FLOW FIELD CONFIGURATION FOR FUEL CELL PLATE
BACKGROUND
[0001] This disclosure relates to a fuel cell plate. In particular, the disclosure relates
to a flow field configuration for use with porous bipolar plates, for example.
[0002] It is desirable to provide efficient and cost effective fuel cells. Fuel cell
bipolar plates are typically fairly expensive components. One reason that bipolar plates are
expensive is that they use complex flow geometries, which are created by an end milling
machining operation, which is time-consuming and expensive. A less expensive machining
operation, such as gang-milling, can be utilized if the flow channels are linear. While such
plates are more cost effective, they also may be less efficient during fuel cell operation due to
poor mass transport of reactants to the fuel cell electrodes.
SUMMARY
[0003] A method of manufacturing a plate for a fuel cell includes the steps of
providing flow channels in a fuel cell plate. Multiple fuel cell plates are joined into a cell stack
assembly. A blocking plate is affixed to the fuel cell plate and is arranged to at least partially
obstruct the flow channels. The blocking plate is affixed to the fuel cell plate after the plates
have been arranged into the cell stack assembly.
[0004] The resulting fuel cell provides a fuel cell plate having a perimeter with an
edge. The fuel cell plate includes flow channels extending to the edge. The blocking plate is
affixed to the fuel cell plate at the edge to at least partially block the flow channel. In this
manner, an inexpensive fuel cell plate may be used, and the blocking plate can be configured to
create terminated flow channels, which may be used to provide an interdigitated flow field.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The disclosure can be further understood by reference to the following
detailed description when considered in connection with the accompanying drawings wherein:
[0006] Figure 1 is a highly schematic view of an example fuel cell.
[0007] Figure 2 is a top elevational view of an example fuel cell plate.
[0008] Figure 3 is a partial cross-sectional view of a fuel cell stack with a blocking
plate.
[0009] Figures 4A-4B are respectively perspective and side elevational views of an
example cell stack assembly with one example blocking plate.
[0010] Figures 5A-5B are respectively perspective and side elevational views of the
cell stack assembly with another example blocking plate.
DETAILED DESCRIPTION
[0011] A fuel cell 10 is schematically illustrated in Figure 1. The fuel cell 10
includes a cell stack assembly 12 comprising multiple cells 14 joined to one another. Each cell
14 includes a unitized electrode assembly (UEA) 2 1 arranged between an anode plate 22 and a
cathode plate 24. In one example, the anode and cathode plates 22, 24 are bipolar. The UEA 2 1
includes catalyst layers 18 arranged on either side of a proton exchange membrane (PEM) 16. A
gas diffusion layer (GDL) 20 adjoins each catalyst layer 18.
[0012] Each anode and cathode plate 22, 24 respectively includes anode and cathode
flow channels 26, 28. A fuel source 30 is in fluid communication with and provides fuel the
anode flow channels 26. An oxidant source 32 is fluidly connected with and provides oxidant to
the cathode flow channels 28.
[0013] The cathode plate 24 is schematically illustrated in Figure 2. Although a
cathode plate is shown, this disclosure also relates to and can be used for anode plates. The
cathode plate 24 has a perimeter 34 that defines the exterior surface of the flat plate when
arranged in the cell stack assembly 12. The anode flow channels 28 comprise passages that in the
example are parallel to one another and extend in a linear direction between opposing edges 36
where they terminate at ends 38. Other passage configurations may be used if desired.
[0014] In one example, the cathode plate 24 is provided by a porous bipolar plate,
which is constructed from a graphite material. The cathode plate 24 is manufactured using a flat
sheet of porous graphite, which is extruded or gang-milled, for example, to provide the cathode
flow channels 28. In this manner, the cathode plate 24 may be manufactured inexpensively.
[0015] Linearly extending flow channels may not provide the best fuel cell efficiency
during some operating conditions. Accordingly, it is desirable to at least partially obstruct the
cathode flow channels 28 at least some of the ends 38 to promote uniform distribution of the
oxidant across the entire flow field. Referring to Figure 3, a blocking plate 40 is affixed,
permanently in the example, to the one edge 36 of the perimeter 34 and may be affixed to both of
the opposing edges if desired. In one example, a sealant 42 is used to adhere the blocking plate
40 to the exterior of the cell stack assembly 12 and accommodate any irregularities in its exterior
surface. In the example, the sealant 42 is not provided axially between the components of the
cell stack assembly 12, but rather, the sealant 42 is provided at the perimeter 34 in a location
exterior to the cell stack assembly 12. The sealant may be of a type suitable for use in fuel cells.
[0016] The blocking member 40 may be constructed from a phenolic laminate, such
as a NEMA G-series phenolic material. The blocking plate 40 may be integrated with a
manifold 44 that is secured over the cell stack assembly 12 to provide an external manifold, as
illustrated in Figure 3. The manifold 44 is secured relative to a structure 46 with a seal 48. An
manifold cavity 45 is provided between the manifold 44 and the cell stack assembly 12, which
receives oxidant. The blocking plate 40 may be connected to the manifold 44 by one or more
ribs 50, which may be integrally formed with the manifold 44 and blocking plate 40 enabling
installation of onto the cell stack assembly 12 as a unitary structure.
[0017] Referring to Figures 4A-4B, an arrangement is illustrated in which the
blocking plate 40 partially blocks ends 38 of the cathode flow channels 28. In the example, the
blocking plate 40 includes support members 52 between which multiple blocking members 54
extend. The blocking members 54 are parallel to one another and provide spaces 56. One
example area of the ends 38 is a width of 0.8-1.2 mm (0.03 - 0.05 inches) and a depth of 0.4-
0.64 mm (0.2 - 0.03 inches). The blocking members 54 provide a blocking width 60. The ends
38 provide a channel width 58 that, in the example, is larger than the blocking width 60. As
illustrated in Figure 4B, only portions of the ends 38 are obstructed.
[0018] Another arrangement is illustrated in Figures 5A-5B. Like numerals indicate
like elements. The cell stack assembly 112 includes a blocking plate 140 that completely
obstructs the ends 38 of the cathode flow channel 28. The sealant seals about the ends 38. The
channel width 158 is less than the blocking width 160 such that the blocking members 154 cover
the ends 38. Figure 5B illustrates alternating rows of blocked channels 62 and unblocked
channels 64, which provides an inter-digitated flow field. A blocking plate 140 is provided at
either end of flow field such that one end of the flow field is open and the other end of the flow
field is closed to provide an interdigitated configuration. Other flow field configurations may be
used if desired.
[0019] The resulting fuel cell provides a bipolar plate having a perimeter with an
edge. The plate includes flow channels extending to the edge. One blocking plate is affixed to
the reactant inlet side of the fuel cell assembly at the edge to at least partially create a flow
blockage in half of the inlet flow channels. A second blocking plate is affixed to reactant exit
side of the fuel cell assembly to create a flow blockage in half of the exit channels. The blocking
plates are designed and arranged such that half of the channels have flow blockage at the reactant
inlet side only and half of the channels are blocked at the reactant exit side only. In this manner,
an inexpensive fuel cell flow field design may be created which provides an interdigitated flow
field, which has been shown to increase fuel cell performance.
[0020] Although an example embodiment has been disclosed, a worker of ordinary
skill in this art would recognize that certain modifications would come within the scope of the
claims. For that reason, the following claims should be studied to determine their true scope and
content.

CLAIMS
What is claimed is:
1. A method of manufacturing a plate for a fuel cell comprising the steps of:
a) providing flow channels in a fuel cell plate;
b) joining multiple fuel cell plates into a cell stack assembly; and
c) affixing a blocking plate to the cell stack assembly and at least partially
obstructing the flow channels, subsequent to performing step b).
2. The method according to claim 1, wherein step a) includes forming flow channels
that extend to an edge of an outer perimeter of the fuel cell plate.
3. The method according to claim 2, wherein step a) includes forming parallel flow
channels that extend to the edge of the fuel cell plate.
4. The method according to claim 3, wherein step a) includes forming the flow
channels to opposing edges of the fuel cell plate.
5. The method according to claim 4, wherein step a) includes gang milling the flow
channels.
6. The method according to claim 2, comprising step d) securing an external
manifold to the cell stack assembly.
7. The method according to claim 6, wherein step d) includes providing a manifold
cavity between the blocking plate and the external manifold.
8. The method according to claim 2, wherein step c) includes applying sealant on an
exterior of the cell stack assembly at the edge to adhere the blocking plate to the fuel cell plate.
9. The method according to claim 1, wherein the fuel cell plate is a porous plate.
10. The method according to claim 1, wherein step c) includes providing an
interdigitated flow field with the two blocking plates arranged on opposing sides of the flow
channels.
11. A fuel cell comprising:
a plate having a perimeter providing an edge, the plate include flow channels extending
to the edge; and
a blocking plate affixed to the plate at the edge to at least partially block the flow
channels.
12. The fuel cell according to claim 11, comprising a second blocking plate affixed to
the fuel cell assembly at the reactant exit to at least partially block half of the flow channels that
were not blocked at the reactant inlet, and the blocking plate at least partially blocking half of the
flow channels at the reactant inlet.
13. The fuel cell according to claim 11, comprising a sealant adhering the blocking
plate to the plate.