Low contact resistance bonding method for bipolar plates in a PEM fuel cell
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 method for manufacturing a separator assembly for a fuel cell, comprising:
providing a first and a second electrically conductive metal substrate, said metal substrate susceptible to formation of metal oxides in the presence of oxygen;
removing any of said metal oxides from a first and a second surface of said first and said second substrates, respectively;
depositing an ultra-thin electrically conductive metal coating on select regions of said first and said second metal surfaces;
positioning said select regions of said first and said second surfaces to confront one another; and
contacting said select regions of said first and said second surfaces at one or more contact regions, wherein said contact regions form an electrically conductive path between said first and said second substrates.
2. The method according to claim 1 , wherein prior to said contacting sealing is conducted to provide fluid isolation between an internal and an external sealed region formed between said first and said second substrates.
3. The method according to claim 2 , wherein said internal sealed region corresponds to said select regions, and non-select regions correspond to said external sealed region.
4. The method according to claim 1 , wherein said removing and said depositing are conducted essentially simultaneously by ion beam sputtering and electron beam evaporation deposition, respectively.
5. The method according to claim 1 , wherein said select regions correspond to electrically conductive areas and non-select regions along said surface are electrically non-conductive.
6. The method according to claim 1 , wherein each of said first and said second surfaces have a flow field formed therein, said flow field being defined by lands interspersed with grooves that form flow channels, wherein said lands of said first and said second substrates contact one another to form said contact regions and correspond to said select regions, and said depositing of said electrically conductive metal coating onto said select regions is preceded by masking of any non-select regions that are electrically non-conductive.
7. The method according to claim 1 , wherein said electrically conductive region is centrally located on both said first and said second surfaces of said first and second substrates, respectively, and said electrically non-conductive region circumscribes said centrally located electrically conductive region.
8. The method according to claim 1 , wherein said depositing is conducted by a process selected from the group consisting of: electron bean evaporation, magnetron sputtering, physical vapor deposition, electrolytic deposition, and electroless deposition.
9. The method according to claim 1 , wherein said removing is conducted by electrolytic cleaning, etching, pickling, mechanical abrasion, and sputtering.
10. The method according to claim 1 , wherein said electrically conductive metal coating is deposited at a thickness of less than about 15 nm.
11. The method according to claim 1 , wherein said electrically conductive metal coating is deposited at a thickness of between about 2 to about 10 nm.
12. The method according to claim 1 , wherein said electrically conductive metal coating is deposited at a thickness of less than or equal to the depth of two atomic monolayers of metal atoms.
13. The method according to claim 1 , wherein said electrically conductive metal coating comprises gold.
14. The method according to claim 1 , wherein said contacting is accomplished by applying a compressive stress.
15. The method according to claim 1 , wherein an electrical contact resistance across said first substrate to said second substrate through said contact region is less than 10 mOhm-cm 2 when a compressive stress of 1400 kPa or greater is applied.
16. The method according to claim 1 , wherein said contacting is accomplished by applying a compressive stress of 1400 kPa or greater.