ELECTROCHEMICAL OZONIZER AND HYDROGEN GENERATOR

Abstract

The electrochemical ozonizer comprising at least one cell, each consisting of an anode, a cathode and an interposed full-area, cation-conducting membrane which is chemically stable to ozone as a solid electrolyte, is characterized in that the membrane conductively connects the anode and the cathode while forming flow channels for water that are separated from one another as anode and cathode chambers.

Description

Under a first aspect the present invention refers to the structure of an electrochemical ozonizer which consists of anode, cathode and full-area membrane disposed thereinbetween. A cell with an active dual chamber, consisting of anode chamber and cathode chamber, can here be formed by direct contacting, and further layers can also be created by inserting interposed conductive electrode layers as electrolytically active layers with stepped voltage potentials. The interspaces are formed by full-area membrane elements which are only conductive for protons, positively charged hydrogen ions H⁺ and corresponding oxonium ions H3O⁺. These membrane elements establish a cation-conductive connection between the electrodes, and they ensure very distinct flow conditions. The membrane elements are represented by a solid electrolyte having shaped flow channels, which as proton conductor is conducive to an electrochemical reaction.

A second aspect of the invention refers to the structure of a hydrogen generator or a fuel cell, respectively, with a reversible mode of operation.

The electrochemical ozone generation in water is based on two essential factors:

• • 1. OH′ excess on anode and H⁺ or H3O′ deficiency
  • 2. catalytic surface on anode, whereby O₃ is formed and not O2 known: lead-dioxide PBO₂/boron-doped crystalline diamond layer BDD/ . . . .

This results in a stable reaction, whereby ozone is formed on the anode:

3H₂O→O3+6H⁺+6e⁻

The intermediate reactions that happen catalytically hidden from view on the anode surface shall here be mentioned in part:

H2O→HO.+H⁺e⁻

HO.+→O.+H⁺+e⁻

H₂O+HO.+O.→O₃+3H⁺+3e⁻

Hydrogen and intermediate products are produced on the cathode:

2H⁺+2e⁻→H₂

2H₂O+2e⁻→H₂+2OH⁻

Hardness deposits also occur in the presence of hardness-producing agents in water.

Electrolytic ozonizers that have so far been known in the pure water sector operate with porous electrodes, or untight electrodes, which are normally implemented as expanded metals. These are clamped against one another with a solid electrolyte with the electrochemically active layer, normally DLC diamond-like carbon layer which is produced by CVD chemical vapor deposition or PVD physical vapor deposition and which is conductive, normally BDD boron-doped diamond layer. See DE29504323 U1, DE19606606 C2, DE 10025167 B4, DE20318754 U1 and DE 102004015680A1.

A cation-conducting membrane that is chemically stable with respect to ozone, preferably a sulfonated tetrafluoroethylene membrane (PTFE), e.g. a DuPont Nafion PFSA membrane, is used as the solid electrolyte.

This solid-electrolyte membrane is firmly clamped between the electrodes.

Hence, ultrapure water applications have the drawback that the flow does not neatly reach the anode layer which is chemically active for ozone generation because the electrodes themselves are in direct contact with the solid electrolyte and present an obstacle. This prevents a neat removal of the reaction product, here ozone O3, and counteracts the reaction.

Moreover, the electrically driving field is only operative between the membranes, and the predominant part of the reaction start products, of the water, is thus in the weaker area of the electrical field which is however separated by the neutral plate area from the strong electrical field in the effective surface assigned to the membrane. This is shown in FIG. 1 in the left portion.

Moreover, the necessary fixation of the electrodes, mostly implemented via a screw connection, is rather complex because this is done in pairs and requires penetrations of the electrodes. The electrodes are fixed at a distance when used in the dirty-water sector.

Hence, although the electrical field fully acts on the water, the electrochemical process is activated and maintained by higher voltages due to the rather large distance.

The drawback is here that the interspace formed by the electrolyte between the electrodes has to be overcome with the required higher voltage.

In this case, too, the fixation of the electrodes is very complex.

According to the invention a cell structure is suggested that arranges the solid electrolyte such that said electrolyte conductively connects the planar electrodes, but simultaneously represents flow channels and separates the anode chamber and the cathode chamber from one another over the whole area. The electrical field is thereby maintained up to the effective surfaces, resulting in a very high efficiency.

A schematic structure is shown in FIG. 1.

Preferably, the carrier material of the planar electrodes consists of niobium which is coated with a boron-doped diamond layer.

To obtain membranes with a high ozone yield together with a long service life, fluorinated polysulfonic acid (PFSA) has turned out to be a useful membrane base material. However, for increasing the service life of the membrane, additional substances, e.g. montmorillonite, and/or also ceroxide, and/or also manganese oxide, have to be added in powder form at a ratio of about 2% to the preferably granulated membrane base substance PFSA.

Montmorillonite inter alia improves the water absorption within the membrane and thereby reduces the concentration gradient; ceroxide and manganese oxide increase the oxidation resistance of the membrane to ozone.

Measurements have shown that very high power yields are possible.

A very high packing density is achieved at the same time, which minimizes the required space.

This shall be illustrated in more detail hereinafter.

The structure enables a simple modular extensibility permitting a high economic flexibility.

The ozonizer according to the invention can be inserted into a line of a pure-water supply system e.g. for dialysis devices, so as to kill possibly existing germs etc. in the water flowing therethrough, or to oxidize organic substances. The hydrogen that is also produced can here outgas in a feed tank or the like, if necessary, if the solubility limit is exceeded.

The structure according to the invention can be implemented by a solid-electrolyte membrane which is present in the form of a sawtooth, trapezium or rectangle function between anode and cathode. The shapes themselves may here be rounded off up to a sine curve. Grids may here be used onto which the membrane is threaded or put over, or which give the membrane its shape.

See FIG. 2a

Likewise, unidirectional fabrics may be used that give the membrane its shape.

See FIG. 2b

Another possibility consists in implementing a solid-electrolyte membrane which has contacting elevations touching the anode and cathode, and thereby forms distianct flow channels. Diverse optimizable shapes are here conceivable; these may be configured in the form of knobs or as struts.

See FIG. 3

A transverse inflow with pierced electrodes in the case of a partial-area electrolyte, as suggested in DE 1020040156801 A1, would also be conceivable, but the flow is of minor importance, whereby the full-area membrane separation according to the invention with a simultaneous conductive connection is impaired.

The cell structure according to the invention allows a stacking, which multiplies the active area without any further contacting between two outer electrodes to which voltage is applied. The voltage must here be multiplied accordingly.

See FIG. 4a

Stacking with alternating polarity is also possible.

See FIG. 4b

This stack may be integrated in a rather simple way into an insulating housing which directs the inflow and outflow and provides the hydraulic as well as the electrical connections.

See FIG. 5, which show a block with a clamp connection and a possible structure.

Owing to the suggested design the solid-electrolyte membrane can also be used as a winding grid “spacer”, thereby permitting a cell structure as a winding module. This can be carried out with an alternating polarity of the electrode layers, with continuous electrodes, i.e. electrodes that are continuous over several windings; in this instance, each electrode would have to be contacted. It is also conceivable to contact only the outer and inner tube if flexible intermediate electrodes are used that are conductive over not more than the winding length of a part of the circumference. This permits the economic production of great amounts of ozone.

See FIG. 6. The figure no longer shows the flow channels in detail.

All of the structures that have so far been shown permit a change in polarity and are thus also suited for groundwater and surface water, but also for waste-water treatments. In a configuration that is not suited for changes in polarity, the structure may also be used, apart from the ozone production, for discharging and exploiting the evolving hydrogen.

See FIGS. 7a and b.

FIG. 7a shows a winding module; in this instance e.g. with four hydrogen collecting pockets that are wound up starting from the inner tube.

The inner tube and the outer tube represent the electrodes by which the electrical field is created.

The collecting pockets are provided at one side with circumferentially interrupted anode pieces, i.e. anode pieces that are only conductive in segments, to the outside with a catalyst layer. The anode segments are glued to one another tightly but in an insulating manner. The other sides of the pockets are formed towards the other outside with the solid-electrolyte membrane. On the outside it provides the flow plane, e.g. flow channels for the water, and the liquid electrolytes, respectively, and a conductive connection with the quasi “cathode side” of the conductive anodes to the inside.

In the pockets a conductive nonwoven, e.g. stainless steel mesh, can also ensure the gas flow to the inner collection tube.

In FIG. 7b the inner tube is e.g. chosen as a cathode, and a pocket segment is cut open. In the right part of the figure the solid-electrolyte membrane is cut open. The outer flow formations, here: elevated struts, can be seen. This membrane is glued on the edge to the anode segments. The anode segments can be represented by conductive sheets, e.g. unilaterally BDD diamond-coated niobium sheets, other sheets with a catalytically active surface, or even conductive plastic films that have an effective catalytic layer.

The winding according to the invention, the variant with the anode segments, corresponds to a series circuit or the stack with only outer contacting. A winding according to the invention with continuously contacting electrodes, which corresponds to a parallel circuit, shall be suggested hereinafter.

Under the second aspect of the invention a winding module structure is suggested that can be operated both as a hydrogen generator and as a fuel cell, depending on the excess of power or the lack of power.

FIG. 8 outlines such a structure.

In the case of mains overvoltages, an overriding electronic system switches to hydrogen generator operation. In the case of undervoltage, the system switches to fuel-cell operation.

FIG. 8a shows a corresponding block-diagram sketch.

FIG. 8b shows such a winding module.

FIG. 8c picks out a winding-module area element.

During generator operation incoming power is consumed to produce hydrogen.

A pump that pumps produced hydrogen into a gas supply tank maintains a low pressure level in the middle collection tube. As a result, hydrogen flows out of the solid-electrolyte-membrane pockets and collects there.

In this case the pockets are filled with a conductive stainless steel grid which serves as a porous flow plane and is conductively connected to the inner tube at the same time.

The grids which are positioned in the pockets work at both sides as a cathode and take from the adjacent solid-electrolyte areas the protons which are obtained on the anode as a reaction product, and donate electrons to them, whereby hydrogen is generated.

The solid-electrolyte-membrane pockets are structured at both sides such that they are always oriented to the outside and are each abutting on the next anode area.

The structure ensures a flow of the electrolyte, in the generator operation pure water, e.g. with a conductivity of 1-5 μS or less. The anode areas have a catalytically active layer to generate oxygen or also ozone. This is enforced by an outwardly applied voltage as a process, and electrical power is thus consumed.

The produced ozone or the oxygen is removed from the pure water circuit and consumed in a superior process, also intermediately stored or discharged to the atmosphere.

In the fuel-cell operation, hydrogen is pumped out of the supply tank into the collection tube and is conveyed at a slight pressure in the porous area of the stainless steel grid up into the pocket tips. At that place the hydrogen is split at the contact points with the solid electrolyte with donation of two electrons into protons which migrate via the solid electrolyte to the oxygen molecules enriched in the water and oxidize with the same with absorption of electrons into water.

The area acting in the generator process as an anode is here active as a cathode which catalytically binds the oxygen which is present and enriched in water, and converts it with the protons present in the solid electrolyte into water.

The invention shall now be explained with reference to the following drawings, in which:

FIGS. 1a and 1b.—Scheme of the cell structure with voltage curve and potential curve.

FIG. 1a. Scheme of an ozone cell according to the prior art. The applied voltage 1 acts via the electrode 2 and the counter electrode 3 on the medium which flows past in the intermediate space 4. The electrode 2 and the counter electrode 3 are screwed relative to each other with an interposed solid-electrolyte membrane 5. Recesses or also pores in the electrodes permit a supply and transportation of the starting materials and the reaction products. The voltage difference is always operative between the plates through the respective distance, whereby the corresponding electrical field acts on the ions as a driving force. As can be seen, the driving electrical field is subject to a gap in the plate area.

The effective anode area for the ozone generation exists three times.

FIG. 1b. Scheme of an ozone cell having a structure according to the invention. The applied voltage 1 acts via the electrode 2 and the counter electrode 3 on the medium which flows past in the intermediate space 4. The electrode 2 and the counter electrode 3 are conductively connected relative to each other to the interposed solid-electrolyte membrane 5. Flow channels in the arranged membrane permit a supply and transportation of the starting materials and the reaction products. The voltage difference is each time operative between the plates via the respective distance, whereby the corresponding electrical field acts on the ions as the driving force. Said driving force is operative without interruption up to the active reaction plane. The reaction products are supplied and transported away in a reaction-promoting manner by the directly acting flow.

The high packing density is here clearly visible in that at the same number of electrodes the effective electrode area is increased from 3 to 5.

FIGS. 2 and 3—Schematic structure of a single cell according to the invention with a view in flow direction

FIG. 2a with membrane formed by additional grid 6

FIG. 2b with membrane formed by fabric inserts 7

FIG. 3 with membrane which as such is configured as a shaped profile 5.

FIG. 4—cell stack, view in flow direction

FIG. 4a—cell stack with contacting of only the outer electrodes. The middle electrodes assume interposed potentials according to a series arrangement. Current flows through all cells and the voltages add up to form the total voltage.

FIG. 4b—cell stack with continuous alternating contacting, conforming to a parallel circuit with the same voltage on all cells and summation of the current.

FIG. 5a—ozone generator 10 according to the invention with cells stack in a side view, consisting of block lid 11, block bottom part 12, inlet clamp 13 and outlet clamp 14. Instead of the clamp connection, the block may also be provided with a flange connection, plug type connection, connection with union nut, threaded connection or other types of connections.

FIG. 5b—The generator with a view obliquely from above. What can be seen is the outlet clamp 14 with visible O-ring seat 16, the splash-proof cable glands 15, and the cell stack 17.

FIG. 5c shows a section through an ozone generator with obliquely positioned cell stack 17. The liquid is here guided via the liquid reversal 60 through the flow channels 70 of the membrane 5 such that there is no gas formation, particularly hydrogen formation, inside the ozone generator 10. The cell stack is pressed together by the generator clamping plates 67 in form-fit manner, resulting in intimate connections between electrodes 2 and membranes 5. To reduce the flow resistance in the ozone generator 10, the generator clamping plates 67 may be configured with lateral liquid channels (here not shown) that are opposite to the cell stack.

The electrode power supply is carried out via connection 61 which is preferably configured as a round material and conductively mounted on the face of the electrode 2.

As for the liquid sealing of the electrode connections 61, a seal 62 with seal pressure plate 63 and the pressure plate screws 64 is used.

FIG. 5f shows the position and mounting of the generator clamping plates 67 by means of clamping plate screws 69. The form-fit installation of the clamping plates in the ozone generator can also be seen there.

5g shows the obliquely upwardly extending flow channels 70 of the membrane 5, the structure of which is shown in FIG. 5h.

FIG. 5i shows the mounted cell stack 68 having electrode connections 61 projecting into the wiring chamber 71. The closure is accomplished with the lid 65.

5j and 5k show the mounted cell stack 68 at the side and an electrode 2 with connection 61, respectively.

It is within the meaning of the invention to configure the inclination angle of the stack or the connections of the electrodes also in another sealing manner. Moreover, a hydraulic type of connection differing from the clamp connection as shown here is e.g. possible with all available hydraulic connecting techniques.

FIG. 6—schematic winding module with a winding pocket

FIG. 7a—winding module opened with 4 pockets, inner tube 21, hydrogen collection pockets 22, outer tube 23.

FIG. 7b—winding module pocket according to the invention in cut-open state. What can be seen are the conductive anode segments 24 which are tightly glued, but at a distance and thus in an insulating manner relative to one another 25. These are also tightly glued on the edge 26 against the solid-electrolyte membrane 27. The solid-electrolyte membrane 27 is evidently provided with flow profiles that permit a flow in flow direction 28 and, nevertheless, have a conductive connection to the next winding plane, thus onto the pocket outsides of the anode segments 24.

Within the pockets a conductive connection is established with the side 29 of the anode segments, which acts as a cathode, via a conductive nonwoven or tangentially extending profiles, which simultaneously ensures an outflow of the hydrogen.

FIG. 8—H2-O2/O3—cells/generator structure

FIG. 8a—block diagram sketch

Shown in the figure is the generator operation and indicated in brackets is the fuel-cell operation. During generator operation, hydrogen is pumped with a pump 41 out of the cell winding 40 according to the invention into the hydrogen tank 42. In this process, current 43 flows due to the applied outer voltage from the outer jacket tube 44 to the inner collection tube 45. At the same time pure water is pumped out of the pure water tank 46 via the pure water pump 47 through the cell winding 40. In the pure water tank, the oxygen or the ozone is deposited as a gas phase, and is pumped with a pump 48 into the oxygen/ozone tank 49. A gas release valve with downstream pressure reducer for both the hydrogen 50 and the oxygen 51 is closed.

A pure-water fill-level monitor signalizes the upper energy storage limit.

In the fuel-cell operation 52 the gas release valves 50 and 51 permit the gas transportation via the pressure reducers. Oxygen/ozone is supplied atomized via a venturi tube 53 to the pure water flow.

FIG. 8b—winding module with continuously contacting electrodes is opened.

The four pockets 54 can be seen; these end on the outside and embed thereinbetween the anodes 55 contacted to the outer tube.

FIG. 8c—winding module pocket in the cut-open state. The winding module pocket 54 consists of two solid-electrolyte planes that have flow profiles 55 relative to the pocket outside and are tightly glued to one another on the outside on edge 57 or are folded from a ribbed flexible tube. Inside the pockets the cathode 58 establishes a gas flow plane and the conductive connection to the inner collection tube 45. The cathode may consist of wire grid or conductive synthetic woven or synthetic nonwoven.

Claims

1. An electrochemical ozonizer comprising at least one cell, each including an anode, a cathode and an interposed full-area, cation-conducting membrane which is chemically stable to ozone as a solid electrolyte, wherein the membrane conductively connects the anode and the cathode while forming flow channels for water that are separated from one another as anode and cathode chambers.

2. The electrochemical ozonizer according to claim 1, wherein the membrane extends in the shape of a sawtooth, trapezium, rectangle or sine between the anode and the cathode.

3. The electrochemical ozonizer according to claim 2, wherein the shape of the extension of the membrane is created by a carrier, a grid or a unidirectional fabric (8), in the case of which warp threads and weft threads differ from one another in their thickness to a very great extent, and applied to the membrane.

4. The electrochemical ozonizer according to claim 2, wherein the membrane is shaped to be self-supporting.

5. The electrochemical ozonizer according to claim 1, wherein the ozonizer has a multilayered structure with a plurality of cells which are stacked side by side.

6. The electrochemical ozonizer according to claim 1, wherein the cell is configured as a winding module with an outer tube and an inner tube.

7. The electrochemical ozonizer according to claim 6, wherein the winding module comprises at least one hydrogen collection pocket.