Convective flow field for a fuel cell stack

Abstract

Flow field plate (1) for a fuel cell comprising: a main surface for the distribution of a reactant; a reactant opening (3, 5) for the inlet of the reactant; a reactant opening (4, 5) for the outlet of the reactant;and a flow field for the reactant, which is formed in the main surface of the plate (1), wherein the inlet of the flow field for the reactant is fluidically connected to the inlet-reactant opening (3, 5), wherein the outlet of the flow field for the reactant is fluidically connected to the outlet-reactant opening (4, 5), wherein the flow field for the reactant comprises a parallel channel region (7) which includes a plurality of parallel channels (8) and webs (9) separating the channels, and wherein the parallel channel region (7) includes at least one projection region (10), wherein the plurality of the parallel channels (8) includes a plurality of projections (2a, 2b) which impede the flow in the channels (8); wherein the projections (2a, 2b) in each channel (8) in the projection region (10) are arranged in a sequence along the length of each channel;and the continuous projections (2a, 2b) in any given channel (8) in the projection region (10) along the length of the channel (8) are offset with respect to the continuous projections (2a, 2b) in the channels (8) which are immediately adjacent to the arbitrary given channel (8); and wherein the sequence is regular but not periodic, and wherein the distances between the projections (2a, 2b) are harmonics of a shortest distance.;

Description

BACKGROUND Area of ​​the invention

[0001] The invention relates to embodiments of flow field plates for solid polymer electrolyte fuel cells. Description of the related prior art

[0002] Solid-state polymer electrolyte or proton exchange membrane fuel cells (PEMFCs) electrochemically convert reactants, namely a fuel (such as hydrogen) and an oxidant (such as oxygen or air), to generate electrical power. PEMFCs generally use a proton-conducting polymer electrolyte membrane between two electrodes, namely a cathode and an anode. A structure comprising a proton-conducting polymer membrane positioned between two electrodes is called a membrane electrode assembly (MEA).In a typical fuel cell, each side of a MEA (Mechanical Energy Exchanger) has an anodic flow field plate and a cathodic flow field plate, each with numerous distribution channels for the reactants. These channels distribute the fuel and oxidant to the respective electrodes and remove byproducts of the electrochemical reactions occurring within the fuel cell. Water is the primary byproduct in a cell operating with hydrogen and air as reactants. Since the output voltage of a single cell is on the order of 1 V, multiple cells are typically stacked in series for commercial applications. In such a stack, the anodic flow field plate of one cell is adjacent to the cathodic flow field plate of the next cell.For assembly purposes, a set of anodic flow field plates is often connected to a corresponding set of cathodic flow field plates before the stack is assembled. A connected pair of anodic and cathodic flow field plates is called a bipolar plate array. In some embodiments, bipolar plates can be made from a single piece of material (for example, carbon) in which the cathodic and anodic flow fields are formed on opposite sides of the material. Fuel cell stacks can also be connected in series or parallel in groups of interconnected stacks for use in automotive applications and the like.

[0003] Along with water, heat is a significant byproduct of the electrochemical reactions that take place within the fuel cell. Therefore, means of cooling a fuel cell stack are generally required. Stacks designed to achieve high power density (for example, stacks for automotive applications) typically circulate a liquid coolant through the stack to dissipate heat quickly and efficiently. To achieve this, coolant flow fields, comprising numerous coolant channels, are typically integrated into the electrochemically inactive surfaces of the flow field plates of the cells within the stack (that is, the coolant flow field is located within the bipolar plate array).To supply both the reactants and the coolant to and from the individual cells in the stack, rows of openings are generally provided at opposite ends of each cell, forming manifolds for these fluids when the cells are stacked. Further necessary design features include passages in the plates to distribute the bulk of the fluids in these manifolds to and from the various channels within the plate's reactant and coolant flow fields. These passages are referred to as transition zones. The transition zones themselves may contain numerous distribution channels for a fluid, for example, transition channels for oxidizer and / or fuel.

[0004] Although this seems simple enough in principle, achieving the desired distribution of reactants across the electrodes and the desired removal of byproducts from them in high-power-density fuel cell designs is nonetheless quite complex, and many factors must be considered. For example, the struts that separate the distribution channels for a fluid in typical flow field plates provide mechanical support and therefore cannot be too thin. However, the distribution of gases to and from these areas in the gas diffusion layers directly adjacent to the struts is not as efficient as in those areas directly adjacent to the channels.

[0005] Another factor to consider is that the composition of the supplied reaction gases changes considerably as they flow through a fuel cell of practical size. As reactants are consumed and byproducts in the form of gaseous and liquid water are produced, the composition of these gases changes significantly, and designs must be incorporated to accommodate this changing nature.

[0006] Considerable effort has been invested in improving the distribution of gases to and from the electrodes of a fuel cell and in understanding the details of the flow within such fuel cell stacks. For example, convective flow in gas diffusion layers and various flow field configurations has been discussed in publications such as CY Soong et al., “Analysis of reactant gas transport in a PEM fuel cell with partially blocked fuel flow channels”, Journal of Power Sources, 143 (2005) 36–47; and T. Kanezaki et al., “Cross-leakage flow between adjacent flow channels in PEM fuel cells”, Journal of Power Sources, 162 (2006) 415–425.

[0007] In particular, designs were considered that incorporate protrusions or similar features in the flow field channels, offering various advantages. For example, JP2004241141 incorporates protrusions within the gas channels, and turbulence occurs in the reaction gas, which spreads with an effect that improves the generation of electrical current. In document US 20040151973, throttle orifices are strategically placed in the flow field channels to achieve specific desired pressure differentials. Furthermore, JP2004327162 effectively incorporates throttles to maintain a more uniform surface pressure within the cells.

[0008] However, although such designs may offer modest advantages for gas distribution or other purposes under certain operating conditions, there remains a need for improved distribution of reaction gases under other and different operating conditions. The invention addresses such issues and provides further related advantages. Summary

[0009] It has been found that certain organized arrangements of protrusions in the flow field channels of such fuel cells can provide better control of the crossflow achieved in the gas diffusion layers adjacent to the flow field plate's struts. With this improved control, the overall concentrations of reactants adjacent to and below the struts can be increased, and byproducts can be removed more efficiently. Consequently, the fuel cell's performance can be further enhanced.

[0010] The flow field plate for such a solid-state electrolyte fuel cell comprises a main surface for reactant distribution, a reactant inlet, a reactant outlet, and a reactant flow field formed within the main surface of the plate. The inlet of the reactant flow field is fluidically connected to the inlet reactant opening, and the outlet of the reactant flow field is fluidically connected to the outlet reactant opening. The reactant flow field includes a parallel channel region comprising a plurality of essentially parallel channels and struts separating the channels.The parallel channel area itself includes a protrusion area in which the majority of the parallel channels comprise a majority of arranged protrusions that impede the flow in the channels.

[0011] Specifically, the projections in each channel in the projection area are arranged in a sequence along the length of each channel, and the continuous projections in any given channel in the projection area are offset along the length of the channel with respect to the continuous projections in the channels which are immediately adjacent to the given channel.

[0012] The parallel channels in the parallel channel region are parallel curves, but in particular, they are essentially linear. Furthermore, a periodic sequence may be preferred, although various sequences are conceivable. And although various offsets are conceivable, for symmetry purposes, it may be preferred that the periodic protrusions in any given channel in the protrusion region are offset by substantially half a period with respect to the periodic protrusions in the channels immediately adjacent to the given channel.

[0013] The invention is suitable for use in embodiments of flow field plates in which the parallel channel region occupies the largest part of the main surface of the flow field plate (i.e., more than 50%) and in which the projection region occupies the largest part of the parallel channel region (i.e., more than 50%). The invention is particularly suitable for use in embodiments of flow field plates for an oxidizing agent in which the reactant is an oxidizing agent.

[0014] In certain embodiments, the protrusion area can be incorporated in such a way that it does not occupy the area of ​​the flow field for the reactant which borders the inlet of the flow field for the reactant in which, during normal operation, the oxygen concentration is greater than 50% or, alternatively, in which the relative humidity is less than 100% during normal operation.

[0015] Numerous shapes and sizes can be considered for the projections, and they need not be constant across the sequence. In other words, one dimension of the projections can vary across the sequence and, for example, be wider adjacent to the outlet of the flow field for the reactant than adjacent to the inlet of the flow field for the reactant. In other embodiments, the dimensions of the projections can be essentially constant across the sequence.

[0016] Modeling has shown that advantages can be expected in applied solid-polymer electrolyte fuel cells with dimensions suitable for automotive applications, which incorporate protrusions according to the invention. In particular, advantages can be expected for embodiments that have one or more of the following features: a period of the protrusions arranged in each channel within the protrusion area of ​​approximately 20 to 30 mm, protrusions that occupy approximately 0.4 to 0.6 times the depth of the channel, protrusions that occupy the width of the channel, protrusions with a length of approximately 1 to 2 mm, and widths of the webs in the flow field plate that are greater than 0.3 mm.

[0017] The invention provides a method for improving the distribution of reactants in a solid-polymer fuel cell, and in particular the convective flow in gas diffusion layers therein. A better distribution of the reactants with greater control than certain prior art embodiments can be achieved. These and other aspects of the invention are evident with reference to the attached figures and the following detailed description. Brief description of the drawings

[0018] Fig. Figure 1a shows a schematic representation of a flow field plate for a solid polymer electrolyte fuel cell, which has protrusions in a periodic sequence in the parallel linear flow field channels of the plate.

[0019] Fig. Figure 1b shows a schematic representation of a flow field plate, which corresponds to the one described by Fig. 1a is similar, except that the projections are arranged in a non-periodic sequence.

[0020] Fig. Figure 1c shows a schematic representation of a cross-section along a flow field plate similar to the section along AA in Fig. 1a, except that the dimension in the height of the projections extending from the bottoms of the canals varies along the length of the canals.

[0021] Fig. Figure 2a shows a schematic representation of the simplified model in the examples with two half channels and a bridge between them and further shows the velocity vectors of the reactant in the GDL for an exemplary flow of gas in the channels.

[0022] Fig. Figure 2b shows the calculated, expected contours of oxygen mole fractions in the channels and under the bridge in the GDL at specific locations in the simplified model of Fig. 2a, if no projections were incorporated into the channels.

[0023] Fig. Figure 2c shows the calculated expected contours of oxygen mole fractions in and under the bridge in the GDL at specific locations in the simplified model of Fig. 2a, if the protrusions were present in the channels.

[0024] Fig. Figure 3 shows graphical representations of the cell voltage versus the concentration of oxygen at the inlet at several current densities for two embodiments of fuel cells which have protrusions of different sizes, and compares these with graphical representations of a comparative fuel cell with no protrusions. Detailed description

[0025] The following definitions were used here.

[0026] "Parallel" describes a curve that is offset from a base curve by a constant amount and is thus considered equidistant from it. Every normal to such a curve is also a normal to the base curve. In this case, a channel is essentially parallel to another channel if the fundamental and new properties of the channels do not fundamentally differ from those of actual channels shaped like parallel curves.

[0027] In a quantitative context, the expression “approximately” can be interpreted as being in the range of up to plus 10% and up to minus 10%.

[0028] “Normal operation” refers to the operation of a fuel cell within its nominal operating ranges (current density, temperature).

[0029] The invention is particularly useful for increasing the concentration of reactants in the gas diffusion layers and removing reaction products from them, which are located directly adjacent to and below the areas of the webs in flow field plates of typical solid polymer electrolyte fuel cells.

[0030] Fig. Figure 1a shows a schematic representation of a flow field plate. 1 for an oxidant for a typical solid-state polymer electrolyte fuel cell for automotive applications. The flow field plate 1 is of ordinary design, except that it has protrusions 2a , 2b according to the invention. As in Fig. As shown in 1a, the flow field plate comprises 1 an inlet opening 3 for an oxidizing agent, an outlet opening 4 for the oxidizing agent and other openings 5for the inlet and outlet of fuel and coolant. A flow field. 6 The oxidizing agent is located in the depicted surface of the plate. 1 trained and includes a parallel channel area 7 , which has a plurality of parallel channels 8 for the oxidizing agent, which includes bridges 9 are separated from each other. (For the sake of clarity, the schematic representation of Fig. 1a only three channels 8 and two footbridges 9 as shown. In actual embodiments, there would probably be an order of magnitude more channels and webs. As shown in Fig. The flow field is shown in 1a. 6 The flow field is essentially formed entirely of parallel channels and bridges for the oxidizing agent. 6 Essentially the same as the parallel channel area 7and occupies more than 50% of the surface of the plate 1 one. In other embodiments, the flow field can 6 additional areas with different flow field structures are included.

[0031] Parallel, linear channels 8 of the flow field in the plate 1 This also includes the protrusions. 2a , 2b , which are arranged in a periodic sequence and extend over a projection area 10 extend. Where present, the projections have sufficient height to create local pressure gradients by obstructing the flow of gas; for example, the heights of the projections are greater than about 1 / 4 the depth of the channel. As shown, the projections are 2a , 2b from an area near the inlet opening 3 absent for the oxidizing agent, but on the other hand they appear along the length of the channels 8on. Thus, the lead area extends 10 here from the projection which is the inlet opening 3 nearest to the end of the parallel channel area 10 and thus occupies more than 50% of the parallel channel area 7 a.

[0032] As shown, the advantages are 2a and 2b in a periodic sequence along the length of the channels 8 arranged (that is, they are spaced apart by a constant distance, where this distance is the period). And the periodic projections 2b in their associated channel are offset by essentially half a period with respect to the periodic protrusions 2a in the immediately adjacent canals.

[0033] Although the periodic sequence of the embodiment is determined by the Fig. 1a. By giving the design of the flow field plate and the transverse flows of gas in the GDL a desired symmetry, the composition of the gases and their velocities change as they traverse the length of the flow field plate from the inlet to the outlet, due to the electrochemical reactions that take place therein. In a certain case, it may be preferable to use a sequence of protrusions that is regular but not periodic (for example, where the spacings are harmonics of the shortest distance or even other alternative sequences). For example, shows Fig. 1b an alternative schematic embodiment of a flow field plate, which is the one described by Fig. 1a is similar, except that the projections are arranged in a non-periodic sequence (certain projections were placed at the inlet). 3the next one is omitted, and so the distances are not constant, but they are harmonics).

[0034] The introduction of the advantages 2a , 2b into the canals 8The convection is enhanced by introducing repeated local pressure gradients between adjacent channels, resulting from the gas flow restrictions created by the periodic protrusions. A comparatively small fraction of the flow in one channel can be forced through the adjacent gas flow channel (GDL) under the bridge to a neighboring channel. The protrusions increase convection in the GDL, thereby increasing the reactant concentration under the bridge and also the pressure drop in the channel. Efficiency can be improved by removing water vapor (and possibly liquid water) from the GDL, while delivering a higher concentration of oxidant to the catalyst layer. However, excessive flow from channel to channel can cause drying and / or locally high reactant concentrations.Optimizing the design of the projections thus creates a conflict of objectives between convection under the bridge, the pressure drop in the canal, and water management.

[0035] Regarding design considerations, the lateral velocity v in the GDL can be estimated using Darcy's law. ν = k μ ΔP w where: k = the permeability in the plane ΔP = the pressure gradient between two adjacent channels μ = the viscosity of the fluid w = the width of the bridge.

[0036] The fluid velocity in the GDL therefore depends on specific design parameters of the flow field and the GDL itself. For a given fluid viscosity, the velocity can be increased by increasing the pressure gradient or the permeability in the plane, or by decreasing the width of the rib. Those skilled in the art will recognize that, although it is simple in principle to increase convection in the GDL with a wide range of rib designs, the size, number, and spacing of the ribs should be chosen to achieve improved convection under an equilibrium of the key conditions. Numerous parameters must be considered for a given set of conditions. And, as revealed in the following examples, a rib design may be preferable for one set of operating parameters, while being comparatively poor under another set of operating conditions.In summary, a different design may be preferable to achieve an improvement under a balance of operating conditions rather than under any specific operating condition. Although complex, suitable considerations and the necessary calculations can be expected from a person skilled in the art. The examples below provide a useful guide in this regard.

[0037] In general, the distance (or period in Fig. 1a) The gaps between the projections must be sufficiently large to prevent strong lateral impacts, without being so large that they lack a transverse effect over most of the length of the channel. Furthermore, various shapes may be considered for the projections, but a streamlined design is advantageous to avoid flow splitting and turbulence behind the projections. For ease of manufacture, the width of the projections may be chosen to be the full width of the channel.

[0038] Since the inlet area of ​​fuel cells is relatively dry, it can be particularly advantageous to avoid incorporating any protrusions at all. For example, it may be preferable to omit protrusions in the area of ​​the reactant flow field near the inlet where the oxygen concentration is greater than 15% during normal operation, or alternatively, where the relative humidity is less than 100% during normal operation.

[0039] However, at the opposite end of the fuel cell, comparatively more liquid water is expected near the outlet than in most of the flow field, and higher gas velocities can be expected to be permissible or even preferred. Therefore, the protrusions can be designed to present a greater obstacle near the outlet, and can thus have larger dimensions, and / or more protrusions can be used.

[0040] The design of protrusions for a fuel cell, with no protrusions in the inlet area and with more obstructive protrusions in the outlet area, is exemplified in the schematic representation of Fig. 1c shown. Fig. Figure 1c shows a cross-section along a channel of a flow field plate, corresponding to the section AA along a section in Fig. 1a is similar, except that the dimension in the height of the projections varies along the length of the channel. Specifically, there are no projections near the inlet area, and also projections 2bb The protrusions near the outlet are larger in height than the ledges. 2b in the middle of the canal 8 .

[0041] Other embodiments than those described in the Fig. 1a to Fig. The methods shown in Figure 1c can of course be taken into consideration in order to obtain the benefits of the invention.

[0042] The following examples illustrate the invention, but should not be considered restrictive in any way. Examples

[0043] The velocity vectors for the flow of the oxidant under the struts in the gas diffusion layer (GDL) for the oxidant in an exemplary solid-polymer electrolyte fuel cell according to the invention were calculated on the basis of the simplified model, which is schematically shown in Fig. Figure 2a shows the exemplary fuel cell of a conventional design, using a flow field for the oxidant comprising numerous parallel linear channels. However, in this case, the channels also included staggered periodic sequences of protrusions along their length.

[0044] The simplified model comprises two channels, each with the same depth as a conventional channel (0.52 mm deep) but only half the width (i.e., half of 0.49 mm or 0.245 mm wide), separated by a single 0.5 mm wide web. Within each channel, the protrusions were periodically spaced 22.8 mm apart, but the protrusions in one channel were offset from those in the other by half a period. The protrusions were 1.5 mm long, as wide as the channel, and occupied half the channel depth (i.e., 0.26 mm). Based on symmetry, the simplified model should therefore be expected to achieve approximately equal flow velocities under all webs in the GDL for the exemplary fuel cell.

[0045] Fig. Figure 2a shows a section of the model over only one period of the protrusions. The model comprises two half-channels. 21 , a footbridge22 and protrusions 23 in each of the half channels 21 Representative velocity vectors 25 for the flow of the oxidizing agent under the bridges into the GDL are in Fig. 2a also shown.

[0046] In the exemplary embodiment, the thickness of the GDL was 0.18 mm and the permeability in the plane of the GDL under the web was 1.9 × 10 –12 m 2 The supply air was assumed to be the oxidizing agent, which has a density of 2.4 kg / m³. 3 at 60°C.

[0047] Representative velocity vectors for the flow of the oxidizing agent into the GDL under the bridge were then calculated for this model when air, which is guided by an arrow 24 This illustrates each half-channel from the left in Fig. 2a is supplied at a typical average velocity of 10 m / s. Fluid dynamics software (STAR-CCM+) was used for the calculations. Fig. 2a presents these calculated representative velocity vectors. 25 The magnitude of each velocity vector. 25 can be determined by comparing its length with the scale which is in Fig. 2a is given. The estimated average lateral velocity in the GDL under the bridge was determined to be approximately 3 cm / s. (Note: the model was not corrected for porosity.)

[0048] However, in a conventional fuel cell without protrusions in the flow field channels, significant net crossflows of the oxidant in the GDL under the protrusions would only be expected if / when droplets of liquid water happen to form in the channels. Therefore, incorporating protrusions into the channels in this specific periodic sequence is expected to lead to a significant change in the lateral flow into the GDL under the protrusions.

[0049] Representative, expected molar fractions of oxygen were then calculated for the model in the channels and under the walkways in the GDL (Ground Flow Area). For comparison purposes, calculations were also performed for a similar model, but without the projections incorporated into the channels. Contours of the molar fractions of oxygen were determined along the flow direction at four locations, which were Fig. 2a are labelled i, ii, iii and iv.

[0050] Fig. 2b and Fig. Figure 2c shows the contours of the oxygen mole fractions for the model with no protrusions in the channels and, correspondingly, for the model with protrusions in the channels. The contour is defined according to its position along the channel as shown in Fig. Figure 2a is shown and marked. Note that the model should be oriented so that the GDL appears at the bottom of the figures. The horizontal component of these contours therefore indicates the mole fraction of oxygen in the GDL, while the vertical components of the contour represent the mole fraction of oxygen in the two adjacent channels.

[0051] The in Fig. 2b and Fig. The scales shown in 2c indicate the gradient of the mole fractions of oxygen. The darker the shading, the lower the mole fraction of oxygen. The model without protrusions ( Fig. 2b) shows that the contours are essentially the same at every point and that the mole fraction of oxygen falls to a very low value (0.06) in the GDL, which borders the center of the webs.

[0052] The model with protrusions ( Fig. 2c), on the other hand, shows a consistently much more uniform mole fraction of oxygen. There is a much smaller drop in the mole fraction of oxygen in the GDL than in Fig. 2b is the case.

[0053] In Fig. 2c is an advantage 2The minimum oxygen mole fractions at locations i and ii are located on the right side between points ii and iii. Although it may be difficult to see, they are shifted to the left in the GDL adjacent to the ribs at locations i and ii. Conversely, the minimum oxygen mole fraction in the contours at locations iii and iv is shifted to the right in the GDL adjacent to the ribs. This is a result of convection and the periodic nature of the upstream and downstream ridges in the channels.

[0054] Next, a series of experiments was conducted on a single fuel cell. The cell's flow field plates comprised a set of 36 parallel, linear flow field channels. The overall dimensions of the plate were 185 mm by 90 mm, and the active area was slightly larger than that occupied by the channels. The channel dimensions were 114 mm in length, 0.49 mm in width, and 0.52 mm in depth. The width of the webs was 0.5 mm. Where protrusions were used, they were spaced 22.8 mm apart. The protrusions in each channel were offset by half a period relative to those in adjacent channels. Each protrusion had a length of 1.5 mm and a width that filled the channel. The feed lengths (the distance from the edge of the plate to the first protrusion) were 17.1 mm and 28.5 mm (i.e., 17.1 mm plus half a period) for adjacent channels.However, the heights of the projections varied between the cells examined. An ordinary cell without projections was examined for comparison, and two cells with projections of 0.26 mm height (50% of the channel depth) and 0.34 mm height (66% of the channel depth) were also examined separately. These plates will subsequently be referred to as comparative, moderate, and offensive plate formations, respectively.

[0055] The cells were operated under different operating conditions, using fully humidified hydrogen and various mixtures of oxygen and nitrogen as reactants. To investigate the effects of different protrusion heights under specific operating conditions, the cells were operated at various combinations of temperatures (including 40, 60, and 80°C) and current densities (1.5, 2, 2.5, and 3 A / cm²). 2included), oxygen concentration as introduced into the oxidizing agent stream at the inlet (from 9 to 21% [O2]), and flow rates of the oxidizing agent (flow rates of 10 to 20 slpm, which translate into respective flow velocities of about 10 m / s and 20 m / s at the respective inlets of the plates for the oxidizing agent).

[0056] For example, the cell using the moderate plate showed comparatively better performance at 80°C compared to all the plates tested. The aggressive plate showed poor performance, possibly due to excessive drying that occurred within the cell.

[0057] At 60°C, the offensive plate outperformed the other two plates only at lower oxygen concentrations (for example, less than 15% [O2]), and the difference was less significant at lower current densities.

[0058] Furthermore, the offensive plate exceeded 2.5 A / cm. 2 and 40°C, the other two plates at all tested oxygen concentrations. At 1.5 A / cm² 2 The cell voltages obtained using each plate were essentially similar at oxygen concentrations of 15% and above. Under these conditions, the offensive plate again showed the best performance.

[0059] Fig. Figure 3 shows a set of graphical representations obtained at 80°C for the three investigated embodiments at several different current densities and an oxidant flow rate of 20 slpm. (In Fig. Figure 3 shows data for the comparative, moderate, and offensive designs, each represented by short dashed, long dashed, and solid lines, respectively. Data for 1.5, 2.0, 2.5, and 3.0 A / cm². 2(are represented by squares, rhombuses, triangles and crosses, respectively.) However, it is worth noting that a preferred boundary line for operation is found at current densities of 2.5 A / cm². 2 or more, and can be found at oxygen concentrations between approximately 12 and 15%. Within this boundary, both the moderate and the offensive cell configurations exceeded the comparative configuration (by approximately 200 mV at 2.5 A / cm²). 2 and 12% [O2]), with the moderate design being somewhat preferred.

[0060] Regarding the effect of different gas velocities, it was observed, for example, that the cell's performance would not change significantly at 80°C. Reducing the inlet flow rate to 10 slpm in the temperate plate (and consequently the gas velocity in the channels from 20 m / s to 10 m / s) did not result in a significant difference in performance.

[0061] The results obtained from the three plates differed depending on the combinations of parameters investigated. In some cases, no significant differences were found. In other cases, a plate according to the invention showed significantly better performance than the comparison plate. Therefore, the selection of a preferred design requires an investigation that evaluates performance, pressure loss, and water management under the relevant operating conditions.

[0062] The person skilled in the art will therefore understand that properly incorporating protrusions according to the invention can be a complex process. Although significant effects can be achieved, various factors must be taken into account, and all possible required operating conditions for a given embodiment must also be considered, and performance trade-offs will likely be necessary under some of these conditions.

[0063] All of the above-mentioned US patents, publications of US patent applications, foreign patents, foreign patent applications and publications not belonging to patent literature, to which reference has been made in this description, are hereby included in their entirety by reference.

[0064] Although certain elements, embodiments, and applications of the present invention are shown and described, it is naturally understood that the invention is not limited thereto, since modifications can be made by a person skilled in the art without departing from the essence and scope of the present disclosure, particularly in light of the preceding teachings. Such modifications are to be considered within the scope and extent of the following claims. QUOTES INCLUDED IN THE DESCRIPTION

[0065] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0066] JP 2004241141

[0007] US 20040151973

[0007] JP 2004327162

[0007] Zitierte Nicht-Patentliteratur

[0067] C. Y. Soong et al., ”Analysis of reactant gas transport in a PEM fuel cell with partially blocked fuel flow channels”, Journal of Power Sources, 143 (2005) 36–47

[0006] T. Kanezaki et al., ”Cross-leakage flow between adjacent flow channels in PEM fuel cells”, Journal of Power Sources, 162 (2006) 415–425

[0006]

Claims

[1] Flow field plate for a fuel cell comprising: a major surface for the distribution of a reactant; a reactant opening for the entry of the reactant; a reactant opening for the outlet of the reactant; and a flow field for the reactant which is formed in the main surface of the plate, wherein the inlet of the flow field for the reactant is fluidically connected to the inlet-reactant opening, wherein the outlet of the flow field for the reactant is fluidically connected to the outlet-reactant opening, wherein the flow field for the reactant comprises a parallel channel region which includes a plurality of parallel channels and webs separating the channels, and wherein the parallel channel region includes at least one projection region, wherein the plurality of the parallel channels includes a plurality of projections which impede the flow in the channels; characterized by , that the projections in each channel are arranged in a sequence along the length of each channel within the projection area; and the continuous projections in any given channel are offset in the projection area along the length of the channel with respect to the continuous projections in the channels which are directly adjacent to the given channel. [2] Flow field plate according to claim 1, wherein the parallel channels in the parallel channel region are essentially linear. [3] Flow field plate according to claim 1, wherein the sequence is a periodic sequence. [4] Flow field plate according to claim 3, wherein the periodic projections in any given channel are offset in the projection region by substantially half a period with respect to the periodic projections in the channels which are directly adjacent to the given channel. [5] Flow field plate according to claim 1, wherein the parallel channel area occupies more than 50% of the main surface of the flow field plate. [6] Flow field plate according to claim 5, wherein the projection area occupies more than 50% of the parallel channel area. [7] Flow field plate according to claim 6, wherein the flow field plate is a flow field plate for an oxidizing agent. [8] Flow field plate according to claim 1, wherein one dimension of the projections varies over the sequence. [9] Flow field plate according to claim 8, wherein the dimension of the projections adjacent to the outlet of the flow field for the reactant is larger than adjacent to the inlet of the flow field for the reactant. [10] Flow field plate according to claim 1, wherein the dimensions of the projections are constant over the sequence. [11] Flow field plate according to claim 3, wherein the period of the projections which are arranged in each channel in the projection region is about 20 to 30 mm. [12] Flow field plate according to claim 10, wherein the projections occupy between 0.4 and 0.6 of the depth of the channel. [13] Flow field plate according to claim 1, wherein the projections occupy the width of the channel. [14] Flow field plate according to claim 1, wherein the projections are between about 1 and 2 mm long. [15] Flow field plate according to claim 1, wherein the width of the webs is greater than 0.3 mm. [16] Solid polymer electrolyte fuel cell comprising a solid polymer electrolyte, a catalyst electrode adjacent to the solid polymer electrolyte, a gas diffusion layer adjacent to the catalyst electrode, and a flow field plate according to claim 1 adjacent to the gas diffusion layer. [17] Method for improving the distribution of a reactant in a solid polymer electrolyte fuel cell, wherein the fuel cell comprises a solid polymer electrolyte, a catalyst electrode adjacent to the solid polymer electrolyte, a gas diffusion layer adjacent to the catalyst electrode, and a flow field plate adjacent to the gas diffusion layer, wherein the method comprises integrating the flow field plate according to claim 1 as the flow field plate adjacent to the gas diffusion layer. [18] Method according to claim 17, which comprises arranging the projections in a periodic sequence. [19] Method according to claim 18, which comprises offsetting the periodic projections in any given channel in the projection region substantially by half a period with respect to the periodic projections in the channels which are directly adjacent to the given channel. [20] Method according to claim 17, wherein the integrated flow field plate is a flow field plate for an oxidizing agent. [21] Method according to claim 20, which comprises arranging the projections such that the projection region does not include the area of ​​the flow field for the reactant which is adjacent to the inlet of the flow field for the reactant, wherein the oxygen concentration during normal operation is greater than 15%. [22] Flow field plate according to claim 20, which comprises arranging the projections such that the projection region does not occupy the area of ​​the flow field for the reactant near the inlet of the flow field for the reactant, wherein the relative humidity during normal operation is less than 100%.

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