And Method of Manufacture

Technical Field

[0001] The present disclosure relates to fuel cells that are suited for usage in transportation vehicles, portable power plants, or as stationary power plants, and especially to a fuel cell including a barrier to migration of an acid electrolyte from the fuel cell into an adjacent fuel cell.

Background Art

[0002] Fuel cells are well known and are commonly used to produce electrical current from hydrogen containing reducing fluid fuel and oxygen containing oxidant reactant streams, to power various types of electrical apparatus. Many fuel cells use a liquid electrolyte such as phosphoric acid, and such fuel cells are typically adjacent other fuel cells to form a well known fuel cell stack having manifolds and associated plumbing to deliver and remove reactant and exhaust stream, etc.

[0003] Phosphoric acid electrolyte fuel cells are frequently associated with a problem of migration of acid out of one cell into an adjacent cell. Many efforts have been undertaken to resolve this problem. Such efforts are disclosed, for example, in commonly owned U.S. Patents No. 5,079,104 to Roche et al . , No. 5,156,929, to Dec et al . , No. 5, 178, 968 to Roche, No. 5, 270, 132 to Breault et al . , No. 5,837,395 to Breault et al . , and No. 6,050,331 to Breault et al . , and in commonly owned Published International Application under the PCT Nos. WO 2010/123478 Al and WO 2010/123479 Al, which patents and applications are hereby incorporated herein by reference thereto .

[0004] Such phosphoric acid fuel cells contain excess acid to accommodate acid loss due to evaporation into the reactant streams, loss due to absorption by cell components and loss by reaction with materials within the cell. This excess acid is stored in electrolyte reservoir plates which may be a separate component or the electrolyte storage function may be integrated into a porous electrode substrate. Managing the liquid electrolyte within a fuel cell is a significant design challenge .

[0005] Carbonaceous materials at the edges of planar components of the fuel cell that are exposed to the air inlet and air exit manifolds are oxidized due to chemical reaction. The extent of oxidation is a function of the electrochemical potential, the partial pressure of water vapor and the local temperature. Oxidation is normally greater at the air inlet edge of the cell due to higher temperatures than at the air exit edge of the cell. Oxidation typically is minimal on the edges exposed to the reactant fuel.

[0006] Oxidation of the carbonaceous materials results in the materials at the edge of the cell becoming wettable and leads to the presence of an acid film along the edge of a separator plate assembly within the fuel cell. This acid film results in an ionic shunt current path along the edge of the fuel cell. This shunt current path results in protons (hydrogen ions) flowing from the positive end of a substack of cells to the negative end of the substack along the edges of the cells. A "substack" of fuel cells is a group of typically 4 - 8 cells disposed between cooling plates within the fuel cell stack. There are two consequences to these shunt currents. The first consequence is that the shunt current lowers the electrolyte potential such that carbon corrosion occurs at the positive end of the substack. Carbon corrosion is a significant issue for fuel cells operating at elevated reactant pressures where the electrode potentials are higher than at ambient pressure. The second consequence is that the shunt current results in the flow of anions (di-hydrogen phosphate) from the negative end of the sub-stack to the positive end of the sub-stack. The hydrogen ions and the di-hydrogen phosphate ions combine at the positive end of the sub- stack. This results in acid being pumped from the negative end of the sub-stack to the positive end of the sub-stack along the edge of the stack. The consequences of this acid pumping is that the cells at the negative end will fail due to reactant cross-over due to the loss of acid; and the positive cell will fail due to poor performance due to the excess acid. Acid pumping from cell to cell significantly reduces the useful life of the fuel cell. The acid pumping problem is most severe in cells with small electrolyte reservoirs.

[0007] FIG. 1 presents a schematic, cross-section representation of the above described acid pumping or acid migration between "Cell A" and "Cell B", wherein such cells would be two of many fuel cells in a fuel cell stack assembly 10. "Cell A" is represented by reference numeral 11 and virtually identical "Cell B" is represented by reference numeral 13. Each cell 11, 13 includes a cathode electrode 12, an anode electrode 14, a matrix 16 between the electrodes 12, 14 for holding a liquid electrolyte. A separator plate assembly 18 is located between electrodes 12, 14 of adjacent cells 11, 13, as shown in FIG. 1. FIG. 1 also shows portions of two additional, virtually identical separator plate assemblies 18. The separator plate assembly 18 also defines a first flow field surface 20 and an opposed second flow field surface 21 for directing flow of an oxidant reactant and a hydrogen rich fuel reactant for both adjacent electrodes. FIG. 1 also shows schematically how acid migrates as a film along an edge of the separator plate assembly between cells A and B, 11, 13.

Summary

[0008] The disadvantages and limitations of the background art discussed above are overcome by the present disclosure. The disclosure includes a monolithic separator plate assembly with an integral acid transfer barrier for use in a fuel cell. The separator plate assembly includes a monolithic structure having a first flow field surface defining at least one first reactant flow edge and an opposed second flow field surface defining at least one second reactant flow edge. The reactant flow edges are entry and exit edges for transfer of the oxidant and hydrogen rich fuel containing reactants. The assembly also has a perimeter surface extending between the first and second flow field surfaces, and the perimeter surface defines a complete circumference of the monolithic structure

[0009] The monolithic structure has a uniformly consistent material composition comprising flake graphite and thermoplastic, hydrophobic resin throughout the structure that extends between the first and second flow field surfaces and the perimeter surface so that there is no material or physical demarcation within the monolithic separator plate assembly.

[0010] An acid transfer barrier is secured between the first flow field surface and the second flow field surface and is flush with the perimeter surface. The acid transfer barrier is made of material selected from the group consisting of a fluoropolymer and a mixture of fluoropolymers . The barrier extends from the perimeter surface into the monolithic structure toward an opposed perimeter surface, and also extends to be coextensive with at least one of the first reactant flow edge and the second reactant flow edge. The acid transfer barrier also has a minimum thickness of about 0.40 millimeters ("mm") and is integral with the monolithic structure. (For purposes herein, the word "integral" is to mean that when an assembly is described as having a first component that is "integral with" a second component, the components cannot be separated from each other without destroying the assembly. Also, for purposes herein, the word "about" is to mean plus or minus ten percent.)

[0011] It has been found that the acid transfer barrier having a thickness of about 0.40 mm produces optimal results irrespective of a thickness of the separator plate assembly. A thicker separator plate assembly does not benefit from having a thicker barrier. An additional optimal dimension of the acid transfer barrier has a width of between about 5.0 mm and about 25.4 mm .

[0012] By making the acid transfer barrier flush with the perimeter surface of the monolithic structure and integral with the structure, the present disclosure substantially enhances efficiency of manufacture of the separator plate and assembly and production of the fuel cell, and fuel cell stacks utilizing them. Prior art efforts to utilize acid barriers in the form of flaps extending away from perimeter surfaces of a separator plate assembly have proven to be too difficult and costly to efficiently manufacture and install within fuel cell stacks. The present disclosure achieves equally effective restriction of acid transfer between cells by having the barrier flush with perimeter surfaces of the monolithic separator plate assembly. The disclosure includes embodiments of the assembly wherein machining, grinding or otherwise polishing of the acid transfer barrier at the perimeter surface of the monolithic structure is performed prior to installing the assembly within a fuel cell stack. This insures effective exposure of the acid transfer barrier at the perimeter surface of the separator plate assembly.

[0013] The disclosure also includes methods of manufacturing the monolithic separator plate assembly with an integral acid barrier. An exemplary method includes depositing a mixture of graphite powder and hydrophobic resin into a mold, wherein the mixture includes between about 80% to about 85% of a graphite powder and between about 15% and about 20% of a hydrophobic resin. The mixture is densified within the mold by compressing the mixture with between about 2000 pounds per square inch (hereafter, "p.s.i.") and about 4000 p.s.i. to form the mixture into a first solid plate. Then, acid transfer barrier strips are positioned adjacent perimeter surfaces of a top surface of the first solid plate and adjacent interior surfaces of the mold so that the acid barrier strips are flush with a perimeter surface of the first solid plate. The acid transfer barrier strips are constructed of a rigid material selected from the group consisting of a fluoropolymer and a mixture of fluoropolymers .

[0014] Then a second mixture of graphite powder and hydrophobic resin is deposited onto the acid transfer barrier strips and the densified first solid plate, wherein the mixture is the same as the mixture that formed the first solid plate, including between about 80% and about 85% of a graphite powder and between about 15% and about 20% of a hydrophobic resin. The second mixture is densified within the mold by compressing the mixture with between about 2000 p.s.i. and about 4000 p.s.i. to form the mixture into a second solid plate which is bonded to the acid transfer barrier strips and the first solid plate.

[0015] The resulting monolithic structure has the acid transfer barrier strips flush with the perimeter surfaces of the structure and is formed so that the barrier is integral with the monolithic structure. The acid transfer barrier strips extend to be coextensive with at least one of the first reactant flow edge and the second reactant flow edge of the monolithic structure. The structure is further densified by compression molding of the monolithic structure at 275-350°C at a pressure of 500-1000 p.s.i., and cooling to below 200°C before releasing the pressure. Flow channels are also formed within at least one of the first flow field surface and the second flow field surface to form the monolithic separator plate assembly.

[0016] Alternative methods of manufacture are described in more detail below and include forming steps adjacent perimeter surfaces of the monolithic structure during molding of the first solid plate of the structure, and then laying in various forms of the acid transfer barriers within the steps prior to forming the second solid plate on the first plate. Additionally, the acid transfer barrier may be in the form of an expanded tape applied to the first solid plate, or may be in the form of a granular powder deposited onto perimeter edges of, or steps defined within, the first solid plate prior to forming the second solid plate. The acid barrier may also be in the form of strips including slits defined within an interior edge of the strips to compensate for any bowing due to varying coefficients of thermal expansion of the strips and the monolithic structure.

Brief Description of the Drawings

[0017] Figure 1 is a simplified, cross-sectional schematic representation of a "Cell A" and a "Cell B" showing components of the cells, development of acid migration from "Cell A" to "Cell B".

[0018] Figure 2 is a fragmentary, simplified perspective view of a fuel cell stack showing exemplary dispositions of integral barriers to acid migration out of fuel cells of the stack constructed in accordance with the present disclosure.

[0019] Figure 3 is a simplified, fragmentary, cross-sectional, schematic representation of a monolithic separator plate assembly with an integral acid transfer barrier constructed in accordance with the present disclosure .

[0020] Figure 4 is a simplified schematic representation of an acid barrier strip showing a plurality of slits defined at an interior surface of the within the strip.

[0021] Figure 5 is sequence of simplified, cross- sectional, schematic drawings showing a first method of forming a monolithic structure having an integral acid barrier of the present disclosure.

[0022] Figure 6 is a sequence of simplified, cross-sectional, schematic drawings showing a second method of forming a monolithic structure having an integral acid barrier of the present disclosure.

Description of the Preferred Embodiments

[0023] Referring to the drawings in detail, portions of a fuel cell stack 30 showing a schematic, simplified representation of a first fuel cell 32 and a second fuel cell 34 are illustrated in FIG. 2. The first fuel cell 32 includes an anode electrode 36 adjacent a matrix 38 for holding a liquid electrolyte, and a cathode electrode 40 on an opposed side of the matrix 38. Similarly, the second fuel cell 34 includes an anode electrode 36' an adjacent matrix 38', and a cathode electrode 40' on an opposed surface of the matrix 38' . Partial components of additional cells are shown in the fragmentary FIG. 2 drawing, including a cathode electrode 40" at the bottom of the FIG. 2 portion of the stack 30 and another anode electrode 36" at the top of the portion of the stack 30. [0024] The FIG. 2 cell stack 30 also shows three separate monolithic separator plate assemblies. The first is identified by reference numeral 42 between the anode electrode 36 of the first cell 32 and the cathode electrode 40" at the bottom of the portion of the stack 30. The second separator plate assembly is identified by reference numeral 44 located between the cathode electrode 40 of the first cell 32 and the anode electrode 36' of the second fuel cell 34. The third separator plate assembly is identified by reference numeral 46 and is located between the cathode electrode 40' of the second fuel cell 34 and the anode electrode 36" of the partial fuel cell at the top of the FIG. 2 portion of the stack 30.

[0025] For purposes of efficiency, the following description of the first monolithic separator plate assembly 42 will include details and reference numerals within FIG. 2. However, comparable reference numerals will not be shown in FIG. 2 for the second and third assemblies 44, 46, even though those assemblies 44, 46 include the same characteristics as the first assembly 42. The first separator plate assembly 42 includes a monolithic structure 48 having a first flow field surface 50 defining at least one first reactant flow edge 52. The first flow field surface 50 defines a plurality of first reactant flow channels 54A, 54B and 54C. Because the first flow field surface is adjacent a cathode electrode 40", the first flow channels 54A, 54B and 54C would direct flow of an oxidant reactant through the fuel cell 32. The first reactant flow field edge 52 would therefore be an oxidant flow field edge 52 such as an oxidant inlet flow field 52 edge and/or an opposed oxidant exit flow edge (not shown) .

[0026] The first separator plate assembly 42 also defines an opposed second flow field surface 56 that includes at least one second reactant flow edge 58. The second flow field surface 56 also defines plurality of second flow channels 60 (only one of which is shown in FIG. 2) . Because the second reactant flow field edge 58 is adjacent the anode 36 of the first fuel cell 32, the second flow channel 60 would direct flow of a hydrogen rich reactant through the fuel cell 32 and the second reactant flow field edge 58 would therefore be a fuel reactant flow edge 58 such as a fuel inlet flow edge 58 and/or an opposed fuel exit flow edge (not shown) . The first separator plate assembly also has a perimeter surface 62 extending between the first flow field surface 50 and the second flow field surface 56. The perimeter surface 62 defines a complete circumference of the first monolithic separator plate 42.

[0027] The first separator plate assembly 42 is composed of a monolithic structure that has a uniformly consistent material composition comprising flake graphite and thermoplastic, hydrophobic resin throughout the structure that extending between the first and second flow field surfaces 50, 56 and the perimeter surface 62 so that there is no material or physical demarcation within the first monolithic separator plate assembly 42.

[0028] A first acid transfer barrier 64 is secured between the first flow field surface 50 and the second flow field surface 56 and is flush with the perimeter surface 62. (For purposes herein, the phrase "flush with" is to mean that tangents extending from adjacent points on the first acid transfer barrier 64 and the perimeter surface 62 are coplanar.) The acid transfer barrier 64 is selected from the group consisting of a fluoropolymer and a mixture of fluoropolymers . The barrier 64 extends from the perimeter surface 62 into the monolithic structure 42 toward an opposed perimeter surface 66, and also extends to be coextensive with the second reactant flow edge 58. The first acid transfer barrier 64 also has a minimum thickness of about 0.40 millimeters ("mm") and is integral with the monolithic structure separator assembly 42.

[0029] FIG. 2 shows usage of a second acid transfer barrier 68 in the second monolithic separator plate assembly 44, and usage of a third acid transfer barrier 70 in the third separator plate assembly 46 so that the second and third barriers 68, 70 are utilized within the assemblies 44, 46 in different positions. It is noted that such utilization is exemplary only for demonstrating alternative utilization of the acid barriers 64, 68, 70. A typical fuel cell stack actually being used (not shown) would invariably utilize acid transfer barriers in position throughout the fuel cell stack. For example, all of the acid transfer barriers would be in the position of barrier 68, or all would be in the position of barrier 70, etc.

[0030] In the first separator plate assembly 42 described above, the first acid transfer barrier 64 is shown as being coextensive with the second reactant flow field edge 58. That edge 58 is adjacent the anode electrode 36 of the first fuel cell, and therefore the first acid transfer barrier 64 is coextensive with a fuel reactant flow edge 58 of the separator plate assembly 42. The second separator plate assembly 44 the second acid transfer barrier 68 is shown as being coextensive with all reactant flow field edges of the second separator plate 44. This positioning of the second acid transfer barrier is to represent the acid transfer barrier being coextensive with an entire circumference or entire perimeter edge 62 of the assembly 44. Within the third separator plate assembly 46, the third acid transfer barrier 70 is shown being coextensive with an oxidant reactant flow edge 72. It is known that oxidant flow edges such as 72 experience deleterious effects of acid migration more than fuel reactant flow edges 58. Consequently, a particular embodiment of the present monolithic separator plate assembly 44 includes the third acid transfer barrier 70 secured to be coextensive with the oxidant reactant flow edge 72, and in particular, an oxidant inlet flow edge 72 of the assembly 46. Additionally, such an embodiment may also include another acid transfer barrier (not shown) that would be coextensive with an opposed oxidant reactant outlet flow edge of the assembly 46. (For purposes herein, the phrase "coextensive with" is to mean that the acid transfer barriers 64, 68, 70 completely overlie the nearby reactant flow edges.)

[0031] FIG. 3 shows a simplified fragmentary cross-section representation of a monolithic separator plate assembly 74 that includes a monolithic structure 76 having a first flow field surface 78 defining a first reactant flow channel 79 (shown in cross-hatching in Fig. 3) , an opposed second flow field surface 80 defining a plurality of second reactant flow channels 81, a perimeter surface 83 extending between the flow field surfaces 78, 80, a first reactant inlet flow edge 82 and a first reactant exit flow edge 84, and a second reactant inlet flow edge 86. This particular view shows a first acid transfer barrier 88 disposed so that it is coextensive with the first reactant inlet flow edge 82, for example an oxidant inlet edge 82. A second acid transfer barrier 90 is disposed so that it is coextensive with the first reactant exit flow edge 84, for example, an oxidant exit edge 84 of the monolithic separator plate assembly 74.

[0032] FIG. 4 shows a rigid acid transfer barrier strip 92 that includes an exterior edge 94 configured to be flush with a perimeter surface 83 of a monolithic separator plate assembly 74, such as shown in FIG. 3. The rigid acid transfer barrier strip 92 may also include a plurality of slits 96 extending from an interior surface 98 toward the exterior surface 94 a distance that is at least one-half and preferably two-thirds of a width distance of the strip 92, wherein a "width distance" is a shortest distance between the exterior edge 94 and the opposed interior surface 98. An exemplary rigid acid transfer barrier strip would have a width distance of about 12.7 mm, or about 0.5 inches. The plurality of slits 96 may be defined along the strip 92 so that there is a slit 96 every 12 mm to about one every 25.4 mm, or one slit 96 every 0.5 inches to every 1.0 inches.

[0033] FIG. 5 shows a sequence of cross-sectional schematic drawings showing a first method of manufacturing a monolithic separator plate assembly 100 with integral acid barriers 102, 104. The sequence of drawings in FIG. 5 starts at the top left hand corner and proceeds following directional arrows 105 to the right side of the drawing, then down to the right side of the bottom half of the drawing and concludes at the bottom left hand side of the drawing. The exemplary method shown in FIG. 5 includes first depositing a first mixture 106 of flake graphite powder and hydrophobic resin into a mold 108, wherein the mixture includes between about 80% to about 85% of a flake graphite powder and between about 15% and about 20% of a hydrophobic resin. The mixture 106 is densified within the mold 108 by compressing the mixture 106 with between about 2000 p.s.i. and about 4000 p.s.i. to form the mixture 106 into a first solid plate 110. Then, acid transfer barrier strips 112, 114 are positioned adjacent perimeter surfaces 116, 118 of a top surface 120 of the first solid plate 110 and adjacent interior surfaces of the mold 122 so that the acid barrier strips 112, 114 are flush with a perimeter surface 124 of the first solid plate 110. The acid transfer barrier strips 112 are constructed of a rigid material selected from the group consisting of a fluoropolymer and a mixture of fluoropolymers .

[0034] A second mixture 126 of flake graphite powder and hydrophobic resin is then deposited onto the acid transfer barrier strips 112, 114 and the densified first solid plate 110, wherein the mixture is the same as the mixture that formed the first solid plate 110, including between about 80% and about 85% of a flake graphite powder and between about 15% and about 20% of a hydrophobic resin. The second mixture is densified within the mold 108 by compressing the mixture with between about 2000 p.s.i. and about 4000 p.s.i. to form the mixture into a second solid plate 128 which is bonded to the acid transfer barrier strips 112, 114 and the first solid plate 110 to form the resulting monolithic structure 100 having the first and second acid transfer barriers 102, 104 flush with the perimeter surfaces 124 of the structure 100.

[0035] The acid transfer barriers 102, 104 are integral with the monolithic structure 100. The acid transfer barriers 102, 104 also extend to be coextensive with at least one of a first reactant flow edge 130 and the second reactant flow edge 132 of the monolithic structure 100. First reactant flow channels 134 may be defined adjacent the first reactant flow edge 130 within a first flow field surface 136 of the structure 100. A second reactant flow channels 138 may be defined adjacent the second reactant flow edge 132 and within a second flow field surface 140 of the structure 100 to form the monolithic structure into a monolithic plate assembly 100. The monolithic structure 100 is further densified by compression molding of the monolithic structure at 275- 350°C at a pressure of 500-1000 p.s.i., and cooling to below 200°C before releasing the pressure. This results in the first solid plate 110, the second solid plate 128 and the acid barrier strips 112, 114 becoming integral with each other. The flow channels 134, 138 may be formed during the molding process described above or thereafter within at least one of the first flow field surface and the second flow field surface to form the monolithic separator plate assembly 100.

[0036] FIG. 6 shows a sequence of simplified, cross-sectional, schematic drawings of a second method of forming a monolithic structure 150 having integral acid barriers 152, 154. It is pointed out that FIG. 6 is cross-sectional, so that the acid transfer barriers 152, 154 simply may be two separate barriers on opposed sides of the structure 150, or may represent one acid transfer barrier 152 that is coextensive with an entire circumference of the monolithic structure 150. The sequence of drawings in FIG. 6 starts at the top left hand corner and proceeds following directional arrows 105 to the right side of the drawing, then down to the right side of the bottom half of the drawing and concludes at the bottom left hand side of the drawing.

[0037] The second method of making the monolithic separator plate assembly 150 with the integral acid transfer barriers 152, 154 starts with depositing a first mixture 156 of flake graphite powder and hydrophobic resin into a mold 158. The first mixture 156 includes between about 80% to about 85% of a flake graphite powder and between about 15% and about 20% of a hydrophobic resin. The first mixture 156 is then densified within the mold 158 by compressing the first mixture 156 with between about 2000 p.s.i. and about 4000 p.s.i. to form the first mixture 156 into a first solid plate 160. Then, an acid transfer barrier boundary mold insert 162 is positioned onto the first solid plate 160 so that the mold insert defines a barrier perimeter 164 between the mold insert 162 and walls 166 of the mold that ascend from the base 168 of the mold 158. Next, an acid transfer barrier powder 170 is deposited into the barrier perimeter 144. The acid transfer powder 170 includes about 100% of a hydrophobic polymer.

[0038] The acid transfer barrier powder 170 is then compressed within the mold 158 and within the barrier perimeter 164 with between about 1000 p.s.i. and about 4000 p.s.i. to densify the acid transfer barrier from a powder 170 into a solid acid transfer barrier 152 or barriers 152, 154. The mold insert 162 is then removed from the mold 158. Next, a second mixture 172 of flake graphite powder and hydrophobic resin is deposited onto the acid transfer barriers 152, 154 and first solid plate 160 within the mold 158. The second mixture also includes between about 80% and about 85% of a flake graphite powder and between about 15% and about 20% of a hydrophobic resin. The second mixture 172 is then densified within the mold 158 by compressing the mixture 172 with between about 2000 p.s.i. and about 4000 p.s.i. to form the mixture into a second solid plate 174 that is bonded to the acid transfer barriers 152, 154 and the first solid plate 160 to form the monolithic structure 150. The acid transfer barrier 152 is, or barriers 152, 154 are flush with perimeter surfaces 176 of the monolithic structure 150 and the barriers 152, 154 are integral with the monolithic structure 150. The structure 150 is then further densified by compression molding the monolithic structure 150 at 275-350°C at a pressure of 500-1000 p.s.i., and cooling to below 200°C before releasing the pressure. This further densification results in the first solid plate 160, the second solid plate 174 and the acid barriers 152, 154 becoming integral with each other.

[0039] As described with reference to FIG. 5, reactant flow channels may be defined within the monolithic structure 150 to form a monolithic plate assembly, such as shown in FIG. 3 at reference numerals 79, 81 during the aforesaid molding process or thereafter. Such reactant flow channels 79, 81 would thereby define at least one reactant flow edge 178, and the integral acid transfer barrier 152 is configured to be coextensive with the reactant flow edge 178.

[0040] The aforesaid methods of manufacture describes in FIGS. 5 and 6 and the resulting monolithic separator plate assemblies 42, 44, 46, 74, 100 and 150 such as shown in FIGS. 2, 3, 5, 6 may include additional components and manufacturing processes. For example, the acid transfer barrier strip may be a solid strip of PTFE (polytetrafluoroethylene) ; PTFE powder; a mixture of PTFE and FEP (a copolymer of tetrafluoro-ethylene and hexafluoropropylene) ; heat bondable PTFE; or combinations thereof. Additionally, with respect to the first method of manufacture described with respect to FIG. 5, the acid transfer barrier strips 112, 114 may be set within steps 180, 182 (shown in hatched lines in FIG. 5) defined within the first solid plate 110, as shown in FIG. 5. Also, the barrier strips 112, 114 may be rigid as described above, or may be an expanded PEFE tape available from the GORE Company of Philadelphia, PA U.S.A. under the part number "Gore Series 600", or modified PTFE products available from the same Gore Company under "Fluoro-Plastics" product names. The tape provides a lower coefficient of thermal expansion than solid PTFE strips. The acid transfer barrier strips 112, 114 may also be mixture of about 75% Granular PTFE and about 25% FEP powders deposited in on the first solid plate 110 of the FIG. 5 method, or within the barrier perimeter 164 of the FIG. 6 method.

[0041] Exemplary specifications of the above described monolithic separator plate assembly 42, 44, 46 include the assembly 42 having thickness of about 4.00mm

[0042] For purposes herein, the word "about" is to mean plus or minus ten percent. [0043] While the above disclosure has been presented with respect to the described and illustrated embodiments of the monolithic separator plate assembly and method of manufacture, it is to be understood that the disclosure is not to be limited to those alternatives and described embodiments. For example, primary usage of the invention is within fuel cells having liquid electrolytes such as phosphoric acid and fluoroborate acid. Accordingly, reference should be made primarily to the following claims rather than the forgoing description to determine the scope of the disclosure.