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A method of flowing reactants over an ion exchange membrane in a fuel cell flow field plate is provided. The flow field plate is provided, comprising a network of flow channels in the plate bounded by an electrochemically active electrode, the network comprising a series of passages having parallel

A method of flowing reactants over an ion exchange membrane in a fuel cell flow field plate is provided. The flow field plate is provided, comprising a network of flow channels in the plate bounded by an electrochemically active electrode, the network comprising a series of passages having parallel grooves, the passages being interconnected by a header providing a substantially even redistribution of fluid flow received from grooves of one passage to grooves of the next passage. A reactant fluid is supplied to create a flow across the network to achieve a desired reactant utilization, wherein a flow rate and a concentration of reactant molecules per active area of membrane in the grooves increase by less than 80% across the header.

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What is claimed is: 1. A flow field plate for a fuel cell stack, the flow field plate comprising: an inlet manifold; an outlet manifold; and a flow field communicating with said inlet manifold and said outlet manifold, the flow field comprising at least three passages, each one of said passages hav

What is claimed is: 1. A flow field plate for a fuel cell stack, the flow field plate comprising: an inlet manifold; an outlet manifold; and a flow field communicating with said inlet manifold and said outlet manifold, the flow field comprising at least three passages, each one of said passages having grooves thereon, adjacent ones of said passages being interconnected by a header providing a substantially even redistribution of a fluid flow received from grooves of one passage to grooves of a next passage, a number of said grooves for each one of said passages decreasing from one of said passages to another from said inlet manifold to said outlet manifold, said decreasing following an exponential rule in order to maintain substantially constant one of a flow rate and a concentration of reactant molecules per active area of a membrane in said grooves across said flow field. 2. The flow field as claimed in claim 1, wherein said flow field plate is an anode flow field plate. 3. The flow field plate as claimed in claim 1, wherein said flow field plate is a cathode flow field plate. 4. The flow field plate as claimed in claim 1, wherein said grooves of each one of said at least three passages are parallel. 5. The flow field plate as claimed in claim 4, wherein said grooves of each one of said at least three passages have constant cross-section dimensions, said header acting as a manifold interconnecting many grooves of an upstream passage to many grooves of a downstream passage, a ratio in a number of grooves in interconnected passages being less than 2:1. 6. The flow field plate as claimed in claim 1, wherein said header is positioned at an angle so that a reactant fluid flowing in said flow field changes from a first direction of flow in said grooves of one passage, as it passes through said header, to a second direction of flow in said grooves of a next passage. 7. The flow field plate as claimed in claim 6, wherein said second direction of flow of said reactant fluid in said grooves of a next passage is at substantially 90° from said first direction of flow. 8. The flow field plate as claimed in claim 7, wherein said passages are interconnected to form a U-turn, said header being positioned at one corner of said U-turn and wherein said first direction of flow is a downward direction and said second direction of flow is an upward direction. 9. The flow field plate as claimed in claim 6, wherein said angle is given by wherein said angle is φ, n is a number of flow channels, wc is a width of a flow channel, ws is a width of a land, and i is a number identifying a passage. 10. The flow field plate as claimed in claim 1, wherein a desired reactant utilization is greater than 40%. 11. The flow field plate as claimed in claim 1, wherein said one of said flow rate and said concentration of reactant molecules per active area is substantially the same at entrances of said at least three passage of grooves. 12. The flow field plate as claimed in claim 1, wherein said one of said flow rate and said concentration of reactant molecules per active area of membrane in said grooves increases by less than 40% across each said header. 13. The flow field plate as claimed in claim 1, wherein said number of grooves is given by wherein n0 is a number of grooves in a first one of said at least three passages, N is a total number of said at least three passages, η0 is a fluid reactant utilization efficiency and i is a number identifying a passage. 14. The flow field plate as claimed in claim 1, wherein said number of grooves is given by n0 is a number of grooves in a first one of said at least three passages, γ0 is a fluid reactant volumetric concentration, N is a total number of said at least three passages, η0 is a fluid reactant utilization efficiency and i is a number identifying a passage.