Coated steel bipolar plates

• US 20070015029A1
• Filed: 07/12/2005
• Published: 01/18/2007
• Est. Priority Date: 07/12/2005
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Vyas, Gayatri, Moore, John, Budinski, Michael, Kunrath Neto, Augusto
• Granted Patent: US 7,771,858 B2
• Time in Patent Office: Days
• US Class Current: 429/210
• CPC Class Codes: H01M 2008/1095 Fuel cells with polymeric electrolytes
• CPC Class Codes: H01M 2250/20 Fuel cells in motive systems, e.g. vehicle, ship, plane
• CPC Class Codes: H01M 8/0204 Non-porous and characterised by the material
• CPC Class Codes: H01M 8/0206 Metals or alloys
• CPC Class Codes: H01M 8/021 Alloys based on iron
• CPC Class Codes: H01M 8/0213 Gas-impermeable carbon-containing materials
• CPC Class Codes: H01M 8/0228 in the form of layered or coated products
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y02T 90/40 Application of hydrogen technology to transportation, e.g. using fuel cells

Abstract

In accordance with one embodiment of the present invention, an electrochemical conversion assembly comprises a plurality of electrochemical conversion cells and a plurality of electrically conductive bipolar plates. The electrochemical conversion cells are configured to communicate with first and second reactant supplies. Adjacent ones of the electrochemical conversion cells are separated by respective ones of the plurality of bipolar plates. The bipolar plates comprise an alloy comprising Fe and Cr. Respective surface portions of the bipolar plates are provided with electrically conductive, corrosion resistant layers that are placed in contact with portions of the electrochemical conversion cells. The corrosion resistant electrically conductive layers may comprise graphitic layers characterized predominantly by sp2 hybridized carbon-carbon bonding, molybdenum doped indium oxide layers, an electrically conductive Cr+N layer, or an electrically conductive MoSi₂ layer.

Claims

1. A device comprising an electrochemical conversion assembly, said electrochemical conversion assembly comprising a plurality of electrochemical conversion cells and a plurality of electrically conductive bipolar plates, wherein:

said electrochemical conversion cells are configured to communicate with first and second reactant supplies;

adjacent ones of said electrochemical conversion cells are separated by respective ones of said plurality of bipolar plates;

said bipolar plates comprise an alloy comprising Fe and Cr;

respective surface portions of said bipolar plates comprise graphitic layers characterized predominantly by sp² hybridized carbon-carbon bonding; and

respective graphite layers of said bipolar plates are in contact with portions of said electrochemical conversion cells.

2. A device as claimed in claim 1 wherein said graphitic layers are characterized substantially entirely by sp² hybridized carbon-carbon bonding.

3. A device as claimed in claim 1 wherein said graphitic layers are characterized by an interfacial contact resistance less than about 10 mΩ

-cm² under compression of at least about 100 psi (690 kPa).

4. A device as claimed in claim 1 wherein said graphitic layers are defined on opposite sides of a selected bipolar plate so as to contact one of a pair of electrochemical conversion cells separated by said selected bipolar plate.

5. A device as claimed in claim 1 wherein respective ones of said graphitic layers define a plurality of component graphitic layers collectively defining a single graphitic layer.

6. A device as claimed in claim 1 wherein respective ones of said graphitic layers are formed over an underlayer formed on said bi-polar plate alloy.

7. A device as claimed in claim 1 wherein respective ones of said graphitic layers define a thickness of less than about 10 μ

m.

8. A device as claimed in claim 1 wherein said single phase nitrided structure defines between about 0.1% and about 10.0% of a thickness of respective ones of said bipolar plates.

9. A device as claimed in claim 1 wherein said alloy further comprises Ni, Mo, Mn, Si, C, N and combinations thereof.

10. A device as claimed in claim 1 wherein said alloy comprises Fe, Cr, Ni, Mn, Si, and C.

11. A device as claimed in claim 1 wherein said alloy comprises an austenitic stainless steel.

12. A device as claimed in claim 1 wherein said first reactant supply comprises a source of hydrogenous gas and said second reactant supply comprises a source of air.

13. A device as claimed in claim 1 wherein said bipolar plates comprise a flowfield defined between opposite, electrically conductive sides of said bipolar plate.

14. A device as claimed in claim 1 wherein said electrochemical conversion cells comprise respective membrane electrode assemblies.

15. A device as claimed in claim 1 wherein said electrochemical conversion cells comprise respective electrolytic membranes, gaseous diffusion layers, catalytic components, carbonaceous components, electrically conductive components, and combinations thereof.

16. A device as claimed in claim 1 wherein said device further comprises a fuel processing system or fuel source for providing a hydrogenous gas to said electrochemical conversion assembly.

17. A device as claimed in claim 1 wherein:

said device further comprises a vehicle; and

said electrochemical conversion assembly is configured to at least partially provide said vehicle with motive power.

18. A device comprising an electrochemical conversion assembly, said electrochemical conversion assembly comprising a plurality of electrochemical conversion cells and a plurality of electrically conductive bipolar plates, wherein:

said electrochemical conversion cells are configured to communicate with first and second reactant supplies;

adjacent ones of said electrochemical conversion cells are separated by respective ones of said plurality of bipolar plates;

said bipolar plates comprise an alloy comprising Fe and Cr;

respective surface portions of said bipolar plates comprise an electrically conductive molybdenum doped indium oxide layer; and

respective doped indium oxide layers of said bipolar plates are in contact with portions of said electrochemical conversion cells.

19. A device as claimed in claim 18 wherein said indium oxide layer is doped with less than about 4 wt. % molybdenum.

20. A device as claimed in claim 18 wherein said indium oxide layer is doped with about 2 wt. % molybdenum.

21. A device as claimed in claim 18 wherein said doped indium oxide layers are defined on opposite sides of a selected bipolar plate so as to contact one of a pair of electrochemical conversion cells separated by said selected bipolar plate.

22. A device as claimed in claim 18 wherein said doped indium oxide layers are characterized by an interfacial contact resistance less than about 15 mΩ

-cm² under compression of at least about 100 psi (690 kPa).

23. A device as claimed in claim 18 wherein respective ones of said doped indium oxide layers define a thickness of between about 1.0 μ

m and about 3.0 μ

m.

24. A device as claimed in claim 18 wherein respective ones of said doped indium oxide layers define between about 0.2% and about 2.5% of a thickness of respective ones of said bipolar plates.

25. A device as claimed in claim 18 wherein said doped indium oxide layers comprise material deposited on said bipolar plates through sputter deposition, thermal reactive evaporation, pulsed laser deposition, and combinations thereof.

26. A device comprising an electrochemical conversion assembly, said electrochemical conversion assembly comprising a plurality of electrochemical conversion cells and a plurality of electrically conductive bipolar plates, wherein:

said electrochemical conversion cells are configured to communicate with first and second reactant supplies;

adjacent ones of said electrochemical conversion cells are separated by respective ones of said plurality of bipolar plates;

said bipolar plates comprise an alloy comprising Fe and Cr;

respective surface portions of said bipolar plates comprise an electrically conductive Cr+N layer; and

respective doped indium oxide layers of said bipolar plates are in contact with portions of said electrochemical conversion cells.

27. A device as claimed in claim 26 wherein said Cr+N layer comprises a layer of CrN.

28. A device as claimed in claim 26 wherein said Cr+N layer comprises a layer of Cr₂N.

29. A device as claimed in claim 26 wherein said Cr+N layer comprises a layer of Cr and N in solid solution.

30. A device as claimed in claim 26 wherein said Cr+N layers are defined on opposite sides of a selected bipolar plate so as to contact one of a pair of electrochemical conversion cells separated by said selected bipolar plate.

31. A device as claimed in claim 26 wherein said Cr+N layers are characterized by an interfacial contact resistance less than about 45 mΩ

-cm² under compression of at least about 100 psi (690 kPa).

32. A device as claimed in claim 26 wherein respective ones of said Cr+N layers define a thickness of between about 1.0 μ

m and about 2.5 μ

m.

33. A device as claimed in claim 26 wherein respective ones of said doped indium oxide layers define between about 0.2% and about 2.5% of a thickness of respective ones of said bipolar plates.

34. A device as claimed in claim 26 wherein said Cr+N layers comprise material deposited on said bipolar plates through magnetron sputtering.

35. A device comprising an electrochemical conversion assembly, said electrochemical conversion assembly comprising a plurality of electrochemical conversion cells and a plurality of electrically conductive bipolar plates, wherein:

said electrochemical conversion cells are configured to communicate with first and second reactant supplies;

adjacent ones of said electrochemical conversion cells are separated by respective ones of said plurality of bipolar plates;

said bipolar plates comprise an alloy comprising Fe and Cr;

respective surface portions of said bipolar plates comprise an electrically conductive MoSi₂ layer; and

respective MoSi₂ layers of said bipolar plates are in contact with portions of said electrochemical conversion cells.

36. A device as claimed in claim 35 wherein said MoSi₂ layers are defined on opposite sides of a selected bipolar plate so as to contact one of a pair of electrochemical conversion cells separated by said selected bipolar plate.

37. A device as claimed in claim 35 wherein said MoSi₂ layers are characterized by an interfacial contact resistance less than about 40 mΩ

-cm² under compression of at least about 100 psi (690 kPa).

38. A device as claimed in claim 35 wherein respective ones of said MoSi₂ layers define a thickness of between about 1 μ

m and about 2 μ

m.

39. A device as claimed in claim 35 wherein:

respective ones of said bipolar plates are characterized by a thickness of less than about 500 μ

m; and

respective ones of said MoSi₂ layers define a thickness of between about 1 μ

m and about 2 μ

m.

40. A device as claimed in claim 35 wherein respective ones of said MoSi₂ layers define between about 0.2% and about 2.0% of a thickness of respective ones of said bipolar plates.

41. A device as claimed in claim 35 wherein said MoSi₂ layers comprise material deposited on said bipolar plates through sputter deposition.

42. A device as claimed in claim 35 wherein said MoSi₂ layers comprise material deposited on said bipolar plates through biased-substrate sputter deposition.