Electrolysis device with natural circulation

Abstract

The invention relates to an electrolysis device (1) for producing hydrogen through electrochemical reaction from an aqueous alkali solution, wherein the electrolysis device (1) comprises an anodic half cell (2) and a cathodic half cell (3). The anodic half cell (2) and the cathodic half cell (3) are separated by means of a membrane (4) and the alkali solution can flow through the cathodic half cell (3). The anodic half cell (2) comprises an anodic electrode (5) and the cathodic half cell (3) comprises a cathodic electrode (6), wherein the anodic electrode (5), the cathodic electrode (6) and the membrane (4) form a membrane-electrode unit (7). Furthermore, in normal operation of the electrolysis device, an initial fill quantity of alkali solution in the cathodic half cell (3) can be changed only by diffusion processes through the membrane-electrode unit (7) and / or by electrochemical reaction of the alkali solution in the membrane-electrode unit (7).

Description

[0001] ELECTROLYSIS DEVICE WITH NATURAL CIRCULATION

[0002] The invention relates to an electrolysis device for producing hydrogen by electrochemical reaction from an aqueous, alkaline solution.

[0003] EP3831986A1 describes a gas generation device comprising an electrolysis vessel including an anode chamber, a cathode chamber, and an ion-permeable separation membrane separating the anode chamber and the cathode chamber. The anode chamber accommodates an anode and generates oxygen gas, and the cathode chamber accommodates a cathode and generates hydrogen gas. The gas generation device further comprises a first electrolyte circulation system, a second electrolyte circulation system, and an electrolyte exchanger. The first electrolyte circulation system comprises a first circulation tank that receives and stores a first electrolyte flowing out of the anode chamber, and a first circulation pump that supplies the first electrolyte stored in the first circulation tank to the anode chamber.The second electrolyte circulation system comprises a second circulation tank that receives and stores a second electrolyte flowing from the cathode chamber; and a second circulation pump that supplies the second electrolyte stored in the second circulation tank to the cathode chamber. The electrolyte exchanger transfers, on the one hand, a portion of the first electrolyte present in the first electrolyte circuit to the second electrolyte circuit, and, on the other hand, a portion of the second electrolyte present in the second electrolyte circuit to the first electrolyte circuit.

[0004] Furthermore, W02011004343A1 describes a device for the electrolytic production of hydrogen from an alkaline, aqueous solution, starting from the dry cathode, the device comprising:

[0005] - two half-cells, one anodic and one cathodic, separated by an anion exchange membrane, the surface of which in contact with the cathodic half-cell is a membrane electrode assembly (MEA), and

[0006] - where the alkaline solution is only present in the anodic half-cell.

[0007] The object of the present invention was to overcome the disadvantages of the prior art and to provide a device and a method by means of which particularly advantageous effects with regard to the operational reliability and effectiveness of the device are achieved. This object is achieved by a device and a method according to the claims.

[0008] In contrast to the gas generation device disclosed in EP3831986A1, the electrolysis device according to the invention can be operated without active means for flow generation or circulation. This has several advantages and, in particular, surprising effects, which are explained in more detail in the following introduction to the description.

[0009] In contrast to the device of WO2011004343A1, the electrolysis device according to the invention is operated in such a way that, during operation of the electrolysis device, an electrolyte is present in both the anodic half-cell and the cathodic half-cell of the device. This, in turn, has several advantages, which are described below.

[0010] The electrolysis device according to the invention for producing hydrogen by electrochemical reaction from an aqueous, alkaline solution comprises an anodic half-cell and a cathodic half-cell. The anodic half-cell and the cathodic half-cell are separated by a membrane, and the cathodic half-cell can be flooded with the alkaline solution. The anodic half-cell comprises an anodic electrode, and the cathodic half-cell comprises a cathodic electrode, whereby the anodic electrode, the cathodic electrode, and the membrane form a membrane-electrode unit. During normal operation of the electrolysis device, an initial fill quantity of alkaline solution in the cathodic half-cell can be changed exclusively by diffusion processes through the membrane-electrode unit and / or by electrochemical reaction of the alkaline solution in the membrane-electrode unit.

[0011] In the anodic half-cell, as in the cathodic half-cell, an alkaline solution can be used for the electrolysis process. However, it is conceivable that ultrapure water could also be used in the anodic half-cell, especially with an appropriately adapted membrane or membrane-electrode assembly.

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

[0013] Diffusion processes are understood to mean all transport processes through the membrane or through the membrane-electrode assembly, which include gas diffusion, water transport mechanisms, gas permeation or the diffusion of other reactants or products of the electrochemical reaction of the electrolysis device.

[0014] In this sense, the membrane or membrane-electrode assembly is not considered an active means of flow generation. The introduction of electrical energy at the electrodes, the outgassing or production of products of the electrochemical reaction, and the flow induced by these products in the half-cells are also not considered active means of flow generation.

[0015] The process of electrolysis results in a mass transport through the membrane of the membrane electrode assembly due to diffusion processes, which mass transport results as a passive effect of the electrochemical reaction or the concentration difference between the anodic half-cell and the cathodic half-cell of the respective solutions or liquids or electrolytes in the half-cells and a resulting osmotic pressure.

[0016] Normal operation refers to an operating condition in which a product such as molecular hydrogen is continuously produced by means of an electrochemical reaction. Thus, operating conditions such as maintenance, purging, and the like are not considered normal operation.

[0017] The electrolysis device can comprise a cathode inlet and a cathode outlet, wherein the cathode inlet and the cathode outlet can be fluidically coupled to the cathodic half-cell. The cathode inlet and the cathode outlet can also be fluidically coupled.

[0018] The cathode circuit of the electrolysis device can initially be filled with an alkaline electrolyte or an aqueous alkaline solution, thereby flooding the cathodic half-cell. The anodic half-cell can be filled with the same alkaline solution or an alkaline solution with the same, higher, or lower molar concentration, or with ultrapure water.

[0019] During normal operation of the electrolysis device, water on the cathode side can be split into hydrogen and OH ions, and the OH ions can be transported through the membrane into the anodic half-cell. This increases the molar concentration of the alkaline solution on the cathode side during normal operation, creating a chemical gradient between the anode and cathode electrolytes.

[0020] The transport of OH ions from the cathodic half-cell to the anodic half-cell can be ensured by H2O carrier molecules. Through osmosis or the effort to achieve concentration equilibrium in the system, since the initial electrolyte fill level in the cathodic half-cell is not changed by active agents during normal operation, ultrapure water or water molecules are transported through the membrane from the anodic half-cell to the cathodic half-cell during normal operation. Thus, ultrapure water or water molecules can be provided as a reactant for the production of molecular hydrogen in the cathodic half-cell exclusively through diffusion processes through the membrane. Subsequently, during normal operation of the electrolysis device, the ultrapure water required for the production of hydrogen is supplied exclusively to the anodic half-cell.

[0021] An advantage of the electrolysis device according to the invention is that, during normal operation, the electrolyte concentration in the cathodic half-cell is higher than in the anodic half-cell, thereby improving the conductivity of the electrolyte in the cathodic half-cell and thus the efficiency of the electrolysis device. Furthermore, when the power applied to the electrodes changes, the electrolysis device automatically regulates itself by adjusting the difference in the molar concentration between the anode-side electrolyte and the cathode-side electrolyte, which subsequently results in a self-regulating demand for ultrapure water in the cathodic half-cell. This allows the supply of ultrapure water to the cathodic half-cell to be controlled and regulated in a simple and robust manner.

[0022] A further advantage of the electrolysis device according to the invention is that, by completely filling the cathodic half-cells with the alkaline solution during normal operation, a natural flame barrier is provided for the hydrogen produced during hydrogen electrolysis. Another advantage is that the membrane is completely wetted with the alkaline solution at all times during normal operation, so that the membrane is not exposed to the risk of drying out or local overload due to overheating, thus improving the service life of the membrane used.

[0023] Furthermore, it may be advantageous if the membrane is designed as an anion exchange membrane.

[0024] Furthermore, it can be provided that the initial filling quantity of alkaline solution can be accommodated in the cathodic half-cell and in a fluid channel and / or fluid tank fluidically coupled to the cathodic half-cell, whereby a receiving volume is defined, wherein for the alkaline solution in the receiving volume during normal operation of the electrolysis device, no forced circulation, no forced circulation and / or no forced movement can be experienced, except for the movement which is self-established by the electrochemical reaction.

[0025] In addition to the advantages already mentioned, the effectiveness and overall efficiency of the electrolysis device is improved because no additional energy needs to be provided. For example, it is conceivable that the cathode inlet and the cathode outlet can be fluidically coupled using the fluid channel. By producing hydrogen during hydrogen electrolysis, a circulation of the alkaline solution through the cathodic half-cell can be created without the need for active agents if the electrolysis device is positioned accordingly. This reduces the thermal stress on the membrane in particular and simultaneously improves the efficiency of the electrolysis device. Natural circulation can occur during normal operation of the electrolysis device.

[0026] Furthermore, it can be provided that no means for circulating and / or pumping the cathode-side alkaline solution, which are active during normal operation of the electrolysis device, are provided. In addition to the advantages already mentioned, this improves the effectiveness of the electrolysis device during normal operation. It also improves the safety of the electrolysis device during normal operation, as it does not rely on any active means, and potential sources of error or malfunctions are minimized. Another advantageous embodiment is one in which it can be provided that the receiving volume is designed without a pump. This again minimizes sources of error and improves the effectiveness of the electrolysis device.

[0027] According to a further development, it is possible that the initial filling quantity of the alkaline solution in the cathodic half-cell is dimensioned such that the cathodic half-cell is completely flooded with the alkaline solution at all times during operation of the electrolysis device.

[0028] The advantage here is that, by completely filling the cathodic half-cells with the alkaline solution during normal operation, a natural flame barrier is created for the hydrogen produced during hydrogen electrolysis. Another advantage is that, during normal operation, the membrane is completely wetted with the alkaline solution at all times, preventing the membrane from drying out and thus being exposed to local overloads due to overheating, thus improving the service life of the membrane used.

[0029] Furthermore, it may be expedient if the receiving volume is designed such that the cathodic half-cell of the electrolysis device is completely flooded with alkaline solution at all times during normal operation of the electrolysis device, wherein a separation device can be fluidically coupled to the receiving volume so that the discharge of the alkaline solution from the receiving volume during the removal or separation of product gas from the receiving volume can be prevented.

[0030] This allows the alkaline solution to remain in the designated receiving volume, while at the same time the product of the electrochemical reaction can be removed from the cathodic half-cell by means of the separation device. Another advantage is that it allows for simple pressurized operation of the electrolysis device, provided the separation device provides the counterpressure to the receiving volume. Since the receiving volume holds at least a certain minimum amount of alkaline liquid during normal operation, so that the membrane is constantly wetted with it, the proportion of gas relative to the alkaline liquid in the receiving volume is low, thus improving the safety of pressurized operation of the electrolysis device.

[0031] Furthermore, it can be provided that in a steady-state and stationary operating state of the electrolysis device, the supply of reactants for the electrochemical reaction in the cathodic half-cell can be provided exclusively by diffusion processes of the reactants through the membrane electrode unit.

[0032] This simplifies the design of the electrolysis device, as fresh water or ultrapure water only needs to be supplied via the anodic half-cell during normal operation. This also allows the electrolysis device to be manufactured more economically, especially if it is intended for pressure operation on the cathode side, since fewer components and pressure-resistant components are required.

[0033] Furthermore, it can be provided that the cathodic electrode and / or a cathode-side surface of the membrane is / are hydrophilic. This promotes the diffusion processes described above and the entire course of the electrochemical reaction in the electrolysis device, which increases the effectiveness and, consequently, the cost-effectiveness of the electrolysis device.

[0034] According to a particular embodiment, it is possible that the anodic electrode and / or the cathodic electrode is / are formed by applying catalytically active materials to the membrane and / or by applying catalytically active materials to porous support structures contacted with the membrane.

[0035] In particular, the use of a porous carrier material such as a metal foam or similar improves the diffusion or transport processes of the reactants and products of the electrochemical reaction in the electrolysis device.

[0036] According to an advantageous development, the anodic electrode and / or the cathodic electrode can be precious metal-free. This offers the economic advantage of allowing the use of cheaper materials than precious metal-based metals.

[0037] In particular, it may be advantageous if ultrapure water or a lye with a first molar concentration in the range between 0.1 mol / l and 2 mol / l or in particular between 0.5 mol / l and 1 mol / l can be absorbed in the anodic half-cell.

[0038] Furthermore, the lye can be a potassium hydroxide solution or a sodium hydroxide solution. Furthermore, it is also conceivable that solutions containing (bi)carbonate are used.

[0039] Furthermore, it can be provided that the alkaline liquid for the initial filling quantity in the cathodic half-cell is a lye with a second molar concentration, wherein the first molar concentration is equal to or higher than the second molar concentration.

[0040] This creates an osmotic pressure between the half-cells even in standby mode without voltage applied to the electrodes. This allows the electrolysis device to operate under pressure for longer and with greater stability. During standby mode or when the electrolysis device is shut down, the diffusion of products such as molecular hydrogen is at least partially prevented or can be prevented more easily.

[0041] Also advantageous is a form of embodiment according to which it can be provided that the membrane electrode unit can absorb a differential pressure between the anodic half-cell and the cathodic half-cell, wherein the differential pressure is in the range between 0 bar and 100 bar, or in particular between 5 bar and 30 bar.

[0042] The advantage here is that the intended pressure of the electrolysis product does not need to be generated by any additional means, since the electrolysis device is already operated under pressure. This is advantageous with regard to the overall efficiency of the electrolysis device when integrated into a production plant for hydrogen, for example. In conjunction with the electrolysis device according to the invention, in which the half-cells are completely flooded with electrolyte, this is advantageous because the gas volume in the half-cells is particularly low, allowing the electrolysis device to be operated responsively and dynamically.

[0043] According to the invention, an electrolysis cell stack is claimed, which electrolysis cell stack comprises several sequentially arranged anodic half-cells, cathodic half-cells, and membrane electrode units corresponding to the functional configuration of the electrolysis device according to the invention in terms of the electrochemical reaction. The cathodic half-cells can be fluidically coupled by means of at least one flow channel, wherein the cathodic half-cells and the at least one flow channel form a cathode volume. During operation of the electrolysis cell stack, an initial filling quantity of alkaline solution in the cathode volume can be changed exclusively by diffusion processes through the membrane electrode units and / or by electrochemical reaction of reactants or the alkaline solution in the membrane electrode units.

[0044] An advantage here is that the cathode volume can be provided as a combination of all cathodic half-cells of the electrolysis cell stack to accommodate the alkaline solution. This dampens transient effects during startup into normal operation, especially when the individual electrolysis devices are operating at high power. This increases the safety of the electrolysis process.

[0045] According to the invention, an electrolysis system is claimed, which electrolysis system comprises a plurality of electrolysis cell stacks according to the invention. The electrolysis system comprises at least one connecting line, wherein the cathode volumes of the electrolysis cell stacks can be fluidically coupled by means of the connecting line, wherein the electrolysis system comprises a gas separation device, wherein the gas separation device can be fluidically coupled to the cathode volumes and is designed to separate the product generated by means of an electrochemical reaction from the alkaline solution, wherein the discharge of the alkaline solution from the cathode volumes can be prevented by means of the gas separation device. It is advantageous that the fluidically coupled cathode volumes can be provided as a combination of all cathodic half-cells of the electrolysis system for receiving the alkaline solution.This dampens transient effects during startup, especially at high electrolysis plant power levels. This increases the safety of the electrolysis process.

[0046] In particular, the use of the electrolysis plant according to the invention is advantageous when the product is molecular hydrogen.

[0047] According to the invention, a process for producing hydrogen by electrochemical reaction from an aqueous alkaline solution is further claimed, which process comprises the following process steps:

[0048] - Providing an electrolysis device, wherein the electrolysis device comprises an anodic half-cell and a cathodic half-cell, wherein the anodic half-cell and the cathodic half-cell are separated by a membrane and the cathodic half-cell can be flooded by the alkaline solution and the anodic half-cell can be flooded by an aqueous, alkaline solution or by ultrapure water, wherein the anodic half-cell comprises an anodic electrode and the cathodic half-cell comprises a cathodic electrode, wherein the anodic electrode, the cathodic electrode and the membrane form a membrane-electrode unit;

[0049] - Filling the anodic half-cell with an aqueous alkaline solution or with ultrapure water and filling the cathodic half-cell with an initial amount of alkaline solution so that the half-cells are completely flooded or so that the membrane electrode assembly on the cathode side is completely immersed in the alkaline solution;

[0050] - applying a voltage between the anodic electrode and the cathodic electrode; characterized in that the initial fill quantity of alkaline solution in the cathodic half-cell during normal operation of the electrolysis device or when a voltage is applied between the anodic electrode and the cathodic electrode is changed exclusively by diffusion processes through the membrane-electrode unit or through the membrane and / or by electrochemical reaction of the alkaline solution in the membrane-electrode unit. In particular, it can be provided that an anion exchange membrane is used as the membrane.

[0051] Furthermore, it can be provided that the initial filling quantity of alkaline solution is received in the cathodic half-cell and in a fluid channel and / or fluid tank fluidically coupled to the cathodic half-cell, thereby defining a receiving volume, wherein the alkaline solution in the receiving volume does not experience any forced circulation, forced circulation and / or forced movement during normal operation of the electrolysis device, except for the movement that occurs automatically as a result of the electrochemical reaction.

[0052] In addition to the advantages already mentioned, the effectiveness and overall efficiency of the electrolysis device is improved because no additional energy needs to be provided. For example, it is conceivable that the cathode inlet and the cathode outlet can be fluidically coupled using the fluid channel. By producing hydrogen during hydrogen electrolysis, a circulation of the alkaline solution through the cathodic half-cell can be created without the need for active agents if the electrolysis device is positioned accordingly. This reduces the thermal stress on the membrane in particular and simultaneously improves the efficiency of the electrolysis device. Natural circulation can occur during normal operation of the electrolysis device.

[0053] Also advantageous is an embodiment according to which it can be provided that during normal operation of the electrolysis device no active means are used to generate a flow of the cathode-side alkaline solution, the membrane electrode unit being excluded therefrom.

[0054] In addition to the advantages already mentioned, this improves the effectiveness of the electrolysis device during normal operation. It also improves the safety of the electrolysis device during normal operation, as it does not rely on any active agents and potential sources of error or malfunctions are minimized. The method according to the invention can further comprise the following method step:

[0055] - Dimensioning of the cathode-side alkaline solution such that the cathodic half-cell is completely flooded with the alkaline solution at all times during normal operation of the electrolysis device.

[0056] The advantage here is that, by completely filling the cathodic half-cells with the alkaline solution during normal operation, a natural flame barrier is created for the hydrogen produced during hydrogen electrolysis. Another advantage is that, during normal operation, the membrane is completely wetted with the alkaline solution at all times, preventing the membrane from drying out and thus being exposed to local overloads due to overheating, thus improving the service life of the membrane used.

[0057] The method according to the invention may further comprise the following method step:

[0058] - Supplying an operating fluid in the anodic half-cell, wherein the operating fluid is ultrapure water and / or an aqueous alkaline solution, wherein the operating fluid is supplied exclusively on the anode side during normal operation of the electrolysis device.

[0059] This reduces the number of fittings and lines required for the electrolysis device during normal operation, which improves the safety and effectiveness of the electrolysis device.

[0060] According to a further development, it is possible that a noble metal-free electrode is used as the anodic electrode and / or a noble metal-free electrode is used as the cathodic electrode.

[0061] This brings with it the economic advantage that cheaper materials can be used than precious metal-based metals.

[0062] Furthermore, it may be expedient for ultrapure water or a lye with a first molar concentration in the range between 0.1 mol / l and 2 mol / l, or in particular between 0.5 mol / l and 1 mol / l, to be accommodated in the anodic half-cell. Furthermore, it may be provided that a lye with a second molar concentration is used as the alkaline liquid for the initial fill quantity in the cathodic half-cell, wherein the first molar concentration is equal to or higher than the second molar concentration.

[0063] This creates an osmotic pressure between the half-cells even in standby mode without voltage applied to the electrodes. This allows the electrolysis device to operate under pressure for longer and with greater stability. During standby mode or when the electrolysis device is shut down, the back diffusion of products such as molecular hydrogen is at least partially prevented or can be prevented more easily.

[0064] In particular, it may be advantageous if a potassium hydroxide solution or a sodium hydroxide solution is used as the lye.

[0065] For a better understanding of the method according to the invention, an exemplary and detailed description of possible process steps of the method according to the invention or of process steps that can take place in the electrolysis device is given below.

[0066] • Initial filling of the cathodic half-cell: the cathodic half-cell and any connecting lines or fluid channels or fluid tanks, hereinafter referred to as cathode volume, are filled with a certain amount of alkaline solution.

[0067] • Fill level and positioning of the cathode volume: Any fluid channels, fluid tanks, or connecting lines of the cathode volume are located mostly above the highest fill level of the respective cathodic half-cells. This ensures complete wetting of the membrane on the cathode side, even with minimal fill levels. • Inerting of the cathodic half-cell: The remaining air is flushed from the remaining cathode volume using nitrogen, and the cathode volume is sealed. This can be implemented using the separation device or gas separation device if necessary. This ensures that no explosive atmosphere can develop in the cathode volume.

[0068] • Initial anode state: The anodic half-cell initially contains an alkaline electrolyte or an alkaline solution with a first molar concentration that corresponds at most to the second molar concentration of the electrolyte in the cathodic half-cell. It is also conceivable that the anodic half-cell can be operated with ultrapure water.

[0069] • Starting the electrolysis: By applying an electric current to the electrolysis device or to the electrodes of the electrolysis device, the reactant water (H2O) from the cathodic half-cell is initially split into H+ and OH- ions. While molecular hydrogen (H2) is deposited in gaseous form in the cathodic half-cell, OH- ions diffuse through the membrane into the anodic half-cell. The hydrophilic membrane used is exclusively conductive to OH- anions and impermeable to cations. The membrane can also be referred to as an anion exchange membrane.

[0070] • Initial dilution of the electrolyte in the anodic half-cell: In the anodic half-cell, the introduced OH- ions produce one part O2 and * parts H2O. While the former is separated from the anodic half-cell in gaseous form, H2O lowers the molar concentration of the electrolyte in the anodic half-cell. The electrolyte in the anodic half-cell is thus diluted.

[0071] • Gas separation and electrolyte circulation in the cathodic half-cell: Due to its low density, the molecular hydrogen produced in the cathodic half-cell rises through the outgoing connecting lines or flow lines at the highest point of the half-cell in the cathode volume and collects at the highest point or can be separated there. While the alkaline solution or the entrained KOH separates by gravity, remains in the cathodic volume, and can flow back into the half-cell at the lowest point. This creates a natural circulation.

[0072] • Gas separation from the cathodic half-cell and differential pressure: The product gas is discharged from the system at the highest point of the cathode volume. The discharge of the alkaline solution from the cathode volume is prevented by structural design or by means of the separation device or the gas separation device. External pressure maintenance devices can keep the hydrogen gas or the entire cathode volume under pressure. The penetration of higher external system pressures into the cathode volume during start-up of the electrolysis device can be prevented by a check valve in the gas line.

[0073] • Increase in osmotic pressure: During operation, the molar concentration of the alkaline electrolyte in the cathodic half-cell continuously increases due to the conversion of the reactant water, while in the anodic half-cell, the molar concentration decreases due to the introduction of H2O, or the electrolyte in the anodic half-cell is diluted. A molar concentration gradient develops between the two half-cells, creating an osmotic pressure that promotes the transport of water across the membrane from the anodic half-cell to the cathodic half-cell.

[0074] • Reaching the equilibrium state: If the mass transport due to the osmotic pressure is exactly as great as the consumption of the reactant water in the cathodic half-cell, only fresh water that was transported through the hydrophilic membrane from the anodic half-cell to the cathodic half-cell is used to split the water into H+ and OH- ions. From this point on, the fill quantity or fill level of electrolyte in the cathodic half-cell or the concentration in the cathodic volume remains constant. • Equilibrium state under differential pressure: If molecular hydrogen H2 is kept under pressure in the cathodic half-cell, the pressure gradient between the cathodic half-cell and the anodic half-cell dampens the mass transport due to the osmotic pressure and the equilibrium state is only reached when the molar concentration of the electrolyte in the cathodic half-cell is higher and therefore when the fill level or fill level is lower.a smaller filling quantity of electrolyte or alkaline solution in the cathode volume.

[0075] • Concentration increase in the anodic half-cell: Once this equilibrium state is reached, only reactant water from the anodic half-cell is used for electrolysis, causing the molar concentration in the anodic half-cell to increase, or the fill level or fill quantity of electrolyte in the anodic half-cell to decrease. The molar concentration gradient decreases, thus also decreasing the osmotic pressure. This leads to further consumption of reactant water from the cathodic half-cell, thus further increasing the molar concentration of the electrolyte or alkaline solution in the cathodic half-cell.

[0076] • Regulation of the electrolyte concentration in the anodic half-cell: To prevent an unacceptable increase in the molar concentration, fresh water is added to the anodic half-cell, thereby keeping the molar concentration of the electrolyte in the anodic half-cell constantly at a low level. This level is independent of the current applied to the electrodes and the prevailing pressure in the cathodic half-cell.

[0077] • Self-regulating system: Unlike conventional systems, this difference in molar concentration and mass between the anodic half-cell and the cathodic half-cell is not compensated for by pumps or piping, but is deliberately induced. By deliberately regulating the electrolyte concentration or the molar concentration of the electrolyte in the anodic half-cell, a specific liquid level or fill volume or electrolyte concentration is established in the cathodic half-cell, depending on the applied electrical power and the prevailing differential pressure between the anodic half-cell and the cathodic half-cell. By enclosing and circulating the liquid electrolyte in the cathodic volume, combined with the controlled supply of fresh water to the anodic half-cell, the system is virtually self-regulating or self-stabilizing.

[0078] • Shutting down the system: As soon as the applied current is removed, no further reactant water is consumed in the cathodic half-cell. The osmotic pressure resulting from the molar concentration gradient and the upright water transport from the anodic half-cell to the cathodic half-cell cause the fill level in the cathode volume to rise again rapidly and the molar concentration of the liquid electrolyte to decrease. Since the anodic half-cell is constantly being refilled with fresh water and the molar concentration in the anodic half-cell is kept constant, a molar concentration balance is established between the anodic half-cell and the cathodic half-cell in the range of the initial state. The fill level or fill volume in the cathodic volume then again corresponds at most to the initial fill volume.

[0079] • Maintenance and service: The alkaline liquid in the cathode volume is replaced at regular maintenance intervals. To do this, the entire liquid is drained from the lowest point and the cathode volume is then refilled. In contrast, the alkaline liquid in the anodic half-cell is treated or replaced centrally in an electrolysis system according to the invention.

[0080] For a better understanding of the invention, it is explained in more detail using the following figures.

[0081] They show in a highly simplified, schematic representation:

[0082] Fig. 1 shows an electrolysis device with an anodic half-cell and a cathodic half-cell;

[0083] Fig. 2 shows an electrolysis cell stack comprising several electrolysis devices; Fig. 3 shows an electrolysis system comprising several electrolysis cell stacks;

[0084] By way of introduction, it should be noted that in the variously described embodiments, identical parts are provided with identical reference symbols or component designations. The disclosures contained throughout the description can be applied analogously to identical parts with identical reference symbols or component designations. Furthermore, the positional information chosen in the description, such as top, bottom, side, etc., refers to the directly described and illustrated figure, and these positional information must be applied analogously to the new position in the event of a change in position.

[0085] Fig. 1 shows an electrolysis device 1 with an anodic half-cell 2 and a cathodic half-cell 3 in a highly simplified, schematic representation. The cathodic half-cell 3 and the anodic half-cell 2 are separated from one another by a membrane 4. The anodic half-cell 2 comprises an anodic electrode 5, wherein the anodic electrode 5 can be arranged adjacent to the anode-side surface of the membrane 4. The cathodic half-cell 3 comprises a cathodic electrode 6, wherein the cathodic electrode 6 can be arranged adjacent to the cathode-side surface of the membrane 4. The anodic electrode 5, the cathodic electrode 6 and the membrane 4 together form a membrane-electrode unit 7, which membrane-electrode unit 7 can comprise further elements.The anodic half-cell 3 is separated from the cathodic half-cell 2 by the membrane 4, which can be designed as an anion exchange membrane. The anodic electrode 5 and the cathodic electrode 6 can be formed by a porous metallic conductor, such as a metal foam, or can be applied directly to the membrane 4.

[0086] The anodic half-cell 2 can be flooded with an aqueous, alkaline solution or even ultrapure water during operation of the electrolysis device 1. The cathodic half-cell 3 can be flooded with an aqueous, alkaline solution during operation of the electrolysis device 1. To enable operation of the electrolysis device 1, the cathodic half-cell 3 is filled with an initial fill quantity of alkaline solution. During normal operation of the electrolysis device 1, i.e. with the exception of maintenance, rinsing, and the like, no further alkaline solution is actively added to or removed from the cathodic half-cell 3. During normal operation of the electrolysis device 1, the initial fill quantity of alkaline solution in the cathodic half-cell 3 is determined exclusively by diffusion processes through the membrane electrode unit 7 orthrough the membrane 4 and / or through electrochemical reactions of the alkaline solution in the membrane electrode unit 7.

[0087] In the anodic half-cell 2, as in the cathodic half-cell 3, an alkaline solution can be used for the electrolysis process. However, it is conceivable that ultrapure water could also be used in the anodic half-cell 2, especially with a correspondingly adapted membrane 4 or membrane-electrode assembly 7.

[0088] In this description, a membrane 4 is understood to mean a separating, yet electrolytically conductive partition in the electrolysis device 1, which is essentially an electrochemical cell. In the broadest sense, a diaphragm, for example, can be considered a synonym for the membrane 4 in electrochemistry. The separation of the half-cells 2, 3 by the membrane 4 allows operation with different concentrations of the alkaline solution or with different liquids or electrolytes in the half-cells 2, 3.

[0089] The membrane 4 can be designed to be so robust that a differential pressure in the range between 0 bar and 100 bar can be present between the anodic half-cell 2 and the cathodic half-cell 3. Filling both half-cells 2, 3 with an electrolyte or with ultrapure water or an alkaline solution, in particular, promotes the absorption of such differential pressures. Synergistically, filling both half-cells 2, 3 improves the safety of the electrolysis device 1, since the filling creates a flame barrier during the production of products that are flammable in the open air.

[0090] Diffusion processes are understood to mean all those transport processes through the membrane 4 or through the membrane-electrode unit 7, which include gas diffusion, water transport mechanisms, gas permeation or the diffusion of other reactants or products of the electrochemical reaction of the electrolysis device 1.

[0091] In this sense, the membrane 4 or the membrane-electrode assembly 7 is not considered an active means of generating flow. The input of electrical energy at the electrodes 5, 6 and the outgassing or production of products of the electrochemical reaction and the flow induced by the products in the half-cells 2, 3 are also not considered active means of generating flow. The electrolysis process at the membrane-electrode assembly 7 results in mass transport through the membrane 4 due to diffusion processes. This mass transport results as a passive effect of the electrochemical reaction or the concentration difference between the anodic half-cell 2 and the cathodic half-cell 3 of the respective solutions or liquids in the half-cells 2, 3 and the resulting osmotic pressure.

[0092] By filling both half-cells 2, 3 with electrolyte or with an alkaline solution or with ultrapure water, the electrolysis device 1 is ready for operation. The initial fill quantity of alkaline solution can be accommodated in the cathodic half-cell 3 and in a fluid channel 8 that can be fluidically coupled to the cathodic half-cell 3 and / or a fluid tank. This defines a receiving volume 9 that can be filled with the initial fill quantity. The initial fill quantity of alkaline solution in the receiving volume 9 is dimensioned such that the membrane electrode assembly 7 on the cathode side can be wetted with alkaline liquid at any time during normal operation of the electrolysis device 1.

[0093] Normal operation here refers to an operating state in which a product such as molecular hydrogen is continuously produced by means of an electrochemical reaction. Thus, operating states such as maintenance, purging, and the like are not considered normal operation.

[0094] During normal operation of the electrolysis device 1, the amount of alkaline liquid in the receiving volume 9 does not experience any circulation, forced circulation, and / or forced movement initiated by active means. The amount of alkaline liquid in the receiving volume 9 can only experience a passively induced flow, which can arise from the electrochemical reaction and / or the diffusion processes described above and / or from the outgassing of products of the electrochemical reaction. In any case, no active means for generating a flow during normal operation are provided in the devices or elements forming the receiving volume 9. However, it is not excluded that such active means, such as a pump, could be provided for a different operating state.

[0095] Furthermore, a separating device 10 can be provided, which separating device

[0096] 10 is fluidically coupled to the fluid channel 8. By means of the separation device 10, it can be ensured that a product or product gas produced during the electrolysis process can be removed without the alkaline solution being discharged from the receiving volume 9.

[0097] The initial fill volume of alkaline liquid in the receiving volume 9 can change during normal operation of the electrolysis device 1 due to diffusion processes and the ongoing electrochemical reaction. During normal operation of the electrolysis device 1, no additional alkaline liquid is added to the receiving volume 9 from outside. However, in a steady-state operating state, which is also to be understood as normal operation, the reactants or the reactant for the electrochemical reaction are provided at least in part by diffusion processes through the membrane electrode assembly 7.

[0098] This creates the need for ultrapure water to be supplied to the anodic half-cell 2 side of the electrolysis device 1, at least after a certain operating time in the case of hydrogen electrolysis. The diffusion processes can be further promoted by making the cathodic electrode 6 and / or the cathode-side surface of the membrane 4 hydrophilic. Furthermore, the electrodes 5, 6 can be produced by applying catalytically active materials to the membrane 4. It is also conceivable for the electrodes 5, 6 to be produced by applying catalytic materials to a porous support structure such as a metal foam. The electrodes 5, 6 can in any case be made free of precious metals.

[0099] The liquid present in the anodic half-cell 2 during operation can be, as already described, ultrapure water or a lye with a first molar concentration in the range between 0.1 mol / l and 2 mol / l. The lye can be sodium hydroxide solution, potassium hydroxide solution, or another lye with similar electrochemical properties. The alkaline solution present in the cathodic half-cell 3 during operation of the electrolysis device 1 can be a lye with a second molar concentration. The first molar concentration can be equal to or higher than the second molar concentration.

[0100] Fig. 2 shows an electrolysis cell stack 11 comprising a plurality of electrolysis devices 1, wherein the same reference numerals or component designations are used for the same parts as in the preceding Fig. 1. To avoid unnecessary repetition, reference is made to the detailed description in the preceding Fig. 1.

[0101] An electrolysis cell stack 11 can comprise several anodic half-cells 2, cathodic half-cells 3, and membrane electrode assemblies 7 arranged in a row. The individual elements, for example plate-shaped, can be arranged in an alternating sequence, whereby the functional design of each electrolysis device 1 in the assembly in the electrolysis cell stack 11 must be ensured. The cathodic half-cells 3 of the electrolysis cell stack 11 can be fluidically coupled by means of at least one flow channel 12. The cathodic half-cells 3, which can thus be fluidically coupled, and the at least one flow channel 12 thus define a cathode volume 13. It can also be provided that the at least one flow channel 12 can be fluidically coupled to another line or a tank.The cathode volume 13 can be expanded in order to ensure optimal operation of the electrolysis cell stack, because in any case the alkaline solution should completely wet the respective membrane 4 of a cathodic half-cell 3 during normal operation.

[0102] Analogous to the electrolysis device 1, the initial filling quantity of alkaline solution in the cathode volume 13 can be changed exclusively by diffusion processes through the membrane electrode units 7 and / or by electrochemical reaction of a reactant(s) or of the alkaline solution in the membrane electrode unit 7.

[0103] Fig. 3 shows an electrolysis system 14 comprising a plurality of electrolysis cell stacks 11, wherein the same reference numerals or component designations are used for the same parts as in the preceding Fig. 1 and Fig. 2. To avoid unnecessary repetition, reference is made to the detailed description in the preceding Fig. 1 and Fig. 2.

[0104] The electrolysis system 14 can comprise a plurality of electrolysis cell stacks 11, wherein the respective cathode volumes 13 of the individual electrolysis cell stacks 11 can be fluidically coupled by means of a connecting line 16. Furthermore, the cathode volumes 13 can be coupled to a gas separation device 15. The gas separation device 15 can be designed to remove product gas from the electrolysis, such as gaseous molecular hydrogen, without removing the alkaline solution in the cathode volumes 13. The cathode volumes 13 of the electrolysis cell stacks 11 can further be fluidically coupled to a tank. In any case, analogous to the electrolysis device 1, the initial fill quantity of alkaline solution in the cathode volumes 13 is determined exclusively by diffusion processes through the membrane electrode units 7 and / or by electrochemical reaction of a reactant(s).the alkaline solution in the membrane electrode unit 7 can be changed.

[0105] The embodiments show possible embodiments, whereby it should be noted at this point that the invention is not limited to the specifically illustrated embodiments thereof, but rather various combinations of the individual embodiments with each other are also possible and this possibility of variation lies within the skill of the person skilled in the art in this technical field due to the teaching of technical action by means of the objective invention.

[0106] The scope of protection is determined by the claims. However, the description and drawings must be used to interpret the claims. Individual features or combinations of features from the various embodiments shown and described may represent independent inventive solutions. The problem underlying these independent inventive solutions can be derived from the description.

[0107] All information on value ranges in this description is to be understood as including any and all sub-ranges thereof, e.g. the information 1 to 10 is to be understood as including all sub-ranges starting from the lower limit of 1 and the upper limit of 10, ie all sub-ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0108] For the sake of clarity, it should be noted that, for a better understanding of the structure, some elements have been shown not to scale and / or enlarged and / or reduced in size.

[0109] Electrolysis device anodic half-cell cathodic half-cell membrane anodic electrode cathodic electrode

[0110] Membrane electrode assembly

[0111] Fluid channel

[0112] Recording volume

[0113] From sheath device

[0114] Electrolysis cell stack

[0115] Flow channel cathode volume

[0116] Electrolysis plant

[0117] Gas - Ab separator

[0118] Connecting line

Claims

Patent claims 1. Electrolysis device (1) for producing hydrogen by electrochemical reaction from an aqueous alkaline solution, — wherein the electrolysis device (1) comprises an anodic half-cell (2) and a cathodic half-cell (3), — wherein the anodic half-cell (2) and the cathodic half-cell (3) are separated by a membrane (4) and the cathodic half-cell (3) can be flooded with the alkaline solution, — and wherein the anodic half-cell (2) comprises an anodic electrode (5) and the cathodic half-cell (3) comprises a cathodic electrode (6), — wherein the anodic electrode (5), the cathodic electrode (6) and the membrane (4) form a membrane electrode unit (7), characterized in that an initial filling quantity of alkaline solution in the cathodic half-cell (3) in normal operation of the electrolysis device (1) can be changed exclusively by diffusion processes through the membrane electrode unit (7) and / or by electrochemical reaction of the alkaline solution in the membrane electrode unit (7).

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

3. Electrolysis device (1) according to one of the preceding claims, characterized in that the initial filling quantity of alkaline solution can be accommodated in the cathodic half-cell (3) and in a fluid channel (8) and / or fluid tank that can be fluidically coupled to the cathodic half-cell (3), thereby defining a receiving volume (9), wherein no forced circulation, no forced circulation and / or no forced movement can be experienced for the alkaline solution in the receiving volume (9) during normal operation of the electrolysis device (1), apart from the movement that is self-established by the electrochemical reaction.

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

5. Electrolysis device (1) according to claim 3, characterized in that the fluid channel (8) is designed without a pump.

6. Electrolysis device (1) according to one of the preceding claims, characterized in that the initial filling quantity of the alkaline solution in the cathodic half-cell (3) is dimensioned such that the cathodic half-cell (3) is completely flooded with the alkaline solution at all times during operation of the electrolysis device (1).

7. Electrolysis device (1) according to claim 3, characterized in that the receiving volume (9) is designed such that the cathodic half-cell (3) of the electrolysis device (1) is completely flooded with alkaline solution at all times during normal operation of the electrolysis device (1), wherein a separation device (10) can be fluidically coupled to the fluid channel (8) so that the discharge of the alkaline solution from the receiving volume (9) can be prevented during the removal or separation of product gas from the receiving volume (9).

8. Electrolysis device (1) according to one of the preceding claims, characterized in that in a steady and stationary operating state of the electrolysis device (1), the supply of reactants for the electrochemical reaction in the cathodic half-cell (3) can be provided exclusively by diffusion processes of the reactants through the membrane-electrode unit (7).

9. Electrolysis device (1) according to one of the preceding claims, characterized in that the cathodic electrode (6) and / or a cathode-side surface of the membrane (4) is / are hydrophilic.

10. Electrolysis device (1) according to claim 9, characterized in that the anodic electrode (5) and / or the cathodic electrode (6) are formed by applying catalytically active materials onto the membrane (4) and / or by applying catalytically active materials to porous support structures contacted with the membrane (4).

11. Electrolysis device (1) according to one of the preceding claims, characterized in that the anodic electrode (5) and / or the cathodic electrode (6) is free of precious metals.

12. Electrolysis device (1) according to one of the preceding claims, characterized in that in the anodic half-cell (2) ultrapure water or a lye with a first molar concentration in the range between 0.1 mol / l and 2 mol / l or in particular between 0.5 mol / l and 1 mol / l can be accommodated.

13. Electrolysis device (1) according to claim 12, characterized in that the alkaline liquid for the initial filling quantity in the cathodic half-cell (3) is a lye with a second molar concentration, wherein the first molar concentration is equal to or higher than the second molar concentration.

14. Electrolysis device (1) according to one of claims 12 or 13, characterized in that the lye is a potassium hydroxide solution or a sodium hydroxide solution.

15. Electrolysis device (1) according to one of the preceding claims, characterized in that a differential pressure between the anodic half-cell (2) and the cathodic half-cell (3) can be absorbed by the membrane electrode unit (7), wherein the differential pressure is in the range between 0 bar and 100 bar, or in particular between 5 bar and 30 bar.

16. Electrolysis cell stack (11) comprising a plurality of anodic half-cells (2), cathodic half-cells (3) and membrane electrode units (7) arranged in series according to the functional design of the electrolysis device (1) according to one of the preceding claims in terms of the electrochemical reaction, characterized in that the cathodic half-cells (3) are fluidically connected by means of at least one flow channel (12). can be coupled, wherein the cathodic half-cells (3) and the at least one flow channel (12) form a cathode volume (13), wherein during operation of the electrolysis cell stack (11) an initial filling quantity of alkaline solution in the cathode volume (13) can be changed exclusively by diffusion processes through the membrane electrode units (7) and / or by electrochemical reaction of a reactant or reactants or of the alkaline solution in the membrane electrode units (7).

17. Electrolysis system (14) comprising a plurality of electrolysis cell stacks (11) according to claim 16, characterized in that the electrolysis system (14) comprises at least one connecting line (16) or one connecting channel, wherein the cathode volumes (13) of the electrolysis cell stacks (11) can be fluidically coupled by means of the connecting line (16), wherein the electrolysis system (14) comprises a gas separation device (15), wherein the gas separation device (15) can be fluidically coupled to the cathode volumes (13) and is designed to separate the product produced by means of electrochemical reaction from the alkaline solution, wherein the discharge of the alkaline solution from the cathode volumes (13) can be prevented by means of the gas separation device (15).

18. Electrolysis plant (14) according to claim 17, characterized in that the product is molecular hydrogen.

19. A process for producing hydrogen by electrochemical reaction from an aqueous alkaline solution, comprising the process steps: - Providing an electrolysis device (1), wherein the electrolysis device (1) comprises an anodic half-cell (2) and a cathodic half-cell (3), wherein the anodic half-cell (2) and the cathodic half-cell (3) are separated by a membrane (4) and the cathodic half-cell (3) can be flooded with the alkaline solution, wherein the anodic half-cell (2) comprises an anodic electrode (5) and the cathodic half-cell (3) comprises a cathodic electrode (6), wherein the anodic electrode (5), the cathodic electrode (6) and the membrane (4) form a membrane-electrode unit (7); - Filling the anodic half-cell (2) and filling the cathodic half-cell (3) with an initial amount of alkaline solution so that the half-cells (2, 3) are completely flooded or so that the membrane electrode assembly (7) on the cathode side is completely immersed in the immersed in alkaline solution; - applying a voltage between the anodic electrode (5) and the cathodic electrode (6); characterized in that the initial filling quantity of alkaline solution in the cathodic half-cell (3) during normal operation of the electrolysis device (1) or when a voltage is applied between the anodic electrode (5) and the cathodic electrode (6) is changed exclusively by diffusion processes through the membrane-electrode unit (or through the membrane) (4) and / or by electrochemical reaction of the alkaline solution in the membrane-electrode unit (7).

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

21. Method according to one of claims 19 or 20, characterized in that the initial filling quantity of alkaline solution is received in the cathodic half-cell (3) and in a fluid channel (8) and / or fluid tank fluidically coupled to the cathodic half-cell (3), whereby a receiving volume (9) is defined, wherein the alkaline solution in the receiving volume (9) during normal operation of the electrolysis device (1) does not experience any forced circulation, forced circulation and / or forced movement, except for the movement which is self-established by the electrochemical reaction.

22. Method according to one of claims 19 to 21, characterized in that in normal operation of the electrolysis device (1) no active means are used to generate a flow of the cathode-side alkaline solution, the membrane electrode unit (7) being excluded therefrom.

23. Method according to one of claims 19 to 22, further comprising the method step: - Dimensioning of the cathode-side alkaline solution such that the cathodic half-cell (3) during normal operation of the electrolysis device (1) it is completely flooded with the alkaline solution at all times.

24. The method according to any one of claims 19 to 23, further comprising the step of: - Supplying an operating fluid in the anodic half-cell (2), wherein the operating fluid is ultrapure water and / or an aqueous alkaline solution, wherein the operating fluid is supplied exclusively on the anode side during normal operation of the electrolysis device (1).

25. Method according to one of claims 19 to 24, characterized in that a noble metal-free electrode is used as the anodic electrode (5) and / or a noble metal-free electrode is used as the cathodic electrode (6).

26. Method according to one of claims 19 to 25, characterized in that ultrapure water or a lye with a first molar concentration in the range between 0.1 mol / l and 2 mol / l or in particular between 0.5 mol / l and 1 mol / l is taken up in the anodic half-cell (2).

27. The method according to claim 26, characterized in that an alkali with a second molar concentration is used as the alkaline liquid for the initial filling quantity in the cathodic half-cell (3), wherein the first molar concentration is equal to or higher than the second molar concentration.

28. A process according to any one of claims 26 or 27, characterized in that a potassium hydroxide solution or a sodium hydroxide solution is used as the lye.

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