WO2008040835A1

WO2008040835A1 - Bipolar plate for uniform flow distribution in fuel cells

Info

Publication number: WO2008040835A1
Application number: PCT/ES2007/070167
Authority: WO
Inventors: Felix Barreras Toledo; Antonio Lozano Fantoba; Luís VALIÑO GARCÍA; Carlos MARÍN HERNÁNDEZ
Original assignee: Consejo Superior De Investigaciones Científicas
Priority date: 2006-10-06
Filing date: 2007-10-03
Publication date: 2008-04-10
Also published as: ES2315126B1; WO2008040835B1; ES2315126A1

Abstract

The invention relates to a bipolar plate for distributing the reactant flow over the diffusion layers of a fuel cell, having a cascade geometry (see Figure 1) designed specifically to produce an extremely uniform flow distribution over the catalytic layer. The device enables the flow in the plate to have a velocity and pressure field with high uniformity owing to the novel design in which the inlet channel is branched in the form of a cascade by means of ribs formed by obstacles generally having a greater width than thickness (Figure 2) and separated from one another by a suitable distance. The branching process is inverted from the largest part of the plate and the different flow sections meet to form a single outlet channel.

Description

TITLE

BIPOLAR PLATE FOR HOMOGENIC DISTRIBUTION OF FLOW IN FUEL BATTERIES.

SECTOR OF THE TECHNIQUE

Energy and electrical sectors. Bipolar plates for fuel cells with applications in domestic installations and the automotive industry, among others.

STATE OF THE TECHNIQUE The increasing scarcity of fossil fuels, together with the recent and strict limitations on greenhouse gas emissions imposed by current international commitments, is forcing the search for alternative energy production methods to combustion. As is well known, an interesting possibility in this energy scenario is the use of fuel cells. Fuel cells, first proposed by Sir William R. Grove in 1839, are devices capable of generating electricity from chemical reactions. Its principle of operation is based on the decomposition of the fuel in the anode, thanks to the presence of a catalyst, in electrons and ions. An electrolytic layer separates the anode from the cathode, and allows only the passage of ions through it, preventing electrons from passing through it. When the electronic current is circulated outside the battery, the device acts as an electricity generator. Finally, electrons and ions recombine at the cathode. In the case that the fuel is hydrogen and the oxidizing agent is oxygen, the reaction that occurs in the cathode is the recombination of oxygen, protons and electrons, so that the only products of the reaction are water and heat. Among the advantages of fuel cells, its low level of environmental pollution, its high efficiency and its low noise level stand out. A very useful type of battery for portable applications (laptops, mobile phones, etc.) and automotive transport, since it has a small size and works at low temperatures, is characterized by having a proton exchange membrane as an electrolyte. They are the batteries denominated like of type PEM, according to the acronym coming from the English language.

In a PEM type battery, the fuel (hydrogen or methanol) and oxygen react electrochemically producing electrical energy and heat, and water as Only resulting byproduct. For this transformation to take place, the concurrence of a series of strongly coupled fluid dynamics processes such as biphasic flow dynamics, and heat and mass transfers, which influence the operation of the battery, is required. It is obvious that the optimization of the operation of a PEM battery is a complex study that requires a thorough knowledge of the behavior of the current distribution in the battery depending on the design of the different elements of which it is composed and the operating conditions. With this objective, since the end of the decade of the 90s, a large number of works have been developed, both through numerical simulations [Gurau, V., Liu, H., Kakac, S., Two-dimensional model for proton exchange membrane fuel cells, AIChE Journal, vol. 44 (11): 2410-2422, 1998; Costamagna, P., Transport phenomena in polymeric membrane fuel cells, Chemical Engineering Science, vol. 56: 323-332, 2001; Wang, L., Húsar, A., Zhou, T., Liu, H., A parametric study of PEMFC performance, Int. J. of Hydrogen Energy, vol. 28: 1263-1272, 2003] as experimental [Geiger, AB, Tsukada, A., Lehmann, E., Vontobel, P., Scherer, GG, In situ investigation of two-phase flow patterns in flow fields of PEFCs using neutron radiography, Fuel Cells, vol. 2 (2): 92-98, 2002; Bender, G., Wilson, MS, Zawodzinski, TA, Further refinements in the segmented cell approach to diagnosing performance in polymer electrolyte fuel cells, J. of Power Science, vol. 123: 163-171, 2003; Tüber, K., Pócza, D., Hebling, Ch., Visualization of water buildup in the cathode of a transparent pem fuel cell, J. of Power Science, vol. 124 (2): 403-414, 2003; Mench, MM, Dong, QL, Wang, CY, In situ water distribution measurements in a polymer electrolyte fuel cell, J. of Power Science, vol. 124 (1): 90-98, 2003], highlighting the effort that has been made to understand the influence of water flow on the mass transport of the cell and its production of electrical energy.

An important element of the proton exchange membrane batteries is the bipolar plate, which distributes the flow of fuel and oxidant over the catalyst, provides rigidity to the whole battery, and can act as an outlet for the generated current and dissipate part of the heat produced. The fluids that circulate through the bipolar plates react in the electrodes with catalyst, after passing through a diffuser layer, generally formed by carbon paper or carbon cloth. It is understood that for the cell to function efficiently, the distribution of gases over the catalytic layer must be as homogeneous as possible. Hopefully if the Speed field (and the same can be said for pressure) is not uniform and stagnations or dead zones occur, the battery will not work properly, and its performance will be significantly reduced. Hence the importance of the design of the flow geometry of bipolar plates. Very varied geometries have been tested over the last decade (square, interdigitated, coil, spiral, coil-parallel, etc.), and even the use of porous plates has been tested. A comparative study of various typologies with their advantages and disadvantages can be found in several review articles [Carrette, L., Friedrich, KA, Stimming, U., Fuel cells-fundamentals and applications, Fuel Cells, 1 (1), 5- 39, 2001]. Recently, studies have been carried out using numerical simulations of the interaction of the diffuser layer and the flow circulating through a bipolar plate of meandering channel [Dohle, H., Jung, R., Kimiaie, N., Mergel, J., Müller, M ., Interaction between the diffusion layer and the flow field of polymer electrolyte fuel cells - experiments and numerical simulations, /. of Power Source, 124 (2), 371-384, 2003], and it has been concluded that, in effect, the distribution was not homogeneous. Also recently, it has been studied numerically and experimentally [Barreras, F., Lozano, A., Valiño, L., Marín, C, Pascau, A., Flow distribution in a bipolar piate of a proton exchange membrane fuel cell: experiments and numerical simulation studies, / of Power Sources, 144, 54-66, 2005] the flow structure inside a commercial bipolar plate without diffusion. Given the complexity of the problem in question, normally the fluid field is obtained through studies that do not consider the diffusion of gases through the porous diffuser layer. However, the results obtained through these studies may not be sufficient to ensure the good design of the flow geometry of the bipolar plate. In particular, a geometry that generates a seemingly homogeneous velocity profile, but that introduces very large pressure drops in the circulating flow (as is the case with the geometries of simple or parallel-serpentine coils) can lead to diffusion not homogeneous and, consequently, a bad distribution of gases on the catalyst. For all these reasons, engineers and researchers have tested many particular designs of flow geometries for bipolar plates, and have carefully analyzed the best materials for their construction and the various possible processes for their manufacture. Various patents describe suitable materials such as plate constituents: metals [Douglas, DL, Cairns, EJ., Fuel battery, US Pattent 3,134,696, May 26, 1964], metal oxides [May, B., Hodgson, DR, Bipolar piate for fuel cells, International Patent WO 00/22689, April 20, 2000], carbon / polymer compounds [Lawrence RJ. , Low cost bipolar current collector-separator for electrochemical cells, US Patent 4,214,969, Juy 29, 1980], graphite [Wilkinson, DP, Lamont, GJ., Voss, HH, Schwab, C, Embossed flow field piate for electrochemical fuel cells, International Patent WO 95/16287, June 15, 1995]. Other patents claim specific designs: channels in parallel or coil [Tawfik, H., Hung, Y., Bipolar piate for electrolyte application, International Patent WO 2006/029318 A2, March 16, 2006], devices with channels on both sides [Hanlon , GA, Henderson, G., Electrochemical cell bipolar píate, US Patent US 2006/0068265 Al, March 30, 2006], designs with parallel lines of obstacles preferably in the form of a diamond [Steidle, B., Rensink, D., Bipolar píate channel structure with knobs for the improvement of water management in particular on the cathode side of a fuel cell, US Patent US 2006/0054221 Al, March 16, 2006], etc. However, unlike our invention, none of them analyzes in detail and much less guarantees that the flow of reactants is distributed homogeneously over the electrodes of the cell.

DESCRIPTION OF THE INVENTION Brief description of the invention

The device object of this invention is a bipolar plate for distribution of reagent flow over the diffuser layers of a fuel cell, characterized by a specific design of its geometry in which the fluid is distributed over the active area in a cascade distribution . The flow geometry consists of an input channel that branches into different passages by means of a series of ribs arranged in parallel lines separated from each other with the appropriate distance for each application, and in turn formed by a series of obstacles in a row of variable width in general greater than its thickness (Figure 2) and a separation between them also dependent on each application. Once the central diagonal of the active area is reached, the process is reversed, the number of obstacles in each nerve decreases and the different passages are grouped together to converge in a single exit channel, all encompassed within an area defined by a quadrilateral with diagonals equal or of different dimensions, or by a curved perimeter surface. In the case of bipolar plates square, the inlet and outlet ducts shall be arranged at both ends of a diagonal. The flow direction of the fluid as well as the angle defined by the nerves with the horizontal can be any and will be set according to the specific applications. According to the design and construction criteria, the device can be manufactured by machining, molding or stamping, using metal plates, polymeric compounds (composites), graphite or any other of the materials that are typically used in the manufacture of bipolar plates .

DETAILED DESCRIPTION OF THE INVENTION The present invention responds to the need to adequately and homogeneously distribute, under typical operating conditions, reactant fluids on the catalytic layers of a fuel cell, which, according to the inventors, does not it is achieved with the elements currently available in the market.

The invention is based on the fact that the inventors have observed that the design of the plate of the invention with a cascade geometry allows an extremely homogeneous distribution of reactant fluids over the diffusion or catalytic layers of a fuel cell (see Figures 1 and 2) . In this way, the flow in the plate has a field of speeds and pressures of high uniformity thanks to the novel design, in which the inlet channel is cascaded by parallel ribs, separated from each other by a suitable distance for each application. Each nerve is formed by a row of obstacles of varying width, generally greater than its thickness (see Figure 2), aligned and spaced apart by openings of varying width. Once the central diagonal of the active area is reached, the branching process is reversed from the section of greater area of the plate, and the number of obstacles in each nerve decreases, converging the different sections of passage to give rise to a single channel of exit. All this geometry is encompassed within an area defined by a quadrilateral with equal diagonals or different dimensions, or by a curved perimeter surface.

The device object of the present invention consists of a bipolar plate to be used in fuel cells preferably type PEM. The following concepts are understood within this frame of reference. Thus, "cascade geometry" means the geometry described in the previous paragraph. By "reactant fluids" are meant the oxidant (oxygen or air), and the fuel that can be gaseous (for example, hydrogen) or liquid (for example, methanol in aqueous solution).

"Operating conditions" means the pressures and flow rates of both the fuel fluid and the oxidizing fluid, as well as the way the battery operates.

Normally the bipolar plates used in the cathodes usually work in an open or intermittent regime. In the case of an "open" regime, the gas outlet duct is always open, allowing fresh oxygen to enter the plate at all times. In the case of the "intermittent" regime, by means of a control system, the outlet duct is closed for a given time, causing the cathode to be slightly overpressured, thus allowing the gas to be dragged by the drainage valve The chemical reaction more efficiently. In the case of the anode, if the fuel used is hydrogen, in practical applications always work in a "closed" regime with anode pressures ranging between 2-3 bar. The entry of fuel to the anode is regulated by a control system that checks the value of the pressure, which decreases when hydrogen is consumed by the electrochemical reaction. On the other hand, when using hydrogen as a fuel, it is usually work in an "open" regime only in laboratory conditions, although this way of operating is common, in addition to the "closed" mode, when methanol is used in aqueous solution as fuel.

Therefore, an object of the present invention is a bipolar plate with cascade flow geometry (Figures 1 and 2) that allows the distribution of reactant fluid flow over the diffuser layers or electrodes (anode and cathode) of a cell of fuel, preferably PEM type, hereinafter bipolar plate of the invention, and comprising: a) a flow area of the plate, which coincides with the active area of the electrode, which includes a series of ribs (1), in turn formed by a row of aligned obstacles (2), of varying width (b) generally greater than their thickness (δ), separated from each other by a suitable distance that may be such that all obstacles are equally equally spaced, such that adding the section of total passage in each nerve the result is constant, or any other separation that is considered convenient, depending on the geometry and the specific application, which are arranged within a defined area to by a geometry with diagonals of equal or different dimensions and straight or curved sides, b) an input channel (3) that initially branches into different flow channels or passages (4) by means of the described ribs arranged in parallel lines , and that once the central diagonal of the active area is reached the process is reversed, that is, the number of obstacles in each nerve decreases and the different passages are grouped until they converge in a single exit channel (5), c) Upper (6), lower (7) and lateral (8) channels that delimit the active area.

In this bipolar plate the relationship between the input and output channels is designed in one way or another depending on the geometry of the plate so that the active area is divided symmetrically. The direction of circulation of the reactant fluids will be set according to the specific applications, as well as the angle defined by the direction of the nerves with the horizontal, which in principle can be any, and where the inlet and outlet ducts are arranged perpendicularly to the nerves of the plaque.

A particular object is the bipolar plate of the invention with a geometry of its square or rectangular transverse active area, where the inlet (3) and outlet (5) ducts will be arranged at the two opposite ends of the same diagonal (see Figure X).

Another particular object is a bipolar plate of the invention with a geometry of its curved perimeter active area, preferably an elliptical or round bipolar plate (see Figure 3), where the inlet and outlet ducts will be located in the line perpendicular to the nerves, so that it divides the active area symmetrically.

Another particular object is a bipolar plate of the invention in which the outlet ducts comprise a control valve to be able to work in an intermittent opening and closing mode.

As described above, an alternative is a PEM type fuel cell where the fuel is a liquid, for example, methanol in aqueous solution. In this case and due to the generation of CO ₂ bubbles by chemical reaction In the catalytic layer of the anode, the bipolar plate of the invention used in these electrodes should be designed in such a way as to allow optimum extraction of these bubbles. This new variant would include a channel that acts as a collector where CO ₂ bubbles will migrate due to the difference in densities. Therefore, the width of this channel will be sized by the flow rate to be handled and the battery power, which defines the amount of gas produced.

Thus, a particular object of the invention is a bipolar plate in which there is an upper channel (6) that surrounds the horizontally located flow area with respect to the inlet conduit and small gas evacuation holes (9) that communicate the upper channel (6) with an additional manifold (10) that will have a gas vent valve (11) with pressure control, as shown in Figure 4 a). A particular embodiment is a bipolar plate in which the entire flow area of the bipolar plate is rotated at any angle (α), preferably between 5-25 °, with respect to the outer edges of the plate, as shown in the Figure 4 b). In this case, the ribs that define the passage channels will form an angle (45-α) ° with respect to the horizontal edge and the upper channel an angle α with respect to the same edge. In turn, methanol will enter the plate through the lower hole (3) and out through the upper one so that if CO ₂ bubbles are formed, these will float to the highest point, which is the exit hole (5), facilitating the extraction of biphasic flow through it.

If bipolar plates with this cascade flow geometry are used in the cathodes, the situation will be analogous, that is, drops of water are produced that must be removed from the battery. Thus, a particular object of the invention is a bipolar plate in which there is a lower channel (7) with a series of channels (12) that surrounds the horizontally located flow area with respect to the outlet duct and acts as a collector where they will migrate, due to the difference in densities, the drops of water generated by chemical reaction and will be extracted when dragged by the flow of air or oxygen (see Figure 5 a). Another particular embodiment is a bipolar plate in which the entire flow area of the bipolar plate is inclined at any angle (β), preferably between 5-25 °, with respect to the outer edges of the plate, as can be seen in Figure 5 b), and where a flow of oxygen or descending air will be imposed on the plate. In this way, the water drainage flow, facilitated by gravity, is It will produce through the outlet duct itself (5) which, obviously, will be conveniently sized to allow water and oxygen / air to escape.

As is known, in general in most practical applications several monocells are usually grouped together forming a stack to increase the power delivered by the device and for which the arrangement of the bipolar plate of the invention must be adapted so that The bipolar plate has flow geometries on both sides, one for the cathode of one of the monocells and another for the anode of the next. Thus, a particular object of the present invention is a bipolar plate that presents the design of cascading channels on one of its faces, while the opposite face has the same design in which the rows of obstacles are aligned perpendicularly to those arranged on the first face so that the input and output channels corresponding to the first face and those corresponding to the second face are located at the ends of the opposite diagonals of the plate (Figure 6 a).

Also, and in the case that several monocells are grouped in series forming a stack, the fluids are supplied centrally to all bipolar plates of the different monocells through a single collector. Therefore, another particular embodiment of the present invention is a bipolar plate with flow geometries on both sides where the arrangement of the inlet and outlet ducts have any angle (γ), preferably between 5-40 ° with respect to the plane It contains the active surface of the plate, as shown in Figures 6 a) and 6 b). The definition of the value of this angle will also depend on the depth of the nerves, so that the diameter of the inlet (3) and outlet (5) ducts within the active area is less than or equal to the depth of the channels.

Another particular embodiment of the present invention is the bipolar plate of the invention if used as end plates ("end-plates", according to English literature). These plates will have flow geometries on only one of the faces, serving as an anode or cathode, respectively, similar to those used in monocells.

Also, these plates are characterized in that they can have an opening in the central plane, parallel to the faces of the flow geometries by which they can (or not) circulate a fluid (air, water, etc.) that will be used as a method of cooling the system, helping to extract heat.

As previously mentioned, the manufacturing techniques of a bipolar plate for fuel cells is well established in the state of the art, whereby the bipolar plate of the invention can be manufactured, by way of illustration and without limiting the scope of the invention. , by machining, molding or stamping; using different starting materials such as metals, metal oxides, polymeric compounds (composites), graphite or any other of the materials.

Finally, another object of the invention is the use of the bipolar plate of the invention for the manufacture of a fuel cell, preferably a PEM type battery, which can also be used in flat oxide-solid batteries and alkaline batteries.

BRIEF DESCRIPTION OF THE CONTENT OF THE FIGURES

Figure L- Photo of a prototype of bipolar machined plate with cascade geometry in methacrylate and polished to facilitate its study. In this case study, the active area is 49 cm ² , with the plate counting 32 nerves 1 mm thick and 2 mm deep.

Figure 2.- Diagram of a front view of a bipolar plate with cascade flow geometry and with a square cross section. (1) nerves of variable length, (2) obstacles of variable length, (3) fluid inlet channel, (4) variable width passage channels, (5) output channel, (6) upper channel (manifold) , (7) lower channel, (8) lateral channels, (b) width of the nerves and (δ) thickness of the nerves.

Figure 3.- Front view of a bipolar plate with cascade flow geometry and circular cross section. In this configuration, the inlet and outlet ducts will be placed perpendicular to the nerves that make up the fluid passageways. Figure 4.- Two configurations of bipolar plates with cascade flow geometry to be used in anodes of PEM type batteries that use direct methanol as fuel: a) without rotating, b) rotated an angle α with respect to the horizontal outer edge. The numbers 3) to 8) represent the same elements of Figure 2; 9) gas evacuation holes, 10) additional manifold, 11) vent valve with pressure regulation.

Figure 5.- Two configurations of bipolar plates with cascade flow geometry to be used in the cathodes of PEM type batteries: a) without rotating, b) rotated an angle β with respect to the horizontal outer edge. The numbers 3) to 7) represent the same elements of Figure 2; 12) water drain holes.

Figure 6.- Bipolar plate to be used in case of stacked monocells in a stack, which shows the flow geometry (nerves) on both sides, as well as the angle (γ) of the input and output channels: a) isometric; b) lateral views corresponding to the cuts in the planes of the two main diagonals in a): A-A anode face, B-B cathode face.

Figure 7.- Results of the numerical simulation of the flow distribution in the bipolar plate with cascade geometry: a) velocity field and b) pressure field.

Figure 8.- Temporal evolution of the diffusion of gases behind the Toray ™ paper (diffuser layer): a) 0.5 seconds after starting the experiment, b) 2 seconds, c) 4 seconds, and d) stationary condition (t »5 s after the experiment started).

EXAMPLE OF REALIZATION OF THE OBJECT OF THE INVENTION

The example described below should not be understood only as a limitation of the scope of the invention. On the contrary, the present invention seeks to cover all alternatives, variants, modifications and equivalences that may be included within the spirit and scope of the object of the invention. The bipolar plate of the present invention described in this example has external dimensions of 70 x 70 mm. The active area is 49 cm and has 32 nerves 1 mm thick and 2 mm deep. It has been carried out in methacrylate by machining, and polishing with abrasive polishing liquid to facilitate its study. The input and output channels, located at opposite vertices as seen in Figure 1, have an internal diameter of 2 mm. The four lateral channels parallel to the sides of the rhombus that delimits the surface on which the nerves are located have a width of 2 mm, the same as the separation between the parallel rows of nerves. Within each nerve the obstacles have been separated so that the total fluid passage section is constant and equal to that of the inlet channel, thus preventing local fluid acceleration. All channels have a depth of 1 mm.

The characteristics of the flow when a fluid circulates in this plate have been studied experimentally and by numerical simulations. The specific geometry of this design must ensure that, in addition to a homogeneous distribution of the velocity field, the pressure drop produced by the arrangement of the channels is also homogeneous.

During the study using computational simulations, an isothermal, incompressible and laminar flow has been considered, obtaining a final steady-state solution, conditions that coincide with the real experimental conditions in the laboratory, when it is considered excess flow. The equations used to simulate the process are those of Navier-Stokes for the conservation of mass and the amount of movement. Given the simple geometry of the problem, their solution has been obtained by discretizing them using the finite volume method. To improve the speed-pressure coupling in these equations, a decayed Cartesian mesh has been used, which was implemented numerically using the SIMPLE algorithm. Finally, to perform the iterative solution of the resulting linear equation system, a conjugate gradient technique has been applied. Although the actual flow is stationary, the numerical scheme requires an initial condition to begin the simulation. Therefore, a very small constant speed (in module) and equal for all channels has been imposed as the initial condition of the process. This numerical value has been selected so that the condition of conservation of the mass was satisfied. The results obtained are shown in Figures 7 a) and 7 b). Indeed, it can be seen that the distribution of velocities that is obtained throughout the active area is very homogeneous without there being also large pressure gradients. With these results, it is predictable that the distribution of gases over the catalytic layers is also very homogeneous, thus guaranteeing the proper functioning of the fuel cell.

To verify that, indeed, the fluid is distributed homogeneously after passing through a diffuser layer, the bipolar plate has been covered with a sheet of carbon paper (Toray ™), which is one of the diffusion layers most used in commercial PEM batteries. In order to visualize the diffusion of the flow through the diffuser layer, the laser-induced planar fluorescence technique has been used. To apply it, a stream of air seeded with acetone vapor has been circulated through the plate. Sowing has been done by previously passing the air through a bubbler containing liquid acetone. To induce fluorescence, the emergent flow through the diffuser layer has been illuminated with ultraviolet radiation (λ = 266 nm) of a pulsed laser of Nd: YAG, with an energy of about 70 mJ / pulse, formed in a plane parallel to the diffuser layer and separated from it at a distance of 2 mm. Fluorescent emission has been recorded with a CCD camera with a 1024x1024 pixel matrix. Sequences of 10 images separated from each other 0.5 seconds have been acquired. The plane of light 8 cm high and 0.5 mm thick in the image area was formed using three cylindrical lenses of amorphous quartz.

The results of Figure 8 show a sequence of images of the diffusion through the diffuser layer during the process of filling the bipolar plate with the mixture of air and 20% acetone vapor, with a flow rate of 1 , 5 1 / min. In particular, the images shown correspond to time intervals of 0.5, 2, 4 and much greater than 5 seconds (stationary condition) after the fluid circulation has begun, respectively.

As you can see, as the area of the plate is filled with the fluid, it is distributed with a very flat and homogeneous front (a). Subsequently, the flow covers the entire active area without observing more intense lighting zones which would denote an excessive pressure gradient in that region (b, c). Finally, once the steady state (d) is reached and it is guaranteed that the entire plate area is full of fluid, a completely homogeneous distribution of the gas diffuses behind the diffuser layer.

It is confirmed with these studies that the particular design of the plate, object of the present invention, produces a homogeneous distribution of reagents on the catalytic layer of a PEM cell, as claimed.

Claims

1. Bipolar plate with cascade flow geometry (Figures 1 and 2) that allows the distribution of reactant fluid flow over the diffuser layers or electrodes (anode and electrode) of a fuel cell, preferably PEM type, hereinafter bipolar plate of the invention, and comprising: a) a flow area of the plate, which coincides with the active area of the electrode, which includes a series of ribs (1), in turn formed by a row of aligned obstacles (2), of variable width (b), generally greater than its thickness (δ), separated from each other by a suitable distance that may be such that all obstacles are equally equally spaced, such that by adding the total passage section in each nerve the result is constant, or any other separation that is considered convenient, depending on the specific geometry and application, which are arranged within an area defined by a geometry with diagonals of equals or differ The dimensions and sides are straight or curved, b) an input channel (3) that initially branches into different flow channels or passages (4) by means of the described ribs arranged in parallel lines, and that once the The central diagonal of the active area the process is reversed, that is, the number of obstacles in each nerve decreases and the different passages are grouped together to converge into a single exit channel (5), c) Some upper (6), lower ( 7) and lateral (8) that delimit the active area.

The design of the input and output channels depends on the geometry of the plate, so that the active area is symmetrical. The geometry can be transverse square, rectangular or curved perimeter.

The direction of circulation of the reactant fluids and the angle defined by the direction of the nerves with the horizontal can be any and will be set according to the specific applications of use of the plate and where in addition, the input and output channels will be arranged perpendicular to the nerves that make up the flow channels.

2. Bipolar plate according to claim 1 characterized in that the transverse geometry of its active area is square or rectangular and that the inlet and outlet ducts are located on opposite diagonals coinciding on the same line.

3. Bipolar plate according to claim 1 characterized in that the geometry of its active area is curved perimeter, preferably round or elliptical, (Figure 3) and because the inlet and outlet ducts are located perpendicular to the nerves.

4. Bipolar plate according to claims 1 to 3, characterized in that in the case of being used in anodes using direct methanol as fuel, the upper channel (6) that surrounds the flow area and located horizontally with respect to the inlet duct, has about small holes for evacuation of gases (9) communicated with an additional manifold (10) have a valve for venting gases (11) with pressure control to evacuate the _CO2 generated by the reaction (Figure 4).

5. Bipolar plate according to claims 1 to 4 characterized in that the entire flow area will be rotated at any angle (α), preferably between 5-25 °, with respect to the outer edges of the plate (Figure 4b), so that the nerves that define the passage channels will form an angle (45-α) ° with respect to the horizontal edge, and in which methanol will enter the plate through the lower hole (3) and exit through the upper one (5) so that it drags CO ₂ bubbles deposited by flotation in the upper channel (6), thus facilitating the extraction of the biphasic flow.

6. Bipolar plate according to claims 1 to 3 characterized in that in the case of being used in the cathodes, the lower channel (7) acts as a collector where the water droplets generated by chemical reaction will migrate due to the difference in densities and which will be extracted through a series of channels (12), when carried by the air flow of air or O ₂ (Figure 5 a).

7. Bipolar plate according to claims 1, 2, 3 and 6 characterized in that the entire flow area will be rotated at any angle (β), preferably between 5-25 °, with respect to the outer edges of the plate (Figure 5 b) of so that the nerves that define the passageways will form an angle (45-β) ° with respect to the horizontal edge, and in which the gas will enter the plate through the upper hole (3) and out through the lower one so that the water formed will tend to go to the point lower (5), facilitating the extraction of biphasic flow through it.

8. Bipolar plate according to claims 1 to 7 characterized in that in case of grouping together forming a stack, it will have flow geometries on both sides, one for the cathode of one of the monocells and another for the anode of the next (Figures 6 a) and 6 b).

9. Bipolar plate according to claims 1 to 8, characterized in that the rows of obstacles of one face are oriented perpendicularly to those of the opposite face and, with the corresponding entry and exit holes located on each face on the diagonal perpendicular to the ribs.

10. Bipolar plate according to claims 1 to 9 characterized in that the reactant fluids are supplied centrally through a single collector to all bipolar plates of the different monocells.

11. Bipolar plate according to claims 1 to 10 characterized in that the inlet and outlet ducts have any angle (γ), preferably between 5-40 ° with respect to the plane containing the active surface of the plate that will depend on the depth of the nerves, so that the diameter of the ducts within the active area (5, 6) is equal to or less than the depth of the channels.

12. Bipolar plate according to claims 1 to 11, characterized in that in the case of end-plates, they will have flow geometries on only one of the faces, serving as an anode or cathode respectively, similar to those used in monocells.

13. Bipolar plate according to claims 1 to 12 characterized in that it can have an opening in the central plane parallel to the faces of the flow geometry, through which a fluid (air, water, etc.) that can be circulated (or not) It will be used as a method of cooling the system, helping to extract heat.

14. Bipolar plate according to claims 1 to 13 characterized in that it comprises a control valve to be able to work in intermittent opening and closing regime.

15. Use of the bipolar plate according to claims 1 to 14 for the manufacture of a fuel cell, preferably a PEM cell, and also flat and alkaline solid oxide batteries.