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:

3H ₂ 0 - 0 ₃ + 3H ⁺ + 6e- and

2H ₂ 0 - 0 ₂ + 4H ⁺ + 4e- (E ₀ = 1.23 VSHE)

H ₂ 0 + 0 ₂ - 0 ₃ + 2H ⁺ + 2e- (E ₀ = 2.07 VSHE)

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 (Pb0 ₂ ), tin oxide (Sn0 ₂ ), 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 1741676 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. WO 2013/109789 discloses a water purification system for disinfecting incoming water.

WO 2010/129338 discloses a disposable cartridge for an electrolytic cell. A water treatment device is disclosed in CA 2816191.

WO 2012/058774 discloses a system for providing ozonated liquid without the use of a holding tank. 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 water, the device comprising:

a vessel for containing water and having an inlet and an outlet;

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

a sensor for detecting the presence of ozone in solution in the water in the vessel; and

a processor for receiving an indication from the sensor and determining if the concentration of ozone in the water is below a threshold value and, if the concentration is below the threshold value, activating the electrochemical cell.

In a second aspect, the present invention provides a method for producing ozonated water from water in a vessel, the method comprising: providing an electrochemical cell assembly operable to electrolyse water in the vessel to produce ozone, the electrochemical cell assembly having a first electrode assembly and a second electrode assembly;

determining the concentration of ozone in the water in the vessel;

determining if the concentration exceeds a threshold value; and

if the concentration is below the threshold value, activating the electrochemical cell.

The device of the present invention is for use in disinfecting a volume of water by the electrochemical generation of ozone. The device may be used to supply a volume of ozonated water to any installation or facility that requires disinfection and sanitizing. The size or scale of the device may be varied, so as to accommodate different volumes of water, for example by varying such features as the size of the vessel and 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 volume of water in the vessel, for subsequent discharge into a water system, for example through a pipe.

The device of the present invention comprises a vessel for holding a volume of water to be ozonated. The vessel has an inlet to receive feed water and an outlet through which ozonated water is discharged. In use, the device is temporarily or permanently installed with the inlet of the vessel connected to a supply of water. The device is arranged to operate to maintain a desired or threshold concentration of ozone in the water in the vessel. The ozonated water is discharged from the vessel, upon demand, by the installation receiving the ozonated water.

The device of the present invention may be used in any system supplying water 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 being supplied to the installation downstream of the vessel. 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 volumes of water. Embodiments of the device for treating larger volumetric flows of water may be provided by combining two or more modules, each module having a vessel with the total volume of the vessels being matched to the demand for ozonated water. The number of modules required will be determined by the duty to be performed. Alternatively, the device may be scaled to suit the duty to be performed, in particular the volumetric flowrate of ozonated water to be supplied. In this case, the size of the vessel of the device may be sized according to the demand for ozonated water.

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 number of electrochemical cells employed in the device will depend upon such factors as the size or rating of the electrochemical cells, the volume of water to be ozonated within the vessel, the required ozone concentration and the time required for the water in the vessel to be ozonated to the desired concentration. In one preferred embodiment, the electrochemical cell is modular.

The device of the present invention comprises a vessel. The vessel has an inlet and an outlet. In use, water to be ozonated enters the vessel through the inlet. Ozonated water leaves the vessel through the outlet. The vessel may have any suitable form. For example, the vessel may be tubular.

The vessel is constructed to receive and hold water at the required pressure, in particular the pressure of water required in the downstream installation. In many applications, the vessel will be provided with water at an elevated pressure. The water pressure may be up to 20 bar, for example, or higher. When the device is to be used in an installation employing water from a mains water supply, such as in a domestic location, the operating pressure of the water is the pressure of the mains water supply, for example up to 6 bar.

The vessel may be of any suitable volume. The volume of the vessel will be determined by the volume of ozonated water required by the downstream installation. For example, the vessel may hold 10 L of water or more, for example at least 20 L, such as at least 50 L or 100 L or more. Vessels having a volume of up to 200 L are particularly suitable for many installations and applications.

The device of the present invention comprises an electrochemical cell assembly. In operation, the electrochemical cell assembly electrolyses water within the vessel to produce ozone, which remains in solution in the water. In one embodiment, the electrochemical cell assembly is disposed within the vessel and in contact with water within the vessel. In this way, water entering the vessel is ozonated to the desired concentration of ozone, before being discharged from the vessel through the outlet. In an alternative embodiment, the electrochemical cell assembly is located outside the vessel in an external conduit. Water is drawn from the vessel through a second outlet and passes to the electrochemical cell assembly for ozonation, after which it is returned to the vessel through a second inlet. The water may be removed from the vessel, passed to the electrochemical cell assembly and returned to the vessel using any suitable means, for example a pump. Suitable pumps are known in the art and are commercially available. One suitable form of pump is a centrifugal pump.

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 source, 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. 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 or industrial 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 a domestic or commercial water supply, for example in a toilet installation or wash room facility.

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 in the vessel to produce ozone. Ozone produced by the electrolysis remains in solution in the water in the vessel. 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 within the vessel or flowing through the external conduit to be ozonated and operates to electrolyse water in contact with the electrodes and the membrane. The products of the electrolysis, including ozone, diffuse away from the electrodes and the membrane into the bulk fluid. 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.

In embodiments in which the electrochemical cell assembly is disposed within the vessel, the electrode assemblies are preferably fully immersed in water. The electrode assemblies may be in any suitable orientation within the vessel.

In embodiments in which the electrochemical cell is located in the external conduit, the electrode assemblies are preferably arranged 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 along 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 second outlet to the second inlet of the vessel. 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, but is preferably 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 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 size of the electrode body will depend upon the duty of the electrochemical cell, which in turn is dependent upon the rating of the device, in particular the volume of water to be ozonated and the time required.

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 one 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 one preferred embodiment, the electrode body is rectangular, for example square. Such an electrode body may be used in an electrochemical cell assembly that is disposed within the vessel of the device. In an alternative 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. An elongate electrode body is preferred when the electrochemical cell assembly is disposed to ozonate water flowing in the external conduit. 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 are selected according to the duty to be performed when in use. In addition, the dimensions of the electrode body may be determined by the construction of the electrode body and its method of manufacture. For many applications, the electrode body is preferably at least 3 mm in length, more preferably 5 mm in length, more preferably at least 10 mm, still more preferably at least 20 mm, more preferably still at least 30 mm. The maximum electrode body length may be limited by the construction and method of manufacture. Lengths of up to 200 mm may be employed, for example up to 150 mm. In the case of one preferred embodiment, in which the electrode body is cut from a wafer of solid diamond material prepared by chemical vapour deposition (CVD), the maximum length of the electrode body is up to about 140 mm. For many embodiments, a length of from 30 to 50 mm, in particular from 35 to 45 mm, for example about 40 mm, is particularly suitable.

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

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

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.

As noted above, the device of the present invention operates to ozonate water within the vessel, to be discharged to a downstream installation. The operation of the electrochemical cell assembly is controlled according to the concentration of ozone in the water within the vessel. Accordingly, the device further comprises a sensor for providing a signal to allow the concentration of ozone in the water in the vessel to be determined. Suitable sensors for measuring the concentration of ozone in the water in the vessel are known in the art. In one embodiment, the sensor is operable to measure the total oxidant content of the water, which include a measurement of the presence of ozone in solution in the water of the vessel. One suitable sensor is a redox or oxidation- reduction potential (ORP) sensor. The ORP sensor measures the oxidation potential of the water in the vessel and provides an indication of the total oxidant content of the water, including the ozone content. However, the presence of other oxidants, for examplechlorine, hypochlorite, hypochlorous, chlorine dioxide, chloramines and other chlorine-based disinfectants and oxidants, may limit the accuracy of the ORP sensor in measuring the concentration of ozone in solution in the water.

More preferably, the sensor is an ozone sensor. Ozone sensors are specific and provide a measurement of the concentration of ozone in solution in the water. Generally, measurements of ozone concentration made using ozone sensors are not affected by the presence of other oxidants in solution in the water in the vessel. One suitable type of ozone sensor is a polarographic membrane sensor, having a pair of electrodes separated by a membrane. Such sensors are known in the art and are commercially available. Preferably, the sensor is operated with a reverse polarity regime, to reduce or avoid contamination of the electrodes. Such operating regimes for ozone sensors are also known in the art.

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.

In operation, the processor receives a signal from the sensor indicating the concentration of ozone in solution in the water in the vessel. The processor is provided with a minimum or threshold concentration value. When the processor determines that the concentration of ozone in solution in the water in the vessel is below the threshold concentration, the processor activates the electrochemical cell by switching on the supply of electrical current to the cell, to electrolyse water and generate ozone in solution.

The minimum concentration of ozone in solution in the water in the vessel may be selected to suit the duty to be performed, for example the appliance or installation to be treated. Preferably, the minimum ozone concentration in the water in the vessel is 0.05 mg/L, more preferably at least 0.1 mg/L, still more preferably at least 0.15 mg/L, more preferably still at least 0.2 mg/L. The ozone concentration may be up to 2.0 mg/L, more preferably up to 1.5 mg/L, with ozone concentrations up to 1.0 mg/L being suitable for many applications. An ozone concentration of from 0.05 to 0.4 mg/L is preferred for many applications, more preferably from 0.1 to 0.3 mg/L, still more preferably from 0.15 to 0.25 mg/L.

In embodiments in which water is removed from the vessel and passed through a conduit to the electrochemical cell for electrolysis, the device may comprise a flow sensor. The flow sensor detects the presence of a flow of water in the conduit past the electrochemical cell. In operation, 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. Alternatively, the threshold flow rate value to turn the electrochemical cell on is a flow rate greater than zero. The non-zero flow rate may be dependent upon such factors as the diameter of the conduit and the rating of the electrochemical cell being employed. The minimum threshold flow for a conduit with a 250 mA cell installed is 0.25 L/minute and 2.0 L/minute for a conduit with a 2A cell or larger installed. Below the threshold value for flow rate, 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 below the threshold 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 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. For example, in embodiments in which the electrochemical cell is located within the vessel, the conductivity sensor is preferably located at a level within the vessel above the level of the electrodes of the electrochemical cell. In embodiments in which the electrochemical cell is located outside the vessel in a conduit, the conductivity sensor is preferably located on the downstream side of the electrochemical cell. In operation, as the membrane of the electrochemical cell 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 may be 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 for a period of time sufficient to allow the membrane to hydrate. This is advantageous, for example, when the vessel has been emptied of water and refilled and prevents the electrochemical cell being activated too quickly after water has reached the electrodes of the cell.

The time required for the membrane to hydrate will depend upon such factors as the material of the membrane. 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 10 ms, more preferably at least 20 ms, still more preferably at least 40 ms, more preferably still at least 50 ms. A discharge period of from 50 to 100 ms is particularly suitable for many embodiments, preferably from 60 to 90 ms, more preferably from 70 to 85 ms. A discharge period of at least 80 ms is preferred for many embodiments. 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/cm ² , 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/cm ² (10,000 Amps/m ² ). 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/cm ² . Preferably, the current density is in the range of from 0.1 to 1.0 Amps/cm ² , more preferably from 0.5 to 1.0 Amps/cm ² , and still more preferably in the range 0.75 to 1.0 Amps/cm ² 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 cm ² (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/cm ² .

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 to 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 pre- set 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 schematic representation of a device of one embodiment of the present invention;

Figure 3 is a schematic representation of a device of a further embodiment of the present invention; and

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

Each electrode body 4a, 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. Polyimide resins are particularly preferred. 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 either within the vessel or a conduit of the device. In embodiments in which the electrochemical cell is disposed within the vessel, the electrodes are arranged to be immersed in water in normal use. In embodiments in which the electrochemical cell is disposed within a conduit extending from the vessel, the electrode bodies 4a, 6a extend 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 diagrammatical representation of a device according to one embodiment of the present invention. The device, generally indicated as 102, comprises a vessel 104 having an inlet 106 in the lower end of the vessel, connected to a feed line 108 for supplying fresh water to the vessel, and an outlet 1 10 in the upper end of the vessel connected to a delivery line 1 12 for supplying ozonated water from the vessel 102 to a downstream installation or device. A valve 114a is arranged in the feed line 108 and may be used to isolate the vessel 104 from the feed line 108. A valve 1 14b is arranged in the delivery line 1 12 and may be used to isolate the vessel from the delivery line 108 A by-pass circuit comprises a by-pass line 1 16 extending between the feed line 108 and the delivery line 112 and valves 118a, 1 18b for controlling the flow of water through the by-pass circuit.

In operation, fresh water enters the vessel from the feed line 108 through the inlet 106. Ozonated water leaves the vessel 104 through the outlet 1 10 and enters the delivery line 112.

An ozonation assembly 130 is provided to ozonate water in the vessel 104. The assembly 130 comprises an electrochemical cell assembly 132 and a processor assembly 134. A feed conduit 136 is connected to a feed outlet 138 in the upper portion of the vessel 104 and is connected to an inlet side of the electrochemical cell assembly 132. Valves 140a, 140b, 140c and 140d are provided in the feed conduit 136. A return conduit 142 is connected to an outlet side of the electrochemical cell assembly 132 and to a return inlet 144 in the lower portion of the vessel 104. Valves 146a and 146b are provided in the return conduit 142.

A flow sensor 150 is provided in the feed conduit 136 and functions to measure the flowrate of water being fed to the electrochemical cell assembly from the feed outlet 138 of the vessel 104.

An ozone sensor 152 is provided in the feed conduit 136 and functions to measure the concentration of ozone in water leaving the vessel 104 through the feed outlet 138.

The flow sensor 150 and the ozone sensor 152 are connected to the processor assembly 134 by signal lines 154 and 156. The processor assembly 134 comprises a printed circuit board (PCB) having the processor components thereon and a power supply for providing electrical energy to the electrochemical cell assembly 132 under the control of the processor.

A centrifugal pump 160 is provided in the feed conduit 136 and operates to draw water from the vessel 104 and supply water under pressure to the inlet side of the electrochemical cell assembly 132.

The electrochemical cell assembly 132 comprises an electrochemical cell of the configuration shown in Figure 1 and described above, generally indicated in Figure 2 as 170.

In operation, water is drawn from the vessel 104 through the feed outlet 138 by the pump 160 and supplied to the electrochemical cell assembly 132. The concentration of ozone in the water is measured by the ozone sensor 152 and a signal passed to the processor 134. When the processor 134 determines that the concentration of ozone in the water is below a required or threshold level, it activates the electrochemical cell assembly 132, in particular by switching on a supply of electrical current to the electrochemical cell 170. The electrochemical cell 170 operates to electrolyse water and produce ozone, which enters into solution in the water. The thus ozonated water is returned to the vessel 104 via the return conduit 142 and the return inlet 144. Should the flow sensor 150 indicate to the processor that there is insufficient flow of water in the return conduit 142, for example due to failure of the pump 160, the processor 134 switches off the supply of electrical current to the electrochemical cell 170. Similarly, once the concentration of ozone in the water being drawn from the vessel 104 is above the required or threshold concentration, the processor 134 switches off the supply of electrical current to the electrochemical cell 170. Turning now to Figure 3, there is a shown a device of a further embodiment of the present invention. The device, generally indicated as 202 comprises a generally cylindrical vessel 204 having a top flange 206 and a removable top plate 208 overlying the top flange. A gasket is present between the top flange 206 and the top plate 208 to provide for a fluid-tight seal. An inlet 210 for water to be ozonated is provided, comprising an inlet pipe 212 extending through the top plate 208 and into the vessel 204. An outlet 214 for ozonated water is also provided and comprises an outlet pipe 216 extending from the top plate 208.

A support tube 218 is attached to the removable top plate 208 and extends into the vessel. An electrochemical cell assembly 220 is mounted on the lower end of a tube 222 extending from a cap 224 threadably mounted to the upper end of the support tube 218. The electrochemical cell assembly 220 comprises an electrode assembly 226 of the general configuration shown in Figure 1 and described above. The electrode assembly 226 extends from a holder 228 in the lower end of the tube 222. The lower end portion 230 of the support tube 218 is perforated, to allow water to contact the electrodes of the electrode assembly 226.

A cable 232 extends through the cap 224 and within the tube 222 for supplying electrical energy to the electrochemical cell assembly 220. The cable 232 is connected to a processor 234, which controls the operation of the electrochemical cell assembly 220. The processor 234 may be housed in a suitable enclosure and may be located at a distance from the vessel 204 at any suitable location. A threaded plug 236 is mounted in the lower end of the vessel, to allow the vessel to be drained, for example for maintenance purposes.

An ozone sensor 250 is mounted to the top plate 208 and extends into the vessel. The ozone sensor 250 is connected to the processor 234 by a suitable cable or wirelessly, to provide the processor with an indication of the ozone concentration in the water within the vessel 204 during operation.

In use, the electrochemical assembly 220 may be removed from within the vessel 204 by unscrewing the cap 224 and withdrawing the tube 222 and the electrochemical cell assembly 220.

Referring to Figure 4, there is shown a further embodiment of the device of the present invention. The device, generally indicated as 302 comprises a generally cylindrical vessel 304 having a fixed top flange 306 and a removable top plate 308 overlying the fixed top plate. An inlet 310 for water to be ozonated is provided, comprising an inlet pipe 312 extending through the top plate 308 and into the vessel 304. An outlet 314 for ozonated water is also provided and comprises an outlet pipe 316 extending from the top plate 308.

A support tube 318 is attached to a mounting boss 320 in the lower side portion of the vessel 304 and extends into the vessel through an opening in the wall of the vessel 304. An electrochemical cell assembly 322 is mounted in the end portion of a tube 324 extending from a cap 326 threadably mounted to the outer end of the support tube 318. The electrochemical cell assembly 322 comprises an electrode assembly 326 of the general configuration shown in Figure 1 and described above. The electrode assembly 326 extends from a holder 328 in the end of the tube 324. The inner end portion 330 of the support tube 318 is perforated, to allow water to contact the electrodes of the electrode assembly 326.

A cable 332 extends through the cap 326 and within the tube 324 for supplying electrical energy to the electrochemical cell assembly 322. The cable 332 is connected to a processor 334, which controls the operation of the electrochemical cell assembly 322. The processor 334 may be housed in a suitable enclosure and may be located at a distance from the vessel 304 at any suitable location.

A threaded plug 336 is mounted in the lower end of the vessel, to allow the vessel to be drained, for example for maintenance purposes.

An ozone sensor 350 is mounted to the top plate 308 and extends into the vessel. The ozone sensor 350 is connected to the processor 334 by a suitable cable or wirelessly, to provide the processor with an indication of the ozone concentration in the water within the vessel 304 during operation.