DE102015111918A1 - Current collector, membrane unit, electrochemical cell, method for producing a current collector, a membrane unit and an electrochemical cell - Google Patents

Abstract

In order to improve a method for producing a current collector for an electrode of an electrochemical cell, in particular an anode of a proton exchange membrane electrolyzer so that in particular a function of the electrochemical cell is improved, it is proposed that a substrate is provided and that Forming the current collector at least one microporous, consisting of titanium or titanium-containing layer is applied to the substrate by plasma spraying in vacuo.

Description

The present invention relates to a method for producing a current collector for an electrode of an electrochemical cell, in particular an anode of a proton exchange membrane electrolyzer.

Furthermore, the present invention relates to a method for producing a membrane unit of an electrochemical cell, in particular a proton exchange membrane electrolyzer, in which a proton exchange membrane is provided, on one side of which a first catalyst layer is applied.

Furthermore, the present invention relates to a method for producing an electrochemical cell, in particular a proton exchange membrane electrolyzer.

Furthermore, the present invention relates to a current collector for an electrode of an electrochemical cell, in particular an anode of a proton exchange membrane electrolyzer.

Furthermore, the present invention relates to a membrane unit of an electrochemical cell, in particular of a proton exchange membrane electrolyzer, comprising a proton exchange membrane, on one side of which a first catalyst layer is applied.

Finally, the present invention relates to an electrochemical cell, in particular in the form of a proton exchange membrane electrolyzer, comprising two bipolar plates and a membrane unit arranged between them.

Proton exchange membrane electrolyzers are becoming increasingly important. With them, hydrogen can be obtained as an energy source, in particular with electricity generated by the use of renewable energy sources such as wind and / or solar energy.

In principle, proton exchange membrane electrolyzer systems consist of a stack of several electrolysis cells in which water is split electrochemically into hydrogen and oxygen. These systems also include an electromechanical plant periphery and required control technology. The stack of electrolyzers, also referred to as a "stack", covers 60 percent of the investment costs of the entire system ("Study on development of water electrolysis in the EU, Final Report: E4tech Fuel Cells and Hydrogen Joint Undertaking, 2014"). A significant proportion of the costs of the electrolyzer stack is attributable to the current collector on the anode side of the electrolyzers. This anodic current collector is intended to ensure efficient transport of water to the catalyst layer and efficient removal of oxygen gas bubbles produced, in particular to a so-called flow field, a channel system which is part of the respective electrodes of the bipolar plates forming the electrolyzers.

Because of their similar function compared to the porous or hydrophobic carbon structures in polymer electrolyte fuel cells, electrolyser current collectors are often referred to as gas diffusion layers.

• – Er sollte eine hohe Korrosionsbeständigkeit bei hohen Spannungen von mehr als 2 V in seiner Umgebung mit einem pH-Wert von etwa 0 aufweisen.
• – Vorzugsweise sollte der Stromkollektor eine geringe Porosität und Porengröße aufweisen.
• – Des Weiteren sollte der Stromkollektor eine hohe mechanische Stabilität und Beständigkeit gegenüber einer H₂-Versprödung für den Einsatz des Stromkollektors auf der Kathodenseite aufweisen.
• – Idealerweise ist der Stromkollektor hinreichend dünn, um einen effizienten Abtransport von Sauerstoff-Gasblasen gewährleisten zu können.
• – Außerdem sollte ein Kontaktwiderstand zwischen dem Stromkollektor und der Bipolarplatte sowie zwischen dem Stromkollektor und der Katalysatorschicht möglichst klein ist.
• – Ein Ziel ist es zudem, Protonen-Austausch-Membran-Elektrolyseur-Systeme im Megawatt-Bereich verfügbar zu machen.
• – Ferner soll eine Fertigung geometrischer Strukturen mit Oberflächen von mehr als 1500 cm² ermöglicht werden.
• – Und schließlich sollen auch Kosten für die Herstellung der elektrochemischen Zellen reduziert werden.

A current collector of an electrolytic cell should in particular meet the following requirements:

• It should have a high corrosion resistance at high voltages of more than 2 V in its environment with a pH of about 0.
• Preferably, the current collector should have a low porosity and pore size.
• - Furthermore, the current collector should have a high mechanical stability and resistance to H ₂ -Versprödung for the use of the current collector on the cathode side.
• - Ideally, the current collector is sufficiently thin to ensure efficient removal of oxygen bubbles.
• - In addition, a contact resistance between the current collector and the bipolar plate and between the current collector and the catalyst layer should be as small as possible.
• - Another goal is to make megawatt-range proton exchange membrane electrolyzer systems available.
• - Furthermore, a production of geometric structures with surfaces of more than 1500 cm ^{2 is} to be made possible.
• - And finally, costs for the production of electrochemical cells are to be reduced.

According to the currently known state of the art, the current collector of a proton exchange membrane electrolyzer consists of a porous titanium structure, in particular in the form of sintered plates, foams, felts or expanded gratings. A thickness of these sintered structures is about 1000 microns and can not usually be reduced while retaining all structural and mechanical properties on. In such sintered titanium structures, the porosity and pore size can only be controlled by a suitable choice of size and shape of the titanium particles used. However, it is clear that an adjustment of porosity and pore size with the available means is very limited.

It is therefore an object of the present invention to improve a current collector, a membrane unit, an electrochemical cell and methods for producing a current collector, a membrane unit and an electrochemical cell of the type described above so that in particular a function of the electrochemical cell is improved.

This object is achieved in a method for producing a current collector of the type described above according to the invention that a substrate is provided and that for forming the current collector at least one microporous, consisting of titanium or titanium-containing layer is applied to the substrate by plasma spraying in vacuo.

In particular, the at least one microporous layer makes it possible to improve the contact with the catalyst layer and in particular can also improve mass transport. In particular, it is possible to set a specific porosity of the at least one microporous layer, for example by varying the process parameters during plasma spraying of the layer in a vacuum. This makes it possible, in particular, to carry out the vacuum plasma spraying of the at least one microporous layer with a single particle size as starting material. In particular, the proposed method also allows the formation of multilayer or multi-layer systems with thicknesses that are significantly lower overall than the 1000 μm specified above, which are practically not to be undershot during the sintering of titanium layers. The plasma spraying of titanium powder to form titanium or titanium-containing microporous layers can also achieve very high roughness, especially when the at least one microporous layer is applied to a substrate formed of sintered titanium. The at least one microporous layer has in particular a high roughness and a low porosity. A layer thickness of the current collector thus formed can be easily controlled and reduced to thicknesses of only about 10 microns. Manufacturing costs can be significantly reduced, especially in mass production. In particular, a multilayer or multilayer construction of the current collector allows the porosity of individual microporous layers or layers to be adapted to those layers which are in contact with the current collector. Thus, in particular, an inner layer or layer of the current collector which is in contact with the catalyst layer may have a low porosity, whereas an outer layer which is in contact with a biopolar plate of an electrochemical cell may have significantly larger pores, for example in the case of an electrolyzer To allow O ₂ gas bubbles.

It is favorable if the at least one layer consisting of titanium is applied by plasma spraying of titanium powder. Thus, a pure and substantially pure titanium layer can be formed. Also, multi-layer or multi-layer systems are possible, wherein porosities of different layers or layers or can be formed differently.

Furthermore, it is advantageous if the titanium-containing layer is applied by plasma spraying a mixture of titanium powder and at least one metal powder, wherein the at least one metal powder is a powder of a base metal. In particular, the base metal can be aluminum, iron or zinc. The microporous layer, which contains at least one base metal, can be specifically treated to form larger pores, in particular. The base metal powder thus serves only as a placeholder for pores still to be formed, which are formed, for example, by removing the base metal powder. All that is left then is a microporous layer made of titanium, since the sprayed-on base metal powder is ideally no longer contained in the microporous layer.

Preferably, the substrate is made by sintering titanium powder or formed by a titanium expanded metal mesh. Thus, in particular, a current collector can be formed which comprises the sintered titanium powder substrate and the at least one microporous layer which consists of titanium or contains titanium.

Conveniently, the current collector is formed by the substrate and the at least one titanium layer. Thus, in particular, a substrate can be formed as part of the current collector, which has a high porosity.

It is also advantageous if unalloyed steel or copper is provided as the substrate. In particular, such a substrate makes it possible to form a self-supporting layer, since unalloyed steel and copper can be removed in a simple manner, for example by means of a chemical reaction, so that the microporous layer sprayed with at least plasma remains alone.

In order to improve the production of current collectors and in particular of membrane units and electrochemical cells as a whole, it is advantageous if the current collector is formed in the form of a self-supporting layer. A self-supporting layer has the particular advantage that it can be connected to other layers which, for example, are not sufficiently stable, so that the microporous layer can be applied to it by plasma spraying. For example, self-supporting, microporous layers with catalyst layers or proton exchange membranes by pressing, in particular hot pressing, are connected.

Preferably, the substrate is removed to form the self-supporting layer. For example, removal of the substrate may be by corrosion or chemical reaction with an oxidizing agent. In this way, the substrate can be removed and the at least one microporous layer or the layer system comprising several microporous layers or layers can be further processed as an independent current collector.

It is advantageous if the at least one base metal contained in the titanium-containing layer is removed. In particular, it can be removed by corrosion or chemical reaction with an oxidizing agent. Wherever the base metal in the microporous sprayed-on layer contains base metal, pores are formed by removing the same, so that in this way large pores can be deliberately introduced into the microporous layer.

Conveniently, potassium hydroxide (KOH) or sulfuric acid (H ₂ SO ₄ ) or perchloric acid (HClO ₄ ) is used as the oxidizing agent. In particular, base metals can be quickly and easily oxidized by acids. For example, the following reaction equations result for the oxidation of aluminum: 2 Al (s) + 2 KOH (aqueous) + 6 H ₂ O (liquid) → 2 KAl (OH) ₄ (aqueous) + 3 H ₂ (gaseous) 2 Al (solid) + 6 H ₂ SO ₄ (concentrated) = Al ₂ (SO ₄ ) ₃ (solid) + 3 SO ₂ (solid) + 6 H ₂ O (liquid)

Preferably, the current collector is formed with an average current collector layer thickness in a range of about 10 μm to about 100 μm. It is thus significantly thinner than known current collectors made of sintered titanium and can thus be formed with a significantly reduced use of materials. In particular, the current collector layer thickness can be selectively varied by the number of microporous layers or layers.

It is advantageous if two, three, four, five, six, seven, eight or more microporous layers or layers for the formation of the current collector are applied to the substrate. In particular, such a quasi-continuous transition of a large porosity of a microporous layer or layer of the current collector adjacent to a bipolar plate of an electrochemical cell may be adjusted to a small porosity towards a microporous layer adjacent to a catalyst layer of the electrochemical cell. The more layers or layers are formed, the finer the porosities of the same can be graded.

It is advantageous if the at least one microporous layer having a pore size in a range from about 0.1 μm to about 10 μm is formed. In particular, it may be formed with a pore size in a range of about 1 μm to about 2 μm. In the areas indicated, a desired removal, in particular of oxygen gas bubbles in electrolyzers, can be achieved well.

Furthermore, it is advantageous if the at least one microporous layer having a porosity in a range of about 5% to about 28% is formed. In particular, the porosity may range from about 8% to about 15%. So as well as in the setting of the pore sizes optimal values for the porosity can be achieved, which allow a good removal, in particular of developing oxygen in electrolysers.

It is advantageous if the at least one microporous layer is formed with an outflow rate in a range from about 0.01 mbar l cm ^-2 s ^-1 to about 500 mbar l cm ^-2 s ^-1 . In particular, the outflow rate may be in a range from about 0.1 mbar 1 cm ^-2 s ^-1 to about 150 mbar 1 cm ^-2 s ^-1 . In this way, a very dense microporous layer can be formed. Layer systems with multiple layers can have different outflow rates, which improve the discharge of oxygen produced at the anode of an electrolyzer.

It is advantageous if the at least one microporous layer with a plasma enthalpy in a range of about 8 MJ kg ^-1 to about 30 MJ kg ^{-1 is} sprayed. In particular, the layer may be sprayed with a plasma enthalpy in a range of about 15 MJ kg ^-1 to about 23 MJ kg ^-1 . With plasma enthalpies in the specified range can form qualitatively excellent layers with desired properties.

Furthermore, it is advantageous if the at least one microporous layer is sprayed with a flame deflection speed in a range from about 300 mm s ^-1 to about 600 mm s ^-1 . In particular, the flame deflection speed may range from about 350 mm s ^-1 to about 500 mm s ^-1 . For example, an outflow rate of the at least one microporous layer can be adjusted in a targeted manner via the deflection speed. Denser layers with lower outflow rates can be formed in particular if the flame deflection speed, ie the turn-off speed, is reduced. The flame deflection speed is the speed with which the flame is moved over the surface to be coated. The higher the flame deflection speed, the more porous and rougher the microporous layer becomes.

Preferably, two or more microporous layers are formed by plasma spraying with the same titanium powder. Unlike sintering, therefore, different powders with different particle or grain sizes are not required, but the production of the current collector can be done with a single titanium powder. For example, the titanium powder Gd1 can be spiked particles from the company TLS Technik with an average particle size of about 45 μm.

In order to obtain high quality current collectors, it is advantageous to provide titanium powder having a purity of at least about 99.6%. The purer the titanium powder used to form the at least one microporous layer, the purer and free of contaminants are the current collectors. In particular, undefined foreign substances can impair a function of the electrochemical cell.

In order to optimize the removal of forming gas, in particular in electrolyzers, it is advantageous if two or more microporous layers or layers are formed such that porosities of successive layers or layers starting from the substrate are the same or decrease. In particular, porosities can decrease towards a catalyst layer, which in turn facilitates the removal of oxygen which forms at the anode of an electrolysis cell.

Furthermore, it is favorable if a porosity of the at least one microporous layer is set by predetermining a plasma enthalpy and / or a flame deflection speed. In particular, by adjusting one or both said process parameters in plasma spraying, the porosity can be varied. Layers become denser, ie less porous, the lower the flame deflection speed. Porosity also decreases with increasing plasma enthalpy. Flow rates of process gases in vacuum plasma spraying, in particular a nitrogen, argon or hydrogen flow rate, allow an accurate and reproducible adjustment of porosity, roughness, pore size and thickness of the microporous layer.

In order to minimize an undesirable anodic oxidation reaction, it is advantageous if a corrosion protection layer is applied to the at least microporous layer. In particular, the anticorrosive layer can form a cover layer of the current collector, that is to say be applied to only one of the at least one microporous layers. Preferably, the corrosion protection layer is dense, thin, conductive, corrosion resistant and / or hydrophilic. In particular, it is favorable if the corrosion protection layer does not close the micropores of the at least one microporous layer.

An optimal passivation of the current collector can be achieved, in particular, by forming the anticorrosion layer from at least one noble metal or a porous electrocatalyst. In particular, these may be gold, platinum and / or iridium. The corrosion protection layer can be deposited in particular electrochemically. The porsöse electrocatalyst may be formed in particular in the form of an electrocatalytic layer. For example, this may be in the form of layers of SnO ₂ : Sb, Ti ₄ O ₇ , SnO ₂ : M (with M = Sb, In, Nb) or TiO ₂ : M (with M = W, Nb, Mo).

It is advantageous if the substrate is provided with a substrate thickness and if the at least one microporous layer is applied with a layer thickness which is smaller than the substrate thickness. In this way, particularly thin microporous layers and layer systems can be formed.

The object stated in the introduction is also achieved in a method for producing a membrane unit of the type described in the introduction by applying to the first catalyst layer a current collector which is produced by one of the methods described above.

In this way, membrane units can be formed, which can be used for the production of electrochemical cells, in particular electrolysis cells. Thus, a total of membrane units can be formed with the advantages described above.

It is advantageous if the current collector is made self-supporting and pressed with the first catalyst layer. In particular, the pressing can take place under the action of heat, that is, in the form of a hot pressing. In this way, defined, high-quality, thin current collectors can be connected to catalyst layers to form membrane units.

It is advantageous if a second catalyst layer is applied to the other side of the proton exchange membrane. Thus, a membrane unit may in particular comprise the proton exchange membrane, two catalyst layers and at least one current collector.

Furthermore, it is favorable if a further current collector is applied to the second catalyst layer. In particular, the further current collector can be produced by one of the methods described above. Overall, it is thus possible to form a membrane unit having a proton exchange membrane which carries a catalyst layer on both sides, which in turn may each be connected to a current collector, wherein in particular the anodic catalyst layer is formed with a current collector comprising at least one microporous layer.

The object stated in the introduction is further achieved in a method for producing an electrochemical cell according to the invention in that one of the membrane units described above is produced and arranged between two bipolar plates.

With the proposed method, electrochemical cells can be formed with small interfacial contact resistances of current collectors to a catalyst layer and to a bipolar plate.

It is advantageous if the bipolar plates are provided with flow channels which are formed in the form of grooves opened onto the membrane unit. Through the flow channels, also referred to as the flow field of the bipolar plates, forming oxygen can be optimally dissipated, in particular at the anode side of the electrolysis cell forming bipolar plates.

The object stated in the introduction is further achieved, according to the invention, in a current collector of the type described above, comprising at least one microporous layer consisting of titanium or titanium and formed by plasma spraying in a vacuum.

In particular, such a current collector can be formed significantly thinner than conventional current collector sintered titanium powder. As described above, properties of the current collector, in particular porosity, pore size, roughness and layer thickness and outflow rate can be set in the desired manner by means of the special manufacturing process.

Preferably, the at least one titanium layer is formed by plasma spraying titanium powder. In particular, more layers or layers may be formed, which are sprayed with the same titanium powder, for example, in the same injection molding.

It is favorable if the titanium-containing layer is formed by plasma spraying a mixture of titanium powder and at least one metal powder, wherein the metal powder is a powder of a non-noble metal. In particular, the base metal may be aluminum, iron or zinc. The microporous layer formed from a mixture of titanium powder and a metal powder has the particular advantage that the base metal after spraying the layer can be easily removed to very large pores or pores of defined size, namely with a size of the base metal powder forming particles to form in the microporous layer. In other words, this means that the base metal is only temporarily part of the microporous layer and thus characterizes the current collector only at an intermediate stage in the production.

Preferably, the at least one microporous layer is applied by plasma spraying onto a substrate produced by sintering of titanium powder. It is therefore possible to form the current collector by means of a conventional current collector of sintered titanium powder, which additionally comprises at least one microporous layer which has been applied by plasma spraying. In particular, the at least one microporous layer improves the adhesion of a corrosion protection layer, for example of a noble metal or a thin ceramic film, and the connection with a catalyst layer of the electrochemical cell.

The current collector can be produced particularly easily if it is formed by the substrate and the at least one microporous layer made of titanium. The at least one microporous layer can be applied directly to the substrate and this unit can thus be used as a current collector. Further process steps for the production of the current collector are then not required.

It is advantageous if the at least microporous layer is applied by plasma spraying onto a substrate formed from an unalloyed steel or copper. Such a current collector makes it possible, in particular, to remove the substrate from unalloyed steel, copper or another corrodible or oxidizable metal so as to form a self-supporting current collector comprising only the at least one microporous layer in a further method step.

Preferably, the current collector is self-supporting. This makes it possible, in particular, to manufacture it separately and to connect it to form membrane units for electrochemical cells or for the formation of electrochemical cells with catalyst layers on the one hand and bipolar plates on the other hand.

Conveniently, the at least one microporous layer is formed substratlos. In particular, a very thin layer for forming the current collector can be obtained. In particular, the microporous layer can be formed in a simple manner self-supporting by the substrate to which the at least one layer has been applied by vacuum plasma spraying is removed, for example by corrosion or oxidation.

According to a further preferred embodiment of the invention it can be provided that the at least one base metal contained in the titanium-containing layer is removed. In particular, it may be removed by corrosion or chemical reaction with an oxidizing agent. It then left cavities or pores, which are formed by the spraying of the mixture of a titanium and at least one metal powder by base metals.

Conveniently, the oxidizing agent is or contains potassium hydroxide (KOH) or sulfuric acid (H ₂ SO ₄ ) or perchloric acid (HClO ₄ ). In particular, base metals can be quickly and easily oxidized by acids.

It is advantageous if the current collector has an average current collector layer thickness in a range from about 10 μm to about 100 μm. In particular, the current collector may comprise a plurality of microporous layers. The current collector is thus significantly thinner compared to 1000 μm thick conventional current collectors made of sintered titanium powder and allows a more compact construction of electrochemical cells. In particular through thin layers, an improved transport of matter can take place.

In order to be able to set properties of the current collector, in particular porosity, pore size, layer thickness, outflow rate and / or a roughness factor in the desired manner, it is advantageous if the current collector has two, three, four, five, six, seven, eight or more microporous layers includes.

It is favorable if the at least one microporous layer has a pore size in a range from about 0.1 μm to about 10 μm. In particular, the pore size may be in a range from about 1 μm to about 2 μm. In particular, the pore size can be selected as a function of a position of the microporous layer or layer in the membrane unit or of the electrochemical cell, in order to achieve optimal removal of, for example, oxygen arising in an electrolysis cell.

It is favorable if the at least one microporous layer has a porosity in a range from about 5% to about 28%. In particular, the porosity may range from about 8% to about 15%. Again, different layers may have different porosities, so that this is preferably the greater the further this microporous layer is removed from a catalyst layer of the electrochemical cell.

It is advantageous if the at least one microporous layer has an outflow rate in a range from about 0.01 mbar 1 cm ^-2 s ^-1 to about 500 mbar 1 cm ^-2 s ^-1 . In particular, the outflow rate may be in a range from about 0.1 mbar 1 cm ^-2 s ^-1 to about 150 mbar 1 cm ^-2 s ^-1 . Such outflow rates are particularly favorable for forming highly efficient electrochemical cells, in particular electrolysers.

Particularly dense or in their porosity as desired adjusted microporous layers and layer systems can be produced when the at least one microporous layer is injected with a plasma enthalpy in a range of about 8 MJ kg ^-1 to about 30 MJ kg ^-1 . In particular, the plasma enthalpy may range from about 15 MJ kg ^-1 to about 23 MJ kg ^-1 .

According to a further preferred embodiment of the invention, it can be provided that the at least one microporous layer is sprayed with a flame deflection speed in a range from about 300 mm s ^-1 to about 600 mm s ^-1 . In particular, the at least one microporous layer may be sprayed at a flame deflection speed in a range of about 350 mm s ^-1 to about 500 mm s ^-1 . In particular, a porosity and a size of the pores of the at least one microporous layer can be adjusted by the flame deflection speed. The smaller the flame deflection speed, the smaller the pores and the smaller the outflow velocity.

It is advantageous if two or more microporous layers or layers are formed by plasma spraying with the same titanium powder. It must therefore not be used different titanium powder and with different particle sizes to adjust different pore sizes and porosities of the current collector. Rather, by simple variation of the process parameters during plasma spraying of the at least one microporous layer, its characteristic parameters can be set, for example thickness, roughness, pore size, porosity and outflow rate.

It is favorable if the titanium powder has a purity of at least about 99.6% in order to form the at least one microporous layer. With such a pure starting material can be current collectors desired purity and thus form with the desired properties.

It is advantageous if two or more microporous layers are formed such that porosities of successive layers are the same or decrease, in particular starting from the substrate onto which the at least two microporous layers or layers are sprayed. In this way, a flow of material can be improved towards microporous layers with larger pores, for example, a derivative of originated oxygen in electrolysis cells to a bipolar plate of the anode.

It is advantageous if the porosity of the at least one microporous layer is set by predetermining a plasma enthalpy and / or a flame deflection speed during spraying. This can be recognized in particular by how porosities of superimposed microporous layers or layers differ. In addition, the quality of the microporous layers is significantly better than by sintering of titanium powder of different particle size formed current collectors.

In order to prevent the current collector from oxidizing anodically, a corrosion protection layer is applied to the at least one microporous layer. In particular, the corrosion protection layer can form a thin surface layer of the current collector. It protects the current collector in particular from corrosion. The corrosion protection layer may in particular be formed from a thin ceramic layer which protects the current collector from oxidation.

It is advantageous if the corrosion protection layer is formed from at least one noble metal or contains at least one noble metal or is formed from a porous electrocatalyst. In particular, the noble metal may be gold, platinum and / or iridium. Such a corrosion protection layer can be produced in particular by electrochemical deposition. The electrocatalyst may in particular be SnO ₂ : Sb, Ti ₄ O ₇ , SnO ₂ : M (with M = Sb, In, Nb) or TiO ₂ : M (with M = W, Nb, Mo).

It is advantageous if the substrate has a substrate thickness and if the at least one microporous layer has a layer thickness which is smaller than the substrate thickness. In this way, particularly thin microporous layers and layer systems can be formed.

Advantageously, the corrosion protection layer has a corrosion protection layer thickness which is smaller than the layer thickness of the at least one microporous layer. In this way costs can be reduced. Furthermore, a large roughness of the at least one microporous layer can thus be obtained, in order in particular to improve adhesion or a connection to a catalyst layer. The roughness of the at least one microporous layer also improves the adhesion of the corrosion protection layer.

The object stated in the introduction is also achieved according to the invention in a membrane unit of the type described above in that one of the current collectors described above is applied to the first catalyst layer. The membrane unit then also has the advantages described in connection with preferred embodiments of current collectors.

It is advantageous if the current collector is made self-supporting and pressed with the first catalyst layer. In particular, it may be hot-pressed with the first catalyst layer. In this way, it is possible to form particularly compact membrane units and thus also particularly compact electrochemical cells.

Preferably, a second catalyst layer is applied on the other side of the proton exchange membrane. This may in particular be a cathodic catalyst layer.

It is also advantageous if a further current collector is applied to the second catalyst layer. In particular, this may be one of the current collectors described above. Thus, a total of membrane units can be formed comprising a proton exchange membrane, two catalyst layers and two current collectors. These can be manufactured as a unit and combined or provided with bipolar plates or other layers to form electrochemical cells.

The object stated in the introduction is achieved according to the invention in an electrochemical cell of the type described in the introduction by arranging one of the above-described advantageous membrane units between the two bipolar plates.

Such an electrochemical cell will then collectively have the advantages described above in connection with preferred embodiments of current collectors.

Furthermore, it is favorable if the two bipolar plates have flow channels which are formed in the form of grooves opened onto the membrane unit. Bipolar plates with such flow channels, which are also referred to as flow fields, make it possible in a simple manner to divert resulting gases, for example oxygen, at the anode of an electrolysis cell.

• 1. Verfahren zur Herstellung eines Stromkollektors (26) für eine Elektrode einer elektrochemischen Zelle (10), insbesondere einer Anode eines Protonen-Austausch-Membran-Elektrolyseurs (12), dadurch gekennzeichnet, dass ein Substrat (50) bereitgestellt wird und dass zur Ausbildung des Stromkollektors mindestens eine mikroporöse, aus Titan bestehende oder Titan enthaltende Schicht (44) auf das Substrat (50) durch Plasmaspritzen im Vakuum aufgebracht wird.
• 2. Verfahren nach Satz 1, dadurch gekennzeichnet, dass die mindestens eine aus Titan bestehende Schicht (44) durch Plasmaspritzen von Titanpulver aufgebracht wird.
• 3. Verfahren nach Satz 1, dadurch gekennzeichnet, dass die Titan enthaltende Schicht (44) durch Plasmaspritzen einer Mischung aus Titanpulver und mindestens einem Metallpulver aufgebracht wird, wobei das mindestens eine Metallpulver ein Pulver aus einem unedlen Metall ist, insbesondere aus Aluminium, Eisen oder Zink.
• 4. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass das Substrat (50) durch Sintern von Titanpulver hergestellt oder durch ein Titan-Streckgitter gebildet wird.
• 5. Verfahren nach Satz 4, dadurch gekennzeichnet, dass der Stromkollektor (26) durch das Substrat (50) und die mindestens eine aus Titan bestehende Schicht (44) ausgebildet wird.
• 6. Verfahren nach einem der Sätze 1 bis 3, dadurch gekennzeichnet, dass als Substrat unlegierter Stahl oder Kupfer bereitgestellt wird.
• 7. Verfahren nach einem der Sätze 1 bis 3 oder 6, dadurch gekennzeichnet, dass der Stromkollektor (26) in Form einer selbsttragenden Schicht ausgebildet wird.
• 8. Verfahren nach Satz 7, dadurch gekennzeichnet, dass zur Ausbildung der selbsttragenden Schicht (44) das Substrat entfernt wird, insbesondere durch Korrosion oder chemische Reaktion mit einem Oxidationsmittel.
• 9. Verfahren nach einem der Sätze 3 bis 8, dadurch gekennzeichnet, dass das mindestens eine in der Titan enthaltenden Schicht (44) enthaltene unedle Metall entfernt wird, insbesondere durch Korrosion oder chemische Reaktion mit einem Oxidationsmittel.
• 10. Verfahren nach Satz 9, dadurch gekennzeichnet, dass als Oxidationsmittel Kaliumhydroxid (KOH) oder Schwefelsäure (H₂SO₄) oder Perchlorsäure (HClO₄) eingesetzt werden.
• 11. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass der Stromkollektor (26) mit einer mittleren Stromkollektorschichtdicke in einem Bereich von etwa 10 μm bis etwa 100 μm ausgebildet wird.
• 12. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass zwei, drei, vier, fünf, sechs, sieben, acht oder mehr mikroporöse Schichten (44) zur Ausbildung des Stromkollektors (26) auf das Substrat (50) aufgebracht werden.
• 13. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) mit einer Porengröße in einem Bereich von etwa 0,1 μm bis etwa 10 μm ausgebildet wird, insbesondere in einem Bereich von etwa 1 μm bis etwa 2 μm.
• 14. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) mit einer Porosität in einem Bereich von etwa 5 % bis etwa 28 % ausgebildet wird, insbesondere in einem Bereich von etwa 8 % bis etwa 15 %.
• 15. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) mit einer Ausflussrate in einem Bereich von etwa 0,01 mbar l cm^–2 s^–1 bis etwa 500 mbar l cm^–2 s^–1 ausgebildet wird, insbesondere in einem Bereich von etwa 0,1 mbar l cm^–2 s^–1 bis etwa 150 mbar l cm^–2 s^–1.
• 16. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) mit einer Plasma-Enthalpie in einem Bereich von etwa 8 MJ kg^–1 bis etwa 30 MJ kg^–1 aufgespritzt wird, insbesondere mit einer Plasma-Enthalpie in einem Bereich von etwa 15 MJ kg^–1 bis etwa 23 MJ kg^–1.
• 17. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) mit einer Flammen-Auslenkgeschwindigkeit in einem Bereich von etwa 300 mm s^–1 bis etwa 600 mm s^–1 aufgespritzt wird, insbesondere mit einer FlammenAuslenkgeschwindigkeit in einem Bereich von etwa 350 mm s^–1 bis etwa 500 mm s^–1.
• 18. Verfahren nach einem der Sätze 2 bis 17, dadurch gekennzeichnet, dass zwei oder mehr mikroporöse Schichten (44) ausgebildet werden durch Plasmaspritzen mit dem gleichen Titanpulver.
• 19. Verfahren nach einem der Sätze 2 bis 17, dadurch gekennzeichnet, dass Titanpulver mit einer Reinheit von mindestens etwa 99,6% bereitgestellt wird.
• 20. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass zwei oder mehr mikroporöse Schichten (44) derart ausgebildet werden, dass Porositäten aufeinanderfolgender Schichten (44) ausgehend vom Substrat (50) gleich sind oder abnehmen.
• 21. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass eine Porosität der mindestens einen mikroporösen Schicht (44) eingestellt wird durch Vorgabe einer Plasma-Enthalpie und/oder einer Flammen-Auslenkgeschwindigkeit.
• 22. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass auf die mindestens eine mikroporöse Schicht (44) eine Korrosionsschutzschicht (64) aufgebracht wird.
• 23. Verfahren nach Satz 22, dadurch gekennzeichnet, dass die Korrosionsschutzschicht aus mindestens einem Edelmetall ausgebildet wird, insbesondere aus Gold, Platin und/oder Iridium, oder durch einen porösen Elektrokatalysator, insbesondere SnO₂:Sb, Ti₄O₇, SnO₂:M (mit M = Sb, In, Nb) oder TiO₂:M (mit M = W, Nb, Mo).
• 24. Verfahren nach einem der voranstehenden Sätze, dadurch gekennzeichnet, dass das Substrat (50) mit einer Substratdicke (d₁) bereitgestellt wird und dass die mindestens eine mikroporöse Schicht (44) mit einer Schichtdicke (d₅) aufgebracht wird, die kleiner als die Substratdicke (d₁) ist.
• 25. Verfahren nach einem der Sätze 22 bis 24, dadurch gekennzeichnet, dass die Korrosionsschutzschicht (64) mit einer Korrosionsschutzschichtdicke (d₆) aufgebracht wird, welche kleiner als die Schichtdicke (d₅) der mindestens einen mikroporösen Schicht (44) ist.
• 26. Verfahren zur Herstellung einer Membraneinheit (14) einer elektrochemischen Zelle, insbesondere eines Protonen-Austausch-Membran-Elektrolyseurs (12), bei welchem eine Protonen-Austausch-Membran (18) bereitgestellt wird, auf deren einer Seite eine erste Katalysatorschicht (20) aufgebracht wird, dadurch gekennzeichnet, dass auf die erste Katalysatorschicht (20) ein Stromkollektor (26) aufgebracht wird und dass der Stromkollektor (26) mit einem Verfahren nach einem der voranstehenden Sätze hergestellt wird.
• 27. Verfahren nach Satz 26, dadurch gekennzeichnet, dass der Stromkollektor (26) selbsttragend hergestellt und mit der ersten Katalysatorschicht (20) verpresst wird, insbesondere heißverpresst.
• 28. Verfahren nach Satz 26 oder 27, dadurch gekennzeichnet, dass auf die andere Seite der Protonen-Austausch-Membran (18) eine zweite Katalysatorschicht (22) aufgebracht wird.
• 29. Verfahren nach einem der Sätze 26 bis 28, dadurch gekennzeichnet, dass auf die zweite Katalysatorschicht (22) ein weiterer Stromkollektor aufgebracht wird, insbesondere dass der weitere Stromkollektor (24) mit einem Verfahren nach einem der Sätze 1 bis 25 hergestellt wird.
• 30. Verfahren zur Herstellung einer elektrochemischen Zelle (10), insbesondere eines Protonen-Austausch-Membran-Elektrolyseurs (12), dadurch gekennzeichnet, dass eine Membraneinheit (14) nach einem der Sätze 26 bis 29 hergestellt und zwischen zwei Bipolarplatten (28, 30) angeordnet wird.
• 31. Verfahren nach Satz 30, dadurch gekennzeichnet, dass die zwei Bipolarplatten (28, 30) mit Strömungskanälen (32, 34) versehen werden, die in Form von auf die Membraneinheit (14) hin geöffneten Nuten ausgebildet werden.
• 32. Stromkollektor (26) für eine Elektrode einer elektrochemischen Zelle (10), insbesondere einer Anode eines Protonen-Austausch-Membran-Elektrolyseurs (12), gekennzeichnet durch mindestens eine mikroporöse, aus Titan bestehende oder Titan enthaltende und durch Plasmaspritzen im Vakuum ausgebildete Schicht (44).
• 33. Stromkollektor nach Satz 32, dadurch gekennzeichnet, dass die mindestens eine aus Titan bestehende Schicht (44) durch Plasmaspritzen von Titanpulver ausgebildet ist.
• 34. Stromkollektor nach Satz 32, dadurch gekennzeichnet, dass die Titan enthaltende Schicht (44) durch Plasmaspritzen einer Mischung aus Titanpulver und mindestens einem Metallpulver ausgebildet ist, wobei das Metallpulver ein Pulver aus einem unedlen Metall ist, insbesondere aus Aluminium, Eisen oder Zink.
• 35. Stromkollektor nach einem der Sätze 32 bis 34, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) durch Plasmaspritzen auf ein durch Sintern von Titanpulver hergestelltes Substrat (50) aufgebracht ist.
• 36. Stromkollektor nach Satz 35, dadurch gekennzeichnet, dass der Stromkollektor (26) durch das Substrat (50) und die mindestens eine aus Titan bestehende Schicht (44) ausgebildet wird.
• 37. Stromkollektor nach Satz 32 bis 35, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) durch Plasmaspritzen auf ein aus einem unlegierten Stahl oder Kupfer gebildetes Substrat aufgebracht ist.
• 38. Stromkollektor nach einem der Sätze 32 bis 34 oder 35, dadurch gekennzeichnet, dass der Stromkollektor (26) selbsttragend ausgebildet ist.
• 39. Stromkollektor nach Satz 38, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) substratlos ausgebildet ist.
• 40. Stromkollektor nach einem der Sätze 34 bis 39, dadurch gekennzeichnet, dass das mindestens eine in der Titan enthaltenden Schicht (44) enthaltene unedle Metall entfernt ist, insbesondere durch Korrosion oder chemische Reaktion mit einem Oxidationsmittel.
• 41. Stromkollektor nach Satz 40, dadurch gekennzeichnet, dass das Oxidationsmittel Kaliumhydroxid (KOH) oder Schwefelsäure (H₂SO₄) oder Perchlorsäure (HClO₄) ist oder enthält.
• 42. Stromkollektor nach einem der Sätze 32 bis 41, dadurch gekennzeichnet, dass der Stromkollektor (26) eine mittlere Stromkollektorschichtdicke in einem Bereich von etwa 10 μm bis etwa 100 μm aufweist.
• 43. Stromkollektor nach einem der Sätze 32 bis 42, dadurch gekennzeichnet, dass der Stromkollektor (26) zwei, drei, vier, fünf, sechs, sieben, acht oder mehr mikroporöse Schichten (44) umfasst.
• 44. Stromkollektor nach einem der Sätze 32 bis 43, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) eine Porengröße in einem Bereich von etwa 0,1 μm bis etwa 10 μm aufweist, insbesondere in einem Bereich von etwa 1 μm bis etwa 2 μm.
• 45. Stromkollektor nach einem der Sätze 32 bis 44, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) eine Porosität in einem Bereich von etwa 5 % bis etwa 28 % aufweist, insbesondere in einem Bereich von etwa 8 % bis etwa 15 %.
• 46. Stromkollektor nach einem der Sätze 32 bis 45, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) eine Ausflussrate in einem Bereich von etwa 0,01 mbar l cm^–2 s^–1 bis etwa 500 mbar l cm^–2 s^–1 aufweist, insbesondere in einem Bereich von etwa 0,1 mbar l cm^–2 s^–1 bis etwa 150 mbar l cm^–2 s^–1.
• 47. Stromkollektor nach einem der Sätze 32 bis 46, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) mit einer Plasma-Enthalpie in einem Bereich von etwa 8 MJ kg^–1 bis etwa 30 MJ kg^–1 gespritzt ist, insbesondere mit einer Plasma-Enthalpie in einem Bereich von etwa 15 MJ kg^–1 bis etwa 23 MJ kg^–1.
• 48. Stromkollektor nach einem der Sätze 32 bis 47, dadurch gekennzeichnet, dass die mindestens eine mikroporöse Schicht (44) mit einer Flammen-Auslenkgeschwindigkeit in einem Bereich von etwa 300 mm s^–1 bis etwa 600 mm s^–1 gespritzt ist, insbesondere mit einer Flammen-Auslenkgeschwindigkeit in einem Bereich von etwa 350 mm s^–1 bis etwa 500 mm s^–1.
• 49. Stromkollektor nach einem der Sätze 33 bis 48, dadurch gekennzeichnet, dass zwei oder mehr mikroporöse Schichten (44) ausgebildet sind durch Plasmaspritzen mit dem gleichen Titanpulver.
• 50. Stromkollektor nach Satz 49, dadurch gekennzeichnet, dass das Titanpulver zur Ausbildung der mindestens einen mikroporösen Schicht (44) eine Reinheit von mindestens etwa 99,6% aufweist.
• 51. Stromkollektor nach einem der Sätze 32 bis 50, dadurch gekennzeichnet, dass zwei oder mehr mikroporöse Schichten (44) derart ausgebildet sind, dass Porositäten aufeinanderfolgender Schichten (44) gleich sind oder abnehmen, insbesondere ausgehend vom Substrat (50).
• 52. Stromkollektor nach einem der Sätze 32 bis 51, dadurch gekennzeichnet, dass die Porosität der mindestens einen mikroporösen Schicht (44) durch Vorgabe einer Plasma-Enthalpie und/oder einer Flammen-Auslenkgeschwindigkeit beim Spritzen eingestellt ist.
• 53. Stromkollektor nach einem der Sätze 32 bis 52, dadurch gekennzeichnet, dass auf die mindestens eine mikroporöse Schicht (44) eine Korrosionsschutzschicht (64) aufgebracht ist.
• 54. Stromkollektor nach Satz 53, dadurch gekennzeichnet, dass die Korrosionsschutzschicht (64) aus mindestens einem Edelmetall gebildet ist oder mindestens ein Edelmetall enthält, insbesondere ein Gold, Platin und/oder Iridium, oder in Form einer elektrokatalytischen Schicht ausgebildet ist.
• 55. Stromkollektor nach einem der Sätze 35 bis 54, dadurch gekennzeichnet, dass das Substrat (50) eine Substratdicke (d₁) aufweist und dass die mindestens eine mikroporöse Schicht (44) eine Schichtdicke (d₅) aufweist, die kleiner als die Substratdicke (d₁) ist.
• 56. Stromkollektor nach einem der Sätze 53 bis 55, dadurch gekennzeichnet, dass die Korrosionsschutzschicht (64) eine Korrosionsschutzschichtdicke (d₆) aufweist, welche kleiner als die Schichtdicke (d₅) der mindestens einen mikroporösen Schicht (44) ist.
• 57. Membraneinheit (14) einer elektrochemischen Zelle (10), insbesondere eines Protonen-Austausch-Membran-Elektrolyseurs (12), umfassend eine Protonen-Austausch-Membran (18), auf deren einer Seite eine erste Katalysatorschicht (20) aufgebracht ist, dadurch gekennzeichnet, dass auf die erste Katalysatorschicht (20) ein Stromkollektor (26) nach einem der Sätze 32 bis 56 aufgebracht ist.
• 58. Membraneinheit nach Satz 57, dadurch gekennzeichnet, dass der Stromkollektor (26) selbsttragend hergestellt und mit der ersten Katalysatorschicht (20) verpresst ist, insbesondere heißverpresst.
• 59. Membraneinheit nach Satz 57 oder 58, dadurch gekennzeichnet, dass auf die andere Seite der Protonen-Austausch-Membran (18) eine zweite Katalysatorschicht (22) aufgebracht ist.
• 60. Membraneinheit nach Satz 59, dadurch gekennzeichnet, dass auf die zweite Katalysatorschicht (22) ein weiterer Stromkollektor (24) aufgebracht ist, insbesondere ein Stromkollektor (24) nach einem der Sätze 32 bis 56.
• 61. Elektrochemische Zelle (10), insbesondere in Form eines Protonen-Austausch-Membran-Elektrolyseurs (12), umfassend zwei Bipolarplatten (30, 32) und eine zwischen diesen angeordnete Membraneinheit (14) nach einem der Sätze 58 bis 60.
• 62. Elektrochemische Zelle nach Satz 61, dadurch gekennzeichnet, dass die zwei Bipolarplatten (30, 32) Strömungskanäle (32, 34) aufweisen, die in Form von auf die Membraneinheit (14) hin geöffneten Nuten ausgebildet sind.

The above description thus includes in particular the embodiments of current collectors, membrane units, electrochemical cells and methods for producing the same, which are defined below in the form of numbered sets:

• 1. Method for producing a current collector ( 26 ) for an electrode of an electrochemical cell ( 10 ), in particular an anode of a proton exchange membrane electrolyzer ( 12 ), characterized in that a substrate ( 50 ) and that for forming the current collector at least one microporous, titanium-containing or titanium-containing layer ( 44 ) on the substrate ( 50 ) is applied by plasma spraying in a vacuum.
• 2. Method according to sentence 1, characterized in that the at least one titanium layer ( 44 ) is applied by plasma spraying of titanium powder.
• 3. Process according to sentence 1, characterized in that the titanium-containing layer ( 44 ) is applied by plasma spraying a mixture of titanium powder and at least one metal powder, wherein the at least one metal powder is a powder of a base metal, in particular of aluminum, iron or zinc.
• 4. Method according to one of the preceding sentences, characterized in that the substrate ( 50 ) is produced by sintering titanium powder or is formed by a titanium expanded metal mesh.
• 5. Method according to sentence 4, characterized in that the current collector ( 26 ) through the substrate ( 50 ) and the at least one titanium layer ( 44 ) is formed.
• 6. The method according to any one of sentences 1 to 3, characterized in that is provided as the substrate unalloyed steel or copper.
• 7. Method according to one of the sentences 1 to 3 or 6, characterized in that the current collector ( 26 ) is formed in the form of a self-supporting layer.
• 8. Method according to sentence 7, characterized in that for the formation of the self-supporting layer ( 44 ) the substrate is removed, in particular by corrosion or chemical reaction with an oxidizing agent.
• 9. Method according to one of the sentences 3 to 8, characterized in that the at least one layer containing titanium ( 44 ) is removed, in particular by corrosion or chemical reaction with an oxidizing agent.
• 10. The method according to sentence 9, characterized in that as the oxidizing agent potassium hydroxide (KOH) or sulfuric acid (H ₂ SO ₄ ) or perchloric acid (HClO ₄ ) are used.
• 11. Method according to one of the preceding sentences, characterized in that the current collector ( 26 ) is formed with an average current collector layer thickness in a range of about 10 microns to about 100 microns.
• 12. Method according to one of the preceding sentences, characterized in that two, three, four, five, six, seven, eight or more microporous layers ( 44 ) for the formation of the current collector ( 26 ) on the substrate ( 50 ) are applied.
• 13. Method according to one of the preceding sentences, characterized in that the at least one microporous layer ( 44 ) is formed with a pore size in a range of about 0.1 microns to about 10 microns, in particular in a range of about 1 micron to about 2 microns.
• 14. Method according to one of the preceding sentences, characterized in that the at least one microporous layer ( 44 ) having a porosity in a range of about 5% to about 28%, in particular in a range of about 8% to about 15%.
• 15. Method according to one of the preceding sentences, characterized in that the at least one microporous layer ( 44 ) is formed with an outflow rate in a range from about 0.01 mbar l cm ^-2 s ^-1 to about 500 mbar l cm ^-2 s ^-1 , in particular in a range of about 0.1 mbar l cm ^-2 s ^{- 1} to about 150 mbar l cm ^-2 s ^-1 .
• 16. Method according to one of the preceding sentences, characterized in that the at least one microporous layer ( 44 ) having a plasma enthalpy in a range of about 8 MJ kg ^-1 to about 30 MJ kg ^-1 , in particular with a plasma enthalpy in a range of about 15 MJ kg ^-1 to about 23 MJ kg ^-1 .
• 17. Method according to one of the preceding sentences, characterized in that the at least one microporous layer ( 44 ) is sprayed at a flame deflection speed in a range of about 300 mm s ^-1 to about 600 mm s ^-1 , in particular with a flame sweep speed in a range of about 350 mm s ^-1 to about 500 mm s ^-1 .
• 18. Method according to one of the sentences 2 to 17, characterized in that two or more microporous layers ( 44 ) are formed by plasma spraying with the same titanium powder.
• 19. A method according to any one of sentences 2 to 17, characterized in that titanium powder having a purity of at least about 99.6% is provided.
• 20. Method according to one of the preceding sentences, characterized in that two or more microporous layers ( 44 ) are formed such that porosities of successive layers ( 44 ) starting from the substrate ( 50 ) are equal or decrease.
• 21. Method according to one of the preceding sentences, characterized in that a porosity of the at least one microporous layer ( 44 ) is set by specifying a plasma enthalpy and / or a flame deflection speed.
• 22. Method according to one of the preceding sentences, characterized in that the at least one microporous layer ( 44 ) a corrosion protection layer ( 64 ) is applied.
• 23. Method according to sentence 22, characterized in that the corrosion protection layer is formed from at least one noble metal, in particular from gold, platinum and / or iridium, or by a porous electrocatalyst, in particular SnO ₂ : Sb, Ti ₄ O ₇ , SnO ₂ : M (with M = Sb, In, Nb) or TiO ₂ : M (with M = W, Nb, Mo).
• 24. Method according to one of the preceding sentences, characterized in that the substrate ( 50 ) is provided with a substrate thickness (d ₁ ) and that the at least one microporous layer ( 44 ) is applied with a layer thickness (d ₅ ) which is smaller than the substrate thickness (d ₁ ).
• 25. Method according to one of the sentences 22 to 24, characterized in that the corrosion protection layer ( 64 ) having a corrosion protection layer thickness (d ₆ ) which is smaller than the layer thickness (d ₅ ) of the at least one microporous layer ( 44 ).
• 26. Method for producing a membrane unit ( 14 ) an electrochemical cell, in particular a proton exchange membrane electrolyzer ( 12 ), in which a proton exchange membrane ( 18 ) is provided, on one side of which a first catalyst layer ( 20 ) is applied, characterized in that on the first catalyst layer ( 20 ) a current collector ( 26 ) is applied and that the current collector ( 26 ) is produced by a method according to one of the preceding sentences.
• 27. Method according to sentence 26, characterized in that the current collector ( 26 ) self-supporting and with the first catalyst layer ( 20 ) is pressed, in particular hot pressed.
• 28. Method according to sentence 26 or 27, characterized in that on the other side of the proton exchange membrane ( 18 ) a second catalyst layer ( 22 ) is applied.
• 29. Method according to one of the sentences 26 to 28, characterized in that the second catalyst layer ( 22 ) a further current collector is applied, in particular that the further current collector ( 24 ) is produced by a method according to any one of sentences 1 to 25.
• 30. Method for producing an electrochemical cell ( 10 ), in particular a proton exchange membrane electrolyzer ( 12 ), characterized in that a membrane unit ( 14 ) according to one of the sentences 26 to 29 and between two bipolar plates ( 28 . 30 ) is arranged.
• 31. Method according to sentence 30, characterized in that the two bipolar plates ( 28 . 30 ) with flow channels ( 32 . 34 ) provided in the form of on the membrane unit ( 14 ) are formed open towards grooves.
• 32. current collector ( 26 ) for an electrode of an electrochemical cell ( 10 ), in particular an anode of a proton exchange membrane electrolyzer ( 12 ), characterized by at least one microporous layer consisting of titanium or titanium and formed by plasma spraying in a vacuum ( 44 ).
• 33. Current collector according to sentence 32, characterized in that the at least one layer consisting of titanium ( 44 ) is formed by plasma spraying of titanium powder.
• 34. current collector according to sentence 32, characterized in that the titanium-containing layer ( 44 ) is formed by plasma spraying a mixture of titanium powder and at least one metal powder, wherein the metal powder is a powder of a base metal, in particular of aluminum, iron or zinc.
• 35. Current collector according to one of the sentences 32 to 34, characterized in that the at least one microporous layer ( 44 by plasma spraying onto a substrate produced by sintering of titanium powder ( 50 ) is applied.
• 36. Current collector according to sentence 35, characterized in that the current collector ( 26 ) through the substrate ( 50 ) and the at least one titanium layer ( 44 ) is formed.
• 37. current collector according to sentence 32 to 35, characterized in that the at least one microporous layer ( 44 ) is applied by plasma spraying onto a substrate formed of a non-alloyed steel or copper.
• 38. Current collector according to one of the sentences 32 to 34 or 35, characterized in that the current collector ( 26 ) is self-supporting trained.
• 39. current collector according to sentence 38, characterized in that the at least one microporous layer ( 44 ) is formed substratlos.
• 40. Current collector according to one of the sentences 34 to 39, characterized in that the at least one layer containing titanium ( 44 ) is removed, in particular by corrosion or chemical reaction with an oxidizing agent.
• 41. current collector according to sentence 40, characterized in that the oxidizing agent is potassium hydroxide (KOH) or sulfuric acid (H ₂ SO ₄ ) or perchloric acid (HClO ₄ ) or contains.
• 42. Current collector according to one of the sentences 32 to 41, characterized in that the current collector ( 26 ) has an average current collector layer thickness in a range of about 10 μm to about 100 μm.
• 43. current collector according to one of the sentences 32 to 42, characterized in that the current collector ( 26 ) two, three, four, five, six, seven, eight or more microporous layers ( 44 ).
• 44. Current collector according to one of the sentences 32 to 43, characterized in that the at least one microporous layer ( 44 ) has a pore size in a range from about 0.1 μm to about 10 μm, in particular in a range from about 1 μm to about 2 μm.
• 45. Current collector according to one of the sentences 32 to 44, characterized in that the at least one microporous layer ( 44 ) has a porosity in a range of about 5% to about 28%, more preferably in a range of about 8% to about 15%.
• 46. Current collector according to one of the sentences 32 to 45, characterized in that the at least one microporous layer ( 44 ) has an outflow rate in a range of about 0.01 mbar l cm ^-2 s ^-1 to about 500 mbar l cm ^-2 s ^-1 , in particular in a range of about 0.1 mbar l cm ^-2 s ^-1 to about 150 mbar l cm ^-2 s ^-1 .
• 47. Current collector according to one of the sentences 32 to 46, characterized in that the at least one microporous layer ( 44 ) having a plasma enthalpy in a range of about 8 MJ kg ^-1 to about 30 MJ kg ^-1 , in particular having a plasma enthalpy in a range of about 15 MJ kg ^-1 to about 23 MJ kg ^-1 .
• 48. Current collector according to one of the sentences 32 to 47, characterized in that the at least one microporous layer ( 44 ) having a flame deflection speed in a range of about 300 mm s ^-1 to about 600 mm s ^-1 , in particular having a flame deflection speed in a range of about 350 mm s ^-1 to about 500 mm s ^-1 .
• 49. Current collector according to one of the sentences 33 to 48, characterized in that two or more microporous layers ( 44 ) are formed by plasma spraying with the same titanium powder.
• 50. current collector according to sentence 49, characterized in that the titanium powder for forming the at least one microporous layer ( 44 ) has a purity of at least about 99.6%.
• 51. Current collector according to one of the sentences 32 to 50, characterized in that two or more microporous layers ( 44 ) are formed such that porosities of successive layers ( 44 ) are the same or decrease, in particular starting from the substrate ( 50 ).
• 52. Current collector according to one of the sentences 32 to 51, characterized in that the porosity of the at least one microporous layer ( 44 ) is set by setting a plasma enthalpy and / or a flame deflection speed during spraying.
• 53. Current collector according to one of the sentences 32 to 52, characterized in that the at least one microporous layer ( 44 ) a corrosion protection layer ( 64 ) is applied.
• 54. current collector according to sentence 53, characterized in that the corrosion protection layer ( 64 ) is formed from at least one noble metal or contains at least one noble metal, in particular a gold, platinum and / or iridium, or in the form of an electrocatalytic layer is formed.
• 55. Current collector according to one of the sentences 35 to 54, characterized in that the substrate ( 50 ) has a substrate thickness (d ₁ ) and that the at least one microporous layer ( 44 ) has a layer thickness (d ₅ ) which is smaller than the substrate thickness (d ₁ ).
• 56. Current collector according to one of the sentences 53 to 55, characterized in that the corrosion protection layer ( 64 ) has a corrosion protection layer thickness (d ₆ ) which is smaller than the layer thickness (d ₅ ) of the at least one microporous layer ( 44 ).
• 57. membrane unit ( 14 ) an electrochemical cell ( 10 ), in particular a proton exchange membrane electrolyzer ( 12 ) comprising a proton exchange membrane ( 18 ), on one side of which a first catalyst layer ( 20 ) is applied, characterized in that on the first catalyst layer ( 20 ) a current collector ( 26 ) is applied to one of the sentences 32 to 56.
• 58. Membrane unit according to sentence 57, characterized in that the current collector ( 26 ) self-supporting and with the first catalyst layer ( 20 ) is pressed, in particular hot pressed.
• 59. membrane unit according to sentence 57 or 58, characterized in that on the other side of the proton exchange membrane ( 18 ) a second catalyst layer ( 22 ) is applied.
• 60. membrane unit according to sentence 59, characterized in that the second catalyst layer ( 22 ) another current collector ( 24 ), in particular a current collector ( 24 ) according to one of the sentences 32 to 56.
• 61. Electrochemical cell ( 10 ), in particular in the form of a proton exchange membrane electrolyzer ( 12 ) comprising two bipolar plates ( 30 . 32 ) and a membrane unit ( 14 ) according to one of the sentences 58 to 60.
• 62. Electrochemical cell according to sentence 61, characterized in that the two bipolar plates ( 30 . 32 ) Flow channels ( 32 . 34 ), in the form of on the membrane unit ( 14 ) are formed toward open grooves.

The following description of preferred embodiments of the invention is used in conjunction with the drawings for further explanation. Show it:

1 a schematic representation for comparing pore sizes of current collectors according to the prior art and according to the invention for use in proton exchange membrane electrolyzers;

2a FIG. 2 is a schematic sectional view of a prior art proton exchange membrane electrolyzer; FIG.

2 B Fig. 1 is a schematic sectional view of a proton exchange membrane electrolyzer according to the invention comprising an anodic current collector with one or more microporous layers applied by vacuum plasma spraying;

2c FIG. 4 is a schematic sectional view of a proton exchange membrane electrolyzer similar to that in FIG 2 B the electrolyzer shown, wherein between the cathodic catalyst layer and the cathodic bipolar plate, a current collector is formed with a microporous layer or a microporous layer system;

3a FIG. 2: a schematic sectional view through the anode of a proton exchange membrane electrolyzer with a sintered titanium current collector without a microporous layer according to the invention; FIG.

3b FIG. 4: a schematic sectional view through the anode of a proton exchange membrane electrolyzer similar. FIG 3a However, according to the invention, a microporous layer for forming the current collector with a corrosion protection layer to the catalyst layer is additionally formed.

3c FIG. 2 is a schematic sectional view through another embodiment of a proton exchange membrane electrolyzer in which the anticorrosion layer of the microporous layer is formed by a porous electrocatalyst to form oxygen by electrolysis of water; FIG.

4a FIG. 2 is a fragmentary schematic sectional view through the anode of a proton exchange membrane electrolyzer with a current collector formed of sintered titanium powder; FIG.

4b FIG. 2 is a fragmentary schematic sectional view through the anode of a proton exchange membrane electrolyzer having a plurality of microporous layers of different porosity; FIG.

5a : Scanning electron microscope sectional view of a current collector comprising a sintered titanium plate and a vacuum deposited by plasma spraying titanium layer;

5b : Scanning electron microscope sectional view of a self-supporting titanium multilayer coating for forming a current collector;

6a FIG. 2 is an exemplary plot of interfacial contact resistance (ICR) versus compression pressure of a sintered titanium current collector (SC) (prior art) and a current collector comprising a sintered titanium microporous layer (MPL) current collector; FIG. and

6b FIG. 2 shows an example of the dependency of a cumulative pore volume as a function of the pore diameter and of a relative pore volume as a function of a pore diameter of a self-supporting current collector comprising a multilayer system of microporous titanium layers.

In 1 schematically illustrates the types in which current collectors can be formed by proton exchange membrane (PEM) electrolysers. These may be foams, felts, expanded or sintered porous plates. Such current collectors are known.

However, it is not known to apply microporous layers (MPL) by plasma spraying to sintered porous titanium battens. In this way, pore sizes of less than 2 microns can be achieved. Such a current collector is thus formed by a sintered porous titanium plate, on which a microporous layer is applied by plasma spraying. Such microporous layers are not known, in particular in proton exchange membrane electrolysers, to form anodic current collectors.

Furthermore, the present invention proposes to produce free-standing or self-supporting systems with controlled porosity, that is, for example, multilayer systems of two or more microporous layers without substrate, which can be prepared in the manner described above.

The types of current collectors that are in 1 in black deposited boxes refer to the invention, the types of current collectors shown in white boxes refer to the state of the art.

2a shows a schematic sectional view of an electrochemical cell 10 in the form of a proton exchange membrane electrolyzer 12 , It comprises a membrane unit 14 , in particular a unit 16 comprising a proton exchange membrane 18 comprising, on one side, an anodic catalyst layer 20 and on the other side, a cathodic catalyst layer 22 wearing. The cathodic catalyst layer 22 carries a cathodic current collector 24 , which is formed by a porous gas diffusion layer of carbon with a microporous layer of carbon powder and polytetrafluoroethylene (PTFE).

The anodic catalyst layer 20 is in contact with an anodic current collector 26 formed by sintered titanium particles or a porous titanium structure without a microporous layer. The membrane unit 14 is between a cathodic bipolar plate 28 and an anodic bipolar plate 30 arranged. The bipolar plates 28 and 30 each include flow channels 32 respectively 34 for forming a flow field, wherein the flow channels 32 filled with hydrogen and water, the flow channels 34 with oxygen and water.

A contact surface between the cathodic bipolar plate 28 and the cathodic current collector 24 is in 1 with the reference number 36 designated.

A contact surface of the microporous layer of the cathodic current collector 24 with the cathodic catalyst layer 22 is in 2a With 38 designated. Further, the reference numeral designates 40 a contact surface between the anodic bipolar plate 30 and the anodic current collector 26 , And finally is in 2a a contact surface 42 between the anodic current collector 26 and the anodic catalyst layer 20 with the reference number 42 designated.

As already stated, the schematic sectional view in FIG 2a the known prior art.

In 2 B on the other hand is a sectional view of an electrochemical cell 10 in the form of a proton exchange membrane electrolyzer 12 schematically, which differs from the prior art in that the sintered titanium layer 50 in the prior art, the anodic current collector 26 forms a microporous layer by vacuum plasma spraying of a titanium powder is applied. A contact surface between the microporous layer 44 and the sintered titanium layer 50 which together form the anodic current collector 26 train is in 2 B With 46 designated. Further, a contact surface between the microporous layer 44 and the anodic catalyst layer 20 With 48 designated.

In 2c is another variant of an electrochemical cell 10 in the form of a proton exchange membrane electrolyzer 12 shown schematically. The anodic part of the electrochemical cell of 2c corresponds to the anodic part of the electrochemical cell 10 of the 2 B ,

Unlike the electrochemical cell 2 B is at the electrochemical cell 10 , in the 2c is shown, also the cathodic current collector 24 through a sintered titanium layer 50 that with the anodic bipolar plate 30 in contact, and one on the titanium layer 50 by vacuum plasma spraying applied microporous layer 52 formed with the cathodic catalyst layer 22 a contact surface 54 Are defined. A contact surface 56 is further defined by the sintered titanium layer 50 and the microporous layer 52 which adjoin one another.

The structure of the electrochemical cell 10 is based on the proton exchange membrane 18 substantially symmetrical, with different or identical catalysts for the formation of the catalyst layers 20 and 22 can be used.

The operation of the electrochemical cell 10 out 2a in the region of whose anode is schematically in 3a shown.

Through the flow channels 34 in the anodic bipolar plate 30 Water (H ₂ O) is passed through the anodic bipolar plate 30 due to the prevailing pressure to the proton exchange membrane 80 directed. The bipolar plates are clamped by means of bolts against the current collectors and the membrane unit arranged between them, so that the entire cell is compressed. At the anodic catalyst layer 20 the water molecules are split up. This produces oxygen (O ₂ ). It is not shown that the protons formed during the cleavage of the water, the proton exchange membrane 80 through and in conjunction with two electrons on the cathodic catalyst layer 22 form molecular hydrogen.

Submitting two electrons through the anodic current collector 26 and the anodic bipolar plate 30 are derived, oxygen molecules form, resulting in small bubbles 58 agglomerate with increasing distance from the anodic catalyst layer 20 to medium bubbles 60 enlarge and finally in the form of large bubbles 62 through the flow channels 34 be derived.

In 3a is the thickness of the current collector 36 denoted by d ₁ , a thickness of the anodic catalyst layer 20 with d ₂ , a thickness of the proton exchange membrane 18 with d ₃ and a thickness of the cathodic catalyst layer 22 with d ₄ .

In 3b an electrochemical cell according to the invention is shown schematically. It differs from the electrochemical cell according to the prior art as in 3a represented by the fact that on the sintered titanium layer 50 additionally by a vacuum plasma spraying a microporous layer 44 is applied, which may comprise one or more layers. In addition, there is between the microporous layer 44 and the anodic catalyst layer 20 a corrosion protection layer 64 applied. This prevents anodic oxidation of the microporous layer 44 , The corrosion protection layer 64 may be formed by electrolytic deposition of a noble metal, such as gold, platinum or iridium, or in the form of a thin ceramic layer.

An average layer thickness d _{5 of} the microporous layer 44 is significantly smaller than the thickness d _{1 of} the sintered titanium layer 50 , Furthermore, a thickness d _{6 of} the corrosion protection layer 64 significantly smaller than the thickness d ₅ .

The microporous layer 44 Already allows the formation of even smaller oxygen bubbles than in the sintered titanium layer 50 is possible. Discharging the oxygen bubbles towards the flow channels is thereby improved.

The in the 3a and 3b given thicknesses may in particular have the following values. The thickness d ₁ may be in a range of 700 μm to 1200 μm, depending on the size and shape of the titanium particles and compaction thereof.

The thickness d _{2 of} the anodic catalyst layer may range from about 3 μm to about 7 μm, depending on the type of anodic catalyst used.

The thickness d _{3 of} the proton exchange membrane 18 may range from about 30 microns to about 150 microns, depending on the type of sulfonated tetrafluoroethylene polymer or perfluorosulfuric acid (PFSA) used.

The thickness d _{4 of} the cathodic catalyst layer 22 may range from about 3 microns to about 7 microns, depending on the type of cathodic catalyst used.

The thickness d _{5 of} the microporous layer 44 may range from about 14 microns to about 250 microns, depending on the number of sprayed layers or layers. In other words, the microporous layer 44 be formed in the form of a multilayer coating system.

The thickness d _{6 of} the anticorrosion layer may be in a range of about 0.01 μm to about 3 μm. It depends mainly on the nature of the deposition of the anti-corrosion layer 64 and the deposition time.

3c shows a part of a variant of an electrochemical cell 10 in the form of a proton exchange membrane electrolyzer 12 , The microporous layer 44 , which is applied by vacuum plasma spraying on the sintered titanium layer, is coated with a thin electrocatalytic layer 68 Mistake. This can be formed in particular in the form of metallic iridium or iridium dioxide (IrO ₂ ). At the contact surface 70 between the microporous layer 44 and the electrocatalytic layer 68 Oxygen forms from water by electrooxidation. The electrocatalytic layer 68 assumes in this embodiment of the invention, on the one hand, the function of the anticorrosion layer 64 and on the other hand, the anodic catalyst layer 20 , The electrocatalytic layer may in particular also be SnO ₂ : Sb, Ti ₄ O ₇ , SnO ₂ : M (with M = Sb, In, Nb) or TiO ₂ : M (with M = W, Nb, Mo).

Optionally, the catalyst layer 20 with an ionomer on the one sprayed layer comprising microporous layer 44 be applied. Subsequently, this structure can interact with the proton exchange membrane 18 be hot pressed.

4 Again, schematically shows the difference between the structure of current collectors according to the prior art and the invention.

So is in 4a a section through a sintered titanium layer 50 shown directly with the anodic catalyst layer 20 in contact. titanium particles 72 are shown schematically in the form of spheres. As a result of the sintering process are between titanium particles 72 pore 74 educated. This causes the contact surface 42 the anodic catalyst layer 20 in the area of the pores 74 not in contact with titanium particles 72 stands. This is a contact between the anodic current collector 26 and the anodic catalyst layer 20 minimized. Connections between the titanium particles 72 form necks 76 ,

In contrast, in the case of 4b schematically illustrated section of a microporous layer 44 thermally on the sintered titanium layer 50 sprayed. It has a thickness d ₅ and may in particular comprise a plurality of layers which are sprayed on one after the other under different process conditions. This creates small pores 78 , medium pores 80 and big pores 82 ,

The size of the pores increases starting from the contact surface 46 between the sintered titanium layer 50 and the microporous layer 44 successively from. The microporous layer 44 is passivated by applied the corrosion protection layer 44 , The high roughness of the microporous layer 44 provides a particularly good connection to the anodic catalyst layer 20 for sure. The very thin corrosion protection layer 44 changes the roughness of the microporous layer 44 practically not.

5a shows a scanning electron micrograph of a section through a current collector 26 comprising a sintered titanium layer 50 on which a microporous layer 44 is sprayed by means of vacuum plasma spraying. You recognize pores 74 in the sintered titanium layer and irregularly shaped titanium particles 72 ,

The microporous layer 44 is rough and made of high purity titanium. It comprises two layers which have been sprayed on successively with different process parameters, in particular different flame deflection speeds.

The contact surface 48 the microporous layer 44 that in a membrane unit 14 in contact with the anodic catalyst layer 20 is, is very rough, so has a large roughness, so that here is an optimal contact with the anodic catalyst layer 20 can be ensured.

In 5b is a section through a self-supporting microporous layer in the form of a scanning electron micrograph shown. Overall, the microporous layer comprises eight layers, which were thermally sprayed with different process parameters.

The self-supporting microporous layer 44 , in the 5b is shown by thermal spraying of eight layers of a titanium powder Gd1 spherical particles having an average particle size of 45 microns from TLS Technik sprayed on unalloyed steel. Subsequently, the substrate was corroded by electrochemical oxidation. The coating was applied with a plasma enthalpy of 14.7 MJ kg ^-1 and with a flame deflection speed of 350 mm s ^-1 . A first area 84 the microporous layer 44 shows only a small pore size. An outer surface of the first area 84 During the spraying of the titanium powder on the non-alloyed steel with this substrate in contact. It later preferably forms the contact surface 48 to the anodic catalyst layer 20 and optionally with a corrosion protection layer 64 be provided, for example, by depositing a noble metal or by applying a thin ceramic layer.

A second area 86 the microporous layer 44 shows significantly larger pores. One from the contact surface 48 away-facing surface in the formation of the electrochemical cell 10 a contact surface to the anodic bipolar plate 30 ,

6a Figure 4 shows the dependence of interfacial contact resistance (ICR) of a sintered titanium current collector and a current collector comprising a sintered titanium substrate with a microporous layer of compression pressure. It can be clearly seen that the interfacial contact resistance is significantly lowered due to the applied microporous layer. This significant conductivity increase is achieved by the high roughness of the microporous layer, which is achieved by the application by means of vacuum plasma spraying. Due to the high roughness, the adhesion of the corrosion protection layer, also referred to as surface modification, is also markedly improved. In the 6a The measured values shown were measured according to the standard of the US Department of Energy (DOE) as a function of the compaction pressure.

The following table shows characteristics of different samples, namely the mean layer thickness of the microporous layer, roughness as roughness factor in arbitrary units, pore size, porosity and outflow rate.

The samples were deposited on a stainless steel substrate with a plasma enthalpy of 21.27 MJ kg ^-1 and a flame deflection speed of 500mm s ^-1 . The pore texture and roughness measurements were made by digital image analysis. A thicker layer with an outflow rate of only 0.0043 mbar l cm ^-2 s ^-1 could, for example, be achieved by reducing the deposition rate, ie the flame deflection speed, from 500 mm s ^-1 to 350 mm s ^-1 .

In 6b On the one hand, the cumulative pore volume and, on the other hand, the relative pore volume as a function of the pore diameter of 5b applied microporous layer. The pore size measurement was determined by mercury adsorption. An average pore size is about 1.3 microns and varies approximately between 0.1 microns and 10 microns.

With the formation of microporous layers, which form together with a sintered titanium layer or as a self-supporting layer current collectors of electrochemical cells, in particular of proton exchange membrane electrolysers, an interface contact resistance between the catalyst layer and the current collector can be significantly reduced.

By applying the microporous layer by means of plasma spraying, properties such as pore size and porosity of the current collector can be very well controlled. In addition, a layer thickness of the current collector can be reduced while maintaining all structural characteristics well below 1000 microns. As indicated in the above table, layers with a thickness of only about 10 μm can be formed. In addition, the very high roughness of the microporous layer makes it possible to produce a particularly good contact with the catalyst layer.

Electrochemical cells comprising a microporous layer according to the invention as a current collector or as part thereof can find application in low-temperature electrical engineering in various fields. As already indicated, proton exchange membrane electrolyzers or polymer electrolyte membrane electrolyzers can be equipped with this technique, as well as alkaline electrolyzers and reversible fuel cells, polymer electrolyte fuel cells, high temperature polymer electrolyte fuel cells, and direct methanol fuel cells , Further applications are, for example, microfluidic fuel cells, solid oxide or high-temperature fuel cells and solid oxide or high-temperature electrolyzers. The use of microporous layers as current collectors or part of them is also possible with lithium-ion, lithium-air and lithium-sulfur batteries and redox flow batteries (RFB) or (redox) flow batteries. Of course, the microporous layer can also be on the cathodic Current collector can be applied to reduce a contact resistance between the current collector and the catalyst layer of the electrochemical cell on the cathode side.

Finally, in the following table, a comparison of the essential differences between current collectors known from the prior art and current collectors according to the invention is given:

LIST OF REFERENCE NUMBERS

10

 electrochemical cell

12

 Proton exchange membrane electrolyzer

14

 membrane unit

16

 unit

18

 Proton exchange membrane

20

 anodic catalyst layer

22

 cathodic catalyst layer

24

 cathodic current collector

26

 Anodic current collector

28

 cathodic bipolar plate

30

 Anodic bipolar plate

32

 flow channel

34

 flow channel

36

 contact area

38

 contact area

40

 contact area

42

 contact area

44

 microporous layer

46

 contact area

48

 contact area

50

 sintered titanium layer

52

 microporous layer

54

 contact area

56

 contact area

58

 small bubble

60

 middle bladder

62

 big bubble

64

 Corrosion protection layer

66

 bladder

68

 electrocatalytic layer

70

 contact area

72

 titanium particles

74

 pore

76

 neck

78

 small pore

80

 middle pore

82

 big pore

84

 first area

86

 second area

88

 contact area

Claims (20)

Method for producing a current collector ( 26 ) for an electrode of an electrochemical cell ( 10 ), in particular an anode of a proton exchange membrane electrolyzer ( 12 ), characterized in that a substrate ( 50 ) and that for forming the current collector at least one microporous, titanium-containing or titanium-containing layer ( 44 ) on the substrate ( 50 ) is applied by plasma spraying in a vacuum. Method according to claim 1, characterized in that the current collector ( 26 ) is formed in the form of a self-supporting layer and that for forming the self-supporting layer ( 44 ) the substrate is removed, in particular by corrosion or chemical reaction with an oxidizing agent. Method according to one of the preceding claims, characterized in that two, three, four, five, six, seven, eight or more microporous layers ( 44 ) for the formation of the current collector ( 26 ) on the substrate ( 50 ) are applied. Method according to one of the preceding claims, characterized in that the at least one microporous layer ( 44 ) is formed with an outflow rate in a range from about 0.01 mbar l cm ^-2 s ^-1 to about 500 mbar l cm ^-2 s ^-1 , in particular in a range of about 0.1 mbar l cm ^-2 s ^{- 1} to about 150 mbar l cm ^-2 s ^-1 . Method according to one of the preceding claims, characterized in that the at least one microporous layer ( 44 ) having a plasma enthalpy in a range of about 8 MJ kg ^-1 to about 30 MJ kg ^-1 , in particular with a plasma enthalpy in a range of about 15 MJ kg ^-1 to about 23 MJ kg ^-1 . Method according to one of the preceding claims, characterized in that the at least one layer consisting of titanium ( 44 ) is applied by plasma spraying of titanium powder and that two or more microporous layers ( 44 ) are formed by plasma spraying with the same titanium powder. Method according to one of the preceding claims, characterized in that a porosity of the at least one microporous layer ( 44 ) is set by specifying a plasma enthalpy and / or a flame deflection speed. Method according to one of the preceding claims, characterized in that on the at least one microporous layer ( 44 ) a corrosion protection layer ( 64 ) is applied. Method for producing a membrane unit ( 14 ) an electrochemical cell, in particular a proton exchange membrane electrolyzer ( 12 ), in which a proton exchange membrane ( 18 ) is provided, on one side of which a first catalyst layer ( 20 ) is applied, thereby characterized in that the first catalyst layer ( 20 ) a current collector ( 26 ) is applied and that the current collector ( 26 ) is produced by a method according to any one of the preceding claims. A method according to claim 9, characterized in that on the other side of the proton exchange membrane ( 18 ) a second catalyst layer ( 22 ) is applied. Method for producing an electrochemical cell ( 10 ), in particular a proton exchange membrane electrolyzer ( 12 ), characterized in that a membrane unit ( 14 ) according to claim 9 or 10 and between two bipolar plates ( 28 . 30 ) is arranged. Current collector ( 26 ) for an electrode of an electrochemical cell ( 10 ), in particular an anode of a proton exchange membrane electrolyzer ( 12 ), characterized by at least one microporous layer consisting of titanium or titanium and formed by plasma spraying in a vacuum ( 44 ). Current collector according to claim 12, characterized in that the at least one microporous layer ( 44 by plasma spraying onto a substrate produced by sintering of titanium powder ( 50 ) is applied and that the current collector ( 26 ) through the substrate ( 50 ) and the at least one titanium layer ( 44 ) is formed. Current collector according to claim 12, characterized in that the current collector ( 26 ) is self-supporting trained. Current collector according to one of claims 12 to 14, characterized in that the current collector ( 26 ) has an average current collector layer thickness in a range of about 10 μm to about 100 μm. Current collector according to one of Claims 12 to 15, characterized in that two or more microporous layers ( 44 ) are formed such that porosities of successive layers ( 44 ) are the same or decrease, in particular starting from the substrate ( 50 ). Current collector according to one of Claims 12 to 16, characterized in that the at least one microporous layer ( 44 ) a corrosion protection layer ( 64 ) is applied. Current collector according to one of claims 13 to 17, characterized in that the substrate ( 50 ) has a substrate thickness (d ₁ ) and that the at least one microporous layer ( 44 ) has a layer thickness (d ₅ ) which is smaller than the substrate thickness (d ₁ ). Membrane unit ( 14 ) an electrochemical cell ( 10 ), in particular a proton exchange membrane electrolyzer ( 12 ) comprising a proton exchange membrane ( 18 ), on one side of which a first catalyst layer ( 20 ) is applied, characterized in that on the first catalyst layer ( 20 ) a current collector ( 26 ) is applied according to one of claims 12 to 18. Electrochemical cell ( 10 ), in particular in the form of a proton exchange membrane electrolyzer ( 12 ) comprising two bipolar plates ( 30 . 32 ) and a membrane unit ( 14 ) according to claim 19.

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