Process for recovering gold, silver, and platinum metals from components of a fuel cell stack or an electrolyzer

Description

[0001] The present invention relates to a method for extracting gold and / or silver and / or at least one platinum metal from components of a fuel cell stack of a fuel cell or an electrolyzer. Furthermore, the present invention relates to a device for extracting gold and / or silver and / or at least one platinum metal from components of a fuel cell stack of a fuel cell or an electrolyzer, which device is suitable for carrying out the method. State of the art

[0002] Fuel cell stacks and electrolyzers require gold, silver, and platinum metals such as platinum, palladium, ruthenium, and iridium as essential raw materials. Their recovery from the fuel cell stacks or electrolyzers can be achieved using pyrometallurgical or hydrometallurgical processes. Pyrometallurgical recovery occurs by pyrolyzing the entire fuel cell. The resulting precious metal-rich ash can then be processed using various methods. However, this is highly energy-intensive and associated with the generation of toxic emissions.

[0003] In hydrometallurgical recovery, the fuel cell stacks are removed from the fuel cells. The recovered metals are then complexed into an aqueous solution. Hydrometallurgical processes are typically carried out at very high or very low pH values, i.e., using aggressive acids or alkalis. The complexing agents used are often toxic, so these processes also lead to hazardous emissions. For example, the use of aqua regia at high temperatures leads to dangerous nitrogen oxide emissions.

[0004] The article by N. Hodnik and C. Baldizzone, "Platinum recycling going green via induced surface potential alteration enabling fast and efficient dissolution," 2016, Nature Communications, Vol. 7, describes how platinum and palladium can be recovered from an industrial catalyst using chloride as a complexing agent at a pH of 1. The recovery of ruthenium and iridium using chloride as a complexing agent can occur in the pH range of 13 to 14. An oxidizing agent and a reducing agent are used alternately.

[0005] JP 2015 161019 A discloses a method for recovering precious metals from a membrane electrode assembly of a fuel battery. Disclosure of the invention

[0006] The method according to claim 1 and the device according to claim 8 serve to extract gold and / or silver and / or at least one platinum group metal from components of a fuel cell stack of a fuel cell or an electrolyzer to enable recycling of these materials. Platinum group metals (PGMs) are understood to mean the light platinum group metals ruthenium, rhodium, and palladium, and the heavy platinum group metals osmium, iridium, and platinum.

[0007] In one embodiment of the process, the oxidation step can be carried out by first treating the components with the gas and then bringing them into contact with the electrolyte solution. In another embodiment of the process, the at least one gaseous oxidizing agent is introduced into the electrolyte solution before it is brought into contact with the components. The gaseous oxidizing agent can, in particular, be ozone.

[0008] The oxidizing agent causes a transient dissolution of gold and / or silver and / or at least one platinum group metal from the constituents, whose metal cations are complexed in the electrolyte solution. Chloride anions, bromide anions, and / or iodide anions are preferably used as complexing agents, which are present in the electrolyte solution, particularly as alkali chlorides, alkali bromides, and / or alkali iodides. These form halide complexes with the metal cations.

[0009] The pH of the electrolyte solution preferably ranges from more than 0 to less than 14. Therefore, only dilute acids and alkalis are required, making the process safer than conventional methods. Suitable acids for adjusting a pH of less than 7 include, in particular, the strong acids hydrochloric acid (HCl), perchloric acid (HClO4), sulfuric acid (H2SO4), and nitric acid (HNO3). Suitable alkalis for adjusting a pH of more than 7 include, in particular, the strong alkalis sodium hydroxide (NaOH) and potassium hydroxide (KOH).

[0010] In the reduction step, the components in the fuel cell or electrolyzer are treated with a stream of an aqueous electrolyte solution and are treated with at least one gaseous oxidizing agent. In one embodiment of the process, this can be achieved by first treating the components with the gas and then bringing them into contact with the electrolyte solution. In another embodiment of the process, the at least one gaseous reducing agent is introduced into the electrolyte solution before the electrolyte solution is brought into contact with the components. The reducing agent is, in particular, hydrogen or a mixture of hydrogen and carbon monoxide. Although the presence of some reducing agents can lead to the precipitation of the complexed metals depending on their redox potential, they have positive effects that outweigh this disadvantage.Firstly, the surface of the starting materials is reduced and thus freed from surface oxides, for example, allowing the metals to readily dissolve into solution. Furthermore, a transient dissolution of metals can occur, particularly platinum, ruthenium, and iridium. This makes the newly created metal surface accessible for a subsequent reaction with the oxidizing agent. If a halogen is generated by a reaction between the oxidizing agent and halide ions in the electrolyte solution, this halogen can be reduced back to a halide by a reaction between the halogen and the reducing agent. The oxidation and reduction steps can alternate several times in the process.

[0011] To ensure that no oxidizing agent remains in the fuel cell when the reduction step begins, or that no reducing agent remains in the fuel cell when the oxidation step begins, it is preferred to provide a purging step between the oxidation step and the reduction step. In the purging step, the components are treated with at least one inert gas, such as nitrogen or a noble gas. The inert gas can either be passed directly over the components or it can be introduced into the flow of an aqueous electrolyte solution that is brought into contact with the components.

[0012] It is preferred that the same electrolyte solution be used in the oxidation step, the reduction step, and the rinsing step. In embodiments of the process in which gases are introduced into the electrolyte solution, only the gas introduced into the electrolyte solution—that is, the oxidizing agent, the reducing agent, and the inert gas—changes between the different steps. In embodiments of the process in which the components are treated alternately with gases and with the electrolyte solution, the gas is also changed, while the same electrolyte solution is always used. This enables simple process control.

[0013] In one embodiment of the process, the electrolyte solution is conveyed from at least one storage container to the components. The oxidizing agent, reducing agent, or inert gas can be added downstream of the storage container. After contact with the components, the electrolyte solution is collected in a collection container. If the electrolyte solution still contains oxidizing agents and reducing agents from the oxidation and reduction steps that have not reacted with the components, they will react with each other in the collection container at the latest. Once the extraction of the metals from the components is complete, the metals can be precipitated from the solution obtained in the collection container, for example, by reducing them with the addition of hydrogen as a reducing agent. The precipitated metals are then collected for further processing.

[0014] Another embodiment of the process involves a continuous process. The electrolyte solution is circulated, where it is repeatedly brought into contact with the components. Before the electrolyte solution is reintroduced into the fuel cell, it is mixed with the gas required for the respective reaction step—i.e., the oxidizing agent, reducing agent, or inert gas. After metal extraction, the electrolyte solution is drained from the circuit and can then be processed, like the contents of the collection container, in the discontinuous embodiment of the process.

[0015] While some metals form metal complexes that are soluble only in acidic solutions, others form metal complexes that are soluble only in alkaline solutions. For example, ruthenium forms soluble complexes at a pH above 7, while platinum forms soluble hexachloroplatinate(IV) complexes at a pH below 7. In order to recover all metals that are the target of this process from the components of the fuel cell stack or an electrolyzer, it is therefore preferable that the components are treated with an electrolyte solution with a pH above 7 in a first part of the process. In a second part of the process, they are then treated with an electrolyte solution with a pH below 7. The terms "first part" and "second part" should not be understood as a restriction regarding the order in which the parts of the process can be carried out.The second part can also be carried out first, with a pH value of less than 7, and then the first part can be carried out with a pH value of greater than 7.

[0016] The device for extracting gold and / or silver and / or at least one platinum group metal from components of a fuel cell stack, a fuel cell, or an electrolyzer comprises at least one reservoir for an electrolyte solution. If the device comprises multiple reservoirs, these reservoirs can be provided to feed the same electrolyte solution into a line system of the device at different locations, or they can contain electrolyte solutions with different pH values.

[0017] A first line is connected to an outlet opening of the at least one storage container. It has an anode inlet connection, which is connected to an anode inlet of a fuel cell or an electrolyzer. It also has a cathode inlet connection, which is connected to an anode inlet of a fuel cell or an electrolyzer. At least one oxidant inlet is configured to introduce at least one gaseous oxidant into the first line. At least one reducing agent inlet is configured to introduce at least one gaseous reducing agent and / or inert gas into the first line. The first line can be branched singly or multiply and can have valves to control the flow of an electrolyte solution from the storage container and / or a gas flow through the first line.For transporting the electrolyte solution, at least one first pump is also provided, which is arranged in the first line. The device can be connected to the anode inlet and the cathode inlet of a fuel cell via the anode inlet connection and the cathode inlet connection in order to introduce an electrolyte solution from the reservoir into the fuel cell.

[0018] The device is suitable for carrying out the method. In the oxidation step of the method, gaseous oxidizing agent can be introduced into the flow of electrolyte solution by means of the at least one oxidizing agent inlet. Alternatively, in the oxidation step, by suitably switching valves, first a gaseous oxidizing agent and then the electrolyte solution can be passed through the first line. In the reduction step, gaseous reducing agent can be introduced into the flow of electrolyte solution by means of the reducing agent inlet. Alternatively, in the reduction step, by suitably switching valves, first a gaseous reducing agent and then the electrolyte solution can be passed through the first line. In the purging step, the inert gas can be introduced into the flow of electrolyte solution through the reducing agent inlet. Alternatively, in the purging step, only the inert gas can be passed through the first line.If multiple reducing agent inlets are present, it can also be provided that one reducing agent inlet is used exclusively for the gaseous reducing agent, or another reducing agent inlet is used exclusively for the inert gas. The device makes it possible to extract gold and / or silver and / or at least one platinum group metal from the components of the fuel cell stack or an electrolyzer without having to disassemble the fuel cell. Instead, the chemicals required for extraction are introduced into the fuel cell using the connections already present in the fuel cell.

[0019] To drain the electrolyte solution from the fuel cell, different embodiments of the device each provide a second line, which has an anode outlet connection connected to an anode outlet of the fuel cell or electrolyzer. Furthermore, it has a cathode outlet connection connected to a cathode outlet of the fuel cell or electrolyzer. Like the first line, the second line can also be branched singly or multiple times and have valves to control the flow of the electrolyte solution.

[0020] In one embodiment of the device, it further comprises a collecting container for the electrolyte solution, which is connected to the second line. This embodiment of the device enables a discontinuous process.

[0021] In a further embodiment of the device, the second line is connected to the first line upstream of the oxidant inlet and the reducing agent inlet. This embodiment of the device enables a continuous process in which the electrolyte solution is first fed from the storage container into the first line and then circulated via the first line and the second line.

[0022] In yet another embodiment of the device, the second line is connected to an inlet opening of the storage container. This embodiment of the device also allows for continuous operation. However, the electrolyte solution leaving the fuel cell is not fed directly into the first line, but instead flows into the storage container and mixes with the electrolyte solution stored there.

[0023] If ozone is used as an oxidizing agent, it must be generated in the device due to its short lifespan. One embodiment of the device is provided with an electrochemical ozonizer with an ozone outlet and a hydrogen outlet. The ozone outlet acts as the oxidizing agent inlet, and the hydrogen outlet acts as the reducing agent inlet. In this way, hydrogen, which can act as a reducing agent in the process, can also be produced in the device. Short description of the drawings

[0024] Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Fig. 1 shows schematically an apparatus for extracting gold and / or silver and / or at least one platinum metal according to an embodiment of the invention. Fig. 2 shows schematically an apparatus for extracting gold and / or silver and / or at least one platinum metal according to another embodiment of the invention. Fig. 3 shows schematically an apparatus for extracting gold and / or silver and / or at least one platinum metal according to yet another embodiment of the invention. Fig. 4 shows schematically an apparatus for extracting gold and / or silver and / or at least one platinum metal according to yet another embodiment of the invention. Fig. 5 shows schematically an apparatus for extracting gold and / or silver and / or at least one platinum metal according to yet another embodiment of the invention. Fig. 6 shows schematically an apparatus for extracting gold and / or silver and / or at least one platinum metal according to yet another embodiment of the invention. Embodiments of the invention

[0025] In Fig. 1 1 shows a fuel cell 10 connected to a device according to a first exemplary embodiment of the invention. The fuel cell 10 contains a fuel cell stack 11. This contains ruthenium and platinum as catalyst materials on carbon as a support material. An aqueous electrolyte solution containing 0.1 M NaOH and 3 M NaCl is stored in a storage container 20. This electrolyte solution has a pH of 13. The storage container 20 is connected to a first line 30 via an outlet opening 21. The first line 30 branches off to an anode inlet connection 31 and a cathode inlet connection 32 on the fuel cell 10. Upstream of the branch, an oxidant inlet 33 and a reducing agent inlet 34 are arranged on the first line 30, each designed as a Venturi nozzle.Downstream of the oxidant inlet 33 and the reducing agent inlet 34, a pump 35 is arranged in the first line 30 before the branching to pump the electrolyte solution through the first line 30. A second line 40 is connected to the fuel cell 10 via an anode outlet connection 41 and a cathode outlet connection 42. Two sections of this second line 40, which originate from the fuel cell 10, combine to form a common line in which a second pump 43 is arranged. This second pump 43 pumps the electrolyte solution fed into the fuel cell 10 by the first pump 35 out of the fuel cell 10 and directs it into a collecting container 50. The oxidant inlet 33 is connected to an ozonizer 61, which generates a mixture of oxygen and ozone using the corona effect.The reducing agent inlet 34 is connected to a gas line 62, through which hydrogen, carbon monoxide, nitrogen, or mixtures of these gases can be introduced. The collection tank 50 is connected via additional lines to an ozone decomposer 63 for decomposing ozone entering and exiting the storage tank 50.

[0026] In one embodiment of the method according to the invention, in a first oxidation step, electrolyte solution is fed into the fuel cell 10, which is mixed with ozone via the oxidant inlet 33. This results in a superficial oxidation of platinum and ruthenium in the fuel cell stack 11. Since platinum chlorocomplexes are not stable in aqueous solution above a pH value of 7, no platinum dissolves. However, a transient dissolution of ruthenium does occur. After a compact oxide layer has formed on the surface of the metals, the dissolution stops. The introduction of the electrolyte solution is then continued in a rinsing step, but instead of mixing with ozone, it is mixed with nitrogen via the reducing agent inlet 34.After the unreacted ozone has been flushed out of the fuel cell 10 using this inert gas, hydrogen is added to the electrolyte solution stream through the reducing agent inlet 34 in a reduction step. This reduces the oxide layer in the fuel cell stack 11, dissolving further ruthenium. Once all oxides have been reduced, another flushing step is performed in which nitrogen is fed into the electrolyte solution stream to remove unreacted hydrogen from the fuel cell 10. The reaction steps are then repeated, beginning with the oxidation step, until all of the ruthenium has been dissolved. A measuring unit (not shown) is arranged in the second line 40 or in the collecting container 50. This measuring unit can be used to monitor the concentration of ruthenium complexes in the electrolyte solution stream in order to control the transition between the individual reaction steps.After all the ruthenium has dissolved, the ruthenium solution collected in the collection container 50 is removed from it.

[0027] The electrolyte solution in the reservoir 20 is now replaced with an aqueous solution of 0.3 M HCl and 3 M NaCl. This has a pH of approximately 0.5. Using this electrolyte solution, the sequence of oxidation step, rinsing step, reduction step, and further rinsing step already carried out with the first electrolyte solution is now repeated. However, in the reduction step, the electrolyte solution is not mixed with pure hydrogen, but with a mixture of 90 wt.% hydrogen and 10 wt.% carbon monoxide. At this pH, the platinum now forms stable H 2 PtCl 6 and can thus be transiently dissolved by oxidation of the platinum surface and subsequent reduction of the oxides. The carbon monoxide added in the reduction step adsorbs on the platinum surface and thus prevents precipitation of platinum in the reduction step. The dissolution process of the platinum is also monitored using the measuring unit (not shown).Once all the platinum has been dissolved, the platinum solution is removed from the collection container 50. The two metal solutions can now be processed by precipitating the respective metals by introducing hydrogen.

[0028] A second embodiment of the device is shown in Fig. 2 shown. In this exemplary embodiment, the oxidizing agent inlet 33 and the reducing agent inlet 34 are not arranged between the storage tank 20 and the first pump 35. Instead, at the branching point of the first line 30, a further sub-line branches off, into the end of which both the oxidizing agent inlet 33 and the reducing agent inlet 34 open. In this exemplary embodiment of the device, these are not designed as Venturi nozzles, but as valves. The sub-line of the first line 30 between the branching point and the oxidizing agent inlet 33 or the reducing agent inlet 34 does not serve to transport the electrolyte solution, but exclusively to transport the gas. Furthermore, in this exemplary embodiment, it is provided that the ozone decomposer 63 is not arranged downstream of the collecting tank 50.Instead, the second line 40 branches multiple times upstream of the second pump 43 and leads to the ozone decomposer 63 and an outlet line 64. When using this device, the electrolyte solution is not mixed with the gas required for the oxidation step, reduction step, or purging step before being introduced into the fuel cell 10. Instead, ozone is first introduced into the fuel cell 10 during the oxidation step without the electrolyte solution being introduced, with unconverted ozone entering the ozone decomposer 63. Valves prevent gaseous ozone from reaching the outlet line 64 or the pump 43. The aqueous electrolyte solution is then passed through the fuel cell 10 to absorb metal ions. This is passed by means of valves through the second pump 43 into the collection container 50. This is followed by a purging step in which nitrogen is passed through the fuel cell 10 and leaves the device through the outlet line 64.In the reduction step, hydrogen (to reduce ruthenium oxides) or the hydrogen / carbon monoxide mixture (to reduce platinum oxides) is passed through the fuel cell 10, which also leaves the device through the outlet line 64. Then, additional electrolyte solution is introduced into the fuel cell 10 to complex metal ions and convey them into the collection container 50. The second rinsing step is again carried out without using the electrolyte solution, only by introducing nitrogen, after which an oxidation step begins again. The switching between the different electrolyte solutions and the processing of the metal solutions takes place in the same way as when using the device according to the first embodiment of the invention.

[0029] A third embodiment of the device, which is shown in Fig. 3 , provides that ozone and hydrogen are produced by means of an electrochemical ozonizer 70. This is supplied with distilled water from a water tank 71, which is fed into the electrochemical ozonizer 70 by means of a third pump 72. In the oxidation step, ozone is fed from the ozone outlet of the electrochemical ozonizer 70, which functions as the oxidant inlet 33, through the first line 30 into the fuel cell 10. Subsequently, electrolyte solution is fed through the fuel cell 10 from the first storage container 20a and the associated first pump 35a. During the production of ozone, a mixture of hydrogen and water vapor is produced simultaneously. This mixture is fed through the hydrogen outlet of the electrochemical ozonizer 70, which functions as the reducing agent inlet 34a, into a tank 36 and collected there.In the reduction step, the hydrogen / water mixture is first fed from tank 36 into the fuel cell 10, and then electrolyte solution is fed from a second reservoir 20b into the fuel cell 10 by means of the associated first pump 35b. Another first pump 35c is arranged in the first line 30 so that it can convey the water / hydrogen mixture. Downstream of this first pump 35c, a further reducing agent inlet 34b, designed as a Venturi nozzle, is also arranged. By means of this reducing agent inlet 34b, carbon monoxide can be introduced into the water / hydrogen mixture in the reduction step, or nitrogen can be introduced into the flow of electrolyte solution from the second reservoir 20b in the purging step.When using this device, the rinsing step is performed only after the reduction step and before the next oxidation step, but not after the oxidation step and before the subsequent reduction step. Regarding the use of different electrolyte solutions and the processing of the metal solutions, the procedure is as in the previous embodiments.

[0030] Fig. 4 shows a fourth embodiment of the device. This enables continuous operation of the electrochemical ozonizer 70. The hydrogen / water mixture, which is additionally mixed with carbon monoxide during the reduction of platinum oxides, is fed into the fuel cell 10 either through the anode inlet port 31 or through the cathode inlet port 32 by appropriately switching valves in the first line 30. Ozone is simultaneously introduced into the fuel cell 10 through the other of the two ports 31, 32. Both the ozone and the reducing gases are mixed with electrolyte solution from two storage containers 20a, 20b before they enter the fuel cell 10. By switching the valves, the oxidation step and the reduction step can be carried out alternately at the cathode and the anode.The solutions from the oxidation at one electrode and the reduction at the other electrode combine in the second line 40. The rinsing steps are performed simultaneously on both electrodes, with the valves in the first line 30 being switched so that an electrolyte solution from the second reservoir 20b is mixed with nitrogen from the further reducing agent inlet 34b and then fed to the anode inlet port 31 and simultaneously to the cathode inlet port 32. During the rinsing steps, the electrochemical ozonizer 70 is switched off.

[0031] A device according to a fifth embodiment of the invention is shown in Fig. 5 shown. This is intended to circulate the electrolyte solution multiple times. For this purpose, it is fed from a storage tank 20 into the first line 30 and passed through the fuel cell 10. It is then returned through the second line 40 to the first line 30 at a branching point of the first line 30 and the second line 40. Downstream of this branching point, depending on the process step, it can be mixed with ozone, nitrogen, hydrogen, or a hydrogen / carbon monoxide mixture through the oxidizing agent inlet 33 or the reducing agent inlet 34. Once it has absorbed the entire amount of dissolved metal, the electrolyte solution can be pumped back into the storage tank 20 by suitably switching valves and removed therefrom. A new electrolyte solution with a different pH value is then added.

[0032] According to a sixth embodiment of the invention, a further device is provided which in Fig. 6is shown. This also enables the electrolyte solution to be continuously circulated. The storage container 20 is, however, arranged such that its outlet opening 21 is connected to the first line and its inlet opening 22 is connected to the second line, thus forming part of the circuit. The measuring unit 23 for determining the metal content of the electrolyte solution, not shown in the other exemplary embodiments, is arranged in the storage container 20 in this exemplary embodiment. As soon as the extraction of a metal is complete, a valve at the outlet opening 21 of the storage container 20 is closed and the entire electrolyte solution is pumped back into the storage container 20 and removed from it via a removal opening 24. The storage container 20 is then filled with a different electrolyte solution in the same way as in the fifth exemplary embodiment of the invention.

Claims

1. Process for recovering gold and / or silver and / or at least one platinum metal from constituents of a fuel cell stack (11) of a fuel cell (10) or of an electrolyzer, wherein the constituents are treated with a stream of an aqueous electrolyte solution and with at least one gaseous oxidant in at least one oxidation step in the fuel cell (10) or the electrolyzer and the constituents are treated with a stream of an aqueous electrolyte solution and with at least one gaseous reducing agent in at least one reduction step in the fuel cell (10) or the electrolyzer.

2. Process according to Claim 1, characterized in that the constituents are treated with at least one inert gas in a flushing step between the oxidation step and the reduction step.

3. Process according to Claim 2, characterized in that the same electrolyte solution is used in the oxidation step, in the reduction step and in the flushing step.

4. Process according to any of Claims 1 to 3, characterized in that the electrolyte solution is conveyed from at least one stock vessel (20, 20a-b) to the constituents and after contact with the constituents is collected in a collection vessel (50).

5. Process according to any of Claims 1 to 3, characterized in that the electrolyte solution is conveyed in a circuit in which it is brought into contact with the constituents a number of times.

6. Process according to any of Claims 1 to 5, characterized in that the electrolyte solution contains at least one alkali metal chloride, alkali metal bromide and / or alkali metal iodide.

7. Process according to any of Claims 1 to 6, characterized in that the constituents are treated with an electrolyte solution having a pH of greater than 7 in a first part of the process and are treated with an electrolyte solution having a pH of less than 7 in a second part of the process.

8. Apparatus for recovering gold and / or silver and / or at least one platinum metal from constituents of a fuel cell stack (11) of a fuel cell (10) or of an electrolyzer, comprising - at least one stock vessel (20, 20a-b) for an electrolyte solution, - a first conduit (30) which is connected to an outlet opening (21) of the at least one stock vessel (20, 20a-b) and has an anode inlet connection (31) connected to an anode inlet of a fuel cell (10) or of an electrolyzer and has a cathode inlet connection (32) connected to a cathode inlet of a fuel cell (10) or of an electrolyzer, - at least one oxidant feed conduit (33) which is configured for introducing at least one gaseous oxidant into the first conduit (30), - at least one reducing agent feed conduit (34, 34a-b) which is configured for introducing at least one gaseous reducing agent and / or inert gas into the first conduit (30) and - at least one first pump (35, 35a-c) which is arranged in the first conduit (30).

9. Apparatus according to Claim 8, further comprising - a second conduit (40) which has an anode outlet connection (41) and a cathode outlet connection (42) for the fuel cell (20), - a collection vessel (50) for the electrolyte solution which is connected to the second conduit (40) and - at least one second pump (43) which is arranged in the second conduit (40).

10. Apparatus according to Claim 8, further comprising - a second conduit (40) which has an anode outlet connection (41) connected to an anode outlet of the fuel cell (10) or of the electrolyzer and a cathode outlet connection (42) connected to a cathode outlet of the fuel cell (10) or of the electrolyzer and is connected to the first conduit (30) upstream of the oxidant feed conduit (33) and the reducing agent feed conduit (34).

11. Apparatus according to Claim 8, further comprising - a second conduit (40) which has an anode outlet connection (41) connected to an anode outlet of the fuel cell (10) or of the electrolyzer and has a cathode outlet connection (42) connected to a cathode outlet of the fuel cell (10) or of the electrolyzer and is connected to an inlet opening (22) of the stock vessel (20).

12. Apparatus according to any of Claims 8 to 11, further comprising - an electrochemical ozonizer (70) having an ozone outlet and a hydrogen outlet, where the ozone outlet functions as oxidant feed conduit (33) and the hydrogen outlet functions as reducing agent feed conduit (34).