Electrochemical cell and method for producing hydrogen and oxygen from water

Abstract

The invention relates to an electrochemical cell and to a method for producing hydrogen and oxygen from water. By virtue of the electrochemical cell according to the invention, it is possible to carry out an electrochemical reaction at temperatures of 120 °C – 200 °C and pressures of up to 30 bar even under harsh chemical conditions (e.g. KOH mass fractions of up to 35% in the electrolyte) over long periods of time. By virtue of the method according to the invention it is possible to produce hydrogen and oxygen from water at temperatures of 120 °C – 200° C and pressures of up to 30 bar even under harsh chemical conditions (e.g. KOH mass fractions of up to 35% in the electrolyte).

Description

[0001] Electrochemical cell and process for producing hydrogen and oxygen from water

[0002] An electrochemical cell is provided and a process for producing hydrogen and oxygen from water is presented. The electrochemical cell according to the invention makes it possible to carry out an electrochemical reaction at temperatures of 120°C - 200°C and pressures of up to 30 bar, even under harsh chemical conditions (e.g., KOH mass fractions of up to 35% in the electrolyte) over long periods of time. The process according to the invention makes it possible to produce hydrogen and oxygen from water at temperatures of 120°C - 200°C and pressures of up to 30 bar, even under harsh chemical conditions (e.g., KOH mass fractions of up to 35% in the electrolyte). An electrochemical cell for alkaline water electrolysis (AWE) has a cathode and an anode separated by a porous separator (or a porous membrane). The reaction proceeds as follows, using electrical energy:

[0003] The aqueous, alkaline liquid electrolyte of the electrochemical cell (e.g. an aqueous KOH solution) contains the reactant (H2O) and represents the ion-conducting medium for OH _ ions. The electrolyte always wets the cathode and anode and infiltrates the separator. The separator creates electronic insulation both against purely physical contact between the anode and cathode (to prevent short circuits) and against electron conduction via the liquid electrolyte (to prevent leakage currents). Furthermore, the separator prevents the exchange of product gases (H2 at the cathode, O2 at the anode), so that no explosive mixtures (e.g., H2 in O2) form in the respective compartments of the electrochemical cell. At the same time, the porosity of the separator enables OH ion conduction through infiltration of the aqueous, alkaline electrolyte.

[0004] The operating temperature of an electrochemical cell for alkaline water electrolysis is currently typically between 60 °C and 90 °C and is limited by the temperature resistance of the separator. One way to increase the performance of alkaline water electrolysis is to increase the temperature (and possibly the pressure) while maintaining the same KOH concentration in the aqueous electrolyte (mass fraction, e.g., 30% to 35%). In so-called medium-temperature electrolysis, temperatures of 120 °C - 200 °C are targeted at pressures up to 30 bar and KOH mass fractions up to 35% in the electrolyte.

[0005] Kim, S. et al. (Journal of Power Sources, 524:231059) disclose an electrochemical cell for conducting alkaline water electrolysis, which contains a separator with high ionic conductivity and low hydrogen permeability. The separator consists of a Zirfon PERL substrate onto which a layer of polyvinyl alcohol (PVA) cross-linked with glutaraldehyde is applied. The Zirfon PERL substrate consists of zirconium nanoparticles that were applied to a flat polyphenylene sulfide (PPS) substrate using a polysulfone binder (PSU binder). By additionally applying the glutaraldehyde-cross-linked PVA, the hydrogen permeability of the known Zirfon PERL substrate could be significantly reduced, thus increasing the operational reliability of the electrochemical cell with this separator.However, the presented separator has the disadvantage that, due to its organic components (PSU, PPS and cross-linked PVA), it is not suitable for the desired medium-temperature electrolysis at temperatures of 120 °C - 200 °C, pressures of up to 30 bar and KOH mass fractions of up to 35 % in the electrolyte, since the separator is destroyed under these conditions.

[0006] Based on this, the object of the present invention was to provide an electrochemical cell (in particular an electrochemical cell for alkaline water electrolysis) that does not have the disadvantages of the prior art. In particular, the electrochemical cell should be capable of conducting an electrochemical reaction at temperatures of 120°C - 200°C and pressures of up to 30 bar over long periods of time, even under harsh chemical conditions (e.g., KOH mass fractions of up to 35% in the electrolyte). Furthermore, a process for producing hydrogen and oxygen from water that is feasible under these conditions should be presented.

[0007] The object is achieved by the electrochemical cell having the features of claim 1 and the method having the features of claim 16. The dependent claims show advantageous developments.

[0008] According to the invention, an electrochemical cell is provided, comprising: a) a container containing a liquid electrolyte; b) a membrane assembly comprising a planar anode layer having a top side and a bottom side; a planar protective layer having a top side, a bottom side, and pores of a first pore size extending from the top side to the bottom, wherein the planar protective layer contains or consists of an electrically insulating ceramic material; and a planar cathode layer having a top side and a bottom side; wherein the membrane assembly contacts the liquid electrolyte, wherein the membrane assembly is arranged in the container such that it separates the liquid electrolyte into a first compartment and a second compartment, wherein the membrane assembly separates the first compartment from the second compartment in an electrically insulating and ion-conducting manner;wherein the planar protective layer is arranged on the underside of the planar anode layer and the upper side of the planar protective layer contacts the underside of the planar anode layer; wherein i) the cathode layer is arranged on the underside of the planar protective layer and the upper side of the cathode layer contacts the underside of the planar protective layer; or ii) a planar substrate is arranged which has a top side, a bottom side, and pores extending from the top side to the bottom side, which pores have a second pore size that is larger than the first pore size, wherein the top side of the planar substrate contacts the underside of the planar protective layer and the cathode layer is arranged on the underside of the planar substrate; characterized in that the membrane arrangement contains no organic polymer.

[0009] In particular, the term "arranged" does not necessarily mean "contacting." If one layer is arranged on top of another layer, this means that at least one further layer can be arranged between the two layers.

[0010] The electrochemical cell according to the invention makes it possible to conduct an electrochemical reaction at temperatures of 120°C - 200°C and pressures of up to 30 bar over long periods of time, even under harsh chemical conditions (e.g., KOH mass fractions of up to 35% in the electrolyte). This property makes it possible to conduct electrochemical reactions (e.g., alkaline water hydrolysis) with greater efficiency and / or higher power density.

[0011] A further advantage is that the membrane arrangement of the electrochemical cell according to the invention can be produced in larger dimensions (e.g. edge lengths of up to 2 m) compared to polymer-based or ceramic-based membrane arrangements, which can result in larger active areas (e.g. an active area of ​​4 m 2 ). This makes it possible to further increase the efficiency and / or power density of the electrochemical reaction(s) with the electrochemical cell according to the invention.

[0012] Another advantage is that the membrane arrangement of the electrochemical cell and thus the entire electrochemical cell can be manufactured easily and cost-effectively.

[0013] The planar protective layer of the membrane arrangement can be applied to the underside of the planar anode layer, to the top side of the planar cathode layer and / or to the top side of the planar substrate by a method selected from the group consisting of atmospheric plasma spraying, slurry-based coating with subsequent debinding, electrophoretic coating, gas-based coating, wherein the slurry-based coating is preferably selected from the group consisting of immersion bath coating, slot die coating, lamination and combinations thereof.

[0014] Furthermore, the planar protective layer of the membrane arrangement can have a thickness in the range of 10 to 1000 pm, wherein the thickness refers in particular to an extension of the protective layer in a direction perpendicular to the top and / or bottom of the planar protective layer.

[0015] On the underside of the planar substrate of the membrane arrangement (mentioned in the 2nd alternative), a further planar protective layer can be arranged, which has a top side, a bottom side and pores of a first pore size extending from the top side to the bottom, wherein the further planar protective layer contains or consists of an electrically insulating ceramic material, wherein preferably the underside of the planar substrate contacts the top side of the protective layer and the underside of the protective layer contacts the top side of the planar cathode layer.

[0016] The further planar protective layer may have been applied to the underside of the planar substrate by a method selected from the group consisting of atmospheric plasma spraying, slurry-based coating with subsequent debinding, electrophoretic coating, gas-based coating, wherein the slurry-based coating is preferably selected from the group consisting of immersion bath coating, slot die coating, lamination and combinations thereof; and / or

[0017] Furthermore, the further planar protective layer can have a thickness in the range of 10 to 1000 pm, wherein the thickness relates in particular to an extension of the planar protective layer in a direction perpendicular to the top and / or bottom of the planar protective layer.

[0018] The membrane arrangement may have been assembled by a method selected from the group consisting of pressing, joining and combinations thereof, wherein the pressing preferably comprises pressing with a pressure in the range of 50 to 3500 MPa, preferably in the range of 100 to 3000 MPa, particularly preferably in the range of 150 to 2500 MPa, in a direction perpendicular to the membrane arrangement.

[0019] The cathode layer of the membrane assembly may contain or consist of a catalyst that catalyzes a reduction of water to hydrogen, wherein the catalyst preferably contains a material selected from the group consisting of metal, metal alloy, and combinations thereof, wherein the material is optionally selected from the group consisting of nickel, cobalt, molybdenum, manganese, nickel-aluminum, nickel-aluminum-molybdenum, nickel-molybdenum, Raney nickel, and combinations thereof.

[0020] The anode layer of the membrane arrangement may contain or consist of a catalyst that catalyzes an oxidation of water to oxygen, wherein the catalyst preferably contains a material selected from the group consisting of metal, metal alloy, metal oxide, mixed metal oxide, spinel, perovskite, layered double hydroxide and combinations thereof, wherein the material is optionally selected from the group consisting of nickel, cobalt, nickel-aluminum, nickel-aluminum-molybdenum, nickel-molybdenum, Raney nickel, nickel oxide, iridium oxide and combinations thereof.

[0021] The planar substrate may contain or consist of a material selected from the group consisting of metal, metal alloy and combinations thereof, wherein the material is preferably selected from the group consisting of stainless steel, nickel steel, solid nickel and combinations and alloys thereof.

[0022] Furthermore, the sheet-like substrate may contain or consist of a structure selected from the group consisting of nonwoven fabric, solid foam, expanded metal, mesh, fabric, and combinations thereof.

[0023] In addition, the planar substrate can have a thickness in the range from 40 to 1500 pm, preferably in the range from 50 to 1250 pm, particularly preferably in the range from 60 pm to 1000 pm, wherein the thickness relates in particular to an extension of the planar substrate in a direction perpendicular to the top and / or bottom of the planar substrate.

[0024] The pores of the planar substrate may have a second pore size in the range from 5 pm to 1250 pm, preferably in the range from 10 pm to 1000 pm, particularly preferably in the range from 15 pm to 750 pm, wherein the pore size refers to a pore size determinable by mercury porosimetry and / or bubble point measurement; and / or

[0025] Furthermore, the pores of the planar substrate may have a second pore size that decreases from the top side of the planar substrate toward the bottom side of the planar substrate or that decreases from the bottom side of the planar substrate toward the top side of the planar substrate.

[0026] The electrically insulating ceramic material of the planar protective layer, optionally also the electrically insulating ceramic material of a further planar protective layer of the membrane arrangement, can contain or consist of a material selected from the group consisting of nitride ceramic, carbide ceramic, oxide ceramic, silicate ceramic, cermet and combinations thereof.

[0027] Furthermore, the electrically insulating ceramic material of the planar protective layer, optionally also the electrically insulating ceramic material of a further planar protective layer of the membrane arrangement, can contain or consist of particles, wherein the particles preferably have a size in the range from 0.5 pm to 95 pm, preferably in the range from 5 pm to 70 pm, particularly preferably in the range from 9 pm to 45 pm, wherein the particle size refers to a measurement of the particle size distribution.

[0028] The pores of the planar protective layer, optionally also the pores of a further planar protective layer of the membrane arrangement, can have a first pore size in the range of 50 nm to 9 pm, wherein the pore size refers to a pore size that can be determined via mercury porosimetry and / or bubble point measurement.

[0029] The flat protective layer, optionally also another flat protective layer of the membrane arrangement, can have an electrical resistance in the kQ to MQ range.

[0030] Furthermore, the flat protective layer, optionally also a further flat protective layer of the membrane arrangement, can have an ion resistance in the range of <0.3 to 0.8 Ωcm 2 have.

[0031] In addition, the flat protective layer, optionally also a further flat protective layer of the membrane arrangement, can have a gas permeability in the range of 2 to 6 L / min-cm 2 at 5 bar.

[0032] Apart from that, the flat protective layer, optionally also another flat protective layer of the membrane arrangement, can be conductive for ions selected from the group consisting of alkali metal ions, OH ions, H +-ions and combinations thereof. In a preferred embodiment, the membrane assembly of the electrochemical cell contains a first electrically conductive collector layer that contacts the anode layer and a second electrically conductive collector layer that contacts the cathode layer. The first electrically conductive collector layer is preferably arranged on top of the anode layer and / or the second electrically conductive collector layer is preferably arranged on the underside of the cathode layer.

[0033] According to the invention, the membrane arrangement contains no organic polymer, optionally no organic material.

[0034] The membrane arrangement can be stable, preferably not damaged, in particular not dissolved, towards an aqueous solution of 35 wt% KOH, with respect to the total weight of the aqueous solution.

[0035] Furthermore, the membrane arrangement can be stable against a pressure of 30 bar on an upper or lower side of the membrane, preferably not be damaged by this pressure, in particular not be cracked.

[0036] In addition, the membrane arrangement can be stable to a temperature of 200 °C, preferably not be damaged, in particular not melt and / or burn.

[0037] The electrochemical cell may further include an inlet for supplying liquid electrolyte into the first compartment and an outlet for removing a first fluid from the first compartment.

[0038] In addition, the electrochemical cell may further include an inlet for supplying liquid electrolyte into the second compartment and an outlet for discharging a second fluid from the second compartment.

[0039] The electrochemical cell can be selected from the group consisting of electrolysis cell, battery cell, fuel cell and CO2 reduction cell, wherein the electrochemical cell is particularly preferably a water electrolysis cell, most preferably an alkaline water electrolysis cell.

[0040] According to the invention, a process for producing hydrogen and oxygen from water is also presented, comprising the following steps: a) providing an electrochemical cell according to the invention, wherein the liquid electrolyte is an aqueous solution containing 35 to 40 wt.% KOH, based on the total weight of the aqueous solution; and b) applying an electrical voltage between the cathode and anode of the electrochemical cell and carrying out electrolysis.

[0041] With the process according to the invention it is possible to produce hydrogen and oxygen from water at temperatures of 120 °C - 200 °C and pressures of up to 30 bar even under harsh chemical conditions (e.g. KOH mass fractions of up to 35% in the electrolyte).

[0042] In the process, the electrolysis is preferably carried out at a pressure in the range of 1 to 30 bar and / or a temperature in the range of 120 °C to 200 °C.

[0043] The following examples are intended to describe the subject matter of the invention in more detail, without wishing to restrict it to the specific embodiments presented here.

[0044] Figure 1 schematically shows a first membrane arrangement of an electrochemical cell according to the invention. A flat protective layer 2 having pores 3 of a first pore size is arranged on the underside of a flat anode layer 1. A flat cathode layer 4 is arranged on the underside of the flat protective layer 2. A first electrically conductive collector layer 8 is arranged on the top side of the flat anode layer 1, and a second electrically conductive collector layer 9 is arranged on the underside of the flat cathode layer 4.

[0045] Figure 2 schematically shows a second membrane arrangement of an electrochemical cell according to the invention. On the underside of a flat anode layer 1, a flat protective layer 2 is arranged, which has pores 3 of a first pore size. On the underside of the flat protective layer 2, a flat substrate 5 is arranged, which has pores 6 of a second pore size. On the underside of the flat substrate 5, a further flat protective layer 7 is arranged, which has pores of a first pore size 3. On the underside of the further flat protective layer 7, a flat cathode layer 4 is arranged. The membrane arrangement shown here does not (yet) have an electrically conductive conductor (e.g., no conductor layers).

[0046] Figure 3 schematically shows a third membrane arrangement of an electrochemical cell according to the invention. On the underside of a flat anode layer 1, a flat protective layer 2 is arranged, which has pores 3 of a first pore size. On the underside of the flat protective layer 2, a flat substrate 5 is arranged, which has pores 6 of a second pore size. On the underside of the flat substrate 5, a further flat protective layer 7 is arranged, which has pores 3 of a first pore size. On the underside of the further flat protective layer 7, a flat cathode layer 4 is arranged. On the top side of the flat anode layer 1, a first electrically conductive conductor layer 8 is arranged, and on the underside of the flat cathode layer 4, a second electrically conductive conductor layer 9 is arranged.

[0047] Example 1 - First method for producing a membrane assembly

[0048] An anode layer is first applied to the underside of an electrically conductive conductor layer. The application can be carried out using a process selected from the group consisting of atmospheric plasma spraying (APS), slurry-based coating (e.g., immersion bath, slot nozzle, and / or lamination) with subsequent debinding, electrophoretic coating, or gas-based coating (e.g., CVD, optionally with subsequent chemical conversion of precursors into the target materials). The anode layer is preferably applied with a thickness of at least 5 μm. To apply a ceramic protective layer to the underside of the anode layer, a powder consisting of an electrically non-conductive ceramic material is applied to the underside of the anode layer.The powder is preferably applied by atmospheric plasma spraying until a pore size in the range of 50–5000 nm and a layer thickness in the range of 15 to 250 pm is achieved. The pore size of the ceramic protective layer can be adjusted by selecting the powder and the coating process settings.

[0049] Subsequently, a cathode layer is applied to the upper surface of another electrically conductive conductor layer. The application can be carried out using a process selected from the group consisting of atmospheric plasma spraying (APS), slurry-based coating (e.g., immersion bath, slot die, and / or lamination) with subsequent debinding, electrophoretic coating, and gas-based coating (e.g., CVD, optionally with subsequent chemical conversion of precursors into the target materials). The cathode layer is preferably applied with a thickness of at least 5 pm.

[0050] The ceramic protective layer applied to the underside of the anode layer is then applied to the top side of the cathode layer to complete the membrane assembly. This assembly can be carried out using a method selected from the group consisting of pressing, joining, and combinations thereof, wherein the pressing preferably comprises pressing with a pressure in the range of 50 to 3500 MPa, preferably in the range of 100 to 3000 MPa, particularly preferably in the range of 150 to 2500 MPa, in a direction perpendicular to the membrane assembly.

[0051] Preferably, the manufactured membrane assembly is then annealed at a temperature in the range of 400 °C to 700 °C for 30 to 300 minutes. The arrangement of the layers in such a membrane assembly is shown in Figure 1.

[0052] Due to its pore size, the ceramic protective layer ensures high ionic conductivity (e.g., for hydroxide ions) and low permeability for hydrogen. Example 2 - Second process for producing a membrane assembly

[0053] A cathode layer is first applied to the upper surface of an electrically conductive conductor layer. The application can be carried out using a process selected from the group consisting of atmospheric plasma spraying (APS), slurry-based coating (e.g., immersion bath, slot die, and / or lamination) with subsequent debinding, electrophoretic coating, or gas-based coating (e.g., CVD, optionally with subsequent chemical conversion of precursors into the target materials). The cathode layer is preferably applied with a thickness of at least 5 pm.

[0054] To apply a ceramic protective layer to the top side of the cathode layer, a powder consisting of an electrically non-conductive ceramic material is applied to the underside of the anode layer. The powder is preferably applied by atmospheric plasma spraying until a pore size in the range of 50–5000 nm and a layer thickness in the range of 15–250 pm is achieved. The pore size of the ceramic protective layer can be adjusted by selecting the powder and the coating process settings.

[0055] Subsequently, an anode layer is applied to the underside of another electrically conductive conductor layer. The application can be carried out using a process selected from the group consisting of atmospheric plasma spraying (APS), slurry-based coating (e.g., immersion bath, slot die, and / or lamination) with subsequent debinding, electrophoretic coating, or gas-based coating (e.g., CVD, optionally with subsequent chemical conversion of precursors into the target materials). The anode layer is preferably applied with a thickness of at least 5 pm.

[0056] The ceramic protective layer applied to the top side of the cathode layer is then applied to the underside of the anode layer to complete the membrane assembly. This assembly can be carried out using a method selected from the group consisting of pressing, joining, and combinations thereof, wherein the pressing preferably comprises pressing with a pressure in the range of 50 to 3500 MPa, preferably in the range of 100 to 3000 MPa, particularly preferably in the range of 150 to 2500 MPa, in a direction perpendicular to the membrane assembly.

[0057] Preferably, the manufactured membrane assembly is then annealed at a temperature in the range of 400 °C to 700 °C for 30 to 300 minutes. The arrangement of the layers in such a membrane assembly is shown in Figure 1.

[0058] Due to its pore size, the ceramic protective layer ensures high ionic conductivity (e.g. for hydroxide ions) on the one hand and low permeability for hydrogen on the other.

[0059] Example 3 - Third method for producing a membrane assembly

[0060] A porous flat substrate (metal substrate) is first degreased in ethanol or other alcohols and then sandblasted to increase the adhesion of the surface to be coated. The grain size of the sand should be larger than the substrate pore size.

[0061] A ceramic protective layer is then applied to the top and bottom of the flat substrate. For this purpose, a powder consisting of an electrically non-conductive ceramic material is applied to both sides of the porous metal substrate. The powder is preferably applied using atmospheric plasma spraying until a pore size in the range of 50–5000 nm and a layer thickness in the range of 15 to 250 pm is achieved. The pore size of the ceramic protective layer can be adjusted by selecting the powder and the coating process settings.

[0062] The ceramic protective layer applied to the porous metal substrate electrically insulates the porous metal substrate and, due to its pore size, ensures high ionic conductivity (e.g., for hydroxide ions) and low permeability for hydrogen. Subsequently, an anode layer is applied to the top side of the flat substrate (more precisely, to the ceramic protective layer applied there), and a cathode layer is applied to the underside of the flat substrate (more precisely, to the ceramic protective layer applied there). The application can be carried out using a process selected from the group consisting of atmospheric plasma spraying (APS), slurry-based coating (e.g., immersion bath, slot nozzle, and / or lamination) with subsequent debinding, electrophoretic coating, gas-based coating (e.g.,CVD, optionally with subsequent chemical conversion of precursors into the target materials). The anode layer and cathode layer are preferably applied with a thickness of at least 5 pm each.

[0063] Preferably, the manufactured membrane arrangement is then annealed at a temperature in the range of 400 °C and 700 °C for 30 to 300 minutes.

[0064] The result is a membrane arrangement that does not yet have any electrically conductive conductors. The arrangement of the layers in such a membrane arrangement is shown in Figure 2.

[0065] Alternatively, the anode layer is first applied to the underside of an electrically conductive collector layer, and the cathode layer is applied to the top side of another electrically conductive collector layer. The application can be carried out using a method selected from the group consisting of atmospheric plasma spraying (APS), slurry-based coating (e.g., immersion bath, slot die, and / or lamination) with subsequent debinding, electrophoretic coating, and gas-based coating (e.g., CVD, optionally with subsequent chemical conversion of precursors into the target materials). The anode layer and cathode layer are preferably each applied with a thickness of at least 5 pm.

[0066] Subsequently, the anode layer (provided with the electrically conductive conductor layer) is applied to the top side of the flat substrate (more precisely: to the ceramic protective layer applied there), and the cathode layer (provided with the further electrically conductive conductor layer) is applied to the underside of the flat substrate (more precisely: to the ceramic protective layer applied there). This assembly can be carried out using a method selected from the group consisting of pressing, joining, and combinations thereof, wherein the pressing preferably comprises pressing with a pressure in the range of 50 to 3500 MPa, preferably in the range of 100 to 3000 MPa, particularly preferably in the range of 150 to 2500 MPa, in a direction perpendicular to the membrane arrangement.

[0067] Preferably, the manufactured membrane arrangement is then annealed at a temperature in the range of 400 °C and 700 °C for 30 to 300 minutes.

[0068] This alternative creates a membrane arrangement that already has two electrically conductive conductors. The arrangement of the layers in such a membrane arrangement is shown in Figure 3.

[0069] 1: flat anode layer;

[0070] 2: flat protective layer;

[0071] 3: Pores of first pore size;

[0072] 4: flat cathode layer;

[0073] 5: flat substrate;

[0074] 6: Pores of second pore size;

[0075] 7: additional flat protective layer;

[0076] 8: first electrically conductive conductor layer;

[0077] 9: second electrically conductive conductor layer.

Claims

Patent claims 1. An electrochemical cell comprising: a) a container containing a liquid electrolyte; b) a membrane assembly comprising a sheet-like anode layer having a top side and a bottom side; a sheet-like protective layer having a top side, a bottom side, and pores of a first pore size extending from the top side to the bottom, wherein the sheet-like protective layer contains or consists of an electrically insulating ceramic material; and a sheet-like cathode layer having a top side and a bottom side; wherein the membrane assembly contacts the liquid electrolyte, wherein the membrane assembly is arranged in the container such that it separates the liquid electrolyte into a first compartment and a second compartment, wherein the membrane assembly separates the first compartment from the second compartment in an electrically insulating and ion-conducting manner;wherein the planar protective layer is arranged on the underside of the planar anode layer and the upper side of the planar protective layer contacts the underside of the planar anode layer; wherein i) the cathode layer is arranged on the underside of the planar protective layer and the upper side of the cathode layer contacts the underside of the planar protective layer; or; ii) a planar substrate is arranged, which has a top side, a bottom side, and pores extending from the top side to the bottom side of a second pore size that is larger than the first pore size, wherein the top side of the planar substrate contacts the bottom side of the planar protective layer, and the cathode layer is arranged on the bottom side of the planar substrate; characterized in that the membrane arrangement contains no organic polymer.

2. Electrochemical cell according to the preceding claim, characterized in that the planar protective layer i) was applied to the underside of the planar anode layer, to the top side of the planar cathode layer and / or to the top side of the planar substrate using a method selected from the group consisting of atmospheric plasma spraying, slurry-based coating with subsequent debinding, electrophoretic coating, gas-based coating, wherein the slurry-based coating is preferably selected from the group consisting of immersion bath coating, slot die coating, lamination and combinations thereof; and / or ii) has a thickness in the range of 10 to 1000 pm, wherein the thickness relates in particular to an extension of the protective layer in a direction perpendicular to the top side and / or underside of the planar protective layer.

3. Electrochemical cell according to one of the preceding claims, characterized in that on the underside of the planar substrate there is arranged a further planar protective layer which has a top side, a bottom side and pores of a first pore size extending from the top side to the bottom side, wherein the further planar protective layer contains or consists of an electrically insulating ceramic material, wherein preferably the underside of the flat substrate contacts the top side of the protective layer and the underside of the protective layer contacts the top side of the flat cathode layer.

4. Electrochemical cell according to the preceding claim, characterized in that the further planar protective layer i) was applied to the underside of the planar substrate using a method selected from the group consisting of atmospheric plasma spraying, slurry-based coating with subsequent debinding, electrophoretic coating, gas-based coating, wherein the slurry-based coating is preferably selected from the group consisting of immersion bath coating, slot die coating, lamination and combinations thereof; and / or ii) has a thickness in the range from 10 to 1000 pm, wherein the thickness relates in particular to an extension of the planar protective layer in a direction perpendicular to the top and / or bottom of the planar protective layer.

5. Electrochemical cell according to one of the preceding claims, characterized in that the membrane arrangement was assembled by a method selected from the group consisting of pressing, joining and combinations thereof, wherein the pressing preferably comprises pressing with a pressure in the range of 50 to 3500 MPa, preferably in the range of 100 to 3000 MPa, particularly preferably in the range of 150 to 2500 MPa, in a direction perpendicular to the membrane arrangement.

6. Electrochemical cell according to one of the preceding claims, characterized in that the cathode layer contains or consists of a catalyst which catalyzes a reduction of water to hydrogen, wherein the catalyst preferably contains a material which is selected from the group consisting of metal, metal alloy and combinations thereof, wherein the material optionally is selected from the group consisting of nickel, cobalt, molybdenum, manganese, nickel-aluminum, nickel-aluminum-molybdenum, nickel-molybdenum, Raney nickel, and combinations thereof.

7. Electrochemical cell according to one of the preceding claims, characterized in that the anode layer contains or consists of a catalyst which catalyzes an oxidation of water to oxygen, wherein the catalyst preferably contains a material selected from the group consisting of metal, metal alloy, metal oxide, mixed metal oxide, spinel, perovskite, layered double hydroxide and combinations thereof, wherein the material is optionally selected from the group consisting of nickel, cobalt, nickel-aluminum, nickel-aluminum-molybdenum, nickel-molybdenum, Raney nickel, nickel oxide, iridium oxide and combinations thereof.

8. Electrochemical cell according to one of the preceding claims, characterized in that the planar substrate i) contains or consists of a material selected from the group consisting of metal, metal alloy and combinations thereof, wherein the material is preferably selected from the group consisting of stainless steel, nickel steel, solid nickel and combinations and alloys thereof; and / or ii) contains or consists of a structure selected from the group consisting of nonwoven fabric, solid foam, expanded metal, mesh, woven fabric and combinations thereof; and / or iii) has a thickness in the range of 40 to 1500 pm, preferably in the range of 50 to 1250 pm, particularly preferably in the range of 60 pm to 1000 pm, wherein the thickness relates in particular to an extension of the planar substrate in a direction perpendicular to the top and / or bottom of the planar substrate.

9. Electrochemical cell according to one of the preceding claims, characterized in that the pores of the flat substrate i) have a second pore size in the range from 5 pm to 1250 pm, preferably in the range from 10 pm to 1000 pm, particularly preferably in the range from 15 pm to 750 pm, wherein the pore size refers to a pore size determinable via mercury porosimetry and / or bubble point measurement; and / or ii) have a second pore size which decreases from the top side of the planar substrate towards the underside of the planar substrate or which decreases from the underside of the planar substrate towards the top side of the planar substrate.

10. Electrochemical cell according to one of the preceding claims, characterized in that the electrically insulating ceramic material of the planar protective layer, optionally also the electrically insulating ceramic material of a further planar protective layer of the membrane arrangement, i) contains or consists of a material selected from the group consisting of nitride ceramic, carbide ceramic, oxide ceramic, silicate ceramic, cermet and combinations thereof; and / or ii) contains or consists of particles, wherein the particles preferably have a size in the range from 0.5 pm to 95 pm, preferably in the range from 5 pm to 70 pm, particularly preferably in the range from 9 pm to 45 pm, wherein the particle size refers to a measurement of the particle size distribution.

11. Electrochemical cell according to one of the preceding claims, characterized in that the pores of the planar protective layer, optionally also the pores of a further planar protective layer of the membrane arrangement, have a first pore size in the range from 50 nm to 9 pm, wherein the pore size refers to a pore size determinable via mercury porosimetry and / or bubble point measurement.

12. Electrochemical cell according to one of the preceding claims, characterized in that the planar protective layer, optionally also a further planar protective layer of the membrane arrangement, i) has an electrical resistance in the kΩ to MΩ range; and / or ii) an ionic resistance in the range of <0.3 to 0.8 Ωcm 2 and / or iii) a gas permeability in the range of 2 to 6 L / min-cm 2 at 5 bar; and / or iv) is conductive for ions selected from the group consisting of alkali metal ions, OH ions, H+ -ions and combinations thereof.

13. Electrochemical cell according to one of the preceding claims, characterized in that the membrane arrangement i) contains no organic material; and / or ii) is stable towards an aqueous solution of 35 wt.% KOH, based on the total weight of the aqueous solution, preferably is not damaged, in particular does not dissolve; and / or iii) is stable towards a pressure of 30 bar on an upper or lower side of the membrane, preferably is not damaged by this pressure, in particular does not crack; and / or iv) is stable towards a temperature of 200°C, preferably is not damaged, in particular does not melt and / or burn.

14. An electrochemical cell according to any one of the preceding claims, characterized in that the electrochemical cell further comprises i) an inlet for supplying liquid electrolyte into the first compartment and an outlet for discharging a first fluid from the first compartment; and ii) an inlet for supplying liquid electrolyte into the second compartment and an outlet for removing a second fluid from the second compartment.

15. Electrochemical cell according to one of the preceding claims, characterized in that the electrochemical cell is selected from the group consisting of electrolysis cell, battery cell, fuel cell and CCh reduction cell, wherein the electrochemical cell is particularly preferably a water electrolysis cell, most preferably an alkaline water electrolysis cell.

16. A process for producing hydrogen and oxygen from water, comprising the following steps: a) providing an electrochemical cell according to any one of the preceding claims, wherein the liquid electrolyte is an aqueous solution containing 35 to 40 wt.% KOH, based on the total weight of the aqueous solution; and b) applying an electrical voltage between the cathode and anode of the electrochemical cell and performing electrolysis; wherein the electrolysis is preferably carried out at a pressure in the range of 1 to 30 bar and / or a temperature in the range of 120°C to 200°C.

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