Insert-molded, externally manifolded, sealed membrane based electrochemical cell stacks
View Patent ↗The present invention provides, among other things, membrane cassettes and stacks thereof which are suitable for a use in a variety of electrochemical applications. The invention further provides membrane cassettes which comprise one or more external manifolds which deliver reagents and/or coolant to one or more reactant or coolant flow fields of the membrane cassettes. In particular, the present invention describes the insert molding method, whereby the plenums of the external manifolds are created during the stack encapsulation step. The invention describes several methods for creating the manifold runner geometry via insert-molding, machining, or with separate components.
1. A fuel cell stack comprising:
a) at least one fuel cell including:
i) a membrane electrode assembly;
ii) a reductant flow field disposed proximate a first side of the membrane electrode assembly, the reductant flow field including a reductant flow channel extending to a periphery of the fuel cell;
iii) an oxidant flow field disposed proximate a first side of the membrane electrode assembly, the oxidant flow field including an oxidant flow channel extending to the periphery of the fuel cell;
b) a unitary plenum housing formed about the periphery of the fuel cell, the unitary plenum housing at least partially defining:
i) a reductant manifold in fluid communication with the reductant flow channel, the reductant manifold and the reductant flow channel cooperating to form a reductant plenum; and
ii) an oxidant manifold in fluid communication with the oxidant flow channel, the oxidant manifold and the oxidant flow channel cooperating to form an oxidant plenum, wherein at least one of the reductant and oxidant manifolds includes a portion of sealant having a negative impression of a manifold insert defining a volume at least partially bounded by the sealant.
2. The fuel cell stack of claim 1 , wherein:
a) the fuel cell further includes a coolant plate in thermal communication with the membrane electrode assembly, the coolant plate including a coolant flow channel extending to the periphery of the fuel cell; and
b) the unitary plenum housing further defines a coolant manifold in fluid communication with the coolant flow channel, the coolant manifold and the coolant flow channel cooperating to form a coolant plenum.
3. The fuel cell stack of claim 2 , wherein the unitary plenum housing defines at least one of (i) the reductant manifold, (ii) the oxidant manifold and (iii) a coolant manifold in cooperation with a portion of the periphery of the fuel cell.
4. The fuel cell stack of claim 1 , wherein at least one of (i) the reductant manifold, (ii) the oxidant manifold and (iii) the coolant manifold is not defined by the periphery of the fuel cell.
5. The fuel cell stack of claim 1 , wherein the fuel cell stack includes a plurality of fuel cells electrically connected in series.
6. The fuel cell stack of claim 1 , wherein the reductant flow field and oxidant flow field are each integrally formed into a separator plate, the separator plate being chosen from the group consisting of (i) a bipolar plate and (ii) a cooling plate.
7. The fuel cell stack of claim 6 , wherein the separator plate includes material selected from the group consisting of (i) a carbon/polymer composite material, (ii) graphite and (iii) metal.
8. The fuel cell stack of claim 6 , wherein the separator plate is stamped from a metal sheet.
9. The fuel cell stack of claim 7 , wherein the graphite includes graphite tape.
10. The fuel cell stack of claim 1 , further comprising a first end plate at a first end of the stack and a second end plate at the second end of the stack.
11. The fuel cell stack of claim 10 , wherein at least one of the end plates includes recesses formed therein proximate an extremity of one of the manifolds, the recess being adapted and configured to receive a removable mold when the plenum housing is being formed.
12. The fuel cell stack of claim 1 , further comprising an electrical current collector electrically coupled to the membrane electrode assembly.
13. The fuel cell stack of claim 7 , wherein each separator plate defines a contoured feature proximate a port of a flow channel at the periphery of the fuel cell, the contoured feature being adapted and configured to mate with a removable mold when the plenum housing is being formed.
14. The fuel cell stack of claim 13 , wherein the contoured feature is substantially concave in shape and is adapted to receive a mold that is substantially cylindrical in shape when the plenum housing is being formed.
15. The fuel cell stack of claim 10 , wherein one of the end plates includes a fill hole and the other end plate includes a vent hole to facilitate forming the plenum housing by way of a molding process.
16. The fuel cell stack of claim 2 , further comprising a vapor barrier insert disposed proximate at least one of the oxidant, reductant and coolant manifolds, the vapor barrier insert being adapted and configured to reduce egress of fluids through a periphery of the fuel cell stack.
17. The fuel cell stack of claim 16 further comprising a vapor barrier layer disposed proximate the external periphery of the plenum housing, the vapor barrier layer being adapted and configured to reduce egress of fluids through a periphery of the fuel cell stack.
18. The fuel cell stack of claim 1 , wherein at least one of the manifolds has a tapered configuration from a first end of the manifold to a second end of the manifold.
19. The fuel cell stack of claim 18 , wherein the tapered manifold has a smaller transverse dimension that enlarges to a larger transverse dimension along a length of the manifold toward an external port of the fuel cell stack.
20. The fuel cell stack of claim 1 , further comprising a tubular insert integrally formed into one end of one of the manifolds, the tubular insert made from a material that is compatible with the material of the plenum housing, wherein the tubular insert forms a portion of a fluid flow path including the manifold to which it is attached.