the central cathode 12. In this embodiment, the ultrasonic generators are 30 to 40 kHz transducers.

Advantageously, the frame 33 of the membrane unit 14 allows ultrasound energy to pass therethrough, whilst supporting the porous membrane material 31 such that there is enough exposed surface area for the porous membrane material 31 to perform its function of slowing down the migration of ions within the electrolyser 10 to enable the pH at the cathode to remain strongly alkaline. Thus, the ultrasound energy from the ultrasonic generators 15a is to 15d is able to travel through the membrane unit 14 to reach the central cathode 12 to mitigate passivation by removing the double layer.

Referring now to Figures 4A and 4B, there is shown a membrane unit 14' according to a further embodiment of the invention. The membrane unit 14' is similar to that shown in Figure 3A and Figure 3B. The features which are similar are labelled with the same reference number followed by a prime 0 symbol, and perform the same function. Only the differences are described.

In this embodiment, the porous membrane material 31' comprises five openings 31a', 31b', 31c', 31d', and 31e and a solid portion A'. The support member 32 comprises five openings 32a', 32b', 32c', 32d', 32e and a main aperture B'. The frame 33' comprises five solid portions 33a', 33b', 33c', 33d', 33e and a cut-out portion C'.

When the membrane unit 14' is assembled, the five openings 31a', 31b', 31c', 31d', 31e of the porous membrane material 31' align with the five openings 32a', 32b', 32c', 32d', 32e of the support member 32, and the five solid portions 33a', 33b', 33c', 33d', 33e of the frame 33'. The solid portion A' of the porous membrane material 31' aligns with the main aperture B' of the support member 32' and the cut-out portion C' of the frame 33'. The particular shape and configuration of the components in this membrane unit 14' provide an exposed surface area of the porous membrane material 31' of 48%.

Referring now to Figures 5A and 5B, there is shown a membrane unit 14" according to a further embodiment of the invention. The membrane unit 14" is similar to that shown in Figure 5A and Figure 5B. The features which are similar are labelled with the same s reference number followed by a prime 0 symbol, and perform the same function. Only the differences are described.

In this embodiment, the porous membrane material 31" comprises five openings 31a", 31b", 31c", 31d", and 31e' and a solid portion A". The support member 32 comprises five openings 32a", 32b", 32c", 32d", 32e' and a main aperture B" comprising multiple cut-out portions. The frame 33" comprises five solid portions 33a", 33b", 33c", 33d", 33e' and a cut-out portion C" comprising multiple separate cut-out portions.

When the membrane unit 14" is assembled, the five openings 31a", 31b", 31c", 31d", 31e' is of the porous membrane material 31" align with the five openings 32a", 32b", 32c", 32d", 32e' of the support member 32', and the five solid portions 33a", 33b", 33c", 33d", 33e' of the frame 33". The solid portion A" of the porous membrane material 31" aligns with the main aperture B" of the support member 32" and the cut-out portion C" of the frame 33". The particular shape and configuration of the components in this membrane unit 14" provide an exposed surface area of the porous membrane material 31' of 44%.

Experimental Results A first experimental set up of an electrolyser was provided. The electrolyser had a housing which contained the following components layered in the following order: a cathode providing a housing, a first membrane, an anode, a second membrane, and a cathode. The first and second membrane was a porous PTFE membrane. The anode was a 3mm titanium anode. A test cathode of aluminium foil (12 micron thick) was provided.

Ultrasound generators were mounted to the external surface of the housing, and were used to provide ultrasound energy directed towards the test cathode, through the first and second membranes, and the anode.

Referring now to Figure 6A, there is shown a photograph of the test cathode after the experiment was performed. It is shown that there is no damage to the foil of the test cathode, which demonstrates than no ultrasound energy was able to reach the test cathode.

A second experimental set up of an electrolyser was provided. The electrolyser had a housing which contained the following components layered in the following order: a cathode providing a housing, a first u-PVC sheet, an anode, a second u-PVC sheet, and a cathode.

s The first u-PVC sheet and the second u-PVC sheet had a thickness of 1.5 mm. The anode was a 3mm titanium anode. A test cathode of aluminium foil (12 micron thick) was provided.

Ultrasound generators were mounted to the external surface of the housing, and were used to provide ultrasound energy directed towards the test cathode, through the first and second io u-PVC sheets, and the anode.

Referring now to Figure 6B, there is shown a photograph of the test cathode after the experiment was performed. It is shown that there is damage to the foil of the test cathode, which demonstrates than ultrasound energy was able to reach the test cathode through the is u-PVC sheets.

This demonstrates that u-PVC sheet may be used to provide the second portion of the body of the invention to allow transmission of ultrasonic energy, whilst the membrane provides the first portion of the body of the invention and allows transmission of ions.

Advantageously, the body according to the invention allows ultrasound energy to travel through the second portion to reach the cathode to prevent passivation, whilst allowing ions to travel through the first portion such that the membrane can perform its function of slowing down the migration of ions in the electrolyte to increase the efficiency of the electrochemical reaction. Thus, the body minimises losses of ultrasound energy caused by the membrane whilst allowing the membrane to function for reaction efficiency.

We have further determined that by forming the membrane unit wherein the membrane represents at least 30% of the total surface area allows sufficient passage of ions to allow electrolysis of the sea water, and that by providing a sufficient surface area of solid material sufficient ultrasonic energy can be transmitted to the internal electrode(s) to at least partially inhibit passivation.

It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. For example, the overall shape of the components within the membrane unit 14, 14', 14" can vary whilst maintaining its function. The shape, size, and position of the plural openings of the support member and/or porous membrane material may vary, for example, depending on the position and number of ultrasonic generators used in the electrolyser of the invention.

It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.

Claims

CLAIMS1. An electrolyser comprising a housing for containing electrolyte in use, an anode and a cathode, an ultrasound generator, and a body for the transmission of at least a part of incidental ultrasonic energy, the body comprising a peripheral support for an inboard portion, the inboard portion comprising a first portion comprising membrane for the transmission of ions and a second portion for the transmission of ultrasonic energy, the second portion having a higher propensity for the transmission of ultrasonic energy than the first portion.
2. An electrolyser according to any preceding Claim, wherein the transmission coefficient of ultrasound energy relative to water through the second portion of the body is greater than 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or 0.99.
3. An electrolyser according to any preceding Claim, wherein the transmission coefficient of ultrasound energy relative to water through the first portion of the body is less than 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01.
4. An electrolyser according to any preceding Claim, wherein the surface area of the first portion of the body is greater than 30% of the total surface area of the body, e.g. greater than 35%, or greater than 40%, or greater than 45%, or greater than 50%, or greater than 55%, or greater than 60%, or greater than 65%, or greater than 70%, or greater than 75%, or greater than 80% of the total surface area of the body.
5. An electrolyser according to any preceding Claim, wherein the peripheral support is provided by a frame, for example the second portion of the body is provided as an extension of the frame, e.g. the frame (or peripheral support) is formed (e.g. moulded) as a single piece with the second portion.
6. An electrolyser according to any preceding Claim, wherein the membrane of the first portion of the body comprises a main body and one or more aperture(s), for example wherein the one or more aperture(s) of the membrane of the first portion of the body, and the second portion of the body, e.g. an extension of the frame, are in registry, and/or align with one another.
7. An electrolyser according to any preceding Claim, wherein the membrane is a porous membrane, e.g. comprising pores having a diameter of from 0.01 to 1.0 pm, and/or comprising pores having a density of between 50 to 100%, e.g. from 60 to 90%, or from 70 to 80%.
8. An electrolyser according to any preceding Claim, wherein the membrane, e.g. the io porous membrane, has a thickness of from 50 to 500 pm, e.g. from 60 pm to 400 pm, or from 70 to 300 pm, or from 80 to 200 pm, e.g. 100 pm.
9. An electrolyser according to any preceding Claim, wherein at least part of, or all of, the membrane, e.g. the porous membrane, is fabricated from one or more of is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polypropylene, polyethersulfone and/or polysulfone.
10. An electrolyser according to any preceding Claim, wherein the peripheral support, (e.g. the frame) has a thickness of from 1 to 5 mm.
11. An electrolyser according to any preceding Claim, wherein at least part of, or all of, the peripheral support (e.g. the frame) is fabricated from a polymer, e.g. one or more of polyvinylchloride (PVC), unplasticized PVC (uPVC), polytetrafluoroethylene (PTFE), or polyamide (e.g. Nylon).
12. An electrolyser according to any preceding Claim, further comprising a support member for location adjacent the membrane, e.g. comprising at least one, or two, three, four, five, six, or more, or plural apertures, for example wherein the at least one, e.g. plural, aperture(s) of the support member align with the at least one, e.g. plural, aperture(s) of the membrane.
13. An electrolyser according to any preceding Claim, wherein at least part of, or all of, the support member is fabricated from a mesh, e.g. polypropylene mesh.
14. An electrolyser according to any preceding Claim, wherein the support member has a thickness of between 100 to 1000 pm, e.g. from 200 to 800 pm, or from 300 to 600 pm, e.g. 400 pm.
15. An electrolyser according to any preceding Claim, wherein the membrane and the support member have a combined thickness of between 0.1 to 1.0 pm, e.g. from 0.2 to 0.8 pm, or from 0.3 to 0.7 pm, or from 0.4 to 0.6 pm, e.g. 0.5 pm.
16. An electrolyser according to any preceding Claim, wherein the membrane, e.g. the to porous membrane, is coated onto the support member.
17. An electrolyser according to any preceding Claim, comprising an outer cathode and a further, e.g. central, cathode.is
18. An electrolyser according to any preceding Claim, wherein the anode comprises a first anode and a second anode, e.g. wherein the first anode and/or the second anode is a flat plate electrode comprising a first major surface and a second major surface.
19. An electrolyser according to any preceding Claim, comprising an outer cathode, a central cathode, and a first and second anode, wherein the first anode is located between the outer cathode and a first major surface of the central cathode, the second anode is located between the outer cathode and the second major surface of the central cathode, wherein a body comprising a membrane, e.g. membrane unit, is located between each of the outer cathode and the first anode, the first anode and the central cathode, the central cathode and the second anode, and the second anode and the outer cathode.
20. An electrolyser according to any preceding Claim, comprising more than one ultrasound generator, e.g. two, three, four, or more, or plural ultrasound generators.
21. An electrolyser according to any preceding Claim, wherein one or more or all of the ultrasound generators are piezoelectric transducers.
22. An electrolyser according to any preceding Claim, wherein one or more or all of the ultrasound generators generate ultrasound energy having a frequency of 20 to 50 kHz, for example 30 to 40 kHz.
23. An electrolyser according to any preceding Claim, wherein the one or more ultrasound generators is located on, e.g. fixed or mounted to, the housing, e.g. the outer cathode, of the electrolyser.
24. A body for the transmission of at least a part of incidental ultrasonic energy, the body comprising a peripheral support for an inboard portion, the inboard portion comprising a first portion comprising membrane for the transmission of ions and a second portion for the transmission of ultrasonic energy, the second portion having a higher propensity for the transmission of ultrasonic energy than the first portion.is
25. A method of treating seawater to remove dissolved carbon dioxide using the electrolyser according to any of Claims 1 to 23, the method comprising introducing seawater into the housing, applying a voltage across the anode and cathode to produce an electrolytic current, and providing power to the ultrasound generator.
26. A method of removing carbonic acid from water (e.g. sea water) using an electrolyser, the method comprising continuously feeding water into a tank of the electrolyser, the electrolyser comprising at least one cathode and at least one anode and a membrane unit provided therebetween, the method further comprising allowing or causing ions to pass through first portion of the membrane unit comprising a membrane whilst passing ultrasound through a second portion of the membrane unit comprising a solid portion.