GB2508992A - Electrochemical cell comprising electrically conductive diamond electrodes - Google Patents

Abstract

An electrochemical cell for treating a fluid comprises a plurality of electrodes 50, 52, 54 comprising solid sheets of electrically conductive diamond material, and a support structure (59, figure 6) for supporting the plurality of electrodes, with a fluid flow path 55 defined between the plurality of electrodes. The plurality of electrodes includes at least a first set of electrodes at a first point along the fluid flow path and at least a second set of electrodes at a second point along the fluid flow path, wherein the second point lies downstream from the first point along the fluid flow path, wherein the first and second set of electrodes have separate electrical connections 56, 58, and wherein the electrical connections for each of the first and second sets of electrodes are configured to periodically switch polarity. This arrangement is therefore stated to be an improvement over the prior art since it comprises an alternating polarity electrode structure, rather than a bipolar electrode structure. The electrodes 50, 52, 54 may include apertures (62, figure 7) through which the fluid to be treated can flow.

Description

ELECTROCHEMICAL CELL COMPRISING ELECTRICALLY CONDUCTIVE

DIAMOND ELECTRODES

Field of Invention

The present invention relates to an electrochemical cell comprising a plurality of electrically conductive diamond electrodes.

Background of Invention

The use of an electrochemical cell for treating waste water to break down biological and chemical pollutants prior to re-use or release of the waste water into the environment is known in the art. For example, W003/082750 describes that by applying high potentials to electrodes in contact with waste water it is possible to generate highly reactive radicals, such as hydroxyl radicals, and these create an aggressive oxidising environment in which pollutants are broken down. W003/082750 discloses an electrochemical cell configuration comprising a series of alternating anode and cathode electrodes which are closely spaced together and to which is applied a series of current pulses utilizing high voltage, high frequency, and high current densities. A range of possible electrode materials are suggested for the anode and cathode electrodes. Examples of anode materials are described as including: titanium coated with various metal oxides; titanium coated with iridium doped ruthenium oxide; carbon fiber fabric; composite materials having a free carbon surface; allotropes of Carbon such as graphite; other materials having a carbon surface; and any material that is not subject to electrolytic corrosion. Examples of cathode materials are described as including: stainless steel; titanium coated with various metal oxides; titanium coated with iridium doped mthenium oxide; carbon fiber fabric; composite materials having a free carbon surface; allotropes of carbon such as graphite; other materials having a carbon surface; and any material that is not subject to electrolytic corrosion, It has also been suggested in the art that electrically conductive diamond electrodes may be used in such waste water treatment applications. For example, EPO65969 describes such a use for electrically conductive diamond electrodes. Electrically conductive diamond material is believed to have a number of advantageous features in these applications including high hardness, high thermal conductivity, chemical inertness, and wide potential window. These features are considered to give electrically conductive diamond material the best combination :i.

of properties for electrochemical generation of highly reactive radicals for waste water purification while not damaging the electrodes thus allowing for prolonged use.

JP2004-237]65 also discloses the use of electrically conductive diamond electrodes in an electrochemical cell for treatment of waste water. JP2004-23 7165 describes a problem with using electrically conductive diamond electrodes in that it is not easy to provide electrical connections to such electrodes when compared with conventional metal electrodes in an electrochemical cell comprising a large number of electrically conductive diamond electrodes. As such, JP2004-237 185 would appear to teach away from using a configuration such as that described in W003/082750 which comprises a large number of electrodes with alternating anodes and cathodes having individual electrical connections, JP2004-237 165 illustrates one possible configuration in which a series of electrochemical cells are linked together in series. Each electrochemical cell only includes a single pair of electrodes and a flow path is provided such that fluid flows from one electrochemical cell to the next in series.

JP2004-237165 then proposes a single electrochemical cell comprising an improved bipolar electrode configuration in which a stack of bipolar electrodes are provided between a single anode electrical connection and a single cathode electrical connection. In such a bipolar configuration, a plurality of clcctrodcs arc disposed bctwccn thc cnd anodc and cathodc such that when a large electric field is applied between the end anode and end cathode each intermediate electrode will have one side functioning as an anode and an opposite side ftmnctioning as a cathode (i.e. each intermediate electrode will be bipolar). Such an arrangement ensures that both sides of each electrically conductive diamond electrode are active which can be important given that the rate of electrochemical reaction is dependent on the active surface area of the electrodes, Furthermore, such a bipolar electrode configuration does not require electrical connections to be made to the intermediate bipolar electrodes which is indicated as being problematic for electrodes made of electrically conductive diamond material when compared with conventional metal electrodes.

US6306270 also discloses an electrochemical cell comprising bipolar electrodes in the form of diamond coated electrodes. In this regard, it may be noted that there are two basic forms of electrically conductive diamond electrode, ones which comprise a non-diamond substrate which is coated with diamond material and ones which are formed of a free-standing piece of electrically conductive diamond material without any requirement for a non-diamond support substrate. While 1JS6306270 suggests using coated diamond electrodes in a bipolar electrochemical cell configuration, W02008/029258 describes that solid, free-standing diamond electrodes have better lifetime in such applications but that achieving the required electrically conductivity in such thick, free-standing diamond electrodes can be difficult. As such, W02008/029258 described a method of achieving high boron doping concentrations in thick, free-standing diamond electrodes to achieve suitably high electrical conductivity and describes the use of such electrodes in a bipolar electrochemical cell configuration. Both parallel flow and serpentine flow configurations are suggested for use in a bipolar configuration with a parallel flow configuration being indicated as preferable. The reason for the parallel flow configuration being preferred is that it increases the volume of liquid being treated. However, it is noted that merely changing between serpentine and parallel flow does not alter the fluid volume between the electrodes and actually the parallel flow configuration will have a reduced path length between the electrodes for individual parallel paths. As such, it is presumed that the increase in volume of liquid being treated is achieved by increased flow rate in a parallel configuration when compared with a serpentine configuration. While a higher flow rate could be achieved in a serpentine fluid flow configuration by increasing the fluid pressure it is possible that such an increase in pressure may fracture the solid diamond electrodes.

In relation to the above, Figure 1 illustrates a bipolar electrochemical cell with a parallel flow configuration according to W02008/029258 whereas Figure 2 illustrates a bipolar electrochemical cell with a serpentine flow configuration according to W02008/029258.

Both these configurations comprise a bipolar stack of electrically conductive diamond electrodes including an end anode 2, an end cathode 4, and a plurality of intermediate bipolar electrodes 6 disposed between the anode 2 and cathode 4, The anode 2 and cathode 4 each comprise a single electrical connection 8, 10 coupled to a switching DC power supply t t.

The configuration illustrated in Figure 1 comprises a plurality of parallel fluid paths 12 disposed between the plurality of electrically conductive diamond electrodes, In contrast, the configuration illustrated in Figure 2 comprises a serpentine flow path 13 passing between the plurality of electrically conductive diamond electrodes.

W02012/0495 12 identifies a number of further problems with bipolar electrochemical cell configurations such as the one described in W02008/029258 associated primarily with the fact that the diamond electrodes are supported only at the ends of the electrodes, These problems include the following: (1) thin, free standing (i.e. no support substrate) diamond electrodes are prone to mechanical failure; (2) thick diamond electrodes are expensive to manufacture; (3) the practical lower limit of electrode spacing to ensure that no electrical shorting occurs is higher than optimal for electrochemical performance; and (4) insufficient turbulence in the cell reduces mass transport rate at electrode surfaces. W02012/049512 proposes that all these problems can be at least partially solved by providing a porous support structure (e.g. made of a corrosion resistant plastic) between the diamond electrodes in a bipolar cell configuration. Such a support structure allows relatively thin diamond electrodes to be utilized without mechanical failure. Furthermore, such a support structure allows the electrode spacing to be narrowed without risk of electrical shorting. Further still, the support structure can function to increase turbulence and mass transport rate at electrode surfaces.

In light of the above, it would appear that W020l2/0495U represents the state of the art to date with respect to electrochemical cell configurations comprising free-standing, electrically conductive diamond electrodes. Such a bipolar electrochemical cell configuration is illustrated in Figure 3 with Figure 4 showing an example of a porous support structure which can be disposed in the fluid paths between the diamond electrodes of the electrochemical cell of Figure 3. The configuration illustrated in Figure 3 is similar to that illustrated in Figure 1 and comprises a bipolar stack of electrically conductive diamond electrodes including an end anode 2, an end cathode 4, and a plurality of intermediate bipolar electrodes 6 disposed between the anode 2 and cathode 4. The anode 2 and cathode 4 each comprise a single electrical connection 8, 10 coupled to a switching DC power supply 11. As in Figure 1, the configuration illustrated in Figure 3 comprises a plurality of parallel fluid paths t2 disposed between the plurality of electrically conductive diamond electrodes, The difference between the configuration illustrated in Figure and the configuration illustrated in Figure 3 is that the configuration illustrated in Figure 3 comprises a porous support structure 14 which is disposed in the fluid paths between the diamond electrodes of the electrochemical cell, An example of such a porous support structure 14 is illustrated in Figure 4 and comprises a network of corrosion resistant plastic members 16 forming a porous wafer which can be sandwiched between adjacent electrically conductive diamond electrodes to support the electrodes while allowing fluid to flow between the adjacent electrically conductive diamond electrodes as indicated by the arrows in Figure 4, A configuration according to that illustrated in Figure 3 and 4 includes a number of advantageous features including the following: (I) Provision of multiple bipolar solid diamond electrodes and use of both surfaces of each bipolar electrode increasing active electrode surface area.

(2) Switching polarity thus mitigating fouling.

(3) Dry electrical connections.

(4) Simple two electrical feed-through.

(5) Low electrode spacing increasing efficiency.

(6) Physical robustness.

(7) hicreased inter-electrode turbulence via suitable support structure design.

(8) Easily scalable to 11 cells via one pair of end electrodes and applying > 2xn Volts.

However, some problems can still be identified in terms of realizing a commercially viable electrochemical cell configuration comprising free-standing, electrically conductive diamond electrodes for waste water treatment. These may include one or more of the following: (1) A bipolar cell configuration such as that illustrated in Figure 3 requires the use of a high operating voltage which can be costly from an operating perspective.

(2) A bipolar cell configuration such as that illustrated in Figure 3 requires the use of a high operating voltage which can exacerbate potential current leakage pathways / short circuits and power losses across the electrochemical cell.

(3) A bipolar cell configuration such as that illustrated in Figure 3 comprises a relatively short path length for the fluid passing between the electrodes, The fluid path length between the electrodes can be increased by recirculating the fluid to provide a multi-pass system (as is required in practice utilizing the configuration illustrated in Figure ito break down pollutants to satisfactory levels) but this results in the fluid spending a significant length of time outside of the electrode configuration reducing efficiency.

(4) The fluid path length in a bipolar cell configuration such as that illustrated in Figure 3 is determined by the size of the electrodes, Accordingly, it is advantageous in such arrangements to provide large diamond electrodes to improve efficiency. However, larger diamond electrodes are more expensive to manufacture and are more prone to fracture.

(5) The potential difference between each adjacent pair of electrodes in a bipolar cell configuration such as that illustrated in Figure 3 is not individually controllable such that different regions of the electrochemical cell can be individually optimized to different levels of solute/target species in the solvent.

It is an aim of certain embodiments of the present invention to at least partially solve one or more of the aforementioned problems.

Summary of Invention

According to one aspect of the present invention there is provided an electrochemical cell for treating a fluid, the electrochemical cell comprising: a plurality of electrodes comprising solid sheets of electrically conductive diamond material; and a support structure for supporting the plurality of electrodes with a fluid flow path defined between the plurality of electrodes, wherein the plurality of electrodes includes at least a first set of electrodes at a first point along the fluid flow path and at least a second set of electrodes at a second point along the fluid flow path, wherein the second point lies downstream from the first point along the fluid flow path, wherein the first and second set of electrodes have separate electrical connections, and wherein the electrical connections for each of the first and second sets of electrodes are configured to periodically switch polarity.

According to one example the electrochemical cell is configured such that the plurality of electrodes comprise two end electrodes and a plurality of central electrodes disposed between the two end electrodes in a parallel stack configuration with a fluid path disposed between opposed major faces of each adjacent pair of electrodes whereby in use each of the central electrodes has both of its major faces exposed to the fluid being treated. Each of the plurality of electrodes comprises two electrical connections with two associated electrical contact points on the surface of each electrode such that in use the plurality of central electrodes are alternately positively and negatively charged thereby forming a parallel stack of alternating anodes and cathodes with separate electrical connections thereby forming the first and second set of electrodes as defined above. Furthermore, the support structure comprises a porous support structure disposed within the fluid paths between each of the plurality of electrodes.

According to another example the electrochemical cell is configured such that each set of electrodes is in the form of a bipolar stack whereby the electrochemical cell comprises a series of bipolar stacks connected such that in use fluid flows from one bipolar stack to a subsequent bipolar stack in series, each bipolar stack having a separate electrical connection such that the bipolar stacks form the first and second set of electrodes as previously defined.

According to yet another example the electrochemical cell is configured such that the support structure comprises a first support sheet in which is disposed a first plurality of electrodes and a second support sheet in which is disposed a second plurality of electrodes. The first and second support sheets are configured to define the fluid flow path therebetween with each of the first plurality of electrodes being disposed opposite a corresponding one of the second plurality of electrodes thereby forming an anode-cathode pair, The anode-cathode pairs have separate electrical connections thereby forming the first and second set of electrodes as previously defined.

Brief Description of the Drawings

For a better understanding of the present invention and to show how the same may be carried into effect, embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a bipolar electrochemical cell with a parallel flow configuration according to Figure 2 illustrates a bipolar electrochemical cell with a serpentine flow configuration according to W02008/029258; Figure 3 illustrates a bipolar electrochemical cell with a parallel flow configuration and a plurality of porous support structures disposed between the electrodes according to Figure 4 illustrates an example of a porous support structure according to W02012/049512; Figure 5 illustrates an example of an electrochemical cell comprising a modified porous support structure shown in Figure 6 and configured to include modified electrically conductive diamond electrodes including fluid through-holes as shown in Figure 7; Figure 6 illustrates an example of a modified porous support structure including a non-porous peripheral ring; Figures 7(a) and (b) illustrate two examples of modified electrically conductive diamond electrodes including fluid through holes; Figure 8 illustrates another example of an electrochemical cell comprising a series of bipolar stacks; Figure 9 illustrates a modified version of the electrochemical cell shown in Figure 8 wherein each bipolar stack comprises the modified porous support structure shown in Figure 6 and is configured to include modified electrically conductive diamond electrodes including fluid through holes as shown in Figure 7; Figure 10 illustrates another example of an electrochemical cell comprising opposing support sheets comprising a plurality of electrically conductive diamond electrodes; and Figure 11 illustrates a portion of one of the support sheets of the electrochemical cell configuration shown in Figure 10,

Detailed Description of Certain Embodiments

The present inventors have identified that there are advantages and disadvantages with both bipolar and individually addressable electrically conductive diamond electrodes in prior art configurations. Prior art bipolar electrically conductive diamond electrode configurations snch as described in JP2004-237165, W02008/029258, and W02012/049512 are advantageous in that they are relatively simple and robust in construction and do not require a large number of electrical connections to diamond material. However, such bipolar configurations require high operating voltages and large area electrically conductive diamond electrodes, have a relatively short fluid flow path between the electrically conductive diamond electrodes, and do not allow for the application of variable voltage along the fluid flow path. In contrast, prior art individually connected electrically conductive diamond

S

electrode configurations such as described in JP2004-237]65 are advantageous in that a lower operating voltage may be utilized as the voltage is not dropped over a large bipolar stack of electrodes. Furthermore, a serial electrode configuration can provide a longer fluid flow path between the electrodes and can allow the applied voltage to be varied along the fluid flow path, e.g. as may be desired as the concentration of pollutants changes during treatment. However, as described in JP2004-237]65, a series of many individual electrochemical cells is required with a large number of electrical connections to the diamond material adding significant complexity to the configuration. Furthermore, as suggested in JP2004-237]65, in operation there are problems of electrode fouling leading to a drop off in efficiency in such a serial configuration.

Embodiments of the present invention seek to combine some advantageous aspects from both bipolar and individually addressable electrically conductive diamond electrode configurations. A series of significantly different examples of electrochemical cells are described herein, However, they share some common underlying structural features as discussed below.

First, all the embodiments utilize a plurality of electrodes comprising solid sheets of electrically conductive diamond material as opposed to coated diamond electrodes. Problems of pealing in coated diamond electrodes are thus avoided and the electrodes have a significantly longer lifetime, Furthermore, it has been found that coated diamond electrodes do not function well if the polarity of the electrodes is periodically switched to avoid fouling issues.

Secondly, a support structure is provided for supporting the plurality of electrically conductive diamond electrodes in a single electrochemical cell with a fluid flow path defined between the plurality of electrically conductive diamond electrodes. The plurality of electrically conductive diamond electrodes includes at least a first set of electrically conductive diamond electrodes at a first point along the fluid flow path and at least a second set of electrically conductive diamond electrodes at a second point along the fluid flow path, wherein the second point lies downstream from the first point along the fluid flow path, Furthermore, the first and second sets of electrically conductive diamond electrodes have separate electrical connections This electrode structure is distinguished over prior art bipolar electrode stacks in that the configuration comprises a series of electrically conductive diamond electrodes along the fluid flow path which have separate electrical connections. In contrast, in parallel flow bipolar configurations the flow path only extends across the diameter of the electrically conductive diamond electrodes. While the flow path between bipolar electrodes can be extended by utilizing a serpentine flow configuration as described in W02008/029258, the electrodes do not have separate electrical connections and thus do not allow for the application of variable voltage along the fluid flow path, e.g. as may be desired as the concentration of pollutants changes during treatment. Furthermore, by providing a serial configuration of separately connected electrically conductive diamond electrodes a lower operating voltage may be utilized as the voltage is not dropped over a large bipolar stack of electrodes.

The aforementioned electrode structure is also distinguished over the multi-cell serial configuration described in 1P2004-237165 by providing a serial configuration of separately connected sets of electrodes supported by a support structure in a single electrochemical cell configuration.

Thirdly, the electrical connections for each of the first and second sets of electrically conductive diamond electrodes are configured to periodically switch polarity. JP2004- 237165 suggests that in operation there are problems of electrode fouling in a serial configuration leading to a drop off in efficiency. However, by periodically switching the polarity of the electrodes it is possible to alleviate the problems of electrode fouling. While W02008/029258 suggests that the polarity of bipolar diamond electrodes may be reversed periodically to prevent build-up of a passivation layer on bipolar diamond electrodes, there is no suggestion that such a polarity switching method can be applied to solve problems of electrode fouling in a serial diamond electrode configuration as described in JP2004-237t65.

In light of the above, it will be evident that configurations according to the present invention are advantageous over prior art bipolar configurations in that they can be operated at lower operating voltage, they can provide a longer fluid flow path between the electrodes, and they can allow the applied voltage to be varied along the fluid flow path, e.g. as may be desired as the concentration of pollutants changes during treatment. Furthermore, it will be evident that configurations according to the present invention are advantageous over prior art serial multi-cell configurations in that they can be made more simple in construction by supporting a series of sets of electrodes in a single electrochemical cell configuration and they can avoid previously described problems of electrode fouling in serial configurations by providing the series of sets of electrodes with electrical connections configured to periodically switch polarity Individual examples of electrochemical cells according to embodiments of the present invention will now be described.

A first example of an electrochemical cell is illustrated in Figures 5, This electrochemical cell comprises a solid diamond electrode configuration comprising two end electrodes 50, 52 and a plurality of central electrodes 54 disposed between the two end electrodes 50, 52 in a parallel stack configuration. A fluid path 55 is disposed between opposed major faces of each adjacent pair of electrodes (doffed lines) whereby in use each of the central electrodes has both of its major faces exposed to the fluid being treated. Each of the plurality of electrodes comprises two electrical connections with two associated electrical contact points 56, 58 on the surface of each electrode such that in use the plurality of central electrodes 54 are alternately positively and negatively charged thereby forming a parallel stack of alternating anodes and cathodes with separate electrical connections thereby forming the first and second set of electrodes. The electrical connections are coupled to a power supply 57.

Furthermore, a porous support structure is disposed within the fluid path between each adjacent pair of electrodes.

The electrical contact points 56, 58 are disposed at edges of each of the plurality of electrodes 50, 52, 54 although it is envisaged that the electrical contact points could be located on a major face of each electrode. One advantage of providing edge contact points is that the contact points can be more easily isolated from the fluid to be treated.

The electrical contact points 56, 58 may each comprise a metallized region of the electrodes.

When the contact points are provided at an edge of the electrodes, the contact points can be isolated by providing a porous support structure which comprises a plurality of electrical contact point isolation portions for isolating the electrical contact points from the fluid being treated in use. Such a modified porous support structure 59 is illustrated in Figure 6 in which a solid edge region 60 of the porous support structure 59 serves to seal the fluid in a central region of the electrode stack and prevent the electrical contact points 56, 58 from contacting the fluid to be treated.

Each adjacent fluid path is connected in series such that in use fluid flows through each adjacent fluid path in series (as illustrated by the dotted lines in Figure 5). While in one arrangement the fluid may flow around edge regions of the electrodes such an arrangement makes it more difficult to isolate the electrical contact points 56, 58. As such, an alternative arrangement provides each electrode 50, 52, 54 with at least one though-hole 62 linking adjacent fluid paths as illustrated in Figure 7 (a) and (b) such that in use fluid flows through each adjacent fluid path in series via said through-holes 62 as shown in Figure 5. In such a configuration the fluid flows through the electrode stack via through holes in the electrodes and the porous support structure 59 comprises a non-porous ring 60 disposed between edge portions of adjacent electrodes to prevent the fluid leaking out in a radial direction of the electrode stack.

The aforementioned configuration thus provides a stack of alternating polarity solid diamond electrodes where each electrode is unipolar. The electrical connections are configured to periodically switch polarity in order to avoid electrode fouling in use. The configuration illustrated in Figure 5 provides all anodes connected in parallel and all cathodes connected in parallel. If it is desired to provide variable voltage along the solid diamond electrode stack thcn controllcrs (c.g. variablc rcsistors) can bc providcd for cach clcctrodc to vary thc voltage. Alternatively, the electrodes can be provided with separate electrical addressing lines in addition to separate electrical contacts to individually address the electrodes.

The configuration as described above is novel over arangements such as that disclosed in J7P2004-237165, W02008/029258, and W02012/049512 in that it comprises an alternating polarity electrode structure rather than a bipolar electrode structure, While JP2004-237t65, W02008!029258, and W020]2/0495U teach away from the use of alternating polarity diamond electrode structures, the advantage of providing such a structure is that it can be operated at a lower voltage thus reducing power consumption and cost. Furthermore, while a more complex electrical connection configuration is required, the modified support structure configuration aids in isolated electrical connections from the fluid in use. Further still, by providing electrical connections which are configured to periodically switch polarity problems of electrode fouling during use can be reduced, Furthermore, the serpentine fluid path provides a longer flow path through the electrode structure with increased turbulence which can aid mass transport to the electrode surfaces improving efficiency.

One problem with the edge connection configuration is that, due to the in-plane resistance of the solid diamond electrodes, such a configuration can result in the electrodes being most electrochemically active around their peripheral region rather than in a central axial region of the electrode stack. This problem can be alleviated by providing thicker, more conductive electrodes or otherwise reducing the diameter of the electrodes. The serpentine flow configuration enables the diameter of each electrode to be reduced while maintaining a reasonably long fluid path between the electrodes when compared to previous parallel flow configurations.

It may be noted that WO2008/029258 mentions a serpentine serial flow system in a bipolar stack but suggests that parallel flow is better for treating higher volumes of fluid, However, merely changing being serpentine and parallel flow does not alter the fluid volume between the electrodes and actually the parallel flow configuration will have a reduced path length between the electrodes for individual parallel paths. As such, the increase in volume of liquid being treated in the parallel flow configuration as per the statement in W02008/029258 is achieved by increased flow rate in a parallel configuration when compared with a serpentine configuration. While a higher flow rate could be achieved in a serpentine fluid flow configuration by increasing the fluid prcssurc, an increase in prcssurc can fracturc the solid diamond electrodes, The provision of a suitable support structure aids in increasing physical robustness and thus allows a higher pressure to be used to increase volume flow using a serpentine type arrangement, This arrangement also increases the fluid flow path relative to any recycle path which could potentially increase efficiency. There does not appear to be any suggestion in the prior art that a support structure such as that disclosed in WO2012/049512 can be used in a serpentine flow configuration allowing increased pressures and flow rates in a direction perpendicular to the diamond electrode sheets without fracturing the sheets thus off-setting the drawbacks of using a serpentine arrangement as described in WO2008/029258.

The electrode structure as described with reference to Figures 5 to 7 may thus comprise advantageous features in terms of lower operating voltages, reduced current and power losses, reduced cost of electrode fabrication and increased electrode robustness, and/or application of variable voltage along the fluid flow path.

A second example of an eleetrochemical cell is illustrated in Figure 8, The electrochemical cell is configured to provide two sets of electrodes 80, 82, each set of electrodes in the form of a bipolar stack whereby the electrochemical cell comprises a plurality of bipolar stacks.

The bipolar stacks 80, 82 are connected such that in use fluid flows from one bipolar stack 80 to a subsequent bipolar stack 82 in series. In the configuration illustrated in Figure 8 the electrodes 84 and fluid flow paths 86 are configured to provide a parallel flow configuration.

Porous support structures can be located between adjacent electrodes to make the configuration more robust as previously described. Furthermore, each bipolar stack 80, 82 has separate electrical connections 88, 90 to a power supply 92 such that the bipolar stacks 82, 84 form the first and second set of electrodes as previously defined.

Such an arrangement combines some advantageous features of bipolar configurations and serial configurations. By providing a plurality of bipolar stacks in series the number of electrodes in each stack can be reduced while maintaining the same overall electrode surface area contacting the fluid. By reducing the size of each stack, the operating voltage can be reduced thus saving power and cost. Additionally, or alternatively, the diameter of each electrode can be reduced while maintaining the same overall electrode surface area contacting the fluid when compared with a single bipolar stack configuration.

in light of the above, it will be evident that a series of bipolar stacks may have advantages in terms of lower operating voltages, reduced current and power losses, reduced cost of electrode fabrication and increased electrode robustness, and/or application of variable voltage along the fluid flow path.

In Figure 8, the bipolar stacks are electrically connected in parallel. If it is desired to provide variable voltage along the fluid flow path then controllers (e.g. variable resistors) can be provided for each bipolar stack to vary the voltage. Alternatively, each bipolar stack can be provided with separate electrical addressing lines in addition to separate electrical contacts to individually address the electrodes.

Figure 9 shows a modified version of the second example which effectively combines the features of the electrochemical cell of FigureS with the features of the electrochemical cell of Figure 8. Each bipolar stack 94, 96 is provided with a serpentine configuration (as illustrated by dotted lines) utilizing a modified support structure 98 and electrodes 100 similar in structure to those illustrated in Figures 6 and 7. This configuration provides a longer fluid flow path within each bipolar stack 94, 96 with increased turbulence which can improve mass transport to the electrode surfaces and thus improve efficiency. Each bipolar stack has its own power supply 102, 104 such that the bipolar stacks can be separately addressed.

Figure 10 shows a third example of an electrochemical cell. The electrochemical cell is configured such that the support structure comprises a first support sheet 110 in which is disposed a first plurality of electrodes 112 and a second support sheet 114 in which is disposed a second plurality of electrodes 116. The first and second support sheets 110, 114 are configured to define a fluid flow path 118 therebetween with each of the first plurality of electrodes 112 being disposed opposite a corresponding one of the second plurality of electrodes lii thereby forming a plurality of anode-cathode pairs.

Although this configuration appears to be significantly different to the previously described arrangements, it shares the common feature of providing sets of electrodes disposed along the fluid path with a suitable support structure and separate electrical connections which are configured to periodically change polarity. As such, this electrode structure also shares the common advantageous features in terms of lower operating voltages, reduced current and power losses, reduced cost of electrode fabrication and increased electrode robustness, arid/or application of variable voltage along the fluid flow path.

Figure 11 shows a portion of the electrode structure illustrated in Figure 10. The size and distribution of electrodes 112 within a support sheet 110 can be optimized such that each electrode generates oxidizing species in a substantially hemi-spherical dome region 120 of fluid above each electrode 112 with the hemi-spherical dome region 120 of each electrode extending to the edge of an adjacent hemi-spherical dome region. Such a configuration thus optimizes the functional performance of the array of electrodes 112.

All three examples as described above thus address one or more of the problems identified in the background section utilizing common underlying structural and functional features.

Providing individual current feeds to a series of sets of electrodes along the fluid flow paths permits the current and voltage to be controlled along the fluid flow path. This has the advantage that current and voltage can be optimised for the condition of the fluid under treatment at different points along the fluid flow path and thus an effective treatment of the fluid in a single pass can in principle be achieved. As such, certain embodiments may avoid the need for treatment as a batch process which is a major weakness of current technologies.

Accordingly, commercial advantages may include in-stream processing in addition to potentially more efficient processing. Furthermore, the fluid flow can be serpentine and/or the electrodes can be perforated with fluid flowing through the perforations axially down the array of electrodes. This latter arrangement has the advantage that the fluid is more effectively stirred and brought into contact with the e1ectrodes, ensuring high process efficiency, and simplifies the internal mechanical consiruction of the cell. The diameter of the electrodes can be smaller, making their production more cost effective and improving current access across the electrode discs. Electrical contact to the electrode discs can be from the periphery, preferably from substantially the whole of the periphery, and the cell may be configured such that the contact regions are not wetted by the fluid under process.

it may be noted that in operation the anode electrodes function to generate oxidizing species.

As such, in one configuration the plurality of electrodes comprise a plurality of opposing pairs of electrodes, each opposing pair of electrodes comprising one electrode which is fbrmed of a solid sheet of electrically conductive diamond material and another electrode which is formed of non-diamond material such as a metal or metal composite material.

However, in preferred configurations the plurality of electrodes comprise a plurality of opposing pairs of electrodes where both electrodes in each opposing pair of electrodes are lbrmed of a solid sheet of electrically conductive diamond material.

in addition to water treatment applications as described in the background section, embodiments of the present invention can also be used to generate ozone via oxidation of water.

While this invention has been particularly shown and described with reference to preferred embodiments, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appendant claims.