ELECTROCHEMICAL CELL

Description

[0001] The invention relates to an electrochemical cell according to the preamble of claim 1 (see e.g. DE 10 2007 042171 A1).

[0002] Such electrochemical cells have long been known in various embodiments from the prior art. They are used, for example, to produce electrolyzed water or ozonated water. Such cells are described, for example, in DE 10 2014 203 374 A1 or DE 10 2014 203 376 A1. They use diamond electrodes that have a plurality of depressions, grooves, or channels and that are in direct contact with the membrane separating the cathode chamber from the anode chamber. The membrane is designed to be ion-permeable. The structure of the electrodes, which is described, for example, in DE 10 2014 203 372 A1, generates a directed flow in the electrode chamber, which is essentially formed by the depressions in the electrode, so that ions formed at the electrode can be distributed as quickly and homogeneously as possible in the flowing liquid.

[0003] Electrochemical cells have at least two electrodes, an anode and a cathode. They can be designed as split cells, with the anode located in an anode chamber and the cathode in a cathode chamber. In this case, the two chambers are separated from each other by an ion-conductive membrane, which can be, for example, a semipermeable membrane or a diaphragm.

[0004] By applying an electric current to the electrodes, a medium in the anode and / or cathode chamber can be decomposed and / or converted, as in the electrolysis of water, for example. However, it is also possible to use the electrochemical cell in the context of so-called electrosynthesis for the production of certain organic or inorganic compounds.

[0005] Electrolytes are liquids with dissolved substances. These substances are, for example, starting materials for electrosynthesis. The electrolytes are introduced into the anode and / or cathode chamber, for example, or flow continuously through them. An electrolyte introduced into the anode chamber is also called an anolyte, and an electrolyte introduced into the cathode chamber is called a catholyte.

[0006] Split electrochemical cells, in which an ion-permeable membrane or diaphragm is located between the anode and cathode chambers, typically have a relatively large distance between the anode and cathode, resulting in a relatively high ohmic resistance and thus a significant energy requirement. In the cells mentioned above, this is solved by placing the anode and / or cathode in direct contact with the respective membrane. While this minimizes the distance between the two electrodes, it exposes the membrane to considerable mechanical and electrochemical stress. Furthermore, a structure in the electrode surface is necessary to achieve a sufficient chamber volume in the anode and / or cathode chambers.On the one hand, this is technically complex to manufacture, and on the other hand, it often results in insufficient membrane service life, especially at high current densities. Furthermore, this cell type exhibits widely varying local current densities due to the structured surface of the electrode.

[0007] Diamond electrodes with correspondingly structured electrode surfaces are also particularly susceptible to mechanical stress, such as impacts. The diamond coating, which is usually applied to a metallic or semiconductor base or substrate, often flakes off under such stresses. This can happen particularly after many years of operation, including in the case of hydrodynamically induced pressure surges. This flaking is very detrimental because the underlying base body is exposed at these points and, particularly at high current densities, is exposed to chemical and electrochemical attack at the edges as a result of the strong electric fields generated. Since these base bodies are generally far less corrosion-resistant than a diamond coating, rapid electrode failure often occurs in this case.

[0008] The invention is based on the object of proposing an electrochemical cell with which it is possible to synthesize, in particular, per compounds with high efficiency.

[0009] An electrochemical cell according to the invention is defined in claim 1.

[0010] Further embodiments of the invention are defined in the dependent claims.

[0011] This has several advantages. In the inventive design, the cathode base body now fulfills additional functions, as it accommodates at least part of the anolyte supply line and / or the anolyte discharge line. In the prior art, there is a preconception that the anolyte must under no circumstances come into contact with the cathode or any component of the cathode in order to avoid a reduction in the oxidative species generated in the anode chamber. This is, of course, particularly known for the anolyte discharge line. The invention is based on the finding that contact can be almost completely or entirely avoided, and the residual contact is almost completely harmless. The reduction is minimal and does not outweigh the advantages.

[0012] By positioning the anolyte supply line and / or the anolyte discharge line, with both lines preferably located in the cathode base body, the anode chamber can be designed almost freely and meets the requirements of industrial production of peroxide compounds. Peroxide compounds include, in particular, peroxo compounds, inorganic peracids and their salts, as well as other peroxide compounds that do not contain oxygen. Peroxo compounds are characterized by the presence of OO groups in their molecular structure, which therefore exhibit a high oxidation potential and can be used for typical oxidative reactions.The cell according to the invention can be adapted to the optimal requirements in the production of these substances in particular, particularly preferably peroxomonosulfates, peroxodisulfates, disulfides, perchlorates, perbromates, permanganates, uranates and periodates, by positioning the anolyte supply line and / or the anolyte discharge line in the cathode base body.

[0013] According to the invention, the anode chamber is defined by a chamber frame that is fluidically connected to the anolyte supply line and / or the anolyte discharge line. The chamber frame is preferably made of a plastic, particularly preferably of a polymer such as PTFE (polytetrafluoroethylene or polytetrafluoroethene) or PVDF (polyvinylidene fluoride or polyvinylidene difluoride). According to the invention, the anode chamber is defined on one side by the anode and on the opposite side by the membrane. The side surfaces between these two sides are defined by the chamber frame, so that it defines the anode chamber in four directions. The chamber frame is preferably formed with a recess that forms the actual anode chamber.The chamber frame itself is fluidically connected to the anolyte supply line and / or the anolyte drain line located in the cathode base body, so that anolyte supplied from the cathode base body through the anolyte supply line enters the chamber frame and from there is guided to the anode chamber. The anolyte exiting the anode chamber leaves the anode chamber into the chamber frame and from there is guided via the fluidic connection to the anolyte drain line. This means that, on the one hand, the anode itself does not have to perform any of these functions and can therefore be optimally selected for the production of the respective substance. On the other hand, the volume and, in particular, the thickness of the anode chamber, i.e., the distance between the electrode and the membrane, is determined by the thickness of the chamber frame and is thus freely adjustable.If the chamber frame is made of the plastics mentioned, it is ensured that the substances produced are not changed or react.

[0014] The chamber frame preferably has at least one distribution chamber that is fluidically connected to the anolyte supply line and / or the anolyte discharge line. The chamber frame preferably has two distribution chambers, one of which is fluidically connected to the anolyte supply line and one of which is fluidically connected to the anolyte discharge line. The distribution chambers preferably extend across the entire extent of the anode chamber in one spatial direction. This ensures a homogeneous and, as far as possible, laminar flow of the anolyte into and out of the anode chamber.

[0015] The chamber frame preferably has flow guide elements that are designed to direct a flow of an anolyte flowing from the distribution chamber into the anode chamber and / or an anolyte flowing from the anode chamber into the distribution chamber. Consequently, the anolyte particularly preferably flows from the anolyte supply line in the cathode base body into the first distribution chamber of the chamber frame, where it is distributed in one spatial direction over a large part, particularly preferably the entire extent, of the anode chamber. The flow guide elements that homogenize and calm the flow are preferably located between the actual anode chamber and the respective distribution chamber. If possible, further flow guide elements that establish the connection between the actual anode chamber and the second distribution chamber are located on the opposite side of the chamber frame. This second distribution chamber is preferably in fluidic contact with the anolyte discharge line.

[0016] In a preferred embodiment, the anode is a diamond electrode, which preferably has a structureless surface, preferably a structureless, flat surface. This ensures that the diamond electrode has no holes, edges, depressions, or undercuts that are sensitive to mechanical stress and at which the diamond layer could flake off from the substrate. This significantly increases the durability and service life of the electrode. In addition, a homogeneous current density and thus also a homogeneous electric field are generated. This allows the entire anode surface that comes into contact with the anolyte to be used to produce the desired substance, thereby increasing efficiency and yield. The use of such a diamond electrode represents a separate invention. This electrode is preferably also arranged in an electrochemical cell according to claim 1.

[0017] Preferably, the chamber frame rests directly against the diamond electrode. To operate, the electrochemical cell is subjected to a mechanical stress that presses the chamber frame against the diamond electrode. Through clever material selection, particularly the use of the aforementioned plastics for the chamber frame, an additional seal or sealing element is unnecessary. This makes the electrochemical cell structurally simpler and more cost-effective to manufacture.

[0018] The cathode preferably has a cathode surface arranged on the cathode base body, which is preferably made of a metal, for example steel. The cathode surface forms the actual cathode, which is supplied with electrical current. Of course, it is also possible to form the cathode surface integrally with the cathode base body. The advantage of a separate cathode surface is that the cathode base body is made of a different material, preferably a polymer, particularly preferably PTFE or PVDF. This applies in particular to the area where the anolyte supply line and / or the anolyte discharge line are located. In this case, it is ensured that the produced substances do not come into contact with a metal, for example steel, when they are discharged from the anode chamber.

[0019] In a preferred embodiment, at least one spacer element is located between the membrane and the anode and / or between the membrane and the cathode. This spacer element prevents the membrane from coming into mechanical contact with the anode or the cathode, which could cause damage. The spacer element, which can in particular be designed as a spacer grid, is preferably made of a polymer, in particular PTFE or PVDF. The structure of the spacer grid or the spacer element should be designed such that it does not disrupt the homogeneous flow in the anode chamber as much as possible and such that the lowest possible flow resistance can be offered to a catholyte in the cathode chamber.

[0020] The cell preferably has a catholyte supply line through which a catholyte can be conducted into the cathode chamber, and a catholyte drain line through which the catholyte can be drained from the cathode chamber. The catholyte supply line and the catholyte drain line are preferably located in the cathode base body.

[0021] The membrane is preferably arranged between the cathode base body and the chamber frame, with it being particularly preferably clamped between the two components. To avoid damage to the membrane and at the same time achieve sufficient tightness of the cathode chamber, it is advantageous to use a separate sealing element, such as a sealing ring. This is inserted, for example, into a groove provided in the cathode base body and seals the cathode chamber to the outside. The membrane is then clamped between the chamber frame and the sealing element. Both elements are elastic, or at least flexible, elements, thus achieving sufficient tightness.

[0022] The distance between the anode and the cathode is preferably less than 5 mm, preferably less than 3 mm, and particularly preferably less than 2 mm. The distance can be selected and adjusted by selecting the thickness of the chamber frame.

[0023] In a particularly preferred embodiment of an electrochemical cell arrangement, two of the electrochemical cells described here are arranged mirror-symmetrically next to one another. The substrate with the two diamond layers applied to two opposite sides of the substrate, which form the two diamond electrodes, is located at the center. They can be supplied with electrical current through a single electrical contact and preferably both form the anode. If one works outwards from this innermost region, the anode chamber follows the anode, each formed by a chamber frame. The chamber frames are preferably identical and lie directly against the two diamond electrodes. They are each covered by a membrane that defines the outer limits of the two anode chambers.This is followed by two cathode base bodies which have the properties described here and in particular have the two anolyte supply lines and / or anolyte discharge lines.

[0024] As an alternative to this symmetrical design, a temperature control device can also be arranged on the side of the corresponding substrate facing away from a diamond electrode. This temperature control device makes it possible to cool or heat the anode. However, the main application is likely to be cooling the anode, since a lot of energy is supplied to the anode, particularly at high current densities, thereby heating it up. In addition to or as an alternative to cooling the anode, the anolyte can also be cooled so that the anode is supplied to the coldest possible state. The temperature control device is therefore preferably a cooling device, for example a metallic heat sink, with channels through which a coolant is conducted.

[0025] Preferably, an ultrasonic sonotrode is assigned or can be assigned to the cathode base body. For this purpose, the cathode base body preferably has at least one sonotrode receptacle. A sonotrode can be used to remove any deposits on the cathode using ultrasound.

[0026] Some embodiments of the present invention are explained in more detail below with reference to the accompanying figures. They show: Figure 1 - a schematic sectional view of an embodiment of the present invention, Figure 2 - an exploded view of a further embodiment of the present invention, Figure 3 - a perspective view of an embodiment of the cathode base body, Figure 4 - a front view of a further embodiment of the cathode base body, and Figure 5 - a perspective view of an embodiment of a sealing frame.

[0027] In Figure 1A section through an electrochemical cell 2 according to an embodiment of the present invention is shown. This cell has an anode chamber 4 with an anode 6 and a cathode chamber 8 with a cathode surface 10.

[0028] The cathode surface 10 is formed in a recess of a cathode base body 12 and, together with the latter, forms the cathode. The cathode chamber 8 is bounded on the one hand by the cathode base body 12 and the cathode surface 10, and on the other hand by an ion-conductive membrane 14.

[0029] The cathode base body 12 has a catholyte supply line 16 and a catholyte discharge line 18, each of which is fluidically connected to the cathode chamber 8. In addition, the cathode base body 12 has an anolyte supply line 20 and an anolyte discharge line 22, each of which is fluidically connected to the anode chamber. The anolyte supply line 20 opens into a first distribution chamber 24 of a chamber frame 26. The chamber frame 26 has a plurality of Figure 1 flow guide elements 28, not shown, which form a fluidic connection between the anode chamber 4 and the first distribution chamber 24.

[0030] On the side opposite the first distribution chamber 24, the chamber frame 26 has a second distribution chamber 30, which is fluidly connected to the anode chamber 4 via a plurality of flow guide elements 32 (not shown in Figure 1). At the same time, the second distribution chamber 30 is fluidly connected to the anolyte discharge line 22.

[0031] The anolyte consequently flows via the anolyte supply line 20 into the first distribution chamber 24 of the chamber frame 26 and from there via the flow guide elements 28 into the anode chamber 4. From the anode chamber 4, the anolyte flows via the flow guide elements 28 into the second distribution chamber 30 and from there via the anolyte discharge line 22 out of the cathode base body 12.

[0032] The anode chamber 4 is formed by the anode 6, which has an anode base body 34, for example made of graphite, silicon or a metal, which is coated with a diamond layer 36, in particular a boron-doped one, as well as the chamber frame 26 and the ion-conductive membrane 14. For this purpose, the chamber frame 26 has a Figure 1 The chamber has an anode chamber recess 38 (not shown), the side surfaces of which laterally delimit the anode chamber 4. The chamber frame 26 rests against the anode 6 and the ion-conductive membrane 14 in such a way that the anode chamber 4 is liquid-tight.

[0033] In the present embodiment, the cathode base body 12 has a sealing element recess 40 extending around the cathode surface 10, in which a sealing element 42 in the form of an O-ring is mounted. This represents, in particular, a safety measure to ensure the liquid-tightness of the cathode chamber 8, i.e., between the ion-conductive membrane 14 on the one hand and the cathode base body 12 on the other. In a further, not-shown embodiment of the invention, no sealing element recess 40 and sealing element 42 are present. In this case, the sealing of the cathode chamber 8 is achieved exclusively via the cathode base body 12 and the ion-conductive membrane 14.

[0034] On the side of the anode 6 facing away from the anode chamber 4, the electrochemical cell 2 has a heat sink 44, preferably made of steel, in particular stainless steel, with a cooling line 46 by means of which a coolant can be conducted along the anode 6 to cool or temperature-control it. For this purpose, a coolant seal 48 is arranged between the heat sink 44 and the anode 6.

[0035] In Figure 2 Another embodiment of an electrochemical cell 2 is shown. This has a central anode 6, to which Figure 2A chamber frame 26 adjoins each of the anode chambers 4 to the rear and to the front. In the assembled state, the electrochemical cell 2 consequently has two anode chambers 4 with only one anode 6, which, however, has an anode surface, in particular a diamond coating, on each side. The chamber frame 26 is followed, to the front and to the rear, by an ion-conductive membrane 14. Adjoining each of these is a sealing element 42 in the form of a rubber seal, which, in the assembled state, is arranged in a sealing element recess 40 of the respective adjoining cathode base body 12. The sealing element recess 40 extends around the respective cathode surface 10.

[0036] On both sides of the anode 6, the electrochemical cell 2 has an anode chamber 4 and a cathode chamber 8, which are separated from each other by an ion-conductive membrane 14. The corresponding anode chambers 4 and cathode chambers 8 each form a cell, so that the Figure 2 The electrochemical cell arrangement shown has two electrochemical cells 2.

[0037] The cathode base bodies 12 each have a catholyte supply line 16 and a catholyte outlet line 18, as well as an anolyte supply line 20 and an anolyte outlet line 22. In the rear of the two cathode base bodies 12, parallel rows of openings are indicated, which serve as outlets for the aforementioned lines. The lowest outlets are those of the anolyte supply line 20. In the assembled state, these are in fluid communication with the first distribution chamber 24 of the associated chamber frame 26, so that the anolyte can flow into the anode chamber 4 via the flow guide elements 28. The respective anode chamber 4 is laterally delimited by the side surfaces of the anode chamber recess 38 of the chamber frame 26.

[0038] The row of outlets above this belongs to the catholyte supply line 16, and the row above this to the catholyte discharge line 18. The top row belongs to the anolyte discharge line 22, which, when assembled, is in fluid communication with the second distribution chamber 30. The second distribution chamber 30, in turn, is in fluid communication with the anode chamber 4 via the flow guide elements 32.

[0039] In addition, a plurality of fastening means 50 are shown, by means of which the components can be secured to one another. For this purpose, the cathode base bodies 12 have a corresponding number of fastening recesses 52. Preferably, the ion-conductive membranes 14, the chamber frames 26, and the anode 6 are secured relative to one another by a clamping force between the two cathode base bodies 12. This clamping force is generated in particular by the fastening means 50. The entire electrochemical cell 2 is also arranged on a base plate 54.

[0040] In addition, electrolyte connection elements 66 are connected to the anolyte supply lines 20 and the anolyte outlet lines 22, as well as to the catholyte supply lines 16 and the catholyte outlet lines 18 of the cathode base body 12. Via these, they are preferably each connected to, in Figure 2 not shown, external supply and discharge lines for anolyte and catholyte are fluidically connected.

[0041] Figure 3 shows an embodiment of a cathode base body 12 for an electrochemical cell 2 according to an exemplary embodiment of the present invention. This body has a cathode surface 10 formed integrally with the cathode base body 12, in this case made of steel. The cathode surface 10 has a so-called flow field 56 consisting of a plurality of channels that run along an imaginary grid. The catholyte flows through these channels during operation of an electrochemical cell 2 with the cathode base body 12.

[0042] A sealing element recess 40 extends around the cathode surface 10, in which a sealing element 42 is arranged when the electrochemical cell 2 is assembled. The cathode base body 12 has a catholyte supply line 16, a catholyte discharge line 18, an anolyte supply line 20, and an anolyte discharge line 22. The anolyte supply line 20 is fluidly connected to a series of anolyte supply openings 58 in the cathode base body 12, through which an anolyte can be supplied to an anode chamber 4 (not shown).

[0043] In addition, catholyte supply openings 60 are formed in the cathode base body 12, which are fluidically connected to the catholyte supply line 16. They are arranged in the lower ends of the channels of the flow field 56 and serve to supply a catholyte to the cathode chamber 8 (not shown).

[0044] Furthermore, the cathode base body 12 has a series of catholyte discharge openings 62, which are arranged in the upper ends of the channels of the flow field 56 and are fluidically connected to the catholyte discharge line 18. They serve to discharge a catholyte from the cathode chamber 8. The cathode base body 12 also has a series of anolyte discharge openings 64, through which anolyte can be discharged from the anode chamber 4. They are fluidically connected to the anolyte discharge line 22. The cathode base body 12 also has a plurality of fastening recesses 52 for fastening means 50 (not shown).

[0045] Figure 4shows another embodiment of a cathode base body 12. A chamber frame 26 is placed on top of the latter. Through the anode chamber recess 38 of the chamber frame 26, the cathode surface 10 with a flow field 56 of channels arranged in a grid-like manner can be seen. In the operating state, an ion-conducting membrane 14 is arranged between the chamber frame 26 and the cathode base body 12, so that the cathode surface 10 and the flow field 56 are not visible. This ion-conducting membrane 14 is not shown in Figure 4 for the sake of clarity.

[0046] The cathode surface 10 is formed as a separate component, in particular as a steel or stainless steel plate, from the cathode base body 12. The cathode base body 12 is preferably made of a plastic, in particular PEEK. The cathode surface 10 has a catholyte supply opening 60 and a catholyte discharge opening 62 through which a catholyte can flow into and out of the cathode chamber 8 (not shown). The catholyte supply opening 60 is fluidically connected to a catholyte supply line 16 (not shown), and the catholyte discharge opening 62 is fluidically connected to a catholyte discharge line 18 (not shown).

[0047] The cathode base body 12 also has an elongated anolyte supply opening 58, which is fluidically connected on the one hand to an anolyte supply line 20 (not shown) and on the other hand to a distribution space 24 of the chamber frame 26.

[0048] In addition, the cathode base body 12 has an elongated anolyte discharge opening 64, which is fluidically connected on the one hand to an anolyte discharge line 22 (not shown) and on the other hand to the distribution space 30 of the chamber frame 26. The chamber frame 26, in turn, has a plurality of flow guide elements 28 and flow guide elements 32, which are each fluidically connected to the distribution spaces 24, 30 of the chamber frame 26 and the anode chamber recess 38. The cathode base body 12 has six fastening recesses 52 for fastening means 50 (not shown).

[0049] Figure 5 shows a perspective view of an embodiment of a chamber frame 26 for an electrochemical cell 2. The chamber frame 26 is preferably made of a plastic, in particular PTFE or PVDF, and has three recesses: a distribution chamber 24, a distribution chamber 30, and an anode chamber recess 38.

[0050] The distribution chamber 24 is fluidically connected to the anode chamber recess 38 via flow guide elements 28. The distribution chamber 30 is fluidically connected to the anode chamber recess 38 via flow guide elements 32. List of reference symbols

[0051] 2 Electrochemical cell 4 Anode chamber 6 Anode 8 Cathode chamber 10 Cathode surface 12 Cathode base body 14 Ion-conductive membrane 16 Catholyte supply line 18 Catholyte drain line 20 Anolyte supply line 22 Anolyte drain line 24 Distributor chamber 26 Chamber frame 28 Flow guide elements 30 Distributor chamber 32 Flow guide elements 34 Anode base body 36 Diamond coating 38 Anode chamber recess 40 Sealing element recess 42 Sealing element 44 Heat sink 46 Cooling line 48 Coolant seal 50 Fasteners 52 Fastening recesses 54 Base plate 56 Flow field 58 Anolyte supply opening 60 Catholyte supply opening 62 Catholyte drain opening 64Anolyte discharge opening 66Electrolyte connection element

Claims

1. An electrochemical cell (2) comprising: a. an anode chamber (4) with an anode (6), b. an anolyte inlet (20) through which an anolyte can be conducted into the anode chamber (4), c. an anolyte outlet (22) through which the anolyte can be discharged from the anode chamber (4), d. a cathode chamber (8) with a cathode that has a cathode base body (12), e. a membrane (14) arranged between the anode chamber (4) and the cathode chamber (8) and f. a chamber frame (26), wherein the anolyte inlet (20) and / or the anolyte outlet (22) run(s) through the cathode base body (8), characterized in that the anode chamber (4) is bounded on one side by the anode (4), on the opposite side by the membrane (14) and on the side surfaces lying therebetween by the chamber frame (26), which is fluidically connected to the anolyte inlet (20) and / or the anolyte outlet (22).

2. The electrochemical cell (2) according to claim 1, characterized in that the chamber frame (26) is made of a plastic, particularly preferably of a polymer, such as PTFE or PVDF, for example.

3. The electrochemical cell (2) according to claim 2, characterized in that the chamber frame (26) has at least one distribution space (24) which is fluidically connected to the anolyte inlet (20) and / or to the anolyte outlet (22).

4. The electrochemical cell (2) according to claim 3, characterized in that the chamber frame (26) comprises flow-directing elements (28) which are designed to direct a flow of an anolyte entering the anode chamber (4) from the distribution space (24) and / or exiting the anode chamber (4) into the distribution space (30) .

5. The electrochemical cell (2) according to any of the preceding claims, characterized in that the anode (6) is a diamond electrode that preferably has a smooth surface, more preferably a smooth flat surface.

6. The electrochemical cell (2) according to claim 5, characterized in that the chamber frame (26) is in direct contact with the diamond electrode.

7. The electrochemical cell (2) according to any one of the preceding claims, characterized in that the cathode has a cathode surface (10) arranged on the cathode base body (12), which is preferably made of a metal, in particular steel.

8. The electrochemical cell (2) according to any one of the preceding claims, characterized in that a spacer element, in particular a spacer grid, is arranged between the membrane and the anode (6) and / or between the membrane and the cathode, said spacer element preferably being made of a polymer, in particular PTFE or PVDF.

9. The electrochemical cell (2) according to any one of the preceding claims, characterized in that the cell (2) has a catholyte inlet (16) through which a catholyte can be conducted into the cathode chamber (8) and a catholyte outlet (18) through which the catholyte can be discharged from the cathode chamber (8), wherein the catholyte inlet (16) and the catholyte outlet (18) run through the cathode base body (12).