Low contact resistance bonding method for bipolar plates in a pem fuel cell
View Patent ↗A separator assembly for use in a stack of electrochemical cells is provided, having a first conductive metallic substrate with a first surface and a second conductive metallic substrate with a second surface, wherein each of the first and second surfaces are overlaid with an ultra-thin electrically conductive metal coating. The first and second surfaces form electrically conductive paths at regions where the metal coating of the first and second layer contact one another. The contact of the surfaces overlaid with metal coating is sufficient to join the first and second substrates to one another. Preferred metal coatings comprise gold (Au). Methods of making such separator assemblies are also provided.
1. A separator assembly for use in a stack of electrochemical cells, comprising:
a first conductive metallic substrate having a first surface and a second conductive metallic substrate having a second surface; each of said first and said second surfaces having an electrically conductive central region and a non-conductive peripheral region;
an ultra-thin electrically conductive metal coating overlying one or more areas of said electrically conductive regions of said respective first and said second surfaces;
electrically conductive paths formed by physical contact between said coated areas of said respective first and said second surfaces; and
a seal isolating each said central electrically conductive region from each said peripheral non-conductive region, wherein said seal is an adhesive polymer that is selected from the group consisting of: thermoset and thermoplastic polymers.
2. The separator assembly according to claim 1 , wherein a flow field is formed in said electrically conductive region of said first and said second substrates, respectively, each of said flow fields defined by lands interspersed with grooves along said surface and said metal coating is on said lands, and said electrically conductive paths are formed by physical contact between opposing lands of said first substrate and second substrates.
3. The separator assembly according to claim 2 , wherein said grooves are non-conductive.
4. The separator assembly according to claim 2 , wherein said physical contact between opposing lands of said first and said second surfaces defines fluid flow channels through which a coolant circulates.
5. The separator assembly of claim 1 , wherein said substrates are arranged together in a stack and said physical contact is achieved by said stack imparting a compressive stress biasing said substrates towards one another.
6. The separator assembly according to claim 1 , wherein said seas creates a barrier that substantially impedes fluid migration from said electrically conductive region to said electrically non-conductive region.
7. The separator assembly according to claim 1 , wherein a contact resistance across said first substrate to said second substrate through said electrically conductive paths is less than 10 mOhm-cm 2 , under a compressive stress of 1400 kPa or greater.
8. The separator assembly according to claim 1 , wherein said electrically conductive metal coating comprises gold.
9. The separator assembly according to claim 1 , wherein said electrically conductive metal coating has a thickness greater than about 2 nm.
10. The separator assembly according to claim 1 , wherein said adhesive polymer is selected from the group consisting of: epoxides, phenolics, polymethyl methacrylates, polyurethanes, silicones, polysulfides, butyls, fluoroelastomers, fluorosilicones, polyamides, polyesters, polyolefins, polyvinyl acetate, and polyurethane.
11. The separator assembly according to claim 1 , wherein said first and said second conductive metallic substrates are selected from the group consisting of stainless steel, aluminum, and titanium.
12. A separator assembly for use in a stack of electrochemical cells, comprising:
a first conductive metallic substrate having a first surface and a second conductive metallic substrate having a second surface; each of said first and said second surfaces having an electrically conductive central region and a non-conductive peripheral region;
an ultra-thin electrically conductive metal coating overlying one or more areas of said electrically conductive regions of said respective first and said second surfaces;
electrically conductive paths formed by physical contact between said coated areas of said respective first and said second surfaces; and
a seal isolating each said central electrically conductive region from each said peripheral non-conductive region, wherein said seal is a laser weld.
13. A separator assembly for use in a stack of electrochemical cells, comprising:
a first conductive metallic substrate having a first surface and a second conductive metallic substrate having a second surface; each of said first and said second surfaces having an electrically conductive central region and a non-conductive peripheral region;
an ultra-thin electrically conductive metal coating overlying one or more areas of said electrically conductive regions of said respective first and said second surfaces;
electrically conductive paths formed by physical contact between said coated areas of said respective first and said second surfaces;
a seal isolating each said central electrically conductive region from each said peripheral non-conductive region,
wherein said first substrate has a first opposite side to said first side and said second substrate has a second opposite side to said second side, wherein said first and said second opposite sides are overlaid with said electrically conductive metal coating.
14. The separator assembly according to claim 13 , wherein said electrically conductive metal coating has a thickness of less than 15 nm.
15. The separator assembly according to claim 14 , wherein said electrically conductive metal coating has a thickness of between about 2 to about 10 nm.
16. The separator assembly according to claim 13 , wherein said physical contact between opposing lands of said first and said second surfaces defines fluid flow channels through which a coolant circulates.
17. The separator assembly according to claim 13 , wherein said substrates are arranged together in a stack and said physical contact is achieved by said stack imparting a compressive stress biasing said substrates towards one another.
18. The separator assembly according to claim 13 , wherein said seal creates a barrier that substantially impedes fluid migration from said electrically conductive region to said electrically non-conductive region.
19. The separator assembly according to claim 13 , wherein a contact resistance across said first substrate to said second substrate through said electrically conductive paths is less than 10 mOhm-cm 2 , under a compressive stress of 1400 kPa or greater.
20. The separator assembly according to claim 13 wherein said electrically conductive metal coating comprises gold.
21. The separator assembly according to claim 20 , wherein said electrically conductive metal coating has a thickness of less than 15 nm.
22. The separator assembly according to claim 13 , wherein said first and said second conductive metallic substrates are selected from the group consisting of stainless steel, aluminum, and titanium.