Adaptive purge control to prevent electrode redox cycles in fuel cell systems

• US 20080075985A1
• Filed: 09/21/2006
• Published: 03/27/2008
• Est. Priority Date: 09/21/2006
• Status: Active Grant

• Current Assignee: Bloom Energy Corporation
• Original Assignee: Bloom Energy Corporation
• Inventors: Gottmann, Matthias
• Granted Patent: US 7,846,600 B2
• Time in Patent Office: Days
• US Class Current: 429/13
• CPC Class Codes: H01M 2004/8684 Negative electrodes
• CPC Class Codes: H01M 2008/1293 Fuel cells with solid oxide electrolytes
• CPC Class Codes: H01M 8/04201 Reactant storage and supply, e.g. means for feeding, pipes
• CPC Class Codes: H01M 8/04231 Purging of the reactants
• CPC Class Codes: H01M 8/04559 of fuel cell stacks
• CPC Class Codes: H01M 8/04746 Pressure; Flow
• CPC Class Codes: H01M 8/04753 of fuel cell reactants
• CPC Class Codes: H01M 8/04791 Concentration; Density H01M8/04828 takes precedence
• CPC Class Codes: H01M 8/04798 of fuel cell reactants
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A method of operating a fuel cell system during a fuel outage or shortage includes detecting an open circuit voltage (OCV) of the fuel cell system, and providing a reducing purge gas flow to anode electrodes of fuel cells of the fuel cell system when the OCV approaches, reaches or falls below a threshold value below which oxidation of the anode electrodes occurs.

Claims

1. A method of operating a fuel cell system during a fuel outage or shortage, comprising:

detecting an open circuit voltage (OCV) of the fuel cell system; and

providing a reducing purge gas flow to anode electrodes of fuel cells of the fuel cell system when the OCV approaches, reaches or falls below a threshold value below which oxidation of the anode electrodes occurs.

2. The method of claim 1, further comprising terminating the purge gas flow to the anode electrodes when the OCV increases above the threshold value.

3. The method of claim 2, further comprising intermittently providing the purge gas flow to the anode electrodes a plurality of times when the OCV approaches, reaches or falls below the threshold value.

4. The method of claim 1, wherein the purge gas flow is provided to the anode electrodes when the OCV approaches the threshold value.

5. The method of claim 1, wherein the purge gas flow is provided to the anode electrodes when the OCV reaches the threshold value.

6. The method of claim 1, wherein the purge gas flow is provided to the anode electrodes when the OCV falls below the threshold value.

7. The method of claim 1, wherein the purge gas flow comprises at least one of hydrogen, forming gas and carbon monoxide.

8. The method of claim 1, wherein the fuel cells comprise solid oxide fuel cells.

9. The method of claim 1, wherein the OCV is detected by an operator and the purge gas flow is turned on by the operator.

10. The method of claim 1, wherein the OCV is detected by a control system and the purge gas flow is turned on by the control system.

11. The method of claim 1, wherein the purge gas flow is provided to the anode electrodes when the OCV approaches, reaches or falls below a predetermined threshold value.

12. The method of claim 1, wherein the purge gas flow is provided to the anode electrodes when the OCV approaches, reaches or falls below the threshold value which corresponds to a plateau in a plot of OCV versus time.

13. The method of claim 1, further comprising storing a liquid, gel or solid purge material and evaporating the purge material to provide the purge gas flow.

14. A fuel cell system, comprising:

a fuel cell stack comprising a plurality of fuel cells;

a purge material storage vessel; and

a means for providing a reducing purge gas flow using purge material stored in the purge material storage vessel to anode electrodes of the plurality of the fuel cells when an open circuit voltage (OCV) of the stack approaches, reaches or falls below a threshold value below which oxidation of the anode electrodes occurs.

15. The system of claim 14, wherein the means for providing is a means for terminating the purge gas flow to the anode electrodes when the OCV increases above the threshold value.

16. The system of claim 15, wherein the means for providing is a means for intermittently providing the purge gas flow to the anode electrodes a plurality of times when the OCV approaches, reaches or falls below the threshold value.

17. The system of claim 14, wherein:

the purge material storage vessel comprises at least one of a hydrogen gas storage vessel, a forming gas storage vessel, or a carbon monoxide gas storage vessel; and

the fuel cells comprise solid oxide fuel cells.

18. The system of claim 14, wherein:

the purge material storage vessel comprises a liquid, gel or solid material storage vessel located in fluid communication with an evaporator; and

the fuel cells comprise solid oxide fuel cells.

19. A fuel cell system, comprising:

a fuel cell stack comprising a plurality of fuel cells;

a purge material storage vessel; and

a control system, which in operation, provides a reducing purge gas flow using purge material stored in the purge material storage vessel to anode electrodes of the plurality of the fuel cells when an open circuit voltage (OCV) of the stack approaches, reaches or falls below a threshold value below which oxidation of the anode electrodes occurs.

20. The system of claim 19, wherein the control system, in operation, terminates the purge gas flow to the anode electrodes when the OCV increases above the threshold value and intermittently provides the purge gas flow to the anode electrodes a plurality of times when the OCV approaches, reaches or falls below the threshold value.

21. The system of claim 19, wherein:

the purge material storage vessel comprises at least one of a hydrogen gas storage vessel, a forming gas storage vessel or a carbon monoxide storage vessel; and

the fuel cells comprise solid oxide fuel cells.

22. The system of claim 19, wherein:

the purge material storage vessel comprises a liquid, gel or solid material storage vessel located in fluid communication with an evaporator; and

the fuel cells comprise solid oxide fuel cells.

23. The system of claim 19, further comprising:

a fuel inlet conduit;

a purge gas inlet conduit; and

a least one valve, which in operation seals off the fuel inlet conduit and opens the purge gas inlet conduit to allow a purge gas flow to be provided from the purge material storage vessel through the purge gas inlet conduit into the fuel cell stack.