Hydrating a fuel cell

1. A method of operating a fuel cell to control fluid distribution within a fuel cell comprising:

adjusting an amount of fuel entering the fuel cell and an amount of oxidant entering the fuel cell, the adjusting including;

holding an oxidant utilization rate of the fuel cell constant to maintain a constant flow of oxidant moving through oxidant channels of the fuel cell; and

while holding the oxidant utilization rate constant, decreasing a fuel utilization rate of the fuel cell, the decreasing of the fuel utilization rate increasing a flow of fuel moving through fuel channels of the fuel cell so that a first amount of water exiting the fuel cell in a fuel stream is about the same as a second amount of water exiting the fuel cell in an oxidant stream.

2. The method of claim 1 , wherein the flow of fuel is increased while the flow of oxidant is held constant to approach a desired fuel/oxidant flow ratio of about 1.

3. The method of claim 1 , wherein the flow of fuel contains a portion of fuel recycled from a fuel cell exit.

4. The method of claim 1 , including balancing the water exiting the fuel cell in the fuel stream with the water exiting the fuel cell in the oxidant stream to increase the water within the membrane of the fuel cell.

5. The method of claim 1 , wherein the fuel flows through the fuel cell in a first direction and the oxidant flows through the fuel cell in a second direction that is counter to the first direction.

6. A fuel cell system comprising:

an electrode assembly;

a first plate adjacent the electrode assembly, the first plate having at least one fuel flow channel configured to transport fuel in a first direction from a fuel inlet to a fuel outlet, wherein, during operation, a first amount of water and at least some of the fuel are exhausted from the fuel cell through the fuel outlet; and

a second plate adjacent the electrode assembly on an opposite side of the electrode assembly from the first plate, the second plate having at least one oxidant flow channel configured to transport oxidant in a second direction from an oxidant inlet to an oxidant outlet, wherein, during operation, a second amount of water and at least some of the oxidant is exhausted from the fuel cell through the oxidant outlet; and

at least one controller configured to, during at least a portion of operation of the fuel cell;

hold an oxidant utilization rate of the fuel cell constant to maintain a constant volumetric flow rate of oxidant through the at least one oxidant flow channel of the second plate;

while holding the oxidant utilization rate constant, decrease a fuel utilization rate of the fuel cell to increase a volumetric flow rate of fuel moving through the at least one fuel flow channel of the first plate so that the first amount of water exhausted from the fuel cell through the fuel outlet is about the same as the second amount of water exhausted from the fuel cell through the oxidant outlet.

7. The fuel cell system of claim 6 , wherein the first direction is counter to the second direction.

8. The fuel cell system of claim 6 , wherein one of the first plate or the second plate is a solid plate.

9. A fuel cell system comprising:

an electrode assembly of a fuel cell;

a first plate adjacent the electrode assembly, the first plate having at least one first channel configured to communicate a volumetric flow of fuel in a first direction from a fuel inlet to a fuel outlet;

a second plate adjacent the electrode assembly on an opposite side of the electrode assembly from the first plate, the second plate having at least one second channel configured to carry a volumetric flow of oxidant in a second direction from an oxidant inlet to an oxidant outlet; and

at least one controller configured to, during at least a portion of operation of the fuel cell;

hold an oxidant utilization rate of the fuel cell constant to maintain a constant volumetric flow rate of oxidant through the at least one second channel of the second plate; and

while holding the oxidant utilization rate constant, decrease a fuel utilization rate of the fuel cell to a value below which water imbalance increases, the decreasing of the fuel utilization rate of the fuel cell causing an increase in a volumetric flow rate of fuel moving through the at least one first channel of the first plate.

10. The fuel cell system of claim 9 , wherein the first direction is counter to the second direction.

11. The fuel cell system of claim 9 , wherein one of the first plate or the second plate is a solid plate.

12. The fuel cell system of claim 9 , wherein the ratio of a depth of the first channel to a depth of the second channel is 1:3.

13. The fuel cell system of claim 6 , further comprising:

a recycle blower, and

wherein the at least one controller is operatively coupled to the recycle blower to control the recycle blower to supply the increased volumetric flow rate of fuel transported through the at least one fuel flow channel of the first plate.

14. The method of claim 1 wherein decreasing the fuel utilization rate of the fuel cell includes decreasing the fuel utilization rate to a value below which water imbalance increases.

15. The method of claim 1 wherein decreasing the fuel utilization rate of the fuel cell includes decreasing the fuel utilization rate to a value that maximizes output voltage.

16. The method of claim 1 wherein the constant flow of oxidant is a flow of non-humidified oxidant which moves through oxidant channels of the fuel cell.

17. The fuel cell system of claim 6 wherein the controller is configured to decrease the fuel utilization rate to a value below which water imbalance increases.

18. The fuel cell system of claim 6 further comprising a source of non-humidified oxidant, the source supplying the non-humidified oxidant which flows at the constant volumetric flow rate through the at least one oxidant channel of the second plate.

19. The fuel cell system of claim 9 further comprising a source of non-humidified oxidant, the source supplying the non-humidified oxidant which flows at the constant volumetric flow rate through the at least one second channel of the second plate.