Method for operating fuel cells with passive reactant supply

1. A method of operating a passive reactant supply fuel cell system, the method comprising:

obtaining or providing a fuel cell system comprising a planar array of fuel cells, the planar array of fuel cells comprising

a plurality of anodes and a plurality of cathodes separated by an ion-conducting electrolyte; and

a dead-ended fuel supply fluidly in contact with the plurality of anodes;

exposing the cathodes of the planar array to ambient air; and

supplying fuel to the anodes of the planar array at a pressure greater than that of the ambient air.

2. The method of claim 1 , wherein the fuel comprises hydrogen gas.

3. The method of claim 1 , wherein the fuel supply comprises at least one material chosen from a metal hydride, a composite metal hydride, carbon-graphite nanofibers, compressed hydrogen gas, and a chemical hydride.

4. The method of claim 1 , wherein exposing cathode portions of the planar array to ambient air comprises supplying the ambient air to the cathode substantially by diffusion.

5. The method of claim 1 , wherein the planar array further comprises one or more protective layers on the exposed cathode portions, the one or more protective layers comprising at least one of a carbon layer and a hydrophobic layer.

6. The method of claim 1 , wherein the planar array further comprises a porous protective cover proximate the exposed cathode portions, wherein the porous protective cover comprises at least one of a hydrophobic sheet, an activated carbon filter, a screen, and a mesh.

7. The method of claim 1 , wherein a fuel utilization of the system is greater than 75%.

8. The method of claim 1 , further comprising modulating a pressure of the fuel supplied to the anodes.

9. The method of claim 1 , further comprising controlling a pressure of the fuel supplied to the anodes using at least one pressure regulator.

10. The method of claim 1 , comprising supplying the fuel to the plurality of anodes at a substantially constant pressure.

11. The method of claim 1 , comprising supplying the fuel to the anodes at a pressure that is independent of a power demand of the fuel cell system.

12. The method of claim 1 , comprising supplying the fuel to the anodes without providing pressure regulation between the dead-ended fuel supply and the plurality of anodes.

13. The method of claim 1 , comprising providing the fuel to the anodes at a pressure that is dependent on a power demand of the fuel cell system.

14. The method of claim 1 , wherein an area of each individual fuel cell in the planar array is independently in the range of approximately 0.000,000,01 cm 2 to approximately 1,000 cm 2 .

15. The method of claim 1 , wherein supplying the fuel comprises providing the fuel to each of the plurality of anodes in parallel.

16. The method of claim 1 , wherein supplying the fuel comprises providing the fuel to at least a portion of the plurality of anodes in series.

17. The method of claim 1 , wherein the fuel cell system is integrated into one or more of a portable electrical power source and a portable electronic device.

18. The method of claim 1 , further comprising:

coupling the planar array of fuel cells to an electrical load; and

transferring electrical energy from the planar array of fuel cells to an electrical load.

19. A method of operating a planar array of fuel cells, comprising:

providing an enclosure proximate to anode portions of the planar array that sealably encloses the anode portions of the planar array;

admitting a fuel into the enclosure and retaining the fuel within the enclosure while maintaining a predetermined fuel pressure greater than a pressure of the ambient air; and

exposing cathode portions of the planar array to ambient air.

20. The method of claim 19 , wherein admitting fuel into the enclosure comprises admitting fuel from a dead-ended fuel supply fluidly in contact with the plurality of anodes.