Fuel cell unit, fuel cell assembly and method

Abstract

The invention relates to a fuel cell unit (10) for implementing an energy source with an oxidizer in a reaction zone, in particular over an active area (32), with electrical energy being generated, wherein the fuel cell unit (10) comprises, as functional components (11), at least two electrodes (15) and an electrolyte (18) arranged between the electrodes (15). Simplified monitoring of the operation of the fuel cell unit (10) is rendered possible by way of at least one sensor element (40), which is in the form of an optical waveguide (42), for fibre-optic temperature determination and / or determining mechanical deformation within the fuel cell unit (10) being arranged within the at least one fuel cell unit (10).

Description

[0001] Fuel cell unit, fuel cell assembly and method

[0002] The invention relates to a fuel cell unit for reacting an energy carrier, in particular hydrogen, with an oxidizer, in particular oxygen and / or air, in a reaction zone, in particular via an active surface, to generate electrical energy. The fuel cell unit comprises, as functional components, at least two electrodes and an electrolyte arranged between the electrodes. The invention further comprises a fuel cell arrangement and a method for operating a fuel cell unit.

[0003] Such a fuel cell unit is described in US 2017 / 0 229 724 A1. The fuel cell unit is provided with at least one integrated optical fiber sensor element for the fiber-optic determination of parameter values ​​of the chemical composition and / or temperature of functional components of the fuel cell unit, wherein an optical fiber is inserted into a spacer disk with sheath elements. DE 10 2011 002 841 A1 also shows an electrochemical energy storage device, including a fuel cell unit, with a sensor element embodied as an optical fiber for spatially resolved temperature detection, e.g., with Bragg gratings formed in the optical fiber.

[0004] In addition to costs, the service life and / or long-term stability of a fuel cell pose a challenge. One option for assessing the functionality of a fuel cell in both mobile and stationary applications is voltage monitoring of individual cells in a fuel cell stack. This method monitors individual cells, cell groups, and / or the entire stack using their voltage values. If these voltage values ​​are within a previously defined, acceptable range, the stack is considered functional; otherwise, it is considered defective. This method does not allow for the localization of defects.

[0005] For localization, a method for spatially resolved temperature measurement on or within a fuel cell was developed. A so-called "segmented bipolar plate" was equipped with a finely distributed network of sensors on its surface for spatially resolved measurement of current density and / or temperature. The method is comparatively complex.

[0006] The invention is based on the object of providing a fuel cell unit (as a single cell) and a fuel cell arrangement which enables simplified monitoring of the operation of a fuel cell unit, as well as a corresponding method for operating a fuel cell unit.

[0007] The problem is solved for the fuel cell unit with the features of claim 1. It is provided that within the at least one fuel cell unit, at least one sensor element designed as an optical fiber is arranged for fiber-optic temperature determination and / or determination of a mechanical deformation within the fuel cell unit. Mechanical deformation, e.g., stretching due to compressive stress, for example, can arise in particular due to changed material stress on the functional components present in the fuel cell unit, e.g., due to changed contact forces across the entire fuel cell arrangement (cell group and / or stack of individual cells). The optical fiber or fiber must be positioned such that it does not reduce the gas flow and gas distribution of the reactants hydrogen and air.

[0008] In this case, the reaction area is the area within the fuel cell unit in which the reaction gases (energy carrier, in particular hydrogen, and oxidizer, in particular air or the oxygen contained therein) react with each other.

[0009] In this case, the active area is the two-dimensional (areal) extent of the reaction area within the fuel cell unit.

[0010] In this case, functional components are individual components of the fuel cell unit to which a specific function is assigned for the operation of the fuel cell unit.

[0011] For measuring purposes, the sensor element is connected in particular to further measuring technology to complete a measuring system for measuring by means of fiber optic sensors, e.g. a (light) source and / or a control / evaluation unit, which are arranged in particular outside the fuel cell unit.

[0012] The optical fiber particularly comprises or consists of quartz glass, with the quartz glass forming, for example, a light-conducting core of the optical fiber. While prior art teachings use electrical signals for parameter acquisition, temperature acquisition is achieved in the present case using light-reflecting fiber optic cables. With this measurement technique, light rays emanating from a source are projected into the optical fiber (as a fiber optic cable). The light rays are reflected in the optical fiber and their properties, particularly frequency and / or amplitude, are altered by temperature-induced cable expansion. The changes in the incoming light rays are compared with the emitted light rays, which enables the temperature and / or expansion to be determined.

[0013] In addition to the comparatively simple integration of the sensor element, this measurement technology offers further advantages, such as easy adaptation to the geometric shape of the fuel cell unit, comparatively short setup times, no electromagnetic influences or other influences from electrical conduction or fields that could distort the parameter measurement, a compact design, and high chemical and corrosion resistance of the sensor element.

[0014] Detailed diagnostic options arise if the at least one sensor element for spatially resolved, in particular planar, temperature and / or strain determination in the fuel cell unit is arranged in a measuring plane, wherein the surface area of ​​the measuring plane corresponds to at least a large part of the active area, at least 50% or more, preferably at least 80% or more, e.g., 100%. This allows temperature and / or strain determination in a spatially resolved, sequenced temperature field and / or strain field, wherein the distance between the measuring points is, e.g., a maximum of 2 cm, e.g., a maximum of 1 cm, preferably a maximum of 5 mm. The sensor element is preferably elongated, wherein the length depends in particular on the spatial resolution, the size of the measuring plane (in particular, corresponding to the size of a temperature and / or strain field), and / or the number of sensor elements in the measuring plane.To ensure the most compact arrangement of the sensor element within the fuel cell unit, at least one sensor element is designed for measurement with a continuous sequence of measuring points, wherein the optical fiber has a distributed or quasi-continuous arrangement of measuring points. In this way, a multitude of temperatures at different measuring points can be determined using just one fiber in the core of the optical fiber, not a fiber bundle, within the sensor element (of which only one or more is / are present in the fuel cell unit). The diameter of the fiber or core can be, for example, between 5 pm and 15 pm, preferably between 6 pm and 8 pm. To protect against external influences (in particular corrosion protection), the core is preferably surrounded by a sheath. The outer diameter of the sheath can be, for example, between 50 pm and 400 pm, preferably between 100 pm and 200 pm.

[0015] A suitable measurement technique using a distributed measurement point sequence includes, for example, the design of the sensor element with a fiber Bragg grating. A suitable measurement technique using a quasi-continuous measurement point sequence includes, for example, the design of the sensor element for performing Rayleigh-C-OFDR (coherent optical frequency domain reflectometry).

[0016] In one embodiment, the fuel cell unit is designed according to the principle of a polymer electrolyte (PEM) fuel cell (with a proton exchange membrane as the electrolyte) and / or further comprises, as functional component(s), at least one, preferably two, bipolar plate(s) (for supplying and / or separating the reaction gases, insulation, cooling, etc.) and / or at least one, preferably two, gas diffusion component(s) (for transporting the reaction gases to the electrodes while homogenizing the flow). The functional components are designed in particular as, e.g., flat layers and arranged in layers, with one electrode, one gas diffusion component, and, as the outermost layer, a bipolar plate arranged on each side of the electrolyte. The electrolyte and the electrodes can be combined into a single unit (MEA: membrane electrode assembly).

[0017] The design of the fuel cell unit according to the invention is also possible with another fuel cell type (e.g. an alkaline fuel cell (AFC), direct methanol fuel cell (DMFC), etc.).

[0018] The at least one sensor element is expediently arranged taking the flow field within the fuel cell unit into account, wherein in particular the sensor element (or ribs for its attachment) runs at least partially parallel to gas channels and / or walls delimiting the gas channels. The gas channels are located for conducting a reaction gas, in particular on the bipolar plate(s), e.g., as part of a conducting structure, and thus contribute to the formation of the flow field. Between the gas channels, in particular, webs (encompassing the walls) can be arranged. In this way, a negative influence on the flow field within the fuel cell unit can be kept as low as possible. As a result, the gas flow and gas distribution of the reactants hydrogen and air are not reduced.It is particularly beneficial if the sensor element(s) and / or ribs for their fastening are arranged at least partially overlapping with the webs.

[0019] In a preferred, particularly compact and easy-to-implement embodiment, the at least one sensor element is arranged on or in one and / or between two functional components of the fuel cell unit. The corresponding functional component and / or a separate carrier layer can serve as a carrier structure for mechanical stabilization and / or vibration-proof fixation within the fuel cell unit, with the sensor element being fastened on and / or in the functional component and / or to the carrier layer. It is important that the fastening prevents the fiber or optical waveguide from slipping during assembly and is not displaced, for example, from the webs into the flow channels of the bipolar plate. A small amount of a hydrogen-resistant adhesive can also be used for fixation.Advantageously, the architecture and / or structure of the fuel cell unit can be at least largely retained.

[0020] In this case, it may be particularly expedient if the at least one sensor element is arranged on and / or in the gas diffusion component(s). The gas diffusion component comprises, in particular, a type of large-pore nonwoven material, e.g., comprising or consisting of metal, in particular steel. The sensor element can be introduced into the gas diffusion component, e.g., by means of a laser or mechanical drilling process, wherein channels are milled into the gas diffusion component, for example, and the sensor element(s) are inserted into the channels. This design variant is particularly suitable when the electrodes and the electrolyte are arranged separately from one another.

[0021] In a particularly preferred embodiment, the at least one sensor element is arranged in a separate, e.g., frame-like, carrier layer. The carrier layer assumes the function of the support structure. Thus, the sensor element(s) is / are arranged in a separate component from the other functional components. In this way, the sensor element can be easily and, in particular, vibration-proof fixed and / or securely implemented in the fuel cell unit with the least possible disruption of the flow field.

[0022] The carrier layer is particularly advantageous to implement when it is arranged between the bipolar plate and the gas diffusion component (or one of the bipolar plates and the gas diffusion component arranged on the same side of the electrolyte). The surface of the carrier layer preferably corresponds to a shape that allows it to be arranged in a gas-tight manner between two functional components. In particular, the carrier layer is flat. This arrangement has proven advantageous in preliminary studies, particularly in the presence of an MEA. Depending on the architecture of the fuel cell unit, the carrier layer can also advantageously be arranged between the gas diffusion component and the electrode (or one of the gas diffusion components and the electrode arranged on the same side of the electrolyte).

[0023] In a preferred embodiment, the carrier layer has a support structure in the measuring plane, in particular a rib-like support structure, in which the at least one sensor element is at least partially arranged (e.g., inserted, e.g., in a form-fitting manner, in a channel located in one of the ribs). The support structure comprises a plurality of ribs, in particular parallel to one another (and preferably to the webs), wherein preferably a section of the sensor element runs in each rib. If only one sensor element is present, this can, for example, run in a meandering manner, being laid with a bend from one rib of the support structure to the following rib of the support structure. The ribs can be attached to at least one, e.g., two, transverse webs running transversely thereto for stabilization. Preferably, the carrier layer is, for example,between the ribs and / or crossbars, and / or between the support structure and an edge region of the carrier layer, gas is permeable (by means of cavities), without carrier layer material.

[0024] Alternatively or additionally, at least one sensor element, in particular a plurality of sensor elements, e.g. parallel to one another, is clamped in the carrier layer so as to run across the measuring plane. The mechanical stabilization of the sensor element(s) is achieved by means of mechanical tension. Preferably, the carrier layer is designed to be gas-permeable in the measuring plane, in particular without carrier layer material. With both types of fastening, the fastening is expediently such that longitudinal expansion of the sensor element(s) for measuring purposes in the fuel cell unit or a functional component is possible. By means of these arrangements, the sensor element(s) can be integrated into the fuel cell unit in a mechanically stable, in particular vibration-proof, manner, while at the same time as little carrier layer material as possible is in the flow path in order not to limit mass transport.

[0025] For easy insertion of the carrier layer into the fuel cell unit, an outer contour, in particular an edge region, of the carrier layer preferably corresponds at least substantially to an outer contour, in particular an edge region, of the bipolar plate, particularly with regard to its shape and / or surface area. The edge region of the bipolar plate and / or the edge region of the carrier layer surrounds the conductive structure of the bipolar plate. Thus, the carrier layer has at least substantially the same profile as the bipolar plate. The carrier layer can thus be easily and stably integrated into the layer structure of the fuel cell unit and secured therein.

[0026] For reliable temperature measurement, it is advantageous if the carrier layer consists of or comprises a thermally conductive material (e.g. with a thermal conductivity of more than 1 W / (mK)), e.g. an aluminum alloy. In particular, the carrier layer can advantageously consist of or comprise the same material as the bipolar plate(s). The carrier layer should be sufficiently mechanically stable to securely fix the sensor element or the optical fiber and / or be thin enough, for example between 0.5 mm and 10 mm, to have as little impact as possible on mass transport within the fuel cell unit. Depending on the material, a 3D printing process and / or a roll bonding process are suitable for production.The uninterrupted functionality of the fuel cell unit is contributed to if at least one sealing means is introduced between the carrier layer and at least one of the functional components of the fuel cell unit, in particular the bipolar plate, through which sealing means the at least one sensor element is guided gas-tight into the interior of the fuel cell unit. A sealing cord can serve as the sealing means, which is, for example, flattened accordingly in the inlet region of the sensor element. The sealing means can be arranged, in particular, all the way around the edge region of the carrier layer and / or the bipolar plate. If necessary, a sealing means can also be introduced between the carrier layer and another component, in particular the gas diffusion component.

[0027] The problem is solved for the fuel cell arrangement with the features of claim 14. It is provided that the fuel cell arrangement comprises at least two fuel cell units, wherein at least one of the fuel cell units comprises a sensor element designed as an optical waveguide for fiber-optic temperature determination and / or determination of a mechanical deformation according to one of the preceding claims.

[0028] In a cost-effective embodiment of the fuel cell arrangement, the fuel cell unit with a sensor element designed as an optical fiber for fiber-optic temperature determination and / or determination of mechanical deformation forms a fuel cell unit arranged close to the media inlet / outlet (reaction gases, cooling medium), in particular the first and / or last fuel cell unit after the media inlet / outlet into the fuel cell arrangement. The highest temperature gradients generally occur near the media inlet / outlet. Furthermore, another fuel cell unit, for example in a central arrangement, with a generally comparatively homogeneous temperature distribution during undisturbed operation, can be monitored. For economic reasons, an advantageous embodiment may consist in arranging only one measuring plane within a fuel cell unit.The problem is solved for the method with the features of claim 16. In the method for operating a fuel cell unit according to one of the above-described embodiments, at least one temperature, preferably a spatially two-dimensional temperature field, and / or a mechanical deformation within the fuel cell unit is determined using fiber optics. Further advantageous embodiments of the method are indicated in conjunction with the description of the fuel cell unit and / or the fuel cell arrangement.

[0029] The invention will be explained in more detail below using exemplary embodiments with reference to the drawings. They show:

[0030] Fig. 1 shows a fuel cell unit with an optical waveguide arranged on a gas diffusion component in a schematic exploded view,

[0031] Fig. 2 a bipolar plate with gas channels and schematically shown optical waveguides in plan view,

[0032] Fig. 3 shows a part of the fuel cell unit according to Fig. 1 with the optical waveguide arranged on a gas diffusion component in a schematic view in cross section,

[0033] Fig. 4 shows part of a further embodiment of the fuel cell unit, with the optical waveguide arranged in a separate carrier layer, in a schematic view in cross section, Fig. 5 shows functional components of the fuel cell unit with the optical waveguide arranged in a separate carrier layer in a schematic exploded view and

[0034] Fig. 6 a possible embodiment of the carrier layer in perspective view from above.

[0035] Fig. 1 shows a schematic exploded view of a fuel cell unit 10 for converting reaction gases, specifically an energy carrier, in particular hydrogen, with an oxidizer, in particular air, to generate electrical energy. The fuel cell unit 10 can, in particular, be part of a fuel cell arrangement comprising at least two fuel cell units 10, forming a so-called "fuel cell stack" (not shown here).

[0036] The fuel cell unit 10 is designed in particular as a polymer electrolyte fuel cell, which has a proton exchange membrane as the electrolyte 18. The inventive design is also possible with another fuel cell type (e.g., an alkaline fuel cell (AFC), direct methanol fuel cell (DMFC), etc.). As further functional components 11, the fuel cell unit 10 comprises, in addition to the electrolyte 18, two bipolar plates 12, 12', two gas diffusion components 14, 14', an anode 16 and a cathode 20 as electrodes 15, and a catalyst 22 arranged on both sides of the electrolyte 18.

[0037] The functional components 11 are arranged in layers. The electrolyte 18 and the electrodes 15 can be combined into a single unit (MEA: membrane electrode assembly).

[0038] The bipolar plates 12, 12' are each arranged as the outermost layer on both sides of the fuel cell unit 10. Their function includes, in particular, the gas supply and separation (gas distribution) of the energy carrier or the oxidizer, and / or insulation and / or cooling of the fuel cell unit 10. For gas distribution within the fuel cell unit 10, the bipolar plates 12, 12' each have conducting structures 24, 24', which create a flow field. The conducting structures 24, 24' correspond approximately in their surface area to an active area 32, 32' of the fuel cell unit 10. The active area 32, 32' is the two-dimensional extent of a reaction region (over a height x and a width y) of the fuel cell unit 10, in which the reaction gases react with one another. The conducting structures 24, 24' each comprise, here, for example,meandering gas channels 26, 26', which run between webs 28, 28' with walls to define the gas channels 26, 26'.

[0039] The conductive structures 24, 24' are surrounded by edge regions 30, 30' of the bipolar plates 12, 12'. In particular, further functional elements of the fuel cell unit 10 can be arranged in the edge regions 30, 30' (see Fig. 2), for example, openings 34 for forming channels for media conduction (cooling medium, reaction gas), fastening structures 36, and / or sealing regions 38.

[0040] The gas diffusion components 14, 14' serve to further transport the reaction gases (oxidizer and / or energy carrier) to the electrodes 15 while equalizing the flow.

[0041] As shown schematically in Fig. 1, an elongated sensor element 40 is arranged within the fuel cell unit 10, which is routed from the outside into the interior of the fuel cell unit 10 via an inlet 48. The sensor element 40 is designed as an optical fiber 42 in the manner of a fiber for fiber-optic temperature determination and / or determination of mechanical deformation due to material expansion within the fuel cell unit 10.

[0042] For measurement purposes, the optical waveguide 42 is exposed to light beams 44 of different frequencies or wavelengths by a source (not shown here) arranged outside the fuel cell unit 10. The light beams are reflected off the walls of the optical waveguide 42 and their frequency and amplitude are altered by temperature-induced cable expansion. The light beams returning to the source and / or their changes are compared with the emitted light beams, and the temperature at defined measuring points is determined (e.g., from changes in frequency and / or amplitude and / or phase shift).

[0043] Particularly preferably, the sensor element 42 is designed for measurement with a continuous sequence of measurement points, wherein the optical fiber 42 has a distributed or quasi-continuous arrangement of measurement points. Thus, using only one fiber as the optical fiber 42, temperature determination can be performed at a plurality of measurement points, which is particularly beneficial for a compact design of the fuel cell unit.

[0044] The optical waveguide 42 comprises, in particular, quartz glass, which forms, for example, a light-conducting core of the optical waveguide 42. The diameter can be, for example, between 5 pm and 15 pm, preferably between 6 pm and 8 pm.

[0045] To protect against external influences (especially corrosion protection), the core is preferably surrounded by a sheath. The outer diameter can be, for example, between 50 pm and 400 pm, preferably between 100 pm and 200 pm.

[0046] By way of example, the sensor element 40 for spatially resolved, areal temperature determination in the fuel cell unit 10 is arranged in a measuring plane 58 (see Fig. 6). The surface area of ​​the measuring plane 58 preferably corresponds to at least a large part of the active area 32, for example, at least 50% or more, preferably at least 80% or more. The spatial resolution in the measuring plane 58 is such, for example, that the distance between two measuring points is no more than 2 cm, preferably no more than 1 cm, particularly preferably no more than 5 mm or 2 mm.

[0047] By determining the temperature and / or the mechanical deformation within the fuel cell unit 10, a detailed assessment of the actual condition of the fuel cell unit 10 is possible, which can be used, for example, for diagnostic purposes and / or in product development. A spatially resolved temperature inhomogeneity can indicate malfunctions such as an insufficient media supply and / or production inaccuracies. Such malfunctions can irreversibly damage the performance of the fuel cell unit 10 and even lead to cell and / or stack failure.

[0048] Fig. 2 schematically shows, by way of example, an advantageous alignment of one or more sensor elements 40 within the fuel cell unit 10 relative to one of the bipolar plates 12. Six sensor elements 40 are arranged within the fuel cell unit 10, taking into account the flow field imposed on the bipolar plate 12 by the conductive structure 24. The orientation of the sensor elements 40 is parallel to the gas channels 26 and / or the webs 28. The sensor elements 40 are arranged at least partially overlapping the webs 28 of the conductive structures 24. This minimizes disruption to the flow field of the reaction gases.

[0049] In order not to falsify the measurement accuracy, it is necessary to fix the sensor elements 40 or optical fibers 42 firmly and, in particular, vibration-proof in the fuel cell unit 10, whereby the longitudinal expansion required for the measurement is enabled. For this purpose, a mechanical stabilization of the sensor element 40 by means of a support structure serves in particular. The sensor element 40 (or several sensor elements 40) can be arranged on or in a functional component 11 and / or between two functional components 11 of the fuel cell unit 10. As a suitable fastening option, Fig. 3 shows a part of the fuel cell unit according to Fig. 1 with the sensor element 40 arranged on one of the gas diffusion components 14 in a schematic cross-sectional view. In this way, the gas diffusion component 14 acts as a support structure. The sensor element 40 can, for example,be introduced into the gas diffusion component 14 by means of a laser or mechanical drilling process, wherein, for example, channels are milled into the gas diffusion component 14 and the sensor element(s) 40 are inserted into the channels.

[0050] It is also possible to attach it to the bipolar plate 12.

[0051] Fig. 4 shows a further, particularly preferred variant in which the sensor element 40 or several sensor elements 40 are arranged between two functional components 11. According to Fig. 4, the carrier structure is formed by a separate carrier layer 50 in which the at least one sensor element 40 is arranged. In the exemplary embodiment, the carrier layer 50 is arranged between the bipolar plate 12 and the gas diffusion component 14.

[0052] Fig. 5 shows the arrangement of the sensor element 40 or the optical waveguide 42 in the carrier layer 50 in an exploded view with functional components 11 of the fuel cell unit 10. The carrier layer 50 is preferably designed as a type of frame 52.

[0053] Furthermore, Fig. 5 schematically shows a measuring / evaluation technology 46 for arrangement outside the fuel cell unit 10.

[0054] Fig. 6 shows in more detail an embodiment of the carrier layer 50. Preferably, an outer contour 57 of the carrier layer 50 or of the frame 52 and / or an entire edge region 56 of the carrier layer 50 or of the frame 52 surrounding the measuring plane 58 corresponds at least substantially in terms of its course and / or surface area to the outer contour 31 and / or the edge region 30 of the bipolar plate 12. Thus, the profile of the carrier layer 50 corresponds at least substantially to that of the bipolar plate 12. For example, the carrier layer 50 in the edge region 56 also comprises openings 55 for forming channels for the media line and / or fastening structures 59. In this way, the carrier layer 50 can be easily and stably integrated as a separate layer into the fuel cell unit 10, at least largely without impairing the operation of the fuel cell unit 10.

[0055] As Fig. 6 further shows, the carrier layer 50 can have a support structure 54 for mechanically stabilizing the sensor element 40 in the measuring plane 58, in which the at least one sensor element 40 is arranged at least in sections.

[0056] In the embodiment shown in Fig. 6, the support structure 54 has ribs 53 running parallel to one another, with a section of the sensor element 40 guided in each rib 53. At each end of the ribs 53, the sensor element 40 protrudes beyond the ribs and is transferred via a bend into the next rib 30, so that a meandering course of the sensor element 40 or the optical waveguide 42 is created. The ribs 53 are each attached with their longitudinal ends to a transverse web 51 running transversely, in particular at right angles to them. Apart from the support structure 54, the carrier layer 50 is formed in the measuring plane 58 between the ribs 53 and / or transverse webs 51, and / or between the support structure 54 and the edge region 56 of the carrier layer 50, gas-permeable, without carrier layer material. In particular, cavities are present there so that the reaction gas can pass from the bipolar plate 12 into the gas diffusion component 14.

[0057] In another variant not shown here, for example, several sensor elements 40 or optical fibers 42 can be arranged or attached to the carrier layer 50. These are clamped in particular parallel to one another, and preferably parallel to the course of the gas channels 26, and are mechanically stably fixed in the carrier layer 50, extending across the measuring plane 58.

[0058] Within a fuel cell arrangement comprising multiple fuel cell units 10 (not shown here), at least one fuel cell unit 10 can, for example, be configured with at least one sensor element 40 for temperature and / or strain determination in the manner described above. A fuel cell unit 10 is particularly suitable for this purpose in which, due to its arrangement, a comparatively high temperature inhomogeneity naturally occurs, for example, in the first and / or last fuel cell unit 10 after the media enters or exits the fuel cell arrangement.

[0059] In particular for control purposes, a further fuel cell unit 10 can be designed in this way (if necessary additionally), for example a middle one, in which, as a rule, in undisturbed operation, a comparatively uniform temperature distribution prevails.

[0060] In summary, the fuel cell unit 10 according to the invention and the method according to the invention provide comparatively easy-to-implement, detailed diagnostic options. This allows measures to be initiated to maintain and / or restore the long-term stability of the fuel cell unit 10 even before a malfunction of a fuel cell unit and / or fuel cell arrangement occurs, thus extending its service life.

Claims

Claims 1. Fuel cell unit (10) for converting an energy carrier with an oxidizer in a reaction area, in particular via an active surface (32), generating electrical energy, wherein the fuel cell unit (10) comprises as functional components (11) at least two electrodes (15) and an electrolyte (18) arranged between the electrodes (15), characterized in that at least one sensor element (40) designed as an optical waveguide (42) for fiber-optical temperature determination and / or determination of a mechanical deformation within the fuel cell unit (10) is arranged within the at least one fuel cell unit (10).

2. Fuel cell unit (10) according to claim 1, characterized in that the at least one sensor element (40) for spatially resolved, in particular planar, temperature and / or strain determination in the fuel cell unit (10) is arranged in a measuring plane (58), wherein the area of ​​the measuring plane (58) corresponds to at least a large part of the active area (32), at least 50% or more, preferably at least 80% or more, e.g. 100%.

3. Fuel cell unit (10) according to claim 1 or 2, characterized in that the at least one sensor element (40) is designed for measurement with a continuous measurement point sequence, wherein the optical waveguide (42) has a distributed or quasi-continuous measurement point arrangement. Fuel cell unit (10) according to one of the preceding claims, characterized in that the fuel cell unit (10) is designed according to the principle of a polymer electrolyte fuel cell and / or further comprises as functional component(s) at least one, preferably two, bipolar plate(s) (12, 12') and / or at least one, preferably two, gas diffusion component(s) (14, 14'). Fuel cell unit (10) according to one of the preceding claims, characterized in that the at least one sensor element (40) is arranged within the fuel cell unit (10) taking into account a flow field, wherein, in particular, the sensor element (40) runs at least section by section parallel to gas channels (26) and / or the walls bounding the gas channels (26).Fuel cell unit (10) according to any one of the preceding claims, characterized in that the at least one sensor element (40) is arranged on and / or between two functional component(s) of the fuel cell unit (10). Fuel cell unit (10) according to any one of claims 4 to 6, characterized in that the at least one sensor element (40) is arranged on and / or in the gas diffusion component(s) (14, 14'). Fuel cell unit (10) according to claim 6 or 7, characterized in that the at least one sensor element (40) is arranged in a separate carrier layer (50). Fuel cell unit (10) according to claim 8, characterized in that the support layer (50) is arranged between the bipolar plate (12, 12') and the gas diffusion component (14, 14') and / or between the gas diffusion component (14, 14') and the electrode (15, 15'). Fuel cell unit (10) according to claim 8 or 9, characterized in that the support layer (50) has a support structure (54), in particular a rib-like structure, in the measuring plane (58), in which the at least one sensor element (40) is at least partially arranged, and / or that the at least one sensor element (40), in particular several sensor elements (40), are clamped in the support layer, e.g. parallel to each other, extending over the measuring plane (58).Fuel cell unit (10) according to one of claims 8 to 10, characterized in that an outer contour (57), in particular an edge region (56), of the support layer (50) corresponds at least substantially to an outer contour (31), in particular an edge region (30), of the bipolar plate (12, 12'). Fuel cell unit (10) according to claims 8 to 11, characterized in that the support layer (50) consists of or comprises a thermally conductive material, e.g., an aluminum alloy. Fuel cell unit (10) according to any one of claims 8 to 12, characterized in that at least one sealing medium is introduced between the support layer (50) and at least one of the functional components of the fuel cell unit (10), in particular the bipolar plate (12, 12'), through which the at least one sensor element (40) is guided gas-tight into the interior of the fuel cell unit (10). Fuel cell arrangement with at least two fuel cell units (10), wherein at least one of the fuel cell units (10) comprises a sensor element (40) designed as an optical waveguide (42) for fiber-optical temperature determination and / or determination of a mechanical deformation according to any one of the preceding claims.Fuel cell arrangement according to claim 14, wherein the fuel cell unit (10) with a sensor element (40) designed as an optical waveguide (42) for fiber-optical temperature determination and / or determination of a mechanical deformation forms the first and / or last fuel cell unit (10) after media entry / exit into the fuel cell arrangement. Method for operating a fuel cell unit (10) according to any one of claims 1 to 13, in which at least one temperature, preferably a locally two-dimensional temperature field, and / or a mechanical deformation, preferably a strain field, within the fuel cell unit (10) is determined fiber-optically.

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