Electrolysis device with natural circulation

Abstract

The invention relates to an electrolysis device (1) for producing hydrogen gas from an aqueous alkaline solution by electrochemical reaction, comprising an anode half-cell (2) and a cathode half-cell (3). The anode half-cell (2) and the cathode half-cell (3) are separated by a membrane (4), and the cathode half-cell (3) can be filled with the aqueous alkali. The anode half-cell (2) comprises an anode electrode (5) and the cathode half-cell (3) comprises a cathode electrode (6), the anode electrode (5), the cathode electrode (6) and the membrane (4) forming a membrane electrode unit (7). Furthermore, during normal operation of the electrolysis device (1), the initial filling amount of the alkaline solution in the cathode half-cell (3) can be varied exclusively by a diffusion process through the membrane electrode unit (7) and / or by an electrochemical reaction of the alkaline solution in the membrane electrode unit (7).

Description

Technical Field

[0001] The invention relates to an electrolysis device and a method for producing hydrogen from an aqueous alkaline solution by electrochemical reaction. Background Art

[0002] EP3831986A1 describes a gas generating device, which includes an electrolysis container, which includes an anode chamber, a cathode chamber and an ion-permeable separator separating the anode chamber from the cathode chamber, the anode chamber accommodating an anode and producing oxygen, and the cathode chamber accommodating a cathode and producing hydrogen. The gas generating device also includes a first electrolyte circulation system, a second electrolyte circulation system and an electrolyte exchanger. The first electrolyte circulation system includes a first circulation tank and a first circulation pump, wherein the first circulation tank accommodates and stores the first electrolyte flowing out of the anode chamber, and the first circulation pump supplies the first electrolyte stored in the first circulation tank to the anode chamber. The second electrolyte circulation system includes a second circulation tank and a second circulation pump, wherein the second circulation tank accommodates and stores the second electrolyte flowing out of the cathode chamber, and the second circulation pump supplies the second electrolyte stored in the second circulation tank to the cathode chamber. The electrolyte exchanger transfers a portion of the first electrolyte present in the first electrolyte circulation to the second electrolyte circulation on the one hand and transfers a portion of the second electrolyte present in the second electrolyte circulation to the first electrolyte circulation on the other hand.

[0003] Furthermore, WO2011004343A1 describes a device for electrolytically producing hydrogen from an aqueous alkaline solution starting from a dry cathode, the device comprising:

[0004] - two half-cells (an anode half-cell and a cathode half-cell), the two half-cells being separated by an anion exchange membrane, the surface of the anion exchange membrane being in contact with the cathode half-cell being a membrane electrode unit MEA, and

[0005] - The alkaline solution is present only in the anode half-cell. Summary of the invention

[0006] The object of the present invention is to overcome the disadvantages of the prior art and to provide a device and a method by means of which particularly advantageous effects are achieved with regard to the operational safety and efficiency of the device.

[0007] This object is achieved by a device and a method according to the claims.

[0008] Unlike the gas generation device known from EP 3831986 A1, the electrolysis device according to the invention can be operated without active means for generating a flow or circulation. This has many advantages and in particular unexpected effects, which are explained in detail in the following description.

[0009] In contrast to the device of WO 2011004343 A1, the electrolysis device according to the invention is operated such that during operation of the electrolysis device, electrolyte is present in both the anode half-cell and the cathode half-cell of the device. This in turn has a number of advantages described below.

[0010] The electrolysis device according to the invention for producing hydrogen from an aqueous alkaline solution by electrochemical reaction comprises an anode half-cell and a cathode half-cell. The anode half-cell and the cathode half-cell are separated by means of a membrane, and the cathode half-cell can be filled with the alkaline solution. The anode half-cell comprises an anode electrode, and the cathode half-cell comprises a cathode electrode, the anode electrode, the cathode electrode and the membrane forming a membrane electrode unit. In normal operation of the electrolysis device, the initial filling amount of the alkaline solution in the cathode half-cell can only be changed by diffusion processes through the membrane electrode unit and / or by electrochemical reactions of the alkaline solution in the membrane electrode unit.

[0011] In the anode half-cell and in the cathode half-cell, alkaline solutions can be used for the electrolysis process. However, it is conceivable that ultrapure water can also be used in the anode half-cell, in particular with a correspondingly adapted membrane or adapted membrane electrode unit.

[0012] In this description, a membrane is to be understood as a separating, but still electrolytically conductive, partition wall in an electrolysis device, which is essentially an electrochemical cell. Synonymous with a membrane in the broadest sense of electrochemistry, for example, a diaphragm is to be considered. The separation of the half-cells by a membrane allows operation with different concentrations of alkaline solutions or with different liquids or electrolytes in each half-cell.

[0013] Diffusion processes are understood to be all transport processes through a membrane or through a membrane electrode unit, including gas diffusion, water transport mechanisms, gas permeation or diffusion of other decomposition products or products of the electrochemical reactions of the electrolyzer.

[0014] In this sense, the membrane or membrane electrode unit is not considered an active means for generating a flow. Neither is the input of electrical energy at the electrodes and the degassing or production of the products of the electrochemical reaction and the flow caused by the products in the half-cell considered an active means for generating a flow.

[0015] The process of electrolysis forms a mass transport through the membrane on the membrane electrode unit due to diffusion processes, which results as a passive effect of the concentration difference between the anode half-cell and the cathode half-cell of the corresponding solution or liquid or electrolyte in the electrochemical reaction or half-cell and the resulting osmotic pressure.

[0016] Normal operation is to be understood as an operating state in which products, such as molecular hydrogen, are continuously produced by means of an electrochemical reaction. Thus, operating states such as maintenance, flushing, etc. are not to be understood as normal operation.

[0017] The electrolysis device may include a cathode inlet and a cathode outlet, the cathode inlet and the cathode outlet being fluidically coupled to the cathode half-cell. The cathode inlet and the cathode outlet may also be fluidically coupled.

[0018] The cathode loop of the electrolyzer can be initially filled with an alkaline electrolyte or an aqueous alkaline solution and thereby fill the cathode half-cell. In the anode half-cell, the same alkaline solution or alkaline solution can be filled with the same high concentration, a high or low substance concentration or ultrapure water.

[0019] In normal operation of the electrolyzer, water on the cathode side can be decomposed into hydrogen and OH ions and the OH ions can be transported through the membrane to the anode half-cell. Thus, in continued normal operation, the molar concentration of the alkaline solution is increased on the cathode side and a chemical gradient is formed between the electrolyte on the anode side and the electrolyte on the cathode side.

[0020] The transport of OH ions can be ensured from the cathode half-cell to the anode half-cell by means of H2O carrier molecules. Ultrapure water or water molecules are transported from the anode half-cell to the cathode half-cell through the membrane in normal operation by osmosis or after concentration equalization of the system, because the initial filling amount of the electrolyte in the cathode half-cell is not changed by active devices in normal operation. As a result, ultrapure water or water molecules can be provided as a decomposition product for producing molecular hydrogen in the cathode half-cell only via a diffusion process through the membrane. Subsequently, in the normal operation of the electrolysis device, the ultrapure water required for producing hydrogen is supplied only to the anode half-cell.

[0021] In the electrolysis device according to the invention, it is advantageous that in normal operation, in the cathode half-cell there is an increased substance concentration of the electrolyte relative to the anode half-cell, thereby improving the conductivity of the electrolyte in the cathode half-cell and thus improving the efficiency of the electrolysis device. In addition, when the power applied to the electrodes is changed, the electrolysis device automatically adjusts by compensating for the difference in substance concentration between the electrolyte on the anode side and the electrolyte on the cathode side, which then leads to the need for its own regulation of the ultrapure water in the cathode half-cell. As a result, the supply of ultrapure water to the cathode half-cell can be controlled or regulated in a simple and robust manner.

[0022] Another advantage of the electrolysis device according to the invention is that in normal operation, by virtue of the complete filling of the cathode half-cell with alkaline solution, a natural flame barrier for the hydrogen produced during hydrogen electrolysis is present. It is also advantageous that in normal operation the membrane is completely wetted with alkaline solution at all times, so that the membrane is not exposed to the threat of drying out or local overloading due to overheating and thus the service life of the membrane used is improved.

[0023] Furthermore, it may be expedient for the membrane to be designed as an anion exchange membrane.

[0024] In addition, it can be provided that the initial filling amount of the alkaline solution can be contained in the cathode half-cell and in a fluid channel and / or a fluid tank fluidically coupled to the cathode half-cell, thereby defining a holding volume, and for the alkaline solution in the holding volume, during normal operation of the electrolysis device, no forced circulation, forced circulation and / or forced movement can be obtained except for the movement generated by the electrochemical reaction itself.

[0025] In addition to the advantages already mentioned above, the efficiency or the overall efficiency of the electrolyzer is thereby improved, since no additional energy has to be provided. For example, it is conceivable that the cathode inlet and cathode outlet can be fluidically coupled by means of a fluid channel. By producing hydrogen during hydrogen electrolysis, a circulation of alkaline solution through the cathode half-cell can still be formed when the electrolyzer is positioned accordingly without active components. In particular, the thermal load on the membrane is thereby reduced and the efficiency of the electrolyzer is simultaneously improved. Natural circulation can occur during normal operation of the electrolyzer.

[0026] Furthermore, it can be provided that in normal operation of the electrolysis device, no active means are provided for circulating and / or pumping the alkaline solution on the cathode side. In addition to the advantages already mentioned, this improves the efficiency of the electrolysis device in normal operation. This also improves the safety of the electrolysis device in normal operation, since this safety does not depend on active means and possible sources of faults or malfunctions are also minimized.

[0027] An advantageous embodiment is also one according to which it can be provided that the receiving volume is designed without a pump. This in turn minimizes sources of error and improves the efficiency of the electrolysis device.

[0028] According to one development, it is possible for the initial filling quantity of the alkaline solution in the cathode half cell to be dimensioned such that during operation of the electrolysis device the cathode half cell is completely filled with the alkaline solution at any time.

[0029] It is advantageous here that by completely filling the cathode half-cell with alkaline solution during normal operation, a natural flame barrier for the hydrogen produced is present during hydrogen electrolysis. It is also advantageous that during normal operation the membrane is completely wetted with alkaline solution at all times, so that the membrane is not threatened with drying out and is thus not subjected to local stresses due to overheating, and the service life of the membrane used is thus improved.

[0030] Furthermore, it may be suitable that the storage volume is constructed in such a way that during normal operation of the electrolysis device the cathode half-cell of the electrolysis device is completely filled with the alkaline solution at any time, and that the separation device is fluidically coupled to the storage volume so that the alkaline solution is prevented from being discharged from the storage volume when the product gas is removed or separated from the storage volume.

[0031] This makes it possible to keep the alkaline solution in the storage volume provided for this purpose, while the products of the electrochemical reaction can be removed from the cathode half-cell by means of the separator. It is also advantageous that pressure operation of the electrolyzer can be achieved in a simple manner, as long as the separator provides a counterpressure relative to the storage volume. Since the storage volume holds at least a certain minimum amount of alkaline liquid in normal operation, so that the membrane is always wetted with it, the ratio of gas to alkaline liquid in the storage volume is very small, so that the pressure operation of the electrolyzer has improved safety.

[0032] Furthermore, it can be provided that in a steady-state and stable operating state of the electrolyzer, the supply of decomposition products for the electrochemical reaction in the cathode half-cell can be provided exclusively by diffusion processes of the decomposition products through the membrane electrode unit.

[0033] This simplifies the structural design of the electrolyzer, since in normal operation of the electrolyzer, fresh water or ultrapure water must be supplied only via the anode half-cell. This also makes it possible to produce the electrolyzer more economically, in particular if it is provided for pressure operation on the cathode side, since fewer components or pressure-resistant parts are required.

[0034] Furthermore, it can be provided that the cathode electrode and / or the cathode-side surface of the membrane is designed to be hydrophilic. This facilitates the already described diffusion process or the entire sequence of the electrochemical reaction in the electrolyzer, which increases the efficiency and subsequent economy of the electrolyzer.

[0035] According to a particular embodiment, it is possible for the anode electrode and / or the cathode electrode to be formed by applying a catalytically active material to the membrane and / or by applying the catalytically active material to a porous support structure in contact with the membrane.

[0036] In particular, the diffusion or transport processes of decomposition products and products of the electrochemical reaction in the electrolysis device are improved by using porous support materials such as, for example, metal foams or the like.

[0037] According to an advantageous development, it can be provided that the anode electrode and / or the cathode electrode is / are free of noble metals.

[0038] This brings with it the economic advantage that cheaper materials than metals based on precious metals can be used.

[0039] It may be advantageous in particular if ultrapure water or an alkaline solution having a first molar concentration in the range of between 0.1 mol / l and 2 mol / l or in particular between 0.5 mol / l and 1 mol / l can be accommodated in the anode half-cell.

[0040] Furthermore, it can be provided that the lye is a potassium hydroxide lye or a sodium hydroxide lye. Furthermore, it is also conceivable that a solution containing a carbonate (bi) salt is used.

[0041] Furthermore, provision can be made for the alkaline liquid used for the initial filling amount in the cathode half-cell to be an alkaline liquid having a second substance amount concentration, the first substance amount concentration being equal to or higher than the second substance amount concentration.

[0042] As a result, the osmotic pressure between the half-cells also acts during the preparatory operation, when no voltage is applied to the electrodes. As a result, the electrolyzer can be operated for a longer time and with a stable pressure, and the diffusion of products, such as molecular hydrogen, can be at least partially suppressed or can be suppressed more easily during the preparatory operation or when shutting down the electrolyzer.

[0043] A configuration is also advantageous according to which provision can be made for the membrane electrode unit to be able to accommodate a pressure difference between the anode half-cell and the cathode half-cell, which pressure difference is in the range between 0 bar and 100 bar or in particular between 5 bar and 30 bar.

[0044] The advantage here is that it is not necessary to generate the normal pressure of the electrolysis product with another device, since the electrolyzer is already operated under pressure. This is advantageous with regard to the overall efficiency of the electrolyzer when integrated, for example, in a device for producing hydrogen. In conjunction with an electrolyzer according to the invention, in which the half-cell is completely filled with electrolyte, this is advantageous, since the gas volume in the half-cell is particularly small and the electrolyzer can therefore be operated in a fast and dynamic manner.

[0045] According to the invention, an electrolysis cell stack is claimed, comprising a plurality of anode half cells, cathode half cells and membrane electrode units arranged in a row, the anode half cells, the cathode half cells and the membrane electrode units corresponding to the design of the electrolysis device according to the invention that functions in the sense of an electrochemical reaction. The cathode half cells can be fluidically coupled by means of at least one flow channel, the cathode half cells and the at least one flow channel forming a cathode volume, the initial filling amount of the alkaline solution in the cathode volume being changeable only by diffusion processes through the membrane electrode units and / or by electrochemical reactions of one or more decomposition products or alkaline solution in the membrane electrode units during operation of the electrolysis cell stack.

[0046] It is advantageous here that the cathode volume can be provided as a combination of all cathode half-cells of the electrolysis cell stack for accommodating the alkaline solution. This makes it possible to know the instantaneous efficiency of the individual electrolysis devices when they are increased in power to normal operation, especially at high power. This increases the safety during the electrolysis process.

[0047] According to the invention, an electrolysis device is claimed, which comprises a plurality of electrolysis cells stacked according to the invention, the electrolysis device comprising at least one connecting line, by means of which the cathode volume of the electrolysis cell stack can be fluidically coupled, the electrolysis device comprising a gas separation device, which can be fluidically coupled to the cathode volume and is designed to separate products produced by means of an electrochemical reaction from the alkaline solution, the discharge of the alkaline solution from the cathode volume being prevented by means of the gas separation device.

[0048] It is advantageous here that the fluidically coupled cathode volume can be provided as a combination of all cathode half-cells of the electrolysis system for accommodating the alkaline solution. This suppresses transient efficiencies when the electrolysis system is increased to normal operation, especially at high power. This increases safety during the electrolysis process.

[0049] In particular, the use of the electrolysis device according to the invention is advantageous if the product is molecular hydrogen.

[0050] According to the present invention, a method for producing hydrogen by electrochemical reaction of an aqueous alkaline solution is also claimed, the method comprising the following method steps:

[0051] - providing an electrolysis device, the electrolysis device comprising an anode half-cell and a cathode half-cell, the anode half-cell and the cathode half-cell being separated by a membrane and the cathode half-cell being able to be filled with the alkaline solution, and the anode half-cell being able to be filled with an aqueous alkaline solution or with ultrapure water, the anode half-cell comprising an anode electrode and the cathode half-cell comprising a cathode electrode, the anode electrode, the cathode electrode and the membrane constituting a membrane electrode unit;

[0052] - filling the anode half-cell with an aqueous alkaline solution or with ultrapure water and the cathode half-cell with the initial filling amount of the alkaline solution, so that each half-cell is completely filled or the membrane electrode unit is completely immersed in the alkaline solution on the cathode side;

[0053] - applying a voltage between the anode electrode and the cathode electrode;

[0054] It is characterized in that

[0055] During normal operation of the electrolysis device or when a voltage is applied between the anode electrode and the cathode electrode, the initial filling amount of the alkaline solution in the cathode half-cell changes only by diffusion processes through the membrane electrode unit or through the membrane and / or by electrochemical reactions of the alkaline solution in the membrane electrode unit.

[0056] In particular, it can be provided that an anion exchange membrane is used as membrane.

[0057] In addition, it can be provided that the initial filling amount of the alkaline solution is contained in the cathode half-cell and in a fluid channel and / or a fluid tank fluidically coupled to the cathode half-cell, thereby defining a holding volume, and during normal operation of the electrolysis device, the alkaline solution does not obtain forced circulation, forced circulation and / or forced movement in the holding volume, except for the movement generated by the electrochemical reaction itself.

[0058] In addition to the advantages already mentioned above, the efficiency or the overall efficiency of the electrolyzer is thereby improved, since no additional energy has to be provided. For example, it is conceivable that the cathode inlet and cathode outlet can be fluidically coupled by means of a fluid channel. By producing hydrogen during hydrogen electrolysis, a circulation of alkaline solution through the cathode half-cell can still be formed when the electrolyzer is positioned accordingly without active components. In particular, the thermal load on the membrane is thereby reduced and the efficiency of the electrolyzer is simultaneously improved. Natural circulation can occur during normal operation of the electrolyzer.

[0059] According to the invention, an advantageous embodiment can also be provided according to which provision can be made that in normal operation of the electrolysis device no active device is used for generating a cathode-side alkaline solution flow, the membrane electrode unit not comprising said active device.

[0060] In addition to the advantages already mentioned, the efficiency of the electrolysis device in normal operation is thereby improved. The safety of the electrolysis device in normal operation is thereby also improved, since this safety is not dependent on active components and possible sources of error or malfunctions are also minimized.

[0061] The method according to the present invention may also include the following method steps:

[0062] The alkaline solution on the cathode side is dimensioned such that during normal operation of the electrolysis device the cathode half cell is completely filled with the alkaline solution at any time.

[0063] It is advantageous here that by completely filling the cathode half-cell with alkaline solution during normal operation, a natural flame barrier for the hydrogen produced is present during hydrogen electrolysis. It is also advantageous that during normal operation the membrane is completely wetted with alkaline solution at all times, so that the membrane is not threatened with drying out and is thus not subjected to local stresses due to overheating, and the service life of the membrane used is thus improved.

[0064] The method according to the present invention may also include the following method steps:

[0065] An operating liquid is supplied in the anode half-cell, the operating liquid being ultrapure water and / or an aqueous alkaline solution, which operating liquid is supplied only on the anode side during normal operation of the electrolysis device.

[0066] As a result, the number of fittings and lines required for the electrolysis device during normal operation is reduced, which improves the safety and efficiency of the electrolysis device.

[0067] According to one development, it is possible to use an electrode that does not contain precious metals as an anode electrode and / or to use an electrode that does not contain precious metals as a cathode electrode.

[0068] This brings with it the economic advantage that cheaper materials than metals based on precious metals can be used.

[0069] Furthermore, it may be expedient to accommodate ultrapure water or an alkaline solution having a first molar concentration in the range of between 0.1 mol / l and 2 mol / l or in particular between 0.5 mol / l and 1 mol / l in the anode half-cell.

[0070] Furthermore, provision can be made for an alkaline liquid having a second substance amount concentration, which is equal to or higher than the second substance amount concentration, to be used as the alkaline liquid for the initial filling amount in the cathode half-cell.

[0071] As a result, the osmotic pressure between the half-cells also acts during the preparatory operation, when no voltage is applied to the electrodes. As a result, the electrolyzer can be operated for a longer time and with a stable pressure, and the diffusion of products, such as molecular hydrogen, can be at least partially suppressed or can be suppressed more easily during the preparatory operation or when shutting down the electrolyzer.

[0072] It can be advantageous in particular to use potassium hydroxide solution or sodium hydroxide solution as the alkali solution.

[0073] For a better understanding of the method according to the invention, an exemplary and detailed description of possibly performed process steps of the method according to the invention or of possibly performed process steps in the electrolysis device is provided below.

[0074] Initial filling of the cathode half-cell: The cathode half-cell and any connecting lines or fluid channels or fluid tanks (referred to as cathode volumes in the further text) are filled with a defined amount of alkaline solution.

[0075] Filling and positioning of the cathode volume: Any fluid channels, fluid tanks or connecting lines of the cathode volume are mostly located above the maximum filling level of the corresponding cathode half-cell. This ensures complete wetting of the membrane on the cathode side even at the minimum filling level.

[0076] Inerting the cathode half-cell: flushing the remaining air from the remaining cathode volume with nitrogen and sealing the cathode volume, which can optionally be done with the aid of a separator or gas separator, ensures that no explosive atmosphere can form in the cathode volume.

[0077] Initial anode state: An alkaline electrolyte or an alkaline solution having a first molar concentration is initially present in the anode half-cell, which corresponds to the second molar concentration of the electrolyte in the cathode half-cell. It is also conceivable that the anode half-cell can be operated with ultrapure water.

[0078] Start the electrolysis: By applying an electric current to the electrolysis device or to the electrodes of the electrolysis device, the decomposed water H2O from the cathode half-cell is initially decomposed into H+ and OH- ions. Molecular hydrogen H2 is separated in a gaseous state in the cathode half-cell, while the OH- ions diffuse through the membrane into the anode half-cell. The hydrophilic membrane used is conductive only for OH- anions and impermeable for cations. The membrane can also be called anion exchange membrane.

[0079] Initial dilution of the electrolyte in the anode half-cell: In the anode half-cell, a portion of O2 and a portion of 1 / 2 of H2O are formed from the OH- ions supplied. The starting substances are separated from the anode half-cell in a gaseous state, while the H2O reduces the substance concentration of the electrolyte or in the anode half-cell. The electrolyte in the anode half-cell is thus diluted.

[0080] Gas separation and electrolyte flow in the cathode half-cell: The molecular hydrogen installed in the cathode half-cell rises due to its low density through the outgoing connecting line or flow line at the highest point of the half-cell in the cathode volume and collects at the highest point or can separate there, while the alkaline solution or the KOH entrained along separates due to gravity, remains in the cathode volume and can flow back into the half-cell at the lowest point. In this way, a natural flow or natural circulation can be formed.

[0081] Separation of gases and pressure differences from the cathode half-cell: The discharge of product gas from the system takes place at the highest point of the cathode volume. The discharge of alkaline solution from the cathode volume is prevented by means of a structural design or by means of a separation device or a gas separation device. The hydrogen or the entire cathode volume can be kept under pressure by means of an external pressure-maintaining device. A non-return valve in the gas line can prevent a high external system pressure from entering the cathode volume when starting up the electrolysis device.

[0082] Increase of osmotic pressure: During operation, the molar concentration of the alkaline electrolyte in the cathode half-cell is continuously increased by the conversion of decomposed water, while in the anode half-cell, the molar concentration is reduced or the electrolyte in the anode half-cell is diluted by the input of H2O. A molar concentration gradient is generated between the two half-cells, thereby forming an osmotic pressure, which facilitates the transport of water from the anode half-cell to the cathode half-cell through the membrane.

[0083] Reaching equilibrium: If the mass transport due to the osmotic pressure is exactly as great as the consumption of decomposed water in the cathode half-cell, only a relatively large amount of fresh water is used for the decomposition into H+ and OH- ions, which is transported from the anode half-cell to the cathode half-cell through the hydrophilic membrane. From this point on, the filling amount or filling level of the electrolyte in the cathode half-cell or the concentration in the cathode volume remains constant.

[0084] · Equilibrium state under pressure difference: If molecular hydrogen H2 is kept under pressure in the cathode half-cell, the pressure gradient between the cathode half-cell and the anode half-cell inhibits mass transport due to osmotic pressure and the equilibrium state only occurs when the substance concentration of the electrolyte in the cathode half-cell is high and therefore the filling level or filling amount of the electrolyte or alkaline solution in the cathode volume is low.

[0085] Increased concentration in the anode half-cell: From the moment this equilibrium state is reached, only decomposed water from the anode half-cell is used for electrolysis, whereby the mole concentration in the anode half-cell begins to rise or the filling level or filling amount of the electrolyte in the anode half-cell begins to fall. The mole concentration gradient falls in order to also reduce the osmotic pressure, which leads to further consumption of decomposed water from the cathode half-cell and thus a further increase in the mole concentration of the electrolyte or alkaline solution in the cathode half-cell.

[0086] Controlling the electrolyte concentration in the anode half-cell: In order to avoid an inadmissible increase in the amount of substance concentration, fresh water is supplied to the anode half-cell and the amount of substance concentration of the electrolyte in the anode half-cell is thereby kept constantly at a low level. This level is independent of the current applied to the electrodes and the prevailing pressure in the cathode half-cell.

[0087] Self-regulating system: In contrast to known systems, the mass concentration differences and mass differences between the anode half-cell and the cathode half-cell are not compensated by means of pumps or pipes, but are instead brought about in a targeted manner. By deliberately regulating the electrolyte concentration or mass concentration of the electrolyte in the anode half-cell, a defined liquid level or fill or electrolyte concentration is generated in the cathode half-cell as a function of the applied electrical power and the prevailing differential pressure between the anode half-cell and the cathode half-cell. By containing and circulating the liquid electrolyte in the cathode volume in combination with a controlled supply of fresh water to the anode half-cell, the system is virtually self-regulating or self-stabilizing.

[0088] Shutting down the system: If the applied current is canceled, no further decomposed water is consumed in the cathode half-cell. Due to the osmotic pressure caused by the concentration gradient mass and the vertical water transport from the anode half-cell to the cathode half-cell, the filling level in the cathode volume increases rapidly again and the mass concentration of the liquid electrolyte decreases. Since the anode half-cell is always replenished with fresh water and the mass concentration in the anode half-cell is kept constant, a mass concentration equilibrium is generated between the anode half-cell and the cathode half-cell within the scope of the initial state. The filling level or filling amount in the cathode volume then also corresponds to the initial filling amount to the greatest extent.

[0089] Maintenance and service: At regular maintenance intervals, the alkaline liquid in the cathode volume is replaced. To this end, all the liquid is drained at the lowest point and the cathode volume is then refilled. In contrast, in the electrolysis device according to the invention, the alkaline liquid in the anode half-cell is centrally processed or replaced. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] In order to better understand the present invention, the present invention is explained in detail with reference to the following drawings.

[0091] Respectively in a strongly simplified schematic:

[0092] Figure 1 An electrolysis device having an anode half-cell and a cathode half-cell is shown;

[0093] Figure 2 An electrolysis cell stack comprising a plurality of electrolysis devices is shown;

[0094] Figure 3 An electrolysis apparatus comprising a stack of multiple electrolysis cells is shown. DETAILED DESCRIPTION

[0095] First of all, it should be pointed out that in the different described embodiments, the same parts are provided with the same reference numerals or the same component names, and the disclosure contained in the entire description can be transferred to the same parts with the same reference numerals or the same component names. The selected positional descriptions in the description, such as top, bottom, sideways, etc., also refer to the directly described and shown figures and these positional descriptions are transferred to the new positions in the case of a change in position.

[0096] Figure 1 An electrolysis device 1 having an anode half-cell 2 and a cathode half-cell 3 is shown in a greatly simplified schematic diagram. The cathode half-cell 3 and the anode half-cell 2 are separated from each other by means of a membrane 4. The anode half-cell 2 comprises an anode electrode 5, which can be arranged in a manner connected to the anode side surface of the membrane 4. The cathode half-cell 3 comprises a cathode electrode 6, which can be arranged in a manner connected to the cathode side surface of the membrane 4. The anode electrode 5, the cathode electrode 6 and the membrane 4 together form a membrane electrode unit 7, which can also include other elements. The anode half-cell 3 is separated from the cathode half-cell 2 by means of a membrane 4, which can be configured as an anion exchange membrane. The anode electrode 5 and the cathode electrode 5 can be composed of a porous metal conductor, such as, for example, a metal foam, or can be directly applied to the membrane 4.

[0097] During operation of the electrolysis device 1, the anode half-cell 2 can be filled with an aqueous alkaline solution or ultrapure water. During operation of the electrolysis device 1, the cathode half-cell 3 can be filled with an aqueous alkaline solution. In order to enable operation of the electrolysis device 1, the cathode half-cell 3 is filled with an initial filling amount of the alkaline solution. During continuous normal operation of the electrolysis device 1, that is to say, for example, except for maintenance, flushing, etc., no other alkaline solution is actively supplied to the cathode half-cell 3 or discharged from it. During normal operation of the electrolysis device 1, the initial filling amount of the alkaline solution in the cathode half-cell 3 can only be changed by diffusion processes through the membrane electrode unit 7 or the membrane 4 and / or by electrochemical reactions of the alkaline solution in the membrane electrode unit 7.

[0098] An alkaline solution can be used for the electrolytic process in the anode half cell 2 and in the cathode half cell 3. However, it is conceivable to also use ultrapure water in the anode half cell 2, in particular with a correspondingly adapted membrane 4 or membrane electrode unit 7.

[0099] In the present description, membrane 4 is to be understood as a separating, but still electrolytically conductive, partition wall in electrolysis device 1, which is essentially an electrochemical cell. Synonymously, membrane 4 is to be considered in the broadest sense of electrochemistry, for example, as a diaphragm. The separation of half cells 2, 3 by membrane 4 allows operation with different concentrations of alkaline solutions or with different liquids or electrolytes in each half cell 2, 3.

[0100] The membrane 4 can be designed so robustly that a differential pressure in the range of 0 bar to 100 bar can be applied between the anode half cell 2 and the cathode half cell 3. In particular, the absorption of this pressure difference is facilitated by filling the two half cells 2, 3 with an electrolyte or ultrapure water or an alkaline solution. In conjunction with this, the safety of the electrolysis device 1 is improved by filling the two half cells 2, 3, since a flame barrier is formed by means of the filling when producing products that are flammable in a free atmosphere.

[0101] In this case, diffusion processes are understood to be all transport processes through the membrane 4 or through the membrane electrode unit 7 , including gas diffusion, water transport mechanisms, gas permeation or diffusion of other decomposition products or products of the electrochemical reaction of the electrolysis device 1 .

[0102] In this sense, the membrane 4 or the membrane electrode unit 7 is not considered an active means for generating a flow. The input of electrical energy at the electrodes 5, 6 and the degassing or production of the products of the electrochemical reaction and the flow caused by the products in the half-cells 2, 3 are also not considered active means for generating a flow.

[0103] By the process of electrolysis, a mass transport occurs through the membrane 4 on the membrane electrode unit 7 due to diffusion processes, which results as a passive effect of the electrochemical reaction or the concentration difference between the anode half cell 2 and the cathode half cell 3 of the corresponding solutions or liquids in the half cells 2, 3 and the resulting osmotic pressure.

[0104] The electrolysis device 1 is made operationally ready by filling the two half cells 2, 3 with an electrolyte or an alkaline solution or ultrapure water. The initial filling amount of the alkaline solution can be accommodated in the cathode half cell 3 and in the fluid channel 8 and / or the fluid tank which can be fluidically coupled to the cathode half cell 3. As a result, a storage volume 9 is defined, which can be filled with the initial filling amount. The initial filling amount of the alkaline solution in the storage volume 9 is determined in such a way that the membrane electrode unit 7 can be wetted with alkaline liquid at any time on the cathode side during normal operation of the electrolysis device 1.

[0105] Here, normal operation is to be understood as an operating state in which products, such as molecular hydrogen, are continuously produced by means of an electrochemical reaction. Thus, operating states such as maintenance, flushing, etc. are not to be understood as normal operation.

[0106] In the continuous normal operation of the electrolysis device 1, the amount of alkaline liquid in the storage volume 9 does not obtain circulation, forced circulation and / or forced movement introduced by active devices. The amount of alkaline liquid in the storage volume 9 can only obtain a passively induced flow, which can be formed by the electrochemical reaction and / or the diffusion process described above and / or by the degassing of the products of the electrochemical reaction. During normal operation, no active device for generating flow is provided in the device or element constituting the storage volume 9. However, it should not be excluded that such active devices, such as pumps, can be provided for other operating states.

[0107] Furthermore, a separation device 10 can be provided, which can be fluidically coupled to the fluid channel 8 . By means of the separation device 10 , it can be ensured that the products or product gases formed during the electrolysis can be discharged without the alkaline solution being discharged from the receiving volume 9 .

[0108] During normal operation of the electrolysis device 1, the initial filling amount of the alkaline liquid in the storage volume 9 can be changed by diffusion processes and the electrochemical reactions that are taking place. In normal operation of the electrolysis device 1, at least no further alkaline liquid is supplied from the outside to the storage volume 9. However, in a steady-state and stable operating state, which can also be understood as normal operation, the decomposition products for the electrochemical reaction are provided at least partially by diffusion processes through the membrane electrode unit 7.

[0109] This results in the necessity to supply ultrapure water on the side of the anode half-cell 2 during hydrogen electrolysis, at least from a certain operating duration of the electrolyzer 1. The diffusion process can be further facilitated by the cathode electrode 6 and / or the cathode-side surface of the membrane 4 being designed to be hydrophilic. Furthermore, the electrodes 5, 6 can be produced by applying a catalytically active material to the membrane 4. It is also conceivable that the electrodes 5, 6 are produced by applying a catalytic material to a porous support structure, such as, for example, a metal foam. The electrodes 5, 6 can be designed to be free of precious metals in any case.

[0110] The liquid in the anode half cell 2 during operation can be ultrapure water as described above or an alkaline solution with a first substance concentration in the range between 0.1 mol / l and 2 mol / l. Sodium hydroxide solution, potassium hydroxide solution or other alkaline solutions with similar electrochemical properties can be used as alkaline solution. The alkaline solution in the cathode half cell 3 during operation of the electrolysis device 1 can be an alkaline solution with a second substance concentration. The first substance concentration can be equal to or higher than the second substance concentration.

[0111] exist Figure 2 1 shows an electrolytic cell stack 11 comprising a plurality of electrolytic devices 1, and the same components are used as in the previous Figure 1 In order to avoid unnecessary repetition, refer to or refer to the previous Figure 1 Detailed description in .

[0112] The electrolysis cell stack 11 can include a plurality of anode half cells 2, cathode half cells 3 and membrane electrode units 7 arranged in a row. The arrangement of the individual unit components, for example in the form of plates, can be in an alternating sequence, which must at least ensure the functional design of the respective electrolysis device 1 in the composite structure in the electrolysis cell stack 11. The cathode half cells 3 of the electrolysis cell stack 11 can be fluidically coupled by means of at least one flow channel 12. The cathode half cells 3 and the at least one flow channel 12 that can be fluidically coupled in this way define a cathode volume 13. It can also be provided that the at least one flow channel 12 can be fluidically coupled to another pipeline or tank. The cathode volume 13 can be enlarged in this way in order to ensure optimal operational management of the electrolysis cell stack, since the alkaline solution should in any case completely wet the corresponding membrane 4 of the cathode half cell 3 in normal operation.

[0113] Analogously to the electrolysis device 1 , the initial filling level of the alkaline solution in the cathode volume 13 can only be changed by diffusion processes through the membrane electrode unit 7 and / or by electrochemical reactions of one or more decomposition products or of the alkaline solution in the membrane electrode unit 7 .

[0114] exist Figure 3The electrolysis device 14 is shown in FIG. 1 and includes a plurality of electrolysis cell stacks 11, the same components being used as in the previous Figure 1 and Figure 2 In order to avoid unnecessary repetition, refer to or refer to the previous Figure 1 and Figure 2 Detailed description in .

[0115] The electrolysis device 14 can include a plurality of electrolysis cell stacks 11, and the respective cathode volumes 13 of the individual electrolysis cell stacks 11 can be fluidically coupled by means of connecting lines 16. Furthermore, the cathode volumes 13 can be coupled to a gas separation device 15. The gas separation device 15 can be configured to discharge product gases of the electrolysis, such as, for example, gaseous molecular hydrogen, without discharging alkaline solution in the cathode volume 13.

[0116] Furthermore, the cathode volume 13 of the electrolysis cell stack 11 can be fluidically coupled to the tank. Similar to the electrolysis device 1, at least it is applicable that the initial filling amount of the cathode volume 13 with alkaline solution can only be changed by diffusion processes through the membrane electrode unit 7 and / or by one or more decomposition products or electrochemical reactions of the alkaline solution in the membrane electrode unit 7.

[0117] The various embodiments illustrate possible implementation schemes. It should be noted that the present invention is not limited to the particularly illustrated implementation schemes. On the contrary, different combinations of various implementation variants are possible and such variation possibilities are within the capabilities of those skilled in the art based on the teaching of the technical means through the specific present invention.

[0118] The scope of protection is determined by the claims. However, the description and the drawings are to be taken into account for the interpretation of the claims. Individual features or combinations of features in the various exemplary embodiments shown and described can themselves be independent inventive solutions. Tasks based on independent inventive solutions can be derived from the description.

[0119] All descriptions of numerical ranges in a specific specification should be understood as including any and all sub-ranges resulting therefrom, for example, the description 1 to 10 should be understood as including all sub-ranges starting from a lower limit of 1 and an upper limit of 10, that is, all sub-ranges starting with a lower limit of 1 or greater and ending with an upper limit of 10 or less, for example 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0120] Finally, it should be pointed out that, in order to facilitate a better understanding of the construction, some elements are shown not to scale and / or enlarged and / or reduced in size.

[0121] Reference numerals

[0122] 1 Electrolysis device

[0123] 2 Anode half-cell

[0124] 3 Cathode half-cell

[0125] 4 Membrane

[0126] 5 Anode electrode

[0127] 6 Cathode Electrode

[0128] 7 Membrane Electrode Unit

[0129] 8 Fluid channels

[0130] 9. Accommodation capacity

[0131] 10 Separation device

[0132] 11 Electrolytic Cell Stacks

[0133] 12 flow channels

[0134] 13 Cathode volume

[0135] 14Electrolysis equipment

[0136] 15Gas separation device

[0137] 16Connect the pipeline.

Claims

1. An electrolysis device (1) for producing hydrogen from an aqueous alkaline solution by electrochemical reaction, The electrolysis device (1) comprises an anode half-cell (2) and a cathode half-cell (3), the anode half-cell (2) and the cathode half-cell (3) are separated by means of a membrane (4), and the cathode half-cell (3) can be filled with the alkaline solution, - and the anode half-cell (2) comprises an anode electrode (5), and the cathode half-cell (3) comprises a cathode electrode (6), ---The anode electrode (5), the cathode electrode (6) and the membrane (4) constitute a membrane electrode unit (7), It is characterized in that During normal operation of the electrolysis device (1), the initial filling amount of the alkaline solution in the cathode half-cell (3) can only be changed by diffusion processes through the membrane electrode unit (7) and / or by electrochemical reactions of the alkaline solution in the membrane electrode unit (7).

2. The electrolysis device (1) according to claim 1, characterized in that The membrane (4) is designed as an anion exchange membrane.

3. The electrolysis device (1) according to any one of the preceding claims, characterized in that An initial filling amount of the alkaline solution can be contained in the cathode half-cell (3) and in a fluid channel (8) and / or a fluid tank that can be fluidically coupled to the cathode half-cell (3), thereby defining a holding volume (9), and for the alkaline solution in the holding volume (9), during normal operation of the electrolysis device (1), no forced circulation, forced circulation and / or forced movement can be obtained except for the movement generated by the electrochemical reaction itself.

4. The electrolysis device (1) according to claim 3, characterized in that In normal operation of the electrolysis device (1), no active means are provided for circulating and / or pumping the alkaline solution on the cathode side.

5. The electrolysis device (1) according to claim 3, characterized in that The fluid channel (8) is designed to be pumpless.

6. The electrolysis device (1) according to any one of the preceding claims, characterized in that The initial filling amount of the alkaline solution in the cathode half-cell (3) is determined such that during operation of the electrolysis device (1), the cathode half-cell (3) is completely filled with the alkaline solution at any time.

7. The electrolysis device (1) according to claim 3, characterized in that The storage volume (9) is designed so that during normal operation of the electrolysis device (1), the cathode half-cell (3) of the electrolysis device (1) is completely filled with the alkaline solution at any time, and the separation device (10) can be fluidically coupled to the fluid channel (8) so that the alkaline solution can be prevented from being discharged from the storage volume (9) when the product gas is removed or separated from the storage volume (9).

8. The electrolysis device (1) according to any one of the preceding claims, characterized in that In the steady-state and stable operating state of the electrolysis device (1), the supply of decomposition products for the electrochemical reaction in the cathode half-cell (3) can be provided solely by diffusion processes of the reactants through the membrane electrode unit (7).

9. The electrolysis device (1) according to any one of the preceding claims, characterized in that The cathode electrode (6) and / or the cathode-side surface of the membrane (4) are configured to be hydrophilic.

10. The electrolysis device (1) according to claim 9, characterized in that The anode electrode (5) and / or the cathode electrode (6) are formed by applying a catalytically active material to the membrane (4) and / or by applying a catalytically active material to a porous support structure in contact with the membrane (4).

11. The electrolysis device (1) according to any one of the preceding claims, characterized in that The anode electrode (5) and / or the cathode electrode (6) are free of noble metals.

12. The electrolysis device (1) according to any one of the preceding claims, characterized in that Ultrapure water or an alkaline solution having a first molar concentration in the range between 0.1 mol / 1 and 2 mol / 1 or in particular between 0.5 mol / 1 and 1 mol / 1 can be accommodated in the anode half-cell (2).

13. The electrolysis device (1) according to claim 12, characterized in that The alkaline liquid used for the initial filling amount in the cathode half-cell (3) is an alkaline liquid having a second substance amount concentration, wherein the first substance amount concentration is equal to or higher than the second substance amount concentration.

14. The electrolysis device (1) according to claim 12 or 13, characterized in that The alkali solution is potassium hydroxide alkali solution or sodium hydroxide alkali solution.

15. The electrolysis device (1) according to any one of the preceding claims, characterized in that The membrane electrode unit (7) can accommodate a pressure difference between the anode half-cell (2) and the cathode half-cell (3), which pressure difference is between 0 bar and 100 bar or in particular in the range between 5 bar and 30 bar.

16. An electrolysis cell stack (11), comprising a plurality of anode half cells (2), cathode half cells (3) and membrane electrode units (7) arranged in a row, wherein the anode half cells, the cathode half cells and the membrane electrode units correspond to a design scheme of the electrolysis device (1) according to any one of the preceding claims that functions within the meaning of an electrochemical reaction, characterized in that: The cathode half-cell (3) can be fluidically coupled by means of at least one flow channel (12), the cathode half-cell (3) and the at least one flow channel (12) forming a cathode volume (13), and during operation of the electrolytic cell stack (11), the initial filling amount of the alkaline solution in the cathode volume (13) can only be changed by diffusion processes through the membrane electrode unit (7) and / or by electrochemical reactions of one or more decomposition products or alkaline solutions in the membrane electrode unit (7).

17. An electrolysis device (14) comprising a plurality of electrolysis cells stacked (11) according to claim 16, characterized in that: The electrolysis device (14) comprises at least one connecting pipe (16) or connecting channel, and the cathode volume (13) of the electrolysis cell stack (11) can be fluidically coupled by means of the connecting pipe (16). The electrolysis device (14) comprises a gas separation device (15), which can be fluidically coupled to the cathode volume (13) and is configured to separate the product produced by means of the electrochemical reaction from the alkaline solution. The discharge of the alkaline solution from the cathode volume (13) can be prevented by means of the gas separation device (15).

18. The electrolysis device (14) according to claim 17, characterized in that The product is molecular hydrogen.

19. A method for producing hydrogen from an aqueous alkaline solution by electrochemical reaction, the method comprising the following method steps: - providing an electrolysis device (1), the electrolysis device (1) comprising an anode half-cell (2) and a cathode half-cell (3), the anode half-cell (2) and the cathode half-cell (3) being separated by means of a membrane (4), and the cathode half-cell (3) being able to be filled with the alkaline solution, the anode half-cell (2) comprising an anode (5), and the cathode half-cell (3) comprising a cathode electrode (6), the anode electrode (5), the cathode electrode (6) and the membrane (4) constituting a membrane electrode unit (7); - filling the anode half-cell (2) and the cathode half-cell (3) with an initial filling amount of alkaline solution, so that each half-cell (2, 3) is completely filled or the membrane electrode unit (7) is completely immersed in the alkaline solution on the cathode side; - applying a voltage between the anode electrode (5) and the cathode electrode (6); It is characterized in that During normal operation of the electrolysis device (1) or when a voltage is applied between the anode electrode (5) and the cathode electrode (6), the initial filling amount of the alkaline solution in the cathode half-cell (3) is changed only by diffusion processes through the membrane electrode unit (or through the membrane) (4) and / or by electrochemical reactions of the alkaline solution in the membrane electrode unit (7).

20. The method according to claim 19, characterized in that An anion exchange membrane was used as membrane (4).

21. The method according to claim 19 or 20, characterized in that An initial filling amount of the alkaline solution is contained in the cathode half-cell (3) and in a fluid channel (8) and / or a fluid tank fluidically coupled to the cathode half-cell (3), thereby defining a containing volume (9). During normal operation of the electrolysis device (1), the alkaline solution does not obtain forced circulation, forced circulation and / or forced movement in the containing volume (9) except for the movement generated by the electrochemical reaction itself.

22. The method according to any one of claims 19 to 21, characterized in that In normal operation of the electrolysis device (1), no active device is used to generate a flow of alkaline solution on the cathode side, and the membrane electrode unit (7) does not include such active device.

23. The method according to any one of claims 19 to 22, further comprising the following method steps: The alkaline solution on the cathode side is dimensioned in such a way that, during normal operation of the electrolysis device (1), the cathode half cell (3) is completely filled with the alkaline solution at any time.

24. The method according to any one of claims 19 to 23, further comprising the following method steps: An operating liquid is supplied to the anode half-cell (2), the operating liquid being ultrapure water and / or an aqueous alkaline solution, and in normal operation of the electrolysis device (1) the operating liquid is supplied only on the anode side.

25. The method according to any one of claims 19 to 24, characterized in that An electrode free of noble metals is used as the anode electrode (5) and / or an electrode free of noble metals is used as the cathode electrode (6).

26. The method according to any one of claims 19 to 25, characterized in that Ultrapure water or an alkaline solution having a first molar concentration in the range between 0.1 mol / 1 and 2 mol / 1 or in particular between 0.5 mol / 1 and 1 mol / 1 is contained in the anode half-cell (2).

27. The method according to claim 26, characterized in that An alkaline liquid having a second substance amount concentration, which is equal to or higher than the second substance amount concentration, is used as an alkaline liquid for an initial filling amount in the cathode half-cell (3).

28. The method according to claim 26 or 27, characterized in that Potassium hydroxide lye or sodium hydroxide lye is used as the lye.

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