EP3914753A1 - Electrolyser and method for splitting water - Google Patents
Electrolyser and method for splitting waterInfo
- Publication number
- EP3914753A1 EP3914753A1 EP20701731.0A EP20701731A EP3914753A1 EP 3914753 A1 EP3914753 A1 EP 3914753A1 EP 20701731 A EP20701731 A EP 20701731A EP 3914753 A1 EP3914753 A1 EP 3914753A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- cathodic
- anodic
- catalyst
- electrolyte
- half cell
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/02—Hydrogen or oxygen
- C25B1/04—Hydrogen or oxygen by electrolysis of water
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B13/00—Diaphragms; Spacing elements
- C25B13/04—Diaphragms; Spacing elements characterised by the material
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
- C25B9/40—Cells or assemblies of cells comprising electrodes made of particles; Assemblies of constructional parts thereof
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
- H01M8/184—Regeneration by electrochemical means
- H01M8/188—Regeneration by electrochemical means by recharging of redox couples containing fluids; Redox flow type batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Definitions
- the present invention relates to an electrolyzer for splitting mo 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 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 being an anodic catalyst comprises and wherein the cathodic half cell comprises a cathodic catalyst.
- 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 cal cell being separated from one another by a separator, the anodic half cell comprising an anodic electrolyte which is associated with the Anode is in contact, 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.
- the electrolytes used are another problem.
- 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.
- producing potassium hydroxide is an energy-intensive process.
- Potassium hydroxide is also highly corrosive.
- hydroxide ions are consumed during 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.
- the object is achieved according to the invention in an electrolyzer of the type described at the outset in that the cathodic half cell for generating a mediator ion contains at least one cation which can be reduced by electron absorption and in that the reducible cation and the mediator ion form a redox pair.
- protons in the cathodic half-cell are not formed in the electrolyser designed as proposed reduced directly with the support of a catalyst on the cathode, but in the interaction of the mediator ion and the cathodic catalyst.
- the reducible cation is reduced by taking up at least one electron on the cathode to generate a mediator ion.
- the mediator ion releases the at least one electron that has been taken up, thus enabling the reduction of protons in molecular hydrogen.
- the mediator ion is oxidized again and converted into the original reducible cation.
- a cathodic catalyst which is not in direct contact with the cathode but is, for example, suspended in the cathodic electrolyte.
- an effective surface area of the cathodic catalyst in the cathodic half cell can be enlarged.
- Heterogeneous chemical hydrogen development catalysts can be used to support a chemical process for the development of hydrogen.
- chemical and electrochemical processes can be coupled to produce hydrogen.
- the use 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 energy consumption can be significantly reduced, which means that the operating costs of the electrolyzer, namely in particular the costs for providing electrical energy for electrolysis, can be significantly reduced.
- 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 at 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 development reaction, the cell voltage can be lowered overall.
- the reducible cation is preferably dissolved in the cathodic electrolyte. This makes it possible, in particular, to realize the hydrogen reduction in the presence of the cathodic catalyst at any point in the cathodic half cell. A limitation to the cathode as with conventional electrolyzers can thus be effectively avoided.
- the reducible cation dissolved in the electrolyte is an ion from the group of transition metals.
- it can be a vanadium ion, a chromium ion or an iron ion.
- a redox pair can be formed by V 2+ / V 3+ ions, V 3+ forming the reducible cation and V 2+ the mediator ion, which can be oxidized by releasing an electron.
- the reducible cation is introduced into the cathodic electrolyte by dissolving a salt.
- the salt can be transition metal salt, for example a vanadium salt.
- the vanadium salt can be vanadium oxysulfate (VOSO4), which is also known as vanadyl sulfate. It can be used anhydrous as a green solid or as a hydrate as a blue odorless solid.
- VOSO4 vanadium oxysulfate
- It can be used anhydrous as a green solid or as a hydrate as a blue odorless solid.
- 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 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 allows cathodic and anodic catalysts to be used, which are particularly inexpensive.
- 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.
- the bipolar membrane comprises an anion exchange membrane and a cation exchange membrane.
- the cation exchange membrane can be 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.
- 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 the cathodic half cell.
- the dissociation layer contains a dissociation catalyst. In particular, this can support the breakdown of water molecules into hydroxide ions and protons.
- the splitting of water molecules into hydroxide ions and protons can be improved in particular by the dissociation catalyst being or containing iron oxide.
- the iron oxide can be iron (III) oxide (Fe203). It is advantageous if the dissociation layer has a layer thickness in a range from about 5 nm to about 500 pm.
- the dissociation layer has a layer thickness in a range from about 5 nm to about 500 pm.
- Layer thickness in a range from about 50 nm to about 50 pm.
- unsupported dissociation layers can be formed in this way.
- the cathodic electrolyte is water or an aqueous solution and / or if the anodic electrolyte is water or an aqueous solution.
- an inexpensive electrolyzer can be configured.
- a pH value can be set in the desired manner 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.
- a pH of the anodic electrolyte and a pH 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.
- 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.
- the cathodic half cell Due to different pH values of the anodic electrolyte and the cathodic electrolyte, inexpensive catalysts can be used in the cathodic half cell as well as 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.
- anodic electrolyte is alkaline.
- an inexpensive anodic catalyst can be used for the oxygen evolution reaction.
- cathodic electrolyte is acidic. This made it possible, in particular, 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.
- the anodic catalyst is nickel, iridium or cobalt or contains nickel, iridium and / or cobalt.
- the anodic catalyst can be or contain NiOx, NiCeOx, NiCoOx, NiCuOx, NiFeOx, NiLaOx, IrOx, CoFeOx or CoOx.
- 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.
- 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.
- a particle size of the suspended cathodic catalyst is less than 50 pm, in particular it is advantageous if it is less than 5 pm.
- the cathodic catalyst is preferably or contains M02C, M02S or NiP.
- the cathodic catalysts mentioned support the hydrogen development reaction in interaction with a mediator ion in an excellent manner. They are also available at low cost. Furthermore, they can be easily suspended in the cathodic electrolyte.
- 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 redox -Pair and that protons are reduced to molecular hydrogen by electron uptake of mediator ions with the help of the cathodic catalyst.
- 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.
- this allows operating costs to be reduced, since a lower cell voltage directly results in lower electrical power consumption by the electrolyzer. is linked, as well as investment costs, since, in particular, inexpensive catalysts can also 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 emit protons to form molecular hydrogen with the cooperation of the cathodic catalyst.
- the reducible cation thus serves as an electron carrier, so that the hydrogen development reaction can take place not only at the cathode, as is the case with conventional electrolyzers, but everywhere in the cathodic half cell, for example if the cathodic catalyst is suspended in the electrolyte.
- the process can be carried out in a simple manner if the reducible cation is dissolved in the cathodic electrolyte.
- it can be introduced into the cathodic electrolyte in a simple manner by dissolving a salt.
- 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+ .
- the reducible cation is introduced into the cathodic electrolyte by dissolving a salt.
- a salt can be a transition metal salt.
- it can be a vanadium salt or a chromium salt or an iron salt.
- 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 implement 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.
- inexpensive catalysts can be used in this way. It is therefore no longer necessary to use catalysts that are required in conventional electrolyzers in which the same environment prevails in both half-cells.
- the bipolar membrane is formed with an anion exchange membrane and a cation exchange membrane.
- the cation exchange membrane can be formed in the form of a proton exchange membrane.
- the anion exchange membrane and the cation exchange membrane are separated from one another by a dissociation layer.
- 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.
- the dissociation layer can be formed by the dissociation catalyst.
- a dissociation catalyst which is or contains iron oxide is preferably used.
- the iron oxide can be iron (III) oxide (Fe203).
- iron oxide In the presence of iron oxide, water splits particularly easily into protons and hydroxide ions.
- the dissociation layer is formed with a layer thickness in a range from approximately 5 nm to approximately 500 ⁇ m.
- the layer thickness can be seen in a range from about 50 nm to about 50 pm.
- supported dissociation layers can be formed, i.e. dissociation layers that are not self-supporting.
- an amount of the 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.
- 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.
- water can be used as the anodic electrolyte and / or as the cathodic electrolyte.
- an anodic electrolyte and a cathodic electrolyte are used with differing pH values and define a pH gradient.
- cathodic and anodic catalysts which relate the hydrogen evolution reaction or optimally support the oxygen development reaction.
- catalysts can be used which are not precious metals. In particular, investment costs for the training of electrolyzers can be minimized.
- the pH gradient is at least 1. In particular, it can be at least 3. In particular, 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 can be optimized in particular.
- An acidic cathodic electrolyte is advantageously used. In particular, this makes it possible to optimize the hydrogen evolution reaction in the cathodic half cell.
- 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 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.
- 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.
- the anodic catalyst can be or contain NiOx, NiCeOx, NiCoOx, NiCuOx, NiFeOx, NiLaOx, IrOx, CoFeOx or CoOx.
- the cathodic catalyst is advantageously suspended in the cathodic electrolyte.
- 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.
- the suspended cathodic catalyst is used with a particle size which is less than 50 pm.
- the particle size can be less than 5 pm. In this way, a surface area of the cathodic catalyst can be significantly increased compared to conventional electrolysers in which the surface of the cathode is coated with the cathodic catalyst.
- Figure 1 is a schematic representation of the structure of an embodiment example of an electrolyzer, as is known from the prior art
- FIG. 2 is a schematic representation of the electrode potential difference
- Figure 3 is a schematic representation of an embodiment of a
- FIG. 4 a schematic representation of the electrode potential difference using a mediator ion as part of a V 2+ / V 3+ redox pair
- Figure 5 an overview of the reaction equations in the dissociation layer of the bipolar membrane (1), on the cathode (2) and (3) as well as on the anode (4).
- FIG 1 an embodiment of a prior art electrolyzer 10 for decomposing water 12 into hydrogen 14 and oxygen 16 using electrical energy, which is provided by voltage source 18, is shown schematically.
- the electrolyzer 10 comprises an electrolytic cell 20, which comprises an anodic half cell 22 and a cathodic half cell 24.
- the two half cells 22 and 24 are separated from one another by a separator 26.
- the two half cells 22 and 24 are filled with an electrolyte 28.
- the separator 26 is in the form of a proton exchange membrane (PEM)
- the electrolyte 28 has a pH in the neutral range, that is to say defines a neutral environment, both in the anodic half cell 22 and in the cathodic half cell 24.
- the proton exchange membrane is only permeable to protons 30, i.e. h onen.
- an electrode 32 in the form of a Ka 34 is immersed, which is electrically conductively connected to the negative pole 36 of the voltage source 18.
- an electrode 38 is immersed in the form of an anode 40, which is electrically conductive with the positive pole 42 of the voltage source 18.
- the cathode 34 is made of an electrically conductive material, for example stainless steel or carbon, and coated with a cathodic catalyst 44.
- the cathodic catalyst 44 is platinum.
- the anode 40 is also made of an electrically conductive material, which must be resistant to oxidation, for example titanium, and coated with an anodic catalyst 46. This is iridium.
- the associated electrochemical potentials of the electrolyzer 10 are shown schematically.
- the cell voltage required to decompose water 12 into hydrogen 14 and oxygen 16 is approximately 1.23 volts. If the electrolyte 28 has an acidic pH value, protons 30 generated in the anodic half cell 22 move through the separator 26 to the cathode 34 and are supported there by the cathodic catalyst 44 after receiving electrons (e) to become molecular Hydrogen 14 reduced.
- the hydroxide ions (OH) dissociated from water molecules move towards the anode 40 and are converted into molecular oxygen 16 and water 12 with the emission of electrons. If the electrolyte 28 has a neutral pH value, the anodic half-cell 22 results from the oxidation of Water 12 on the anodic catalyst 46 molecular oxygen and protons 30. The protons 30 move through the separator 26 to the cathode 34 due to the opposite charge.
- separator 26 is replaced by an anion exchange membrane which is permeable to hydroxide ions and an alkaline electrolyte 28 is selected, the cell voltage required for the electrolysis is retained, as is shown schematically in FIG.
- an alkaline electrolyte 28 is that hydroxide ions have to be supplied continuously.
- strongly alkaline electrolytes 28 are highly corrosive.
- FIG. 3 schematically shows an embodiment of an electrolyzer 110 according to the invention. It also serves to decompose water 112 into molecular hydrogen 114 and molecular oxygen 116. Electrical energy is also used for this purpose, which is provided by a voltage source 118.
- 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 separated from one another by a separator 126.
- the anodic half cell 122 is filled with an anodic electrolyte 128, the cathodic half cell 124 with a cathodic electrolyte 129.
- An electrode 132 in the form of a cathode 134 is immersed in the cathodic electrolyte 129 of the cathodic half cell 124.
- the cathode 134 is electrically conductively connected to the negative pole 136 of the voltage source 118.
- An electrode 138 in the form of an anode 140 is immersed in the anodic electrolyte 128 of the anodic half cell 122.
- the anode 140 is electrically connected to the positive pole 142 of the voltage source 118.
- the anode 140 consists of the anodic catalyst 146. In another embodiment, the anode 140 is made of the anodic catalyst 146. In a further exemplary embodiment, the anode 140 contains the anodic catalyst 146. In a further exemplary embodiment, the anode 140 is coated with the anodic catalyst 146. In a further embodiment, the anode 140 is in electrically conductive contact with the anodic catalyst 146.
- the anode 140 is solid. In a further exemplary embodiment, the anode 140 is designed in the form of a network.
- the anodic catalyst 146 is nickel. In a further exemplary embodiment, the anodic catalyst 146 is iridium or cobalt or contains nickel, iridium and / or cobalt. In further exemplary embodiments, the anodic catalyst is or contains NiOx, NiCeOx, NiCoOx, NiCuOx, NiFeOx, NiLaOx, IrOx, CoFeOx or CoOx .
- the cathode 34 is formed from carbon.
- the cathodic catalyst 144 is suspended in the cathodic electrolyte 129.
- the particle size of the suspended cathodic catalyst 144 is less than 50 pm. In a further embodiment, the particle size is less than 5 pm.
- the cathodic catalyst 144 is molybdenum carbide M02C.
- M02C from Sigma- Aldrich ® with the product number 399531 in powder form with a particle size ⁇ 45 pm.
- the cathodic catalyst is M02S or NiP or contains one of these two compounds.
- the separator 126 is designed in the form of a bipolar membrane 148. It comprises an anion exchange membrane 150 and a cation exchange membrane 152. The anion exchange membrane 150 and the cation exchange membrane 152 are separated from one another by a dissociation layer 154. The cation exchange membrane 152 is in the form of a proton exchange membrane 156.
- 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 iron oxide or contains iron oxide in the form of iron (III) oxide (Fe203).
- a layer thickness of the dissociation layer 154 is in a range from approximately 5 nm to approximately 500 pm. In a further exemplary embodiment, the layer thickness of the dissociation layer 154 is in a range from approximately 50 nm to approximately 50 ⁇ m.
- the dissociation catalyst in the dissociation layer 154 splits water molecules into hydroxide ions 158 and protons 130.
- the protons 130 migrate in the electric field of the electrolysis cell 120 through the cation exchange membrane 152 into the cathodic half cell 124.
- the protons 130 are not reduced at the cathode 134.
- a different mechanism is used in the electrolyzer 110.
- the reducible cation 160 is V 3+ ions, which are reduced by taking up an electron 162 on the cathode 134 to V 2+ ions, which serve as mediator ions 164 for the hydrogen evolution reaction.
- the reducible cation 160 is introduced into the cathodic electrolyte 129 by dissolving a salt.
- vanadyl sulfate VOS4
- Sigma-Aldrich ® with the product number 233706.
- 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.
- the reduction of the protons 130 to molecular hydrogen 114 takes place by transferring electrons of the mediator ions 164 in the presence of the cathodic catalyst 144 in the cathodic electrolyte 129. With this chemical reaction path, the mediator ion 164 is oxidized again into the reducible cation 160 .
- the cathodic electrolyte 129 has a pH in the acidic range.
- the anodic electrolyte 128 has a pH in the alkaline range.
- the redox potential of the redox pair V 2+ / V 3+ in an acidic environment is about 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. It is thus only half the cell voltage of conventional electrolysers 10, which is approximately 1.23 volts as described above.
- the exemplary embodiment of the electrolyzer 110 thus has the advantage that it can be operated with a significantly lower cell voltage. Since the power consumption of the electrolyzer 10 or 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, are significantly reduced in comparison with conventional electrolyzers 10 in the electrolyser 110.
- both the cathodic electrolyte 129 and the anodic electrolyte 128 can be water.
- an alkaline pH is established in the anodic half-cell 122 and an acidic pH in the cathodic half-cell 124.
- Equation (1) describes the decomposition of water 112 into 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, which release 144 electrons (e + ) in the presence of the cathodic catalyst and are thus oxidized again to the reducible cation 160 with the formation of molecular hydrogen 114.
- Equation (4) describes the oxygen evolution reaction of the anodic half cell 122. Hydroxide ions 158 are converted into molecular oxygen 116 and water 112 with the emission of electrons (e + ).
- the proposed design of the electrolyser 110 allows in particular the use of inexpensive catalysts 144 and 146 both for the anodic half cell 122 and for the cathodic half cell 124.
- water can be used as the electrolyte 128 or 129.
- the risk of corrosion of the electrolyzer 110 can thereby be minimized.
- the use of weakly acidic cathodic electrolytes 129 and weakly alkaline anodic electrolytes 128 is also possible.
- the electrolyzer 110 can be used in particular to generate hydrogen 114 from electrical energy, which is provided by renewable energies, from water 112. There are significantly lower requirements with regard to costs and safety than are required with electrolyzers 10 according to the prior art. In addition, hydrogen 114 can be generated with a degree of purity.
- the production of carbon dioxide can be reduced to zero by using electrical energy from renewable energies. In principle, this is also conceivable for electrolysers 10. In any case, the purchase and operating costs for the electrolyser 110 are significantly lower compared to the electrolyzer 10 and thus the costs for the production of hydrogen 114 are also lower. In other words, the proposed electrolyser 110 makes it possible to provide more hydrogen 114 for new drive technologies with the same expenditure in terms of costs and energy, and yet to significantly reduce CCh emissions.
- the electrolysers 110 described can be used in particular for the electrolysis of water 112, that is to say in particular for the production of hydrogen 114 and for storing electrical energy.
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Abstract
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DE102019101528 | 2019-01-22 | ||
DE102019104401.4A DE102019104401A1 (en) | 2019-01-22 | 2019-02-21 | Electrolyser and water splitting process |
PCT/EP2020/051452 WO2020152190A1 (en) | 2019-01-22 | 2020-01-22 | Electrolyser and method for splitting water |
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DE102020133775A1 (en) | 2020-12-16 | 2022-06-23 | Forschungszentrum Jülich GmbH | Process and device for electrolysis |
DE102020133773A1 (en) | 2020-12-16 | 2022-06-23 | Forschungszentrum Jülich GmbH | Process and device for electrolysis |
CN112921341B (en) * | 2021-01-25 | 2022-06-21 | 北京化工大学 | Efficient reaction system for coupling small molecular catalytic oxidation and hydrogen production |
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GB201119283D0 (en) * | 2011-11-08 | 2011-12-21 | Univ Glasgow | Apparatus and methods for the electrochemical generation of oxygen and/or hydrogen |
ES2568759T3 (en) * | 2012-03-05 | 2016-05-04 | Eos Holding Sa | Redox flow battery for hydrogen generation |
WO2014035919A2 (en) * | 2012-08-27 | 2014-03-06 | Sun Catalytix Corporation | Gas sparging for transport of dissolved species through a barrier |
KR101586769B1 (en) * | 2013-12-23 | 2016-01-20 | 상명대학교 천안산학협력단 | Manufacturing Method of Thin Ion Exchange Membrane Using High Molecular Support |
GB201416062D0 (en) * | 2014-09-11 | 2014-10-29 | Univ The Glasgow | Hydrogen generation |
JP2018154879A (en) * | 2017-03-17 | 2018-10-04 | 株式会社東芝 | Electrochemical reaction apparatus, and method of producing anode for electrochemical reaction apparatus |
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