Patent Publication Number: US-11387469-B2

Title: Electrochemical cells with improved fluid flow design

Description:
This application claims the benefit of U.S. Provisional Application No. 62/618,221, filed Jan. 17, 2018, which is incorporated by reference in its entirety. 
    
    
     The present disclosure is directed towards electrochemical cells, and more particularly, to electrochemical cells with improved fluid flow design. 
     Electrochemical cells, usually classified as fuel cells or electrolysis cells, are devices used for generating current from chemical reactions, or inducing a chemical reaction using a flow of current. For example, a fuel cell converts the chemical energy of fuel (e.g., hydrogen, natural gas, methanol, gasoline, etc.) and an oxidant (air or oxygen) into electricity and waste products of heat and water. A basic fuel cell comprises a negatively charged anode, a positively charged cathode, and an ion-conducting material called an electrolyte. 
     Different fuel cell technologies utilize different electrolyte materials. A Proton Exchange Membrane (PEM) fuel cell, for example, utilizes a polymeric ion-conducting membrane as the electrolyte. In a hydrogen PEM fuel cell, hydrogen atoms are electrochemically split into electrons and protons (hydrogen ions) at the anode. The electrons then flow through the circuit to the cathode and generate electricity, while the protons diffuse through the electrolyte membrane to the cathode. At the cathode, hydrogen protons combine with electrons and oxygen (supplied to the cathode) to produce water and heat. 
     An electrolysis cell represents a fuel cell operated in reverse. A basic electrolysis cell functions as a hydrogen generator by decomposing water into hydrogen and oxygen gases when an external electric potential is applied. The basic technology of a hydrogen fuel cell or an electrolysis cell can be applied to electrochemical hydrogen manipulation, such as, electrochemical hydrogen compression, purification, or expansion. Electrochemical hydrogen manipulation has emerged as a viable alternative to the mechanical systems traditionally used for hydrogen management. Successful commercialization of hydrogen as an energy carrier and the long-term sustainability of a “hydrogen economy” depend largely on the efficiency and cost-effectiveness of fuel cells, electrolysis cells, and other hydrogen manipulation/management systems. 
     In operation, a single fuel cell can generally generate about 1 volt. To obtain the desired amount of electrical power, individual fuel cells are combined to form a fuel cell stack, wherein fuel cells are stacked together sequentially. Each fuel cell may include a cathode, an electrolyte membrane, and an anode. A cathode/membrane/anode assembly constitutes a “membrane electrode assembly,” or “MEA,” which is typically supported on both sides by bipolar plates. Reactant gases or fuel (e.g., hydrogen) and oxidant (e.g., air or oxygen) are supplied to the electrodes of the MEA through flow fields. In addition to providing mechanical support, the bipolar plates (also known as flow field plates or separator plates) physically separate individual cells in a stack while electrically connecting them. A typically fuel cell stack includes manifolds and inlet ports for directing the fuel and oxidant to the anode and cathode flow fields, respectively. A fuel cell stack also includes exhaust manifolds and outlet ports for expelling the excess fuel and oxidant. A fuel cell stack may also include manifolds for circulating coolant fluid to help expel heat generated by the fuel cell stack. 
     In fuel cells it is desirable to have full and even distribution of the fuel and oxidant throughout the flow fields in order to maximize the active area of the MEA utilized, which improves the overall performance. But, prior art fuel cell designs have struggled to achieve even and full distribution. Additionally, it is desirable not to create excessive pressure drop along the flow path of the fuel and the oxidant, which can otherwise consume some of the electrical energy generated by the fuel cell stack and decrease the overall efficiency of the fuel cells stack. As such, there is a continuing challenge to improve the flow design of fuel cells. 
     Another way to improve the overall performance and power density of a fuel cell stack can be to reduce the pitch (i.e., spacing) between adjacent cells of the fuel cell stack and/or thickness of the cells. Cell thickness can be reduced, for example, by reducing the thickness of the flow fields of each individual fuel cell. This, however, can be difficult to achieve without creating an excessive pressure drop along the fuel and oxidant flow path due to the reduction in the flow path caused by compression of the fuel cell stack, which can increase the load on the fuel cell stack. 
     In consideration of the aforementioned circumstances, the present disclosure is directed toward a fuel cell and fuel cell stack design having improved flow design and improved performance and power density. 
     In one aspect, the present disclosure is directed to an electrochemical cell stack having a plurality of electrochemical cells stacked along a longitudinal axis. The electrochemical cells may each include a membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer, and a polymer membrane interposed between the cathode catalyst layer and the anode catalyst layer. The electrochemical cells may each further include an anode plate and a cathode plate with the membrane electrode assembly interposed therebetween, and the anode plate defines a plurality of channels that form an anode flow field facing the anode catalyst layer. The electrochemical cells may each also include a cathode flow field positioned between the cathode plate and the cathode catalyst layer, wherein the cathode flow field comprises a porous structure. In some embodiments, each electrochemical cell may further comprise a first manifold section that includes an anode feed manifold, a cathode discharge manifold, and a coolant discharge manifold and a second manifold section that includes an anode discharge manifold, a cathode feed manifold, and a coolant feed manifold. The coolant discharge manifold may be positioned between the anode feed manifold and the cathode discharge manifold and the coolant feed manifold may be positioned between the anode discharge manifold and the cathode feed manifold. In some embodiments, the cathode discharge manifold may be on one side of the coolant discharge manifold and the anode feed manifold may be on the opposite side of the coolant discharge manifold while the cathode feed manifold is right of the coolant feed manifold and the anode discharge manifold is left of the coolant feed manifold. In some embodiments, a fluid flow between the anode feed manifold and the anode discharge manifold through the anode flow field is cross and countercurrent to a fluid flow between the cathode discharge manifold and the cathode feed manifold through the cathode flow field. In some embodiments, each electrochemical cell may further comprise a first manifold section that includes a first anode feed manifold, a second anode feed manifold, a first cathode discharge manifold, a second cathode discharge manifold, a first coolant discharge manifold, a second coolant discharge manifold, and a second manifold section that includes a first anode discharge manifold, a second anode feed manifold, a first cathode feed manifold, a second cathode feed manifold, a first coolant feed manifold, and a second coolant feed manifold. The first coolant discharge manifold may be positioned between the first anode feed manifold and the first cathode discharge manifold and the second coolant discharge manifold may be positioned between the second anode feed manifold and the second cathode discharge manifold. The first coolant feed manifold may be positioned between the first anode discharge manifold and the first cathode feed manifold and the second coolant feed manifold may be positioned between the second anode discharge manifold and the second cathode feed manifold. In some embodiments, a fluid flow between the first and second anode feed manifolds and the first and second anode discharge manifolds through the anode flow field may cross and countercurrent to a fluid flow between the first and second cathode discharge manifolds and the first and second cathode feed manifolds through the cathode flow field. In some embodiments, a right half and a left half of the anode plate and the cathode plate may be laid out as a reflection across a bisecting line. In some embodiments, an area of the cathode discharge manifold may be larger than the coolant discharge manifold and the area of the coolant manifold may be larger than the area of the anode feed manifold. In some embodiments, each electrochemical cell may further comprise a gas diffusion layer positioned adjacent to each side of the membrane electrode assembly. In some embodiments, the porous structure includes at least nickel and chromium. The porous structure may include a nickel concentration of 60% to 80% by mass and a chromium concentration of 20% to 40% by mass and at least one surface of the porous structure may include a chromium concentration of about 3% to about 50% by mass. The porous structure may include a chromium concentration of about 3% to about 6%, a tin concentration of about 10% to about 20%, and a nickel concentration of about 74% to about 87%. 
     In another aspect, the present disclosure is directed to an electrochemical cell stack having a plurality of electrochemical cells stacked along a longitudinal axis. The electrochemical cells may each include a membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer, and a polymer membrane interposed between the cathode catalyst layer and the anode catalyst layer. The electrochemical cells may each further include an anode plate and a cathode plate with the membrane electrode assembly interposed therebetween, and the anode plate defines a plurality of channels that form an anode flow field facing the anode catalyst layer. The electrochemical cells may each also include a cathode flow field positioned between the cathode plate and the cathode catalyst layer, wherein the cathode flow field comprises a porous structure and the cathode plate includes a pair of cathode flow field borders along the sides of the porous structure. In some embodiments, the pair of cathode flow field borders extend from the cathode plate to the membrane electrode assembly and may be configured to prevent oxidant from flowing around the cathode flow field. In some embodiments, a distance between the cathode flow field borders may be about equal to a width of the cathode flow field. In some embodiments, the cathode flow field borders may protrude from the cathode plate a depth equal to a depth of the cathode flow field. In some embodiments, the cathode flow field borders may be generally rectangular shaped. In some embodiments, each electrochemical cell may further comprise a gas diffusion layer positioned adjacent to each side of the membrane electrode assembly. In some embodiments, the porous structure includes at least nickel and chromium. The porous structure includes a nickel concentration of 60% to 80% by mass and a chromium concentration of 20% to 40% by mass and at least one surface of the porous structure includes a chromium concentration of about 3% to about 50% by mass. The porous structure includes a chromium concentration of about 3% to about 6%, a tin concentration of about 10% to about 20%, and a nickel concentration of about 74% to about 87%. In some embodiments, a first surface of the porous structure has a higher chromium concentration than an opposite second surface. The first surface may have a chromium concentration ranging from about 3% to about 50% by mass and the second surface has a chromium concentration less than about 3% by mass. The first surface of the porous structure may face the membrane electrode assembly. In some embodiments, the cathode plate of each cell may be formed of uncoated stainless steel. 
     In another aspect, the present disclosure is directed to an electrochemical cell having a membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer, and a polymer membrane interposed between the cathode catalyst layer and the anode catalyst layer. The electrochemical cell may also have an anode plate and a cathode plate with the membrane electrode assembly interposed therebetween, and the anode plate defines a plurality of channels that form an anode flow field facing the anode catalyst layer. The electrochemical cell may further include a cathode flow field positioned between the cathode plate and the cathode catalyst layer, wherein the cathode flow field comprises a porous structure. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed. 
    
    
     
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and together with the description, serve to explain the principles of the disclosure. 
         FIG. 1  is a side schematic view of a plurality of electrochemical cells (e.g., fuel cells) stacked together, according to an exemplary embodiment. 
         FIG. 2  is a partially exploded side-perspective view of portions of adjacent fuel cells of  FIG. 1 , according to an exemplary embodiment. 
         FIG. 3  is a side perspective view of  FIG. 2  illustrating a flow path of fuel through a fuel cell, according to an exemplary embodiment. 
         FIG. 4  is a side perspective view of  FIG. 2  illustrating a flow path of oxidant through a fuel cell, according to an exemplary embodiment. 
         FIG. 5  is a side perspective view of  FIG. 2  illustrating a flow path of coolant fluid through adjacent fuel cells, according to an exemplary embodiment. 
         FIG. 6  is a front view of an anode plate of  FIG. 2 , according to an exemplary embodiment. 
         FIG. 7A  is an enlarged view of portions of  FIG. 6 . 
         FIG. 7B  is a cross-sectional schematic of a portion of a fuel cell, according to an exemplary embodiment. 
         FIG. 8A  is an enlarged view of a portion of  FIG. 6 . 
         FIG. 8B  is a cross-sectional schematic of a portion of  FIG. 8A . 
         FIG. 9  is a cross-sectional schematic of a fuel cell, according to an exemplary embodiment. 
         FIG. 10  is a front view of a cathode plate of  FIG. 2 , according to an exemplary embodiment. 
         FIG. 11A  is a front view of a cathode flow field of  FIG. 2 , according to an exemplary embodiment. 
         FIG. 11B  is a front view of another embodiment of a cathode flow field, according to an exemplary embodiment. 
         FIG. 11C  is a front view of another embodiment of a cathode flow field, according to an exemplary embodiment. 
         FIG. 11D  is a cross-sectional view along cross-section A-A of  FIG. 11C , according to an exemplary embodiment. 
         FIG. 11E  is a cross-sectional view along cross-section B-B of  FIG. 11C , according to an exemplary embodiment. 
         FIG. 11F  is a front view of another embodiment of a cathode flow field, according to an exemplary embodiment. 
         FIG. 12  is a side perspective view of portions of adjacent fuel cells, according to an exemplary embodiment. 
         FIG. 13  is a front view of an anode plate of  FIG. 12 , according to an exemplary embodiment. 
         FIG. 14  is a front view of a cathode plate of  FIG. 12 , according to an exemplary embodiment. 
         FIG. 15  is a front view of a cathode flow field of  FIG. 12 , according to an exemplary embodiment. 
     
    
    
     Reference will now be made in detail to the present exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Although described in relation to an electrochemical cell, in particular, a fuel cell employing hydrogen, oxygen, and water, it is understood that the devices and methods of the present disclosure can be employed with various types of fuel cells and electrochemical cells, including, but not limited to electrolysis cells, hydrogen purifiers, hydrogen expanders, and hydrogen compressors. 
     Throughout the specification the terms “generally parallel” and “generally perpendicular” may be used to describe the arrangement of one or more components in relation to an axis, plane, or other component. The degree of offset from parallel and perpendicular that can be tolerated when describing an arrangement as “generally parallel” or “generally perpendicular” can vary. The allowable offset may be, for example, less than about 20 degrees off, such as an offset less than about 10 degrees, an offset of less than about 5 degrees, and offset of less than about 3 degrees, an offset of less than about 2 degrees, and an offset of less than about 1 degree. 
       FIG. 1  is a side schematic side view of a plurality of electrochemical cells, for example, fuel cells  10  stacked together along a longitudinal axis  5  to form at least a portion of a fuel cell stack  11 , according to an exemplary embodiment. A fuel cell  10  can comprise a cathode catalyst layer  12 , which may also be referred to herein as a cathode, an anode catalyst layer  14 , which may also be referred to herein a anode, and a proton exchange membrane (PEM)  16  interposed between cathode catalyst layer  12  and anode catalyst layer  14 , which collectively may be referred to as a membrane electrode assembly (MEA)  18 . PEM  16  can comprise a pure polymer membrane or composite membrane with other material, for example, silica, heteropolyacids, layered metal phosphates, phosphates, and zirconium phosphates can be embedded in a polymer matrix. PEM  16  can be permeable to protons while not conducting electrons. Cathode catalyst layer  12  and anode catalyst layer  14  can comprise porous carbon electrodes containing a catalyst. The catalyst material, for example platinum, platinum-cobalt alloy, non-PGM, can increase the reaction of oxygen and fuel. In some embodiments, cathode catalyst layer  12  and anode catalyst layer  14  may have an average pore size of about 1 μm. 
     Fuel cell  10  can comprise two bipolar plates, for example, a cathode plate  20  and an anode plate  22 . Cathode plate  20  may be positioned adjacent cathode catalyst layer  12  and anode plate  22  may be positioned adjacent anode catalyst layer  14 . MEA  18  can be interposed and enclosed between cathode plate  20  and anode plate  22 . A cathode compartment  19  may be formed between MEA  18  and cathode plate  20  and an anode compartment  21  may be formed between MEA  18  and anode plate  22 . Cathode plate  20  and anode plate  22  can act as current collectors, provide access flow passages for fuel and oxidant to the respective electrode surfaces (e.g., anode catalyst layer  14  and cathode catalyst layer  12 ), and provide flow passages for the removal of water formed during operation of fuel cell  10 . Cathode plate  20  and anode plate  22  can also define flow passages for coolant fluid (e.g., water, glycol, or water glycol mixture). For example, between cathode plate  20  and anode plate  22  of adjacent fuel cells  10  a coolant compartment  23  may be formed, which is configured to circulate coolant fluid between adjacent fuel cells  10 . Heat generated by fuel cells  10  can be transferred to the coolant fluid and be carried away by the circulation of the coolant fluid. Cathode plate  20  and anode plate  22  may be made from, for example, aluminum, steel, stainless steel, titanium, copper, Ni—Cr alloy, graphite or any other suitable electrically conductive material. 
     In some embodiments, for example, as illustrated in  FIG. 1 , fuel cell  10  may also include electrically-conductive gas diffusion layers (e.g., cathode gas diffusion layer  24  and anode gas diffusion layer  26 ) within fuel cell  10  on each side of MEA  18 . Gas diffusion layers  24 ,  26  may serve as diffusion media enabling the transport of gases and liquids within the cell, provide electrically conduction between cathode plate  20 , anode plate  22 , and MEA  18 , aid in the removal of heat and process water from fuel cell  10 , and in some cases, provide mechanical support to PEM  16 . Gas diffusion layers  24 ,  26  can comprise a woven or non-woven carbon cloth with cathode catalyst layer  12  and anode catalyst layer  14  coated on the sides facing PEM  16 . In some embodiments, cathode catalyst layer  12  and anode catalyst layer  14  may be coated onto either the adjacent GDL  24 ,  26  or PEM  16 . In some embodiments, gas diffusion layers  24 ,  26  may have an average pore size of about 10 μm. 
     Fuel cell  10  may further include flow fields positioned on each side of MEA  18 . For example, fuel cell  10  may include a cathode flow field  28 , which may comprise a porous structure positioned between cathode plate  20  and GDL  24  and an anode flow field  30 , which may be formed by anode plate  22 , as described further herein. The flow fields may be configured to enable fuel and oxidant on each side of MEA  18  to flow through and reach MEA  18 . It is desirable that these flow fields facilitate the even distribution of fuel and oxidant to cathode and anode catalyst layers  12 ,  14  so as to achieve high performance of fuel cell  10 . GDL  24  may provide mechanical protection of cathode catalyst layer  12  from cathode flow field  28 . 
     It is to be understood that although only one fuel cell  10  in  FIG. 1  includes reference numerals for cathode catalyst layer  12 , anode catalyst layer  14 , proton exchange membrane  16 , membrane electrode assembly (MEA)  18 , cathode compartment  19 , cathode plate  20 , anode compartment  21 , anode plate  22 , coolant compartment  23 , gas diffusion layer  24 , gas diffusion layer  26 , cathode flow field  28 , and anode flow field  30 , the other fuel cells  10  of stack  11  may include the same elements. 
     Fuel cell stack  11  may also include a plurality of fluid manifolds  31 A,  31 B extending along longitudinal axis  5  defined by the series of stacked cathode plates  20  and anode plates  22  of fuel cells  10 . Fluid manifolds  31 A,  31 B may be configured for feeding fuel (e.g., hydrogen) and oxidant (e.g., oxygen) to MEA  18  of each fuel cell  10  and discharging reactant products (e.g., unreacted fuel, unreacted oxidant, and water) from MEA  18  of each fuel cell. Fluid manifolds  31 A,  31 B may also be configured for feeding and discharging coolant fluid through coolant compartments  23 . The direction of flow through fluid manifolds  31 A,  31 B, cathode compartments  19 , anode compartments  21 , and coolant compartments  23  may vary. For example, in some embodiments the flow through the manifolds and compartments may be concurrent while in other embodiments, one or more of the flow paths may be countercurrent. For example, in some embodiments, the flow of fuel through anode compartment  21  may be countercurrent to the flow of oxidant through cathode compartments  19 . Fluid manifolds  31 A,  31 B may fluidly connect to MEA  18  via passages and ports. Specific manifolds, passages, and ports may be identified herein by “feed” or “discharge” and “inlet” or “outlet,” but it is to be understood these designations may be determined based on the direction of flow and the direction of flow may be switched. Changing the direction of flow may change these designations. 
       FIG. 2  shows a partially exploded side-perspective view of portions of adjacent fuel cells  10 . For example,  FIG. 2  shows MEA  18 , GDL  24 , and anode plate  22  of one fuel cell  10  and also cathode plate  20 , cathode flow field  28 , MEA  18 , and GDL  24  of an adjacent fuel cell  10 . Anode compartment  21  may be formed between adjacent MEA  18  and anode plate  22 . Coolant compartment  23  may be formed between adjacent anode plate  22  and cathode plate  20 . Cathode compartment  19  may be formed between adjacent cathode plate  20  and MEA  18 , which may contain cathode flow field  28 . As shown in  FIG. 2 , fuel cells  10  may include fluid manifolds  31 A,  31 B, which may also be referred to as upper and lower fluid manifolds. Fluid manifolds  31 A,  31 B may extend along longitudinal axis. 
       FIGS. 3-5  illustrate flow paths of fuel, oxidant, and cooling fluid through fuel cells  10 , according to one illustrative embodiment. But it is to be understood that for other embodiments the direction of one or more of the flow paths may be switched, for example, by reversing the direction of flow.  FIG. 3  illustrates a flow path for fuel circulated through the anode side of MEA  18  of fuel cell  10 ,  FIG. 4  illustrates a flow path for oxidant circulated through the cathode side of MEA  18  of fuel cell  10 , and  FIG. 5  illustrates a flow path for coolant fluid circulated between adjacent fuel cells  10 . 
     Referring now to  FIG. 3 , first fluid manifolds  31 A may include at least one anode feed manifold  32  that may fluidly connect and direct fuel through at least one anode inlet passage  34  through at least one anode inlet port  36  into anode compartment  21 . Fuel (e.g., unreacted fuel) from anode compartment  21  may be directed from anode compartment  21  through at least one anode outlet port  38  through at least one anode outlet passage  40  into at least one anode discharge manifold  42 . Anode inlet passage  34  and anode outlet passage  40  may be located between anode plate  22  and cathode plate  20  of adjacent fuel cells  10 . Perimeters of anode inlet passage  34  and anode outlet passage  40 , as well as anode feed manifold  32  and anode discharge manifold  42 , may be sealed by surface gaskets  43 , as illustrated in  FIG. 3 . Surface gaskets  43  may be made of a polymeric or elastomeric material such as silicone, Viton, Buna, polyethylene, polypropylene, or any other suitable seal material. The cross-sectional shape of surface gaskets  43  may be rectangular, triangular, semi-circular, multi-tooth (triangle), or parabolic. The shape may be determined by the acceptable leak rate, operating pressures, tolerance make-up, or other significant sealing design parameters. Surface gaskets  43  can be applied with any known method such as injection molding, compression molding, pick-and-place, robotic dispensing, and may be adhered directly through a molding process or with the aid of pressure or temperature-sensitive adhesives. Curing of surface gaskets  43  can be accomplished by known processes such as thermal curing, ultraviolet-light curing, or humidity cures. 
     As shown in  FIG. 4 , second fluid manifolds  31 B may include at least one cathode feed manifold  44  that may fluidly connect and direct oxidant through at least one cathode inlet passage  46  through at least one cathode inlet port  48  into cathode compartment  19 . Oxidant from cathode compartment  19  may be directed from cathode compartment  19  through at least one cathode outlet port  50  through at least one cathode outlet passage  52  into at least one cathode discharge manifold  54 . Cathode inlet passage  46  and cathode outlet passage  52  may be located between anode plate  22  and cathode plate  20  of adjacent fuel cells  10 . Perimeters of cathode inlet passage  46  and cathode outlet passage  52 , as well as cathode feed manifold  44  and cathode discharge manifold  54  may be sealed by surface gaskets  43 , as illustrated in  FIG. 4 . 
     As shown in  FIG. 5 , second fluid manifolds  31 B may include at least one coolant feed manifold  56  that may fluidly connect and direct coolant fluid through at least one coolant inlet passage  58  to a coolant flow field  86  within coolant compartment  23 . Within coolant compartment  23  the coolant fluid may flow between anode plate  22  and cathode plate  20  through coolant flow field  86  comprised of a plurality of coolant channels defined by anode plate  22 , as will be described further herein. Heat generated by adjacent fuel cells  10  may be transferred to the coolant fluid and removed from fuel cells  10  by the circulation of the coolant fluid. The coolant fluid from coolant compartment  23  may be directed through at least one coolant outlet passage  60  into at least one coolant discharge manifold  62 . Coolant inlet passage  58  and coolant outlet passage  60  may be located between anode plate  22  and cathode plate  20  of adjacent fuel cells  10 . Perimeters of coolant inlet passage  58  and coolant outlet passage  60 , as well as coolant feed manifold  56  and coolant discharge manifold  62  may be sealed by surface gaskets  43 , as illustrated in  FIG. 5 . 
       FIG. 6  is a front view of anode plate  22 , according to exemplary embodiment. The side visible in  FIG. 6  is the side configured to face the anode side of MEA  18  (i.e., anode catalyst layer  14  and gas diffusion layer  26 ) and define one side of anode compartment  21  (see e.g.,  FIGS. 1 and 2 ). Anode plate  22  may include several sections. These sections may include for example, first manifold section  31 A and second manifold section  31 B, distribution channel sections, for example, a first anode distribution channel  68  and a second anode distribution channel  70 , and anode flow field  30 . As shown in  FIG. 6 , anode plate  22  may include anode feed manifold  32 , cathode discharge manifold  54 , and coolant discharge manifold  62  in first manifold section  31 A while second manifold section  31 B may include anode discharge manifold  42 , cathode feed manifold  44 , and coolant feed manifold  56 . It is to be understood, that the designation of inlet and outlet for each manifold may be switched, for example, by switching the respective flow direction of the fuel, the oxidant, or the coolant fluid flow through fuel cells  10 . 
     The cross-sectional area of each manifold can vary. For example, as shown in  FIG. 6 , cathode feed and discharge manifolds  44 ,  54  may have larger cross-sectional areas than coolant feed and discharge manifolds  56 ,  62  while coolant feed and discharge manifolds  56 ,  62  may have larger cross-sectional areas than anode feed and discharge manifolds  32 ,  42 . The cross-sectional area of each passage may be determined based on a variety of variables, including for example, the number of cells, current density at peak-power operating conditions, design stoichiometry of the reactants, the difference between the inlet and outlet coolant temperature, flow resistance of individual cells, the size of active area, fluid pressure, and fluid flow rate. The cross-sectional area of one or more passages may be sized so as to minimize fluid pressure variations along the length of the electrochemical cell stack, such as during high fluid flow rates. 
     The arrangement of the manifolds within first manifold section  31 A and second manifold section  31 B can also vary. As shown in  FIG. 6 , the arrangement of the manifolds may be different between first manifold section  31 A and second manifold section  31 B. In one illustrative example, as shown in  FIG. 6 , coolant discharge manifold  62  may be positioned between anode feed manifold  32  and cathode discharge manifold  54  and coolant feed manifold  56  may be positioned between anode discharge manifold  42  and cathode feed manifold  44 . In some embodiments, cathode discharge manifold  54  may be left of coolant discharge manifold  62  and anode feed manifold  32  may be right of coolant discharge manifold  62  while cathode feed manifold  44  may be right of coolant feed manifold  56  and anode discharge manifold  42  may be left of coolant feed manifold  56 . Swapping the positioning of the anode and cathode manifolds relative to the coolant manifolds between first manifold section  31 A and second manifold section  31 B may be advantageous because it promotes a diagonal cross countercurrent flow or “z-flow” rather than a straight across flow. The diagonal cross countercurrent flow may provide improved uniform distribution of fuel and oxidant in anode compartment  21  and cathode compartment  19 , which may improve fuel cell performance. The performance may be improved because the diagonal cross countercurrent flow may optimize the active area utilized. With the z-flow pattern, the stream-path distance from inlet to outlet for one or more reactants may be substantially uniform regardless of the flow path. This symmetry may result in fluids distributing and flowing uniformly throughout the flow field. Uniform flow throughout the flow field  30  may result in more uniform and/or linear gradients of reactant composition and coolant temperature, which may result in uniform and/or linear gradients of cell temperature. This may result in higher performance and/or lower variance in performance between cells. 
     The positioning of the coolant manifolds  56 ,  62  in the center of first fluid manifold  31 A and second fluid manifold  31 B may be advantageous because the central region of the coolant compartment is most likely to receive the most coolant fluid flow and this area corresponds to the central region of the active area of fuel cell  10  where there may be increased heat generation and or a tendency for higher operating temperature. In other words, the region of the fuel cell  10  that will tend toward operating at higher temperature will correspond with the region receiving the most coolant fluid flow. In addition, the sides of fuel cell  10  may be aided by ambient cooling so promoting coolant fluid flow through the central region of coolant compartments  23  of each fuel cell is advantageous. 
     As shown in  FIG. 6 , positioned between first and second manifold sections  31 A,  31 B and anode flow field  30  are first and second anode distribution channels  68 ,  70 . First anode distribution channel  68  may be configured to distribute fuel supplied from anode feed manifold  32  via anode inlet passage  34  through anode inlet port  36  to anode flow field  30 . Second anode distribution channel  70  may be configured to collect fuel (e.g., unreacted fuel) from anode flow field  30  and direct fuel through anode outlet port  38  to anode discharge manifold  42  via anode outlet passage  40 . First anode distribution channel  68  and second anode distribution channel  70  may be sandwich between and defined by MEA  18  and anode plate  22 . Perimeters of first anode distribution channel  68  and second anode distribution channel  70  may be sealed by surface gaskets  43 , as illustrated in  FIG. 6 . In some embodiments, a width of first anode distribution channel  68  and a width of second anode distribution channel  70  may be generally equal to a width of anode flow field  30 . 
     First anode distribution channel  68  may be configured so fuel supplied through anode inlet port  36  may be distributed across a width of first anode distribution channel  68  and directed to anode flow field  30  through a plurality of openings  74 . In some embodiments, each opening  74  may be configured as an orifice to produce some back pressure on the fuel within first anode distribution channel  68 . The back pressure may promote the distribution of fuel within first anode distribution channel  68  thereby ensuring first anode distribution channel  68  is fully flooded with fuel. In some embodiments, fully flooding first anode distribution channel  68  enables fuel to be delivered to substantially all channels of anode flow field  30  through all of openings  74 . Fully flooding first anode distribution channel  68  may prevent or reduce the risk of short circuiting the flow of fuel along a path of least resistance through anode flow field  30 , which could reduce the performance of fuel cells  10  due to the reduction in active area being utilized. In some embodiments, orifice openings  74  may be sized to enable the minimum amount of back pressure needed to ensure fully flooding of first anode distribution channel  68 . As illustrated in  FIG. 6 , second anode distribution channel  70  may be configured the same as first anode distribution channel  68  with a plurality of orifice shaped openings  74  fluidly connecting the channels of anode flow field  30  and second anode distribution channel  70 . Openings  74  may have a smaller cross-sectional area than the corresponding channel in anode flow field  30 . Channels in anode flow field  30 , although shown as straight paths, may be wavy or zig-zag paths. Channels in anode flow field  30  have a cross-sectional area that is generally square, semi-circular, parabolic, or any other suitable shape. 
     Compression of fuel cells  10  during assembly and the compressed state maintained during operation may compromise the flow path integrity within distribution channels. For example, compression of fuel cells  10  may cause the volume of the distribution channels to decrease, which can restrict flow of fuel, oxidant, and coolant and increase pressure drop through fuel cells  10 . To prevent or minimize shrinking or collapsing of first anode distribution channel  68  and second anode distribution channel  70  when fuel cell  10  is compressed, first anode distribution channel  68  and/or second anode distribution channel  70 , in some embodiments, may include a plurality of support features  76  spread throughout the distribution channels. Support features  76  may be formed as integrated features of anode plate  22 . Support features  76  may be evenly spaced throughout first anode distribution channel  68  and second anode distribution channel  70 . 
     In one illustrative embodiment,  FIG. 7A  shows an enlarged view of a portion of a plurality of dimple shaped support features  76  that may be formed in first anode distribution channel  68  and/or second anode distribution channel  70 . These dimple shaped support features  76  can extend from anode plate  22  in both directions along longitudinal axis  5 . For example,  FIG. 7B  shows a cross-sectional schematic of the dimple shaped support features  76  formed by anode plate  22 . The dimple shaped support features  76  can extend from anode plate  22  in both directions to contact cathode plate  20  on one side and contact MEA  18  (e.g., subgaskets of MEA  18 ) on the other side. As shown in  FIG. 7B , between anode plate  22  and MEA  18  may be the space that forms first anode distribution channel  68  or second anode distribution channel  70  and enables flow of fuel. In other embodiments, other support features may be formed in other shapes besides dimples, including for example, cone shaped, semi-spherical shaped, cube shaped, and cylinder shaped. 
     As shown in  FIG. 7B , on the opposite side of anode plate  22 , between anode plate  22  and cathode plate  20  may be the space that forms a first and second coolant distribution channels  78 ,  80  fluidly connecting coolant feed manifold  56 , coolant discharge manifold  62  with a coolant flow field  86  contained with coolant compartment  23 . First and second coolant distribution channels  78 ,  80  of coolant compartment  23  can be configured similar to first and second anode distribution channels  68 ,  70 . For example, first and second coolant distribution channels  78 ,  80  may include a plurality of dimple shaped support features  76  evenly spaced throughout. First and second coolant distribution channels  78 ,  80  may be configured to provide full and uniform distribution to coolant flow field  86  (see e.g.,  FIG. 5 ). Additionally, in some embodiments, a plurality of orifice shaped openings may fluidly connect first and second coolant distribution channels  78 ,  80  with coolant flow field  86  (see  FIG. 5 ). These orifice shaped openings may apply some back pressure on the coolant fluid, for example, in first and/or second coolant distribution channels  78 ,  80 —depending on direction of flow—in order to ensure uniform distribution and prevent or reduce the likelihood of short circuiting along a path of least resistance. 
     The number, distribution, and size of the support features  76  may be determined by taking into account a variety of design considerations. For example, too many or too large support features  76  can lead to excessive pressure drop within distribution channels  68 ,  70 ,  78 ,  80  while too few or too small support features  76  can result in insufficient structural support and shrinking of distribution channels  68 ,  70 ,  78 ,  80  when under compression, which can also lead to excessive pressure drop. According to an exemplary embodiment, the arrangement of structural features can be expressed as a function of a distance (Dc) between support features  76  and a thickness (t p ) of cathode plate  20 . For example, a ratio of Dc/t p  can be greater than about 3, but less than about 50. According to an exemplary embodiment, Dc can be about 1.5 mm and t p  can be about 0.1 mm, therefore the ratio of Dc/t p  can be about 15. 
     Due to the compression of fuel cells during operation, it can be challenging to maintain the integrity (e.g., prevent shrinking) of inlet and outlet ports flow area where gaskets are relied up to create or maintain the flow area. Shrinking of the inlet and outlet ports can restrict flow of reactants and reactant products and increase pressure drop through the fuel cells. The one or more anode inlet and outlet ports  36 ,  38  of fuel cell  10 , as described herein, may be configured to prevent or avoid shrinking due to compression. 
     Anode inlet and outlet ports  36 ,  38  may be integrated into one or more support features  82 . For example, as shown in  FIGS. 8A and 8B  anode inlet ports  36  may be formed in a side wall  84  of support feature  82 . Support features  82  may extend from anode plate  22  toward MEA  18 . As a result, the flow directions of fuel may be redirected within support features  82  so that the flow direction through anode inlet and outlet ports  36 ,  38  is generally parallel to anode plate  22 . In other words, this configuration may enable fuel through anode inlet ports  36  to be directed into first anode distribution channel  68  in a direction generally parallel to anode plate  22  rather than perpendicular. Similarly, this configuration may enable fuel through anode outlet ports  38  to be directed from second anode distribution channel  70  in a direction generally parallel to anode plate  22  rather than perpendicular. 
     Such a configuration can prevent or avoid shrinking of the flow path through anode inlet and outlet ports  36 ,  38  because support feature  82  may be designed to withstand the compression during operation thereby generally maintaining the cross-sectional area for flow. In comparison, often prior art fuel cells rely on gaskets in order to maintain spacing for flow and under compression these gaskets compress thereby reducing the available area available for fluid flow causing an increase in pressure drop thereby by restricting flow. 
     Support features  82  may be any suitable shape. For example, in one illustrative embodiment as shown in  FIG. 8A , support features  82  may be a generally rounded rectangular shape. In other embodiments, support features  82  may be circular, oval shaped, square shaped, etc. Support features  82  may each include one or more anode ports (e.g., anode inlet ports  36  and anode outlet ports  38 ). For example, in one illustrative embodiment as shown in  FIG. 8A , support feature  82  may include five anode inlet ports  36  evenly spaced along a length of support features  82 . 
     Anode flow field  30  may be configured as a channel flow field that faces and aligns with the active area of anode catalyst layer  14  on the anode side of MEA  18 . Anode flow field  30  may include a plurality of parallel channels that extend between first anode distribution channel  68  and second anode distribution channel  70 , as shown in  FIG. 6 .  FIG. 9  is a cross-sectional schematic top view of a portion of fuel cell  10 . As shown in  FIG. 9 , anode plate  22  may be shaped to form a plurality of channels  78 A,  78 C, which may be generally square, semi-cylindrical or parabolic-shaped corrugated channels. Anode channels  78 A, which may form anode flow field  30 , may be open to anode compartment  21  and configured to direct the flow of fuel across GDL  26  so the fuel can flow through GDL  26  and reach anode catalyst layer  14 . Coolant channels  78 C, which may form coolant flow field  86 , may be open to and part of coolant compartment  23  and configured to direct coolant fluid flow through coolant compartment  23  so heat generated by fuel cell  10  may be transferred to the coolant fluid and carried from fuel cell  10  by circulation of the coolant fluid. 
     The dimension of channels  78 A,  78 C may be determined based on numerous variables including for example, active area, power, compressive load on fuel cell  10 , desired or designed flow resistance, anode and/or cathode plate thickness and material properties (e.g., elasticity), open flow field properties and/or thickness, gas diffusion layer properties and/or thickness, design flow resistance for the anode, cathode, and/or coolant fluid. In some embodiments, a width (A) of coolant channels  78 C may be equal to a width (B) of anode side channels  78 . In other embodiments, width (B) of anode channels  78 A may be greater than or less than width (A) of coolant channels  78 C. A combined width of an anode channel  78 A and a coolant channel  78 C may be referred to as (C). The anode channels and coolant channels may have a depth (S). According to an exemplary embodiment, the ratio of C/S may be greater than about 1 and less than about 10. Accordingly to an exemplary embodiment the ratio of A/B may range from between greater than about 1 to less than about 6 or greater than about 2 or less than about 4. These ratios may be determined based on a mechanical load due to compression ranging from about 10 kg/cm 2  to about 75 kg/cm 2 . 
     The square corrugate channel design, as described herein, provides improved fluid flow while also minimizing fuel cell  10  thickness by integrating anode flow field  30  and coolant flow field  86  into alternating channels on opposite sides of anode plate  22 . This integration enables the overall thickness (e.g., pitch) of fuel cell  10  to be reduced. In addition, the square corrugated geometry provides sufficient surface area contact between anode plate  22  and GDL  26  as well as cathode plate  20  to prevent deformation when under compression during operation. For example, if the channels are too narrow the small surface areas can act as stress concentrators and may deform or damage the adjacent components (e.g., GDL  26 ). Similarly, if the channels where triangle shaped corrugations the triangle points could create stress concentration points that could deform the adjacent components. 
       FIG. 10  is a front view of cathode plate  20 , according to exemplary embodiment. The side visible in  FIG. 10  is the side configured to face adjacent anode plate  22  (see e.g.,  FIG. 2 ). Cathode plate  20  may include first manifold section  31 A and a second manifold section  31 B like anode plate  22 . As shown in  FIG. 10 , anode plate  22  may include anode feed manifold  32 , cathode discharge manifold  54 , and coolant discharge manifold  62  in first manifold section  31 A while second manifold section  31 B may include anode discharge manifold  42 , cathode feed manifold  44 , and coolant feed manifold  56 . It is to be understood, that the designations of “inlet” or “outlet” for each manifold may be switched, for example, by switching a flow direction of the fuel, the oxidant, or the coolant fluid through fuel cells  10 . 
     Cathode plate  20  may include a plurality of cathode inlet ports  48  configured to fluidly connect cathode compartment  19  and cathode flow field  28  with cathode feed manifold  44  via a cathode inlet passage  46 . Cathode plate  20  may also include a plurality of cathode outlet ports  50  configured to fluidly connect cathode compartment  19  and cathode flow field  28  with cathode discharge manifold  54  via a cathode outlet passage  52 . Cathode inlet and outlet passages  46 ,  52  may be located between anode plate  22  and cathode plate  20  of adjacent fuel cells  10 . Perimeters of cathode inlet and outlet passages  46 ,  52 , as well as cathode feed and discharge manifolds  44 ,  54 , may be sealed by surface gaskets  43 , as illustrated in  FIG. 10 . 
     Cathode inlet and outlet ports  48 ,  50  may be generally rectangular shaped as illustrated in  FIG. 10 . Cathode plate  20  may be configured to have at least two cathode inlet ports  48  arranged generally perpendicular to one another, as illustrated in  FIG. 10 . Cathode plate  20  may be configured to have at least two cathode outlet ports  50  arranged generally perpendicular to one another, as illustrated in  FIG. 10 . Cathode plate  20  may be configured to have at least one cathode inlet port  48  positioned at opposite ends of cathode inlet passage  46 . Cathode plate  20  may be configured to have at least one cathode outlet port  50  positioned at opposite ends of cathode outlet passage  52 . Cathode plate may be configured to have two cathode inlet ports  48  positioned at one end of cathode inlet passage  46  and one cathode inlet port  48  positioned at the opposite end. The two cathode inlet ports  48  positioned at one end may be generally parallel to one another and generally perpendicular to the cathode inlet passage  46  positioned at the opposite end of cathode inlet passage  46 . The shape and arrangement of cathode inlet ports  48 , as described herein, may promote improved distribution of the oxidant as it flows into cathode compartment  19 . 
     Rectangular shaped cathode inlet ports  48  may be advantageous over round shaped ports because the flow through the ports turns 90 degrees immediately after passing through the ports. The greater the perimeter of the hole relative to its area, the more “spill length” the fluid has and therefore the lower its velocity (and pressure drop) as it makes the turn. The net result is that for two holes, one round and one rectangular, with the same cross-sectional area, the pressure drop in this application is lower for the rectangular port than for a round port. The orientation of the rectangle, with the long edge generally facing the incoming fluid flow, may also result in greater “spill length” and lower pressure drop. 
     The total inlet area of the plurality of cathode inlet ports  48  may be greater than a total outlet area of the cathode outlet ports  50 . Cathode outlet ports  50  having a total outlet area less than the total inlet area can produce a back pressure on oxidant flow through cathode compartment  19  and cathode flow field  28 . Such back pressure may promote improved distribution of oxidant across the cathode compartment. 
     As shown in  FIG. 10 , cathode plate  20  may include surface features, for example, cathode flow field borders  88  that protrude out from cathode plate  20  toward MEA  18  along the sides of cathode flow field  28  (see e.g.,  FIG. 2 ). As shown in  FIG. 10 , cathode flow field borders  88  may span between first fluid manifolds  31 A and second fluid manifolds  31 B along opposite sides of cathode plate  20 . Cathode flow field borders  88  may be configured to prevent or reduce the amount of flow of oxidant bypassing cathode flow field  28  and cathode catalyst layer  12  by flowing along the outside of cathode flow field  28  rather than flowing through cathode flow field  28  to cathode catalyst layer  12 . For example, cathode flow field borders  88  can act as border walls on each side of cathode flow field  28  thereby forcing oxidant flow through cathode flow field  28 . Cathode plate  20  may be configured so that a distance between cathode flow field borders  88  is about equal to a width of cathode flow field  28 . Cathode flow field borders  88  may be configured to protrude from cathode plate  20  a depth equal to a depth of cathode flow field  28 . Cathode flow field borders  88  may be generally rectangular shaped with rounded or chamfered outer corners, as shown in  FIG. 10 . Cathode flow field borders  88  may be positioned to provide a tight-fit along the edges of cathode flow field  28  in order to prevent or limit any open flow area for fluid to “run along” the perimeter length of cathode flow field  28 . In some embodiments, cathode flow field borders  88  may be formed by cathode plate  20  or in some embodiments cathode flow field borders  88  may be formed by applying a second material to cathode plate  20  (e.g., a polymer, elastomer, surface gaskets  43  material bonded to the plate in the shape of cathode flow field borders  88 ). 
     In some embodiments, rather than apply surface gaskets  43  to both the cathode plate  20  and anode plate  22 , all the surface gaskets  43  described herein may be applied to either side of cathode plate  20 , which may be generally flat. By consolidating all the surface gaskets  43  on just cathode plate  20 , which can be flat, this can reduce both tooling cost and processing cost. For example, because anode plate  22  has channels  78 A,  78 C, making it not generally flat, applying a surface gasket to anode plate  22  is more complex, thereby increasing the tooling and processing cost. 
     To further reduce the tooling and processing cost, in some embodiments, alignment features  112  (see e.g.  FIGS. 6 and 10 ) may be incorporated in the surface gaskets to facilitate assembling each fuel cell  10  as well as alignment of a plurality of fuel cells  10  into fuel cell stack  11 . For example, the alignment features  112  of anode plate  22  (see  FIG. 6 ) may be holes that aligns with surface gasket protrusions, which may be alignment feature  112  of cathode plate  20  (see  FIG. 10 ). The protrusions may elastically deform upon insertion through the holes of anode plate  22  and recover on the other side, thereby forming an interference fit. Utilizing interference fits to assemble the cell  10  and stack  11  can avoid the need for some welding operations in the assembly process. 
       FIG. 11A  is a front view of cathode flow field  28 , according to exemplary embodiment. The side visible in  FIG. 11A  is the side configured to face adjacent cathode plate  20  (see, e.g.,  FIG. 2 ). Cathode flow field  28  may comprise a porous structure, in particular a porous metallic foam structure having a porous three-dimensional network structure. The porous structure may be sheet-shaped with two opposing surfaces. In some embodiments, the porous metallic foam structure may have an average pore size of about 50 to 500 μm. Cathode flow field  28  may include a first cathode distribution channel  90  and a second cathode distribution channel  92  recessed into the surface of the porous metallic foam structure facing cathode plate  20 . Cathode flow field  28  may have a thickness of for example, about 0.2 mm to about 1.5 mm. First cathode distribution channel  90  and/or second cathode distribution channel  92  may be recessed into cathode flow field a depth of between about 10% and about 75% of the thickness. 
     First cathode distribution channel  90  may extend generally from one side of cathode flow field  28  to the other side along a bottom edge of cathode flow field  28 . Second cathode distribution channel  92  may extend generally from one side of cathode flow field  28  to the other side along a top edge of cathode flow field  28 . When cathode flow field  28  is positioned adjacent cathode plate  20 , cathode inlet ports  48  may be aligned with first cathode distribution channel  90  and cathode outlet ports  50  may be aligned with second cathode distribution channel  92 . 
     Cathode flow field  28  may include a plurality of support features  94  formed throughout first cathode distribution channel  90  and/or second cathode distribution channel  92 . Support features  94  may be generally cylindrical, dimple shaped, or other suitable shape. A height of one or more support features  94  may be about equal to the recess depth of first cathode distribution channel  90  and/or second cathode distribution channel  92 . First cathode distribution channel  90 , second cathode distribution channel  92 , and support features  94  may be formed by stamping, rolling or otherwise plastically deforming the porous metallic foam structure forming cathode flow field  28 . 
     First cathode distribution channel  90  and second cathode distribution channel  92  may be configured to promote uniform flow distribution of oxidant along a width of cathode flow field  28  by providing an open flow path for the oxidant to flow along before flowing into the pores of the porous metallic foam structure. Support features  94  may be configured to provide adequate support during mechanical compression and also during operation to maintain the open flow path provided by first cathode distribution channel  90  and second cathode distribution channel  92  when fuel cell  10  is compressed by preventing or reducing deformation or deflection of cathode plate  20  into first cathode distribution channel  90  and second cathode distribution channel  92 . 
       FIGS. 11B, 11C, and 11F  are front views of additional embodiments of cathode flow fields  28 ′,  28 ″,  28 ″. In some embodiments, cathode flow fields  28 ′,  28 ″,  28 ′″ may be utilized in fuel cell  10  in place of cathode flow field  28 . Cathode flow fields  28 ′,  28 ″,  28 ′″ may include all the features of cathode flow field  28 , as described herein, as well as the additional features as will be described below. The side visible in  FIGS. 11B, 11C, and 11F  may be the side configured to face adjacent cathode plate  20  or the side configured to face adjacent MEA  18 . 
     Cathode flow fields  28 ′,  28 ″ may include a plurality of feed (or first) channels  101  and a plurality of discharge (or second) channels  102 . Feed channels  101  and discharge channels  102  may be stamped, cut, molded, or otherwise formed in cathode flow field  28 ′ on the surface facing cathode plate  20 . As shown in  FIGS. 11B and 11C , feed channels  101  may start at and be in fluid communication with first cathode distribution channel  90  and extend toward second cathode distribution channel  92 . Discharge channels  102  may end at and be in fluid communication with second cathode distribution channel  92  and extend toward first cathode distribution channel  90 . Feed channels  101  and discharge channels  102  may be interdigitated, as shown in  FIG. 11B  such that discharge channels  102  may be positioned between adjacent feed channels  101 . In some embodiments, feed channels  101  and discharge channels  102  may be substantially free of obstructions to fluid flow to enable improved oxidant distribution. In some embodiments, feed channels  101  and discharge channels  102  may include dimples (not shown) similar to dimples  94  found in first and second cathode distribution channels  90 ,  92 . 
     It is contemplated that, in certain embodiments, the plurality of feed channels  101  and discharge channels  102  may have different arrangements, shapes and/or cross-sectional areas. For example, in  FIG. 11B  the width of feed and discharge channels  101 ,  102  may vary along the length of cathode flow field  28 ′. In  FIG. 11B  the feed channels  101  start wide at or near first cathode distribution channel  90  and narrow to a point extending toward second cathode distribution channel  92  while the discharge channels start at a point and widen extending toward second cathode distribution channel  92 . In some embodiments, the distal ends of the feed channels  101  may be flat rather than a point as shown in  FIG. 11B . Similarly, in some embodiments the proximal ends of the discharge channels  102  may be flat rather than a point as shown in  FIG. 11B . With this arrangement, there is not direct fluid communication between the feed channels  101  and discharge channels  102 . Rather, oxidant distributed by first cathode distribution channel  90  to the feed channels  101  may flow through the plurality of feed channels  101  and may be forced to diffuse through the porous structure of cathode flow field  28 ′ to adjacent discharge channels  102 . 
       FIG. 11C  shows another arrangement of feed channels  101  and discharge channels  102  for cathode flow field  28 ″ in which the width of feed and discharge channels  101 ,  102  remain about the same along the length of cathode flow field  28 ″. Although, the width of feed and discharge channels  101 ,  102  remain about the same, a depth of feed and discharge channels  101 ,  102  may vary along the length of cathode flow field  28 ″. For example,  FIG. 11D  shows a cross-section of cathode flow field  28 ″ along cross-section A-A through a feed channel  101 . As shown in  FIG. 11D , feed channels  101  may start deepest (i.e., maximum depth fd 1 ) at or near first cathode distribution channel  90  and the depth may decrease extending toward second cathode distribution channel  92 . As shown in  FIG. 11D , the depth may decrease at a constant rate (e.g., linearly) or in some embodiments, the depth may decrease at a variable rate (e.g., non-linearly, exponentially). As shown in  FIG. 11D , feed channels  101  may dead end flat at the distal end with a minimum depth (fd 2 ). In other embodiments, feed channels  101  may dead end at the distal end with a zero minimum depth fd 2 . 
       FIG. 11E  shows a cross-section of cathode flow field  28 ″ along cross-section B-B through a discharge channel  102 . As shown in  FIG. 11E , discharge channels  102  may start shallowest (i.e., minimum depth dd 1 ) at or near first cathode distribution channel  90  and the depth may increase extending toward second cathode distribution channel  92 . Discharge channels  102  may be deepest (i.e., maximum depth dd 2 ) at or near second cathode distribution channel  92 . As shown in  FIG. 11E , the depth may increase at a constant rate (e.g., linearly) or in some embodiments, the depth may increase at a variable rate (e.g., non-linearly, exponentially). As shown in  FIG. 11E , discharge channels  102  may start flat at the proximal end with minimum depth (dd 1 ). In other embodiments, discharge channels  101  may start at the proximal end with a zero minimum depth dd 1 . 
     By varying the width (e.g., see  FIG. 11B ) or varying the depth (e.g., see  FIGS. 11C-E ) of feed and discharge channels  101 ,  102  the cross-sectional area available for flow of oxidant along cathode flow fields  28 ′,  28 ″ may vary (e.g., increase in discharge channels  102  or decrease in feed channels  101 ). The increase or decrease in the available flow area in feed and discharge channels  101 ,  102  along the length of cathode flow fields  28 ′,  28 ″ may be configured to correspond with the volume of oxidant that has diffused from feed channels  101  into the porous structure and diffused from the porous structure into discharge channels  102 , such that the flow velocity of oxidant along the feed channels  101  and discharge channels  102  remains about constant. In other words, the cross-sectional area of feed channels  101  may decrease at a rate equal to the rate at which oxidant flows out of the feed channels  101  and diffuses into the porous structure so that the velocity of oxidant remains about constant. Similarly, the cross-sectional area of discharge channels  102  may increase at a rate equal to the rate at which oxidant flows out of the porous structure into the discharge channels  102  so that the velocity of oxidant remains about constant. In some embodiments, the width and depth of feed and discharge channels  101 ,  102  may both vary. For example, in some embodiments,  FIGS. 11D  and E may represent cross-sections of  FIG. 11B  in addition to  FIG. 11C . 
     As shown in  FIGS. 11B and 11C , there may be separating sections formed between feed channels  101  and discharge channels  102 , which may be referred to as land sections  104 . A thickness of the land sections  104  between feed channels  101  and discharge channels  102  may be fixed or in some embodiments the thickness may vary. For example, the thickness may be greatest closest to first cathode distribution channel  90  (e.g., between the proximal end of the feed channels  101  and distal end of the discharge channels) and the thickness may decrease towards the second cathode distribution channel  92 . In other embodiments, the thickness may be thinnest closest to the first cathode distribution channel  90  and the thickness may increase towards the second cathode distribution channel  92 . In other embodiments, the thickness of land sections  104  may be thickest or thinnest about midway between the first cathode distribution channel  90  and the second cathode distribution channel  92 . 
     In some embodiments, a plurality of micro channels  106  may be formed in cathode flow fields  28 ′,  28 ″ in land sections  104 . Micro channels  106  may be formed along the entire length or just a portion of land sections  104 . Micro channels  106  may be configured to fluidly connect feed channels  101  with discharge channels  102  in order to create a preferred flow path for oxidant compared to the porous network provided by cathode flow fields  28 ′,  28 ″. For these embodiments, in conjunction with diffusing or rather than diffusing, oxidant may flow through the micro channels from feed channels  101  to discharge channels  102 . The micro channels  106  may be sized and spaced in such a way to provide oxidant availability to a majority of catalyst sites that would otherwise be shadowed by the land sections of cathode flow fields  28 ′,  28 ″. 
     The number of feed and discharge channels  101 ,  102  may be adjusted based on one or more different parameters, including for example, a width of cathode flow fields  28 ′,  28 ″, a width of feed channels  101 , a width of discharge channels  102 , the application of fuel cell  10 , the intended or designed operating pressure for the oxidant, the intended or designed operating flow rate for the oxidant, the intended or designed power output for fuel cell  10 , or any combination of these parameters. 
     Cathode flow fields  28 ′,  28 ″ may present a number of benefits. For example feed channels  101  and discharge channels  102  provide a larger cross-sectional area through which the oxidant can flow, which can reduce the pressure drop across the porous flow field compared to other porous flow field structures. In addition, to the feed channels  101  and discharge channels  102 , the micro channels may also provide an increased cross-sectional area through which the oxidant gas can flow between the feed channels  101  and discharge channels  102 , which can further reduce the pressure drop across the porous flow field. By reducing the pressure drop the amount of energy required to pressurize the oxidant (e.g., blower power) may be reduced, which, in turn, can improve the overall performance and efficiency (e.g., improve power density and reduce parasitic loading) of fuel cell  10 . In addition, the features of cathode flow fields  28 ′,  28 ″ may more uniformly distribute fresh oxidant within the porous flow field in order to increase the oxygen concentration near the outlet of the cathode flow field. (e.g., feed channels  101 , discharge channels  102 , and micro channels). This can enable the incoming flow of oxidant to remain, for example, oxygen rich until the flow is distributed through the porous body, which can result in better cell voltage and potentially higher current density. 
     Cathode flow field, as shown in  FIG. 11F , may include a plurality of channels  110  formed (e.g., pressed, embossed, or cut) into the surface of cathode flow field  28 ′″. The plurality of channels  110  may include a first set of channels  110 A that begin at first cathode distribution channel  90  and extend about halfway toward second cathode distribution channel  92 . The first set of channels  110 A are configured to enable fresh oxidant (e.g., not yet consumed) to travel directly to the second half of the cathode flow field  28 ′″ where oxidant can often have lower oxygen concentrations. The first set of channels  110 A may be dimensioned such that they sit on top of a land. The other channels  110  may be configured to reduce overall pressure drop and facilitate mixing and/or uniform distribution. For some embodiments, the stock material used for cathode flow field  28 ′″ may come with non-uniformity that would result in non-uniform pressure drop and flow characteristics. Channels  110  are designed to help address this issue by enabling more uniform pressure drop and flow characteristics. The first set of channels  110 A, also help reduce flowrate and thus flow velocity at the leading edge of the active area, which in turn reduces the removal of moisture in that region, providing better operation and performance in dry conditions. This also helps balance the humidity and oxygen concentration distribution along the flow path of cathode flow field  28 ′″, which as a result of the electrochemical reactions, balances current and temperature distribution across the active area. This improves the durability and reliability of the fuel cells and stack. In some embodiments, first set of channels  110 A may be positioned opposite any flow channels on the anode or coolant side of the fuel cell to avoid the potential for the high velocity effect to constructively interfere and increase the risk of the cell potentially drying out. 
     The porous structure making up cathode flow field  28  may include one or more metals and/or alloys. For example, the porous structure may include a combination of at least nickel (Ni) and chromium (Cr) (e.g., NiCr) or nickel, tin (Sn), and chromium (e.g., NiSnCr). For NiCr embodiments of the porous structure the concentrate by mass of chromium can range from about 20% to about 40% while nickel may make up the remaining balance—about 60% to about 80%. For NiSnCr embodiments of the porous structure the concentration of chromium can range from about 3% to about 6%, the concentration of tin can range from about 10% to about 20% while nickel may make up the balance—about 74% to about 87%. 
     In some embodiments, at least one surface of the porous structure may include a chromium concentration ranging from about 3% to about 50% by mass. For example, the chromium concentration of one or both surfaces of the porous structure that forms cathode flow field  28  may range from about 3% to about 50%, about 5% to about 40%, or from about 7% to about 40% by mass. Increasing the chromium concentration of the surface of the porous metal body may be advantageous because it increases the corrosion resistance of the porous structure in acidic environments. For example, when at least one of the surfaces of the porous structure forming the cathode flow field has a chromium concentration ranging from about 3% to about 50% by mass, the bipolar plate including the porous structure may be advantageously corrosion resistant in the substantially acidic environment at the cathode. The improved corrosion resistance provided by the porous structure as described herein may advantageously enable the cathode plate to be formed of uncoated stainless steel rather than coated stainless steel, which has been traditionally used because of its corrosion resistance properties. 
     In some embodiments, one surface of the porous structure may have a higher chromium concentration than the other surface of the porous structure. In such instances, the surface having the higher chromium concentration may advantageously be more corrosion resistant. The surface having the higher chromium concentration may be arranged to face MEA  18 . In some embodiments, the more corrosion-resistant surface of the porous structure may have a chromium concentration ranging from about 3% to about 50% by mass while the less corrosion-resistance surface of the metal porous structure may have a chromium concentration of less than about 3% chromium by mass. 
     The various embodiments of the porous structure described herein may be formed by one or more electroplating processes. For example, in some embodiments, a resin-molded body may initially be used as a substrate for the three-dimensional network structure. The resin-molded body may include one or more of polyurethane, melamine, polypropylene, polyethylene, or the like. The resin-molded body may include pores in its three-dimensional network structure. In some embodiments, the resin-molded body may have a porosity ranging from about 80% to about 98% and may have a pore size of about 50 μm to about 500 μm. In some embodiments, the resin molded body may have a thickness of about 150 μm to about 5,000 μm, about 200 μm to 2,000 μm, or about 300 μm to about 1,200 μm. 
     To form the porous structure, metal layers may be plated onto the resin-molded body. For the NiCr embodiments of the porous structure, for example, a nickel layer and a chromium layer may be plated onto the resin-molded body. For the NiSnCr embodiments of the porous structure, for example, a nickel layer, a tin layer, and a chromium layer may be plated onto the resin-molded body. The resin-molded body may be subjected to electrical conduction treatment, such as electroless plating (auto-catalytic plating), vapor deposition, sputtering, and/or application of a conductive metal, such as nickel particles, tin particles, and/or carbon particles. Then, a nickel layer and/or a tin layer may be electrically plated on the surface of the three-dimensional structure or the skeletons of the treated resin-molded body. For example, when the resin molded body is coated with a conductive layer, a nickel layer may be subsequently formed on the skeletons of the resin-molded body through an electroplating process. After a nickel layer is formed, a tin layer may be subsequently formed on the skeletons of the resin-molded body through another electroplating process. Alternatively, when the resin-molded body is coated with a conductive layer, a tin layer may be electroplated first, followed by the electroplating of a nickel layer. In some embodiments, chemical vapor deposition may be used to add chromium to a substantially nickel structure. 
     In some embodiments, after one or more metal layers are plated onto the skeletons of the resin-molded body, such as a nickel layer and/or a tin layer, a chromium layer may be added through an electroplating process. In some embodiments, the chromium plating layer may be formed such that the chromium concentration of at least one surface of the porous structure ranges from about 3% to about 50% by mass. After the chromium plating layer has been plated or after the nickel and/or tin plating layers are plated, the porous structure may be formed by removing the initial resin-molded body by heat treatment. For example, the porous structure may be heated in an inert atmosphere or a reduced atmosphere at a temperature in the range from about 900° C. to about 1300° C. 
     In some embodiments, fuel cells  10  as described herein may be modified to increase the active area of each fuel cell  10 . For example, fuel cells  10  may be modified such that the active area is doubled by doubling the width of the active area.  FIG. 12  shows a side perspective view of portions of adjacent fuel cells  10 ′ in which the active area may be double (2×) the size of the active area of fuel cells  10  (see e.g.,  FIG. 2 ). Fuel cells  10 ′ may be laid out such that a left half of fuel cells  10 ′ may be laid out the same as fuel cells  10  while a right half of fuel cells  10 ′ may be laid out as a reflection of the left half along a bisecting line between the two halves. In some embodiments, left half and right have may be laid out the same rather than a reflection. Fuel cells  10 ′ may include the same elements as fuel cells  10 , as described herein, except the width is wider and the left and right halves are laid out as a reflection. 
     As shown in  FIG. 12 , like fuel cells  10 , fuel cells  10 ′ can comprise a cathode catalyst layer  12 ′, an anode catalyst layer  14 ′, and a proton exchange membrane (PEM)  16 ′ positioned between cathode catalyst layer  12 ′ and anode catalyst layer  14 ′, which collectively may be referred to as a membrane electrode assembly (MEA)  18 ′. Fuel cell  10 ′ can comprise two bipolar plates, a cathode plate  20 ′ and an anode plate  22 ′. Cathode plate  20 ′ may be positioned adjacent cathode catalyst layer  12 ′ and anode plate  22 ′ may be positioned adjacent anode catalyst layer  14 ′. MEA  18 ′ can be interposed and enclosed between cathode plate  20 ′ and anode plate  22 ′. Fuel cells  10 ′ may also include electrically-conductive gas diffusion layers (e.g., cathode gas diffusion layer  24 ′ and anode gas diffusion layer  26 ′) within fuel cell  10  on each side of MEA  18 . Fuel cell  10 ′ may further include flow fields positioned on each side of MEA  18 ′. For example, fuel cell  10 ′ may include a cathode flow field  28 ′, which may comprise a porous structure positioned between cathode plate  20 ′ and GDL  24 ′ and an anode flow field  30 ′, which may be formed by anode plate  22 ′. Fuel cells may also include a plurality of fluid manifolds  31 A′,  31 B′ extending along longitudinal axis  5  defined by the series of stacked cathode plates  20 ′ and anode plates  22 ′. It is to be understood that the description of components, features, operation, and advantageous regarding fuel cells  10 , described herein, are equally applicable to fuel cells  10 ′ based on the similarly as illustrated by at least  FIGS. 2 and 12 .  FIGS. 13, 14, and 15  show front views of anode plate  22 ′, cathode plate  20 ′, and cathode flow field  28 ′, according to an exemplary embodiment of fuel cell  10 ′. In some embodiments, fuel cells  10  may be modified such that the active area is tripled by increasing the active area and repeating the layout of features (e.g., manifolds, passages, and ports, etc.) of fuel cell  10  three times rather than twice as done for fuel cell  10 ′. 
     The foregoing description has been presented for purposes of illustration. It is not exhaustive and is not limited to precise forms or embodiments disclosed. Modifications, adaptations, and other applications of the embodiments will be apparent from consideration of the specification and practice of the disclosed embodiments. For example, the described embodiments of fuel cell  10  may be adapted for used with a variety of electrochemical cells. For example, although the present disclosure primarily focus on fuel cells with a anode channel flow field and cathode porous flow field, it is contemplated that some of these features may be utilized in fuel cells utilizing anode and cathode flow fields or fuel cells utilizing anode and cathode porous flow fields. 
     Moreover, while illustrative embodiments have been described herein, the scope includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations based on the present disclosure. The elements in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as nonexclusive. Further, the steps of the disclosed methods can be modified in any manner, including reordering steps and/or inserting or deleting steps. 
     The features and advantages of the disclosure are apparent from the detailed specification, and thus, it is intended that the appended claims cover all cells and cell stacks falling within the true spirit and scope of the disclosure. As used herein, the indefinite articles “a” and “an” mean “one or more.” Similarly, the use of a plural term does not necessarily denote a plurality unless it is unambiguous in the given context. Words such as “and” or “or” mean “and/or” unless specifically directed otherwise. Further, since numerous modifications and variations will readily occur from studying the present disclosure, it is not desired to limit the disclosure to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the disclosure. 
     Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the present disclosure herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present disclosure being indicated by the following claims.