Measuring device, measuring table comprising a measuring device, and method for measuring the thickness of a flat component, in particular a gas diffusion layer

Abstract

The invention relates to a method for determining the thickness of a gas diffusion layer (11) for an electrochemical cell (31), comprising a lower pressure plate (3), an upper pressure plate (5), and a test weight (9) which is guided via a vertical guide (7) such that a specified testing force can be applied to a flat component (10, 11) to be tested via the gravitational force of the test weight (9) during a measuring process so that a defined surface pressure is produced. A distance sensor (13) is additionally provided, by means of which the span of the flat component (10, 11) between the upper pressure plate (5) and the lower pressure plate (3) under the effect of the specified testing force (F) can be determined as a thickness measurement value (H). The invention additionally relates to a measuring table (27) comprising a measuring device (1) and to a method for measuring the thickness of a flat component (10, 11), in particular a gas diffusion layer (11) for an electrochemical cell (31).

Description

[0001] Description

[0002] Measuring device, measuring table with a measuring device and method for measuring the thickness of a flat component, in particular a gas diffusion layer

[0003] The invention relates to a measuring device for measuring the thickness of a gas diffusion layer of an electrochemical cell, in particular a PEM electrolysis cell. The invention further relates to a measuring table comprising a measuring device and a method for measuring the thickness of a gas diffusion layer.

[0004] Electrochemical cells are generally known and are divided into galvanic cells and electrolysis cells. An electrolysis cell is a device in which an electric current causes a chemical reaction, whereby at least part of the electrical energy is converted into chemical energy. A galvanic cell is a device—complementary to an electrolysis cell—for the spontaneous conversion of chemical energy into electrical energy. A well-known example of such a galvanic cell is a fuel cell.

[0005] The splitting of water by electrical current to produce hydrogen and oxygen gas using an electrolysis cell is well known. A distinction is mainly made between two technical systems: alkaline electrolysis and PEM (proton exchange membrane) electrolysis.

[0006] The core of a technical electrolysis system is the electrolysis cell, comprising two electrodes and an electrolyte. In a PEM electrolysis cell, the electrolyte consists of a proton-conducting membrane with electrodes on both sides. The unit consisting of membrane and electrodes is called an MEA (membrane-electrode assembly). In the assembled state of an electrolysis stack comprising several electrolysis cells, the electrodes are contacted via a gas diffusion layer of so-called bipolar plates, with the bipolar plates separating the individual electrolysis cells in the stack. The Cd side of the electrolysis cell corresponds to the positive pole and the H2 side to the negative pole, separated by the membrane-electrode assembly in between.

[0007] The PEM electrolysis cell is fed on the Cd side with fully demineralized water, which is converted into oxygen gas and protons (H + ) is broken down. The protons migrate through the electrolyte membrane and recombine at the cathode (H2 side) to form hydrogen gas. The gas diffusion layer adjacent to the electrodes ensures not only electrode contact but also optimal water distribution (and thus wetting of the membrane) as well as the removal of product gases. Therefore, an electrically conductive, porous element with good, permanent contact with the electrode is required as the gas diffusion layer. As an additional requirement, any construction tolerances that may arise in the electrolyzer must be compensated to enable uniform contact with the MEA in every tolerance case.

[0008] Sintered metal discs have occasionally been used as a gas diffusion layer in known electrolysis cells. While these meet the requirements for electrical conductivity and porosity, additional tolerance compensation of the electrolysis cell components on both sides of the gas diffusion layer is not possible. Furthermore, the manufacturing costs for such discs are comparatively high, and there are size restrictions due to the pressures required to manufacture such discs. Furthermore, large components are subject to distortion problems that are difficult to control.

[0009] The use of gas diffusion electrodes with resilient elements to establish electrical contact in alkaline electrolysers is described, for example, in WO 2007 / 080193 A2 and EP 2436804 A1.

[0010] EP 1378589 B1 discloses a spring plate in which the individual spring elements are bent alternately upwards and downwards. The spring plate is installed only on the cathode side of an ion-exchange electrolyzer, so that the spring plate directly contacts the cathodes.

[0011] US 2003 / 188966 A1 describes another spring component for an electrolysis cell, which is arranged between a partition wall and a cathode. The spring component comprises a plurality of leaf spring elements that bear against the cathode for uniform adjustment. Further, differently constructed gas diffusion electrodes are described in WO 2002035620 A2, DE 10027339 A1, and DE 102004023161 A1.

[0012] EP 2 957 659 B1 discloses a gas diffusion layer for application between a bipolar plate and an electrode of an electrochemical cell. The gas diffusion layer comprises at least two layers stacked on top of one another, one of the layers being designed as a spring component with a progressive spring characteristic. Progressive spring behavior ensures that the contact pressure is sufficient in all tolerance positions of the adjacent components. Progressive spring behavior is implemented in a gas diffusion layer by the geometric design of the spring component. This makes it possible to compensate for component tolerances that arise in an electrochemical cell, in particular in an electrolysis cell or galvanic cell, in particular in the area of ​​the bipolar plates, at least within certain limits.

[0013] WO 2021 / 018459 A1 describes an electrolysis cell with a cell frame and a method for producing an electrolysis cell. The cell frame has a stepped inner profile. The inner profile comprises at least one support surface for receiving a planar component in the cell frame. The support surface has a recess for a seal. Due to the stepped inner profile, the first gas diffusion layer projects beyond the boundaries of the second gas diffusion layer. The gap dimensions between the cell frame and the membranes or gas diffusion layers can therefore advantageously be larger. This advantageously simplifies and shortens the assembly process. Furthermore, the outer contours of the membranes and / or gas diffusion layers can advantageously be selected largely freely.

[0014] A typical PEM electrolysis cell structure comprises a first gas diffusion layer and a second gas diffusion layer. The proton exchange membrane is positioned between the gas diffusion layers. All layers are arranged in a cell frame. The gas diffusion layers must be arranged with high precision to produce a reliably functioning electrolysis cell and, subsequently, a multitude of electrolysis cells stacked together. This makes the manufacture of the components and assembly very complex.

[0015] In particular, when a large number of electrolysis cells are stacked one after the other to form a stack, the manufacturing-related deviations due to variations in the thickness of the gas diffusion layers of electrolysis cells can add up to a thickness tolerance that is still permissible in the individual case and can lead to inadmissible mechanical stresses when bracing a stack with a large number of electrolysis cells.

[0016] There is therefore a growing need to improve the measurement accuracy and reproducibility of thickness measurements in the manufacture of gas diffusion layers for electrolysis cells with a view to achieving industrial series production. Quality assurance during production at the electrolysis cell level is becoming increasingly important in order to provide marketable electrolyzers in large quantities and with high electrolysis output. Against this background, the object of the invention is to provide a measuring device which is improved in terms of measurement accuracy and reproducibility. Furthermore, the object of the invention is to provide a method for measuring the thicknesses of stacked gas diffusion layers which is characterized by high precision and reproducibility.

[0017] The object is achieved according to the invention by a measuring device for measuring the thickness of a gas diffusion layer for an electrochemical cell, comprising a lower pressure plate and an upper pressure plate and a test weight guided via a vertical guide in such a way that during a measuring process a predeterminable test force can be applied to a flat component to be tested via the weight of the test weight, so that a defined surface pressure is brought about, and further comprising a distance sensor by means of which the distance of the flat component between the upper pressure plate and the lower pressure plate under the predefined test force can be determined as a thickness measurement value.

[0018] The invention is based on the knowledge that gas diffusion layers in electrolysis cells have particularly high demands on their height and thickness profile. Dimensional accuracy and dimensional stability are becoming increasingly important, particularly for large-format, flat gas diffusion layers, such as those currently being developed and designed for use in high-performance electrolyzers. When installed, gas diffusion layers are pressed together and, under pressure, must precisely fill a predetermined installation space in the electrolysis cell. Within certain limits, the gas diffusion layers generally have spring-like force / displacement characteristics. Since in the application a large number of electrolysis cells are connected one after the other and stacked to form a stack, the thickness tolerances add up cumulatively.The invention has recognized that conventional measuring devices and available universal testing machines are not sufficient to measure the thicknesses of the extended and flat gas diffusion layers as accurately as possible with a required measurement uncertainty of < 0.01 mm. In view of the increased requirements for measurement accuracy, dimensional stability and reproducibility, there is therefore a high demand for a measuring device and a measuring method in order to enable application and the simplest possible integration into an industrial production process for electrolysis cells while still maintaining a reasonable outlay for the necessary quality assurance.

[0019] To date, conventional universal testing machines have been used to determine thickness. These are equipped with compression plates and used in "compression test" mode, where the test force is usually regulated via electric drives and a drive spindle. The problem is that these machines deform under applied compressive force, which distorts the measurement results, sometimes 1-2 orders of magnitude above or outside the required measurement accuracy. Very complex compensation of the measured values ​​using compensation curves recorded once is common, but must be checked and corrected regularly. Any changes render the measurement result immediately unusable. If the machine exceeds the force range, the affected component may be irreparably damaged, for example pressed too thin beyond the minimum thickness.In addition to the time required for constant inspection—after each component—and regular corrections, typically between 2 and 10 times per shift, production is therefore heavily dependent on external influences such as fluctuations in humidity, temperature, etc. This measuring principle and the associated disadvantages are the same for all universal testing machines considered. Furthermore, in the standard setup, part of the test force is used to align curved, flat components flat on the table, which is very disadvantageous.

[0020] The measuring device of the invention overcomes these disadvantages, whereby high accuracy requirements of the measuring device for quality assurance on an industrial scale are achieved. By means of the measuring device, for example, the thickness of a spring-elastic gas diffusion layer formed from expanded metal - as a flat component - can be determined under a well-defined test force. The measuring device designed in this way can advantageously be operated on an industrial scale in a production hall in a 3-shift operation. The measuring device is set up in such a way that during a measuring process the test force is introduced into the flat component solely via the predetermined weight of the test weight.This allows a defined surface pressure to be achieved between the upper and lower pressure plates, thus providing an accurate measurement result for the thickness measurement, which can be precisely determined as the distance between the pressure plates using the distance sensor. The vertical guide enables guided vertical lowering and lifting of the test weight and, during a measuring process, a flat contact and pressure transfer of the upper pressure plate to the flat component to be measured.

[0021] The measuring device is particularly advantageously used in the thickness determination of plug-in metal-based gas diffusion layers or gas diffusion layers as flat components to be measured and is particularly advantageously designed for this purpose. In series operation of the measuring device, large-area flat components with a preferably rectangular base area in different sizes can be measured precisely and reproducibly at a high cycle rate. The flat components - such as gas diffusion layers - can therefore be subjected to a shaped cut in the industrial production process and measured with the measuring device at identical points both before and after the cut and subjected to quality assurance. The measuring device is preferably advantageously used for the thickness measurement of flat components with, for example, a length of 600 - 1500 mm, a width of 350 - 450 mm and a height of 0 - 7 mm.The height of the flat component corresponds to the thickness measurement value to be determined, which can be determined with a high degree of accuracy.

[0022] In a particularly preferred embodiment of the measuring device, it comprises a lifting mechanism by means of which the test weight can be lowered and thereby the predetermined test force can be applied to the flat component via the weight force.

[0023] The specified test force can be applied to the flat component in a particularly simple manner using only the weight of the test weight, specifically locally via the contact surface of the upper pressure plate. This means that the rigidity of the measuring device and any higher-level machine structure integrating the measuring device has no influence on the measurement accuracy. Furthermore, a test weight is a force source with only a very limited dispersion and practically constant over time. The lifting device allows the test weight to be lowered for the measurement process, achieving the specified surface pressure.

[0024] In a preferred embodiment of the measuring device, the lifting mechanism is designed in such a way that a decoupling from the test weight is effected during a measuring process, so that no additional force is applied to the flat component beyond the test force imparted by the test weight.

[0025] Thus, the test force is introduced into an inserted flat component by lowering the test weight only locally in the area of ​​the defined contact surfaces of the upper pressure plate and the lower pressure plate. The distance between the upper pressure plate and the lower pressure plate can then be measured with the distance sensor under well-defined test conditions. For flat components designed as gas diffusion layers, a surface pressure of typically, for example, 0.6 N / mm 2 advantageous at a test force of approximately 1180 N. The thickness or height of the flat components is defined as the distance between the upper and lower pressure plate when these are in flat contact with the component and subjected to the test force.

[0026] During a complete measuring procedure with the measuring device, the weight must be removed from the flat component in order to insert and remove the flat component safely. The test weight can be advantageously raised using the lifting mechanism so that, for example, a clear gap of around 40 mm is created between the flat component and the upper pressure plate. The weight is raised and lowered gently so as not to damage the flat component to be tested. For this purpose, the lifting mechanism in the measuring device is controlled and guided in such a way that the acceleration and speed of the test weight are limited. The limit is adjustable, for example by setting a limit valve that must be provided, e.g. in the case of a pneumatic or hydraulic damping and limiting device for raising and lowering.

[0027] The lifting mechanism is designed in such a way that, during the actual measurement phase, only the weight imparted by the test weight acts on the flat component. The lifting mechanism itself is completely decoupled during this phase and does not introduce any additional weight force, thus ensuring that the measurement result is not distorted. For example, a lifting mechanism based on a cable guide with corresponding rollers and drive units for raising and lowering the test weight is conceivable.

[0028] Preferably, the weight force of the test weight is adjustable in the measuring device so that calibration of the test force can be achieved.

[0029] The material and volume of the test weight are selected so that the resulting weight of the structure resting on the flat component, including pressure plates, etc., corresponds to the required test force. Depending on the specific requirements, the specified test force can be determined and adjusted using a scale, for example. For this purpose, the test weight can be composed of a variety of weight units.

[0030] This makes it advantageous to implement an adjustment and calibration option, for example to finely adjust the test force and vary it as needed by specifically adding / removing weight units.

[0031] Preferably, the measuring device therefore has the possibility of varying the test force in the range of 950 (surface pressure 0.5 N / mm 2 ) up to 2000 N (surface pressure 1 N / mm 2) is implemented, e.g., by providing sufficient space for changing the test weight. For industrial production and quality control, this provides the measuring device with flexibility in terms of generous adjustment of the test force to a preferred value of, for example, 1178 ± 10 N.

[0032] In a particularly advantageous embodiment of the measuring device, the vertical guide is fixed against rotation about the vertical axis, so that a precise and reproducible lowering of the test weight is ensured.

[0033] The test weight can be precisely guided linearly up and down via the vertical guide and is also fixed in rotation about the movement axis, so that a linear guide is mechanically implemented under a constraint in the measuring device. The vertical guide is therefore advantageously designed as a vertically aligned longitudinal guide, which is constructed with as little friction as possible in order to be able to transmit the weight of the test weight to the flat component to be tested with as little change as possible. For example, brass bushings can be used in which a rod or vertically aligned metal shaft is guided.

[0034] In a further preferred embodiment, a calibration device is provided in the measuring device, with which a current reference value can be determined as the zero point of the distance measurement and with which the distance measurement between the upper pressure plate and the lower pressure plate can be calibrated.

[0035] This means that a calibration of the zero point of a distance measurement between the upper and lower printing plate is provided as needed, on a rotating basis, or regularly between measuring processes. The distance sensor is thus equipped with a calibration function so that a precise thickness measurement is achieved. The distance and thus the thickness of the flat component introduced into the measuring device therefore results from a length measurement. For this purpose, an automated length measuring device can be provided which includes the distance sensor with the calibration function. The advantageous basic functions of the length measuring device arise from the fact that the position of the test weight can be determined relative to a stationary, i.e. fixed point, for example on the housing of the measuring device.By applying the force of the test weight, the force path of the measurement can be separated from the force path of the lifting mechanism and thus decoupled in order to achieve the best possible measurement results.

[0036] In order to obtain an exact distance measurement between the upper printing plate and the lower printing plate in each measurement, the measuring device must first be referenced, i.e. "zeroed", without a component to be tested inserted. This reference is preferably checked regularly during operation of the measuring device - ideally always between two components. During a zero measurement, the printing plates are moved flat against one another without a component and the measured value output is determined as the "zero value" of the tool distance. If the absolute value of the measured value is greater than a permissible maximum value, for example > 3 pm, the reference is automatically reset and the measuring device is calibrated accordingly. This procedure allows temporal drifts, e.g. due to temperature changes, to be detected and compensated for in situ during operation of the measuring device.This zero-point calibration can be automated by a control and regulation device that is advantageously integrated into the measuring device. The control and regulation device can also implement additional functions for automating the measurement process.

[0037] In a further preferred embodiment of the measuring device, a dead weight is provided which is arranged radially outside the vertically guided upper pressure plate, so that when the upper pressure plate is lowered, a flat component to be tested can be pressed flat onto the base under the weight of the dead weight.

[0038] The dead weight is an additional weight and ensures that the flat component rests flat on the level surface. Due to the arrangement of the dead weight radially outside the pressure plates, the dead weight is completely decoupled from the measuring process and does not participate in the measurement or influence the surface pressure under the specified test weight. The dead weight advantageously serves solely to position and rest flatly on the level measuring surface, particularly at its edges.

[0039] Since the flat components often have a slight curvature due to manufacturing reasons, which can influence the measurement result, a preferred embodiment features a circular dead weight or a circular ring radially surrounding the upper pressure platen integrated into the measuring device. This means that the flat component, in particular a gas diffusion layer made of expanded metal, can be pressed flat onto the base and positioned independently of the test force. The weight of the additional weight is not included in the test force, which is achieved by the additional weight lying outside the plane-parallel measuring surfaces of the upper and lower pressure plates at a predetermined distance. The distance between the support of the dead weight is preferably at least 15 mm from the measuring surfaces. The dead weight in the measuring device is preferably fixed against rotation about the vertical axis, and the dead weight can be locked and removed if necessary.

[0040] This also provides access to the upper pressure plate and other functional parts of the measuring device, for example, during servicing. The dead weight is protected against rotation around the vertical axis and can be locked and removed at a vertically upper point of the measuring device. The locking at the upper point is required to adjust the ball head, clean the pressure plates, and perform measurements even without the dead weight.

[0041] The counter surface of the additional weight or dead weight on the base of the flat component is preferably also designed as a circular ring (circular ring) with the same dimensions as the dead weight itself. The support surface of the component including the lower pressure plate is preferably slightly raised from the base, e.g. a table surface made of granite slab. To make it easier to insert the flat components to be measured into a measuring position, the support surfaces are designed with bevels or chamfers with an angle of, for example, 20 °. The following parameters have proven to be advantageous for the dead weight: The inner diameter of the additional weight ring is 110 mm, the outer diameter of the additional weight ring is 140 mm, the dead weight has a mass of 15 kg. Depending on the measuring task and dimensions of the flat component, adapted diameters can also be used.The contact surfaces of the additional weight with the flat component to be measured are preferably made of hardened and corrosion-resistant stainless steel, e.g. 1. 4923 or 1. 4021 steels can be used.

[0042] In a particularly preferred embodiment of the measuring device, the pressure plates are each designed as circular, flat plates made of hardened stainless steel, which are aligned congruently and plane-parallel to one another. Preferably, the upper pressure plate is connected to a shaft of the test weight via a ball-and-socket joint, so that a plane-parallel alignment of the pressure surfaces of the upper pressure plate and the lower pressure plate can be adjusted.

[0043] For example, both the movable upper pressure plate and the lower pressure plate, which is permanently integrated into the base, are designed as circular plates made of corrosion-resistant, hardened steel, e.g. 1. 4923 or 1. 4021 steel. The diameters of the circles should advantageously be machined to 50 + / - 0.05 mm, with the component contact surfaces being ground (Rz < 4) in order to achieve the best possible plane parallelism of the contact surfaces. A larger chamfer of > 0.1x45° should be avoided in order not to falsify the surface pressure, so that precisely specified circular, congruent and plane-parallel standard surfaces are provided by the pressure plates.

[0044] To ensure the pressure surfaces of the upper and lower pressure plates are precisely aligned parallel to one another, the upper pressure plate is advantageously connected to the shaft of the test weight via a ball head. The ball head is secured and positioned during calibration under the measuring pressure. The ball head is designed to allow rotational movement around the vertical axis, and the ball center is advantageously located on the contact surface of the upper pressure plate. To access the locking mechanism of the ball head joint under the measuring pressure, the dead weight is secured in its upper position.

[0045] The measuring device preferably has a plurality of plate pairs, each comprising an upper pressure plate and a lower pressure plate, wherein the plate pairs are arranged in such a way that, during a measurement, the thickness of a flat component introduced for a measurement can be determined simultaneously at several measuring points. In this way, a thickness measurement at several different locations is possible for a flat component at the same time. A particularly uniform surface pressure and thickness adjustment is thereby possible for extensive flat components such as gas diffusion layers made of stacked expanded metal sheets. The thickness of the components can, for example, be measured simultaneously at 6 locations. The measuring device is particularly advantageously designed and adjusted to provide a surface pressure of, for example, 0.6 N / mm 2between circular pressure plates, each 50 mm in diameter, and a test weight of 1178 N + / - 10 N as an exemplary design. The distances between the measuring points are preferably constant; the distances to the edge of the flat component can vary depending on the component. For this purpose, adjustable stops for positioning the flat component can be provided in the measuring device.

[0046] The thickness or height of the components is defined as the distance between the upper and lower pressure plate when these are in flat contact with the flat component and are subjected to the specified test force.

[0047] In the measuring device, the plate pairs of the upper pressure plate and the lower pressure plate are therefore preferably arranged regularly over the surface so that respective local thickness measurements of a flat component introduced for measurement can be determined. A uniform grid-like arrangement and positioning of the plate pairs as a rectangular grid or as a square grid with regard to the flat component surface is particularly advantageous for local thickness measurements at a large number of measuring points. Since the flat components have very reproducible compression behavior with a spring constant of up to 50 kN / mm, regular positioning of the measuring points on the flat component is preferred. This is particularly the case with gas diffusion layers made of expanded metal, as used for electrolysis cells.The object is further achieved according to the invention by a measuring table with a measuring device comprising a table top into which a lower pressure plate is integrated, wherein a support surface for receiving a flat component for thickness measurement is formed on the table top. The measuring table with the table top is designed in such a way that during the measuring process the flat component only rests on the support surface of the dead weight and the lower pressure plate which is raised above the table surface. The table top also serves to provide good guidance and reproducible positioning of the flat components, in particular when inserting and removing them during the measuring process.

[0048] In a particularly preferred embodiment, the measuring table comprises a control device with an operating panel so that the measuring process can be controlled and monitored, wherein measurement data from the distance sensor can be read into a processor and processed.

[0049] To control and monitor the process, a computer with an operating device comprising an operating panel is preferably provided. At the operating station, the measurement results can also be shown visually to an operator, for example on a monitor or a display. A measurement can be triggered by the operator, for example, using a foot switch. A service function with optional manual operation is advantageously implemented in the control device. This moves the test weights to the lower end position in order to, for example, be able to adjust the ball head and to secure the test weights at the same time.

[0050] Preferably, the measuring table comprises a transport device for loading and unloading a flat component.

[0051] The implementation of an automated feed of the flat components is particularly advantageous here. The object is further achieved by a method for measuring the thickness of a gas diffusion layer of an electrochemical cell, in which a measuring device is provided, a gas diffusion layer being inserted into the measuring device as a flat component, wherein during a measuring process a predetermined test force is applied to the gas diffusion layer via the weight of the test weight by lowering the test weight so that a defined surface pressure is brought about, and wherein the distance between the upper pressure plate and the lower pressure plate is determined under the predetermined test force.

[0052] In the method, a current reference value is preferably determined as the respective zero point and thereby the distance between the upper pressure plate and the lower pressure plate is calibrated.

[0053] The repeatability and precision of the thickness measurement are crucial and are preferably set to values ​​< 5 pm. The measuring system can also be compared with existing measuring systems. To verify the repeatability, a "zero measurement run" is performed without a component in order to reference the measuring system.

[0054] Furthermore, in the method, a thickness measurement is preferably carried out simultaneously at several measuring points distributed over the surface of the gas diffusion layer during one measuring process.

[0055] The measuring points can be distributed evenly and in a grid pattern over the surface of the gas diffusion layer. Only the plane-parallel and congruent surfaces of the upper and lower pressure plates at the respective measuring points act as the effective functional surface for the force application by the specified test weight.

[0056] The advantages of the measuring method according to the invention arise correspondingly from the advantages of the measuring device. Further advantages, features and details of the invention emerge from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the sole figures can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0057] Examples of the invention are explained in more detail with reference to the accompanying drawings. These show schematically and in a highly simplified manner:

[0058] FIG 1 shows the basic structure of an electrochemical cell, which is exemplified as a PEM electrolysis cell;

[0059] FIG 2 shows a simplified representation of the basic measuring principle of the invention for determining the thickness of a flat component designed as a gas diffusion layer;

[0060] FIG 3 Arrangement of several measuring points on a gas diffusion layer;

[0061] FIG 4 shows a view of a measuring device for a selected measuring point of a gas diffusion layer;

[0062] FIG 5 a view of a measuring device before the measurement with inserted gas diffusion layer;

[0063] FIG 6 the measuring device according to FIG 5 during the measurement;

[0064] FIG. 7 shows a sectional view of a lower punch with a lower pressure plate; FIG. 8 shows a plan view of the lower punch according to FIG. 7;

[0065] FIG 9 a schematic plan view of a measuring table with measuring device and inserted gas diffusion layer.

[0066] FIG. 1 schematically shows the structure of an electrochemical cell 31, which is designed as a PEM electrolysis cell. The electrochemical cell 31 is part of an electrolyzer (not shown in detail here) for splitting water using electrical current to produce hydrogen and oxygen.

[0067] The electrochemical cell 31 comprises an electrolyte made of a proton-conducting membrane 33 (proton exchange membrane, PEM), on which the electrodes 35a, 35b are located on both sides. The unit consisting of membrane and electrodes is referred to as a membrane-electrode assembly (MEA). The electrode 35b is referred to as a cathode, and the electrode 35a as an anode. A gas diffusion layer 11 is respectively located on the electrodes 35a, 35b. The gas diffusion layers 11 are contacted by so-called bipolar plates 37, which, in the assembled state of an electrolysis stack consisting of several individual electrolysis cells 31, separate them from one another.

[0068] The electrochemical cell 31 is fed with water, which is converted at the anode 35a into oxygen gas O2 and protons H + is broken down. The protons H +migrate through the electrolyte membrane 33 toward the cathode 35b. On the cathode side, they recombine to form hydrogen gas H2.

[0069] In another embodiment, the electrochemical cell 31 is designed as a galvanic cell or fuel cell designed for power generation. According to the invention, the gas diffusion layers 11 of electrochemical cells 31 designed in this way are to be modified analogously to the electrolysis cell 31 shown in FIG. 1. Without restricting generality, reference is therefore made below by way of example to an electrochemical cell 31 designed as an electrolysis cell.

[0070] The gas diffusion layer 11—also referred to as the gas diffusion layer—is a flat component 10 and a functional layer important for the electrolysis cell 31, performing various tasks during the operation of the electrolysis cell 31. The gas diffusion layer 11 ensures optimal water distribution and the removal of product gases. In the case of a galvanic cell, the gas diffusion layers 11 serve to supply reactants to the respective electrodes. It is essential that the gas diffusion layer 11 is sufficiently permeable to the gaseous products or reactants in each case, so that their removal is possible.

[0071] The gas diffusion layer 8 also serves as a current distributor, particularly in an electrolysis cell. For these reasons, the gas diffusion layer 8 is made of an electrically conductive, porous material.

[0072] In the illustrated embodiment, the gas diffusion layer 11 compensates for component tolerances, particularly those of the adjacent bipolar plates 37. The gas diffusion layer 11 therefore contains stacked layers, with an outer layer being designed as a spring component with a progressive spring characteristic. The gas diffusion layer 11 comprises, in particular, a contact component, a diffusion component, and the spring component, which differ from one another in terms of their structure and / or composition.

[0073] The gas diffusion layer 11 of electrolysis cells 37, comprising several layered diffusion layers, must meet particularly high requirements for the respective height and thickness profile and, due to the specified installation space of the cell frame, must be designed and manufactured with great precision for use in an electrolysis cell 37. Dimensional accuracy and dimensional stability with regard to the permissible thickness are becoming increasingly important, particularly for large-format, flat gas diffusion layers 11, such as those currently being developed and designed for use in high-performance electrolyzers. Therefore, for an industrial manufacturing process with high volumes and large effective functional areas, quality assurance in the thickness adjustment of the gas diffusion layer 11 is very important.In addition, the permissible thickness tolerances must be monitored during the axial stacking and mechanical bracing of a large number of electrolysis cells 31 to form a high-performance electrolyzer.

[0074] FIG 2 shows a schematic representation of the measuring principle in order to demonstrate the thickness measurement on a prefabricated multi-layer gas diffusion layer 11. The gas diffusion layer 11 contains layers (not shown in detail) stacked on top of one another, with an outer layer being designed as a spring component which has a progressive spring characteristic. The gas diffusion layer 11 comprises in particular a contacting component for the electrical supply, a diffusion component for media transport and a spring component for the required elastic properties when installing the gas diffusion layer 11 in a cell frame. The components and layers of a gas diffusion layer can differ from one another in terms of their structure and / or their composition depending on the function and installation situation.A circular upper pressure plate 5 and a corresponding congruent circular lower pressure plate 7 with the same diameter D are arranged vertically one above the other so that an intermediate space is formed. A gas diffusion layer 11 having a plurality of gas diffusion layers is inserted into the intermediate space, the thickness of which is to be determined. The upper pressure plate 5 is guided so as to be vertically movable and can be raised and lowered, while the lower pressure plate 3 is firmly integrated into a solid base. The upper pressure plate 5 and the lower pressure plate 3 have flat, plane-parallel component contact surfaces 23 with the same precise diameter of, for example, D = 50 ± 0.05 mm, in order to bring about a predetermined and well-defined surface pressure during a measuring process using a vertical test force F. The pressure plates 3, 5 are made of hardened and corrosion-resistant steel such as 1.4923 or 1.4021.The component contact surfaces 23 are ground to achieve the best possible plane parallelism.

[0075] Applying the test force F to the upper pressure plate 5 results in a defined surface pressure of, for example, 0.6 N / mm 2 at the selected measuring point of the gas diffusion layer 11. This defined surface pressure results in the thickness measurement value H to be determined for the gas diffusion layer 11, wherein the thickness measurement value H is defined as the distance between the upper pressure plate 5 and the lower pressure plate 3. The measuring arrangement ensures that the upper pressure plate 5 and the lower pressure plate 3 rest flat against the gas diffusion layer 11 with the component contact surface 23 and are subjected to the test force F. The test force F is set to a fixed value of, for example, F = 1178 ± 10 N.

[0076] FIG. 3 shows a view - in this case as a plan view - of a flat component 10 using the example of a flat, rectangular gas diffusion layer 11. Several measuring points 25 are provided, which are evenly distributed on the flat component 10. Each of the measuring points 25 is formed by a circular surface area, which corresponds to the component contact surfaces 23 of a respective upper pressure plate 5 or a lower pressure plate 3 according to FIG. 2. The measuring points 25 are arranged in a grid with a predetermined grid spacing X and Y with respect to the component axes of the flat component 10 in the direction of its longitudinal extent, i.e. along the x-axis, or its width extent, i.e. along the y-axis. In this case, six measuring points 25 are provided, so that simultaneously at six measuring points 25, each applying the same surface pressure per measuring point 25 of, for example, 0.6 N / mm 2the component height can be determined locally. In the view according to FIG 3, the component height is set perpendicular to the component plane of the flat component 10 defined by the x-axis and the y-axis. Typically, the rectangular measuring point grid can be designed with X = 635 mm and Y = 210 mm with constant spacing. The distances of the measuring points 25 to the component edge can vary depending on the flat component 10 and can be adapted as required. The gas diffusion layer 11 as a flat component 10 has particularly well-reproducible compression behavior. The spring constants of the gas diffusion layer 11 are up to 50 kN / m.

[0077] FIG 4 shows a view of a measuring device 1 for a selected measuring point 25 of a gas diffusion layer 11. The measuring device 1 is designed for precise thickness measurement on a gas diffusion layer 11. The measuring device 1 has a lower pressure plate 3 and an upper pressure plate 5 as well as a test weight 9. The test weight 9 is guided vertically via a vertical guide 7 so as to be vertically movable and with low friction and is fixed against rotation about the vertical axis. The lower pressure plate 3 is embedded and fixed in a solid table top 21, for example made of granite. The lower pressure plate 3 is separate and raised but is designed as an integral part of an all-metal lower punch 41 which is embedded in the table top 21. The upper pressure plate 5 is mechanically coupled to the test weight 9.A predetermined weight force can thus be introduced into the upper pressure plate 5 via the test weight 9 and a flat component 10 to be tested can be subjected to a defined surface pressure. For this purpose, the measuring device 1 has a lifting mechanism 15, by means of which the test weight 9 can be lowered vertically, whereby the predetermined test force F (see FIG. 2) can be applied to the flat component 10 solely via the weight of the test weight 9. The lifting mechanism 15 is designed in such a way that during a measuring process there is complete decoupling from the test weight 9, so that no additional falsifying force is applied to the flat component 10 beyond the test force F imparted by the test weight 9. Thickness measurements on a gas diffusion layer 11 to be tested with the measuring device 1 can therefore be carried out very precisely and reproducibly.A cantilever arm 39 designed as a C-profile absorbs the force of the test weight 9 via the lifting mechanism 15. The cantilever arm 39 is designed to be particularly stable and solid. Furthermore, the cantilever arm 29 also serves to attach a guide device 53 of the lifting mechanism 15 - shown in more detail in FIG. 9 -, for example based on a cable pull system, for raising and lowering the test weight 9 during a measuring cycle. To determine an exact thickness measurement value H for the thickness of the gas diffusion layer 11 under the specified test conditions and surface pressure, a distance sensor 13 is provided which is integrated into a higher-level measuring and calibration device 17. In this way, a current reference value can be determined as the zero point of the distance measurement and can be continuously checked, and as a result the distance between the upper pressure plate 5 and the lower pressure plate 3 can be regularly recalibrated if necessary.In addition, a dead weight 19 is provided in the measuring device 1 for stabilization and, above all, for the flat alignment of a gas diffusion layer 11 to be tested. The dead weight 19 is arranged radially at least 15 mm outside the vertically guided upper pressure plate 5 and does not influence the thickness measurement. When the upper pressure plate 5 is lowered over the test weight 9, an introduced gas diffusion layer 11 can be pressed flat onto the base under the weight of the dead weight. The dead weight 19 is also fixed against rotation about the vertical axis and can be locked in the upper position and removed if necessary.

[0078] FIG 5 shows a view of a measuring device 1 with a gas diffusion layer 11 inserted into the measuring device 1 before the start of the measurement. Here the test weight 9 and thus the upper pressure plate 5 are in a vertically upper position. The gas diffusion layer 11 is an extensive, flat component 10 and can be curved, particularly at the edges, due to manufacturing reasons. This is indicated in FIG 5. The dead weight 19 is introduced into the measuring device as an additional weight and is arranged radially on the periphery and concentrically and at a distance around the upper pressure plate 5. The dead weight 19 can be designed as a solid metallic hollow cylinder, with an annular and flat contact surface being provided for the function of the dead weight 19. The inner diameter A of the dead weight 19 is therefore greater than the diameter D of the upper pressure plate 5 and the lower pressure plate 3.The outer diameter B is correspondingly larger than the inner diameter A. Due to the circular design, the dead weight 19 provides an adapted effective surface. The lower pressure plate 3 is designed as part of a lower punch 41 and is configured to exert a defined surface pressure during measurement. The lower punch 41 is integrated into the table plate 21, with the circular lower pressure plate 3 being raised compared to the solid table plate 21. Accordingly, the lower punch 41 has an equally raised circular ring-shaped support surface which is congruent with the circular ring-shaped effective surface of the dead weight 19. The upper pressure plate 5 is connected to the test weight 9 via a ball head joint 43. The ball head joint 43 enables precise adjustment and plane-parallel alignment of the component contact surfaces 23 of the upper pressure plate 5 and the lower pressure plate 3.

[0079] In comparison to FIG 5, FIG 6 shows the measuring device 1 during the thickness measurement on an introduced gas diffusion layer 11, wherein a predetermined pressing force F is introduced via the upper pressure plate 5 due to the weight of the test weight. The test weight 9 with the upper pressure plate 5 is lowered so that the test force F effects a defined local surface pressure on the gas diffusion layer 11. Furthermore, the dead weight 19 is correspondingly lowered and rests on the periphery with an exact fit in relation to the opposite circular ring-shaped raised contact surface of the lower punch 41. This achieves a very precise and reproducible planar alignment of the gas diffusion layer 11 for the measurement, completely decoupled from the test force F introduced via the test weight 9.The measurement can thus be carried out very precisely and at the same time simply, since the test force F is provided in a particularly simple manner as the weight of the solid test weight 9, which is subject to practically no or only very small tolerances. Due to the simplicity of the measuring device 1 and the measuring method, no complex compensation is required, as was the case with previously known universal testing machines for these measuring purposes.

[0080] FIG 7 shows a sectional view of a lower punch 41 with a lower pressure plate 3 and FIG 8 shows a corresponding plan view of the lower punch 41 according to FIG 7 . In the lower punch 41, the lower pressure plate 3 is an integral component . The lower pressure plate 3 is cylindrical with a circular component contact surface 23 with a predetermined diameter D, for example D = 50 mm . The component contact surface 23 is flat and surface-treated, e . g . polished, and has a low average roughness of Rz < 4 . The overall diameter G of the lower punch 41 can typically be G = 190 mm . The inner diameter A can e . g . be A = 110 mm and the outer diameter B can e . g . be B = 140 mm . As a result, a likewise raised circular ring-shaped surface 45 is formed as a support surface, which encloses the component contact surface 23 concentrically and radially.The lower punch 41 is designed as a single piece and is made from solid stainless steel, preferably as a turned part and surface-treated. The transition from the raised annular surface 45 in the radially inward direction to the raised component contact surface 23 and also radially outward to the edge of the lower punch 41 is designed as a bevel 47 with an angle a of typically a = 20 ° for the bevel 47. This provides a concentric depression around the lower pressure plate 3, which advantageously facilitates the introduction and positioning of the gas diffusion layer 11 for a measurement. In this depression around the lower pressure plate 3, a transition region 49, which is flat, adjoins the bevel 47 radially inward.

[0081] FIG. 9 shows a schematic plan view of a measuring table 27. This creates a measuring system for measuring the thickness of a gas diffusion layer 11. The measuring table 27 has a solid table top 21 and integrates the measuring device 1 described above. According to the number of measuring points 25, a corresponding number of lower punches 41 with a respective lower pressure plate 3 is integrated into the table top 21, compare FIG. 7 and FIG. 8. The measuring points 25 are arranged in a grid and at regular intervals on the table top 21. A precise and flexible setting of a desired position and positioning of the gas diffusion layer 11 is possible and adjustable using variable stops 49. Depending on the number and arrangement of the measuring points 25 on the measuring table, each of the measuring points 25 is assigned a cantilever arm 39 as a C-profile with a respective lifting mechanism 15.For raising and lowering the test weights 9 during a measuring sequence, a guide device 53 is attached to the cantilever arm 39 and can be activated, for example, via a cable pull system. To protect the operator 55, a safety device 51 is provided, which has, for example, a light curtain. Furthermore, a control device with an operating panel 29 is provided so that the measuring process can be controlled and monitored automatically. Measurement data from the distance sensor 13 or the calibration device 17 is read into a processor and processed. A transport device (not shown in detail) can be provided for automatic feed. A central computer with an operating device is advantageous for controlling and monitoring the process. At the operating station, the results are displayed and saved on the operating panel 29. A measurement can be triggered by the operator 55, for example, using a foot switch.At the same time, a service function with manual operation as required is implemented on the measuring table 27, in which the lower end position of the test weights 9 is approached in order, for example, to adjust the ball head joint 43.

[0082] During a measuring process for measuring the thickness of a gas diffusion layer 11, a measuring device 1 is provided, a gas diffusion layer 11 being inserted into the measuring device 1 as a flat component 10, a predetermined test force F being applied to the gas diffusion layer via the weight of the test weight 9 during a measuring process by lowering the test weight 9 so that a defined surface pressure is brought about, and the distance between the upper pressure plate 5 and the lower pressure plate 3 is determined under the predetermined test force F. In this case, a current reference value is determined as the respective zero point and the distance between the upper pressure plate 5 and the lower pressure plate 3 is calibrated in this way. During a measuring process, a thickness measurement is carried out simultaneously at several measuring points 25 distributed over the surface of the gas diffusion layer 11.

Claims

Patent claims 1. Measuring device (1) for measuring the thickness of a gas diffusion layer (11) for an electrochemical cell (31), comprising a lower pressure plate (3) and an upper pressure plate (5) and a test weight (9) guided via a vertical guide (7) in such a way that, during a measuring process, a predeterminable test force can be applied to a flat component (10, 11) to be tested via the weight of the test weight (9), so that a defined surface pressure is brought about, and further comprising a distance sensor (13) by means of which the distance of the flat component (10, 11) between the upper pressure plate (5) and the lower pressure plate (3) under the predefined test force (F) can be determined as the thickness measurement value (H).

2. Measuring device (1) according to claim 1, comprising a lifting mechanism (15) by means of which the test weight (9) can be lowered and thereby the predetermined test force (F) can be applied to the flat component (10, 11) via the weight force.

3. Measuring device (1) according to claim 2, wherein the lifting mechanism (15) is designed such that during a measuring process a decoupling from the test weight (9) is effected, so that no additional force is applied to the flat component (10, 11) beyond the test force (F) imparted by the test weight (9).

4. Measuring device (1) according to one of the preceding claims, in which the weight force of the test weight (9) is adjustable so that a calibration of the test force (F) can be achieved.

5. Measuring device (1) according to one of the preceding claims, in which the vertical guide (7) is fixed against rotation about the vertical axis, so that a positionally accurate and reproducible lowering of the test weight (9) is ensured.

6. Measuring device (1) according to one of the preceding claims, in which a calibration device (17) is provided with which a current reference value can be determined as the zero point of the distance measurement and thereby the distance between the upper pressure plate (5) and the lower pressure plate (3) can be calibrated.

7. Measuring device (1) according to one of the preceding claims, in which a dead weight (19) is provided which is arranged radially outside the vertically guided upper pressure plate (5), so that when the upper pressure plate (5) is lowered, a flat component (10, 11) to be tested can be pressed flat onto the base under the weight of the dead weight (19).

8. Measuring device (1) according to one of the preceding claims, in which the dead weight (19) is fixed against rotation about the vertical axis, wherein the dead weight (19) is lockable and removable if necessary.

9. Measuring device (1) according to one of the preceding claims, in which the pressure plates (3, 7) are each designed as circular flat plates made of a hardened corrosion-resistant steel, which are aligned congruently and plane-parallel to one another.

10. Measuring device (1) according to one of the preceding claims, in which the upper pressure plate (5) is connected to a shaft of the test weight (9) via a ball-and-socket joint (43), so that a plane-parallel alignment of the pressure surfaces of the upper pressure plate (5) and the lower pressure plate (3) can be adjusted.

11. Measuring device (1) with a plurality of plate pairs each comprising an upper pressure plate (5) and a lower pressure plate (3), wherein the plate pairs are arranged such that during a measurement respective thickness measurement values ​​(H) of a flat component (10, 11) introduced for a measurement can be determined simultaneously at several measuring points (25).

12. Measuring device (1) according to claim 11, wherein the plate pairs are arranged regularly over the surface so that respective local thickness measurement values ​​(H) of a flat component (10, 11) introduced for a measurement can be determined.

13. Measuring table (27) comprising a measuring device (1) according to one of the preceding claims comprising a table top (21) into which a lower pressure plate (3) is integrated, wherein a support surface for receiving a flat component (10, 11) for thickness measurement is formed on the table top (21).

14. Measuring table (27) according to claim 13, comprising a control device with an operating panel (29) so that the measuring process can be controlled and monitored, wherein measurement data of the distance sensor (13) can be read into a processor and processed.

15. Measuring table (27) according to one of claims 13 or 14, comprising a transport device for loading and unloading a flat component (10, 11).

16. Method for measuring the thickness of a gas diffusion layer (11) of an electrochemical cell (31), in which a measuring device according to one of claims 1 to 12 is provided, wherein the measuring device (1) is incorporated as a flat component (10) a gas diffusion layer (11) is inserted, wherein during a measuring process a predetermined test force (F) is applied to the gas diffusion layer via the weight of the test weight (9) (11) is applied by lowering the test weight (9) so that a defined surface pressure is effected, and wherein the distance between the upper pressure plate (5) and the lower pressure plate (3) is determined under the predetermined test force (F).

17. The method according to claim 16, wherein a current reference value is determined as the respective zero point and thereby the distance between the upper pressure plate (5) and the lower pressure plate (3) is calibrated.

18. Method according to one of claims 16 or 17, wherein during a measuring process a thickness measurement is carried out simultaneously at several measuring points (25) distributed over the surface of the gas diffusion layer (11).

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