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A bipolar assembly for use in electrochemical cell stacks, especially stacks operated at low pressure. The bipolar assembly is lightweight and provides a "post-type" flow field that operates with a low pressure drop. The bipolar assembly comprises a gas barrier having an array of electronically con

A bipolar assembly for use in electrochemical cell stacks, especially stacks operated at low pressure. The bipolar assembly is lightweight and provides a "post-type" flow field that operates with a low pressure drop. The bipolar assembly comprises a gas barrier having an array of electronically conducting posts disposed approximately perpendicular to the gas barrier. Each end of the posts is in electrical communication with the surface of an electrode. Because the bipolar assembly separates a cathode from an anode, the posts contact an anode electrode on one end and a cathode electrode on the other end. The posts provide current conduction through the stack as well as provide the flow fields for the electrochemical reactants. Optionally, the bipolar assembly may contain cooling fluid channels formed by adding additional gas barriers to the bipolar assembly. The space between the gas barriers form a channel through which cooling fluids may be circulated.

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What is claimed is: 1. A fluid-cooled assembly for use in an electrochemical cell stack comprising: at least two gas barriers, wherein a first gas barrier opposes an anode electrode and a last gas barrier opposes a cathode electrode and wherein the gas barriers are approximately parallel; and an ar

What is claimed is: 1. A fluid-cooled assembly for use in an electrochemical cell stack comprising: at least two gas barriers, wherein a first gas barrier opposes an anode electrode and a last gas barrier opposes a cathode electrode and wherein the gas barriers are approximately parallel; and an array of electronically conductive protrusions disposed across the gas barriers, wherein the electronically conductive protrusions enable electrical communication between the anode electrode and the cathode electrode, wherein the protrusions are inserted into an array of holes, indentations, or combinations thereof in the gas barriers, and wherein the protrusions have a cross section approximately matching a cross section of the holes or indentations, and wherein the gas barriers and the protrusions are metallic; and seals around the protrusions formed by metallurgically bonding the protrusions to the gas barriers, wherein the seal is formed with a metal having a melting point substantially lower than the metals of the protrusions or the gas barriers. 2. The assembly of claim 1, wherein the protrusions are sealed to indentations, and the gas barrier is electronically conductive. 3. The assembly of claim 1, wherein the protrusions are of any cross sectional shape. 4. The assembly of claim 1, wherein the protrusions have cross sectional shapes selected from circular, square, rectangular, triangular, diamond, oval, ovoid, pentagonal, hexagonal or heptagonal. 5. The assembly of claim 1, wherein the protrusions are arranged in a pattern selected from triangular or rectangular. 6. The assembly of claim 4, wherein the separation between protrusions is from 1 mm to 3 cm. 7. The assembly of claim 4, wherein the separation between protrusions is from 1 cm to 2 cm. 8. The assembly of claim 1, wherein the protrusions extend between adjacent cells through a distance between 쩍 inch and 1/16 inch. 9. The assembly of claim 1, wherein the anode electrode and the cathode electrode each have a fluid diffusion structure having an electronically conductive grid, wherein the metal grid acts as a current collector. 10. The assembly of claim 9, wherein the protrusions are in electrical communication with the grids. 11. The assembly of claim 9, wherein the grid is made of material selected from nickel, copper, aluminum, stainless steel, graphitized carbon, gold, palladium, ruthenium, platinum or combinations thereof. 12. The assembly of claim 9, wherein the grid is made of titanium. 13. The assembly of claim 9, wherein the grid is a form selected from perforated flat plate, perforated foil, woven wire cloth, non-woven conductive cloth, wherein the perforations or openings have a size less than the area of contact with any one of the protrusions. 14. The assembly of claim 1, wherein the gas barrier is porous with pores permitting fluid communication through the plate and said pores filled with a hydrophilic material that prevents the passage of gas through the gas barrier but permits the passage of water. 15. The assembly of claim 14 where the hydrophilic material is a polymer. 16. The assembly of claim 15 where the polymer is selected from poly-perfluorosulfonic acid, sulfonated polystyrene, sulfonated trifluorostyrene, polyacrylamides, sulfonated styrene copolymers, and blends and copolymers of these materials. 17. The assembly of claim 14 where the hydrophilic material is an inorganic material. 18. The assembly of claim 17 where the inorganic material is selected from phosphates, polyphosphates, hydrous silicates, and the like. 19. The assembly of claim 1, wherein the protrusions form flow fields having a void volume of between about 50% and about 99%. 20. The assembly of claim 1, wherein the protrusions form flow fields having a void volume of between about 80% and about 95%. 21. The assembly of claim 1, wherein at least one of the fluids is a gas. 22. A fluid-cooled assembly for use in an electrochemical cell stack comprising: at least two gas barriers, wherein a first gas barrier opposes an anode electrode and a last gas barrier opposes a cathode electrode and wherein the gas barriers are approximately parallel; and an array of electronically conductive protrusions disposed across the gas barriers, wherein the electronically conductive protrusions enable electrical communication between the anode electrode and the cathode electrode, and wherein the protrusions have a cross section approximately matching a cross section of the holes or indentations, wherein the protrusions are inserted into holes in the gas barriers; and seals around the protrusions, wherein the seals are made of polymeric material. 23. The assembly of claim 22, wherein the polymeric material is selected from epoxies, metal filled epoxies, carbon filled epoxies, self-vulcanizing silicones, metal filled self-vulcanizing silicones, or carbon filled self-vulcanizing silicone. 24. The assembly of claim 22, wherein the gas barriers are made of materials selected from electronically conducting materials, electronically nonconducting material, or combinations thereof. 25. The assembly of claim 22, wherein the protrusions are made of material selected from graphitic carbon, aluminum, titanium or magnesium. 26. The assembly of claim 22, wherein the protrusions are made of any electronically conductive material. 27. The assembly of claim 22, wherein the gas barrier is electronically conductive, the gas barrier is made of material selected from aluminum, titanium, magnesium, or graphitic carbon sheet. 28. The assembly of claim 22 wherein the gas barrier is electronically conductive, the gas barrier is made of a material selected from conductive polymer composites formed from a non-conductive polymer filled with a conductive material such as metal or carbon. 29. The assembly of claim 22 wherein the gas barrier is made of an intrinsically electronically conductive polymer. 30. The assembly of claim 22, wherein the gas barrier is electronically nonconductive, and wherein the gas barrier is made of polymer selected from polycarbonate, polytetrafluoroethylene, polyamide, or polyethersulfone. 31. The assembly of claim 30, wherein the gas barrier is porous with pores permitting fluid communication through the plate and said pores filled with a hydrophilic material that prevents the passage of gas through the gas barrier but permits the passage of water. 32. The assembly of claim 31 where the hydrophilic material is a polymer. 33. The assembly of claim 32 where the polymer is selected from poly-perfluorosulfonic acid, sulfonated polystyrene, sulfonated trifluorostyrene, polyacrylamides, sulfonated styrene copolymers, and blends and copolymers of these materials. 34. The assembly of claim 31 where the hydrophilic material is an inorganic material. 35. The assembly of claim 34 where the inorganic material is selected from phosphates, polyphosphates, hydrous silicates, and the like. 36. The assembly of claim 22, wherein all the gas barriers are made of the same material. 37. The assembly of claim 22, wherein all the gas barriers are not made of the same materials. 38. The assembly of claim 22, wherein at least two gas barriers are electronically conductive, and wherein the electronically conductive protrusions are inserted into an array of holes, indentations or combinations thereof in the at least two gas barriers. 39. The assembly of claim 38, wherein the at least two gas barriers and the protrusions are metallic. 40. The assembly of claim 38, wherein the protrusions are of circular cross sectional shape. 41. The assembly of claim 38, wherein the protrusions have cross sectional shapes selected from circular, square, rectangular, triangular, diamond, oval, ovoid, pentagonal, hexagonal, or heptagonal. 42. The assembly of claim 38, wherein the protrusions are arranged in a pattern selected from triangular or rectangular. 43. The assembly of claim 42, wherein the separation between protrusions is between about 1 mm and about 3 cm. 44. The assembly of claim 43, wherein the separation between protrusions is about 1 cm. 45. The assembly of claim 38, wherein the protrusions extend between adjacent cells through a distance between 쩌 inch and 1/16 inch. 46. The assembly of claim 38, wherein the protrusions are made of material selected from graphitic carbon, aluminum, titanium, or magnesium. 47. The assembly of claim 38, wherein the gas barrier is made of material selected from aluminum, titanium, magnesium, or graphitic carbon sheet. 48. The assembly of claim 38, wherein the gas barrier is made of a conductive polymer composite formed from a non-conductive polymer filled with a conductive material. 49. The assembly of claim 38, wherein the protrusions form flow fields having a void volume of between about 50% and about 99%. 50. The assembly of claim 38, wherein the protrusions form flow fields having a void volume of between about 80% and about 95%. 51. The assembly of claim 38, wherein the two gas barriers are not made of the same material. 52. The assembly of claim 38, wherein the two gas barriers are made of the same material. 53. The assembly of claim 22, wherein the gas barriers are made from different material than the protrusions.