Method for precision application of catalytic inks and device for carrying out this method

Abstract

Method for precision application of catalytic inks, where continuous dispenser (2) and grooved film applicator (3) are placed above plane of deposition substrate (5), grooved film applicator (3) is pressed against deposition substrate (5), continuous dispenser (2) and deposition substrate (5) move relative to each other in such a way that deposition substrate (5) runs under continuous dispenser (2), catalytic ink (1) flows from continuous dispenser (2) onto surface of deposition substrate (5) before grooved film applicator (3), and grooved film applicator (3) adjusts thickness of layer of catalytic ink (1) on surface of deposition substrate (5) forming homogeneously distributed layer of catalytic ink (1). Device comprises continuous dispenser (2) of catalytic ink (1), grooved film applicator (3), and pressure element (7) to press grooved film applicator (3) against deposition substrate (5). Continuous dispenser (2) is placed above plane of deposition substrate (5) and connected to catalytic ink (1) tank.

Description

Method for precision application of catalytic inks and device for carrying out this method

[0001] The invention relates to the field of catalysts production, concerning catalysts containing noble metals of the platinum group deposited on a membrane, primarily for use in fuel cells or in devices for the production of hydrogen using electrolytic decomposition of water, and further within the field of coating liquid and granular substances on surfaces, given condition that the substance flows through an object regulating its coating, while the thickness of the surface is regulated mechanically with grooves or ribbing.

[0002] Ion exchange membranes are one of the key components of fuel cells and electrolytic water decomposition devices. They are made of polymeric materials carrying ionizable groups and their purpose is to transfer protons (Proton Exchange Membrane, PEM) or specific anions (Anion Exchange Membrane, AEM) between the anode and cathode compartments, while at the same time electrically isolating the two compartments from each other, depending on the type of membrane. The membranes also act as carriers for layers of catalytically active noble metals from the platinum group or their oxides. However, current processes for producing catalytically active membranes are complicated and instrumentation intensive. Examples include a physical method known from WO2020064034A1, which involves plasma etching followed by plasma sputtering of the noble metal layer, or a chemical method known from Choi et al., Energy Environ. Sci. 2020, 13, 4921-4929, which involves a synthesis of carbon nanofibers coated with a noble metal layer.

[0003] An alternative method of preparing the catalytic layer, which is suitable for large-scale industrial production, is to deposit it on a PEM or AEM in the form of a catalytic ink, i.e., a suspension of noble metal nanoparticles dispersed in a viscous liquid matrix. Methods of deposition of catalytic ink by inkjet printing (Willert et al., Int. J. Hydrogen. Energ. 2022, 47, 20973-20986), intaglio (JP2009123791A), or slot-die coating (Stähler et al., Int. J. Hydrogen. Energ. 2019, 44, 7053-7058) are known from the prior art. These methods face a significant technical drawback of high requirements for controlling ink viscosity and layer thickness when using suspensions with heavy platinum-metal nanoparticles, which tend to sediment. These reasons preclude the scalability of such printing as it is problematic to maintain a uniform catalytic layer thickness. This creates zones with abundant thickness, leading to waste of precious metals, and with insufficient thickness, which negatively affects the efficiency of the resulting device.

[0004] Goal of the present invention is to introduce a method for depositing catalytic inks, in particular on polymer membranes for use within electrolyzers and fuel cells, without high demands on control of printing parameters while maintaining production scalability and uniformity of the layer.

[0005] The present invention is a method for applying catalytic ink, where catalytic ink is dosed onto a deposition substrate while the thickness of the layer is adjusted by a grooved film applicator, and a device for carrying out this method comprising a print head combining a continuous dispenser of catalytic ink and a grooved film applicator.

[0006] The specific combination of a continuous dispenser of catalytic ink with a grooved film applicator significantly reduces the requirements for complicated adjustment of printing parameters, as the purpose of the continuous dispenser of catalytic ink is only a precise dosing of catalytic ink according to the set value of the catalytic ink flow rate and its pre-distribution, not its homogeneous distribution. Solutions known from the prior art aim to achieve homogeneous distribution by demanding settings of dosing parameters; however, this method is, as reasoned above, unreliable. Homogeneous distribution of the catalytic ink according to the present invention is reliably ensured by a grooved film applicator.

[0007] The method according to the present invention comprises the following steps:1. The continuous dispenser of catalytic ink and the grooved film applicator are placed above the plane of the deposition substrate.2. The grooved film applicator is pressed against the deposition substrate.3. The continuous dispenser of catalytic ink and the deposition substrate move relative to each other in such a way that the deposition substrate runs under the continuous dispenser of catalytic ink.4. Catalytic ink flows from the continuous dispenser of catalytic ink onto the surface of the deposition substrate before the grooved film applicator.5. The grooved film applicator adjusts the thickness of the catalytic ink layer on the surface of the deposition substrate forming a homogeneously distributed layer of catalytic ink.

[0008] According to the present invention, the device comprises a continuous dispenser of catalytic ink and a grooved film applicator. Beneficially, these components are located in a joint print head allowing easy adjustment of printing parameters, and the grooved film applicator is equipped with springs ensuring constant pressure onto the surface of the deposition substrate along the entire length of the grooved film applicator. The grooved film applicator is designed as a rod with wound wire, a rod with engraved spiral or ring grooves, or a flexible bladder of a cylindrical shape with an accordion-like structure allowing a continuous change of groove width.

[0009] Beneficially, the method according to the present invention includes a step where the amount of catalytic ink in the space before the grooved film applicator is monitored by a laser, in a manner that the device is equipped as well with a laser gate located between the continuous dispenser of catalytic ink and the grooved film applicator. The laser gate consists of a laser, a laser-beam-illumination sensor, and a computing unit for evaluating signals from the sensor and adjusting the value of the catalytic ink flow through the continuous dispenser of catalytic ink. If a lack or an excess of the amount of catalytic ink in the space is detected by a change in the intensity of illumination of the sensor by the laser beam, the flow of the catalytic ink through the continuous dispenser of catalytic ink is adjusted accordingly.

[0010] Furthermore, the device according to the invention beneficially includes a variant of a grooved film applicator, where its part is longitudinally coated along its entire length with a flexible layer, for example made of silicone rubber or PTFE, which fills the grooves. This variant of the grooved film applicator has two functions. If its grooved part is in contact with the deposition substrate, the grooved film applicator spreads the catalytic ink as described above. By turning the grooved film applicator along its longitudinal axis so that the flexible layer is in contact with the deposition substrate, the grooved film applicator acts as a cap or a cleaning doctor blade, resulting in no printing. The build-up of wiped ink detected by the laser gate then stops the ink deposition by the continuous dispenser of catalytic ink until the grooved film applicator is rotated back to a position where its grooves are in contact with the deposition substrate. This variant of the present invention allows the printing of rectangular patterns of ink, instead of a continuous belt of ink. Such rectangular patches of catalytic ink are required for use in fuel cells or water electrolyzers and this variant of the present invention further simplifies their entire production process.Fig.1

[0011] depicts a diagram of the device in a longitudinal cross-section perspective according to Example 1.Fig.2

[0012] depicts a diagram of a section of the device with the grooved film applicator according to Example 1.Fig.3

[0013] depicts polarization curves of a fuel cell according to Example 3 using ionomer / carbon ratios of 3 / 10 (squares), 45 / 100 (circles), 6 / 10 (triangles), and 9 / 10 (rhombuses), with current density in A / cm2 plotted on the x-axis and voltage in V plotted on the y-axis.Fig.4

[0014] depicts power curves of a fuel cell according to Example 3 using ionomer / carbon ratios of 3 / 10 (squares), 45 / 100 (circles), 6 / 10 (triangles), and 9 / 10 (rhombuses), with current density in A / cm2 plotted on the x-axis and power density in W / cm2 plotted on the y-axis.Example 1

[0015] Example 1 describes a device for precision application of catalytic inks.

[0016] The device comprises a print head containing a continuous dispenser2of catalytic ink1in the form of a slot-die, a grooved film applicator3in the form of a rod with a wound wire, and a pressure element7in the form of a pressure spring. The continuous dispenser2with a 50 mm long and 0.5 mm wide dispensing slot is located at a distance of 0.2 mm above the plane of the deposition substrate5, which consist of fluorinated polymeric sulfonic acids and has a thickness of 50.8 um, and a tank of catalytic ink1is connected to the continuous dispenser2via a linear dispenser4. The grooved film applicator3is equipped with a 0.7 mm thick wound wire, which is covered by a smooth layer of silicone rubber on the longitudinal half of the grooved film applicator3. The pressure element7applies a constant pressure of the grooved film applicator3onto the surface of the deposition substrate5. The grooved film applicator3is able to rotate along its longitudinal axis. Further, the device comprises a laser gate located between the continuous dispenser2and the grooved film applicator3, with the laser gate consisting of a laser9located on one side of the deposition substrate5, a sensor10illuminated by a laser beam and located on the opposite side of the deposition substrate5, and a computing unit. The laser gate is positioned so that the laser beam passes perpendicularly to the direction of movement of the deposition substrate5and covers the space between the deposition substrate5and the tangent of the highest point of the grooved film applicator3.Example 2

[0017] Example 2 describes a method for precision application of a catalytic ink using the device from Example 1.

[0018] The continuous dispenser2and the grooved film applicator3are placed above the plane of the deposition substrate5. The grooved film applicator3is pressed against the deposition substrate5. The continuous dispenser2and the deposition substrate5move relative to each other in such a way that the deposition substrate5runs under the continuous dispenser2at a speed of 5 cm / s. Catalytic ink1flows from the continuous dispenser2onto the surface of the deposition substrate5before the grooved film applicator3with an average flow rate of 0.25 mL / s. The grooved film applicator3, with its half containing the exposed wire facing the substrate, adjusts the thickness of the layer of catalytic ink1on the surface of the deposition substrate5forming a homogeneously distributed layer of catalytic ink1. The grooved film applicator3rotates along its longitudinal axis at regular intervals, whereby when its longitudinal half covered with silicone rubber faces the deposition substrate5, the grooved film applicator3removes the catalytic ink1from the deposition substrate5and the catalytic ink1accumulates before the grooved film applicator3. Depending on a change in an intensity of illumination of the sensor10by the laser beam, the computing unit adjusts the rate of flow of the catalytic ink1through the continuous dispenser2so that when the illumination intensity decreases, the flow rate decreases, and when the illumination intensity increases, the flow rate increases. The deposition substrate5with a homogeneously distributed layer of catalytic ink1dries producing a uniform layer with a thickness of 50 um.Example 3

[0019] Example 3 describes the experimental verification of a function of a membrane carrying a catalyst prepared according to the method of Example 2 using the device of Example 1.

[0020] To print catalytic layers using the device according to the present invention, a catalytic ink was prepared from Pt / C nano-powder containing 40% platinum dispersed in a solvent consisting of an ionomer and water, using four different ionomer / carbon ratios, namely 3 / 10, 45 / 100, 6 / 10, and 9 / 10. Activity of the catalytic layers was investigated at a cathode of a hydrogen–air fuel cell at a pressure of 1 bar.

[0021] Method for precision application of catalytic inks and device for carrying out this method are industrially applicable in particular in the production of components for fuel cells and electrolyzers.

Claims

Method for precision application of catalytic inks,characterized in thata continuous dispenser (2) and a grooved film applicator (3) are placed above a plane of a deposition substrate (5), the grooved film applicator (3) is pressed against the deposition substrate (5), the continuous dispenser (2) and the deposition substrate (5) move relative to each other in such a way that the deposition substrate (5) runs under the continuous dispenser (2), catalytic ink (1) flows from the continuous dispenser (2) onto a surface of the deposition substrate (5) before the grooved film applicator (3), and the grooved film applicator (3) adjusts a thickness of the layer of catalytic ink (1) on the surface of the deposition substrate (5) forming a homogeneously distributed layer of catalytic ink (1).Method according to claim 1,characterized in thatthe amount of catalytic ink (1) in the space before the grooved film applicator (3) is monitored by a laser beam illuminating a sensor (10), so that when a lack or an excess of the amount of catalytic ink (1) in this space is detected by a change in the intensity of illumination of the sensor (10) by the laser beam, the flow of the catalytic ink (1) through the continuous dispenser (2) of catalytic ink is adjusted accordingly.Method according to claim 1,characterized in thatthe grooved film applicator (3) rotates along its longitudinal axis at regular intervals and when its smooth longitudinal half faces the deposition substrate (5), the grooved film applicator (3) removes the catalytic ink (1) from the deposition substrate (5).Device for precision application of catalytic inks comprising a continuous dispenser (2) of catalytic ink (1) placed above a plane of a deposition substrate (5) and connected to a tank of catalytic ink (1),characterized in thatit further comprises a grooved film applicator (3) and a pressure element (7) to press the grooved film applicator (3) against the deposition substrate (5).Device according to claim 4,characterized in thatthe continuous dispenser (2) of catalytic ink (1) is a slot-die.Device according to claim 4,characterized in thatthe grooved film applicator (3) is a rod with a wound wire.Device according to claim 6,characterized in thatthe grooved film applicator (3) is able to rotate along its longitudinal axis, it is equipped with a grooved and a smooth longitudinal half, and on the smooth longitudinal half, the wire is covered by a smooth layer of silicone rubber.Device according to claim 4,characterized in thatthe pressure element (7) is a pressure spring.Device according to claim 4,characterized in thatit further comprises a laser gate located between the continuous dispenser (2) and the grooved film applicator (3), with the laser gate consisting of a laser (9) located on one side of the deposition substrate (5), a sensor (10) illuminated by a laser beam and located on the opposite side of the deposition substrate (5), and a computing unit, and the laser gate is positioned so that the laser beam passes perpendicularly to the direction of movement of the deposition substrate (5) and covers the space between the deposition substrate (5) and the tangent of the highest point of the grooved film applicator (3).

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