ELECTROCHEMICAL CELL

Abstract

An oxidant production apparatus comprises an electrochemical reactant reservoir, an electrolysis compartment, a porous first electrode and a second electrode. The porous first electrode defines a boundary between the reservoir and the electrolysis compartment and is configured to allow an electrochemical reactant to pass from the reservoir, through the first electrode and into the electrolysis compartment. The second electrode disposed at least substantially in the electrolysis compartment and spaced apart from the first electrode. The apparatus is configured to produce an oxidant in an electrochemical reaction when a voltage is applied across the first and second electrodes and a current is passed through the first and second electrodes and an electrolyte disposed in the electrolysis compartment.

Claims

1. An oxidant production apparatus comprising: an electrochemical reactant reservoir; an electrolysis compartment; a porous first electrode defining a boundary between the reservoir and the electrolysis compartment, wherein the first electrode is configured to allow an electrochemical reactant to pass from the reservoir, through the first electrode and into the electrolysis compartment; and a second electrode disposed at least substantially in the electrolysis compartment and spaced apart from the first electrode, wherein the apparatus is configured to produce an oxidant in an electrochemical reaction when a voltage is applied across the first and second electrodes and a current is passed through the first and second electrodes and an electrolyte disposed in the electrolysis compartment.

2. An apparatus according to claim 1, wherein the first electrode comprises a pore size of between 0.01 m and 5000 m and/or wherein the first electrode comprises a sintered metal having a mean flow pore (MFP) of between 0.1 m and 100 m.

3. (canceled)

4. An apparatus according to claim 1, wherein the reservoir is configured to allow a user access thereto.

5. An apparatus according to claim 1, wherein the electrolysis compartment comprises an outlet configured to allow the liquid to flow out of the electrolysis compartment, optionally wherein the apparatus is configured to conduct batch or semi-batch electrochemical reactions, and the outlet comprises a non-return valve, a check valve or a solenoid valve.

6. An apparatus according to claim 1, wherein the reservoir defines an open top, and the cell is configured to be positioned, in use, to allow a liquid to flow into the reservoir.

7. An apparatus according to claim 1, wherein the apparatus comprises an inlet configured to allow the flow of a liquid into the apparatus, optionally where the inlet is configured to cause the liquid to flow directly into the reservoir.

8. (canceled)

9. An apparatus according to claim 1, wherein the electrochemical reactant reservoir and/or the electrolysis compartment comprise agitation means configured to agitate a liquid therein.

10. An apparatus according to claim 1, wherein the apparatus is configured to conduct continuous electrochemical reactions.

11. (canceled)

12. An apparatus according to claim 1, wherein the apparatus comprises a vent configured to vent hydrogen from the electrolysis compartment, and the vent comprises a catalyst configured to convert the hydrogen into water.

13. An apparatus according to claim 1, wherein the apparatus comprises a power supply configured to apply a voltage across the first and second electrodes.

14. An apparatus according claim 1, wherein the electrolysis compartment comprises an undivided cell or a divided cell.

15. (canceled)

16. An apparatus according claim 1, wherein the first electrode comprises an anode, and the second electrode comprises a cathode.

17. An apparatus according claim 1, wherein the apparatus comprises a control system configured to sense the conductivity or resistance between the first and second electrodes and/or the level of a liquid in the electrolysis compartment.

18. (canceled)

19. A toothbrush, a hand sanitiser, a tap, a toilet cistern, a dish washer, a washing machine, fruit storage, a swimming pool water purification system, soil decontamination, providing a potable water supply, a clinical or hospital environment, a sewer or wastewater treatment plant or an ocean liner comprising the apparatus of claim 1.

20. A method of producing an oxidant, the method comprising: charging an electrochemical reactant reservoir with an electrochemical reactant; passing the electrochemical reactant from the reservoir, through a porous first electrode and into an electrolysis compartment to create an electrolyte; and applying a voltage across first and second spaced apart electrodes and causing a current to flow through the first and second electrodes and the electrolyte, wherein the second electrode is disposed at least substantially in the electrolysis compartment, thereby driving an electrochemical reaction and producing the oxidant.

21. A method according to claim 20, wherein the electrochemical reactant comprises an inorganic salt, optionally wherein the salt is a chloride, a sulfate, a carbonate, a phosphate or a hydroxide; and a sodium salt, a potassium salt or an ammonium salt.

22. (canceled)

23. A method according to claim 21, comprising dissolving the salt in a liquid disposed in the reservoir.

24. A method according to claim 20, wherein the method comprises sensing the conductivity or resistance between the first and second electrodes.

25. A method according to claim 24, wherein the method comprises: applying the voltage across the first and second electrodes for a predetermined time when a desired conductivity or resistance is sensed; then causing a liquid to flow from the electrolysis compartment for a predetermined time; and causing a further liquid to flow into the electrolysis compartment for the predetermined time.

26. A method according to claim 24, wherein the method comprises: applying the voltage across the first and second electrodes and causing the current to flow; simultaneously causing a liquid to flow from the electrolysis compartment; and simultaneously causing a further liquid to flow into the reservoir and/or electrolysis compartment, optionally wherein the method comprises varying the rate of flow of the liquid into and out of the chamber and/or varying the voltage applied across the first and second electrodes as variations in the conductivity or resistance are sensed.

27. (canceled)

Description

[0076] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying Figures, in which:

[0077] FIG. 1 shows an electrochemical cell located in various domestic appliances;

[0078] FIG. 2 is a schematic diagram of a batch electrochemical cell;

[0079] FIG. 3 is a schematic diagram of a further batch electrochemical cell;

[0080] FIG. 4 is a schematic diagram of a still further batch electrochemical cell;

[0081] FIG. 5 is a diagram of a reaction cell;

[0082] FIG. 6 is a diagram of a mesh holder for use with the reaction cell of FIG. 5;

[0083] FIG. 7 is a graph showing the relationship between sodium chloride (NaCl) concentration and conductivity;

[0084] FIG. 8 is a graph showing the rate of NaCl dissolution of different particle sizes and temperatures;

[0085] FIG. 9 is a graph showing the concentration of salt solution in a static solution with the conductivity probe held 40 (blue) and 80 (red) mm above the bottom of the tank, the dotted lines show the temperature of the solution against time;

[0086] FIG. 10 is a graph showing the static dissolution of NaCl in water with the probe held 40 mm above the bottom of the tank, the dotted line shows the temperature of the solution against time;

[0087] FIG. 11 is a graph showing the concentration of salt solution in a static solution, with the conductivity probe held 20 (blue) and 30 (red) mm above the bottom of a column;

[0088] FIG. 12 shows graphs of the gradient of saline diffusion through a static tank (A) and a column (B);

[0089] FIG. 13 shows a graph of rates of filtration through sintered metal disks of different media grades under gravity; and

[0090] FIG. 14 shows further embodiments of an electrochemical cell.

EXAMPLE 1BATCH PRODUCTION OF SODIUM HYPOCHLORITE (BLEACH)

[0091] Oxidants are used to clean and sterilise a number of domestic appliances. However, as explained above, there are a number of disadvantages associated with this use. Accordingly, the inventors have developed an electrochemical cell 2 which may be used in a domestic appliance to produce an oxidant.

[0092] For instance, as shown in FIG. 1a, the electrochemical cell 2 may be disposed in the cistern 18 of a toilet 20. As explained below, the electrochemical cell 2 is configured to automatically produce an oxidant. This is released into the cistern 18, and will flow into a toilet bowl 24 when the toilet 20 is flush. Accordingly, the toilet 20 can be cleaned automatically.

[0093] As shown in FIG. 2, an electrochemical cell 2 comprises an electrolysis compartment 4 adjacent to a reservoir 6. Both the electrolysis compartment 4 and the reservoir 6 are substantially cuboid in shape and share a connecting wall.

[0094] The walls of the reservoir 6 are predominantly defined by a housing 8 comprising a polymer or a composite. In the embodiment illustrated, the reservoir is open at the top 15. The cell 2 is disposed in the toilet cistern 18 such that the top 15 of the reservoir 6 is slightly below the water fill level 17 of the cistern 18. In some embodiments, a metal housing may be used if the electrodes 12, 14 are isolated. Accordingly, the user can add solid sodium chloride (NaCl) 11 to the reservoir, and it will then dissolve in water (H.sub.2O) 13 disposed therein to make a sodium chloride solution. Assuming a user adds excess NaCl 11 to the reservoir 6, the NaCl 11 will dissolve until the solution becomes saturated. A quantity of solid NaCl 11 will then remain in the reservoir.

[0095] The walls of the electrolysis compartment 4 are predominantly defined by a further housing 16. However, in the embodiment illustrated, the connecting wall between the reservoir 6 and the electrolysis compartment 4 comprises an anode 12. A cathode 14 is disposed on the opposite side of the electrolysis compartment 4 to the anode 12, adjacent to an external wall of the housing 16.

[0096] Both the anode 12 and cathode 14 comprise stainless steel. The cathode 14 comprises a solid plate. However, the anode 12 comprises a mesh with a pore diameter typically between 1 m and 500 m and a thickness of about 1 mm. Accordingly, the dissolved NaCl ions will be able to pass through the anode 12 and into the electrolysis compartment 4. The process by which this occurs will be a mixture of convection, diffusion and migration. It will be appreciated that the rate of convection, diffusion and/or migration across the anode 12 will be determined by a number of factors, including pore size and structure in the anode 12, the relative concentration gradient between the reservoir 6 and the electrolysis compartment 4, the thickness of the anode 12 and the hydrophobicity/hydrophilicity of the material comprising the anode 12, for instance see Middelstdt et al., Numerical Investigations on Fluid Flow through Metal Screens, available at hap://elib.dlr.de/87260/1/p308.pdf.

[0097] A control system (not shown) measures the conductivity of the solution between the anode 12 and cathode 14. It will be appreciated that as the concentration of NaCl ions (electrolyte) within the electrolysis compartment 4 increases the conductivity will also increase. When a desired conductivity has been reached, the control system will activate a power supply 26 to apply a voltage across the electrolysis compartment 4 and cause a current to flow through the electrodes 12, 14 and the sodium chloride solution, and to thereby initiate an electrochemical reaction.

[0098] Accordingly, this will cause the following reaction at the cathode:

2H.sub.2O+2e.sup..fwdarw.2OH.sup.+H.sub.2

And, the following reaction at the anode:

2Cl.sup..fwdarw.Cl.sub.2+2e.sup.

[0099] The chlorine (Cl.sub.2) produced at the anode will dissolve in the water (H.sub.2O) and react like so:

Cl.sub.2+H.sub.2O.fwdarw.HOCl+H.sup.++Cl.sup.

[0100] Finally, the hypochlorous acid (HOCl) will react with the hydroxide ions (OH.sup.) produced at the cathode, like so:

HOCl+OH.sup..fwdarw.H.sub.2O+OCl.sup.

[0101] Accordingly, the overall reaction can be written like so:

NaCl+H.sub.2O.fwdarw.NaOCl+H.sub.2

[0102] The cell 2 will also comprise a vent comprising a metal catalyst (not shown), such as palladium or platinum. The vent is configured to vent the hydrogen produced in the reaction from the electrolysis compartment 4 and through the metal catalyst, thereby causing the hydrogen to be converted into water. The vent is configured to then discharge the water into the surrounding environment.

[0103] By controlling the current and the time for which it is applied, the control system is able to control the amount of sodium hypochlorite (NaOCl) that is produced. Some typical values for the cell 2 are given in Table 1, below.

TABLE-US-00001 TABLE 1 Relationship between different changeable parameters Electric power AC transform, 100-200 V Potential 5 V Power 240 W Electroactive area 0.02 m.sup.2 Electrode gap 0.01 m Dwell time 120 s Volume per flush 6 L NaOCl concentration delivered per 539 ppm flush

[0104] When the toilet 20 is flushed, the water level in the toilet cistern 18 is lowered causing the pressure downstream of the diaphragm check valve 22 disposed in the base of the electrolysis compartment 4 to be lower than the pressure upstream of the valve 22. Accordingly, the check valve 22 will open and the solution comprising the sodium hypochlorite will flow through the check valve 22, through the cistern 18 and into a toilet bowl 24, thereby causing the bowl 24 to be cleaned.

[0105] Depending on the flow of the liquid through the first electrode 12, some of the saturated sodium chloride solution will also flow out of the reservoir 6, into the electrolysis compartment 4, through the cistern 18 and into a toilet bowl 24.

[0106] The water in the cistern 18 will then be replaced. Once the water level rises above the level of the check valve 22, the pressure downstream of the check valve 22 will be greater than or equal to the pressure upstream of the check valve 22. Accordingly, this will prevent any further liquid from flowing out of the electrolysis compartment 4.

[0107] Once the water rises to the water fill level 17, water will begin to flow into the reservoir 6. As mentioned above, the NaCl 11 disposed in the reservoir 6 will dissolve in the water and the sodium chloride solution will flow into the electrolysis compartment 4 and the cell 2 may perform a further electrochemical reaction, as described above.

[0108] It is noted that once the reservoir 6 is filled with water some of the NaCl ions in the water may diffuse into the cistern 18. However, since the water will be static the diffusion process will be slow, and minimal amounts of the salt will be lost to the cistern 18.

EXAMPLE 2CONTINUOUS PRODUCTION OF AMMONIUM PERSULFATE ((NH.SUB.4.).SUB.2.S.SUB.2.O.SUB.8.)

[0109] An alternative embodiment of the invention is shown in FIG. 3. Similar to the embodiment described above, the electrochemical cell 2 comprises an electrolysis compartment 4 adjacent to a reservoir 6 and the connecting wall there between comprises an anode 12. In this embodiment, the reservoir 6 comprises a removable lid 10, allowing a user access to the reservoir 6.

[0110] The main difference is that, in the embodiment illustrated, the electrolysis compartment 4 comprises an ion-permeable membrane 28, comprising Nafion, separating the anode 12 and cathode 14, and thereby dividing the compartment 4 into an anolyte compartment 30 and a separate catholyte compartment 32. The membrane 28 prevents the oxidant produced at the anode from being subsequently reduced at the cathode.

[0111] Furthermore, the anode 12 comprises boron doped diamond and the cathode comprises stainless steel. Instead of adding sodium chloride (NaCl) to the reservoir, a user instead adds ammonium bisulfate ((NH.sub.4)HSO4) 33 to the reservoir 6. Finally, the valve in the base of the cell 2 is a flow control valve 38 and water is continuously delivered into the reservoir 6 through an inlet (not shown).

[0112] The cell 2, shown in FIG. 3, is configured to allow continuous production of ammonium persulfate. Accordingly, the control system would monitor the conductivity across the electrolysis compartment 4. Using the continuous flow valve 38, the control system can control the rate that the water flows into the reservoir 6 and out of the electrolysis compartment 4. This ensures that the concentration of the oxidant in the water as it flows out of the electrolysis compartment 6 will be consistent. The power supply 26 would remain on continuously, causing the following reaction at the anode:

2HSO.sub.4.sup..fwdarw.S.sub.2O.sub.8.sup.2+2H.sup.++2e

[0113] And, the following reaction at the cathode:

2H.sup.++2e.sup..fwdarw.H.sub.2

[0114] Accordingly, the overall reaction can be written like so:

2NaHSO.sub.4.fwdarw.Na.sub.2S.sub.2O.sub.8+H.sub.2

[0115] The hydrogen gas will be vented from the electrolysis compartment 4, as described in example 1.

[0116] Persulfate destroy certain organisms, such as biocides. Accordingly, the solution comprising the ammonium persulfate which is produced in using the cell 2 could be used to treat ballast water in ocean-going ships, as described in Ahn et al., Disinfection of Ballast Water with Iron Activated Persulfate, Environ. Sci. Technol., 2013, 47 (20), pp 11717-11725.

EXAMPLE 3BATCH PRODUCTION OF HYDROGEN PEROXIDE (H.SUB.2.O.SUB.2.)

[0117] A further alternative embodiment of the invention is shown in FIG. 4. An electrochemical cell 2 is configured for use in a tap (not shown). The tap has two separate outlets, one to dispense drinking water and the other to dispense the oxidant produced by the cell 2. Accordingly, the oxidant could then be dispensed when required by the user to clean the area around the tap.

[0118] Similar to the embodiment described in example 2, the electrochemical cell 2 comprises an electrolysis compartment 4, a reservoir 6 and an anode 12 comprising a mesh. However, the cell 2 also comprises a dividing wall 42 disposed between the reservoir 6 and the anode 12. The dividing wall 42 comprises a solenoid valve 44 disposed therein.

[0119] Similar to the embodiment discussed in example 2, the electrolysis compartment 4 comprises an ion-permeable membrane 28, comprising Nafion, separating the anode 12 and cathode 14. Furthermore, the anode 12 and cathode 14 comprise stainless steel.

[0120] The valve in the base of the cell 2 is a further solenoid valve 46. To aid the reaction, a user could add a salt, such as sodium sulfate (Na.sub.2SO.sub.4), to the reservoir 6. The electrolysis compartment 4 will also comprise a gas inlet comprising a solenoid valve and a gas vent comprising a back-pressure regulating valve (not shown).

[0121] Instead of adding sodium chloride (NaCl) to the reservoir, a user instead adds water with O.sub.2 pre-disposed 40 therein. Or in an alternative embodiment, the water with O.sub.2 pre-disposed 40 therein could be introduced by an inlet into the reservoir. This liquid would flow through the anode 12 into the electrolysis compartment 4. In operation, the solenoid valves 46 in the base of the cell 2 and in the air inlet would be closed and the solenoid valve 44 in the dividing wall 42 would be open. Accordingly, the water with O.sub.2 pre-disposed 40 therein would flow into the electrolysis compartment 4 and any gas disposed therein would flow out of the vent. The control system would monitor the level of the liquid in the electrolysis compartment 4, and would activate the power supply 26 once a desired level had been reached.

[0122] The following reaction would occur at the cathode:

O.sub.2+H.sub.2O+2e.sup..fwdarw.HO.sub.2.sup.+OH.sup.

And the following reaction would occur at the anode:

HO.sub.2.sup.+H.sub.2O.fwdarw.H.sub.2O.sub.2+OH.sup.

[0123] Accordingly, the overall reaction can be written as:

O.sub.2+2H.sub.2O+2e.sup..fwdarw.H.sub.2O.sub.2+2OH.sup.

[0124] The following unwanted side reactions may occur:

O.sub.2+2H.sub.2O+4e.sup..fwdarw.4OH.sup.1)

2H.sub.2O+2e.sup..fwdarw.H.sub.2+2OH.sup.2)

[0125] If the second side reaction is suppressed no hydrogen gas is produced.

[0126] When the user requires a cleaning solution, they may turn the tap on and the control system will open the solenoid valves 46 in the base of the cell 2 and in the air inlet and close the solenoid valve 44 in the dividing wall 42. Accordingly, this would cause the solution comprising the hydrogen peroxide to flow out of the electrolysis compartment 4 and out of the tap. Since the reservoir 6 has been isolated from the electrolysis compartment, the water with O.sub.2 pre-disposed therein would remain in the reservoir and could be used in future electrolysis reactions, as described above.

EXAMPLE 4EVALUATION OF MESH SIZE ON PERMEATION RATES

[0127] To determine permeation rates, a reaction cell 100, shown in FIG. 5, was built. The cell 100 was made from Perspex acrylic to make it light and enable visibility to the inside. The cell 100 comprises two compartments, a water feeding chamber 102 and a reaction chamber 104, separated by an acrylic wall 106. The total operational volume of the cell 100 is 900 mL, with the reaction chamber 104 comprising 10 mL and the water feeding chamber 102 comprising 890 mL.

[0128] The acrylic wall 106 comprises an aperture 108 allowing a fluid to pass between the water feeding chamber 102 and the reaction chamber 104. A slot 110 in the wall 106 allows a mesh holder 112 to be reversibly located in the slot 110.

[0129] An example mesh holder 112 is shown in FIG. 6, and comprises an acrylic frame 114 defining an aperture 116 therein. The size of the aperture 116 in the acrylic frame 114 corresponds to the size of the aperture 108 in the wall 106. A mesh 118 extends across the aperture 116 and was fixed using silicone to prevent water passing through the gap between the mesh and the acrylic. A rubber seal 120 is disposed around the bottom 122 and sides 124 of the aperture 116 to provide a seal with the wall 106 when the mesh holder 112 is disposed in the slot 110. The inventors designed the experiments so that the water level would not reach the top of the aperture 116, and so no seal was provided along the top edge 126 thereof.

[0130] When the mesh holder 112 is disposed in the slot 110 it is fixed in place with screws 128 which extend through threaded holes 130 in the wall 106 and corresponding threaded holes in the acrylic frame 114 of the mesh holder 112.

[0131] The reaction chamber 104 was graded at different volumes to determine the liquid flow passing through the mesh 118 using a hand-held timer.

[0132] To measure the permeation rate across the mesh a threaded valve (not shown) was fitted to drain the contents of the reaction chamber 104. The internal diameter of the threaded valve is 1.5 cm and the flow rate allows the electrochemical chamber to drain in approximately 3 s. The valve is 10 cm in length and the tap is centred along the body of the valve.

[0133] The inventors obtained stainless steel mesh of different aperture sizes from meshdirect.co.uk. Details on the mesh sizes and characteristics are detailed in Table 2.

TABLE-US-00002 TABLE 2 Stainless steel plain weave mesh description Product Code Description Mesh 150 0.1 mm aperture Mesh 300 0.055 mm aperture Mesh 500 0.026 mm aperture

[0134] The meshed were placed in mesh holders 112 as described above.

[0135] In turn, each mesh holder was placed in the reaction cell and affixed to the reaction chamber against the rubber U-seal 120. The reaction cell was filled with 900 mL of deionised water. The valve was then opened for 5 seconds to allow the reaction chamber to drain and the time taken to refill was recorded.

[0136] None of the woven meshes tested above was found to restrict water flow to any significant degreepermeation from the reservoir to the electrolytic chamber was instantaneous. This is non-ideal for the development of a toilet device, as this will incur significant salt loss per flush.

[0137] The permeation rate can be restricted by one of two methods: (i) changing the type of mesh from a plain weave to an alternate style, e.g. Dutch twilled weave, which can further reduce the aperture (to 6 m); or (ii) increase the tortuosity of the porous electrode by using stainless steel plates.

[0138] The second of these options (sintered stainless steel plates) were adopted in this work due to their positive attributes, including physical robustness, large surface area and the availability of media grades, offering a range of pore sizes and tortuosity.

[0139] A sample pack of sintered stainless steel plates was obtained from Mott corp., and the characteristics of the plates are provided in table 3.

TABLE-US-00003 TABLE 3 Sintered stainless steel (SS316) plates evaluated in this work. Media grade Thickness (mm) 100 2.6 50 2.1 20, 10, 5, 2 1.6 0.5 1.2 0.2 1.1

[0140] Sintered metal media are manufactured by pressing metal powder into porous sheets or tubes, followed by high-temperature sintering. The powder size, as well as the pressing and sintering conditions, determines the pore size and distribution, strength and permeability of the sintered material which is produced. The media grade designation is equivalent to the mean flow pore (MFP) of the filter. Accordingly, a filter with a media grade of 20 has a MFP of 20 M.

[0141] FIG. 13 shows the height of a column of water above sintered discs of media grade 10, 20 and 50 over time. As would be expected, a sintered disc of media grade 10 is much less permeable than discs with a media grade of 20 or 50.

[0142] Based on their experiments, the inventors found that the stainless steel plate of media grade 20, with a thickness of 2 mm, offered a refill time of about 2 min. It will be appreciated that the refill time can be modified by changing the thickness and/or media grade of the plate.

EXAMPLE 5EVALUATION OF CONCENTRATION EVOLUTION IN ELECTRODE GAP

[0143] The apparatus described in example 4 was also used for this experiment. To enable the conductivity to be measured, a conductivity meter probe (not shown) was placed extending into the reaction chamber. The conductivity probe was calibrated using aqueous NaCl solutions between 1-100,000 ppm. Measurements were made at four different temperatures (8, 12, 22 and 35 C.), and the results are shown in FIG. 7.

[0144] As expected, a monomial relationship between conductivity and salt concentration was found:

Salt concentration=(3.9410.sup.3Conductivity).sup.1.090

[0145] As shown in FIG. 7, no relationship between conductivity and temperature was found at the temperatures and concentrations measured.

[0146] While NaCl dissolves very quickly in water to form a saturated solution, the diffusion of the resulting brine solution through the bulk of the solution proves to be very slow. This can be established by two preliminary experiments.

[0147] The first set of experiments measured the dissolution of 20 g of NaCl, added to a 900 mL of water with agitation (magnetic stirring at 850 RPM). Dissolution of the salt was found to be dependent on the particle size and temperature of the water, see FIG. 8.

[0148] In contrast, the addition of 900 mL of waster to 20 g of NaCl in the same tank without agitation showed that diffusion of the salt solution is very slow, see FIG. 9. While the salt dissolves within several hours, the diffusion of the saline solution through the bulk liquid took days. This was further exacerbated by lowered temperature, see FIG. 10.

[0149] To determine the length of time required for the saturated brine solution to form and then diffuse the dissolution experiment was repeated using a static column. 1 g of NaCl was added to a measuring cylinder followed by the addition of 5 mL saturated brine solution, the measuring cylinder was carefully filled to 40 mL with deionised water. The conductivity was measured at heights of 20 mm and 30 mm for 2 days

[0150] The complete dissolution of the salt took less than 12 hours, it took over 24 hours for the diffusion of the saline solution through the static column to reach its peak flux, see FIG. 11.

[0151] Comparing the rate of diffusion of the saline solution through both the static tank and static column (FIG. 12) reveals that the rate is independent of both size of vessel and height. The independence of the rate of change in concentration to both salt concentration and volume of liquid supports our observation that the dissolution of salt (into even near saturated solutions) is much faster than the passive diffusion of saline.

[0152] Accordingly, the inventors suggest that the apparatus of the invention comprises some form of agitation means configured to agitate the fluid therein. For instance, a stirrer could be disposed in the water feeding chamber.

[0153] An alternative solution is shown in FIG. 14. The apparatus 200 shown in FIG. 14A comprises a reservoir 202. On a first side 204 of the reservoir 202 is an electrolysis compartment 206. The connecting wall between the reservoir 202 and the electrolysis compartment 206 comprises a porous anode 208.

[0154] A conduit 210, configured to carry water, extends into the reservoir 202 and terminates at an outlet 212 substantially adjacent to a base 214 and a second side of the reservoir 202, wherein the second side of the reservoir 202 is opposite the first side 204. The reservoir 202 further comprises a weir 218 substantially adjacent to the first side 204 of the reservoir 202. The weir 218 extends between the base 214 and the back and the front of the reservoir 202. Accordingly, water flowing from the outlet 212 will flow through salt disposed on the base 214 of the reservoir 202 and will then have to flow up and over the weir 218. This will cause mixing of the fluid within the reservoir 202 leading to better diffusion of the salt solution.

[0155] The inventors noted that the reaction chamber filled from the top of the sintered stainless steel plate. Additionally, the plate did not restrict the passive diffusion of solution between the weir and reaction chamber when left overnight. Based on these observations, the inventors recommend that a double weir or stepped weir is used for the prototype design.

[0156] A double weir arrangement is shown in FIG. 14B. The apparatus 200 shown in this Figure is identical to the embodiment shown in FIG. 14A except that the reservoir 202 further comprises a second weir 220 disposed between the first side 204 of the reservoir 202 and the first weir 218. The second weir 220 extends from a top 222 of the reservoir 202. Accordingly, water flowing from the outlet 212 will flow through salt disposed on the base 214 of the reservoir 202 and will then have to flow up and over the first weir 218 and down and under the second weir 220.

[0157] A stepped weir arrangement is shown in FIG. 14C. The apparatus 200 shown in this Figure is identical to the embodiment shown in FIG. 14A except a stepped weir 224 is disposed adjacent the first side 204 of the reservoir 202. The stepped weir 224 extends from the base 214 of the reservoir 202 and comprises a first step 226 and a second step. The first step 226 terminates spaced apart from but substantially adjacent to the top 222 of the reservoir 202. A second step 228 is disposed between the first step 226 and the first side 204, and terminates at a greater distance from the top of the reservoir than the first dtep. Accordingly, the second step 228 allows the water to flow to the porous anode 208, but prevents it from flowing to the base 214 of the reservoir 202.

EXAMPLE 6FURTHER APPLICATIONS

[0158] In addition to the examples given above, it will be appreciated that an electrochemical cell in accordance with the present invention may be used in a number of different applications. Some non-limiting examples are discussed below. [0159] 1. A small electrochemical cell 2 could be provided in a toothbrush and be battery powered. The oxidant could be generated after the toothbrush is used, preventing the build-up of bacteria on the toothbrush. Accordingly, in this application, the cell would batch produce the oxidant, which could be hydrogen peroxide or oxygen. [0160] 2. An electrochemical cell 2 could be configured for use in a hand sanitiser. Accordingly, when a user presses a button, the cell could be configured to release a dose of the liquid containing the oxidant allowing the user to clean their hands. In this application, the cell would produce the oxidant in a batch or semi-batch manner, and the oxidant could be hydrogen peroxide or bleach. [0161] 3. An electrochemical cell 2 may be configured for use in a dish washer 34 or washing machine 36, as shown in FIGS. 1b and 1c. Accordingly, the electrochemical cell 2 could dispense the oxidant during the wash cycle. Depending upon the wash cycle, the oxidant could either be produced in a batch, a semi-batch or a continuous manner. The oxidant could be hydrogen peroxide or a percarbonate. [0162] 4. An electrochemical cell 2 may be configured to dispense the oxidant directly into a swimming pool, and to thereby purify the water. Accordingly, the oxidant could either be produced in a batch or a semi-batch manner, and added to the pool water as required. The oxidant could be hydrogen peroxide or a percarbonate. [0163] 5. Finally, similar to example 2, an electrochemical cell 2 could be disposed on an ocean liner. The oxidant could be released from the hull of the liner to dislodge barnacles therefrom and/or to prevent them from becoming attached thereto. For this application, the oxidant could either be produced in a batch, a semi-batch or a continuous manner. The oxidant could be persulfate or bleach.

CONCLUSIONS

[0164] The electrochemical cells described above manufacture oxidants in situ. Accordingly, there is no need to store oxidants prior to use. The cells comprise control systems which carefully control the concentration of oxidants produced, ensuring that there is enough for the desired purpose, and little is wasted or left to contaminant the environment. Furthermore, since the oxidants may be applied automatically, the risk of human exposure to the oxidants is greatly reduced.

[0165] Since a salt may be added directly to the electrochemical cells, there is no need for salt solutions to either be stored in the vicinity of the electrochemical cell, or prepared by a user prior to being added to the cell.

[0166] Delivery of the oxidant may be controlled in a number of ways including: [0167] 1. Electronic active controlwhere a pump may be used to pump a liquid containing the oxidant out of the electrolysis cell 2; [0168] 2. Electronic passive controlwhere solenoid valves in an inlet and/or outlet may be used to control the flow of a liquid containing the oxidant from the electrolysis cell 2; [0169] 3. Mechanical active controlwhere valves in an inlet and/or outlet are configured to open automatically when the pressure downstream of the valve is greater than the pressure upstream of the valve and thereby control the flow of a liquid containing the oxidant from the electrolysis cell 2; and/or [0170] 4. Mechanical passive controlwhere the reservoir 6 is open and the cell is positioned to allow water to flow therein in a controlled manner.

[0171] It will be appreciated that these control methods may be used in combination with each other.