EP4111515A1

EP4111515A1 - Flow field plate for a fuel cell

Info

Publication number: EP4111515A1
Application number: EP21713151.5A
Authority: EP
Inventors: Harika KOMPELLA VENKATA NAGA SATYA; Nileshwar Pramila Rao; Dhinagar Samraj Jabez
Original assignee: TVS Motor Co Ltd
Current assignee: TVS Motor Co Ltd
Priority date: 2020-02-27
Filing date: 2021-02-23
Publication date: 2023-01-04
Also published as: WO2021171307A1; CN115088107A

Abstract

A fuel cell stack (100) including a metallic flow field plate (305) between a pair of fuel cell assemblies (103a, 103b) is provided. The fuel cell stack (100) includes a pair of end plates (101, 102) and a cover plate (107). The pair of fuel cell assemblies (103a, 103b) includes a first membrane electrode assembly (303) and a second membrane electrode assembly (307) with an anode face (303a, 307a) and a cathode face (303b, 307b). The metallic flow field plate (305) includes a first surface (305a) with two or more serpentine first flow channels (401) of air and a second surface (305b) with one or more serpentine second flow channels (501) of hydrogen. The metallic flow field plate (305) prevents crossover of air and hydrogen and avoids seam welding of two monopolar plates.

Description

FLOW FIELD PLATE FOR A FUEL CELL

TECHNICAL FIELD OF INVENTION [0001] The invention generally relates to a fuel cell stack and more particularly to a metallic flow field plate in the fuel cell stack.

BACKGROUND

[0002] A fuel cell is an electrochemical device that generates electricity on reaction between a fuel, that is, hydrogen and oxygen. Pure oxygen or air containing a large amount of oxygen reacts with pure hydrogen or a fuel containing a large amount of hydrogen in the fuel cell. Hydrogen may be generated by reforming a hydrocarbon fuel, such as methanol. The fuel is channeled through a flow field plate to an anode on one side of a proton exchange membrane in the fuel cell and oxygen is channeled through another flow field plate to the cathode on another side of the proton exchange membrane.

Electrochemical reactions occur at the anode and the cathode to produce electricity, water, and heat. The design of the flow field plate is critical to the performance of the fuel cell. SUMMARY OF THE INVENTION

[0003] This summary is provided to introduce a selection of embodiments of the inventive concepts in a simplified form that are further disclosed in the detailed description of the invention. This summary is not intended to determine the scope of the claimed subject matter.

[0004] A metallic flow field plate in a pair of fuel cell assemblies is disclosed herein including a first surface and a second surface, rear of the first surface. The first surface includes two or more serpentine first flow channels and the second surface includes one or more serpentine second flow channels, where the second flow channels are formed by stamping of the first flow channels on the first surface.

[0005] Each of the first flow channels receives air from two or more first inlet legs located on the first surface, wherein the two or more first inlet legs are operably connected to a discharge of an aeration device and discharges air from two or more first outlet legs located on the first surface. Each of the second flow channels receives hydrogen from one or more second inlet legs located on the second surface and discharges hydrogen from one or more second outlet legs located on the second surface. The metallic flow field plate further includes a groove formed on edges of each of the first surface and the second surface, along the length of the first flow channels and the second flow channels for accommodating one or more elastic members. [0006] The first inlet legs and the first outlet legs are located at a first edge of the metallic flow field plate. The second inlet legs are engaged with one or more inlet manifolds positioned on a pair of end plates and the second outlet legs are engaged with one or more outlet manifolds positioned on the pair of end plates. Air and hydrogen reactively engage with a membrane electrode assembly in each of the pair of fuel cell assemblies for supplying electric current to an electric circuit. Air from the first flow channels diffuses towards a cathode surface of the membrane electrode assembly of the fuel cell assembly and hydrogen from the second flow channels diffuses towards an anode surface of the membrane electrode assembly of the fuel cell assembly. The aeration device is a blower or a centrifugal pump.

[0007] In an embodiment, a fuel cell stack is disclosed herein including a pair of end plates, multiple fuel cell assemblies positioned between the pair of end plates, and a cover plate positioned in contact with first edges of the pair of end plates. Each end plate includes one or more inlet manifolds and one or more outlet manifolds for hydrogen. A pair of fuel cell assemblies from the multiple fuel cell assemblies includes a pair of membrane electrode assemblies, a metallic flow field plates positioned between the pair of membrane electrode assemblies, and one or more elastic members. Each of the elastic members is positioned in the groove on the edges of the first surface and the second surface of the metallic flow field plate for reactant tightness. The cover plate accommodates the aeration device. The fuel stack further includes a pair of monopolar collector plates for collecting electric current generated in the fuel assemblies and each of the monopolar collector plate is positioned between an end plate and one of the membrane electrode assemblies.

[0008] The two or more serpentine first flow channels for air on the first surface of the metallic flow field plate creates one or more serpentine second flow channels for hydrogen on the back side of the metallic flow field plate. Creating such a continuous vertical serpentine flow path for both hydrogen and air which starts from the inlet and ends at the outlet without a header solves the issue of water clogging in low temperature proton exchange membrane (PEM) fuel cell. Inlet manifolds and outlet manifolds are provided for hydrogen only and air is sent through first inlet legs. Such a configuration eliminates crossover of gases at inlets as the first inlet legs and the second inlet legs are distant from each other.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing summary, as well as the following detailed description of the invention, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, exemplary constructions of the invention are shown in the drawings. However, the invention is not limited to the specific structures and methods disclosed herein. The description of a structure referenced by a numeral in a drawing is applicable to the description of that structure shown by that same numeral in any subsequent drawing herein.

[0009] Figs. 1A-1B exemplarily illustrate perspective views of a fuel cell stack; [0010] Fig. 2 exemplarily illustrates an exploded view of the fuel cell stack exemplarily illustrated in Fig. 1A;

[0011] Fig. 3 exemplarily illustrates an exploded view of a pair of fuel cell assemblies in the fuel cell stack; [0012] Fig. 4 exemplarily illustrates an elevation view of a metallic flow field plate in the pair of fuel cell assemblies;

[0013] Figs. 5A-5B exemplarily illustrate enlarged elevation views of a first surface and a second surface of the metallic flow field plate;

[0014] Fig. 6 exemplarily illustrates an elevation view of an elastic member that engages with the metallic flow field plate or monopolar collector plates;

[0015] Fig. 7 exemplarily illustrates an elevation view of a membrane electrode assembly of the fuel cell assembly;

[0016] Fig. 8 exemplarily illustrates an elevation view of a monopolar collector plate of the fuel cell assembly with two or more flow channels on a front surface; [0017] Fig. 9 exemplarily illustrates an elevation view of a monopolar collector plate of the fuel cell assembly with one or more flow channels on a front surface; [0018] Fig. 10 exemplarily illustrates an elevation view of an end plate of the fuel cell stack;

[0019] Figs. 11A-11B exemplarily illustrates perspective views of a cover plate of the fuel cell stack; and

[0020] Figs. 12A-12C exemplarily illustrate housing and mounting means for positioning an aeration device on the cover plate exemplarily illustrated in Figs.

11A-11B. DETAILED DESCRIPTION OF THE INVENTION

[0021] Various designs of flow field plates to channelize the fuel and air towards the proton exchange membrane are available. One such design of the flow field plate, for low temperature proton exchange membrane (PEM) fuel cells, is to have two single serpentine channels running parallel to each other such that one serpentine channel covers half of the flow area of the flow field plate and other serpentine channel covers the other half of the flow field plate. These two single serpentine channels are connected to an inlet manifold of the PEM fuel cell through a header. The same design of the flow field plate is used for both hydrogen and air on either side of the flow field plate. The bipolar plate is made in such a way that the flow field of hydrogen on one side (anode side) is at right angle to the flow field of air/oxygen on other side (cathode side).

[0022] However, when a stack is assembled with such bipolar plates, flow field on one side is vertical in direction and another flow field is horizontal in direction. When humidified gases (hydrogen and oxygen) pass through the single serpentine channels, water clogging is observed in a lower portion of the horizontal flow field due to gravity, while upper portion of the horizontal flow field is dried, thereby adversely affecting the performance of the fuel cell. These issues occur due to the presence of the header and the two single serpentine channels running parallel to each other. Thus, there is a need to avoid water clogging from occurring in the bipolar plate for preventing deterioration in the performance of the fuel cell.

[0023] Further, heat is being generated in the fuel cell due to the electrochemical reaction and the generated heat has to be removed continuously with the help of a coolant, for example, air or liquid, to maintain operating temperature of the fuel cell. The operating temperature for low temperature PEM fuel cell is about -30°C to 80°C and the operating temperature for high temperature PEM fuel cell is about 80°C to 160°C. If this operating temperature is not maintained, permanent damage may occur to the membrane electrode assembly and the membrane electrode assembly needs replacement.

[0024] To maintain the operating temperature of the fuel cell stack, a coolant needs to be re-circulated in the stack continuously to maintain the temperature. If air is used as a coolant, then coolant air is sent along with reactant air which flows through the flow field and cools the stack. However, such passage of coolant along the flow field plate along with the reactant air results in leaching of acids from membrane electrode assembly, carbon corrosion of carbon-based materials, such as, gas diffusion layer, catalyst poisoning due to the presence of CO, etc., resulting in degradation of performance of the fuel cell. To address such scenarios of degradation in the performance of the fuel cells, separate manifolds/channels to use air or any liquid coolant apart from the inlet manifolds/channels for the reactive air may be provided. Such an arrangement may require installation of additional components, adding to the cost of manufacturing and maintenance in the PEMFC (Proton Exchange Member Fuel Cell). Therefore, there exists a need for circulating a coolant in the PEMFC without degrading the performance of the PEMFC.

[0025] Furthermore, another existing design of the flow field plate includes forming flow fields for hydrogen and air on two different plates (monopolar) and seam welding the monopolar plates to obtain a bipolar plate. However, the inlets and outlets for hydrogen and air on both sides of the flow field plate are almost near to each other, resulting in difficulties in sealing especially at the inlets and outlets. Inadequate sealing of the inlets and the outlets may lead to internal combustion of gases.

[0026] Therefore, there exists a long felt need for a fuel cell stack with one or more bipolar flow field plates that cater for the flow of coolant and reactant, without adding additional cost to the manufacturing and enabling ease of maintenance of the fuel cell stack. The present subject matter addresses the above need for the bipolar flow field plates that allows flow of a coolant and reactants without additional costs.

[0027] Figs. 1A-1B exemplarily illustrate perspective views of a fuel cell stack 100. The fuel cell stack 100 is a stacked arrangement of multiple fuel cell assemblies 103 that generate higher voltage and power than an individual fuel cell assembly. The fuel cell assemblies 103 are connected in series to form the fuel cell stack 100. In an embodiment, the number of fuel cell assemblies 103 may be increased to increase output voltage of the fuel cell stack 100. A fuel cell assembly is an electrochemical cell that converts chemical energy of hydrogen and oxygen into electric current and heat through a pair of oxidation and reduction. In the fuel cell assembly, chemical reactions occur between an anode and an electrolyte, and a cathode and the electrolyte. At the anode, hydrogen is oxidized generating positive hydrogen ions and negatively charged electrons. The positive hydrogen ions travel through the electrolyte and the electrons travel through an external circuit. At the cathode, the positive hydrogen ions combine with the electron and oxygen to generate water. Based on the types of the cathode, the anode, and the electrolyte, the fuel cell assembly may be a proton exchange membrane fuel cell assembly, a phosphoric acid fuel cell assembly, a solid acid fuel cell assembly, an alkaline fuel cell, etc.

[0028] As exemplarily illustrated in Fig. 1A, such multiple fuel cell assemblies 103 are stacked between a pair of end plates 101 and 102 and a cover plate 107 is positioned on the end plates 101 and 102. The end plates 101 and 102 have guide holes for fasteners 106, for example, nut and bolt assemblies, belt assembly, spring assembly etc., to apply pressure on the fuel cell assemblies 103 to hold the fuel cell stack 100 intact and prevent escape of gases from the fuel cell assemblies 103. The torque of tightening the fasteners 106 is maintained uniform to avoid the leakage of gases. The end plates 101 and 102 further include one or more inlet manifolds, such as, 104 and one or more outlet manifolds, such as, 105. The cover plate 107 is positioned in contact with the first edges of the end plates 101 and 102. As exemplarily illustrated in Fig. 1A, the cover plate 107 accommodates an aeration device 110, such as, a blower. The cover plate 107 includes an air inlet duct 109 of the fuel cell stack 100 removably engaged with a discharge of the aeration device 110, an air outlet duct 108 of the fuel cell stack 100, and a recirculation piping 111 connecting the outlet duct 108 to the discharge of the aeration device 110 through a heat exchanging mechanism, for recirculation of air into the fuel cell stack 100. [0029] As exemplarily illustrated in Fig. IB, the aeration device 110 is housed in a housing 112 and accommodated between the inlet duct 109 and the outlet duct 108 of the fuel cell stack 100 using mounting means exemplarily illustrated in Figs. 12A-12C. In an embodiment, an inlet manifold 104 and an outlet manifold 105 for hydrogen are positioned on the same end plate, such as, 102 as exemplarily illustrated in Fig. 1A. In an embodiment, the inlet manifold 104 and the outlet manifold 105 for hydrogen are positioned on different end plates, such as, 101 and 102, that is, the inlet manifold 104 on one end plate, such as, 101 and the outlet manifold 105 on another end plate, such as, 102.

[0030] Fig. 2 exemplarily illustrates an exploded perspective view of the fuel cell stack 100 exemplarily illustrated in Fig. 1A. As exemplarily illustrated, multiple fuel cell assemblies 103 are stacked together between the end plates 101 and 102 using the fasteners 106 and guides 202. The fasteners 106 and the guides 202 are inserted through guide holes 201 in the end plates 101 and 102. The cover plate 107 is screwably attached to the end plates 101 and 102 at the first edge 101a and 102a of the end plates 101 and 102 respectively using the fasteners 203, for example, screw and nut assembly. Insertion of the guides 202 through the guide holes 201 through the structure of the fuel cell stack 100 ensures rigid & stable assembly of the fuel cell stack 100. The fasteners 106 ensure adequate compression of the structure of the fuel cell stack 100.

[0031] The discharge of the aeration device 110 is connected to the inlet duct 109 of the fuel cell stack 100. The discharge of the aeration device 110 includes both reactive air for the electrochemical reaction in the fuel cell assemblies 103 and coolant air to remove the heat generated in the fuel cell stack 100. Remaining reactive air and the hot coolant air reach the outlet duct 108 of the fuel cell stack 100 and are re-circulated to the discharge of the aeration device 110 via the recirculation piping 111 accommodating a heat exchanging mechanism. The aeration device 110, for example is a blower which increases the velocity and pressure of air through impellers to supply air for the electrochemical reaction and cooling of the fuel cell stack 100. The supplied air acts as a source of oxygen for the electrochemical reaction in each fuel cell assembly of the fuel cell stack 100. Hydrogen is supplied through the inlet manifold 105 and unreacted hydrogen and water vapor remaining after the electrochemical reaction is sent out through the outlet manifold 105 in the end plate 102. Hydrogen may be derived from substances containing hydrogen, such as, methanol, gasoline, natural gas, and water. Pure hydrogen and oxygen, with no impurities are pressurized and injected into the fuel cell stack 100.

[0032] Fig. 3 exemplarily illustrates an exploded view of a pair of fuel cell assemblies 103a and 103b in the fuel cell stack 100. The pair of fuel cell assemblies 103a and 103b is compressed between the pair of end plates 101 and 102. The pair of fuel cell assemblies 103a and 103b includes a pair of membrane electrode assemblies, that is, a first membrane electrode assembly 303 and a second membrane electrode assembly 307 and a metallic flow field plate 305 positioned between the membrane electrode assemblies 303 and 307 with elastic members 302, 304, 306, and 308 disposed on either side of the membrane electrode assemblies 303 and 307. Each of the membrane electrode assemblies 303 and 307 is a combination of an electrolyte, an anode, and a cathode. Each of the membrane electrode assemblies 303 and 307 includes a proton exchange membrane that is selectively permeable, an anode catalyst layer and a cathode catalyst layer on either sides of the proton exchange membrane, and gas diffusion layers on both sides of the proton exchange membrane. The proton exchange membrane conducts positively charged hydrogen ions and blocks the negatively charged electrons. The anode catalyst layer forms an anode surface 303a and 307a of the membrane electrode assemblies 303 and 307 respectively and the cathode catalyst layer forms a cathode surface 303b and 307b of the membrane electrode assemblies 303 and 307 respectively. On the anode surface 303a and 307a of the membrane electrode assemblies 303 and 307, hydrogen oxidation reaction takes place splitting hydrogen into positively charged ions and negatively charged electrons. The half-cell oxidation reaction is represented as:

Hi 2H⁺ + 2e

[0033] The positively charged ions pass through the membrane electrode assemblies 303 and 307 to the cathode surface 303b and 307b, respectively. The electrons travel along an external load circuit to the cathode surface 303b and 307b of the membrane electrode assemblies 303 and 307, thus creating the current output of the fuel cell assemblies 103a and 103b. At the cathode surface 303b and 307b of the membrane electrode assemblies 303 and 307, oxygen molecules react with the protons permeating through the proton exchange membrane and the electrons arriving through the external circuit to form water molecules. The half cell reduction reaction is represented as: 1/2 O2 + 2 H⁺ + 2e H2O.

[0034] On the anode surface 303a and 307a and the cathode surface 303b and 307b of the membrane electrode assemblies 303 and 307, respectively, a platinum catalyst enables initiation of the half-cell oxidation reaction and the half-cell reduction reaction, respectively. The gas diffusion layer is positioned above the anode catalyst layer and the cathode catalyst layer of the membrane electrode assembly 303 and 307. The gas diffusion layer facilitates transport of hydrogen and oxygen into the catalyst layers and also, aids in removal of water generated in the fuel cell assemblies 103a and 103b. The gas diffusion layer has pores through which air and hydrogen diffuse towards the cathode surface 303b and 307b and the anode surface 303a and 307a of the membrane electrode assemblies 303 and 307.

[0035] As exemplarily illustrated, a metallic flow field plate 305 is positioned between the first membrane electrode assembly 303 and the second membrane electrode assembly 307. That is, each fuel cell assembly 103a or 103b in the fuel cell stack 100 is sandwiched between two metallic flow field plates, such as, 305 to separate from adjacent fuel cell assemblies. A first surface 305a of the metallic flow field plate 305 faces the cathode face 303b of the first membrane electrode assembly 303 and a second surface 305b of the metallic flow field plate 305 faces the anode surface 307a of the second membrane electrode assembly 307. The metallic flow field plate 305 uniformly distributes air on the first surface 305a and hydrogen on the second surface 305b towards the membrane electrode assembly 303 and 307. The metallic flow field plate 305 has flow fields on both surfaces 305a and 305b to cater for diffusion of hydrogen and oxygen, respectively. The flow fields may be of different shapes, such as, rectangular, triangular, circular, etc. The flow channels on both surfaces 305a and 305b constitute the flow fields for oxygen and hydrogen. On the first surface 305a of the metallic flow field plate 305, two or more serpentine first flow channels of air are provided and on the second surface 305b of the metallic flow field plate 305, one or more serpentine second flow channels of hydrogen are provided. The first flow channels of the metallic flow field plate 305 cater to the electrochemical reaction in a fuel cell assembly 103a and the second flow channels of the metallic flow field plate 305 cater to the electrochemical reaction in the adjacent fuel cell assembly 103b. The metallic flow field plate 305 with the first surface 305a and the second surface 305b is exemplarily illustrated in Figs. 4, 5A, and 5B.

[0036] An elastic member 304 and 306, for example, a gasket is positioned between the metallic flow field plate 305 and each of the membrane electrode assemblies 303 and 307. The elastic members 304 and 306, exemplarily illustrated in Fig.6 provide a seal to prevent undue leakage of hydrogen or oxygen in the fuel cell stack 100. The fuel cell assemblies 103a and 103b include a pair of monopolar collector plates 301 and 309 for collecting the current generated in the fuel cell assemblies 103a and 103b. Each monopolar collector plate 301 and 309 includes a flow field for oxygen or hydrogen on a front surface 301a and 309a facing the membrane electrode assembly 303 and 307. The front surface 301a of the monopolar collector plate 301 facing the anode surface 303a of the first membrane electrode assembly 303 resembles the second flow channels of hydrogen of the metallic flow field plate 305 and the front surface 309a of the monopolar collector plate 309 facing the cathode surface 307b of the second membrane electrode assembly 307 resembles the first flow channels of oxygen of the metallic flow field plate 305. The monopolar collector plates 301 and 309 connect the fuel cell assemblies 103a and 103b to external loads.

[0037] Another pair of elastic members 302 and 308 is positioned between the monopolar collector plate 301 and 309 and the membrane electrode assembly 303 and 307 of the fuel cell assemblies 103a and 103b, respectively. The elastic members or gaskets 302 and 308, for example, provide a mechanical seal between the front surface 301a and 309a of the monopolar collector plate 301 and 309 and the anode surface 303a or the cathode surface 307b of the membrane electrode assemblies 303 and 307 to prevent leakage of oxygen or hydrogen that flows through the flow field of the monopolar collector plates 301 and 309, respectively.

[0038] Each of the membrane electrode assemblies 303 and 307, the monopolar collector plates 301 and 309, the metallic flow field plate 305, and the elastic members 302, 304, 306, and 308 have guide holes in proximity to the edges of each of them for accommodating the guides 202 and the fasteners 106. The fasteners 106 through the guide holes 201 compress the membrane electrode assemblies 303 and 307, the monopolar collector plates 301 and 309, the metallic flow field plate 305, and the elastic members 302, 304, 306, and 308 together.

[0039] Fig. 4 exemplarily illustrates an elevation view of the metallic flow field plate 305 in the pair of fuel cell assemblies 103a and 103b. The metallic flow field plate 305 consists of the first surface 305a and the second surface 305b. The first surface 305a faces the cathode surface 303b of the first membrane electrode assembly 303 and the second surface 305b, rear of the first surface 305a faces the anode surface 307a of the second membrane electrode assembly 307. The first surface 305a includes, for example, two serpentine flow channels 401 for air to flow and the second surface 305b includes a single serpentine flow channel 501 for hydrogen to flow as exemplarily illustrated in Fig. 5B. The two serpentine first flow channels 401 start at two first inlet legs 402 and end at two first outlet legs 403 to form a flow field for air on the first surface 305a. The single serpentine second flow channel 501 on the second surface 305b of the metallic flow field plate 305 starts at a second inlet leg 405 and ends at a second outlet leg 406, thereby forming a flow field for hydrogen on the second surface 305b. The first inlet legs 402 and the first outlet legs 403 are located at a first edge 404 of the flow field plate 305 on the first surface 305a. The second inlet leg 405 and the second outlet leg 406 are also located proximal to the first edge 404 of the flow field plate 305 on the second surface 305b as exemplarily illustrated in Fig 5B.

[0040] The difference in pressure of air between the first inlet legs 402 and the first outlet legs 403 of the flow field of air drives the flow of air on the first surface 305a. Similarly, the difference in pressure of hydrogen and water vapor between the second inlet leg 405 and the second outlet leg 406 of the flow field of hydrogen drives the flow of hydrogen on the second surface 305b. Pressure drop occurs along the length of the flow channels 401 and 501 and thus, air and hydrogen supplied at the inlet legs 402 and 405 respectively is at a higher pressure from the aeration device 110 and the inlet manifold 104, respectively. The first inlet legs 402 are connected to the inlet duct 109 of the fuel cell stack 100 and the first outlet legs 403 are connected to the outlet duct 108 of the fuel cell stack 100. The second inlet leg 405 is connected to the inlet manifold 104 and the second outlet leg 406 is connected to the outlet manifold 105 positioned on the end plate 102. The first inlet legs 402, also referred to as open cathode, receives air, that is both reactant air and coolant air. The aeration device 110 blows the air onto the fuel cell assemblies 103 at a predetermined pressure. Since the first inlet legs 402 are open, the pressure drop at the first inlet legs 402 is minimal and air flows in the first flow channels 401 at the same pressure as the predetermined pressure. The coolant air removes heat from the fuel cell stack 100 by forced convection and the reactant air flows through the first flow channels 401 to participate in the electrochemical reaction. Reactant air from the first flow channels 401 diffuses towards the cathode surface 303b of the membrane electrode assembly 303 and hydrogen from the second flow channel 501 diffuses towards the anode surface 307a of the membrane electrode assembly 307.

[0041] The two serpentine first flow channels 401 are formed on the first surface 305a of the metallic flow field plate 305 by stamping and this results in the formation of a single serpentine second flow channel 501 on the second surface 305b of the metallic flow field plate 305. The serpentine first flow channels 401 and the serpentine second flow channel 501 force the reactants, that is, air and hydrogen, to flow across the entire active area of the first surface 305a and the second surface 305b to eliminate stagnant areas due to improper reactant distribution. The serpentine first flow channels 401 on the first surface 305a limits the pressure drop along the first flow channels 401 and manages water accumulation in the fuel cell stack 100. Since the first flow channels 401 and the second flow channel 501 are on either sides of the metallic flow field plate 305, crossover of air and hydrogen at the inlets of the metallic flow field plate 305 is prevented.

[0042] The metallic flow field plate 305 further includes a groove 407 formed on the edges of the first surface 305a and the second surface 305b along the length of the first flow channels 401 and the second flow channel 501. The groove 407 accommodates the elastic members 304 and 306, that is, the gaskets. The metallic flow field plate 305 further includes the guide holes, such as, 201a, 201b, ... , 201f to accommodate the fasteners 106 and the guides 202 through them. The metallic flow field plate 305 is made of stainless steel, by virtue of which the metallic flow field plate 305 possesses high strength, high chemical stability, substantially less cost, and is easy to mass produce. In an embodiment, the metallic flow field plate 305 further possess a protective coating of, for example, noble metals to prevent corrosion of the first surface 305a and the second surface 305b.

[0043] Figs. 5A-5B exemplarily illustrate enlarged elevation views of the first surface 305a and the second surface 305b of the metallic flow field plate 305. The first surface 305a exemplarily illustrated in Fig. 5A shows two serpentine first flow channels 401 with two first inlet legs 402. The width of the first inlet legs 402 is same as the width of the first flow channels 401 and thus there is minimal pressure drop in the reactant air from the first inlet legs 402 to the first flow channels 401. The two serpentine first flow channels 401 are contiguous, run parallel to each other, and terminate at the first outlet legs 403.

[0044] The second surface 305b exemplarily illustrated in Fig. 5B shows a single serpentine second flow channel 501 with a second inlet leg 405. The second inlet leg 405 is an aperture in the metallic flow field plate 305 that gets connected to the inlet manifold 104 of the fuel cell stack 100. Similarly, the second outlet leg 406 for hydrogen is an aperture in the metallic flow field plate 305 at the first edge 404 on the second surface 305b that is connected to the outlet manifold 105 of the fuel cell stack 100. There is no header for the first flow channels 401 and the second flow channel 501. The flow of air and hydrogen through the first flow channels 401 and the second flow channel 501 may be laminar or turbulent.

[0045] The metallic flow field plate 305 is referred to as a bipolar plate by virtue of the flow fields on both sides of the metallic flow field plate 305. The first flow channels 401 are formed by stamping on the first surface 305a. The first flow channels 401 are depressions of a certain depth on the first surface 305a of the metallic flow field plate 305, that results in embossed metal on the second surface 305b. Between the embossed metal on the second surface 305b, a serpentine second flow channel 501 is formed of the same depth as the depth of the first flow channels 401. Therefore, formation of two first flow channels 401 on the first surface 305a results in the formation of a single second flow channel 501 on the second surface 305b. Thus, the process of manufacturing the metallic flow field plate 305 is simple and not laborious.

[0046] Fig. 6 exemplarily illustrates an elevation view of an elastic member, such as, 302, 304, 306, and 308 that engages with the metallic flow field plate 305 or the monopolar collector plates 301 and 309. The elastic members 302, 304, 306, and 308 are, for example, a gasket. The elastic members 304 and 306 are accommodated in the groove 407 on the first surface 305a and the second surface 305b of the metallic flow field plate 305, respectively. Similarly, the elastic members 302 and 306 are accommodated in the grooves (not shown) of the monopolar collector plates 301 and 309 respectively. The elastic members 302, 304, 306, and 308 prevent leak of hydrogen and air, that is, the elastic members 302, 304, 306, and 308 provide reactant tightness when the fuel cell assemblies 103 are compressed. The elastic members 302, 304, 306, and 308 also provide vibration and shock resistance to the fuel cell stack 100, and prevent mechanical bonding of components, such as, 301a, 303, 305, 307, and 309 as exemplarily illustrated in Fig. 3, when compressed in the fuel cell stack 100. The elastic members 302, 304, 306, and 308 are made of materials, such as, silicon, PTFE, EPDM rubber, etc., that have greater compressibility and good sealing properties. The elastic members 304 and 306 seal non-active regions of the metallic flow field plate 305 and expose the active regions of the metallic flow field plate 305 to the membrane electrode assemblies 303 and 307. The active regions are the flow fields including the inlet legs 402 and 405 and the outlet legs 403 and 406 on the metallic flow field plate 305. On the monopolar collector plates 301 and 309, the elastic members 302 and 308 seal non-active regions and expose the active regions to the membrane electrode assemblies 303 and 307. The elastic members 302, 304, 306, and 308 may be in pre-cut form or may be formed-in-place. The formed-in-place type elastic member may be cured by activation and exposure to radiation while assembling the fuel cell stack 100. The elastic members 302, 304, 306, and 308, further include multiple guide holes, such as, 201g and 201h similar to and in-line with the guide holes 201a, 201b, ..., 201f of the metallic flow field plate 305 to accommodate the guides 202 and the fasteners 106 to hold the structure of the fuel cell stack 100 intact. The elastic members 302, 304, 306, and 308 are non-conductive and provide electrical insulation between the metallic flow field plate 305 and the membrane electrode assemblies 303 and 307, and the monopolar collector plates 301 and 309 and the membrane electrode assemblies 303 and 307.

[0047] Fig. 7 exemplarily illustrates an elevation view of a membrane electrode assembly, such as, 303 and 307 of the fuel cell assembly, for example, 103a and 103b. The membrane electrode assembly, for example, 303 is a central element of a fuel cell assembly 103a in the fuel cell stack 100 around which the elastic members 302 and 304 and the flow fields are designed and positioned. In the membrane electrode assembly 303, the electrolyte, the electrodes, that is, the anode face and the cathode face, and the reactants, oxygen and hydrogen are all in contact. Since ambient air is used instead of pure oxygen, the amount of oxygen available for the electrochemical reaction is less, and thus, the membrane electrode assembly 303 is thin for lower resistance in the fuel cell assembly 103a. Further, the catalyst layer on the anode face 303a and the cathode face 303b in the membrane electrode assembly 303 reduces the cost of the membrane electrode assembly 303. The membrane electrode assembly 303 optimizes the efficiency of portable applications and stationary application of the fuel cell stack 100. The membrane electrode assembly 303 allows proton transport while obstructing the reactants, that is, hydrogen and oxygen at lower temperatures of about 20°C to about 80°C.

[0048] The active region of the metallic flow field plate 305 and the monopolar collector plate 301 is exposed to the anode face 303a and the cathode face 303b of the membrane electrode assembly 303. Hydrogen from the flow channels of the monopolar collector plate 301 diffuses towards the anode face 303a of the membrane electrode assembly 303 and oxygen from the flow channels 401 of the metallic flow field plate 305 diffuses towards the cathode surface 303b of the membrane electrode assembly 303 to undergo electrochemical reaction in the membrane electrode assembly 303. The by-product of the electrochemical reaction diffuses through the outlet legs 403 and 405 on the metallic flow field plate 305 towards the outlet duct 108 and the outlet manifold 105. As exemplarily illustrated, the membrane electrode assembly 303 also has guide holes, such as, 201i in line with the guide holes 201a, 201b, ..., 201f of the metallic flow field plate 305 to accommodate the fasteners 106 and the guides 202, similar to the elastic members 301, 304, 306, and 308.

[0049] Fig. 8 exemplarily illustrates an elevation view of the monopolar collector plate 309 of the fuel cell stack 100 with two or more flow channels, such as, 801 on the front surface 309a. The flow channels 801 extend from the two inlet legs 802 till the two outlet legs 803. The two inlet legs 802 and the two outlet legs 803 are similar in structure, inline, and serve the same function as the two first inlet legs 402 and the first two outlet legs 403 of the metallic flow field plate 305. The flow channels 801 on the front surface 309 faces the cathode face 307b of the membrane electrode assembly 307. The flow channels 801 carry oxygen for the half-cell reaction at the membrane electrode assembly 307 similar to the first surface 305a of the metallic flow field plate 305. A rear surface, rear to the front surface 309a of the monopolar collector plate 309 is flat and lies against the end plate 102 of the fuel cell stack 100. The monopolar collector plate 309 further includes a groove 804 along the perimeter of the monopolar collector plate 309 for accommodating the elastic member 308. The monopolar collector plate 309 has a support handle 805 extending from the side to facilitate connection of the fuel cell stack 100 to an external circuit to draw current from the fuel cell stack 100. The monopolar collector plate 309 also includes guide holes, such as, 201j and 201k to engage with the fasteners 106 and the guides 202 to hold the fuel cell stack 100 intact.

[0050] Fig. 9 exemplarily illustrates an elevation view of the monopolar collector plate 301 of the fuel cell stack 100 with one or more flow channels, such as, 901 on the front surface 301a. The flow channel 901 extends from the inlet leg 902 till the outlet leg 903. The inlet leg 902 and the outlet leg 903 are similar in structure, inline, and serve the same function as the second inlet leg 405 and the second outlet leg 406 of the metallic flow field plate 305. The flow channel 901 on the front surface 301a faces the anode face 303a of the membrane electrode assembly 303. The flow channel 901 carries hydrogen for the half cell reaction at the membrane electrode assembly 303 similar to the second surface 305b of the metallic flow field plate 305. A rear surface, rear to the front surface 301a of the monopolar collector plate 301 is flat and lies against the end plate 101 of the fuel cell stack 100. The monopolar collector plate 301 further includes a groove 904 along the perimeter of the monopolar collector plate 301 for accommodating the elastic member 302. The monopolar collector plate 301 has a support handle 905 extending from a side to facilitate connection of the fuel cell stack to the external circuit. Current (amperes), voltage, frequency, and other characteristics of the electrical current in the external circuit connected to the monopolar collector plates 301 and 309 are conditioned to suit the electrical needs of application of the fuel cell stack 100. The monopolar collector plate 301 also includes guide holes, such as, 2011 to engage with the fasteners 106 and the guides 202 to hold the fuel cell stack 100 intact.

[0051] Fig. 10 exemplarily illustrates an elevation view of the end plate, for example, 101 of the fuel cell stack 100. The end plate 101 provides mechanical support to the fuel cell stack 100. The metallic flow field plate 305, the membrane electrode assemblies 303 and 307, the monopolar collector plates 301 and 309, and the end plates 101 and 102 are parallel to each other in the fuel cell stack 100. The end plates 101 and 102 are sturdy to support the fuel cell stack 100 and uniformly distribute the compression forces to the fuel cell assemblies 103 in the fuel cell stack 100. The end plates 101 and 102 have substantially high compressive strength, vibration and shock resistance, and stable over the low temperatures of about 20°C to about 80°C. The materials used for the end plates 101 and 102 may be stainless steel, aluminum, titanium, nickel, polyethylene, poly vinyl chloride, etc. The end plate 102 at the other end of the fuel cell stack 100 has the inlet manifold 104 and the outlet manifold 105 for hydrogen in the fuel cell stack 100. The inlet manifold 104 in the end plate 102 is connected to the inlet leg 902 of the monopolar collector plate 301 and the inlet leg 405 of the metallic flow field plate 305 and the outlet manifold 105 in the end plate 102 is connected to the outlet leg 903 of the monopolar collector plate 301 and the outlet leg 406 of the metallic flow field plate 305. The inlet manifold 104 is connected to valves via external conduits to supply measured amount of hydrogen to the fuel cell stack 100. The unused heated hydrogen in the fuel cell stack 100 is ejected out through the outlet manifold 105. The outlet manifold 105 may be connected to external conduits connected to valves, heat exchangers, and any other desired balance-of-plant components to utilize the ejected water vapor. The guides 202 illustrated in Fig. 2 are inserted through guide holes 201 in the end plates 101 and 102

[0052] Figs. 11A-11B exemplarily illustrate perspective views of the cover plate 107 of the fuel cell stack 100. The cover plate 107 rests on the first edge 101a and 102a of the end plates 101 and 102 and accommodates the aeration device 110. The discharge 1101 of the aeration device 110 is connected to the air inlet duct 109 of fuel cell stack 100. The reactant air and the coolant air are passed through the air inlet duct 109 to the fuel cell assemblies 103 in the fuel cell stack 100. Oxygen in the air participates in the electrochemical reactions in the fuel cell stack 100. A stoichiometric amount of reactant air and coolant air are blown into the inlet duct 109 by the aeration device 110 to react with the measured amount of hydrogen entering through the inlet manifold 104. Since the electrochemical reaction is an exothermic reaction, heat generated in the fuel cell assemblies 103 is transmitted to the metallic flow field plate 305, the monopolar collector plate 301 and 309, and the membrane electrode assemblies 303 and 307. The water vapor generated in the electrochemical reaction absorbs some heat and an active coolant, such as, the coolant air fed to the fuel cell stack 100 through the first flow channels 401 in the metallic flow field plate 305 which absorbs the remaining heat in the fuel cell assemblies 103. The hot air along with the water vapor from the fuel cell assemblies 103 is collected in the outlet duct 109. The heat in the hot air and water vapor is extracted by means of an external heat exchanger installed in the recirculation piping 111. The hot air exchanges its heat with a fluid in the heat exchanger and the temperature of hot air is reduced to room temperature. The air at room temperature mixes with the ambient air at the discharge 1101 of the aeration device 110 and is supplied to the fuel cell stack 100 via the air inlet duct 109. The water content in the water vapor may be utilized to humidify the air at the air inlet duct 109. Hydrogen at the inlet manifold 104 is pumped at a higher pressure compared to air at the inlet duct 109. This prevents crossover of reactants and improves stability of the fuel cell assemblies.

[0053] Figs. 12A-12C exemplarily illustrate housing 1201 and mounting means, such as, 1202 and 1203 for positioning the aeration device 110 on the cover plate 107 exemplarily illustrated in Figs. 11A-11B. The aeration device 110 is housed in the housing 1201 and the housing is supported by the mounting means. The mounting means include a clamp 1202 and a clamp washer 1203 that are attached to the housing 1201 via fasteners, such as, nut and bolts. The performance of the fuel cell stack 100 depends on the pressure of the reactant gases, hydrogen and air. The aeration device 110, such as, the blower ensures the pressure of air at the discharge 1101 of the aeration device 110 is about 2-4 times the ambient atmospheric pressure. Fan speed of the aeration device 110 is adjusted to vary the flow rate of the air supplied to the fuel cell assemblies 103. The amount of stoichiometric oxygen into the fuel cell stack 100 is manipulated by a controller which regulates the electrical power of the aeration device, thereby controlling the compression and air flow into the fuel cell stack 100.

[0054] In an embodiment, humidifiers also constitute the membrane electrode assembly, such as, 303 and 307 of the fuel assemblies 103. In the humidifier, humidified air is obtained on flowing dry inlet air on one side of the humidifier, since air from the inlet duct 109 may be dry. In an embodiment, the humidifier may be part of the aeration device 110 and may supply wet air at the inlet duct 109 of the fuel cell stack 100. The wet air interacts with the membrane electrode assemblies 303 and 307, thereby not affecting the performance of the fuel cell stack 100 due to a dry proton exchange membrane. [0055] The fuel cell stack 100 is portable and may function as a backup power generator. The fuel cell stack 100 offers extended runtime, high reliability, high efficiency, and reduced environmental impact. The fuel cell stack 100 can be used in laptops, military equipment, battery chargers, vehicles, etc., as a primary power source or a backup power source. The fuel cell stack 100 provides a technical advancement in battery technology as follows: The fuel cell stack 100 converts chemical potential energy directly into electrical energy. Such a fuel cell stack 100 on implementation in an electric vehicle acts as primary source of electricity and is highly efficient since it avoids thermal bottle neck that usually occurs in an IC engine vehicle. The emissions from such an electric vehicle is only water vapor and a little heat. The heat is also extracted from the fuel cell assemblies 103 using the external heat exchanger. The fuel cell stack 100 is efficient since the exhaust is only water vapor and heat from the fuel cell stack 100, and not greenhouse gases that are harmful to the environment. The fuel cell stack 100 has no moving parts, and thus is much more reliable than traditional IC engines. The reactants supplied to the fuel cell stack 100 are hydrogen and air and hydrogen may be produced in an environmentally friendly manner, in contrast to oil extraction and refining for the IC engines.

[0056] The inlet manifold 104 and outlet manifold 105 of the fuel cell stack 100 are provided only for hydrogen while oxygen is supplied via open cathode, thus crossover of the reactants is prevented. The design of the elastic members 302, 304, 306, and 308 is same and simple for both the surfaces 305a and 305b of the metallic flow field plate 305. The cooling of the fuel cell stack 100 is by a simple installation of an aeration device 110, such as a blower. The coolant air is sent via the same flow channels as the reactant air, thereby keeping the design of the metallic flow field plate 305 simple and lightweight. The issue of water logging in the fuel cell stack 100 is eliminated due to the serpentine flow channels 401 and 501 on both the surfaces 305a and 305b of the metallic flow field plate 305. The serpentine flow channels 401 and 501 push the water droplets downwards entrapped in the cathode face of the membrane electrode assembly, such as, 303. The serpentine flow channels 401 and 501 distribute the reactants uniformly over the membrane electrode assembly 303, thus increase efficiency of the fuel cell stack 100. Since there are two flow fields on either sides of the metallic flow field plate 305, seam welding of two plates is avoided reducing the weight and size of the fuel cell stack 100. The method of assembly of such a fuel cell stack 100 using the guides 202 and the guide holes 201 is also simple.

Claims

We Claim:

1. A metallic flow field plate (305) in a pair of fuel cell assemblies (103a, 103b), the metallic flow field plate (305) comprising: a first surface (305a) comprising two or more serpentine first flow channels (401), wherein each of the two or more serpentine first flow channels (401): receives air from two or more first inlet legs(402) located on the first surface (305a), wherein the two or more first inlet legs (402) are operably connected to a discharge (1101) of an aeration device (110), and discharges air from two or more first outlet legs (403) located on the first surface (305); and a second surface (305b), rear of the first surface (305a), comprising one or more serpentine second flow channels (501) formed by stamping on the first surface (305a), wherein each of the one or more serpentine second flow channels (501): receives hydrogen from one or more second inlet legs (405) located on the second surface (305b), and discharges hydrogen from one or more second outlet legs (406) located on the second surface (305b).

2. The metallic flow field plate (305) of claim 1, further comprises a groove (407) formed on edges of each of the first surface(305a) and the second surface (305b), along the length of the two or more serpentine first flow channels (401) and the one or more serpentine second flow channels (501) for accommodating one or more elastic members (304, 306).

3. The metallic flow field plate (305) of claim 1, wherein the two or more first inlet legs (402) and the two or more first outlet legs (403) are located at a first edge (404) of the metallic flow field plate (305).

4. The metallic flow field plate (305) of claim 1, wherein each of the one or more elastic members (304 and 306) is in one of pre-cut form and formed- in-place by curing using activation and exposure to radiation during assembling of the pair of fuel cell assemblies (103a and 103b).

5. The metallic flow field plate (305) of claim 1, wherein the one or more second inlet legs (405) are engaged with one or more inlet manifolds (104) positioned on a pair of end plates

(102), and wherein the one or more second outlet legs (406) are engaged with one or more outlet manifolds (105) positioned on the pair of end plates (102).

6. The metallic flow field plate (305) of claim 1, wherein air and hydrogen reactively engage with a membrane electrode assembly (303 and 307) in each of the pair of fuel cell assemblies (103a, 103b) for supplying electric current to an electric circuit.

7. The metallic flow field plate (305) of claim 6, wherein: air from the two or more serpentine first flow channels (401) diffuses towards a cathode surface (303b) of the membrane electrode assembly (303) of the fuel cell assembly (103a), and hydrogen from the one or more serpentine second flow channels

(501) diffuses towards an anode surface (307a) of the membrane electrode assembly (307) of the fuel cell assembly (103b).

8. The metallic flow field plate (305) of claim 1, wherein the aeration device (110) is one of a blower and a centrifugal pump.

9. A fuel cell stack (100) comprising: a pair of end plates (101, 102), each of the pair of end plates (101, 102) comprise one or more inlet manifolds (104) and one or more outlet manifolds (105) for hydrogen; a plurality of fuel cell assemblies (103) positioned between the pair of end plates (101, 102), wherein a pair of fuel cell assemblies (103a, 103b) in the plurality of fuel cell assemblies (103) comprises: a pair of membrane electrode assemblies (303, 307), each of a first membrane electrode assembly (303) and a second membrane electrode assembly (307) comprising an anode face (303a, 307a) and a cathode face (303b, 307b); a metallic flow field plate (305) positioned between the first membrane electrode assembly (303) and the second membrane electrode assembly (307), the metallic flow field plate (305) comprises: a first surface (305a), comprising two or more serpentine first flow channels (401) of air, facing the cathode face (303b) of the first membrane electrode assembly (303), and a second surface (305b), rear of the first surface(305a), comprising one or more serpentine second flow channels (501) of hydrogen, facing the anode face (307a) of the second membrane electrode assembly (307), and a cover plate (107) removably attached to first edges (101a, 101b) of the pair of end plates (101, 103) for accommodating an aeration device (110).

10. The fuel cell stack (100) of claim 9, wherein the metallic flow field plate (305) further comprises a groove (407) formed on edges of each of the first surface (305a) and the second surface (305b), along the length of the two or more serpentine first flow channels (401) and the one or more serpentine second flow channels (501) for accommodating one or more elastic members (304, 306), wherein each of the one or more elastic members (304, 306) is positioned in the groove (407) on the edges of the each of the first surface (305a) and the second surface (305b) of the metallic flow field plate (305) for reactant tightness.

11. The fuel cell stack (100) of claim 9, further comprises a pair of monopolar collector plates (301, 309) for collecting electric current generated in the plurality of fuel cell assemblies (103), wherein each of the pair of monopolar collector plates (301, 309), is positioned between an end plate (101, 102) and one of the first membrane electrode assembly (303) or the second membrane electrode assembly (307).

12. The fuel cell stack (100) of claim 9, wherein a plurality of fasteners (106) and guides (202) compress the pair of end plates (101, 102), the plurality of fuel cell assemblies (103), and the pair of monopolar collector plates (301, 309) together.

13. The fuel cell stack (100) of claim 9, wherein the cover plate (107) comprises: an air inlet duct (109) of the fuel cell stack (100) removably engaged with a discharge (1101) of the aeration device (110), an air outlet duct (108) of the fuel cell stack (100) engaged with the metallic flow field plate (305), and a recirculation piping (111) connecting the air outlet duct (108) to the discharge (1101) of the aeration device (110) through a heat exchanging mechanism, for recirculation of air in the fuel cell stack (100).

14. The fuel cell stack (100) of claim 9, wherein each of the elastic member (304 and 306) is in one of pre-cut form and formed-in-place by curing using activation and exposure to radiation during assembling of the fuel cell stack (100).