WO2018100361A1

WO2018100361A1 - Electrochemical cell assembly and method for operation of the same

Info

Publication number: WO2018100361A1
Application number: PCT/GB2017/053584
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: GB201620198D0; GB2557187A

Abstract

A device for producing ozonated water from a reservoir of water is provided, the device comprising: a conduit having an inlet and an outlet and for conveying water between the inlet and the outlet; an electrochemical cell assembly operable to electrolyse water in the conduit to produce ozone and having a first electrode assembly and a second electrode assembly; a flow sensor for detecting a flow of water within the conduit; a processor for receiving an indication of water flow from the flow sensor and determining if the flow of water is above a threshold value and, if the flow of water is above the threshold value, activating the electrochemical cell. A method for producing ozonated water from water flowing in a conduit, the method comprises: providing an electrochemical cell assembly operable to electrolyse water in the conduit to produce ozone, the electrochemical cell assembly having a first electrode assembly and a second electrode assembly; determining the flow of water in the conduit past the electrode assemblies of the electrochemical cell assembly; determining if the flow of water exceeds a threshold value; and if the flow of water is above the threshold value, activating the electrochemical cell.

Description

ELECTROCHEMICAL CELL ASSEMBLY AND METHOD FOR OPERATION OF

THE SAME

The present invention relates to an electrochemical cell assembly and a method of operating the same. The present invention concerns in particular a device comprising an electrochemical cell assembly for the production of ozone and to a method of operating the same. Electrochemical cells find use in a range of applications for conducting a variety of electrochemical processes. In general, the cells comprise an anode and a cathode, separated by a semi-permeable membrane, in particular a Cation Exchange Membrane that may also be described as a Proton Exchange Membrane. One particular application for electrochemical cells is the production of ozone by the electrolysis of water.

Ozone is one of the strongest and fastest acting oxidants and disinfectants available for water treatment. Although ozone is only partially soluble in water, it is sufficiently soluble and stable to disinfect water contaminated by pathogenic micro- organisms and can be utilised for a wide range of disinfection applications. Microorganisms of all types are destroyed by ozone and ozonated water including bacteria, viruses, fungi and fungal spores, oocysts, protozoa and algae.

Ozone decomposes rapidly in water into oxygen and has a relatively short half life. The half life of ozone in water is dependant upon temperature, pH and other factors. However, the short half-life of ozone is a further advantage, as once treatment has been applied, the ozone will rapidly disappear, rendering the treated water safe. Once treatment has been applied, ozone that remains in solution will rapidly decay to oxygen. Unlike chorine based disinfectants, ozone does not form toxic halogenated intermediates and undesirable end products such as trihalomethanes (THMs). The concentration of ozone dissolved in water determines the rate of oxidation and the degree of disinfection in any given volume of water, with the higher the concentration ozone, the faster the rate of disinfection of micro-organisms. Electrolysis of water at high electrode potential produces ozone at the anode in an electrochemical cell according to the following equations:

3H₂0 - 0₃ + 3H⁺ + 6e- and

2H₂0 - 0₂ + 4H⁺ + 4e- (E₀ = 1.23 V_SHE)

H₂0 + 0₂ - 0₃ + 2H⁺ + 2e- (E₀ = 2.07 V_SHE)

Ozone may be produced in higher concentrations from low conductivity water, deionised water, demineralised water, and softened water. Ozone dissolved in water is described as ozonated water.

The production of ozone and ozonated water by electrolysis using an electrolytic cell is known in the art. DE 10025167 discloses an electrode assembly for use in a cell for the electrolytic production of ozone and/or oxygen. The cell comprises an anode and a cathode separated by a membrane in direct contact with each of the electrodes.

WO 2005/058761 discloses an electrolytic cell for the treatment of contaminated water. The cell comprises an anode and a cathode, with water being passed between the two electrodes. The cathode is preferably formed from nickel, titanium, graphite or a conductive metal oxide. The cathode is provided with a coating, preferably boron doped diamond (BDD), activated carbon or graphite. The anode is preferably formed from titanium, niobium, or a conductive non-metallic material, such as p-doped silicon. The anode is preferably provided with a coating, with preferred coatings being boron doped diamond (BDD), lead oxide (Pb0₂), tin oxide (Sn0₂), platinised titanium, platinum, activated carbon and graphite.

US 2007/0023273 concerns a method of sterilization and an electrolytic water ejecting apparatus. Raw water is sterilized by electrolysis in a unit comprising a cell having a cathode and an anode at least having a part containing a conductive diamond material.

US 2008/156642 concerns a system for the disinfection of low-conductivity liquids, in particular water, the system comprising an electrochemical cell in which electrodes are arranged to allow the liquid to flow therearound. Oxidizing agents, such as ozone, are produced from the liquid by the application of an electrical current. US 2010/0006450 discloses a diamond electrode arrangement for use in an electrochemical cell for the treatment of water and/or the production of ozone. The cell comprises an anode and a cathode separated by a proton exchange membrane (PEM). The electrode is formed with a diamond plate and is configured to have one or more slots (described as elongated apertures) therein, to provide a minimum specified apertures length per unit of working area of the electrode.

An electrolytic apparatus and an electrolytic method are disclosed in

JP 2011038145. The electrolysis of water to produce ozone using a cell comprising a solid polymer electrolyte sandwiched between diamond electrodes is described by A. Kraft, et al. 'Electrochemical Ozone Production using Diamond Anodes and a Solid Polymer Electrolyte', Electrochemistry Communications 8 (2006), pages 883 to 886. The production of high-concentration ozone-water by electrolysis is described by K. Arihara et al. 'Electrochemical Production of High-Concentration Ozone-Water using Freestanding Perforated Diamond Electrodes', Journal of the Electrochemical Society, 154 (4), E71 to E75 (2007). EP 1 741676 describes and shows an apparatus for electrolyzing and dispensing water for sterilisation purposes. The apparatus comprises an electrolysis cell having a cathode and an anode having at least a part formed from conductive diamond. The apparatus comprises a manually operated spray assembly for distributing the electrolysed water. KR 101441339 discloses an apparatus for generating an electrolyte-free antiseptic solution. A hub and cartridge assembly for producing and delivering ozonated water is described and shown in WO 2013/036838.

KR 101396145 discloses an apparatus for controlling ozonated water. KR 20150093397 discloses an electrode assembly comprising boron-coated diamond and its use in treating waste water.

A water treatment apparatus comprising an electrolytic cell and a control system therefor is disclosed in JP 2010131546.

JP 2002292370 discloses an apparatus for producing ozonated water.

JP 2014100648 discloses a generator for generating ozonated water and water comprising a hypochlorite.

There is a need for an apparatus for producing ozonated water for disinfection purposes. It would be most advantageous if the apparatus could be used for the disinfection of water in a water supply system, such as a pipeline, to allow the treated water to be dispensed, for example as drinking water at the point of consumption.

In a first aspect, the present invention provides a device for producing ozonated water from a reservoir of water, the device comprising:

a conduit having an inlet and an outlet and for conveying water between the inlet and the outlet;

an electrochemical cell assembly operable to electrolyse water in the conduit to produce ozone and having a first electrode assembly and a second electrode assembly;

a flow sensor for detecting a flow of water within the conduit; a processor for receiving an indication of water flow from the flow sensor and determining if the flow of water is above a threshold value and, if the flow of water is above the threshold value, activating the electrochemical cell. In a second aspect, the present invention provides a method for producing ozonated water from water flowing in a conduit, the method comprising:

providing an electrochemical cell assembly operable to electrolyse water in the conduit to produce ozone, the electrochemical cell assembly having a first electrode assembly and a second electrode assembly;

determining the flow of water in the conduit past the electrode assemblies of the electrochemical cell assembly;

determining if the flow of water exceeds a threshold value; and

if the flow of water is above the threshold value, activating the electrochemical cell.

The device of the present invention is for use in disinfecting a flow of water by the electrochemical generation of ozone, for example upstream or at the point of dispensing the water. The size or scale of the device may be varied, so as to accommodate different flow rates of water, for example by varying such features as the size and/or number of electrochemical cells. The size of the electrochemical cell may be varied, for example by varying the size and/or number of electrodes within the cell.

The various embodiments of the present invention have the general features recited above in common. These features arise from the intended use of the devices, in particular in the ozonation of a flow of water through a conduit, such as a pipe. The device of the present invention comprises a conduit for the flow of water therethrough, the conduit having an inlet and an outlet. In use, the device is temporarily or permanently installed with the inlet of the conduit connected to a supply of water. The device is arranged to operate only when a flow of water through the conduit is detected by the flow sensor.

The device of the present invention may be used in any system supplying water or in which a flow of water occurs during operation. For example, the device may be installed in a water supply system, such as the pipework of a domestic or commercial water system. The device is operated to ozonate the water flowing along the conduit. Water ozonated in this way may be used in a wide range of situations where water is dispensed or employed, for example for drinking, in toilets and washrooms, washing facilities, laundry facilities and the like.

The device of present invention may be arranged to be modular in form. In this respect, a single module having the general features recited above is of a small scale, suitable for the treatment of lower volumetric flows of water. Embodiments of the device for treating larger volumetric flows of water may be provided by combining two or more modules. The number of modules required in the device will be determined by the duty to be performed. The device of the present invention may comprise a single electrochemical cell or may comprise a plurality of electrochemical cells, for example 2, 3, 4 5 or 6 cells. The plurality of electrochemical cells are preferably connected to and controlled by a single processor.

The device may comprise a single flow sensor, for the plurality of electrochemical cells. Alternatively, the device may comprise two or more flow sensors, for example with each of the plurality of electrochemical cells being provided with a respective flow sensor.

In one preferred embodiment, the electrochemical cell is modular.

The number of electrochemical cell assemblies employed is determined by the duty required of the device. In this respect, the duty required of the device is determined by such factors as the volume of water to be ozonated per unit of time and the concentration of ozone required in the water being treated.

The device of the present invention comprises a conduit. The conduit has an inlet and an outlet. In use, water being treated enters the device through the inlet, is led past the electrochemical cell assembly where water contacts the electrodes and membrane of the cell and is ozonated, and leaves the device through the outlet. The conduit may have any suitable form. The conduit is preferably tubular. In one embodiment, the conduit extends in a generally straight line between the inlet and the outlet. In another embodiment, the conduit extends in a generally 'U' shape between the inlet and the outlet. Other configurations for the conduit may also be employed, as is most suitable. The conduit may have any suitable cross-sectional form. One preferred form is a generally circular cross-section.

The device of the present invention comprises an electrochemical cell assembly. In operation, the electrochemical cell is provided with an electrical current from an electrical supply. In one embodiment, the electrical supply for providing electrical energy comprises an electrical energy storage device, in particular one or more batteries. The use of batteries as the source of electrical energy is particularly preferred for the smaller sized devices. Suitable batteries are known and are commercially available. A preferred battery is a rechargeable battery. The device may comprise means for recharging the battery, for example by inductive coupling. Such rechargeable batteries and the means for recharging the batteries are also known in the art and are commercially available. The capacity and number of batteries provided in the device will depend upon the duty rating of the electrochemical cell, which is in turn determined by the volume of water to be treated by the device, and can be readily determined by the person skilled in the art. Alternatively, or in addition to the use of one or more batteries, the electrical supply for providing a source of electrical energy may comprise a cable or the like, for connecting to a source of electrical energy. For example, in a domestic location, the device may be connected to a domestic electrical supply by way of a cable. Embodiments in which the device is connectable to a remote source of electrical power, such as a domestic mains electricity supply, are preferred for the larger scale devices and/or those devices that are to be used in one location for an extended period of time or installed permanently, such as in the treatment of domestic water supply. Alternatively or in addition, the electrical supply may comprise a solar panel or solar array, by which electricity may be generated and provided to the electrochemical cell. As noted above, the device of the present invention comprises an electrochemical cell assembly. The cell assembly is operable to electrolyse water flowing along the conduit to produce ozone. The electrochemical cell assembly comprises a first electrode assembly and a second electrode assembly, each having one or more electrodes. The electrode assemblies are separated by a membrane. In operation, one of the first and second electrode assemblies functions as the anode and the other of the first and second electrode assemblies functions as the cathode, depending upon the polarity of the supply of electrical energy. Ozone is produced at the anode, in particular in the region of contact between the anode, the membrane and the surrounding water.

The cell is most preferably a passive cell, that is water is not pumped or otherwise forced through the cell. Rather, the cell is immersed in the water flowing through the conduit to be ozonated and operates to electrolyse water in contact with the electrodes and the membrane, as it passes through the conduit. The products of the electrolysis, including ozone, diffuse away from the electrodes and the membrane. In this way, ozone is produced in high concentrations at the electrodes and is rapidly dispersed by diffusion into the bulk of the water. This is in contrast to known electrochemical cells, in which water to be electrolysed is pumped or otherwise forced through the cell into contact with the electrodes and the membrane.

Preferably, the electrode assemblies are arranged in the device such that at least a portion, preferably a major portion, more preferably substantially all, of each electrode extends within the conduit so as to be exposed to water flowing within the conduit. The electrode assemblies may extend at any angle within the conduit. Preferably, the electrode assemblies extend in the downstream direction, that is within the conduit in the direction from the inlet to the outlet.

As noted above, the cell comprises a first electrode assembly and a second electrode assembly. Each of the electrode assemblies comprises one or more electrodes. Each electrode comprises one or more diamond electrodes having an active edge or surface. In particular, it has been found that the electrolysis reactions forming ozone occur at edges of the diamond electrodes, in particular at the junction of the edges of the electrodes and the membrane. Suitable diamond materials for forming the active edge or surface of each electrode are known in the art. The electrically conductive diamond material may be a layer of single crystal synthetic diamond, natural diamond, or polycrystalline diamond. Polycrystalline diamond is particularly preferred. Synthetic diamond may be prepared using high pressure high temperature (HPHT) or chemical vapour deposition (CVD) processes. CVD diamond is especially preferred.

The diamond material may consist essentially of carbon. More preferably, the diamond material is doped with one or more elements that provide electrical conductivity. Suitable dopants to provide the diamond with electrical conductivity are known in the art. The diamond of the electrodes is preferably doped with boron to confer electrical conductivity and is described as boron doped diamond (BDD). A particularly suitable and preferred diamond material is polycrystalline boron doped diamond (BDD).

The electrodes of the cell may be of a solid diamond material or a substrate material coated with diamond, that is a substrate material having a layer of diamond formed on a surface thereof.

Most preferably, each electrode comprises a solid diamond material, that is a diamond material formed as a free-standing solid. The solid diamond material may be accompanied by a substrate in the electrode, for example to support the diamond material. The preferred electrode material is electrically conductive, solid, free standing polycrystalline Boron-doped diamond. This diamond material may be manufactured by way of a process of chemical vapour deposition (CVD) in a microwave plasma system.

This diamond material of each electrode is preferably from 200 to 1000 microns in thickness, more preferably from 300 to 800 microns thick. It is particularly preferred that the solid diamond material has a thickness of from 350 to 700 microns, more particularly from 400 to 600 microns. A thickness of 500 microns for the solid diamond material is particular preferred. Alternatively, the active electrode material may be a substrate material coated with conductive diamond. The substrate material may be any suitable material, examples of which include silicon (Si), tungsten (W), niobium (Nb), molybdenum (Mo) or tantalum (Ta). This diamond material is manufactured by known techniques, for example by way of a process of chemical vapour deposition in a hot filament system. The active diamond layer at the surface of the electrode material, in this case, is typically from 1 to 10 microns in thickness, more preferably from 3 to 5 microns thick.

Suitable techniques for manufacturing both solid free-standing electrically conductive boron-doped diamond material and diamond coated material are known in the art. It has been found that diamond material provided as a layer formed on the substrate material is prone to blistering and delaminating under the conditions prevailing in the electrochemical cell during operation. This in turn significantly reduces the longevity and operating life of the cell. Accordingly, it is preferred that the diamond material is provided as a layer of pre-formed solid diamond, preferably as a free-standing solid diamond material, such as the Boron-doped diamond material referred to hereinbefore.

In a particularly preferred embodiment, the electrodes of the cell comprise a free-standing, pre-formed solid diamond material, especially boron-doped diamond as described above. The solid diamond material is preferably in the form of a chip or wafer, that is a sheet of material having opposing major surfaces and a width and length that are at least an order of magnitude greater than the thickness of the chip or wafer.

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.

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 first or second major surfaces of the electrode body. In use, one major surface of the chip or wafer is in contact with the membrane, as discussed in detail below, and contacts the water being electrolysed to produce ozone. Preferably, the membrane is in contact with the growth surface of the wafer.

It is particularly preferred that the other major surface of the chip or wafer is coated with an electrically conductive material, such as a metal or a mixture of metals. The coating allows the chip or wafer to be connected to a conductor, through which an electrical current may be provided to the chip of wafer. In particular, the coating allows the chip or wafer to be connected to the conductor by convenient means, such as soldering. The coating of electrically conductive material is preferably applied to the nucleation surface of the electrode body, that is not the major surface corresponding to the growth side of the wafer.

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.

As noted above, the surface of the diamond chip or wafer is coated with an electrically conductive material, for example a metal or a mixture of metals. Metals or a mixture of metals applied to the surface of the diamond material form an electrically conductive bond with the diamond material. In particular, it is preferred that the coating applied to the surface of the diamond material includes one or more metals that form carbides with the diamond material. Suitable metals for use in coating the surface of the diamond material include metals in Groups IVB and VB of the Periodic Table of the Elements. Preferred metals for use in the coating are platinum, tungsten, niobium, gold, copper, titanium, tantalum and zirconium.

A particularly preferred metal to coat the surface of the diamond material is titanium, especially a titanium coating applied by sputter coating as mentioned above. Titanium may be used in combination with other metals to coat the surface of the diamond material. When the surface of the diamond material is coated with titanium, in particular by sputter coating, titanium carbide (TiC) forms at the interface between the metal coating and the diamond material, providing a strong covalent bond between the metal coating and the diamond material. The metal coating allows the diamond material to be connected to an electrical conductor, such as a metal bus or wire.

Alternatively, the layer of electrically conductive material comprises two or more metals. One preferred metal composition is a mixture of copper and silver or gold.

The electrode body may be provided with a single layer of conductive material or a plurality of layers of conductive material. In one preferred embodiment, the electrode body is provided with a first layer of a first conductive material adjacent the surface of the electrode body and a second layer of a second conductive material adjacent the surface of the first layer. In one preferred embodiment, the first layer consists essentially of a single metal. Titanium is a particularly preferred metal for forming the first layer. In one preferred embodiment, the second layer comprises a mixture of metals. An amalgam of copper and silver is one particularly preferred material for forming the second layer.

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 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. In general, increasing the thickness of the layer of conductive material increases the electrical conductivity of the layer. Thicker layers may be employed. For example, copper may be applied to a thickness of 300 μηι. In embodiments comprising a plurality of layers of conductive material, the layer adjacent the surface of the electrode body is preferably relatively thin and the successive layer or layers relatively thick. In one preferred embodiment, the electrode body is provided with a first layer adjacent the surface of the electrode body and having a thickness of from 600 to 1000 nm, more preferably about 900 nm, and a second layer adjacent the surface of the first layer and having a thickness of from 2000 to 2500 nm, more preferably about 2400 nm.

The layer of electrically conductive material may extend across all or part of a major surface of the electrode body. Preferably, the layer of electrically conductive material extends over a major portion of a major surface of the electrode body. More preferably, the layer of electrically conductive material extends over a major portion of the major surface of the electrode body, with a portion at an edge of the major surface, preferably all edges of the major surface, not being covered by the conductive material. This edge portion may be at least 0.5 mm in width, that is the distance from the edge of the major surface of the electrode body to the edge of the layer of conductive material measured perpendicular to the edge, preferably 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.

The electrical conductor may be connected to the conductive coating by any suitable technique, with soldering being one convenient and preferred way of forming the electrical connection. As noted above, the metal coating may comprise a mixture of metals. In this respect, it is preferred to include in the metal coating metals that allow a conductor to be connected to the coating, in particular by soldering. In one preferred embodiment, the diamond material is coated with a conductive material having at its outer surface a mixture comprising copper and silver, to facilitate the connection of a conductor to the coating by soldering. The electrode body is preferably provided with a layer of electrically insulating material over its major surface. In one preferred arrangement, the electrode body is provided on a major surface with a first layer of an electrical conductive material, as discussed above, and a second layer of an electrically insulating material. The first layer of electrically conductive material may comprise separate layers of one or more electrically conductive materials, as discussed above. The second layer extends over the first layer. In one embodiment, the second layer comprises a material that is both electrically insulating and exhibits hydrophobic properties. Suitable materials for forming the second layer include nitrides, for example of silicon, titanium, zirconium or hafnium. Preferred compounds for inclusion in the second layer are silicon nitride (S13N4), titanium nitride (TiN), Zirconium nitride (ZrN) and hafnium nitride (HfN). Anodised aluminium oxide may also be used as an electrically insulating material.

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

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.

Alternatively, or in addition to the second layer, the electrode body may be coated in 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™.

It has been found that the adhesion of the resin is improved if the aforementioned layer of insulating material is employed. Accordingly, it is particularly preferred to provide the electrode body with a layer of electrically conductive material as hereinbefore described, a layer of insulating material, as hereinbefore described extending over the conductive layer, and a layer of resin extending over the insulating layer. As noted above, the electrode body is connected in use to a supply of electrical current by a suitable conductor. In embodiments in which the electrode body is provided with a layer of electrically conductive material, a conductor connector terminal is preferably connected to the said layer. The layer of electrically conductive material preferably has a composition that allows the terminal to be connected to the layer by soldering. Preferably, the terminal is coated in a resin, as described hereinbefore.

The electrical conductor, such as a cable, may be connected to the conductor connector terminal. Again, this connection is preferably formed by soldering.

The diamond material of the electrodes may have any suitable shape. As discussed below, the electrolysis reactions producing ozone are preferably allowed to occur at the edges of the diamond electrode and a polygonal shape for the diamond material is preferred. In a preferred embodiment, the diamond material is rectangular in shape, for example square. Other shapes may be employed.

The electrochemical cell comprises first and second electrode assemblies, as noted above. Each of the first and second electrode assemblies may comprise a single electrode or, a plurality of electrodes electrically connected to act together. The size and number of the electrodes will be determined by the intended use of the device, which in turn determines such factors as the current to be applied to the electrodes. For example, for an electrochemical cell drawing 100 mA, a diamond electrode having dimensions of 3 mm x 3 mm is suitable. For a larger current, for example 250 mA, an electrode of 5 mm x 5 mm is suitable, with a current 500 mA be appropriate for an electrode having a size of 5 mm x 10 mm.

The electrochemical cell may have two electrodes, an anode and a cathode, as indicated above. The electrode body may be of any suitable shape and configuration. In one embodiment, the electrode body is plate-like, that is having opposing major surfaces, forming the first and second contact surfaces, extending between opposing edge surfaces of the electrode body.

In a preferred embodiment, 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 to extend with its longitudinal axis generally parallel to the general direction of any flow of the water through the conduit.

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.

As noted above, the electrode body preferably has opposing major surfaces extending between opposing edge surfaces and forming the first and second contact surfaces. 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 may be 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.

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 opposition 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. 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.

The electrochemical cell comprises a cation exchange membrane disposed between the electrodes. 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. The membrane permits the movement of ions, including hydrogen ions

(protons), in either direction, depending upon the polarity of the current applied to the cell at any given time.

The membrane is in contact with each electrode. Each electrode is preferably formed to have edges to the active surface of the diamond, with the semi-permeable membrane being in contact with the edges of the diamond material. In this way, at the interface between the edge of the anode electrode, the membrane and the water adjacent the anode, ozone is produced in the water (ozonated water). Hydrogen ions (protons) pass through the membrane to the cathode side of the cell where hydrogen gas is produced. Other positively charged metal cations, such as calcium, magnesium, iron and manganese also pass through the membrane and are deposited on the cathode.

Suitable materials for the membrane are known in the art and are commercially available. One particularly preferred class of materials for use in the membrane are sulfonated tetrafluoroethylene-based fluoropolymers. Such materials are known in the art and are commercially available, for example the Nafion^® range of products. The device of the present invention further comprises a flow sensor for detecting the flow of water within the conduit. The flow sensor is located in the device at a location such that the flow of fluid in the conduit past the electrodes of the electrochemical cell is measured. As described in more detail below, the flow measurement is used to ensure that there is a flow of water past the electrodes of the cell, before the cell is activated. The location of the flow sensor should be such, therefore, that it can be ensured that the flow of water past the electrodes is detected. Preferably, the flow sensor is located to measure the flow of water in the conduit upstream of the electrodes of the electrochemical cell. Suitable flow sensors are known in the art and are commercially available. Suitable flow sensors include invasive flow sensors and non-invasive flow sensors. Non-invasive flow sensors are preferred. Suitable types of flow sensors are, for example, moving magnet sensors and ultrasonic sensors. Ultrasonic flow sensors are preferred. Suitable sensors are commercially available, for example the FS15 and FS22 models for 15 mm and 22 mm pipelines from Cynergy3 Components Ltd., designed for use in liquid flow streams at pressures up to 10 bar and temperatures up to 85°C. These products are based around a moving magnet and a fixed reed switch with a low flow restriction. These flow switches are specifically designed to be used in water flows without significant amounts of suspended solids and operate at flow rates up to 25 L/minute. One suitable ultrasonic flow meter is model UB25B from Cynergy3 Components Ltd. This ultrasonic flow measurement device automatically compensates for viscosity and temperature variations, and has an optional pulse or analogue output.

The device of the present invention further comprises a processor. The processor controls the operation of the electrochemical cell, in particular switching the cell on and turning the cell off. Any suitable arrangement for the processor may be employed and suitable components and processors are known in the art and can be programmed for operation according to the methodology of the present invention using techniques known in the art.

The processor receives an input signal from the flow sensor indicating whether water is flowing through the conduit and past the electrochemical cell. If it is determined that the flow rate of the water is sufficiently high, the processor operates to switch on the electrochemical cell, in particular to allow an electrical current to be provided to the electrodes from the source of electrical energy. In this respect, the processor is provided with a threshold value of flow rate, against which the flow rate measured by the flow sensor is compared. In the event the flow rate measured by the sensor exceeds the threshold value, the processor operates to switch on the electrochemical cell. In the event the flow rate measured by the sensor does not exceed the threshold value, the cell is not switched on. The threshold flow rate value may be zero, in which case the processor operates to activate the electrochemical cell assembly when any flow of water through the conduit is detected by the flow sensor. The threshold flow rate value to activate the electrochemical cell is dependent upon such factors as the pipe diameter and electrochemical cell installed. For example, the minimum threshold flow for a pipeline with an electrochemical cell rated at 250 mA is 0.25 L/minute, increasing to 2.0 L/minute for an electrochemical cell rate at 2A or higher. In general, the threshold flow rate value is preferably greater than zero, more preferably at least 0.1 L/minute, still more preferably at least 0.25 L/minute, more preferably still at least 1.0 L/minute, with higher threshold flow rate values also being possible, such as 1.5 L/minute, 1.75 L/minute and 2.0 L/minute.

At or below the threshold flow rate value, no electrical current is supplied by the processor to the electrochemical cell. During operation of the device, if the flow rate detected by the flow sensor falls to or below the threshold flow rate value, the electrical current to the electrochemical cell is switched off by the processor.

It is possible to arrange the processor to determine the flow rate of water through the conduit using the signal received from the flow sensor and, once water has been determined to be present, simply to activate the cell to commence the production of ozone. Preferably, however, the processor monitors the signal output by the flow sensor continuously or periodically to ensure that the electrodes are still in contact with sufficient water for safe operation of the cell. The processor may check the flow of water, to confirm a sufficient flow rate of water at the electrodes of the electrochemical cell, at any time during the operating cycle of the device. Preferably, the processor checks the output signal of the flow sensor at least every 60 seconds, more preferably at least every 50 seconds, still more preferably at least every 40 seconds, more preferably still at least every 30 seconds. The flow rate of water may be checked more frequently during operation, for example at least every 25 seconds, preferably at least every 20 seconds, more preferably at least every 15 seconds, still more preferably at least every 10 seconds. The flow rate of water may be determined more frequently still, if desired, for example every 5 seconds or less. As discussed in more detail below, in a preferred operating regime, the polarity of the electrochemical cell is periodically reversed. It is preferred that the flow rate of fluid through the conduit is checked by the processor every time the polarity of the electrochemical cell is reversed.

The device of the present invention preferably further comprises a conductivity sensor for determining the conductivity of fluid in the conduit in contact with the electrochemical cell. It has been found that operation of the electrochemical cell when the electrodes are not immersed in water actually damages the membrane (PEM) and may also damage the electrodes in some circumstances. This may arise when the conduit is allowed to be empty, for example an interruption in the supply of water in the system in which the device is installed. If the electrochemical cell is switched on when not immersed in water, the voltage of the cell increases to the maximum value permitted and, at this point, the electrical current falls significantly. The increased voltage causes the cell to heat up and this may damage the membrane and, in some circumstances, the electrodes. Accordingly, to avoid the electrochemical cell from being damaged in this way, the conductivity sensor is used to determine whether the electrodes are immersed in water.

The conductivity of water may vary according to the composition of the water, in particular the concentration of conductive ions in solution in the water. For example, demineralised water may have a conductivity at 25°C of from about 0.5 to 3.0 μβ/αη. Water from a domestic water supply has a conductivity at 25°C of from about 500 to 800 μβ/αη. By comparison, air typically has a conductivity at 25°C closely approaching zero μβ/αη.

The conductivity sensor is located in the device at a location such that the conductivity of the fluid in the vicinity of the electrodes of the electrochemical cell is measured. As described in more detail below, the conductivity measurement is used to ensure that the electrodes of the cell are immersed in water, before the cell is activated. The location of the conductivity sensor should be such, therefore, that it can be ensured that the electrodes are fully immersed in water, thereby permitting the membrane (PEM) to become fully wetted. As the membrane becomes wetted, the conductivity of the membrane increases and the voltage required to drive the cell decreases. Preferably, the conductivity sensor is located in the region of the electrodes of the electrochemical cell.

The conductivity sensor comprises a pair of spaced apart, electrically conducting electrodes. The conductivity sensor may be either an amperometric device or a potentiometric device, with the latter being more accurate. For simplicity the preferred conductivity sensor is amperometric. This sensor applies a known potential (Volts) to a pair of electrodes and measures the current (Amps) between the two electrodes, the higher the current obtained the greater the conductivity of the medium between the electrodes.

The processor receives an input signal from the conductivity sensor indicating whether the electrochemical cell is immersed in water. If it is determined that the conductivity of the water is sufficiently high, indicating that the electrodes are immersed in water, the processor operates to switch on the electrochemical cell, in particular to allow an electrical current to be provided to the electrodes from the source of electrical energy. In this respect, the processor is provided with a threshold value of conductivity, against which the conductivity measured by the conductivity sensor is compared. In the event the conductivity measured by the sensor exceeds the threshold value, indicating that the electrodes are immersed in water, the processor operates to switch on the electrochemical cell. In the event the conductivity measured by the sensor does not exceed the threshold value, the cell is not switched on.

Preferably, the threshold conductivity value to turn the electrochemical cell on is 500 μβ/αη. Below this value of conductivity, no electrical current is supplied by the processor to the electrochemical cell. During operation of the device, if the conductivity detected by the conductivity sensor falls below 500 μβ/οηι, the electrical current to the electrochemical cell is switched off by the processor.

Preferably, the processor is provided with a first threshold value of conductivity, as discussed above and below which the processor prevents electrical current being supplied to the electrochemical cell, and a second threshold value of conductivity, higher than the first threshold value. Preferably, the second threshold value is about 1 ,000 μβ/αη. In operation, if the conductivity sensor indicates to the processor that the conductivity of the water exceeds the second threshold value, the processor shuts off the supply of electrical current to the electrochemical cell. If the conductivity of the water is determined to be below the second threshold value and above the first threshold value, the processor supplies electrical current to the cell. In this way, the electrochemical cell is only provided with electrical current and operated when the conductivity value measured by the conductivity sensor is between the first and second thresholds.

It is possible to arrange the processor to determine the presence of water at the electrodes of the electrochemical cell using the signal received from the conductivity sensor and, once water has been determined to be present, simply to activate the cell to commence the production of ozone. Preferably, however, the processor monitors the signal output by the conductivity sensor periodically to ensure that the electrodes are still in contact with sufficient water for safe operation of the cell. The processor may check the conductivity of the fluid to confirm the presence of water at the electrodes of the electrochemical cell at any time during the operating cycle of the device. Preferably, the processor checks the output signal of the conductivity sensor at least every 60 seconds to ensure that the electrodes are in sufficient water, more preferably at least every 50 seconds, still more preferably at least every 40 seconds, more preferably still at least every 30 seconds. The presence of water may be checked more frequently during operation, for example at least every 25 seconds, preferably at least every 20 seconds, more preferably at least every 15 seconds, still more preferably at least every 10 seconds. The presence of water may be determined more frequently still, if desired, for example every 5 seconds or less. As discussed in more detail below, in a preferred operating regime, the polarity of the electrochemical cell is periodically reversed. It is preferred that the conductivity of the fluid is checked by the processor every time the polarity of the electrochemical cell is reversed. If one of the aforementioned checks determines that the conductivity of the fluid between the electrodes is above the aforementioned threshold value, indicating that insufficient water is present in the region of the electrodes of the cell, the processor switches the cell off by cutting the electrical energy supply. The processor may be arranged to continue monitoring the conductivity of the fluid in the region of the electrodes, for example by checking periodically as discussed above, and when the presence of water is indicated by the signal received from the conductivity sensor, the processor may reactivate the cell to recommence production of ozone. Alternatively, for example, the processor may be configured to switch off the device after one or a preset number of failed conductivity tests, thereafter requiring the user to switch the device back on and restart the operating procedure.

As noted above, the electrochemical cell comprises a membrane, preferably a Nafion^® membrane, between the electrodes. The cell can be operated as soon as the electrodes and the membrane are immersed in water. However, it has been found that operation of the cell while the membrane is dry or substantially dry gives rise to the cell having a high resistance, in turn drawing a high voltage from the electrical energy source. This can lead to damage to the cell. In contrast, allowing the membrane to hydrate once immersed in water reduces the resistance of the cell, resulting in a lower voltage draw when the cell is activated. As a result, it is especially preferred that the membrane is allowed hydrate, once a flow of water through the conduit has been detected, before the cell is activated and electrical energy provided to the cell for electrolysis of the water to ozone commences. Accordingly, it is especially preferred that the processor is arranged to delay activating the electrochemical cell once it has been determined that the electrodes of the cell are immersed in water and water is flowing through the conduit for a period of time sufficient to allow the membrane to hydrate. The time required for the membrane to hydrate will depend upon such factors as the material of the membrane. It is preferred to allow at least 5 seconds for the membrane to hydrate before commencing operation of the electrochemical cell, more preferably at least 10 seconds, still more preferably at least 20 seconds. Most preferably, the membrane is allowed to hydrate for at least 30 seconds before the electrochemical cell is activated. In one embodiment, the processor delays activating the electrochemical cell for from 30 to 100 seconds after it has been determined that the electrodes of the cell are in contact with water, more preferably from 30 to 80 seconds, still more preferably from 30 to 70 seconds, more preferably still from 30 to 60 seconds. A delay of about 60 seconds is preferable for many embodiments.

During operation and the production of ozone at the anode in the electrochemical cell, the metal anions in solution, such as calcium and magnesium migrate to the cathode, causing a build up of these metals and their compounds on the active surface of the cathode. The deposition of these metals and their compounds individually and collectively causes passivation of the cathode and a consequential reduction in the flow of electrical current through the electrochemical cell. This process of electro-deposition of materials on the cathode passivates the electrodes in the electrochemical cell causing the current flowing through the cell to reduce over a period of time, thereby reducing the productivity of the cell over time, to the point when ozone may no longer be produced by the electrodes.

Compounds of calcium and magnesium are found in significant concentration in hard water and it is known that these compounds are the principal cause of electrode passivation within electrochemical cells used in the production of ozone or ozonated water. In particular, it is known that calcium cations readily pass through the cation exchange membrane present between the electrodes in the cell and that calcium is rapidly deposited on the cathode, in the form of insoluble calcium hydroxide within the electrochemical cell.

In the absence of a cathode cleaning system, the cathodes in an electrochemical cell become passivated by the metal cations in solution in the feed water. The build up of substances on the cathode will inevitably cause the cell to fail. Accordingly, to prevent the passivation of the electrochemical cell the polarity of the electric current flowing through the cell is periodically reversed. The processor is therefore arranged to reverse the polarity of the electrodes periodically. When the polarity is reversed in this manner, the deposits on the cathode that, if allowed to build up would passivate the cell, are reconverted into ions that pass back into solution, reversing the deposition process. The time intervals between successive polarity reversals can be varied within wide limits, in particular to optimise cell performance and take account of such operating parameters as the concentration of metal cations, such as calcium and magnesium, and other cations present in the water.

The length of time that the cell is operated in one polarity, so as to produce ozone at one electrode acting as the anode, may be determined by monitoring the condition of the second electrode, that is acting as the cathode, and the amount of substances deposited thereon. This may be achieved, for example, by monitoring one or more operating parameters of the cell, such as the electrical current, measured in Amps, and the potential of the cell, measured in Volts. The processor may therefore be arranged to monitor one or more of the aforementioned parameters of the cell and adjust the period of time that is allowed to elapse between polarity reversals accordingly.

The polarity may be reversed after operation for a period of operation of several minutes, preferably no more than 2 minutes, more preferably less than 1 minute. It is preferred that the processor reverses the polarity of the electrodes after a period of operation at one polarity of no more than 50 seconds, more preferably no more than 40 seconds, still more preferably no more than 30 seconds, more preferably still no longer than 20 seconds, in particular for water with a hardness below 200 mg/L. Reversing the polarity every 15 seconds or less is preferred, more preferably about every 10 seconds, in particular for higher levels of water hardness, that is above 200 mg/L, for example about 300 mg/L.

In operation, the electrodes of the electrochemical cell have a capacitance and, therefore can hold an electrical charge. The procedure for reversing the polarity of the electrochemical cell preferably allows the charge arising due to the capacitance of the electrodes to discharge. More particularly, the polarity reversal procedure preferably comprises shutting off the supply of electrical current to the electrochemical cell, waiting for a discharge period and thereafter switching on the electrical supply in the reverse polarity. The discharge period will vary depending upon the design of the electrochemical cell and is preferably at least 80 ms. A discharge period of from 80 to 200 ms is particularly suitable for many embodiments, preferably from 80 to 175 ms, more preferably from 80 to 150 ms.

It is particularly preferred that the period of time that the first and second electrodes each function as the anode and the cathode is substantially the same, in particular when averaged over an extended period of operation of the cell.

In operation, an electric current is provided to the electrodes of the electrochemical cell. The operating current density, measured in Amps/cm², at the electrodes is a function of the electrical current applied to the cell, measured in Amps, from the electrical power supply, divided by the active surface area of the diamond anodes. The current applied to the electrochemical cell, and therefore the current density at the anodes, may be selected to optimise the performance of the cell and to optimise the production of ozone and ozonated water. In practice, the maximum current density that can be applied to the electrodes in the electrochemical cell is limited by the semi permeable proton exchange membrance (PEM). In the case of the preferred Nafion^® membrane, the maximum current density is about 1.0 Amps/cm² (10,000 Amps/m²). The amount of ozone generated by the electrochemical cell is directly proportional to the current applied and is dependent upon the current efficiency of the particular cell.

The electrochemical cell may be operated at current densities up to 1.0 Amps/cm². Preferably, the current density is in the range of from 0.1 to 1.0 Amps/cm², more preferably from 0.5 to 1.0 Amps/cm², and still more preferably in the range 0.75 to 1.0 Amps/cm² for the production of ozonated water for most applications.

The maximum current that can be applied to the electrochemical cell is a function of the surface area of the electrodes of the cell and the maximum current density. For example, in the case of a cell having electrodes with a surface area of 2.4 cm² (4 cm x 0.6 cm), the maximum current to be applied is 2.4 Amps, giving the maximum current density of 1.0 Amps/cm². The electrochemical cell may be operated at applied voltages up to 36 Volts, depending upon the conductivity of the water stream being treated. According to the operating conditions the voltage is preferably at least 10 Volts, more preferably at least 12 Volts, still more preferably at least 15 Volts, still more preferably at least 18 Volts. Voltages in excess of 24 Volts may also be applied, for example a voltage up to 30 Volts or up to 36 Volts, as required. A voltage of between 12 and 24 Volts is particularly preferred.

The processor is operable to deliver to the electrochemical cell a current appropriate for the desired operation of the cell. The voltage applied to the cell is allowed float (that is increase or decrease) in order to maintain the current at the required level. If the electrical resistance across the cell is high, for example due to reduced conductivity of the water being treated, the voltage is increased up to a preset maximum value. Once the voltage has reached the maximum permitted value, any further changes in the conductivity affect the current being applied, for example a reduction in the conductivity causing the current to fall.

In a further aspect, the present invention provides a water supply system comprising a device as hereinbefore described.

Embodiments of the method and apparatus of the present invention will now be described, by way of example only, having reference to the accompanying figures, in which: Figure 1 is a cross-sectional view of an electrochemical cell assembly comprising an electrode assembly for use in the device of the present invention;

Figure 2 is a cross-sectional view of the interior of the device of one embodiment of the present invention;

Figure 3 is a partial cross-sectional view of the device of a further embodiment of the present invention; and Figure 4 is a diagrammatical representation of one embodiment of the method of operation 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, 4b 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 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 8 is formed from a material that allows for the polarity of the cell to be reversed, in particular Nafion^® type N1 17. As shown in Figure 1 , the membrane 8 extends beyond the edge 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 first layer 10a, 12a of an electrically conductive material, in particular a layer of Titanium (Ti), and a second layer 10b, 12b of a second electrically conductive material, in particular a layer of an alloy of Copper (Cu) and Silver (Ag). The layers of electrically conductive material are applied to each electrode body by sputter coating. As shown in Figure 1 , an edge portion 14a, 14b of each electrode body is not covered by the electrically conductive layer 10a, 10b, 12a, 12b and is exposed. The layers of electrically conductive material 10, 12 total about 5000 nm in thickness. The layers of the alloy of Copper and Silver may be replaced with a layer consisting essentially of Copper having a thickness of about 300 μηι.

A Copper cable connector terminal 16 is soldered to each layer 10b, 12b of the Copper-Silver electrically conductive material.

The exposed surface of each layer of electrically conductive material 10, 12 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 and has a thickness of up to 1000 nm. The layer of electrically insulating material overlaps the layers 10b, 12b of electrically conducting material, as shown in Figure 1.

A layer of thermosetting hydrophobic resin 22, 24 is provided on each layer of electrically insulating material 18, 20. The resin is a polyimide resin, a polyester resin or an epoxy resin. The layer 22, 24 of resin material has a thickness between 1 mm and 3 mm.

The layer of electrically insulating material 18, 20 may be omitted, in which case the layer of resin 22, 24 is provided directly onto the surface of the layer of electrically conductive material 10b, 12b.

It has been found that the resin adheres more readily to the metallised surfaces 10b, 12b after the Copper cable connector terminals 16 have been soldered in position.

Current feed cables 26 are connected to respective cable connector terminals 16 by soldering, to provide an electric current to the respective layers of electrically conductive material 10, 12 and to the electrode body 4a, 6a.

The electrochemical cell 2 of Figure 1 is particularly suitable for use in the device of the present invention. In use of the electrochemical cell 2, the cell is disposed within the conduit of the device, with the electrode bodies 4a, 6a extending in the downstream direction, and water is caused to flow over the assembly 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 6, 4 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 now to Figure 2, there is shown a perspective view of the interior of one embodiment of the device of the present invention. The device, generally indicated as 102, comprises a generally rectangular housing 104 formed from two halves. In the view shown in Figure 2, one half of the housing 104 has been removed, to show the interior of the housing and the components of the device.

The device comprises a conduit 106. The device comprises an inlet 1 10 extending through an opening in one side of the housing 104 and an outlet 112 extending through an opening in the opposite side of the housing. The conduit 106 extends in a U-shape within the housing 104 between the inlet 1 10 and the outlet 112. The conduit 106 is formed from sections of tube connected by unions and can be considered to comprise two side portions 106a, 106b and a central portion 106c.

A flow sensor 120 is disposed within a flow sensor housing 122 extending from one side of the central conduit portion 106c.

An electrochemical cell assembly 130 is disposed within the side portion 106b of the conduit on the outlet side of the flow sensor 120, that is downstream of the flow sensor. The electrochemical cell assembly 130 comprises an electrode assembly as shown in Figure 1 and described above. The electrode assembly extends in the downstream direction along the side portion 106b of the conduit.

To allow the electrochemical cell assembly to be removed and replaced, a branch 106d extends from the conduit 106 at the junction between the central portion 106c and the side portion 106b. The branch 106d is provided with a seal member 132, which acts to seal the branch 106d and prevent the escape of water from the conduit 106. The seal 132 also provides a support for the electrochemical cell assembly 130 and holds the electrochemical cell assembly within the side portion 106b of the conduit 106.

The housing 104 is formed with an access port 134 provided with a removable cap 136. The branch 106d of the conduit 106 extends into the access port 134 and access to the open end of the branch 106d may be obtained by removing the cap 136. In this way, the electrochemical cell assembly 130 may be removed from the conduit 106 and replaced, for example during maintenance or servicing of the device.

A printed circuit board (PCB) 140 is disposed within the housing 104 between the side portions 106a, 106b of the conduit 106. The printed circuit board 140 comprises a processor assembly for controlling the operation of the device, in particular the supply of electrical current to the electrochemical cell assembly 130. The housing 104 may be provided with a removable cover (not shown for clarity) to allow access to the printed circuit board within. In use, the device 102 is installed in a system, such as a water supply system, in particular with the inlet 1 10 and the outlet 112 connected to respective ends of pipes in the system. In normal operation, water is present in and fills the conduit 106. When water is required from the system, water is caused to flow along the conduit 106. The flow sensor 120 detects the flow of water within the conduit 106 and provides a signal to the processor of the printed circuit board 140. When a sufficient flow rate of water is detected, the processor operates to switch on the supply of electrical current to the electrochemical cell assembly 130. Should the flow of water stop, the drop in flow is detected by the flow sensor 120, which signals the change in flow to the processor. When the flow falls below the required minimum required flow rate for proper operation of the device, the processor switches off the supply of electrical current to the electrochemical cell assembly 130.

Turning to Figure 3, there is shown a partial cross-sectional view of one embodiment of the device of the present invention. The device, generally indicated as 202, comprises a housing 204 formed from two halves. In the view shown in Figure 3, one half of the housing 204 has been removed, to show the interior of the housing and the components of the device. The device comprises a conduit assembly comprising a first conduit 206 and a second conduit 208. The device comprises an inlet 210, extending through an opening in one end of the housing 204, and an outlet 212, extending through an opening in the opposite end of the housing. In operation, water flows through the conduits 206, 208 from the inlet 210 to the outlet 212, that is from left to right as viewed in Figure 3. The conduit 206, 208 extends in a generally straight line between the inlet 210 and the outlet 212.

A flow sensor 220 is disposed within a flow sensor housing 222 extending from one side of the conduit 206. The flow sensor 220 is arranged to measure the flow of water through the conduit 206 at a position immediately downstream of the inlet 210. A cable 226 connects the flow sensor 220 with a processor (not shown in Figure 3).

A generally T-shaped pipeline fitting 234 is connected at each of the opposing ends to one of the conduits 206, 208, for example by means of a press-fit fitting, known in the art. A conduit 238 extends through the pipeline fitting 234, substantially perpendicular to the longitudinal axis of the conduits 206, 208. The T-shaped fitting 234 is provided with a watertight plug 242 within its free end around the conduit 238. A cap 244 closes and seals the free end of the T-shaped fitting 234.

An electrochemical cell assembly 240 extends from a support member 236 mounted within the T-shaped fitting 234 between the conduits 206, 208. The electrochemical cell extends from the support member 236 within the conduit 208 in the downstream direction, that is towards the outlet 212. The electrochemical cell assembly 240 comprises an electrode assembly as shown in Figure 1 and described above. A cable 250 extends along the conduit 238 in the T-shaped fitting 234 and allows an electrical current to be supplied to the electrochemical cell under the control of the processor (not shown in Figure 3). Clips 260 and 264 extend from the inner surface of the housing 204 and hold the conduits 206, 208 and the components therebetween in place.

The cables 226 and 250 are connected to the processor by means of a connector 246 mounted on the housing 204, as shown in Figure 3.

In use, the device 202 is installed in a system, such as a water supply system, in particular with the inlet 210 and the outlet 212 connected to respective ends of pipes in the system. In normal operation, water is present in and fills the conduit 206, 208. When water is required from the system, water is caused to flow along the conduit 206, 208. The flow sensor 220 detects the flow of water within the conduit 206 and provides a signal to the processor. When a sufficient flow rate of water is detected, the processor operates to switch on the supply of electrical current to the electrochemical cell assembly 240. Should the flow of water stop, the drop in flow is detected by the flow sensor 220, which signals the change in flow to the processor. When the flow falls below the required minimum required flow rate for proper operation of the device, the processor switches off the supply of electrical current to the electrochemical cell assembly 240.

Referring to Figure 4, there is shown a diagrammatical representation of one embodiment of the method of the present invention in the form of a process scheme for the operation of a processor for controlling the functioning of the electrochemical cell of the device.

The process scheme, generally indicated as 302, is initiated by at 304 by starting the device. This may be by way of the user operating a switch to turn on the device. Alternatively, the device may be permanently activated with a constant electrical supply, the process scheme being started as a result of the processor receiving a signal from the flow sensor indicating a sufficient flow of water through the conduit. Once the device has been activated and the process scheme 302 begun, the next stage is to start the wetting timer function 306 within the processor. The membrane of the electrochemical cell requires a period of time to hydrate, once the cell has been immersed in water. Hydration of the membrane improves the performance of the cell and prolongs the working life of the membrane, whereas operation of the cell with the membrane incompletely hydrated with water reduces the working efficiency of the cell and can damage the membrane, in particular due to the elevated cell voltage. As indicated in Figure 4, the timer 306 is set to wait for a period of 30 seconds for the membrane to hydrate. During this period, the processor delays starting the operation of the other components of the device.

Thereafter, the processor conducts a flow rate test 308. In this test, the signal received from the flow sensor is used by the processor to determine the rate of flow of fluid along the conduit of the device. This may be accomplished by the processor comparing the signal received from the flow sensor with a preset value representing a minimum required or threshold flow rate.

In the event the flow rate sensed by the flow sensor exceeds the minimum required or threshold value, the processor passes to the next stage in the process scheme. Should the flow rate sensed by the flow sensor be below the preset value set in the processor, that is below the minimum flow rate required for safe operation of the device, the processor returns to an early stage in the process scheme. In the embodiment shown in Figure 3, the processor repeats the delay 306.

Once the processor activates the electrochemical cell, the processor checks the flow rate of water through the conduit, as indicated by the signal received from the flow sensor. This check 310, 312 is repeated every 80 ms. Should the flow rate fall below the minimum required flow rate, the processor switches off the supply of electrical current to the electrochemical cell. In the scheme of Figure 3, the processor provides a warning signal 314 of low/no flow in the conduit.

Once the processor has determined that the flow of water through the conduit is sufficient, the electrochemical cell is activated at 316, by switching on the supply of electrical current to the cell. The cell is operated for a period of 10 s, provided there is no indication of a fall in the flow rate below the minimum or threshold value.

During operation of the cell, the processor conducts a measurement 318, 320, 322 of the voltage being applied to the cell. As discussed above, the voltage required to provide a specific electrical current to the cell is an indication of the condition of the cell. The processor is provided with safe upper and lower operating limits for the system voltage. If the voltage outside the safe operating range, the processor switches off the supply of electrical current to the cell at 324 in the scheme. A warning signal 314 is also provided of this condition.

A further function 330 of the processor of the embodiment of Figure 4 is to set the polarity of the electrodes of the electrochemical cell. As discussed above, a preferred mode of operation is periodically to reverse the polarity of the electrodes of the cell, in order to reduce the build up of material deposited on the electrode surfaces, leading to passivation of the electrodes. As indicated in Figure 4, the cell is operated for a period of 10 seconds, after which the cell is switched off by the processor in step 330, the polarity of the electrodes of the cell is reversed, and the cell is restarted and continues to run with the reverse polarity. The electrode polarity is reversed after every 10 seconds of cell operation. After switching off the supply to the electrochemical cell, the processor waits 80 ms, during which time the aforementioned flow test 310 is conducted. This waiting time allows the electrical charge retained in the electrochemical cell due to the capacitance of the electrodes to dissipate.

When the flow test 310 is passed, the processor restarts the cell at 316. Thereafter, the processor follows a loop, as indicated in Figure 4, of switching on the cell, operating for 10 seconds, switching the cell off, reversing the electrode polarity, conducting a flow test during the waiting period, and switching the cell on.

Claims

1. A device for producing ozonated water from a reservoir of water, the device comprising:

a flow sensor for detecting a flow of water within the conduit;

a processor for receiving an indication of water flow from the flow sensor and determining if the flow of water is above a threshold value and, if the flow of water is above the threshold value, activating the electrochemical cell.

2. The device according to claim 1 , comprising a plurality of electrochemical cell assemblies.

3. The device according to claim 2, wherein the plurality of electrochemical cell assemblies are connected to and controlled by the processor.

4. The device according to any preceding claim, comprising a single flow sensor.

5. The device according to any of claims 1 to 4, comprising a plurality of flow sensors.

6. The device according to claim 5, comprising a plurality of electrochemical cell assemblies, each having a respective flow sensor.

7. The device according to any preceding claim, wherein the conduit is tubular.

8. The device according to any preceding claim, wherein the conduit extends in a substantially straight line between the inlet and the outlet.

9. The device according to any of claims 1 to 7, wherein the conduit extends in a U-shape between the inlet and the outlet.

10. The device according to any preceding claim, further comprising an electrical supply for providing electrical energy for operation of the electrochemical cell assembly.

11. The device according to claim 10, wherein the electrical supply comprises a battery.

12. The device according to either of claims 10 or 1 1 , wherein the electrical supply comprises a cable for connecting the device to a source of electrical energy.

13. The device according to any of claims 10 to 12, wherein the electrical supply comprises a solar panel or solar array.

14. The device according to any preceding claim, wherein the electrochemical cell is passive.

15. The device according to any preceding claim, wherein the first and the second electrode assemblies comprise a polycrystalline diamond.

16. The device according to claim 15, wherein the diamond is doped.

17. The device according to claim 16, wherein the dopant comprises boron.

18. The device according to any of claims 15 to 17, wherein the first and second electrode assemblies each comprise an electrode formed from a solid diamond material.

19. The device according to claim 18, wherein the diamond material has a thickness of from 300 to 800 microns.

20. The device according to any of claims 15 to 19, wherein the diamond material has a growth surface, the membrane being in contact with the growth surface of the diamond of each of the first and second electrode assemblies.

21. The device according to any of claims 15 to 20, wherein the first and second electrode assemblies each have an electrode body having a length of at least 3 mm.

22. The device according to claim 21 , wherein the electrode body has a length of at least 5 mm.

23. The device according to either of claims 21 or 22, wherein the electrode body has a length of up to 140 mm.

24. The device according to any of claims 15 to 23, wherein the major surface of the electrode of each of the first and second electrode assemblies is coated in a layer of electrically conductive material.

25. The device according to claim 24, wherein the electrically conductive material is applied by sputter coating.

26. The device according to either of claims 24 or 25, wherein the electrically conductive material comprises a metal.

27. The device according to claim 26, wherein the metal is selected from platinum, tungsten, niobium, gold, copper, titanium, tantalum, zirconium and mixtures thereof.

28. The device according to claim 27, wherein the metal is titanium.

29. The device according to any of claims 24 to 28, wherein the layer of electrically conductive material comprises a first layer of a first electrically conductive material and a second layer of a second electrically conductive material, different to the first electrically conductive material.

30. The device according to claim 29, wherein the first electrically conductive material comprises titanium.

31. The device according to either of claims 29 or 30, wherein the second electrically conductive material comprises copper and silver.

32. The device according to any of claims 24 to 31 , wherein the layer of conductive material has a thickness of at least 500 nm.

33. The device according to any of claims 24 to 32, wherein the layer of electrically conductive material extends over a major portion of the surface of the electrode body, with an edge portion not being covered by the said material.

34. The device according to claim 33, wherein the edge portion has a width of at least 0.5 mm.

35. The device according to any preceding claim, wherein the electrode body of each of the first and second electrode assemblies is provided with a layer of electrically insulating material.

36. The device according to claim 35, wherein the electrically insulating material comprises a nitride of silicon, titanium, zirconium or hafnium.

37. The device according to any preceding claim, wherein the electrode body of each of the first and second electrode assemblies is provided with a layer of resin over its major surface.

38. The device according to any preceding claim, wherein the membrane comprises a sulfonated tetrafluoroethylene-based fluoropolymer.

39. The device according to any preceding claim, wherein each electrode assembly comprises an elongate electrode body having first and second opposing edge surfaces and opposing first and second major faces extending between the first and second opposition edge surfaces; wherein the electrode body has an elongate longitudinal axis; wherein the electrode body comprises:

40. The device according to any preceding claim, wherein the flow sensor is located to determine the flow rate of water upstream of the electrochemical cell assembly.

41. The device according to any preceding claim, wherein the flow sensor is noninvasive.

42. The device according to claim 41 , wherein the flow sensor is an ultrasonic flow sensor.

43. A method for producing ozonated water from water flowing in a conduit, the method comprising:

determining if the flow of water exceeds a threshold value; and

44. The method according to claim 43, wherein the threshold value of flow is at least 0.1 L/min.

45. The method according to claim 44, wherein the threshold value of flow is at least 0.25 L/min.

46. The method according to any of claims 43 to 45, wherein the flow of water is measured periodically during operation of the electrochemical cell.

47. The method according to claim 46, wherein the flow of water is measured at least every 20 seconds.

48. The method according to any of claims 43 to 47, wherein the electrochemical cell is activated only after a delay, to allow the membrane to hydrate.

49. The method according to claim 48, wherein the delay is at least 5 seconds.

50. The method according to any of claims 43 to 49, wherein the polarity of the electrochemical cell is periodically reversed after the electrochemical cell has been activated.

51. The method according to claim 49, wherein the conductivity of the fluid in the region of the electrode assemblies is determined each time the polarity is reversed.

52. The method according to either of claims 50 or 51 , wherein reversing the polarity comprises deactivating the electrochemical cell, allowing the electrical charge present in the electrodes to dissipate, and reactivating the electrochemical with the reverse polarity.