HALF-CELL OF AN ELECTROLYTIC CELL FOR AN ELECTROLYZER AND METHOD FOR PRODUCING A COMPONENT FOR AN ELECTROLYTIC CELL

Description

BACKGROUND

The invention relates to a half-cell of an electrolytic cell for an electrolyzer and to a process for producing a half-cell for an electrolytic cell.

As used herein, the half-cell of an electrolytic cell is the region which extends from a membrane in the direction of a bipolar plate arranged to the side thereof. Since a bipolar plate is generally arranged on both sides of the membrane these two regions may likewise be considered half cells. Two half-cells thus preferably make up an electrolytic cell. Two or more electrolytic cells may be combined in a stack and may represent an electrolyzer.

In order to reduce the dependence on fossil fuels there has been a shift in focus to renewable energies. However, renewable energies typically require additional storage technology. Electrolysis for example is one of many possibilities for converting excess energy in the form of electricity into chemical energy. This process is known as electrolysis, where electrical energy is converted into chemical energy in the form of hydrogen and oxygen. The production of hydrogen from water using electric current is preferably carried out by electrolysis. In an alkaline electrolysis the following reactions are carried out at the cathode and the anode.

40H⁻→2H₂O+O₂+4e⁻  Equation 1 (anode)

2H₂O+2e⁻→20H⁻+H₂  Equation 2 (cathode)

Equations 1 and 2 represent partial reactions of hydrogen and oxygen formation and are carried out spatially separately from one another. The spatial separation is especially affected by means of a separator which allows transport of ions through the cell. This separator is often referred to as a membrane. In the case of anion exchange membrane electrolysis (AEM-water electrolysis) this is affected by utilization of a hydroxide ion-conducting membrane.

In thermodynamic equilibrium, without taking into account the entropy increase or the necessary supply of heat for phase change, a reversible cell voltage of 1.23 V is thus attained. The non-reversible thermoneutral voltage is thus 1.481 V at 25° C. An electrolytic cell and the associated half cells represent electrical assemblies whose components likewise have electrical resistances or impedances. These resistances or impedances thus ultimately influence an operating voltage of the electrolytic cell. Having regard to the resistance, two resistances in particular are relevant in the industrially relevant operating range, namely the activation resistance and the ohmic resistance of the cell.

The activation resistance is very largely determined by the electrode or the catalyst and its environment. By contrast, the ohmic resistance is influenced by all components. Having regard to the ohmic resistance, the membrane resistances, the electrolyte resistances and the contact resistances are of great importance. The ohmic resistance of the electrolytic cell thus has a decisive influence on the efficiency of the electrolysis. The lower the ohmic resistance of the electrolytic cell the more hydrogen can be produced at a predetermined energy amount. An improved electrolytic cell having a lower ohmic resistance or an increased efficiency may be of great importance in the storage of excess electrical energy, in the context of energy transition.

SUMMARY

It is accordingly an object of the present invention to increase the efficiency in electrolysis. This shall especially be achieved by a lower ohmic resistance of the electrolytic cell.

The present invention is based on the finding that in electrolytic cells known hitherto, two or more different intermediate layers are arranged in an electrolytic cell. Thus, for example a gas diffusion layer is often divided into a plurality of different layers. Each different layer can thus represent an intermediate layer which can increase the ohmic resistance of the electrolytic cell. The present invention therefore proposes a novel cell design for a half-cell of an electrolytic cell.

The following describes a first half-cell which relates to an anode-side portion of the electrolysis. A second-half-cell preferably relates to a cathode-side portion of the electrolytic cell. It is to be noted that the terms “first half-cell” and “second-half-cell” do not represent a sequence but rather only a different designation.

This object is achieved according to the invention by the independent claims of the present application. Advantageous developments and alternative embodiments are specified in the subsidiary claims, the description and the figures.

A first aspect relates to a half-cell of an electrolytic cell for an electrolyzer. The half-cell comprises an anode sub-plate of a first bipolar plate. The first bipolar plate is preferably composed of an anode sub-plate and a cathode sub-plate. The anode sub-plate is assigned to an anode-side portion of the electrolysis while the cathode sub-plate is assigned to a further second half-cell, the cathode-side portion of the electrolytic cell. The first half-cell preferably extends from a membrane of the electrolytic cell in the direction of the anode sub-plate which is especially a portion of the first bipolar plate. The first half-cell thus represents the anode side of the electrolytic cell while the second half-cell preferably represents the cathode side of the electrolytic cell. The membrane may be electrically conductive for anions. It may be “anion-conductive”. Alternatively, or in addition, the membrane may be permeable to hydroxide ions. The membrane may especially be permeable exclusively to hydroxide ions.

The anode sub-plate preferably comprises perpendicular elevations. These perpendicular elevations may be rectangular, circular and/or curved. The perpendicular elevations of the anode sub-plate may be made from the same material. The anode sub-plate may be configured as a single-piece, as a monolith and/or homogeneously with the perpendicular elevations. Alternatively, the perpendicular elevations may be separately applied to the anode sub-plate. The perpendicular elevations may be placed on the anode sub-plate for example.

A number, shape and/or arrangement of the perpendicular elevations preferably corresponds to an improved flow profile. This especially means that the number, shape and/or arrangement of the perpendicular elevations lead to a lower pressure drop, preferably to a lowest possible pressure drop, of a fluid flowing through the bipolar plate. The perpendicular elevations are preferably arranged or planned such that the fluid flowing parallel to the anode sub-plate experiences a lowest possible pressure drop.

Circular and/or curved elevations may comprise a planar flattened region which faces a further layer, namely a metallic anode transport layer. The half-cell especially comprises a metallic anode transport layer arranged at a top surface of the elevations of the anode sub-plate. The anode transport layer may be in direct contact with the anode sub-plate. The anode transport layer may be in direct contact with the perpendicular elevations of the anode sub-plate. It is likewise possible for the anode transport layer to be in exclusive contact only with the perpendicular elevations. Respective interspaces may thus be formed between the perpendicular elevations of the anode sub-plate. Depending on the configuration of the anode sub-plate this interspace may be empty or partially filled. The aspect regarding optimization of the elevations in terms of pressure drop may be correspondingly and analogously applied to the interspace. The size, shape and/or constitution of the interspace may be adapted or selected according to a pressure drop of a fluid flowing over the anode sub-plate. For example, the height of the perpendicular elevations may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 mm. The perpendicular elevations may have a semicircular, rectangular and/or curved shape.

The anode transport layer is preferably electrically conductive. This applies especially to predetermined charge carriers such as for example hydroxide ions, protons, electrons and/or hydroxonium ions which may also be described as protonated water molecules (H₃O+ ions). The charge carriers are electrons. The anode transport layer can only be electrically conductive. The charge carriers in the transport layer are preferably electrons. The anode transport layer may preferably be permeable with respect to the electrons as charge carriers and thus be electrically conductive. The half-cell preferably comprises a membrane arranged next to the anode transport layer. This membrane may be in direct contact with the anode transport layer. However, it is also possible for a catalyst layer to be arranged between the anode transport layer and the membrane. The catalyst layer for the anode side, i.e. for the anode transport layer, may comprise or include the following materials:

Nickel-aluminum, nickel-zinc, cobalt-aluminum, cobalt-iron, nickel-iron, nickel-iron-vanadium, nickel-cobalt, nickel-molybdenum, nickel-iron-double layered hydroxide, nickel-iron-cobalt, iridium, ruthenium oxide, nickel hydroxide, nickel oxide and/or nickel. The catalyst layer for the anode transport layer may be applied to fibers or be applied to a fiber structure of the anode sub-plate.

The catalyst layer for the cathode side, i.e. for the cathode transport layer, may comprise or include the following materials:

• • nickel, nickel-molybdenum on carbon black, nickel-molybdenum, nickel-platinum, platinum, nickel on carbon black, nickel phosphate and/or nickel-vanadium. The catalyst layer for the cathode transport layer may also be applied to fibers or to a fiber structure of the cathode sub-plate.

The membrane is preferably arranged at a side of the anode transport layer facing away from the elevations and permeable to predetermined charge carriers. The membrane may especially be permeable to hydroxide ions. The predetermined charge carriers for the membrane may be protons, electrons, hydroxide ions and hydroxonium ions. The charge carriers are preferably hydroxide ions. Alternatively, or in addition, the membrane may be configured to be conductive with respect to anions. The membrane may thus be configured to be anion-conductive. Anions may be electrically conducted along the membrane. Anions are especially negatively charged ions. By contrast it is possible for exclusively hydroxide ions (OH⁻ ions) to be able to diffuse through the membrane, i.e. for the membrane to be permeable only to hydroxide ions (OH⁻). The membrane may be permeable with respect to hydroxide ions, be permeable only to hydroxide ions.

The anode transport layer preferably has a graduated pore structure. The graduated pore structure is especially a structure of the anode transport layer where a respective diameter of the pores in the anode transport layer decreases in the direction perpendicularly facing the membrane. This may especially mean that the pores which are closer to the perpendicular elevations have a larger diameter than other pores which are closer to the membrane, i.e. further away from the perpendicular elevations. Conversely, this especially means that in the perpendicular direction to the anode sub-plate or to the bipolar plate the diameter of the pores becomes larger, i.e. increases. The perpendicular elevations are often referred to as “studs”. The anode transport layer thus does not have a homogeneous distribution with respect to the diameter distribution of the pores. The pore diameter can decrease linearly from an interface of the anode transport layer facing the perpendicular elevations in the direction of the opposite interface. The diameter of the respective pores in the anode transport layer can thus depend on a position of the respective pore within the anode transport layer. A vertical distance to one of the two interfaces of the anode transport layer is especially important here. The anode transport layer may include stainless steel and/or carbon steel. The diameter of the pores, also referred to as pore size, may be up to 50 μm. The pore size may be 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50 μm. A thickness of the transport layer may be 0.2 to 2.0 mm. The thickness of the transport layer may be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2 mm.

The anode transport layer may be subdivided into a plurality of plies. The plurality of plies may form the anode transport layer stacked one atop the other or one behind the other. Predetermined plies may have a support structure integrated into them. For example, the last ply of the anode transport layer or predetermined plies may include a net as the support structure. This may ensure a required stiffness of the anode transport layer. The mesh of the net preferably has a mesh size in the order of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 to 1 mm. The net or the support structure may have a thickness or a diameter of 10, 20, 30, 40, 50, 60, 70, 80, 90 to 100 μm. The join between the anode transport layer and the support structure is form-fitted and force-fitted.

The second half-cell which contains the cathode sub-plate preferably has a similar construction to the first half-cell comprising the anode sub-plate. It is preferable when these two half cells are symmetrical to one another. However, there may be differences with respect to the employed materials or coatings. The anode sub-plate thus on the one hand enables efficient gas exchange on account of its graduated pore structure while on the other hand enabling electrical conductivity for the predetermined charge carriers. This obviates the need for an additional gas diffusion layer. The number of layers within the electrolytic cell, which often significantly increase contact resistance, may be reduced. This cell design makes it possible to reduce the number of intermediate layers and thus also reduce the ohmic resistance of the half-cell. This makes it possible to increase the efficiency of the electrolytic cell. It is especially possible to reduce the number of intermediate layers from 8 to 4, which results in an improvement in the electrical conductivity in the half-cell and thus in an increase in efficiency during the electrolysis.

An additional or alternative embodiment relates to a half-cell, wherein the pores of a first interface of the anode transport layer which faces the elevations of the anode sub-plate have a first diameter and the pores of a second interface of the anode transport layer which faces the membrane have a second diameter. A quotient of the second diameter to the first diameter is preferably within a first interval from 4 to 50. The first diameter may be 50 μm while the second diameter may be only 1 μm. The pores thus tend to get smaller in terms of their diameter from the perpendicular elevations in the direction of the membrane. The change in the respective diameter of the pores as a function of a layer thickness which may define a vertical distance to the first interface may be linear, quadratic and/or exponential. The change in the respective diameter of the pores, i.e. the graduated pore structure, may thus correspond to a predetermined profile. The larger pores on the side of the perpendicular elevations make it possible to more efficiently discharge a product gas formed. Contemplated product gases in electrolysis include hydrogen and oxygen. This graduated pore structure, which is defined by the change in the respective pore diameters along a thickness of the anode transport layer, makes it possible to reduce a pressure drop with respect to the product gases. Gas back-pressure which is harmful to the efficiency of the electrolytic cell can thus be avoided or at least reduced. It is accordingly possible to obtain efficient gas outflow from the half-cell, thus reducing the probability of gas back-pressure.

An additional or alternative embodiment provides that for the pore structure a respective diameter of the pores between the first and the second interface of the anode transport layer is defined by a linear interpolation. The first interface is preferably in contact with the perpendicular elevations of the anode sub-plate while the second interface is preferably in contact with the membrane and/or a catalyst layer. The respective diameter of the pores may be described by the linear interpolation which assigns a respective pore diameter to a distance from the first or second interface. A quadratic, exponential or other interpolation may also be used instead of the linear interpolation. In particular, the selected interpolation may be determined according to a predetermined power capacity of the electrolytic cell, a catalytic coating of the anode sub-plate and/or by material properties of the half-cell. The graduated pore structure may thus be individually adapted to the respective half-cell or electrolytic cell and having regard to the respective specific demands.

In an additional or alternative embodiment for the half-cell the respective diameter of the pores and/or a profile of the respective diameter of the pores within the anode transport layer is determined according to a predetermined pressure drop for an anode product, an electrical resistance caused by the anode transport layer and/or a predetermined gas pressure of the electrolytic cell. The anode product may especially be oxygen gas. Depending on the electrolytic cell a certain production amount for hydrogen and oxygen may be specified. Using this embodiment the pore design, i.e. the respective diameter of the pores within the anode transport layer, may be adapted to the production amount. This likewise applies to pressure drop and electrical resistance. In principle each half-cell may be individually adapted to a respective predetermined gas pressure, pressure drop and/or electrical resistance for the relevant half-cell. The same applies analogously to the second half-cell containing the cathode sub-plate. Thus, a plurality of half cells in a stack of an electrolyzer may each have different pore structures. The respective pore structures are preferably adapted in terms of the respective half-cell based on a pressure drop, electrical resistance and/or gas pressure predetermined in each case. This allows each individual half-cell within an electrolyzer comprising a plurality of electrolytic cells to be individually adjusted to the respective pressure drop, resistance and/or gas pressure having regard to the relevant half-cell. This is especially achieved by adapting the respective pore diameters and the respective profile of the pore diameters.

An additional or alternative embodiment provides that an anode catalyst is embedded in the anode transport layer and/or is arranged as a layer between the membrane and the anode transport layer.

The catalyst layer for the anode side, i.e. for the anode transport layer, or the anode catalyst may comprise or include the following substances or substance compositions:

Nickel-aluminum, nickel-zinc, cobalt-aluminum, cobalt-iron, nickel-iron, nickel-iron-vanadium, nickel-cobalt, nickel-molybdenum, nickel-iron-double layered hydroxide, nickel-iron-cobalt, iridium, ruthenium oxide, nickel hydroxide, nickel oxide and/or nickel.

The catalyst layer for the cathode side, i.e. for the cathode transport layer, or the cathode catalyst may comprise or include the following materials or substance compositions:

• • nickel, nickel-molybdenum on carbon black, nickel-molybdenum, nickel-platinum, platinum, nickel on carbon black, nickel-phosphate and/or nickel-vanadium.

Different catalysts can be used to positively affect not only ohmic resistance but also activation resistance. In the case of a fibrous anode transport layer the respective fibers may be coated with a corresponding catalyst. An efficiency of the electrolytic cell can be enhanced. The coating may comprise one of the aforementioned substance compositions which contributes to the catalytic activity of the electrode or anode transport layer. Fibers may be configured as catalyst supports. The catalyst itself may have a low electrical conductivity. The electrical conductivity may be enhanced by means of a coating with the recited materials. This makes it possible to achieve good electrical conductivity for a catalyst which does not have good electrical conductivity.

By supporting noble metal-free catalysts a cross-conductivity of the catalysts may be increased through direct bonding to an electrically conductive material such as stainless steel, graphite, or carbon. The supporting comprises applying a further layer to a substrate. The catalyst layer may be used as a substrate and coated with a further distinct layer. The further distinct layer may comprise two different metals, i.e. may be bimetallic. Supporting is thus one of a plurality of possible coating methods. Further coating methods that may be employed include baking, vapor deposition and/or sputtering.

The layer of the anode catalyst may have a layer thickness of 0.01 μm to 5 μm. The anode transport layer may be produced by further coating methods such as for example electroplating, PVD, CVD, PA CVT or by wet-chemistry by application of a paste. Having regard to the second half-cell comprising the cathode transport layer, other catalyst materials may be provided. In the second half-cell it is accordingly preferable to provide the cathode transport layer with a corresponding cathode catalyst. This cathode catalyst may have a construction analogous to that elucidated in this working example.

The graduated pore structure may be realized for example using a plurality of different layers. For example, the anode transport layer may comprise different layers, wherein each layer has a corresponding pore diameter. The graduated pore design may thus be a sequence of two or more layers, each having a constant pore diameter. A person skilled in the art is thus familiar with a plurality of options for generating a corresponding graduated pore structure for the anode transport layer.

An additional or alternative embodiment provides a half-cell, wherein the anode catalyst is in the form of a layer between the membrane and the anode transport layer. The layer of anode catalyst preferably has a layer thickness between 100 nm and 5 μm. The anode catalyst may especially be in direct contact with the membrane. The anode catalyst may be disposed directly on the membrane for example.

An additional or alternative embodiment provides that the anode transport layer comprises a support structure having a first thickness. The support structure may be in the form of a grid, rectangular, in the form of a mesh and/or in the form of a wire. The first thickness may correspond to a diameter of the support structure. The support structure is especially connected, contacted and/or interwoven with metallic fibers of a second thickness. As mentioned, the support structure may be in the form of a net, particularly a metal net. The metallic fibers may form a nonwoven, a woven and/or a felt which is connected, contacted and/or interwoven with the support structure of the anode transport layer. The metallic fibers may be many times thinner than for example wires or rods forming the support structure.

The markedly thinner metallic fibers can wrap around the wires of the support structure and thus together with the support structure form a unit in the form of the anode transport layer. The metallic fibers make it possible to realize the graduated pore structure. It is thus possible to provide an anode transport layer which allows effective gas discharging and simultaneously has the necessary mechanical stability or strength on account of the support structure. The support structure preferably has a higher stiffness than the metallic fibers.

An additional or alternative embodiment provides that the first thickness of the support structure and the second thickness of the metallic fibers are determined according to a predetermined stiffness and/or a predetermined elasticity. This allows the anode transport layer to be adjusted according to the respective half-cell in respect of its flexibility and stiffness. It is preferable when the support structure makes it possible to achieve the necessary stiffness of the anode transport layer while the metallic fibers can provide the graduated pore structure. Simultaneously the metallic fibers can have the predetermined elasticity and accordingly be adjusted according to a type of spring strength of the anode transport layer. Stiffness and elasticity may be optimally adjusted in order on the one hand to allow the required stability of the anode transport layer and on the other hand to ensure the also necessary elasticity of the anode transport layer.

An additional or alternative embodiment provides a half-cell, wherein a quotient of the first thickness to the second thickness is between 2 and 100, in particular between 4 and 20, preferably between 5 and 10. The quotient especially represents a term D1/D2, wherein D1 represents the first thickness and D2 represents the second thickness. This means that the metallic fibers may be up to one hundred times smaller than for example wires of the support structure in the form of a grid. The support structure may especially be in the form of a grid, in the form of a net and/or in the form of a mesh. As a result of the markedly thinner metallic fibers the support structure may be correspondingly interwoven with the fibers.

The metallic fibers may comprise stainless steel, titanium and/or nickel. The metallic fibers may in each case form a nonwoven. The metallic fibers can thus form a nonwoven, also known as a nonwoven fabric. The nonwoven can include stainless steel. The nonwoven can be stiffened using the support structure and this makes it possible to attain a stiffer network structure of the stainless-steel nonwoven. The support structure makes it possible to ensure a structural integrity of the porous anode transport layer. Excessive penetration of the perpendicular elevations into the anode transport layer can thus be avoided. The nonwoven makes it possible to provide not only the necessary electrical conductivity but also the required mechanical stability and porosity for the graduated pore structure. The stainless-steel nonwoven can thus include the graduated pore structure.

The anode sub-plate and/or the cathode sub-plate may especially be coated with iridium, nickel and/or alloys of the following materials: nickel, iron, oxygen, cobalt, ruthenium and/or mixed alloys of these recited substances may be suitable for the coating. The following table indicates by way of example which compositions of these recited substances are suitable as a coating for the metallic fibers.

TABLE 1
Coatings for bipolar plates

	Anode sub-plate	Cathode sub-plate
Exemplary	TiN, TiNiNb, TiIr	Blocking
coating		layers for H2
systems	TiC	Ni
	DLC; diamond-like
	carbon layer, e.g. NiCr
	(nickel-chromium), NiV
	(nickel-vanadium)
	Ni/NiO

These recited substances preferably relate to the bipolar plate. The cathode side of the bipolar plate may have a different coating to the anode side of the bipolar plate. Other coatings may also be present for the cathode transport layer.

The support structure may be in the form of a grid and/or in the form of a mesh. The support structure may further comprise stainless steel and/or coated carbon steel. It is preferable to employ stainless steel as the support structure since a stainless material is advantageous in the electrolysis.

An additional or alternative embodiment provides that the number of elevations relative to a predetermined planar base area of the anode sub-plate, a height, a width and/or a shape of the elevations is determined according to a predetermined pressure drop for an anode product, an electrical resistance caused by the anode sub-plate and/or a predetermined gas pressure of the electrolytic cell. According to this embodiment the shape or the design of the bipolar plate which includes the anode sub-plate may be correspondingly adapted. For example, the perpendicular elevations may likewise have a further planar base area which is spaced apart from the predetermined planar base area of the anode sub-plate.

This further planar base area may be in direct contact with the anode transport layer. The size of this further planar area of the perpendicular elevations may be determined according to pressure drop, electrical resistance and/or gas pressure. The anode product is preferably oxygen and the cathode product is preferably hydrogen. In the case of a flexible stainless-steel nonwoven for example the height of the perpendicular elevations may be elevated. This makes it possible for example to increase a contact area between the anode transport layer and the anode sub-plate without filling the interspace necessary between the elevations. The number of perpendicular elevations based on the predetermined planar base area of the anode sub-plate may be regarded as the density of the elevations. It is thus possible to influence the pressure drop, electrical resistance and/or gas pressure by means of an elevation density.

The porous transport layer preferably is preferably in direct areal contact with the studs and can thus produce an electrical contact with the anode sub-plate. In addition, the aforementioned embodiments may be used to adjust the stiffness and elasticity of the anode transport layer. To this end it is possible for example to adapt the first thickness of the support structure and the second thickness of the metallic fibers. The half-cell may thus be adapted in terms of the support structure and the metallic fibers as well as in terms of the density of the studs, whose height and width and shape are individually defined according to the requirements for pressure drop, electrical resistance and gas pressure.

The anode sub-plate may comprise the following materials and/or be coated therewith: these materials include for example stainless steel, titanium, spring steel, nitrogen, carbon, nickel, oxygen, nickel-aluminum, nickel-zinc, cobalt-aluminum, cobalt-iron, nickel-iron, nickel-iron-vanadium, nickel-cobalt, nickel-molybdenum, nickel-iron-double layered hydroxide, nickel-iron-cobalt, iridium, ruthenium oxide, nickel hydroxide, nickel oxide, nickel and/or mixtures thereof. Fibers or a fibrous structure of the anode sub-plate may be coated with the recited substances or substance compositions. The following table recites possible substance compositions of the substances listed.

TABLE 2
Exemplary catalysts for the anode transport
layer or cathode transport layer

		Anode	Cathode
	Exemplary	Ir/IrO2, Ru/RuO2	Pt
	catalysts	NeFeOx, x: number of	NiMO
		atoms
		NeFeCo	NiCo
		NiFe-LDH (LDH	Ni
		“double-layered
		hydroxide”)
		Ni/NiO	Nickel-molybdenum
			(on carbon black)
		Nickel-aluminum	Nickel-platinum
		Nickel-zinc	Platinum
		Cobalt-aluminum	Nickel on carbon black
		Cobalt-iron	Nickel phosphate
		Nickel-iron	Nickel vanadium
		Nickel-iron-vanadium
		Nickel-molybdenum
		Nickel-iron-cobalt
		NiCo and its compounds
		CoPi

Having regard to the cathode sub-plate the following materials or coatings are possible:

Nickel, nickel-molybdenum on carbon black, nickel-molybdenum, nickel-platinum, platinum, nickel on carbon black, nickel phosphate and/or nickel-vanadium. The coating may also be applied to fibers or a fiber structure of the cathode sub-plate.

A different coating may be provided for the first half-cell (anode side) than for the second half-cell (cathode side). The cathode sub-plate may be coated with different materials in contrast with the anode sub-plate. The cathode sub-plate may comprise nickel or be coated with nickel. The anode sub-plate and/or the cathode sub-plate may have a thickness of 0.2 to 1 mm.

An additional or alternative embodiment provides that the anode transport layer has a thickness of 200 μm to 1000 μm and the elevations have a height perpendicular to the anode sub-plate of 1 to 5 mm. The height of the elevations of 1 to 5 mm ensures that there is enough of an interspace between the perpendicular elevations to ensure a required gas outflow in the half-cell.

In an additional or alternative embodiment, the elevations may each have a planar surface parallel to the anode sub-plate which is in direct contact with the anode transport layer. This allows the anode transport layer to be spaced apart from the anode sub-plate. The planar area may be used to adjust a gap between the anode sub-plate and the anode transport layer. The size of the planar area in contact with the anode transport layer may be used to adjust an electrical conductivity and a height of the elevations may be used to adjust a size of the gap and thus a possible gas flow rate of the anode product oxygen. Analogous considerations apply to the elevations of the cathode sub-plate in contact with the cathode transport layer.

An additional or alternative embodiment provides that the anode sub-plate, the anode transport layer and the membrane are secured in a cell frame and the cell frame comprises a seal. The seal is preferably configured such that the membrane, the anode sub-plate and/or the anode transport layer are sealed. The cell frame may comprise two cell frame halves which may secure the anode sub-plate, anode transport layer and/or membrane on respective opposite sides. Especially the first bipolar plate may be sealed using the cell frame. An electrolytic cell may thus include two bipolar plates which may form a complete cell frame using two cell frame halves. The first anode sub-plate may be regarded as part of the first bipolar plate. The membrane may be force-fittingly clamped and thus sealed with a suitable sealing material as the seal between the two cell frame halves. Employable seals include ring gaskets, O-rings and/or other forms of seals. The material of the cell frame may have a metallic or polymeric nature.

A second aspect of this invention relates to an electrolytic cell. The electrolytic cell includes a first half-cell as described in the aforementioned embodiments. The electrolytic cell further comprises a second half-cell which is especially arranged at the membrane. The first and the second half-cell may be arranged symmetrically to one another with regard to the membrane. The second half-cell comprises a cathode sub-plate of a second bipolar plate. The cathode sub-plate comprises perpendicular elevations. At a top surface of the elevations of the cathode sub-plate a metallic cathode transport layer is arranged. The membrane is arranged at a side of the cathode transport layer facing away from the elevations and is permeable to further predetermined charge carriers. The further predetermined charge carriers may be electrons, protons, hydroxonium ions and hydroxide ions. It is preferable when the membrane is exclusively permeable to hydroxide ions (OH-ions). The membrane is preferably electrically conductive with respect to anions, i.e. negatively charged ions. Consequently, hydroxide ions (OH-ions) can diffuse through the membrane and likewise be conducted along the membrane surface. Other anions such as for example hyperoxide anions (O₂⁻) and ozonide anions (O₃⁻) may preferably only be electrically conducted by the membrane as anions but cannot diffuse through the membrane. The cathode transport layer preferably has a further graduated pore structure where a respective diameter of the pores in the cathode transport layer decreases in the direction perpendicularly facing the membrane. The second half-cell in principle has a construction similar to the first half-cell. Especially the arrangement of the cathode transport layer, the cathode sub-plate and any coatings may be analogous to that of the first half-cell. However, differences may result in respect of the employed materials, coatings and/or layer thicknesses, for the catalysts employed in each case.

All embodiments may be correspondingly and analogously applied to the second half-cell comprising the cathode sub-plate and the cathode transport layer. However, for the sake of clarity a further detailed description of the second half-cell in the manner of the first half-cell is omitted. Consequently, all embodiments relating to the first half-cell or to the half-cell may thus be correspondingly applied to the second half-cell. The embodiments which follow relate to the electrolytic cell which includes the first half-cell and the second half-cell. The embodiments preferentially focus on the properties of the second half-cell. In terms of the first half-cell reference is made to the aforementioned embodiments.

An additional or alternative embodiment for the electrolytic cell provides that the cathode sub-plate comprises nickel and/or is coated with nickel. Hydrogen is preferably produced in the second half-cell comprising the cathode sub-plate. Nickel has proven to be a material particularly effective in this regard.

An additional or alternative embodiment for the electrolytic cell provides that a cathode catalyst is embedded in the cathode transport layer and/or is arranged as a layer between the membrane and the cathode transport layer. The cathode catalyst may comprise platinum, nickel, molybdenum, cobalt and/or mixtures thereof. Tables 1 and 2 show by way of example which substances or substance compositions may be suitable as a catalytic coating for the cathode transport layer.

The invention may comprise an electrolytic cell having a first and/or second half-cell, wherein the respective transport layer comprises two or more coatings. The respective half-cell may be a nonwoven which includes stainless steel. This nonwoven may be in the form of fibers. These fibers may be coated with two or more layers. A first layer may comprise nickel for example. A second layer which is preferably in direct contact with the first layer may contain NiFe, NICO, NiFeCo, NiV, NiMo, NiFeO, NiAl and/or NiZn.

A third aspect of the present invention relates to a process for producing a half-cell for an electrolytic cell. The process may comprise the following steps. Initially an anode sub-plate and a cathode sub-plate may be stamped and/or embossed to form perpendicular elevations. The stamped or embossed sub-plates may be welded at the edge regions. This makes it possible to produce a bipolar plate from these two sub-plates. In a further step respective transport layers may be placed on the elevations on both sides of the bipolar plate. It is preferable when the anode transport layer is placed on one side and the cathode transport layer is placed on the opposite side. Each bipolar plate is thus preferably in contact with precisely one anode transport layer and precisely one cathode transport layer. The respective transport layer is pressed together with the bipolar plate using a respective contact pressure. The necessary contact pressure is determined according to a predetermined flow resistance of a respective product of the electrolytic cell and/or an electrical resistance of the respective transport layer. The flow resistance and/or the electrical resistance may be predetermined parameters which define the respective contact pressure. A membrane may be arranged at the respective transport layers. The membrane may be sealed using a cell frame comprising a seal by clamping the seal. During assembly of the electrolytic cell two bipolar plates comprising the cell frame halves may thus form a complete cell frame. The membrane may be force-fittingly clamped using a suitable seal between the cell frame halves. This allows the membrane to be sealed. The porous transport layer may be placed flat directly on the studs, the perpendicular elevations. This makes it possible to ensure electrical contact with the bipolar plate.

The features, embodiments, examples, and advantages thereof specified in connection with the half-cell according to the first aspect of the invention apply correspondingly to the electrolytic cell according to the second aspect of the invention, to the process for producing a half-cell according to the third aspect and vice versa in each case. Apparatus features of the first and/or second half-cell can therefore be applied to the electrolytic cell or an electrolyzer having a plurality of electrolytic cells and vice versa. The same applies to the applicability of apparatus features to process features and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-described properties, features and advantages of the present invention as well as the manner in which these are achieved will become clearer and more understandable in connection with the following description of the working examples which will now be more particularly elucidated with reference to the figures. The invention will therefore now be more particularly elucidated with reference to exemplary figures. It must be noted that the figures are merely exemplary representations of how the invention may be realized. In no sense are the drawings and the accompanying description to be regarded as limiting to the invention. In the figures:

FIG. 1 shows an exemplary cross section of an electrolytic cell;

FIG. 2 shows an exemplary cross section of an electrolyzer comprising a plurality of electrolytic cells;

FIG. 3 shows an exemplary representation of an electrolyzer comprising a centrally arranged bipolar plate clamped between two cell frame halves;

FIG. 4 shows a plan view of a bipolar plate having perpendicular elevations;

FIG. 5 shows a schematic representation of a graduated pore structure in the anode transport layer and cathode transport layer comprising a support structure and metallic fibers;

FIG. 6 shows a schematic representation of an anode transport layer having a support structure and metallic fibers; and

FIG. 7 shows an exemplary scheme for producing a half-cell or an electrolytic cell.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary side view of an electrolytic cell EZ. The electrolytic cell EZ preferably includes a first half-cell H1 and a second half-cell H2. The two half-cells H1 and H2 together form the electrolytic cell EZ. Arranged centrally in the electrolytic cell EZ is a membrane MB. The first half-cell H1 represents the anode-side portion of the electrolytic cell EZ while the second half-cell H2 represents the cathode-side portion of the electrolytic cell EZ. The membrane MB is preferably electrically conductive having regard to anions, such as for example OH⁻, O²⁻, S²⁻, N³⁻ etc. At the same time the membrane MB may be permeable exclusively to hydroxide ions (OH ions).

Following the membrane MB in the x-direction is an anode catalyst AKA. In the case of FIG. 1 the anode catalyst AKA is in the form of a layer. However, it may alternatively or in addition be integrated in an anode transport layer AT or be joined to the anode transport layer AT by coating. In FIG. 1 the anode transport layer AT is shown as perforated. This perforated representation is intended to indicate the porosity of the anode transport layer AT. Following the anode transport layer AT further in the x-direction is the anode sub-plate AP which is part of a first bipolar plate BP1. The anode sub-plate AP comprises perpendicular elevations NP. These perpendicular elevations NP are often referred to as studs. These studs may be rounded, angular, cylindrical and/or triangular. In particular, the perpendicular elevations NP may be in direct contact with the anode transport layer AT. The anode transport layer AT has a first interface G1 which is in partial contact with the perpendicular elevations NP. By contrast, the second interface G2 opposite the first interface G1 is in contact with the anode catalyst AKA.

Alternatively, the second interface G2 may also be in contact with the membrane MB. The second half-cell H2, from the membrane MB in the negative x-direction, has a similar construction to the first half-cell H1. As catalyst the second half-cell H2 comprises a cathode catalyst KKA. The cathode catalyst KKA may likewise be joined to the cathode transport layer KT. The cathode transport layer KT may be in direct contact with the studs of the cathode sub-plate KP which is part of a second bipolar plate BP2. The bipolar plate BP1, BP2 and the membrane MB may be secured via a first cell frame half Z1 and a second cell frame half Z2.

FIG. 2 shows an enlarged exemplary and schematic side view of the two cell frame halves Z1 and Z2 comprising the first bipolar plate BP1. The first bipolar plate BP1 is sealed with a seal DT. The first bipolar plate BP1 comprises the anode sub-plate AP and the cathode sub-plate KP. These two sub-plates AP and KP preferably together form the first bipolar plate BP1. The same applies to the second bipolar plate BP2 and to further bipolar plates. The terms “first” or “second” are used merely for the purposes of distinguishing and especially have no direct technical definition. A seal DT is arranged in the first cell frame half Z1 and in the second cell frame half Z2. The seal DT may be a ring gasket, an O-ring or another seal. The seal DT arranged between the cell frame halves Z1 and Z2 allows force-fitting clamping of the first bipolar plate BP1 and the membrane MB. This makes it possible to achieve reliable sealing.

The first bipolar plate BP1 comprising the anode sub-plate AP may be made of titanium. By contrast, a second bipolar plate BP2 may be made of another material. Accordingly, the first bipolar plate may be made of two different materials. This makes it possible to favor a higher chemical resistance of the anodic first half-cell H1. The anode sub-plate AP and cathode sub-plate KP may be pressed together. The welding of these two sub-plates could be omitted in this case. The pressed-together sub-plates of the first or second bipolar plate BP1 and BP2 may be sealed by the two cell frame halves Z1 and Z2.

FIG. 3 shows an exemplary and highly simplified electrolyzer EY. The electrolyzer EY includes a plurality of electrolytic cells. In the example of FIG. 3 the electrolyzer EY includes two electrolytic cells EZ comprising the first and the second half-cell H1 and H2 and a third half-cell H3 and a fourth half-cell H4. The two electrolytic cells EZ preferably have an identical construction. However, the respective anode transport layers AT and cathode transport layers KT may differ in the respective half cells in respect of their respective pore structure and their coatings.

FIG. 3 shows the second bipolar plate BP2 in a central position. Proceeding in the x-direction from the second bipolar plate BP2 one arrives via the membrane MB at the anode transport layer AT of the first bipolar plate BP1. Since the electrolyzer EY is composed of a plurality of electrolytic cells EZ and a plurality of half cells it is sufficient to concentrate on the mode of operation and the basic construction of a half-cell. Depending on the required production volume of hydrogen and/or oxygen the electrolyzer EY may comprise a different number of electrolytic cells EZ. A plurality of electrolytic cells may be combined in a stack as represented by the electrolyzer EY.

FIG. 4 shows an exemplary plan view of the first or second bipolar plate BP1 or BP2. This may be an anode sub-plate AP or a cathode sub-plate KP depending on the perspective and installation position. In FIG. 4 the perpendicular elevations NP are discernible in the form of round studs NP. The studs NP of the anode sub-plate AT and/or the cathode sub-plate KT may be adapted in terms of their height, width, shape, distribution, and density to optimize a contact resistance and pressure drop. A desired contact area to the anode transport layer AT may thus be predetermined and established via a corresponding stud density, stud shape and stud height or stud width. The anode sub-plate AP may be adjusted in terms of its contact area with the anode transport layer AT via the density of the perpendicular elevations NP (studs), the planar base area of the perpendicular elevations NP and via the height, the width or the diameter of the perpendicular elevations NP. This makes it possible to achieve a uniform current distribution and thus a reduction in the ohmic resistance during operation of the electrolyzer EY. Local current peaks and undesired contact resistances are especially avoided.

FIG. 5 shows a schematic representation of a cross section through the anode transport layer AT and the cathode transport layer KT in contact with the membrane MB. A pore structure of the anode transport layer AT will now be described. The pore structure shown in FIG. 5 may be described as a graduated pore structure. The graduated pore structure especially has the feature that the anode transport layer AT has pores having a first diameter D1 in the region of the first interface G1 while the anode transport layer AT exhibits pores having a second diameter D2 at the second interface G2. The first diameter D1 is greater than the second diameter D2. The pores between these two interfaces G1 and G2 preferably have a diameter between the first diameter D1 and the second diameter D2.

A diameter of the pores may be linearly dependent on the thickness of the anode transport layer AT and/or on a vertical distance to the first interface G1 or the second interface G2. The anode transport layer AT is often referred to as a porous layer since it accordingly comprises pores. The first diameter D1 may be 50 μm for example while the second diameter D2 may be only 5 μm. The ratio of the first diameter D1 to the second diameter D2 may be from 2 to 10. The cathode transport layer KT may have a different graduated pore structure to the anode transport layer AT. This is to be understood as meaning that the pore diameters likewise increase in the negative x-direction in the cathode transport layer KT but to a different extent corresponding to the specific demands. The graduated pore structure in the cathode transport layer KT may thus be different to the graduated pore structure in the anode transport layer AT.

Having regard to a profile of the respective pore diameters the functional protocol or imaging protocol can determine the respective diameters of the pores according to a layer thickness, the direction of which is represented by the x-direction, i.e. along the direction perpendicular to the interface. Instead of a linearly increasing or decreasing profile of the respective pore diameters the profile may instead be quadratic or exponential. This makes it possible for the selected distribution function of the graduated pore diameters along the x-direction to achieve a functional layer which features a generally non-homogeneous distribution of the pore diameters. In the example of FIG. 5 the first interface G1 of the anode transport layer AT is positioned directly on the planar area of the perpendicular elevations NP. The graduated pore structure shown by way of example in FIG. 5 is preferably realized in all embodiments or working examples. It is not explicitly shown in FIGS. 1 to 3 purely for the sake of clarity.

FIG. 6 shows an exemplary plan view of the anode transport layer AT. This applies analogously to the cathode transport layer KT. The right-hand region of FIG. 6 shows a support structure ST. This support structure ST is in the form of a grid in the example of FIG. 6. The grid may be realized by way of interwoven wires. The wires of this grid structure may have a thickness a1. The support structure ST is interspersed/interwoven with a fibrous structure. This fibrous structure comprises metallic fibers FS. In the right-hand side of FIG. 6 only the fiber structure of the metallic fibers FS is discernible. These metallic fibers FS have a thickness a2 which is smaller than the first thickness a1. The first thickness a1 may be 10 or even 100 times greater than the second thickness a2. The metallic fibers FS having the second thickness a2 may be connected to and/or interwoven with the support structure.

It is clearly apparent in the right-hand region of FIG. 6 that the metallic fibers FS wrap around the metal wires of the support structure ST. This can provide the anode transport layer AT with a required mechanical stability and or strength. The graduated pore structure is preferably realized via the metallic fibers FS. The metallic fibers FS may be in the form of a felt, woven and/or a nonwoven. The metallic fibers may especially comprise stainless steel.

The nonwoven comprising the metallic fibers FS may be placed on the studs that are readily apparent in FIG. 4. The stainless-steel nonwoven can thus be positioned directly on the perpendicular elevations NP. During assembly of the respective electrolytic cell EZ a contact pressure to be applied can be used to adjust a contact area between the stainless-steel nonwoven and the perpendicular elevations NP. This also applies in principle to other metallic fibers FS. The metallic fibers FS or the stainless-steel nonwoven can be used to achieve a spring effect in the first half-cell H1 and the electrolytic cell EZ. This spring effect makes it possible to achieve a uniform areal contacting with the anode sub-plate AP or cathode sub-plate KP. This enables a particularly uniform current distribution and at the same time the graduated pore structure in the stainless-steel nonwoven makes it possible to reduce a pressure drop of the anode product or cathode product. These two factors can help to enhance the efficiency of the electrolytic cell EZ or the electrolyzer EY.

The nonwoven or metal nonwoven and the metallic fibers FS may be coated. The coating may be the anode catalyst AKA or the cathode catalyst KKA. These catalysts may have a multilayered construction. An exemplary anode-side layer system for efficient electrodes could be affected via a multi-ply coating of an adhesive coating comprising nickel on stainless steel and a subsequent porous catalytic nickel-iron coating. The coated metal nonwoven comprising the metallic fibers FS may further be coated with an anion exchange polymer. This can bring about an ionic transport channel for the hydroxide ions from the membrane MB to the anode catalyst AKA or cathode catalyst KKA. This simultaneously allows the necessary concentration of a potassium hydroxide solution to be reduced while improving the mechanical stability of the catalytic layer.

The anode transport layer AT may thus comprise a microporous structure and be disposed directly on the membrane MB. This makes it possible to achieve a homogeneous force distribution over the membrane MB. The nonwoven/the metallic fibers FS can thus reduce the risk of damage to the membrane MB by crushing or perforation especially in elevated-pressure operation of the electrolyzer EY.

Materials, layer thicknesses and the configuration of the perpendicular elevations NP are preferably adapted to one another such that outlet pressures of up to 25 bar are realizable on the gas side. The electrolytic cell EZ comprising the first half-cell H1 and the second half-cell H2 is especially characterized by its low complexity. A lower component count in the electrolytic cell EZ results in fewer interfaces and thus brings about a reduction in the associated ohmic resistance. Simultaneously the respective layers are adapted to one another in terms of their structure and extent and the corresponding stud design in such a way that the necessary stability, electrical conductivity, and the necessary gas flow rate can nevertheless be ensured. This novel electrolytic cell EZ makes it possible to employ simple coating technologies, which can markedly reduce the production costs of the electrolyzer EY.

FIG. 7 shows an exemplary possible process. This may be used to produce the first half-cell H1, the second half-cell H2, the electrolytic cell EZ and/or the electrolyzer EY. In addition, the anode sub-plate AP and the cathode sub-plate KP may be stamped and/or embossed in a first step S1. This makes it possible to form the perpendicular elevations NP.

In a second step S2 these two sub-plates may be welded to one another to form the first bipolar plate BP1.

In a third step S3 a respective transport layer is placed on the elevations NP on both sides of the first bipolar plate BP1. The transport layer preferably corresponds to the anode transport layer AT and the other transport layer on the opposite side of the first bipolar plate BP1 is preferably the cathode transport layer KT.

In a fourth step S4 the respective transport layer may be pressed together with the first or second bipolar plate using a respective contact pressure. The contact pressure is especially determined according to a predetermined flow resistance of a respective product of the electrolytic cell EZ and/or an electrical resistance of the respective transport layer AT or KT. In a fifth step S5 the membrane MB may be arranged at the respective transport layers AT, KT. In a sixth step S6 the membrane is clamped via the seal DT using the cell frame, formed by the two cell frame halves Z1 and Z2. The cell frame and the cell frame halves Z1 and Z2 may include the seal.

The working examples and embodiments show how a simpler, more robust and altogether more streamlined cell design can increase efficiency during electrolysis, while simultaneously bringing cost advantages during production. An improved electrolysis in electrolytic cells EZ may be useful in many technical fields and/or in the storage of energy.