Technical Field

The invention relates to a device for precise and uniform application of functional layers comprising metal nanoparticles and polymer electrolyte particles as a binder. Such functional layers have some extraordinary properties that make them increasingly used in many different technical and biotechnological fields. In particular, layers of metal or metal oxide nanoparticles with thicknesses of several tens of micrometers containing polymer electrolyte-type binders can serve as electrodes in electrochemical devices, e.g., hydrogen fuel cells, electrolyzers, electrochemical hydrogen compressors and sensors for detecting the presence of gases. The invention further relates to a method of applying the functional layers of catalytic nanomaterials and catalytic layers prepared or obtained using this method.

Background of the Invention

Prospective applications of functional layers of metal nanoparticles are expected in the near future for hydrogen fuel cells. A hydrogen fuel cell with a polymer electrolyte membrane is an electrochemical device that allows the direct conversion of the chemical energy of the fuel into electrical energy. The use of a solid electrolyte in the form of a polymer membrane enables reliable, long-term, noiseless functioning of the fuel cell in various operating environments and modes of operation. By deploying hydrogen as a fuel and with water as the only waste product of fuel cell operation, this type of device is being promoted as one of the key technologies on the road to sustainable carbon-free energy and electromobility.

The core of a fuel cell is a membrane electrode assembly (MEA) , which typically consists of five layers of materials pressed into a functional unit. The central layer is a proton-conducting polymer membrane. On both sides of the membrane, there are electrodes, from which hydrogen oxidation (H ₂ → 2H ⁺ + 2e-) takes place at the anode and oxygen reduction (O ₂ + 4H ⁺ + 4e- → 2 H ₂ O) takes place at the cathode. The electrodes consist of two layers, i.e., a diffusion layer made mostly of carbon paper and a catalytic layer containing catalyst nanoparticles to accelerate the above chemical reactions. The hydrogen fuel cell catalyst is typically composed of platinum nanoparticles immobilized on nanostructured carbon. Alternatively, the catalyst may contain other metallic additives that may increase the catalytic effect of the platinum, or increase the lifetime of the material, or reduce the overall cost of production. The catalytic layer forms the transition between the membrane and the diffusion layer, and its optimization in terms of composition and structure is critical for the performance of the fuel cell. It also represents a very significant cost item for the fuel cell due to its precious metal content and the complexity of the production processes.

For the purpose of producing membrane electrode assembly, two approaches are currently used for applying catalytic layers of nanoparticles :

1) CCM (catalyst-coated membrane) : The catalytic layer is applied to both sides of the polymer membrane. Diffusion layers are then added on both sides of this three-layer CCM to form a five- layer assembly.

2) GDE (gas-diffusion electrode) : The catalytic layer is applied to the diffusion layer. The bilayer electrodes thus produced are then hot-pressed onto both sides of the polymer membrane to form a five-layer assembly.

Several approaches have been developed to form catalytic layers for CCM or GDE, typically using a catalytic ink. It is a liquid solution of catalytic nanoparticles, an ion-conducting polymer and an organic solvent. The catalytic ink is applied in liquid form to the membrane or diffusion layer and forms a solid catalytic layer several tens of micrometers thick when the solvent evaporates. The catalytic layer has a suitable ratio of catalytic nanoparticles, ion-conducting polymer binder and open pores to ensure catalysis and transport of reactants and products of chemical reactions. The following methods are currently used for applying the catalytic ink:

• Blade-coating: It is a basic method of spreading catalytic ink on a diffusion layer using a controlled feed of a precision razor. The coating of catalytic ink tens to hundreds of micrometers thick is then dried in an oven to form a solid catalytic layer. This basic and simple method is used in laboratory research to produce samples of catalytic layers, but it does not achieve high accuracy in thickness and homogeneity of the resulting layer and precise geometric shapes cannot be achieved .

• Screen printing: This method is traditionally used for printing graphics or producing printed electronics. To form a catalytic layer by screen printing, a higher viscosity catalytic ink must be used. The advantage is high printing capacity, homogeneity of the applied layer and dimensional and shape accuracy of the print .

• Inkjet printing: It is a non-contact layer application technique using ink droplets with a diameter of 10-100 pm. The droplets are generated by a nozzle with an ejection effect induced by a piezoelectric system (piezoelectric crystal) or a heating element. The method allows the printing of complex geometric shapes with high precision. It is also possible to produce functionally graded catalytic layers with variable catalyst concentration in the cross-section of the layer. However, the quality of the catalytic ink must be monitored during application to avoid changes in its properties (viscosity, nanoparticle aggregation) over time.

• Additive manufacturing: The process of applying catalytic layers can be combined with polymer electrolyte application to form CCM via an additive procedure. A first catalytic layer is applied to a carrier film. However, instead of using a traditional polymer membrane in the form of a thin film, the polymer electrolyte is printed similar to the catalytic layer. It is appropriate to apply the polymer electrolyte in several layers to avoid disturbing the properties of the underlying catalytic layer. After application of the polymer electrolyte, a second catalytic layer is applied. Additive manufacturing provides opportunities to reduce costs for polymer electrolyte, allows to eliminate the occurrence of cracks and defects in individual layers, and reduce the number of underlying films required to form and transfer individual CCM layers. The process of laminating the individual CCM layers is also eliminated.

Said methods of catalytic layer production using catalytic ink, which are common today, have certain disadvantages. The catalytic ink may change its properties in terms of viscosity and agglomeration of the contained nanoparticles during application. After the drying of the ink, inhomogeneity of the catalytic layer may then occur in terms of layer thickness and spatial distribution of the catalyst nanoparticles. In addition, during the drying of the catalytic ink, i.e., the evaporation of the organic solvent, cracks may form in the catalytic layer or delamination may occur at the interface between the catalytic layer and the polymer membrane.

For the synthesis of nanoparticles, the spark evaporation method, which is described, e.g., in the publication: Nemec T. , Sonsky J. , Gruber J. , Prado E. , Kupcik J. , Klementova M. : Platinum and platinum oxide nanoparticles generated by unipolar spark discharge . Journal of Aerosol Science, 141, 105502, 2019, may be advantageously used. The spark evaporation method uses a spark discharge generator to form nanoparticles in a carrier gas. This allows the nanoparticles to be applied by direct deposition on a suitable substrate. Synthesis and deposition in the gaseous phase has additional advantages in terms of high purity of the catalytic nanoparticles, high porosity and homogeneity of the applied nanoparticle layer. This publication contains a general description of a chamber for performing the spark discharge, but it does not define, for the purpose of generating a functional layer for a hydrogen fuel cell, what filter can be used and how to place it in the deposition chamber, how to filter through it, and what other particles to deposit along with the metal nanoparticles, which is part of the subject matter of the present invention.

In addition, the spark evaporation method enables the generation of mixed nanoparticles or nanoalloys. The principle of generating nanoalloys is well-known and straightforward, where electrodes of two different metals are used in the spark evaporation, or mixed electrodes are used, prepared, e.g., by sintering a mixture of metals of the desired composition. For use in a hydrogen fuel cell, it is especially alloys of platinum and other metals that may offer advantages over pure platinum. For example, a platinum-ruthenium alloy on the anode side of the fuel cell makes it allows to prevent carbon monoxide poisoning (so-called CO poisoning) of the catalyst, or to use lower-quality hydrogen (with a higher carbon monoxide content) as fuel. On the cathode side of the fuel cell, platinum alloys with transition metals (iron, nickel, cobalt) are used, which offer cost savings while maintaining sufficient catalytic activity of the nanomaterial.

For the purposes of the present invention, the term "platinum nanomaterial" includes any nanoalloy of platinum with other metallic additives formed by the spark evaporation method.

Summary of the Invention

The disadvantages and risks of using catalytic ink to form functional layers of nanoparticles are addressed by a device of the present invention for applying a nanoparticle layer directly from the gaseous phase, wherein the device comprises a first manifold comprising a discharge chamber for generating catalytic nanoparticles and a first flow controller for setting the carrier gas flow in the first manifold, a second manifold comprising a nebuliser for generating droplets of electrolyte aerosol from the polymer electrolyte and a second flow controller for setting the carrier gas flow in the second manifold, furthermore, a deposition chamber and an outlet manifold leading from the deposition chamber, wherein the first manifold and the second manifold are connected and exit into the deposition chamber. The deposition chamber is gas-tight sealed and is adapted to fix the substrate for deposition of the functional catalytic layer. In the deposition chamber, the flowing cross-section for gas is partially blocked by a transversely oriented plate of porous substrate for deposition of the functional layer reinforced by the diffuser support plate.

For application of hybrid functional layers or functionally graded layers of nanoparticles, a follow-up technical solution can be used where, in addition to the first and second manifolds, a third manifold is attached at the inlet of the deposition chamber, which contains an additional discharge chamber for generating nanoparticles of another type.

For pressure control during the application of the functional layer, the above technical solutions can be extended by another element, where in the outlet manifold there is installed an inlet pressure controller which is connected by a data link to a pressure sensor located in the second manifold before the inlet of the deposition chamber.

Description of the Deposition Device

The device shown in Fig. 1 consists of four main units block-wise. These are the first manifold 1 with the discharge chamber 15, which is connected to the second manifold 2 with an ultrasonic nebuliser 22 , which exits into the deposition chamber 3, which is connected to the outlet manifold 4. In Fig. 2, the device is shown in detail. At the inlet of the first manifold 1 , which is typically made of a mechanically strong and chemically resistant material (in particular stainless steel, teflon) , there is installed the first flow controller 11 . This is a standard commercial product used for precise control of carrier gas flow. The manifold 1 continues with an inlet into the discharge chamber 15, which houses the metal electrodes, i.e., the cathode 12 and the anode 14 , and based on the known principle of spark evaporation of electrodes, the discharge chamber 15 is the source of the catalytic nanoparticles 16, which are directed by the carrier gas further down the first manifold 1 .

The second manifold 2 starts in Fig. 2 with an inlet of pressure carrier gas to the second flow controller 21 , which is the same type of controller as the first flow controller 11. The second manifold 2 continues with the inlet to the ultrasonic nebuliser 22 , which via a standard ultrasonic activation method generates droplets of the electrolyte aerosol 24 which are directed by the carrier gas down the second manifold 2.

The two manifolds 1 , 2 are connected together at the inlet to the deposition chamber 3, wherein the carrier gas then contains both the catalytic nanoparticles 16 and the droplets of the electrolyte aerosol 24.

The deposition chamber 3 is gas-tight sealed and fixes a substrate 33 for deposition of a functional catalytic layer 32. The substrate 33 is mechanically supported by a diffuser plate 34.

At the outlet of the deposition chamber, an outlet manifold 4 is connected, which is terminated by an opening open to the atmosphere.

In a preferred embodiment, the inlet pressure controller 43 is attached to the outlet manifold 4 and connected to a pressure sensor 41 located at the inlet to the deposition chamber 3, which is connected to the inlet pressure controller 43 via a data link 42. In another preferred embodiment of Fig. 3, there is attached a third manifold 5, which is schematically identical to the first manifold 1 and which includes its own second discharge chamber 55.

Method of Deposition of the Catalytic Functional Layer

The method of deposition is explained according to Fig. 2. At the inlet of the first manifold 1, which serves to supply the catalytic nanoparticles 16 to the deposition chamber 3_, the first flow controller 11 is located, which ensures precise dosing of the carrier gas for transporting the catalytic nanoparticles 16 and depositing them on the substrate 33 in the deposition chamber 3. The carrier gas, the direction of the stream of which is indicated by arrows in the figures, enters the discharge chamber 15, in which catalytic nanoparticles 16 entrained by the flowing carrier gas are generated by spark discharge 13 on the principle of evaporation of metal electrodes, i.e., cathode 12 and anode 14. The carrier gas is either of an inert nature (argon) , where pure metal nanoparticles are generated, or the carrier gas contains oxygen, which allows the generation of metal oxide nanoparticles. Furthermore, some metals (such as titanium) can form nitrides etc. with nitrogen. The generator of the spark discharge 13 also allows the size and concentration of the generated catalytic nanoparticles 16 to be varied by controlling the energy and repetition rate of the spark discharges 13. Alternatively, by controlling the carrier gas flow, the degree of agglomeration of the catalytic nanoparticles 16 and the degree of their oxidation can be controlled.

Very small droplets of the electrolyte aerosol 24 are fed into the deposition chamber 3. through the second manifold 2. A second flow controller 21 , located in the second manifold 2, ensures precise dosing of the carrier gas stream for transporting the droplets of the electrolyte aerosol 24 and depositing them on the substrate 33. The carrier gas enters the ultrasonic nebuliser 22 and entrains the droplets of the electrolyte aerosol 24 formed by the solution of polymer electrolyte 23 activated by the ultrasonic source 25. The electrolyte 23 both serves as a binder for the applied functional catalytic layer 32 and also provides it with the necessary proton conductivity. By controlling the carrier gas flow by the second flow controller 21 and controlling the power of the ultrasonic source 25, the concentration of the droplets of the electrolyte aerosol 24 in the carrier gas and thus the amount thereof for deposition on the substrate 33 is varied.

As a result of the connection of the manifold 1_ and 2 at the inlet to the deposition chamber 3_, the carrier gas contains both catalytic nanoparticles 16 and droplets of the electrolyte aerosol 24 in the desired concentrations.

The deposition chamber 3_ serves to fix and seal the substrate 33 for deposition of the functional catalytic layer 32. A typical material for the substrate 33 for use in a low-temperature hydrogen fuel cell is a diffusion layer of porous carbon paper. During deposition, the plate of the substrate 33 acts as a filter on which catalytic nanoparticles 16 and droplets of the electrolyte aerosol 24 from the carrier gas stream 31 are deposited simultaneously by filtration. The substrate 33 is mechanically supported by a diffuser plate 34. The diffuser plate 34 both provides mechanical support for the substrate 33 during deposition of the functional catalytic layer 32 and also creates sufficient aerodynamic resistance for laminarization and homogenization of the carrier gas stream 31 . A laminar and uniformly distributed carrier gas flow over the entire surface of the substrate 33 ensures uniform deposition of the functional catalytic layer 32. The diffuser plate 34 is typically composed of a solid porous inert material of the type of sintered metal (e.g., brass) microspheres.

The outlet manifold _4 connected to the outlet of the deposition chamber 3 conducts the carrier gas from the device into the atmosphere .

Pressure Control in the Deposition Chamber During the deposition of the nanoparticles in the deposition chamber _3, the pressure gradually increases. The layer of catalytic nanoparticles 16 deposited on the substrate increases its aerodynamic resistance to the carrier gas flow with its increasing thickness, i.e., pressure loss increases as the carrier gas passes through the functional catalytic layer 32. The increasing pressure in the deposition chamber _3 does not necessarily affect the mechanical properties of the deposited layer, however the increasing pressure is also reflected in the discharge chamber 15. This can change the parameters of the spark discharge 13 , as the breakdown voltage of the carrier gas increases at higher pressures, leading to an increase in the energy of the spark discharges 13 and a higher evaporation intensity of the metal electrodes.

In order to ensure constant parameters of the spark discharges 13 throughout the entire period of the deposition of the catalytic layers 32 , and thus ensure constant parameters of the generated nanomaterials, it is appropriate to actively control the pressure in the device so that it is maintained at a constant value throughout the entire period of the deposition of the functional catalytic layer 32. For this purpose, in Fig. 2, the outlet manifold _4 for conducting the carrier gas from the deposition chamber 3 is equipped with the inlet pressure controller 43 for the pressure control. The inlet pressure controller 43 allows the pressure to be increased above the value of atmospheric pressure throughout the entire deposition device. Advantageously, the inlet pressure controller 43 can be connected via the data link 42 to the pressure sensor 41 located upstream of the carrier gas inlet to the deposition chamber _3. By actively controlling the inlet pressure controller 43 based on the current pressure information from the pressure sensor 41 , a constant pressure is achieved throughout the entire period of the deposition of the catalytic layer 32. Application of Hybrid Layers

In the block diagram in fig. 3, there are two manifold branches at the inlet to the deposition chamber _3, each with its own generator of the spark discharge 13. The first manifold 1. described in detail above is supplemented by an analogous third manifold 5 with its own second discharge chamber 55.. Thus, the first manifold 1_ and the third manifold 5 serve to feed two different kinds of nanoparticles into the deposition chamber 3., In this arrangement, the proportion of each kind of nanoparticles in the resulting hybrid functional layer is controlled by setting the relative power of the individual generators of the spark discharge 13 and the carrier gas flows through these generators.

Application of Functionally Graded Layers

For the preparation of functionally graded layers, where the aim is to create a concentration gradient of the individual nanoparticles in the cross-section of the functional catalytic layer 32., the relative power of the individual generators of the spark discharge 13 is controlled over time, e.g. so as to achieve an increased concentration of one kind of nanoparticles at the beginning of deposition, i.e., in the lower half of the functional catalytic layer 32 , and an increased concentration of another type of nanoparticles at the end of deposition, i.e., in the upper half of the functional catalytic layer 32.

Clarification of Figures in the Drawings

In the three figures attached, an arrangement of a device for applying the functional catalytic layers 32 composed of the catalytic nanoparticles 16 formed by the spark evaporation method and from the polymer electrolyte 23 is indicated. The first two examples in fig. 1 and fig. 2 are topologically identical, with fig. 1 showing a block diagram of the technical solution with the main units labeled and fig. 2 showing all the details. Fig. 3 shows a block diagram of an embodiment with two independent manifolds for feeding two different types of nanoparticles into the deposition chamber 3.

Examples of Embodiments of the Technical Solution

Example 1

Catalytic layer containing platinum nanoparticles and a binder of polymer electrolyte

The active surface of the membrane electrode assembly (MEA) of a low-temperature hydrogen fuel cell of the PEM type, i.e., with a polymer electrolyte membrane, ranges in size from units of cm ² for laboratory test samples to hundreds of cm ² for use in high- performance automotive fuel cells. The shape of the active surface is usually square or even rectangular and is determined by the design of the fuel cell of which the MEA is a part.

For a typical laboratory MEA sample with a 5 cm ² square shaped active surface, we apply the catalytic layer 32 containing 2 mg of platinum nanomaterial so as to achieve a platinum loading of 0.4 mg/cm ² of active surface. This platinum loading value is currently the standard for the production of MEA for use in a low-temperature hydrogen fuel cell with a polymer electrolyte membrane.

The substrate 33 in the deposition chamber 3_ consists of carbon paper (e.g., Sigracet GDL 28BC) with a 5 cm ² square shaped surface. To initiate the deposition of the catalytic layer 32 , the flow of the carrier gas (nitrogen, argon, forming gas, etc. ) is set to the value of 1 slpm (liters per minute) by the first flow controller 11 , and at the same time the generation of the platinum nanoparticles 16 is started by the spark discharge 13 in the discharge chamber 15. The repetition rate of the spark discharges 13 is 2 kHz and the energy of the individual spark discharges 13 is 20 mJ. Under these spark synthesis parameters, 2 mg of platinum nanomaterial is produced in 15 minutes. At the same time as the platinum nanoparticle generation is initiated, the carrier gas flow is set by the second flow controller 21 to the same or a different flow value than the first flow controller 11 (e.g., 0.1 slpm) . In the second manifold 2, the carrier gas then passes through a nebuliser, for example the ultrasonic nebuliser 22 , and entrains droplets of the electrolyte aerosol 24 (Nafion solution, e.g., lonPower Liquion) .

Prior to entering the deposition chamber 3, the carrier gas streams from the manifolds 1 and 2 are mixed and thus the platinum nanoparticles and the droplets of the electrolyte aerosol 24 are mixed. These two types of particles suspended in the carrier gas are then simultaneously deposited into the catalytic layer 32 being formed. The catalytic layer 32 then has both a homogeneous composition throughout its thickness due to the fact that time- constant parameters of the carrier gas flows through both manifolds 1 and 2, and constant parameters for the generation of platinum nanoparticles, and constant parameters for the operation of the ultrasonic nebuliser 22 were set. Second, the catalytic layer 32 has a homogeneous composition over its entire active surface, since it was supported by the diffuser plate 34 during the deposition, ensuring a uniform carrier gas flow over the entire active surface.

Example 2

Catalytic layer containing platinum nanoparticles with subsequent deposition of a binder of polymer electrolyte

Another option for producing a catalytic layer for PEM fuel cells, following example 1, is to temporally separate the processes of the deposition of the platinum nanoparticles and the deposition of the droplets of the electrolyte aerosol 24. In this case, the catalytic layer 32 is deposited by first applying the desired amount of platinum nanomaterial in a first step. Thus, the generator of the spark discharge 13 is started and a non-zero carrier gas flow is set in the first manifold 1 by the first flow controller 11 . The ultrasonic nebuliser 22 in the second manifold is turned off, and likewise the second flow controller 21 shuts off the flow of carrier gas in the second manifold 2. After the deposition of the platinum nanoparticles is completed, the ultrasonic nebuliser 22 and the carrier gas flow in the second manifold 2. are turned on in a second step. In this step, only droplets of the electrolyte aerosol 24 are deposited. The resulting catalytic layer 32 thus obtains a non- homogeneous structure in a cross-section of its thickness, such that the bottom part is dominated by platinum nanoparticles in a higher concentration than in example 1 and the upper part is dominated by the polymer electrolyte 23. The advantage of this deposition method is that the polymer electrolyte 23 forms a solid outer layer of the catalytic layer 32 and fixes the platinum nanoparticles, the layer thereby obtaining more resistance to abrasion during further handling, and in addition obtaining better adhesion to the polymer membrane during MEA pressing.

In a similar manner, after simply reversing the temporal sequence of the two deposition steps described above, a spatially reversed structure of the catalytic layer 32 can be achieved, with the polymer electrolyte 23 dominating in the bottom part and platinum nanoparticles dominating in the upper part.

Example 3

Deposition with constant pressure in the deposition chamber

During the deposition of the catalytic layer 32 with the parameters described in example 1, the pressure in the deposition chamber 3 increases by 15 kPa within 15 minutes of deposition. The pressure increase is caused by the increasing aerodynamic resistance of the deposited catalytic layer 32, which with its increasing thickness exhibits a higher aerodynamic resistance to the passage of the carrier gas. In other deposition procedures, the pressure increase may be even higher, e.g., due to the use of the substrate 33 with a lower porosity and therefore higher aerodynamic resistance, or when higher carrier gas flows are set, etc.

In order to balance the increasing pressure loss on the catalytic layer 32 , an inlet pressure controller 43 is installed on the outlet manifold 4 which allows the pressure in the bottom half of the deposition chamber _3 to be released during deposition such that the pressure in the upper half of the deposition chamber 32 , and thus in the entire system of the inlet manifolds 1 and 2, remains constant .

At the beginning of the deposition process, the inlet pressure controller 43 will be set to a value 15 kPa higher than the atmospheric pressure. During deposition according to the parameters in example 1, the pressure loss on the deposited catalytic layer 32 increases at a rate of 1 kPa per minute. It is necessary to reduce the pressure value on the input pressure controller 43 by the same value. The process of controlling the inlet pressure controller 43 may preferably be automated on the basis of data from a pressure sensor 41 located, e.g., in a manifold before the carrier gas enters to the deposition chamber 3, and connected via the data link 42 to the control of the inlet pressure controller 43.

Example 4

Deposition with controlled pressure increase in the deposition chamber

Following the example 3 of a deposition with constant pressure, it may be preferable for a different type of catalytic layer 32 to increase the pressure in the deposition chamber 3, even beyond the value resulting from the natural increase in pressure in the deposition chamber 3 due to the thickness growth of the deposited catalytic layer 32. At higher pressure, the energy of the spark discharges 13 in the generator of the spark discharge 13 increases, resulting in an increase in the size of the primary nanoparticles or an increase in the degree of agglomeration of the nanoparticles. The effects of the high pressure on the synthesis process of the catalytic nanoparticles 16 will only become apparent at pressure values in units of atmospheres, e.g. , at a pressure of 1 atm, catalytic nanoparticles 16 with a diameter of 5 nm will be generated, and at a pressure of 4 atm, the catalytic nanoparticles 16 will have a diameter of 10 nm. The inlet pressure controller 43 will therefore be used in this example to continuously linearly increase the pressure during the deposition from a value of 1 atm at the start of deposition to a value of, e.g., 4 atm after 15 minutes of the deposition process. In the cross-section of the resulting catalytic layer 32 , the size of the contained catalytic nanoparticles 16 will steadily increase, and the degree of agglomeration of the catalytic nanoparticles 16 will also increase.

Example 5

Hybrid catalytic layer composed of platinum nanoparticles and metal oxi de

An increase in the performance of the hydrogen fuel cell catalytic layer can be achieved by using another type of nanomaterial deposited at the same time as the platinum catalyst. The addition of another nanomaterial, typically a metal oxide (TiO ₂ , ZrO ₂ , etc. ) or even, e.g., a nano-mixture of nitrides and metal oxides such as, e.g., titanium, contributes to the proton conductivity of the catalytic layer .

This method of deposition is an extension of the procedure of example 1, where another manifold, i.e. , the third manifold 5. with its own second discharge chamber 55, is installed in parallel to the inlet manifolds 1 and 2. This second discharge chamber 55 is operated such that the electrode material is composed of titanium and the carrier gas contains a certain proportion of oxygen (air, synthetic air, pure oxygen, etc. ) . The generated nanoparticles are then composed of titanium dioxide, or another non-stoichiometric titanium oxide, or a mixture of titanium oxides and nitrides. The carrier gas with titanium oxide nanoparticles is mixed with the carrier gas from the first manifold 1 containing the platinum catalytic nanoparticles 16 from the first discharge chamber 15, and also with the carrier gas from the second manifold 2 containing droplets of the electrolyte aerosol 24 before entering the deposition chamber 3_.

The resulting catalytic layer 32 is then composed of a homogeneous mixture of platinum nanoparticles, titanium oxide nanoparticles, and polymer electrolyte 23. The ratio of the concentrations of platinum nanoparticles and titanium oxide nanoparticles is controlled by setting the relative powers (i.e., repetition rates of the spark discharges 13 ) of the two generators of the spark discharge 13 used.

Analogous to the addition of the third manifold 5, an additional parallel inlet manifold may be attached to the deposition system to feed additional types of nanoparticles into the deposition cell to form catalytic layers 32 containing three or more kinds of nanoparticles .

Example 6

Functionally graded catalytic layer

In addition to the homogeneous catalytic layer 32 formed in example 5, another option for depositing multiple nanomaterials is to deposit the catalytic layer 32 with a variable ratio of individual components varying across the cross-section of the catalytic layer 32. For this purpose, the power of the individual generators of the spark discharges 13 must be controlled over time by varying the frequency of the spark discharges 13.

For a PEM fuel cell, the preferred solution is a catalytic layer 32 with an increasing ratio of metal oxide (e.g. , titanium oxide from the previous example) towards the upper boundary of the catalytic layer 32. Thus, the density of the metal oxide will increase in the catalytic layer 32 towards its connection with the polymer membrane. As a result of the increasing metal oxide density, the local proton conductivity of the catalytic layer 32 towards the connection with the polymer membrane will also increase. The linear increase in metal oxide concentration is achieved by controlling the frequency of the generator of the spark discharge 13 in the second discharge chamber 55, where the frequency is linearly increased from an initial (e.g. , zero) value to a target frequency (e.g. , 2 kHz) over 15 minutes of the deposition process.

The generator of the spark discharge 13 in the first discharge chamber 15 for generating platinum nanoparticles may be operated in a constant- frequency mode in this example. Alternatively, it may be operated in a linear (or non-linear) frequency decrease mode, where the concentration of the platinum nanoparticles in the catalytic layer 32 will decrease towards its upper edge and thus towards the connection with the polymer membrane.

Example 7

Catalytic layer for a PEM electrolyzer

Analogous to the use of catalytic layers 32 deposited from the gaseous phase for the case of a hydrogen fuel cell of the PEM type, i.e., with a polymer electrolyte membrane, described in example 1, catalytic layers 32 for PEM-type electrolyzers may be further produced. These devices are similar in design to fuel cells but differ in the materials used for their individual components. The substrate 33 for the catalytic layer 32 on the anode of the electrolyzer is not carbon paper, but titanium fabric. This is because carbon structures degrade under electrical potentials during the operation of the electrolyzer and need to be replaced by more resistant materials, e.g., titanium. In addition, in terms of catalyst composition, it is preferable to use an iridium catalyst, or iridium oxide, or an iridium-platinum alloy for the anode of the electrolyzer . Thus, the procedure of producing the catalytic layer 32 for the PEM electrolyzer consists in the use of a substrate 33 in the form of a titanium fabric, e.g., again having a square shaped surface of 5 cm ² . To initiate the deposition of the catalytic layer 32 , the flow of the carrier gas (forming gas for the case of deposition of pure iridium nanoparticles, or air, or synthetic air, or oxygen for the case of deposition of iridium oxide nanoparticles) is set to the value of example 1, the other setting parameters of the generator of the spark discharge 13 also being maintained. Only the deposition time of the nanoparticles will be approximately 2.5 times longer due to the fact that the target iridium loading for the purpose of electrolysis is around 1 mg/cm ² .

Industrial Applicability

A device for applying functional catalytic layers 32 of nanomaterials can be used to produce catalytic layers 32 in the electrodes of a hydrogen fuel cell without the need for using catalytic ink. The deposition of the catalytic nanoparticles 16 proceeds directly from the gaseous phase and excels in the purity of the applied nanomaterials and the homogeneity of the applied layer. The catalytic layer 32 production process is virtually waste-free and allows a high degree of automation for the series production of hydrogen fuel cells .

List of Reference Numerals

1 first manifold

11 first flow controller

12 cathode

13 spark discharge

14 anode

15 discharge chamber

16 catalytic nanoparticles

2 second manifold

21 second flow controller

22 ultrasonic nebuliser

23 electrolyte

24 electrolyte aerosol

25 ultrasonic source

3 deposition chamber

31 carrier gas stream

32 catalytic layer

33 substrate

34 diffuser plate

4 outlet manifold

41 pressure sensor

42 data link

43 inlet pressure controller

5 third manifold

55 second discharge chamber