DE102019104401A1 - Electrolyser and water splitting process - Google Patents

Abstract

An electrolyzer for splitting molecular water into molecular hydrogen and molecular oxygen using electrical energy, which electrolyzer comprises an anodic half cell with an anode and a cathodic half cell with a cathode, the anodic half cell and the cathodic half cell being separated from one another by a separator , wherein the anodic half cell comprises an anodic electrolyte which is in contact with the anode, and wherein the cathodic half cell comprises a cathodic electrolyte which is in contact with the cathode, wherein the anodic half cell comprises an anodic catalyst and wherein the cathodic half cell comprises one To improve cathodic catalyst, it is proposed that the cathodic half-cell for generating a mediator ion contains at least one cation that can be reduced by electron absorption and that the reducible cation and the mediator ion form a redox pair proposes an improved method for splitting water into molecular hydrogen and molecular oxygen using electrical energy.

Description

The present invention relates to an electrolyzer for splitting molecular water into molecular hydrogen and molecular oxygen using electrical energy, which electrolyzer comprises an anodic half cell with an anode and a cathodic half cell with a cathode, the anodic half cell and the cathodic half cell through a separator are separated from one another, the anodic half cell comprising an anodic electrolyte which is in contact with the anode, and the cathodic half cell comprising a cathodic electrolyte which is in contact with the cathode, the anodic half cell comprising an anodic catalyst, and wherein the cathodic half cell comprises a cathodic catalyst.

Furthermore, the present invention relates to a method for splitting molecular water into molecular hydrogen and molecular oxygen using electrical energy, in which method water molecules are dissociated into protons and hydroxide ions, in which method the hydroxide ions in an anodic half cell with an anode with the assistance of an anodic one Catalyst are oxidized and the protons are reduced in a cathodic half cell with a cathode with the participation of a cathodic catalyst, the anodic half cell and the cathodic half cell being separated from one another by a separator, the anodic half cell comprising an anodic electrolyte which is in contact with the anode Contact is made, and wherein the cathodic half cell comprises a cathodic electrolyte which is in contact with the cathode.

Hydrogen as the energy source of the future has the advantage over fossil energy sources that when it is burned as a reaction product, only water is produced and no carbon dioxide.

It is known to use electrolysers to obtain hydrogen. During electrolysis, water molecules are broken down into molecular hydrogen and molecular oxygen. In particular, electrical energy that is generated from renewable or regenerative energies as an energy source can be used here. The formation of carbon dioxide can thus be completely avoided.

Known electrolysers also have disadvantages. They are either inefficient, very expensive or have a complex structure. On the one hand, this is due to the fact that noble metal catalysts have to be used in acidic electrolytes to break down the water.

The electrolytes used are another problem. In currently known commercial systems, the electrolytes must either be alkaline or consist of high-purity water. Alkaline electrolytes with a high pH are achieved by adding potassium hydroxide in water. However, producing potassium hydroxide is an energy-intensive process. Potassium hydroxide is also highly corrosive. In addition, hydroxide ions are consumed in the electrolysis in an alkaline environment, so that alkaline electrolyte must be added continuously. Pure water prevents the poisoning of the catalysts, but has only a very low conductivity.

It is therefore an object of the present invention to improve an electrolyzer and a method of the type described in the introduction.

The object is achieved according to the invention in the case of an electrolyzer of the type described in the introduction in that the cathodic half-cell for generating a mediator ion contains at least one cation which can be reduced by electron absorption and that the reducible cation and the mediator ion form a redox couple.

In contrast to known electrolyzers, protons in the cathodic half cell are not reduced directly with the support of a catalyst on the cathode, but rather in the interaction of the mediator ion and the cathodic catalyst in the electrolyzer designed as proposed. In this process, the reducible cation is reduced by taking up at least one electron on the cathode to generate a mediator ion. When protons are converted with the support of the cathodic catalyst, the mediator ion releases the at least one electron that has been taken up and thus enables the reduction of protons in molecular hydrogen. The mediator ion is oxidized again and converted into the original reducible cation. By using reducible cations in the cathodic half cell, an electrochemical process is used, namely the conversion of the redox pair from the reducible cation into the mediator ion and vice versa. Furthermore, it is in particular possible to use a cathodic catalyst which is not in direct contact with the cathode but is, for example, suspended in the cathodic electrolyte. In this way, an effective surface area of the cathodic catalyst in the cathodic half cell can be enlarged. So heterogeneous chemical hydrogen development catalysts can be used, which support a chemical process for the development of hydrogen. In this way, chemical and electrochemical processes can be coupled to produce hydrogen. The stake of the mediator ion also makes it possible to reduce the cell voltage required for the electrolysis of water. Since the cell voltage is directly proportional to the energy required to split water, the use of energy can be significantly reduced, as a result of which the operating costs of the electrolyzer, namely in particular the costs for providing electrical energy for electrolysis, can be significantly reduced.

It is favorable if the reducible cation can be reduced by at least one oxidation state by electron uptake at the cathode. In particular, this enables the reducible cation on the cathode to accept one or more electrons to form the mediator ion. If the redox potential of the reducible cation is lower than the redox potential of the hydrogen evolution reaction, the cell voltage can be reduced overall.

The reducible cation is preferably dissolved in the cathodic electrolyte. In particular, this makes it possible to implement hydrogen reduction in the presence of the cathodic catalyst at any point in the cathodic half-cell. A limitation to the cathode as in conventional electrolysers can thus be effectively avoided.

It is advantageous if the reducible cation dissolved in the electrolyte is an ion from the group of transition metals. In particular, it can be a vanadium ion, a chromium ion or an iron ion. For example, a redox pair can be formed by V ²⁺ / V ³⁺ ions, where V ^{3+ forms} the reducible cation and V ²⁺ the mediator ion, which can be oxidized by releasing an electron.

It is advantageous if the reducible cation is introduced into the cathodic electrolyte by dissolving a salt. In particular, the salt can be transition metal salt, for example a vanadium salt. In particular, the vanadium salt can be vanadium oxysulfate (VOSO ₄ ), which is also referred to as vanadyl sulfate. It can be used anhydrous as a green solid or as a hydrate as a blue odorless solid. The provision of the reducible cation is thus possible in a simple manner, namely by simply dissolving a suitable salt in the cathodic electrolyte.

The separator is advantageously designed in the form of a bipolar membrane. The separator serves, in particular, the purpose of preventing the molecular hydrogen formed during the electrolysis from coming into direct contact with the molecular oxygen which is also formed and from forming a highly reactive oxyhydrogen mixture in an undesirable manner. Designing the separator in the form of a bipolar membrane also has the advantage that different environments can be set in the cathodic half cell and in the anodic half cell, for example an acidic environment in the cathodic half cell and an alkaline environment in the anodic half cell. This also makes it possible to use cathodic and anodic catalysts, which are particularly inexpensive. In particular, the use of precious metal catalysts such as platinum or iridium can be completely avoided. In this way, significantly cheaper electrolysers can be trained. In this way, investment costs in the manufacture of electrolysers in particular can be minimized.

It is advantageous if the bipolar membrane comprises an anion exchange membrane and a cation exchange membrane. In particular, the cation exchange membrane can be designed in the form of a proton exchange membrane. This design of the bipolar membrane enables the separation of anions and cations that arise during the dissociation of water in a simple manner. Protons can get through the proton exchange membrane into the cathodic half cell, hydroxide ions through the cation exchange membrane into the anodic half cell.

The anion exchange membrane and the cation exchange membrane are preferably separated from one another by a dissociation layer. In the dissociation layer, water molecules in particular can be split into hydroxide ions and protons. These can then pass through the anion exchange membrane and the cation exchange membrane into the anodic half cell or into the cathodic half cell.

In order to facilitate the splitting of water molecules into hydroxide ions and protons, it is advantageous if the dissociation layer contains a dissociation catalyst. In particular, this can support the splitting of water molecules into hydroxide ions and protons.

The splitting of water molecules into hydroxide ions and protons can be improved in particular if the dissociation catalyst is or contains iron oxide. In particular, the iron oxide can be iron (III) oxide (Fe ₂ O ₃ ).

It is favorable if the dissociation layer has a layer thickness in a range from approximately 5 nm to approximately 500 μm. In particular, the layer thickness can be in a range from approximately 50 nm to approximately 50 μm. In particular, unsupported dissociation layers can be formed in this way. For example, a particularly compact design of the electrolyzer can be realized.

It is advantageous if the cathodic electrolyte is water or an aqueous solution and / or if the anodic electrolyte is water or an aqueous solution. In particular, an inexpensive electrolyzer can be designed. In particular, a pH value can be set as desired in aqueous solutions.

The anodic electrolyte and / or the cathodic electrolyte preferably have a pH of 7 or essentially 7. In particular, they can have a neutral pH. In particular, the risk of corrosion on components of the electrolyzer can be minimized.

It is favorable if a pH value of the anodic electrolyte and a pH value of the cathodic electrolyte differ and define a pH gradient. This makes it possible, in particular, to implement different environments in the cathodic half cell and in the anodic half cell, for example an acidic environment in the cathodic half cell and an alkaline environment in the anodic half cell. In particular, an acidic environment in the cathodic half cell and a neutral pH value in the anodic half cell or an alkaline pH value in the anodic half cell and a neutral pH value in the cathodic half cell are also possible. Because of the different pH values of the anodic electrolyte and the cathodic electrolyte, inexpensive catalysts can be used in particular both in the cathodic half cell and in the anodic half cell. Precious metal catalysts can thus be dispensed with.

It is advantageous if the pH gradient is at least 1. In particular, it can be at least 3. Furthermore, it can be at least 5 in particular. The pH gradient is preferably set so that the desired catalysts can be used both in the anodic and in the cathodic half cell.

It is advantageous if the anodic electrolyte is alkaline. In this way, in particular, an inexpensive anodic catalyst can be used for the oxygen evolution reaction.

It is advantageous if the cathodic electrolyte is acidic. In particular, this makes it possible to use an inexpensive cathodic catalyst in the cathodic half cell.

The electrolyzer can be formed in a simple manner if the anode consists of the anodic catalyst or is formed from the anodic catalyst or contains the anodic catalyst or is coated with the anodic catalyst or is in electrically conductive contact with the anodic catalyst. These designs enable an efficient oxygen evolution reaction in the anodic half cell.

The anode can be formed in a simple manner if it is solid or reticulated.

It is advantageous if the anodic catalyst is nickel, iridium or cobalt or contains nickel, iridium and / or cobalt. In particular, the anodic catalyst can be or contain NiO _x , NiCeO _x , NiCoO _x , NiCuO _x , NiFeO _x , NiLaO _x , IrO _x , CoFeO _x or CoO _x .

In order to increase the effective surface area of the cathodic catalyst, it is advantageous if the cathodic catalyst is suspended in the cathodic electrolyte. In this way, the reduction of protons by electron uptake from the mediator ion can take place anywhere in the cathodic half cell. The hydrogen evolution reaction is therefore not limited to the area around the cathode, as is the case with conventional electrolysis, but is possible in the entire cathodic half cell.

In order to achieve the largest possible active surface area of the cathodic catalyst, it is advantageous if a particle size of the suspended cathodic catalyst is less than 50 μm, in particular it is advantageous if it is less than 5 μm.

The cathodic catalyst is preferably or contains Mo ₂ C, Mo ₂ S or NiP. The cathodic catalysts mentioned support the hydrogen evolution reaction in cooperation with a mediator ion in an excellent way. They are also available at low cost. Furthermore, they can be easily suspended in the cathodic electrolyte.

The object stated at the outset is also achieved according to the invention in a method of the type described in the introduction in that a mediator ion is formed in the cathodic half cell from a reducible cation by electron absorption on the cathode, that the reducible cation and the mediator ion are a redox Form a pair and that protons are reduced to molecular hydrogen by electron uptake of mediator ions with the help of the cathodic catalyst.

As already described above, such an electrochemical process, namely the conversion of the reducible cation into the mediator Ion by electron uptake can be combined with a chemical process, namely hydrogen evolution in the presence of the cathodic catalyst by electron uptake from the mediator ion. In particular, a cell voltage of the electrolyzer can be significantly reduced compared to conventional electrolyzers with precious metal catalysts both in the anodic half cell and in the cathodic half cell. On the one hand, this allows operating costs to be reduced, since a lower cell voltage is directly linked to a lower electrical power consumption by the electrolyzer, and also investment costs, since, in particular, inexpensive catalysts can be used both in the anodic half-cell and in the cathodic half-cell.

The reducible cation is preferably reduced by at least one oxidation state by electron uptake at the cathode. The reducible cation can thus take up at least one, in particular also two or more, electrons from the cathode and, with the cooperation of the cathodic catalyst, release them to protons to form molecular hydrogen. The reducible cation thus serves as an electron carrier, so that the hydrogen evolution reaction can take place not only at the cathode, as is the case with conventional electrolysers, but everywhere in the cathodic half-cell, for example if the cathodic catalyst is suspended in the electrolyte.

The method can be carried out in a simple manner if the reducible cation is dissolved in the cathodic electrolyte. For example, it can be introduced into the cathodic electrolyte in a simple manner by dissolving a salt.

It is advantageous if an ion from the group of transition metals, in particular a vanadium ion, a chromium ion or an iron ion, is used as the dissolved reducible cation in the electrolyte. In particular, redox pairs can be formed in a simple manner, namely, for example, V ²⁺ / V ³⁺ , Cr ²⁺ / Cr ³⁺ or Fe ²⁺ / Fe ³⁺ .

It is advantageous if the reducible cation is introduced into the cathodic electrolyte by dissolving a salt. In particular, it can be a transition metal salt. For example, it can be a vanadium salt or a chromium salt or an iron salt. In particular, a concentration of the reducible cation in the cathodic half cell can be set in a simple manner.

The separator is preferably designed in the form of a bipolar membrane. A bipolar membrane makes it possible in particular to realize different environments with different pH values in the cathodic half cell and in the anodic half cell. In particular, this enables the milieus to be optimized both for the hydrogen evolution reaction and for the oxygen evolution reaction in the cathodic half cell or in the anodic half cell. In particular, inexpensive catalysts can be used in this way. It is therefore no longer necessary to use catalysts which are required in conventional electrolysers in which the same environment prevails in both half cells.

It is advantageous if the bipolar membrane is formed with an anion exchange membrane and a cation exchange membrane. In particular, the cation exchange membrane can be designed in the form of a proton exchange membrane. Such a bipolar membrane makes it possible in a simple manner to separate water molecules dissociated in protons and hydroxide ions on the one hand into the cathodic half cell and on the other hand into the anodic half cell.

It is advantageous if the anion exchange membrane and the cation exchange membrane are separated from one another by a dissociation layer. In particular, the dissociation layer can be designed to dissociate water molecules in hydroxide ions and protons. This makes it possible, in particular, to use neutral electrolytes, for example water, both in the cathodic half cell and in the anodic half cell. The protons migrating through the cation exchange membrane automatically create a slightly acidic environment in the cathodic half cell. The hydroxide ions migrating through the anion exchange membrane create a slightly alkaline environment in the anodic half cell.

In order to facilitate the splitting of water into hydroxide ions and protons, it is advantageous if a dissociation catalyst is introduced into the dissociation layer. In particular, the dissociation layer can be formed by the dissociation catalyst.

A dissociation catalyst which is or contains iron oxide is preferably used. In particular, the iron oxide can be iron (III) oxide (Fe ₂ O ₃ ). In the presence of iron oxide, water splits particularly easily into protons and hydroxide ions.

It is advantageous if the dissociation layer is formed with a layer thickness in a range from approximately 5 nm to approximately 500 μm. In particular, the layer thickness can be provided in a range from approximately 50 nm to approximately 50 μm. In particular, it can be worn Form dissociation layers, i.e. dissociation layers that are not self-supporting. In addition, the amount of dissociation catalyst used can be minimized. This also enables a compact design of an electrolyser.

An electrolyzer can be designed to be easy to handle and inexpensive if water or an aqueous solution is used as the cathodic electrolyte and / or if water or an aqueous solution is used as the anodic electrolyte. In particular, pH values of aqueous solutions can be easily adjusted to a desired value.

An anodic electrolyte and / or a cathodic electrolyte with a pH of 7 or essentially 7 are preferably used. For example, water can be used as the anodic electrolyte and / or as the cathodic electrolyte.

In order to optimize the hydrogen evolution reaction in the cathodic half cell and the oxygen evolution reaction in the anodic half cell, it is expedient if an anodic electrolyte and a cathodic electrolyte are used with differing pH values and define a pH gradient. In particular, this makes it possible to use cathodic and anodic catalysts which optimally support the hydrogen evolution reaction or the oxygen evolution reaction. In addition, catalysts can be used that are not precious metals. In particular, investment costs for the training of electrolyzers can be minimized.

It is advantageous if anodic and cathodic electrolytes are used, so that the pH gradient is at least 1. In particular, it can be at least 3. More particularly, the pH gradient can be at least 5. The pH gradient is preferably selected or set so that the hydrogen evolution reaction and the oxygen evolution reaction proceed optimally.

An alkaline anodic electrolyte is advantageously used. In this way, the oxygen evolution reaction in the anodic half cell in particular can be optimized.

An acidic cathodic electrolyte is advantageously used. In particular, this makes it possible to optimize the hydrogen evolution reaction in the cathodic half cell.

According to a preferred embodiment of the invention it can be provided that an anode is formed such that it consists of the anodic catalyst or is formed from the anodic catalyst or contains the anodic catalyst or is coated with the anodic catalyst or electrically conductive with the anodic catalyst is in contact. Forming the anode in this way can in particular ensure that the oxygen evolution reaction can proceed in the desired manner in the anodic half cell.

It is expedient if the anode is made solid or reticulated. In particular, this makes it possible to form the anode in a simple manner.

A particularly efficient oxygen evolution reaction can be achieved if an anodic catalyst is used which is nickel, iridium or cobalt or contains nickel, iridium and / or cobalt. In particular, the anodic catalyst can be or contain NiO _x , NiCeO _x , NiCoO _x , NiCuO _x , NiFeO _x , NiLaO _x , IrO _x , CoFeO _x or CoO _x .

The cathodic catalyst is advantageously suspended in the cathodic electrolyte. In this way, the cathodic catalyst is available not only at the cathode but in the entire cathodic half cell. The hydrogen evolution reaction can thus take place anywhere in the cathodic half cell where the cathodic catalyst, at least one mediator ion and at least two protons meet. This enables a particularly efficient hydrogen development in the cathodic half cell.

In order to obtain a particularly large reactive surface, it is expedient if the suspended cathodic catalyst is used with a particle size which is smaller than 50 μm. In particular, the particle size can be less than 5 μm. In this way, a surface area of the cathodic catalyst can be significantly increased in comparison to conventional electrolysers in which the surface of the cathode is coated with the cathodic catalyst.

Furthermore, the use of one of the electrolysers described above for carrying out one of the methods described above is proposed. In particular, hydrogen can be produced easily and inexpensively with high efficiency.

• 1. Elektrolyseur (110) zum Aufspalten von molekularem Wasser (112) in molekularen Wasserstoff (114) und molekularen Sauerstoff (116) unter Einsatz elektrischer Energie, welcher Elektrolyseur (110) eine anodische Halbzelle (122) mit einer Anode (140) und eine kathodische Halbzelle (124) mit einer Kathode (134) umfasst, wobei die anodische Halbzelle (122) und die kathodische Halbzelle (124) durch einen Separator (126) voneinander getrennt sind, wobei die anodische Halbzelle (122) einen anodischen Elektrolyt (128) umfasst, welcher mit der Anode (140) in Kontakt steht, und wobei die kathodische Halbzelle (124) einen kathodischen Elektrolyt (129) umfasst, welcher mit der Kathode (134) in Kontakt steht, wobei die anodische Halbzelle (122) einen anodischen Katalysator (146) umfasst und wobei die kathodische Halbzelle (124) einen kathodischen Katalysator (144) umfasst, dadurch gekennzeichnet, dass die kathodische Halbzelle (124) zur Erzeugung eines Mediator-Ions (164) mindestens ein durch Elektronenaufnahme reduzierbares Kation (160) enthält und dass das reduzierbare Kation (160) und das Mediator-Ion (164) ein Redox-Paar bilden.
• 2. Elektrolyseur nach Satz 1, dadurch gekennzeichnet, dass das reduzierbare Kation (160) durch Elektronenaufnahme an der Kathode (134) um mindestens eine Oxidationsstufe reduzierbar ist.
• 3. Elektrolyseur nach Satz 1 oder 2, dadurch gekennzeichnet, dass das reduzierbare Kation (160) im kathodischen Elektrolyt (129) gelöst ist.
• 4. Elektrolyseur nach Satz 3, dadurch gekennzeichnet, dass das im kathodischen Elektrolyt (129) gelöste reduzierbare Kation (160) ein Ion aus der Gruppe der Übergangsmetalle ist, insbesondere ein Vanadium-Ion, ein Chrom-Ion oder ein Eisen-Ion.
• 5. Elektrolyseur nach Satz 3 oder 4, dadurch gekennzeichnet, dass das reduzierbare Kation (160) in den kathodischen Elektrolyt (129) durch Lösen eines Salzes, insbesondere eines Übergangsmetall-Salzes, weiter insbesondere eines Vanadium-Salzes, eingebracht ist.
• 6. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass der Separator (126) in Form einer Bipolarmembran (148) ausgebildet ist.
• 7. Elektrolyseur nach Satz 6, dadurch gekennzeichnet, dass die Bipolarmembran (148) eine Anionenaustauschmembran (150) und eine Kationenaustauschmembran (152), insbesondere in Form einer Protonenaustauschmembran (156), umfasst.
• 8. Elektrolyseur nach Satz 7, dadurch gekennzeichnet, dass die Anionenaustauschmembran (150) und die Kationenaustauschmembran (152) durch eine Dissoziationsschicht (154) voneinander getrennt sind.
• 9. Elektrolyseur nach Satz 8, dadurch gekennzeichnet, dass die Dissoziationsschicht (154) einen Dissoziationskatalysator, insbesondere zum Aufspalten von Wassermolekülen (112) in Hydroxidionen (158) und Protonen (130), enthält.
• 10. Elektrolyseur nach Satz 9, dadurch gekennzeichnet, dass der Dissoziationskatalysator Eisenoxid, insbesondere Eisen(III)-Oxid (Fe₂O₃), ist oder enthält.
• 11. Elektrolyseur nach einem der Sätze 8 bis 10, dadurch gekennzeichnet, dass die Dissoziationsschicht (154) eine Schichtdicke in einem Bereich von etwa 5 nm bis etwa 500 µm aufweist, insbesondere in einem Bereich von etwa 50 nm bis etwa 50 µm.
• 12. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass der kathodische Elektrolyt (129) Wasser oder eine wässrige Lösung ist und/oder dass der anodische Elektrolyt (128) Wasser oder eine wässrige Lösung ist.
• 13. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass der anodische Elektrolyt (128) und/oder der kathodische Elektrolyt (129) einen pH-Wert von 7 oder im Wesentlichen 7 aufweisen.
• 14. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass sich ein pH-Wert des anodischen Elektrolyts (128) und ein pH-Wert des kathodischen Elektrolyts (129) unterscheiden und einen pH-Gradient definieren.
• 15. Elektrolyseur nach Satz 14, dadurch gekennzeichnet, dass der pH-Gradient mindestens 1, insbesondere mindestens 3, weiter insbesondere mindestens 5, beträgt.
• 16. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass der anodische Elektrolyt (128) alkalisch ist.
• 17. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass der kathodische Elektrolyt (129) sauer ist.
• 18. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass die Anode (140) aus dem anodischen Katalysator (146) besteht oder aus dem anodischen Katalysator (146) ausgebildet ist oder den anodischen Katalysator (146) enthält oder mit dem anodischen Katalysator (146) beschichtet ist oder mit dem anodischen Katalysator (146) elektrisch leitend in Kontakt steht.
• 19. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass die Anode (140) massiv oder netzförmig ausgebildet ist.
• 20. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass der anodische Katalysator (146) Nickel, Iridium oder Cobalt ist oder Nickel, Iridium und/oder Cobalt enthält, insbesondere in der Form NiO_x, NiCeO_x, NiCoO_x, NiCuO_x, NiFeO_x, NiLaO_x, IrO_x, CoFeO_x oder CoO_x.
• 21. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass der kathodische Katalysator (144) im kathodischen Elektrolyt (129) suspendiert ist.
• 22. Elektrolyseur nach Satz 21, dadurch gekennzeichnet, dass eine Partikelgröße des suspendierten kathodischen Katalysators (144) kleiner als 50 µm ist, insbesondere kleiner als 5 µm.
• 23. Elektrolyseur nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass der kathodische Katalysator (144) Mo₂C, Mo₂S oder NiP ist oder enthält.
• 24. Verfahren zum Aufspalten von molekularem Wasser (112) in molekularen Wasserstoff (114) und molekularen Sauerstoff (116) unter Einsatz elektrischer Energie, bei welchem Verfahren Wassermoleküle (112) in Protonen (130) und Hydroxidionen (158) dissoziiert werden, bei welchem Verfahren die Hydroxidionen (158) in einer anodischen Halbzelle (122) mit einer Anode (140) unter Mitwirkung eines anodischen Katalysators (146) oxidiert werden und die Protonen (130) in einer kathodischen Halbzelle (124) mit einer Kathode (134) unter Mitwirkung eines kathodischen Katalysators (144) reduziert werden, wobei die anodische Halbzelle (122) und die kathodische Halbzelle (124) durch einen Separator (126) voneinander getrennt sind, wobei die anodische Halbzelle (122) einen anodischen Elektrolyt (128) umfasst, welcher mit der Anode (140) in Kontakt steht, und wobei die kathodische Halbzelle (124) einen kathodischen Elektrolyt (129) umfasst, welcher mit der Kathode (134) in Kontakt steht, dadurch gekennzeichnet, dass in der kathodischen Halbzelle (124) ein Mediator-Ion (164) aus einem reduzierbaren Kation (160) durch Elektronenaufnahme an der Kathode (134) gebildet wird, dass das reduzierbare Kation (160) und das Mediator-Ion (164) ein Redox-Paar bilden und dass Protonen (130) durch Elektronenaufnahme von Mediator-Ionen (164) unter Mitwirkung des kathodischen Katalysators (144) zu molekularem Wasserstoff (114) reduziert werden.
• 25. Verfahren nach Satz 24, dadurch gekennzeichnet, dass das reduzierbare Kation (160) durch Elektronenaufnahme an der Kathode (134) um mindestens eine Oxidationsstufe reduziert wird.
• 26. Verfahren nach Satz 24 oder 25, dadurch gekennzeichnet, dass das reduzierbare Kation (160) im kathodischen Elektrolyt (129) gelöst wird.
• 27. Verfahren nach Satz 26, dadurch gekennzeichnet, dass im kathodischen Elektrolyt (129) als gelöstes reduzierbares Kation (160) ein Ion aus der Gruppe der Übergangsmetalle, insbesondere ein Vanadium-Ion, ein Chrom-Ion oder ein Eisen-Ion, eingesetzt wird.
• 28. Verfahren nach Satz 26 oder 27, dadurch gekennzeichnet, dass das reduzierbare Kation (160) in den kathodischen Elektrolyt (129) durch Lösen eines Salzes, insbesondere eines Übergangsmetall-Salzes, weiter insbesondere eines Vanadium-Salzes, eingebracht wird.
• 29. Verfahren nach einem der Sätze 24 bis 28, dadurch gekennzeichnet, dass der Separator (126) in Form einer Bipolarmembran (148) ausgebildet wird.
• 30. Verfahren nach Satz 29, dadurch gekennzeichnet, dass die Bipolarmembran eine Anionenaustauschmembran und eine Kationenaustauschmembran umfasst.
• 31. Verfahren nach Satz 30, dadurch gekennzeichnet, dass die Anionenaustauschmembran (150) und die Kationenaustauschmembran (152) durch eine Dissoziationsschicht (154) voneinander getrennt werden.
• 32. Verfahren nach Satz 31, dadurch gekennzeichnet, dass in die Dissoziationsschicht (154) ein Dissoziationskatalysator, insbesondere zum Aufspalten von Wassermolekülen (112) in Hydroxidionen (158) und Protonen (130), eingebracht wird.
• 33. Verfahren nach Satz 32, dadurch gekennzeichnet, dass ein Dissoziationskatalysator eingesetzt wird, welcher Eisenoxid, insbesondere Eisen(III)-Oxid (Fe₂O₃), ist oder enthält.
• 34. Verfahren nach einem der Sätze 31 bis 33, dadurch gekennzeichnet, dass die Dissoziationsschicht (154) mit einer Schichtdicke in einem Bereich von etwa 5 nm bis etwa 500 µm ausgebildet wird, insbesondere mit einer Schichtdicke in einem Bereich von etwa 50 nm bis etwa 50 µm.
• 35. Verfahren nach einem der Sätze 24 bis 34, dadurch gekennzeichnet, dass als kathodischer Elektrolyt (129) Wasser oder eine wässrige Lösung eingesetzt wird und/oder dass als anodischer Elektrolyt (128) Wasser oder eine wässrige Lösung eingesetzt wird.
• 36. Verfahren nach einem der Sätze 24 bis 35, dadurch gekennzeichnet, dass ein anodischer Elektrolyt (128) und/oder ein kathodischer Elektrolyt (129) mit einem pH-Wert von 7 oder im Wesentlichen 7 eingesetzt werden.
• 37. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass ein anodischer Elektrolyt (128) und ein kathodischer Elektrolyt (129) mit sich unterscheidenden pH-Werten eingesetzt werden und einen pH-Gradient definieren.
• 38. Verfahren nach Satz 37, dadurch gekennzeichnet, dass anodische und kathodische Elektrolyten (129) eingesetzt werden, so dass der pH-Gradient mindestens 1, insbesondere mindestens 3, weiter insbesondere mindestens 5, beträgt.
• 39. Verfahren nach einem der Sätze 24 bis 38, dadurch gekennzeichnet, dass ein alkalischer anodischer Elektrolyt (128) eingesetzt wird.
• 40. Verfahren nach einem der Sätze 24 bis 39, dadurch gekennzeichnet, dass ein saurer kathodischer Elektrolyt (129) eingesetzt wird.
• 41. Verfahren nach einem der Sätze 24 bis 40, dadurch gekennzeichnet, dass eine Anode (140) ausgebildet wird derart, dass sie aus dem anodischen Katalysator (146) besteht oder aus dem anodischen Katalysator (146) ausgebildet ist oder den anodischen Katalysator (146) enthält oder mit dem anodischen Katalysator (146) beschichtet ist oder mit dem anodischen Katalysator (146) elektrisch leitend in Kontakt steht.
• 42. Verfahren nach einem der Sätze 24 bis 41, dadurch gekennzeichnet, dass die Anode (140) massiv oder netzförmig ausgebildet wird.
• 43. Verfahren nach einem der Sätze 24 bis 42, dadurch gekennzeichnet, dass ein anodischer Katalysator (146) eingesetzt wird, welcher Nickel, Iridium oder Cobalt ist oder Nickel, Iridium und/oder Cobalt enthält, insbesondere in der Form NiO_x, NiCeO_x, NiCoO_x, NiCuO_x, NiFeO_x, NiLaO_x, IrO_x, CoFeO_x oder CoO_x.
• 44. Verfahren nach einem der Sätze 24 bis 43, dadurch gekennzeichnet, dass der kathodische Katalysator (144) im kathodischen Elektrolyt (129) suspendiert wird.
• 45. Verfahren nach Satz 44, dadurch gekennzeichnet, dass der suspendierte kathodische Katalysator (144) mit einer Partikelgröße eingesetzt wird, welche kleiner als 50 µm ist, insbesondere kleiner als 5 µm.
• 46. Verfahren nach einem der Sätze 24 bis 45, dadurch gekennzeichnet, dass der kathodische Katalysator (144) Mo₂C, Mo₂S oder NiP ist oder enthält.
• 47. Verwendung eines Elektrolyseurs (110) nach einem der Sätze 1 bis 23 zur Durchführung eines Verfahrens nach einem der Sätze 24 bis 46.

The above description thus includes, in particular, the embodiments of electrolysers defined below in the form of numbered sentences and methods for splitting molecular water into molecular hydrogen and molecular oxygen:

• 1. electrolyser ( 110 ) to split molecular water ( 112 ) in molecular hydrogen ( 114 ) and molecular oxygen ( 116 ) using electrical energy, which electrolyzer ( 110 ) an anodic half cell ( 122 ) with an anode ( 140 ) and a cathodic half cell ( 124 ) with a cathode ( 134 ), the anodic half cell ( 122 ) and the cathodic half cell ( 124 ) by a separator ( 126 ) are separated from each other, the anodic half cell ( 122 ) an anodic electrolyte ( 128 ), which with the anode ( 140 ) is in contact, and the cathodic half cell ( 124 ) a cathodic electrolyte ( 129 ) which is connected to the cathode ( 134 ) is in contact, the anodic half cell ( 122 ) an anodic catalyst ( 146 ) and the cathodic half cell ( 124 ) a cathodic catalyst ( 144 ), characterized in that the cathodic half cell ( 124 ) to create a mediator ion ( 164 ) at least one cation that can be reduced by electron absorption ( 160 ) contains and that the reducible cation ( 160 ) and the mediator ion ( 164 ) form a redox pair.
• 2. Electrolyser according to sentence 1, characterized in that the reducible cation ( 160 ) by electron uptake on the cathode ( 134 ) can be reduced by at least one oxidation state.
• 3. electrolyser according to sentence 1 or 2, characterized in that the reducible cation ( 160 ) in the cathodic electrolyte ( 129 ) is solved.
• 4. electrolyser according to sentence 3, characterized in that in the cathodic electrolyte ( 129 ) reducible cation ( 160 ) is an ion from the group of transition metals, in particular a vanadium ion, a chromium ion or an iron ion.
• 5. electrolyser according to sentence 3 or 4, characterized in that the reducible cation ( 160 ) in the cathodic electrolyte ( 129 ) is introduced by dissolving a salt, in particular a transition metal salt, more particularly a vanadium salt.
• 6. Electrolyser according to one of the preceding sentences, characterized in that the separator ( 126 ) in the form of a bipolar membrane ( 148 ) is trained.
• 7. electrolyser according to sentence 6, characterized in that the bipolar membrane ( 148 ) an anion exchange membrane ( 150 ) and a cation exchange membrane ( 152 ), especially in the form of a proton exchange membrane ( 156 ).
• 8. electrolyser according to sentence 7, characterized in that the anion exchange membrane ( 150 ) and the cation exchange membrane ( 152 ) through a dissociation layer ( 154 ) are separated from each other.
• 9. electrolyser according to sentence 8, characterized in that the dissociation layer ( 154 ) a dissociation catalyst, especially for splitting water molecules ( 112 ) in hydroxide ions ( 158 ) and protons ( 130 ), contains.
• 10. Electrolyzer according to sentence 9, characterized in that the dissociation catalyst is iron oxide, in particular iron (III) oxide (Fe ₂ O ₃ ), or contains.
• 11. Electrolyser according to one of the sentences 8 to 10, characterized in that the dissociation layer ( 154 ) has a layer thickness in a range from approximately 5 nm to approximately 500 μm, in particular in a range from approximately 50 nm to approximately 50 μm.
• 12. Electrolyser according to one of the preceding sentences, characterized in that the cathodic electrolyte ( 129 ) Is water or an aqueous solution and / or that the anodic electrolyte ( 128 ) Is water or an aqueous solution.
• 13. Electrolyser according to one of the preceding sentences, characterized in that the anodic electrolyte ( 128 ) and / or the cathodic electrolyte ( 129 ) have a pH of 7 or essentially 7.
• 14. Electrolyser according to one of the preceding sentences, characterized in that a pH of the anodic electrolyte ( 128 ) and a pH value of the cathodic electrolyte ( 129 ) differentiate and define a pH gradient.
• 15. Electrolyser according to sentence 14, characterized in that the pH gradient is at least 1, in particular at least 3, further in particular at least 5.
• 16. Electrolyser according to one of the preceding sentences, characterized in that the anodic electrolyte ( 128 ) is alkaline.
• 17. Electrolyser according to one of the preceding sentences, characterized in that the cathodic electrolyte ( 129 ) is acidic.
• 18. Electrolyser according to one of the preceding sentences, characterized in that the anode ( 140 ) from the anodic catalyst ( 146 ) consists of or the anodic catalyst ( 146 ) is formed or the anodic catalyst ( 146 ) contains or with the anodic catalyst ( 146 ) is coated or with the anodic catalyst ( 146 ) is in electrically conductive contact.
• 19. Electrolyser according to one of the preceding sentences, characterized in that the anode ( 140 ) is solid or reticulated.
• 20. Electrolyser according to one of the preceding sentences, characterized in that the anodic catalyst ( 146 ) Is nickel, iridium or cobalt or contains nickel, iridium and / or cobalt, in particular in the form of NiO _x , NiCeO _x , NiCoO _x , NiCuO _x , NiFeO _x , NiLaO _x , IrO _x , CoFeO _x or CoO _x .
• 21. Electrolyser according to one of the preceding sentences, characterized in that the cathodic catalyst ( 144 ) in the cathodic electrolyte ( 129 ) is suspended.
• 22. Electrolyser according to sentence 21, characterized in that a particle size of the suspended cathodic catalyst ( 144 ) is less than 50 µm, in particular less than 5 µm.
• 23. Electrolyser according to one of the preceding sentences, characterized in that the cathodic catalyst ( 144 ) Mo ₂ C, Mo ₂ S or NiP is or contains.
• 24.Molecular water splitting process ( 112 ) in molecular hydrogen ( 114 ) and molecular oxygen ( 116 ) using electrical energy, in which process water molecules ( 112 ) in protons ( 130 ) and hydroxide ions ( 158 ) dissociate, in which method the hydroxide ions ( 158 ) in an anodic half cell ( 122 ) with an anode ( 140 ) with the help of an anodic catalyst ( 146 ) are oxidized and the protons ( 130 ) in a cathodic half cell ( 124 ) with a cathode ( 134 ) with the help of a cathodic catalyst ( 144 ) are reduced, the anodic half cell ( 122 ) and the cathodic half cell ( 124 ) by a separator ( 126 ) are separated from each other, the anodic half cell ( 122 ) an anodic electrolyte ( 128 ), which with the anode ( 140 ) is in contact, and the cathodic half cell ( 124 ) a cathodic electrolyte ( 129 ) which is connected to the cathode ( 134 ) is in contact, characterized in that in the cathodic half cell ( 124 ) a mediator ion ( 164 ) from a reducible cation ( 160 ) by electron uptake on the cathode ( 134 ) that the reducible cation ( 160 ) and the mediator ion ( 164 ) form a redox pair and that protons ( 130 ) by electron uptake of mediator ions ( 164 ) with the participation of the cathodic catalyst ( 144 ) to molecular hydrogen ( 114 ) can be reduced.
• 25. The method according to sentence 24, characterized in that the reducible cation ( 160 ) by electron uptake on the cathode ( 134 ) is reduced by at least one oxidation state.
• 26. The method according to sentence 24 or 25, characterized in that the reducible cation ( 160 ) in the cathodic electrolyte ( 129 ) is solved.
• 27. The method according to sentence 26, characterized in that in the cathodic electrolyte ( 129 ) as a dissolved reducible cation ( 160 ) an ion from the group of transition metals, in particular a vanadium ion, a chromium ion or an iron ion, is used.
• 28. The method according to sentence 26 or 27, characterized in that the reducible cation ( 160 ) in the cathodic electrolyte ( 129 ) by dissolving a salt, in particular a transition metal salt, more particularly a vanadium salt.
• 29. The method according to one of the sentences 24 to 28, characterized in that the separator ( 126 ) in the form of a bipolar membrane ( 148 ) is trained.
• 30. The method according to sentence 29, characterized in that the bipolar membrane comprises an anion exchange membrane and a cation exchange membrane.
• 31. The method according to sentence 30, characterized in that the anion exchange membrane ( 150 ) and the cation exchange membrane ( 152 ) through a dissociation layer ( 154 ) be separated from each other.
• 32. The method according to sentence 31, characterized in that in the dissociation layer ( 154 ) a dissociation catalyst, especially for splitting water molecules ( 112 ) in hydroxide ions ( 158 ) and protons ( 130 ) is introduced.
• 33. The method according to sentence 32, characterized in that a dissociation catalyst is used which is or contains iron oxide, in particular iron (III) oxide (Fe ₂ O ₃ ).
• 34. Method according to one of the sentences 31 to 33, characterized in that the dissociation layer ( 154 ) is formed with a layer thickness in a range from approximately 5 nm to approximately 500 μm, in particular with a layer thickness in a range from approximately 50 nm to approximately 50 μm.
• 35. Method according to one of the sentences 24 to 34, characterized in that the cathodic electrolyte ( 129 ) Water or an aqueous solution is used and / or that as an anodic electrolyte ( 128 ) Water or an aqueous solution is used.
• 36. Method according to one of the sentences 24 to 35, characterized in that an anodic electrolyte ( 128 ) and / or a cathodic electrolyte ( 129 ) with a pH of 7 or essentially 7.
• 37. Method according to one of the preceding sentences, characterized in that an anodic electrolyte ( 128 ) and a cathodic electrolyte ( 129 ) with different pH values and define a pH gradient.
• 38. The method according to sentence 37, characterized in that anodic and cathodic electrolytes ( 129 ) are used so that the pH gradient is at least 1, in particular at least 3, furthermore in particular at least 5.
• 39. Method according to one of the sentences 24 to 38, characterized in that an alkaline anodic electrolyte ( 128 ) is used.
• 40. Method according to one of the sentences 24 to 39, characterized in that an acidic cathodic electrolyte ( 129 ) is used.
• 41. Method according to one of the sentences 24 to 40, characterized in that an anode ( 140 ) is formed such that it consists of the anodic catalyst ( 146 ) consists of or the anodic catalyst ( 146 ) is formed or the anodic catalyst ( 146 ) contains or with the anodic catalyst ( 146 ) is coated or with the anodic catalyst ( 146 ) is in electrically conductive contact.
• 42. Method according to one of the sentences 24 to 41, characterized in that the anode ( 140 ) is solid or network-shaped.
• 43. The method according to one of the sentences 24 to 42, characterized in that an anodic catalyst ( 146 ) is used, which is nickel, iridium or cobalt or contains nickel, iridium and / or cobalt, in particular in the form NiO _x , NiCeO _x , NiCoO _x , NiCuO _x , NiFeO _x , NiLaO _x , IrO _x , CoFeO _x or CoO _x .
• 44. Method according to one of the sentences 24 to 43, characterized in that the cathodic catalyst ( 144 ) in the cathodic electrolyte ( 129 ) is suspended.
• 45. The method according to sentence 44, characterized in that the suspended cathodic catalyst ( 144 ) is used with a particle size which is smaller than 50 µm, in particular smaller than 5 µm.
• 46. Method according to one of the sentences 24 to 45, characterized in that the cathodic catalyst ( 144 ) Mo ₂ C, Mo ₂ S or NiP is or contains.
• 47. Using an electrolyser ( 110 ) according to one of the sentences 1 to 23 for carrying out a method according to one of the sentences 24 to 46.

• 1: eine schematische Darstellung des Aufbaus eines Ausführungsbeispiels eines Elektrolyseurs, wie er aus dem Stand der Technik bekannt ist;
• 2: eine schematische Darstellung Elektrodenpotentialdifferenz der Wasserspaltungsreaktion in saurem und alkalischem Medium;
• 3: eine schematische Darstellung eines Ausführungsbeispiels eines Elektrolyseurs gemäß der Erfindung;
• 4: eine schematische Darstellung der Elektrodenpotentialdifferenz unter Verwendung eines Mediator-Ions als Teil eines V²⁺/V³⁺ Redox-Paars; und
• 5: eine Übersicht der Reaktionsgleichungen in der Dissoziationsschicht der Bipolarmembran (1), an der Kathode (2) und (3) sowie an der Anode (4).

The following description of preferred embodiments of the invention serves in conjunction with the drawings for a more detailed explanation. Show it:

• 1 : A schematic representation of the structure of an embodiment of an electrolyzer, as is known from the prior art;
• 2nd : a schematic representation of the electrode potential difference of the water splitting reaction in acidic and alkaline medium;
• 3rd : a schematic representation of an embodiment of an electrolyzer according to the invention;
• 4th : a schematic representation of the electrode potential difference using a mediator ion as part of a V ²⁺ / V ³⁺ redox pair; and
• 5 : an overview of the reaction equations in the dissociation layer of the bipolar membrane (1), at the cathode (2) and (3) and at the anode (4).

In 1 is an embodiment of an electrolyzer known from the prior art 10th for disassembling water 12th in hydrogen 14 and oxygen 16 using electrical energy generated by voltage source 18th is provided, shown schematically.

The electrolyzer 10th comprises an electrolytic cell 20 which is an anodic half cell 22 and a cathodic half cell 24th includes. The two half cells 22 and 24th are through a separator 26 separated from each other.

The two half cells 22 and 24th are with an electrolyte 28 filled. Is the separator 26 formed in the form of a proton exchange membrane (PEM), the electrolyte 28 has a pH value in the neutral range, i.e. defines a neutral milieu, both in the anodic half cell 22 as well as in the cathodic half cell 24th . The proton exchange membrane is only for protons 30th , i.e. H ⁺ ions, permeable.

In the cathodic half cell 24th dips an electrode 32 in the form of a cathode 34 one that is electrically conductive with the negative pole 36 the voltage source 18th connected is.

In the anodic half cell 22 dips an electrode 38 in the form of an anode 40 one that is electrically conductive with the positive pole 42 the voltage source 18th connected is.

At the in 1 illustrated embodiment of the electrolyzer 10th is the cathode 34 made of an electrically conductive material, for example stainless steel or carbon, and with a cathodic catalyst 44 coated. The cathodic catalyst 44 it is platinum.

The anode 40 is also made of an electrically conductive material, which must be resistant to oxidation, for example titanium, and with an anodic catalyst 46 coated. This is iridium.

In 2nd are the associated electrochemical potentials of the electrolyzer 10th shown schematically. The cell voltage required to decompose water 12th in hydrogen 14 and oxygen 16 is about 1.23 volts. Has the electrolyte 28 acidic pH, move in the anodic half cell 22 generated protons 30th through the separator 26 to the cathode 34 there and there, supported by the cathodic catalyst 44 , after taking up electrons (e ^- ) to molecular hydrogen 14 reduced.

The hydroxide ions (OH ^- ) dissociated from water molecules move towards the anode 40 back and forth, releasing electrons into molecular oxygen 16 and water 12th transformed. Has the electrolyte 28 have a neutral pH value in the anodic half cell 22 through the oxidation of water 12th on the anodic catalyst 46 molecular oxygen and protons 30th . The protons 30th move through the separator due to the opposite charge 26 to the cathode 34 .

If you replace the separator 26 through an anion exchange membrane that is permeable to hydroxide ions and selects an alkaline electrolyte 28 , the cell voltage required for electrolysis is retained, as can be seen schematically 2nd results.

One operates the electrolyzer 10th in an alkaline environment can act as an anodic catalyst 46 Nickel and as anodic catalysts 44 Cobalt and / or manganese can be used. The disadvantage of an alkaline electrolyte 28 is, however, that hydroxide ions have to be supplied constantly. There are also strong alkaline electrolytes 28 highly corrosive.

3rd shows schematically an embodiment of an electrolyzer 110 according to the invention. It also serves water 112 in molecular hydrogen 114 and molecular oxygen 116 disassemble. For this, too, electrical energy is used by a voltage source 118 provided.

The electrolyzer 110 comprises an electrolytic cell 120 with an anodic half cell 122 and a cathodic half cell 124 . The half cells 122 and 124 are through a separator 126 separated from each other.

The anodic half cell 122 is with an anodic electrolyte 128 filled, the cathodic half cell 124 with a cathodic electrolyte 129 .

In the cathodic electrolyte 129 the cathodic half cell 124 dips an electrode 132 in the form of a cathode 134 a. The cathode 134 is electrically conductive with the negative pole 136 the voltage source 118 connected.

In the anodic electrolyte 128 the anodic half cell 122 dips an electrode 138 in the form of an anode 140 a. The anode 140 is electrically conductive with the positive pole 142 the voltage source 118 connected.

The anode 140 in one embodiment of the electrolyzer consists of the anodic catalyst 146 . In another embodiment, the anode is 140 from the anodic catalyst 146 educated. In another embodiment, the anode contains 140 the anodic catalyst 146 . In another embodiment, the anode 140 with the anodic catalyst 146 coated. In a further embodiment, the anode is standing 140 electrically conductive with the anodic catalyst 146 in contact.

At the in 3rd The illustrated embodiment is the anode 140 massively trained. In another embodiment, the anode 140 reticulated.

The anodic catalyst 146 is with the in 3rd illustrated embodiment nickel. In another embodiment, the anodic catalyst 146 Iridium or cobalt or contains nickel, iridium and / or cobalt. In further exemplary embodiments, the anodic catalyst is or contains NiO _x , NiCeO _x , NiCoO _x , NiCuO _x , NiFeO _x , NiLaO _x , IrO _x , CoFeO _x or CoO _x .

The cathode 34 is with the in 3rd illustrated embodiment formed from carbon.

The cathodic catalyst 144 is in the cathodic electrolyte 129 suspended. The particle size of the suspended cathodic catalyst 144 is less than 50 µm. In a further exemplary embodiment, the particle size is less than 5 μm.

At the in 3rd The illustrated embodiment is the cathodic catalyst 144 Molybdenum carbide Mo ₂ C. Mo ₂ C from Sigma-Aldrich ^® with the product number was used 399531 in powder form with a particle size ≤ 45 µm.

In further exemplary embodiments, the cathodic catalyst is Mo ₂ S or NiP or contains one of these two compounds.

The separator 126 is in the form of a bipolar membrane 148 educated. It includes an anion exchange membrane 150 as well as a cation exchange membrane 152 . The anion exchange membrane 150 and the cation exchange membrane 152 are through a dissociation layer 154 separated from each other. The cation exchange membrane 152 is in the form of a proton exchange membrane 156 educated.

The dissociation layer 154 contains or is formed from a dissociation catalyst. The dissociation catalyst supports the splitting of water molecules into hydroxide ions 158 and protons 130 .

The dissociation catalyst is in the embodiment of the 3rd Iron oxide or contains iron oxide in the form of iron (III) oxide (Fe ₂ O ₃ ).

A layer thickness of the dissociation layer 154 is in a range from about 5 nm to about 500 µm. In a further exemplary embodiment, the layer thickness of the dissociation layer is 154 in a range from about 50 nm to about 50 µm.

The dissociation catalyst in the dissociation layer 154 splits water molecules into hydroxide ions 158 and protons 130 on. The protons 130 migrate in the electric field of the electrolytic cell 120 through the cation exchange membrane 152 into the cathodic half cell 124 .

Different from the embodiment of the electrolyzer 10th the protons are reduced 130 not on the cathode 134 . At the electrolyser 110 another mechanism is used. For this is in the cathodic electrolyte 128 a reducible cation 160 solved. With the reducible cation 160 it is V ³⁺ ions, which take up an electron 162 on the cathode 134 reduced to V ²⁺ ions, which act as mediator ions 164 serve for the hydrogen evolution reaction.

The reducible cation 160 is done by dissolving a salt in the cathodic electrolyte 129 brought in. In the embodiment of the electrolyzer 110 Vanadyl sulfate (VOS ₄ ) is used by Sigma-Aldrich ^® with the product number 233706 . It is blue powder or blue crystals that contain stored water.

In further exemplary embodiments, Cr ³⁺ and / or Fe ³⁺ are used as reducible cations, those with mediator ions Cr ²⁺ or Fe ²⁺ redox pairs in the form Cr ³⁺ / Cr ²⁺ or Fe ³⁺ / Fe ^{2 +} form.

These alternative redox pairs can be in the cathodic electrolyte 129 be introduced by dissolving appropriate salts, in particular by dissolving chromium or iron salts.

The reduction of protons 130 to molecular hydrogen 114 is done by transferring electrons from the mediator ions 164 in the presence of the cathodic catalyst 144 in the cathodic electrolyte 129 . In this chemical reaction path, the mediator ion 164 back into the reducible cation 160 oxidized.

The cathodic electrolyte 129 has a pH in the acidic range. The anodic electrolyte 128 has a pH in the alkaline range.

The advantage of using the reducible cation 160 that with the mediator ion 164 forms a redox pair results directly from 4th . The redox potential of the redox pair V ²⁺ / V ³⁺ in an acidic environment is approximately 0.26 volts. The half cell voltage for the oxygen evolution reaction (OER) in an alkaline environment is about 0.4 volts. This results in a cell voltage of approximately 0.66 volts. This is only half the cell voltage of conventional electrolysers 10th which is approximately 1.23 volts as described above.

The embodiment of the electrolyzer 110 has the advantage that it can be operated with a significantly lower cell voltage. Because the power consumption of the electrolyzer 10th respectively 110 is defined by the product of current and voltage and the input power is directly correlated with the conversion of water 112 to hydrogen 114 and oxygen 116 , the lowering of the cell voltage means that the input power is reduced and thus the operating costs, in particular for electrical energy, in comparison to conventional electrolysers 10th at the electrolyser 110 are significantly reduced.

In a further embodiment, both the cathodic electrolyte 129 as well as the anodic electrolyte 128 Be water. Through the Dissociation of water molecules in the dissociation layer 154 turns up after a short time in the anodic half cell 122 an alkaline pH in the cathodic half cell 124 an acidic pH.

In 5 are the reaction equations of the electrolyzer 110 shown schematically. Equation (1) describes the decomposition of water 112 in protons 130 and hydroxide ions 158 .

Equation (2) describes the reduction of the reducible cation V ³⁺ by incorporating an electron into the mediator ion V ²⁺ .

Equation (3) describes the chemical conversion of protons 158 in cooperation with mediator ions 164 in the presence of the cathodic catalyst 144 Release electrons (e ⁺ ) and thus again to the reducible cation 160 are oxidized with the formation of molecular hydrogen 114 .

Equation (4) describes the oxygen evolution reaction of the anodic half cell 122 . Hydroxide ions 158 are emitting electrons (e ⁺ ) in molecular oxygen 116 and water 112 transformed.

The proposed training of the electrolyzer 110 enables in particular the use of inexpensive catalysts 144 and 146 both for the anodic half cell 122 as well as for the cathodic half cell 124 . It can also act as an electrolyte 128 respectively 129 Water can be used. The risk of corrosion of the electrolyser 110 can be minimized. Also the use of weakly acidic cathodic electrolytes 129 and weakly alkaline anodic electrolytes 128 is possible.

By the electrolyser described 110 can overcome the disadvantages of conventional electrolysers 10th be overcome.

The electrolyzer 110 can be used in particular to hydrogen 114 from electrical energy provided by renewable energies, from water 112 to create. There are significantly lower requirements in terms of costs and safety than for electrolysers 10th required according to the state of the art. In addition, hydrogen can 114 be produced with a degree of purity.

Taking into account that the global demand for hydrogen is around 60 million a year and is constantly increasing, with current electrolyzers 10th emits a total of approximately 330 million tons of carbon dioxide into the atmosphere to produce hydrogen when fossil fuels are used to provide the electrical energy.

The production of carbon dioxide can be reduced to zero by using electrical energy from renewable energies. This is basically also the case with electrolysers 10th conceivable.

In any case, the purchase and operating costs for the electrolyzer 110 compared to the electrolyzer 10th significantly lower and thus the cost of producing hydrogen 114 also lower. The proposed electrolyzer 110 In other words, it enables more hydrogen with the same effort and cost 114 for new drive technologies and still significantly reduce CO ₂ emissions.

The electrolysers described 110 can be used in particular for the electrolysis of water 112 , in particular for the production of hydrogen 114 as well as for storing electrical energy.

Reference list

10th

Electrolyser

12th

water

14

hydrogen

16

oxygen

18th

Voltage source

20

Electrolytic cell

22

anodic half cell

24th

cathodic half cell

26

separator

28

electrolyte

30th

proton

32

electrode

34

cathode

36

Negative pole

38

electrode

40

anode

42

Positive pole

44

cathodic catalyst

46

anodic catalyst

110

Electrolyser

112

water

114

hydrogen

116

oxygen

118

Voltage source

120

Electrolytic cell

122

anodic half cell

124

cathodic half cell

126

separator

128

anodic electrolyte

129

cathodic electrolyte

130

proton

132

electrode

134

cathode

136

Negative pole

138

electrode

140

anode

142

Positive pole

144

cathodic catalyst

146

anodic catalyst

148

Bipolar membrane

150

Anion exchange membrane

152

Cation exchange membrane

154

Dissociation layer

156

Proton exchange membrane

158

Hydroxide ion

160

reducible cation

162

electron

164

Mediator ion

Claims (20)

Electrolyser (110) for splitting molecular water (112) into molecular hydrogen (114) and molecular oxygen (116) using electrical energy, which electrolyzer (110) has an anodic half cell (122) with an anode (140) and a cathodic half cell (124) with a cathode (134), the anodic half cell (122) and the cathodic half cell (124) being separated from one another by a separator (126), the anodic half cell (122) comprising an anodic electrolyte (128), which is in contact with the anode (140), and wherein the cathodic half cell (124) comprises a cathodic electrolyte (129) which is in contact with the cathode (134), the anodic half cell (122) comprising an anodic catalyst (146 ) and wherein the cathodic half cell (124) comprises a cathodic catalyst (144), characterized in that the cathodic half cell (124) for generating a mediator ion (164) has at least one electr contains the reducible cation (160) and that the reducible cation (160) and the mediator ion (164) form a redox pair. Electrolyser after Claim 1 , characterized in that the reducible cation (160) can be reduced by at least one oxidation state by electron acceptance at the cathode (134). Electrolyser after Claim 1 or 2nd , characterized in that the reducible cation (160) is dissolved in the cathodic electrolyte (129). Electrolyser after Claim 3 , characterized in that a) the reducible cation (160) dissolved in the cathodic electrolyte (129) is an ion from the group of transition metals, in particular a vanadium ion, a chromium ion or an iron ion and / or b) the reducible cation (160) is introduced into the cathodic electrolyte (129) by dissolving a salt, in particular a transition metal salt, more particularly a vanadium salt. Electrolyser according to one of the preceding claims, characterized in that the separator (126) is designed in the form of a bipolar membrane (148). Electrolyser after Claim 5 , characterized in that the bipolar membrane (148) comprises an anion exchange membrane (150) and a cation exchange membrane (152), in particular in the form of a proton exchange membrane (156). Electrolyser according to 6, characterized in that the anion exchange membrane (150) and the cation exchange membrane (152) are separated from one another by a dissociation layer (154). Electrolyser after Claim 7 , characterized in that the dissociation layer (154) a) contains a dissociation catalyst, in particular for splitting water molecules (112) into hydroxide ions (158) and protons (130), the dissociation catalyst in particular iron oxide, in particular iron (III) oxide ( Fe ₂ O ₃ ), is or contains, and / or b) has a layer thickness in a range from approximately 5 nm to approximately 500 μm, in particular in a range from approximately 50 nm to approximately 50 μm. Electrolyser according to one of the preceding claims, characterized in that a) the cathodic electrolyte (129) is water or an aqueous solution and / or that the anodic Electrolyte (128) is water or an aqueous solution and / or b) the anodic electrolyte (128) and / or the cathodic electrolyte (129) have a pH of 7 or essentially 7 and / or c) a pH Distinguish the value of the anodic electrolyte (128) and a pH value of the cathodic electrolyte (129) and define a pH gradient, the pH gradient in particular being at least 1, in particular at least 3, more particularly at least 5, and / or d ) the anodic electrolyte (128) is alkaline and / or e) the cathodic electrolyte (129) is acidic and / or f) the anode (140) consists of the anodic catalyst (146) or is formed from the anodic catalyst (146) or contains the anodic catalyst (146) or is coated with the anodic catalyst (146) or is in electrically conductive contact with the anodic catalyst (146). Electrolyser according to one of the preceding claims, characterized in that a) the anode (140) is solid or reticulated and / or b) the anodic catalyst (146) is nickel, iridium or cobalt or contains nickel, iridium and / or cobalt, in particular in the form NiO _x , NiCeO _x , NiCoO _x , NiCuO _x , NiFeO _x , NiLaO _x , IrO _x , CoFeO _x or CoO _x , and / or c) the cathodic catalyst (144) is suspended in the cathodic electrolyte (129) , in particular a particle size of the suspended cathodic catalyst (144) being less than 50 μm, in particular less than 5 μm, and / or d) the cathodic catalyst (144) is or contains Mo ₂ C, Mo ₂ S or NiP. Process for splitting molecular water (112) into molecular hydrogen (114) and molecular oxygen (116) using electrical energy, in which process water molecules (112) are dissociated into protons (130) and hydroxide ions (158), in which process the Hydroxide ions (158) are oxidized in an anodic half cell (122) with an anode (140) with the help of an anodic catalyst (146) and the protons (130) in a cathodic half cell (124) with a cathode (134) with the help of a cathodic Catalyst (144) are reduced, the anodic half cell (122) and the cathodic half cell (124) being separated from one another by a separator (126), the anodic half cell (122) comprising an anodic electrolyte (128) which is connected to the anode (140) is in contact, and wherein the cathodic half cell (124) comprises a cathodic electrolyte (129) which is in contact with the cathode (134), characterized thereby t that in the cathodic half cell (124) a mediator ion (164) is formed from a reducible cation (160) by electron acceptance at the cathode (134), that the reducible cation (160) and the mediator ion (164) form a redox pair and that protons (130) are reduced to molecular hydrogen (114) by electron acceptance of mediator ions (164) with the cooperation of the cathodic catalyst (144). Procedure according to Claim 11 , characterized in that a) the reducible cation (160) is reduced by at least one oxidation state by electron acceptance at the cathode (134) and / or b) the reducible cation (160) is dissolved in the cathodic electrolyte (129), in particular in the cathodic one Electrolyte (129) as dissolved reducible cation (160) is an ion from the group of transition metals, in particular a vanadium ion, a chromium ion or an iron ion, and / or the reducible cation (160) is used in the cathodic electrolyte (129) by dissolving a salt, in particular a transition metal salt, more particularly a vanadium salt. Procedure according to Claim 11 or 12th , characterized in that the separator (126) is designed in the form of a bipolar membrane (148). Procedure according to Claim 13 , characterized in that the bipolar membrane (148) is formed with an anion exchange membrane (150) and a cation exchange membrane (152), in particular in the form of a proton exchange membrane (156). Procedure according to Claim 14 , characterized in that the anion exchange membrane (150) and the cation exchange membrane (152) are separated from one another by a dissociation layer (154). Procedure according to Claim 15 , characterized in that a) a dissociation catalyst, in particular for splitting water molecules (112) into hydroxide ions (158) and protons (130), is introduced into the dissociation layer (154), in particular using a dissociation catalyst which is iron oxide, in particular iron (III) oxide (Fe ₂ O ₃ ), is or contains, and / or b) the dissociation layer (154) is formed with a layer thickness in a range from approximately 5 nm to approximately 500 μm, in particular with a layer thickness in a range from approximately 50 nm to approximately 50 μm. Procedure according to one of the Claims 11 to 16 , characterized in that a) water or an aqueous solution is used as the cathodic electrolyte (129) and / or that water or an aqueous solution is used as the anodic electrolyte (128) and / or b) an anodic electrolyte (128) and / or a cathodic electrolyte (129) with a pH of 7 or essentially 7 and / or c) an anodic electrolyte (128) and a cathodic electrolyte (129) with different pH values are used and a pH Define gradient, anodic and cathodic electrolytes (129) being used in particular, so that the pH gradient is at least 1, in particular at least 3, more particularly at least 5, and / or d) an alkaline anodic electrolyte (128) is used and / or e) an acidic cathodic electrolyte (129) is used. Procedure according to one of the Claims 11 to 17th , characterized in that an anode (140) is formed such that it consists of the anodic catalyst (146) or is formed from the anodic catalyst (146) or contains the anodic catalyst (146) or with the anodic catalyst (146) is coated or is in electrically conductive contact with the anodic catalyst (146). Procedure according to one of the Claims 11 to 18th , characterized in that a) the anode (140) is solid or reticulated and / or b) an anodic catalyst (146) is used which is nickel, iridium or cobalt or contains nickel, iridium and / or cobalt, especially in the form NiO _x , NiCeO _x , NiCoO _x , NiCuO _x , NiFeO _x , NiLaO _x , IrO _x , CoFeO _x or CoO _x , and / or c) the cathodic catalyst (144) is suspended in the cathodic electrolyte (129), whereby in particular the suspended cathodic catalyst (144) with a particle size which is smaller than 50 μm, in particular smaller than 5 μm, and / or d) the cathodic catalyst (144) is or contains Mo ₂ C, Mo ₂ S or NiP . Use of an electrolyser (110) according to one of the Claims 1 to 10th to carry out a method according to one of the Claims 11 to 19th .

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