WO2018100357A1

WO2018100357A1 - Electrode and electrochemical cell comprising the same

Info

Publication number: WO2018100357A1
Application number: PCT/GB2017/053580
Authority: WO
Inventors: Patrick Simon Bray
Original assignee: Roseland Holdings Limited
Priority date: 2016-11-29
Filing date: 2017-11-28
Publication date: 2018-06-07
Also published as: GB2559111A; GB201620189D0

Abstract

An electrode assembly for use in an electrochemical cell for the production of ozone from water, the electrode assembly comprising an elongate electrode body formed from a polycrystalline diamond, the electrode body comprising first and second opposing contact surfaces, the first contact surface for contacting a semi-permeable membrane; wherein the electrode assembly further comprises a conductor having an elongate conductor portion extending along a major portion of the length of the electrode body, the conductor portion being in electrical contact with the second contact surface of the electrode body along at least a major portion of the length of the electrode body. An electrochemical cell comprising the electrode assembly and its use in the production of ozone by the electrolysis of water is also provided.

Description

ELECTRODE AND ELECTROCHEMICAL CELL COMPRISING THE SAME

The present invention relates to an electrode and to an electrochemical cell comprising the electrode. The electrode and the electrochemical cell are of advantage in the production of ozone by the electrolysis of water.

Electrochemical cells are well known and find use in a range of

electrochemical applications. Electrodes for use in the electrochemical cells are also known. One such application for electrochemical cells is in the production of ozone from water by electrolysis. Electrochemical cells for the production of ozone from water generally comprise an anode and a cathode, with the anode and cathode being separated by a semi-permeable membrane, also referred to as a proton exchange membrane. The electrochemical production of ozone from water may be

represented generally by the following formula:

3H₂0 -> 0₃ + 3H₂ ΔΗ°298 = 207.5 kcal

The reaction at the anode of the electrochemical cell may be represented by the following formula:

3H₂0 -> 0₃ + 6H⁺ + 6e-

An example of the electrochemical production of ozone from water and an electrochemical cell for such use is disclosed in US 5,972, 196 A.

Electrodes for use in electrochemical cells for the production of ozone from water are known in the art. For example, a perforated conductive diamond electrode for ozone generation by the electrolysis of water is disclosed in JP 2005-336607. One recent disclosure of an electrode assembly is US 2010/0006450. This document discloses a diamond electrode and an electrolysis cell. US 2010/0006450 discloses an electrode comprising an electrically conducting diamond plate comprising at least one elongate aperture, in which the aperture edge length per unit working area of the diamond plate is greater than about 4 mm/mm². The electrode may consist essentially of a diamond plate. The diamond plate is preferably CVD diamond, with a preference for CVD polycrystalline diamond being expressed in US 2010/0006450. The apertures in the diamond electrode may be formed by laser cutting. Other techniques for forming the apertures disclosed include ion beam milling and plasma etching. There is also disclosed an alternative to using a diamond plate electrode. In particular, it is disclosed that an electrode assembly may be formed by coating an electrically conductive substrate with a conductive diamond layer. The substrate is formed with at least one elongate aperture. This

arrangement is indicated to have the advantage of allowing a backing plate and flow channels to be incorporated into a single component. In addition, the use of a conductive diamond coating is stated to have cost advantages compared to a monolithic diamond plate.

EP 0949205 discloses a process and apparatus for producing acidic water containing dissolved hydrogen peroxide.

US 2013/0341204 discloses an electrode assembly for use in liquid environments. A membrane-electrode assembly is disclosed in WO 2011/135749.

US 5,900,127 discloses an electrode for electrolysis and an electrolytic cell comprising the same. EP 165228 discloses a diamond-coated porous substrate.

An improved design for an electrode of an electrochemical cell has now been found. The improved electrode is of particular advantage when used in the electrochemical production of ozone from water. According to a first aspect of the present invention, there is provided an electrode assembly for use in an electrochemical cell for the production of ozone from water, the electrode assembly comprising:

an elongate electrode body formed from a polycrystalline diamond, the electrode body comprising first and second opposing contact surfaces, the first contact surface for contacting a semi-permeable membrane;

wherein the electrode assembly further comprises a conductor having an elongate conductor portion extending along a major portion of the length of the electrode body, the conductor portion being in electrical contact with the second contact surface of the electrode body along at least a major portion of the length of the electrode body.

The electrode assembly of the present invention comprises an electrode body. The electrode body is formed from polycrystalline diamond. The

polycrystalline diamond may be formed using any suitable technique and such techniques are known in the art. More particularly, the electrode body is cut from a diamond wafer, for example by means of a laser. The diamond wafer may be formed using any suitable technique. A preferred technique for forming the diamond wafer is chemical vapour deposition (CVD). CVD techniques for forming diamond wafer are known in the art.

A particularly preferred diamond material is a doped diamond material, more preferably boron-doped diamond.

When forming the electrode body from a wafer formed by techniques, such as CVD, in which the wafer has a growth surface, the electrode body is preferably cut such that the growth surface forms one of the contact surfaces of the electrode body and the nucleation surface forms the other of the contact surfaces. Most preferably, the growth side forms the first contact surface of the electrode body and the nucleation side forms the second contact surface and has the conductor portion of the conductor in electrical contact therewith. When installed in an electrolysis cell, the first contact surface of the electrode body is in contact with a semi-permeable membrane, as discussed in more detail hereinafter, and the electrode body is connected to a source of electrical current by a conductor. The electrode assembly of the present invention is provided with a conductor having an elongate conductor portion. The elongate conductor portion extends along at least a major portion of the length of the elongate electrode body and is in electrical contact with the second surface of the electrode body along the length of the elongate conductor portion. In use, electrical current is supplied to the electrode body through the conductor. It has been found that the distribution of electrical charge from the conductor along and across the electrode body is significantly improved by means of the conductor having an elongate conductor portion that extends along at least a major portion of the length of the electrode body. This arrangement in turn provides an improved and more even current density across the surface of the electrode body.

The elongate electrode body may be of any suitable shape and configuration. In one embodiment, the electrode body is in the form of an elongate plate, that is having opposing major surfaces, forming the first and second contact surfaces, extending between opposing edge surfaces of the electrode body.

The electrode body is elongate and has a longitudinal axis. The longitudinal axis discussed herein is the central longitudinal axis of the elongate electrode body. In this respect, the term 'elongate' is a reference to the length of the electrode body being greater than the width of the electrode. In use, when the electrode assembly is incorporated into an electrochemical cell and the cell is operated, water may be caused to flow over or otherwise contact the electrode body. In use, the electrode body is preferably arranged in such embodiments to extend with its longitudinal axis generally parallel to the general direction of any flow of the water through the cell. The ratio of the length of the electrode body to the width of the electrode body may be any suitable ratio. In this respect, the ratio of the length of the electrode body to its width is a reference to the ratio of the length to the width of the body at its widest point, measured across a major surface of the electrode body from one edge surface to the opposite edge surface perpendicular to the longitudinal axis. The ratio is preferably at least 2, more preferably at least 3, still more preferably at least 4. A ratio of at least 5 is preferred, still more preferably at least 6. In a preferred embodiment, the ratio of the length of the electrode body to the width of the electrode body is in the range of from 2 to 12, more preferably from 3 to 10, still more preferably from 4 to 8. A ratio of about 6 to 7 has been found to be particularly suitable for many embodiments.

The electrode body preferably has opposing major surfaces extending between opposing edge surfaces and forming the first and second contact surfaces. In this embodiment, the relative dimensions of the electrode body are such that the body is an elongate plate, that is the width of the major surfaces is significantly greater than the width of the edge surfaces. In this respect, the width of the edge surface can be considered to be the thickness of the electrode body. Preferably, the ratio of the width of each major surface, that is the width of the major surface at its widest point measured across the major surface from one edge surface to the opposite edge surface perpendicular to the longitudinal axis, to the width of the edge surface is at least 2, preferably at least 4, more preferably at least 5, still more preferably at least 6, more preferably still at least 8. In a preferred embodiment, the ratio of the width of each major surface to the width of the edge surfaces is at least 10. In a preferred embodiment, the ratio is in the range of from 2 to 25, more preferably from 4 to 20, still more preferably from 6 to 18, more preferably still from 8 to 15. A ratio of about 12 has been found to be particularly suitable for many embodiments. Similarly, the ratio of the length of the electrode body to the width of the edge surface is at preferably least 10, more preferably at least 20, still more preferably at least 30, more preferably still at least 40, in particular more preferably at least 50. In a preferred embodiment, the ratio of the width of each major surface to the width of the edge surfaces is at least 60. In a preferred embodiment, the ratio is in the range of from 10 to 150, more preferably from 30 to 130, still more preferably from 50 to 120, more preferably still from 60 to 100. A ratio of from 70 to 90, more particularly about 80, has been found to be particularly suitable for many embodiments. The dimensions of the electrode body are selected according to the required duty of the electrode and the electrolytic cell in which it is used. In particular, the dimensions of the electrode may be selected to provide the required current efficiency. In the case of the electrode assembly of the present invention, the current efficiency is a function of the ratio of the length of the edges of the electrode body exposed to liquid being electrolysed, in particular water, to the surface area of the electrode body. In general, a higher ratio of edge length to surface area of the electrode body results in a higher current efficiency of the electrode assembly when in use.

Preferably, the ratio of the total length of the edges of the electrode body to the surface area of the electrode body is at least 0.1 , more preferably a least 0.2, still more preferably at least 0.25, more preferably still at least 0.3. A ratio of up to 2.5 can be provided, preferably up to 2.0, more preferably up to 1.5. A ratio in the range of from 0.1 to 2.5, preferably from 0.2 to 2.0, more preferably from 0.25 to 1.75, still more preferably from 0.3 to 1.6, especially from 0.3 to 1.5 is preferred. A ratio of from 0.35 to 1.4 is particularly suitable for many embodiments.

The ratio of the total length of the edges of the electrode body to the surface area of the electrode body may vary according to the size of the electrode.

Examples of the dimensions and ratio for different sizes of electrode are summarised in the following table.

As noted above, the dimensions of the electrode body are selected according to the duty to be performed when in use. In addition, the dimensions of the electrode body may be determined by the construction of the electrode body and its method of manufacture. For many applications, the electrode body is preferably at least 3 mm in length, more preferably 5 mm in length, more preferably at least 10 mm, still more preferably at least 20 mm, more preferably still at least 30 mm. The maximum electrode body length may be limited by the construction and method of manufacture. Lengths of up to 200 mm may be employed, for example up to 150 mm. In the case of one preferred embodiment, in which the electrode body is cut from a wafer of solid diamond material prepared by chemical vapour deposition (CVD), the maximum length of the electrode body is up to about 140 mm. For many embodiments, a length of from 30 to 50 mm, in particular from 35 to 45 mm, for example about 40 mm, is particularly suitable.

The width of the electrode body, that is the width of the major surfaces of the body between opposing edge surfaces at its widest point, is preferably at least 1 mm, more preferably at least 2 mm, still more preferably at least 3 mm. A width of up to 20 mm, preferably up to 15 mm, more preferably up to 10 mm is particularly suitable for many embodiments. For many embodiments, a length of from 2 to 12 mm, preferably from 3 to 10 mm, more preferably from 4 to 8 mm is particularly suitable, for example from 5 to 7 mm, such as about 6 mm.

The width of the edge surfaces is preferably at least 0.1 mm, more preferably at least 0.2 mm, still more preferably at least 0.3 mm. A width of up to 2 mm may be employed, for example up to 1.5 mm or up to 1 mm. A width of from 0.1 to 1 mm has been found to be particularly suitable for many embodiments, preferably from 0.2 to 0.8 mm, more preferably from 0.3 to 0.7 mm, still more preferably from 0.4 to 0.6 mm, such as about 0.5 mm.

As noted above, the electrode assembly of the present invention comprises a conductor having a conductor portion extending along at least a major portion of the length of the elongate electrode. The conductor portion is in electrical contact with the second contact surface of the electrode body. In this respect, the conductor portion is in electrical contact with the second surface of the electrode body at at least one location along its length. More preferably, the conductor portion is in electrical contact with the second surface of the electrode body at a plurality of locations along the length of both the conductor portion and the electrode body, for example two, three, four, five or more locations. In this way, the distribution of the electrical current across and along the electrode body is more even. In one preferred embodiment, the conductor portion is in electrical contact with the electrode body along a major portion of the length of the conductor portion, more preferably along substantially its entire length.

In this respect, the term 'electrical contact' is a reference to a contact between the conductor portion and the surface of the electrode body, whereby an electrical charge may pass between the electrode body and the conductor portion. In one preferred arrangement, the electrical contact is formed by a direct contact between the conductor portion and the surface of the electrode body. Alternatively, the electrical contact between the conductor portion and the surface of the electrode body may be by means of an intervening electrically conductive material.

The elongate conductor portion of the conductor extends along at least a major portion of the length of the electrode body, that is along at least 50% of the length of the electrode body. Preferably, the elongate conductor portion extends along at least 55%, more preferably at least 60% of the length of the electrode body, more preferably still at least 65%, still more preferably at least 70%. In preferred embodiments, the elongate conductor portion extends along at least 75% of the length of the electrode body, more preferably at least 80%, more preferably still at least 85%, still more preferably at least 90%. In one preferred embodiment, the elongate conductor portion extends along at least 95% of the length of the electrode body.

The elongate conductor portion may be formed from any suitable material that is electrically conductive and may be electrically connected to the second contact surface of the electrode body. The electrically conductive material may be any suitable material that has a sufficient conductivity. A preferred conductive material for forming the conductor portion is a metal or mixture of metals. Examples of suitable metals include Copper (Cu), Silver (Ag), Gold (Au), Platinum (Pt), Tungsten (W), Tantalum (Ta) and Niobium (Nb). Preferably, the conductor portion comprises a metal that forms a bond with the sp³ carbon structure of the diamond material. A particularly preferred electrically conductive material is one comprising titanium. Titanium forms a Ti-C bond with the sp³ carbon structure of the diamond material, in turn providing an improved distribution of current across the electrode body. The conductive material for forming the conductor portion is selected to be compatible with the physical properties of the diamond material of the electrode body, in particular the property of thermal expansion. This is particularly the case where the conductor portion is in contact with the surface of the electrode body at two or more positions along its length and/or the contact between the conductor portion and the electrode body is along a significant portion of the length of the conductor portion.

The conductor portion may be formed from a single electrically conductive material, for example a single metal. Alternatively, the electrically conductive material of the conductor portion may comprise two or more electrically conductive component, for example two or more metals. Suitable mixtures of metals include copper and silver.

The conductor portion of the conductor may have any suitable form. For example, the conductor portion may comprise one or more elongate conductor elements, such as rods, bars or wires, that extend along at least a major portion of the length of the second contact surface of the electrode body. However, one preferred form for the conductor portion is a layer of electrically conductive material that extends along at least a major portion of the length of the second contact surface. In one preferred arrangement, the conductor portion comprises both a layer of electrically conductive material applied to the surface of the electrode body and an elongate conductor element extending along a major portion of the length of the layer. In this arrangement, the elongate conductor element is in electrical contact with the layer of conductive material. For example, the elongate conductor element may be connected directly to the layer of conductive material, such as by soldering. Alternatively, the elongate conductor element may be electrically connected to the layer of conductive material indirectly, for example by way of an electrically conductive terminal connected to the said layer, again such as by soldering. The layer of electrically conductive material may be applied to the electrode body using any suitable technique. One particularly preferred technique is sputter deposition or sputter coating. Different sputter deposition techniques may be employed, with radio frequency (RF) sputter coating being preferred. It has been found that applying the layer by sputter coating results in an improved adhesion between the electrically conductive material and the diamond of the electrode body, in turn improving the distribution of electrical current across the electrode body and the current density. The conductor portion of the conductor may have any suitable size to accommodate the electrical load being applied thereto. In embodiments in which the conductor portion comprises a layer of electrically conductive material, the said layer may have any suitable thickness. The layer of electrically conductive material is preferably at least 200 nm in thickness, more preferably at least 300 nm, still more preferably at least 400 nm, more preferably still at least 500 nm. A thickness of at least 600 nm is particularly preferred, especially at least 1000 nm. The layer may have a thickness of up to 10000 nm, more preferably up to 7500 nm. A thickness of at least 5000 nm is particularly suitable for many embodiments and provides for an improved current distribution and an even current density across the surface of the electrode body.

The layer of electrically conductive material may extend over all or part of the second contact surface of the electrode body. Preferably, the layer of electrically conductive material extends over a major portion but not all of the second contact surface of the electrode body. More preferably, the layer of electrically conductive material extends over a major portion of the second contact surface of the electrode body, with a portion at an edge of the contact surface, preferably all edges of the major surface, not being covered by the conductive material, such that the diamond material is exposed. This edge portion may be at least 0.5 mm in width, that is the distance from the edge of the second contact surface of the electrode body to the edge of the layer of conductive material measured perpendicular to the edge. More preferably, the edge portion has a width of at least 1.0 mm. An edge portion having a width of 1.5 mm or greater is particularly preferred for many embodiments. An edge portion having a width of 2.0 mm or greater is also suitable for many embodiments. In one preferred arrangement, the electrode assembly further comprises an insulating layer of an electrically insulating material extending over the conductor portion of the conductor. The arrangement is particularly preferred in embodiments in which the conductor portion comprises a layer of electrically conductive material. The insulating layer extends over the conductor portion and preferably covers the conductor portion completely.

The insulating layer may comprise any suitable electrically insulating material. In one embodiment, the insulating layer comprises a material that is both electrically insulating and exhibits hydrophobic properties. Suitable materials for forming the insulating layer include nitrides. Suitable compounds for inclusion in the insulating layer are compounds of silicon, titanium, zirconium or hafnium. Preferred

compounds for inclusion in the insulating layer are silicon nitride (S13N4), titanium nitride (TiN), zirconium nitride (ZrN) and hafnium nitride (HfN), or mixtures thereof. Anodised aluminium oxide may also be used as an electrically insulating material.

The insulating layer may be applied using any suitable technique. A preferred embodiment employs a material for the insulating layer that can be applied by sputter coating, for example the silicon, titanium, zirconium and hafnium nitrides, and anodised aluminium oxide mentioned above.

Alternatively, the insulating layer may comprise a resin, preferably a hydrophobic resin, more preferably a thermosetting hydrophobic resin. Examples of suitable resins include polyester resins, polyimide resins and epoxy resins. The resin acts to seal the layers of conductive material and insulating material. The resin may also be employed to seal the conductor connection, discussed in more detail below. One particularly preferred resin material is a polyimide resin, for example a polyimide resin film. Such polyimide resins are commercially available, for example the Kapton^® products from Du Pont™.

The electrode assembly may comprise a single layer of an electrically insulating material. Alternatively, two or more different insulating materials may be employed in two or more layers. It has been found that the resin may exhibit a low adhesion to the surface of the electrically conducting material of the conductor portion. Therefore, it is preferred to provide the electrode body with a layer of insulating material, as discussed above, and to coat the electrode body, including the insulating material, in a layer of resin.

Accordingly, in one preferred embodiment, the electrode assembly comprises a first insulating layer extending over the conductor portion of the conductor, the first insulating layer comprising an electrically insulating material. The material of the first insulating layer is preferably one that may be applied to the conductor portion by sputter coating. The material of the first insulating layer preferably comprises a nitride. Suitable insulating materials are compounds of silicon, titanium, zirconium, and hafnium, in particular silicon nitride (S13N4), titanium nitride (TiN), zirconium nitride (ZrN) and hafnium nitride (HfN), or mixtures thereof. Anodised aluminium oxide (AI2O₃) may also be used as a material for the first insulating layer. In this embodiment, the electrode assembly comprises a second insulating layer extending over the first insulating layer, the second insulating layer comprising a resin, preferably a hydrophobic resin, more preferably a thermosetting hydrophobic resin. Examples of suitable resins include polyester resins and epoxy resins.

The conductor preferably further comprises a terminal connected or formed from part of the conductor portion. The conductor portion of the conductor preferably has a composition that allows the terminal to be connected to the conductor portion by soldering. Preferably, the terminal is coated in a resin, as described hereinbefore.

An electrical supply conductor, such as a cable, may be connected to the conductor, preferably to a terminal of the conductor. Again, this connection is preferably formed by soldering. As noted above, the electrode body may have a range of forms and shapes.

In one preferred embodiment, the electrode assembly comprises an electrode body having an elongate electrode body having first and second opposing edge surfaces and opposing first and second major faces extending between the first and second opposing edge surfaces; wherein the electrode body has an elongate longitudinal axis; wherein the electrode body comprises:

a first body portion having a first width measured in a direction perpendicular to the longitudinal axis and between the longitudinal axis and the first edge surface across the first and second opposing major surfaces; and

a second body portion having a second width measured in a direction perpendicular to the longitudinal axis and between the longitudinal axis and the first edge surface across the first and second opposing major surfaces; wherein the second width is greater than the first width.

It has been found that the form of the electrode body of this embodiment promotes the mass transfer of ozone away from the electrode bodies, in turn further increasing the efficiency and productivity of the electrochemical cell. This is particularly the case when the electrode assembly is being employed in an arrangement in which a fluid, such as water, is caused to flow along the length of the electrode body.

The first and second body portions of the electrode body may have any suitable cross-sectional shape. Preferably, the first and second body portions have the same general cross-sectional shape, with the dimensions of the portions differing, as noted above. A preferred cross-sectional shape is rectangular.

As noted above, the electrode body of this embodiment comprises first and second body portions, in which the first body portion has a first width and the second body portion has a second width, with the second width being greater than the first width. In this respect, the first and second widths are each measured in a direction perpendicular to the longitudinal axis of the electrode body and between the longitudinal axis and the first edge surface across the first and second opposing major surfaces.

The first and second body portions may be asymmetrical about the

longitudinal axis. For example, a first body portion on one side of the longitudinal axis may be opposite a second portion on the opposite side of the longitudinal axis. More preferably, at least one, more preferably both, of the first and second portions are arranged symmetrically about the longitudinal axis of the electrode body. More particularly, a first body portion on one side of the longitudinal axis is preferably opposite a first body portion on the opposite side of the axis and/or a second body portion one side of the longitudinal axis is preferably opposite a second body portion on the opposite side of the longitudinal axis. More preferably, each body portion on one side of the longitudinal axis is opposite a body portion of the same type on the other side of the longitudinal axis. The first body portion is preferably adjacent the second body portion.

As noted, the width of the second body portion is greater than the width of the first body portion. In this respect, the widths of the body portions are references to the width at the widest point of the said body portion. The ratio of the width of the second body portion to the width of the first body portion is preferably at least 1.1 , more preferably at least 1.2, still more preferably at least 1.3, more preferably still at least 1.4. A ratio of at least 1.5 is more preferred, more preferably at least 1.6, still more preferably at least 1.7, more preferably still at least 1.8, for example at least 1.9. A ratio of the width of the second body portion to the width of the first body portion is preferably 2.0 or greater.

The electrode body may comprise one or more first body portions and one or more second body portions. Preferably, the electrode body comprises a plurality of first body portions and a plurality of second body portions, more preferably with the first and second body portions arranged in an alternating pattern along the length of the electrode body.

The first and second body portions may have any suitable shape, that is the shape of the first and second major surfaces of the body portion. For example, the first and/or second body portions may have a rounded shape, that is with the edges of the first and second major surfaces extending in an arc. More preferably, the first and/or second body portions are angular in shape, that is the edges of the first and second major surfaces extend in a plurality of straight lines, each straight line extending at an angle to an adjacent straight line. For example, the first and/or second body portions may comprise an edge having two straight lines, forming a generally triangular form. More preferably, the first and/or second body portions have a generally rectangular shape. Preferably, the first and second body portions have the same general shape.

In embodiments in which the electrode body comprises a plurality of first and/or second body portions, the plurality of first body portions are preferably of the same shape and size and/or the plurality of second body portions are preferably of the same shape and size.

The electrode body may be asymmetrical about the longitudinal axis. More preferably, the electrode body is symmetrical about the longitudinal axis. In a further aspect, the present invention provides an electrochemical cell comprising:

a first electrode;

a second electrode; and

a semi-permeable membrane extending between and in contact with the first electrode and the second electrode;

wherein one or both of the first and second electrodes comprises an electrode assembly as hereinbefore described.

Most preferably, both the first and second electrodes comprise an electrode assembly as hereinbefore described. The first and second electrodes may comprise electrode bodies of different shapes and/or different sizes. Most preferably, the electrode body of the first electrode is substantially the same shape and size as the electrode body of the second electrode. The semi-permeable membrane functions as a cation exchange membrane and is also referred to as a proton exchange membrane (PEM) when the

electrochemical cell is in use, selectively allowing the passage of certain cations and protons (hydrogen ions) from one of the first and second electrodes to the other of the first and second electrodes, depending upon the polarity of operation of the cell, that is from the anode to the cathode, while preventing the passage of anions.

Suitable materials for forming the semi-permeable proton exchange membrane are known in the art and are commercially available. Particularly preferred materials for forming the semi-permeable membrane are fluoropolymers, in particular chemically stabilized perfluorosulfonic acid/PTFE copolymers. Such materials are commercially available under the trade name Nafion^® (ex. Du Pont), for example.

The semi-permeable proton exchange membrane (PEM) extends between the first and the second electrode, in particular between the first contact surface of the first electrode and the first contact surface of the second electrode, and is preferably in contact with both electrodes. During operation of the cell, in particular in the electrolysis of water to produce ozone, the production of ozone occurs along the edges of the electrodes at the interface between the electrode forming the anode, the semi-permeable membrane and water. It has been found that the electrode assembly of the present invention exhibits a high efficiency in the production of ozone at the aforementioned interface.

It is preferred that the semi-permeable proton exchange membrane (PEM) extends across the entire opposing major surfaces of the electrode bodies of the first and second electrodes. More preferably, the semi-permeable proton exchange membrane both extends across the entire opposing major surfaces of the electrode bodies of the first and second electrodes and extends beyond at least one edge, most preferably at all edges, of the electrode body. Preferably, the semi-permeable proton exchange membrane extends beyond the edges of the electrode bodies by at least 1.0 mm, more preferably at least 2.0 mm, still more preferably at least 3.0 mm, more preferably still at least 5.0 mm.

In a further aspect, the present invention provides a method for the production of ozone by the electrolysis of water, the method comprising:

providing an electrochemical cell as hereinbefore described; supplying an electrical current to the first and second electrodes of the electrochemical cell; and

providing water to the interfaces between the semi-permeable membrane and the first and second electrodes.

In the method of the present invention, water is ozonated, that is provided with a concentration of ozone. Water ozonated in this way finds use in a range of applications, including disinfection and sanitisation. The electrochemical cell may be immersed in a body of water, for example water to be ozonated. Alternatively, the water may be provided as a stream of water to flow along the electrode bodies of the first and second electrodes. For example, the electrochemical cell may be disposed in a conduit along which water is caused to flow.

In a still further aspect, the present invention provides the use of an electrochemical cell as hereinbefore described in the production of ozone by the electrolysis of water. Embodiments of the present invention will now be described, by way of example of only, having reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional view of an electrochemical cell comprising an electrode assembly according to one embodiment of the present invention;

Figure 2 is a plan view of an electrode body for use in an electrode assembly according to one embodiment of the present invention;

Figure 3 is a plan view of the electrode assembly of Figure 2 with a conductor portion comprising a layer of electrically conductive material applied to the electrode body;

Figure 4 is a plan view of an electrode assembly of a further alternative embodiment of the present invention; and Figure 5 is a plan view of an electrode assembly of a still further alternative embodiment of the present invention.

Turning first to Figure 1 , there is shown a cross-sectional view of an electrochemical cell according to one embodiment of the present invention. The electrochemical cell, generally indicated as 2, comprises a first electrode assembly 4 having an electrode body 4a and a second electrode assembly 6 having an electrode body 6a.

Each electrode body 4a, 6a is formed from a polycrystalline Boron-doped diamond (BDD), in particular cut from a wafer of the diamond material by a laser. The BDD material may be formed using any suitable technique, in particular CVD. Diamond material of this kind is available commercially. When prepared using a technique such as CVD, the diamond material has a growth face and a nucleation face, which form the major surfaces of the electrode body.

A semi-permeable or proton exchange membrane 8 extends between the first and second electrode assemblies 4, 6 and is in contact with a major surface of the electrode body 4a, 6a of each electrode assembly 4, 6. The membrane 8 preferably contacts the growth face of the electrode bodies 4a, 6a. The membrane is preferably of a type that allows for the reversal of the polarity of the electrochemical cell during use. The membrane 8 is formed from Nafion^® type N117. As shown in Figure 1 , the membrane 8 extends beyond the edges of each electrode body 4a, 6a.

The major surface of each electrode body 4a, 6a not covered by the membrane 8, that is the nucleation face of the electrode body, is provided with a respective conductor having a conductor portion, in the form of layers 10a, 10b, 12a, 12b of an electrically conductive material. In particular, the layers 10a, 12a in contact with the surface of the electrode body are formed from Titanium (Ti). The layers 10b, 12b, overlying the layers 10a, 12a of titanium, are formed from an alloy of Copper (Cu) and Silver (Ag). As shown in the figures, each layer 10a, 10b, 12a, 12b extends along a major portion of the length of the electrode body. As shown in Figure 1 , an edge portion 14a, 14b of each electrode body is not covered by the electrically conductive layers 10a, 10b, 12a, 12b and is exposed. In the embodiment shown, the conductor portion extends about 85% of the length of the electrode body. The layers of electrically conductive material is applied to each electrode body by sputter coating. The layers of electrically conductive material 10a, 10b, 12a, 12b provide each electrode body with a layer of electrically conductive material that is approximately 5000 nm in total thickness. The conductor further comprises connector terminals 16 soldered to each layer of electrically conductive material 10b, 12b. An electrical conductor 30 is soldered to and extends between the connector terminals 16 on each electrode body, to provide and distribute an electric current to the respective electrode body, by way of the connector terminals 16 and the layers of electrically conductive material.

The exposed surface of each layer of electrically conductive material 10b, 12b is coated in a layer of electrically insulating material 18, 20, in particular Silicon Nitride (S13N4) . The layer of electrically insulating material 18, 20 is applied to the layer of electrically conductive material 10, 12 by sputter coating. The layer of electrically insulating material is approximately 1000 nm in thickness.

A layer of thermosetting hydrophobic resin 22, 24 is provided on each layer of electrically insulating material 18, 20. The resin is preferably a polyimide resin, with alternative resins being a polyester resin or an epoxy resin. The resin is from 1 to 3 mm in thickness. A thicker layer of insulating material may be employed, if desired.

The layer of electrically insulating material 16, 18 may be omitted, in which case the layer of resin 20, 22 is provided directly onto the surface of the layer of electrically conductive material 10, 12.

The resin is applied once the electrical terminals 16 and the electrical conductors 30 have been soldered into place. Current feed cables 26 are connected to respective cable connector terminals 16a by soldering, to provide an electric current to the respective electrical conductor and the layers of electrically conductive material 10a, 10b, 12a, 12b and to the electrode body 4a, 6a.

The electrochemical cell 2 of Figure 1 is particularly suitable for use in the electrolysis of water to produce ozone. In use of the electrochemical cell 2, water is caused to flow over or otherwise contact the assembly. In the case of flowing water, the water caused to flow relative to the electrochemical cell in the direction indicated by the arrow A in Figure 1. When an electrical current is applied by way of the current feed cables 26 from a suitable source of electrical power, one of the electrode assemblies 4, 6 operates as the anode and the other assembly 4, 6 as the cathode, depending upon the polarity of the supplied current. Ozone is produced at the edges of the electrode body 4a, 6a of the anode at the interface between the electrode body 4a, 6a, the membrane 8 and the surrounding water. In operation, the polarity of the cell is periodically reversed, to prevent the accumulation of deposits on the electrode bodies.

Turning to Figure 2, there is a shown a plan view of an electrode body for use in the electrode assembly of the present invention. The electrode body, generally indicated as 102, is as described above with respect to Figure 1. The electrode body 102 is elongate, having a length at least six times its width. The electrode body 102 has a longitudinal axis X - X and comprises a plurality of first body portions 104. Each of the first body portions 104 has a first width w measured from the longitudinal axis X - X to the edge of the electrode body 102 perpendicular to the longitudinal axis, as indicated in Figure 2. The electrode body 102 further comprises a plurality of second body portions 106. Each of the second body portions 106 has a second width w² measured from the longitudinal axis X - X to the edge of the electrode body 102 perpendicular to the longitudinal axis, as indicated in Figure 2. The second width w² is greater than the first width w¹. For example, for an electrode body having a total length of 40 mm, the width w² may be 3 mm and the width w 1.5 mm.

The electrode body 102 of Figure 2 has the first body portions 104 and the second body portions 106 arranged in an alternating pattern along the length of the electrode body on both sides of the longitudinal axis X - X. The first and second body portions 104, 106 on one side of the longitudinal axis X - X are positioned along the length of the electrode body the same as the first and second body portions 104, 106 on the opposite side of the longitudinal axis, that the first and second portions 104, 106 on one side of the axis are opposite respective first and second portions 104, 106 on the other side of the axis. The electrode body 102 is symmetrical about the longitudinal axis X - X.

The first and second body portions 104, 106 are shown in Figure 2 to have generally rectangular configurations, with the edges of the body portions being straight. Alternatively, the edges of the body portions 104, 106 may be curved. The corners of the body portions 104, 106 may be rounded.

Referring now to Figure 3, there is shown a plan view of an electrode assembly comprising the electrode body 102 of Figure 2, bearing a layer of electrically conductive material 110. The layer of electrically conductive material 110 is as described above with respect to Figure 1 and forms the conductor portion of a conductor of the electrode assembly. As shown in Figure 3, the layer 1 10 extends over a major surface of the electrode body 102 and covers a major portion of the surface. An edge portion 112 of the surface of the electrode body 102 is left uncovered, such that the BDD diamond material of the electrode body 102 is exposed at the edge portion.

Turning to Figure 4, there is a shown a plan view of an electrode assembly of an alternative embodiment of the present invention. The electrode assembly, generally indicated as 202, comprises an electrode body 204. The electrode body is as described above with respect to Figure 1. The electrode body 204 is elongate, having a length at least six times its width. The electrode body 204 is generally rectangular in plan view, as shown in Figure 4.

The electrode assembly 202 comprises a conductor 206 having a conductor portion 208 comprising two parallel, elongate strips of electrically conductive material 208a and 208b extending longitudinally along the electrode body along a major portion of the length of the electrode body. The strips 208a, 208b are formed from the electrically conductive material and are applied to the surface of the electrode body 204 as described above for the layer of electrically conductive material of Figure 1. The conductor 206 comprises a laterally extending connecting portion 210 extending between and connecting the strips 208a, 208b of the conductor portion 208. The connecting portion 210 is formed in the same manner as the strips 208a, 208b. A terminal 212 is connected to the connecting portion 210 by soldering. An electrical cable is soldered to the terminal 212 when the electrode assembly is incorporated into an electrochemical cell, in the manner described above and shown in Figure 1. The arrangement of the conductor and its conductor portions shown in Figure

4 may be employed with the electrode body of Figures 2 and 3 in analogous manner.

Turning to Figure 5, there is there is a shown a plan view of an electrode assembly of a further alternative embodiment of the present invention. The electrode assembly, generally indicated as 302, comprises an electrode body 304. The electrode body is as described above with respect to Figure 1. The electrode body 304 is elongate, having a length at least six times its width. The electrode body 304 is generally rectangular in plan view, as shown in Figure 5. The electrode assembly 302 comprises a conductor 306 having a conductor portion 308 formed from an elongate strip of electrically conductive material extending longitudinally along the electrode body along a major portion of the length of the electrode body. The conductor portion 308 is formed from the electrically conductive material and are applied to the surface of the electrode body 304 as described above for the layer of electrically conductive material of Figure 1.

A terminal 310 is connected to the conductor portion 308 by soldering. An electrical cable is soldered to the terminal 310 when the electrode assembly is incorporated into an electrochemical cell, in the manner described above and shown in Figure 1.

The arrangement of the conductor and its conductor portions shown in Figure 5 may be employed with the electrode body of Figures 2 and 3 in analogous manner.

The conductor of the embodiments of Figures 3, 4 and 5 may be covered in an electrically insulating material and/or a resin, as described above with reference to the assembly of Figure 1.

Claims

1. An electrode assembly for use in an electrochemical cell for the production of ozone from water, the electrode assembly comprising:

2. The electrode assembly according to claim 1 , wherein the electrode body comprises diamond.

3. The electrode assembly according to claim 2, wherein the electrode body is formed from diamond.

4. The electrode assembly according to claim 3, wherein the diamond is boron- doped diamond (BDD).

5. The electrode assembly according to any preceding claim, wherein the ratio of the length of the electrode body to the width of the electrode body is at least 3.

6. The electrode assembly according to claim 5, wherein the ratio of the length of the electrode body to the width of the electrode body is at least 5.

7. The electrode assembly according to any preceding claim, wherein the ratio of the width of each major surface of the electrode body to the width of the edge surfaces of the electrode body is at least 8.

8. The electrode assembly according to claim 7, wherein the ratio of the width of each major surface of the electrode body to the width of the edge surfaces of the electrode body is at least 10.

9. The electrode assembly according to any preceding claim, wherein the ratio of the length of the electrode body to the width of the edge surface is at least 20.

10. The electrode assembly according to claim 9, wherein the ratio of the length of the electrode body to the width of the edge surface is at least 30.

11. The electrode assembly according to any preceding claim, wherein the ratio of the total length of the edges of the electrode body to the surface area of the electrode body is at least 0.4.

12. The electrode assembly according to claim 11 , wherein the ratio of the total length of the edges of the electrode body to the surface area of the electrode body is up to 2.0.

13. The electrode assembly according to any preceding claim, wherein the conductor portion extends along at least 55% of the length of the electrode body.

14. The electrode assembly according to claim 13, wherein the conductor portion extends a long at least 70% of the length of the electrode body.

15. The electrode assembly according to any preceding claim, wherein the conductor portion comprises a metal.

16. The electrode assembly according to claim 15, wherein the metal is selected from titanium, platinum, tungsten, tantalum, niobium, copper, silver, gold or mixtures thereof.

17. The electrode assembly according to any preceding claim, wherein the conductor portion comprises one or more rods, bars or wires.

18. The electrode assembly according to any preceding claim, wherein the conductor portion comprises at least one layer of electrically conductive material.

19. The electrode assembly according to claim 18, wherein the at least one layer comprises a first layer of a first electrically conductive material and a second layer of a second electrically conductive material.

20. The electrode assembly according to claim 19, wherein the first electrically conductive material is selected from titanium, platinum, tungsten, tantalum and niobium.

21. The electrode assembly according to either of claims 19 or 20, wherein the second electrically conductive material is selected from copper, gold, silver and mixtures thereof.

22. The electrode assembly according to any of claims 18 to 21 , wherein the or each layer of electrically conductive material is applied by sputter deposition.

23. The electrode assembly according to any preceding claim, wherein the electrode body is cut from a diamond wafer having a growth surface and a nucleation surface, the conductor portion being in electrical contact with the nucleation surface.

24. The electrode assembly according to any preceding claim, wherein the conductor portion extends over a major portion of the surface of the electrode body, with an edge portion not being covered in the electrically conductive material.

25. The electrode assembly according to any preceding claim, wherein the electrode body is provided with at least one layer of insulating material over the conductor portion.

26. The electrode assembly according to claim 25, wherein the insulating material is a metal nitride.

27. The electrode assembly according to claim 26, wherein the insulating material is a nitride of silicon, hafnium, titanium or zirconium.

28. The electrode assembly according to any of claims 25 to 27, wherein the insulating material is applied by sputter coating.

29. The electrode assembly according to any preceding claim, wherein the electrode body is provided with a layer of resin.

30. The electrode assembly according to any preceding claim, wherein the electrode body is an elongate electrode body having first and second opposing edge surfaces and opposing first and second major faces extending between the first and second opposing edge surfaces;

wherein the electrode body has an elongate longitudinal axis;

wherein the electrode body comprises:

31. The electrode assembly according to claim 30, wherein the first and second body portions have the same general cross-sectional shape.

32. The electrode assembly according to either of claims 30 or 31 , wherein each body portion on one side of the longitudinal axis of the electrode body is opposite a body portion of the same type on the other side of the longitudinal axis.

33. The electrode assembly according to any of claims 30 to 32, wherein first body portion is adjacent the second body portion.

34. The electrode assembly according to any of claims 30 to 33, wherein the ratio of the width of the second body portion to the width of the first body portion is at least 1.5.

35. The electrode assembly according to any of claims 30 to 34, wherein the electrode body comprises a plurality of first body portions and a plurality of second body portions.

36. The electrode assembly according to any of claims 30 to 35, wherein the first and/or second body portions are angular in shape.

37. The electrode assembly according to claim 36, wherein the first and/or the second body portions are rectangular in shape.

38. The electrode assembly according to any preceding claim, wherein the electrode body is symmetrical about its central longitudinal axis.

39. The electrode assembly according to any preceding claim, wherein the electrode body is at least 3 mm in length.

40. The electrode assembly according to claim 39, wherein the electrode body is up to 140 mm in length.

41. The electrode assembly according to any preceding claim, wherein the width of the electrode body is at least 2 mm.

42. The electrode assembly according to claim 42, wherein the width of the electrode body is up to 10 mm.

43. The electrode assembly according to any preceding claim, wherein the width of the edge surfaces of the electrode body is about 0.5 mm.

44. An electrochemical cell comprising:

a first electrode;

a second electrode; and

a semi-permeable membrane extending between and in contact with the first electrode and the second electrode; wherein one or both of the first and second electrodes comprises an electrode assembly according to any preceding claim.

45. The electrochemical cell according to claim 44, wherein both the first and second electrodes comprise an electrode assembly according to any of claims 1 to 43.

46. The electrochemical cell according to either of claims 44 or 45, wherein the semi-permeable membrane comprises a fluoropolymer.

47. The electrochemical cell according to claim 46, wherein the fluoropolymer is a perfluorosulfonic acid/PTFE copolymer.

48. The electrochemical cell according to any of claims 44 to 47, wherein the semi-permeable membrane extends beyond the edges of the first and second electrode bodies.

49. The electrochemical cell according to claim 48, wherein the semi-permeable membrane extends at least 2.0 mm beyond the edges of the first and second electrode bodies.

50. A method for the production of ozone by the electrolysis of water, the method comprising:

providing an electrochemical cell according to any of claims 44 to 49;

supplying an electrical current to the first and second electrodes of the electrochemical cell; and

51. The use of an electrochemical cell according to any of claims 44 to 49 in the production of ozone by the electrolysis of water.