Direct methanol fuel cell system and operating method thereof

Abstract

A direct methanol fuel cell system includes a fuel cell main body including at least one membrane-electrode assembly having an electrolyte membrane, and an anode and a cathode positioned on opposite sides of the electrolyte membrane; a fuel-supplying unit feeding a mixing tank with high concentration fuel; the mixing tank mixing and storing the fuel fed from the fuel-supplying unit and an outlet stream discharged from the fuel cell main body; a fuel feeder supplying mixed fuel stored in the mixing tank to the fuel cell main body; and a controller controlling the fuel-supplying unit to stop operating in response to a stop request signal, and controlling the fuel feeder to operate to circulate the mixed fuel via the anode of the fuel cell main body until a fuel concentration of the mixed fuel is less than or equal to a reference concentration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention.

FIG. 1 is a graph showing performance deterioration of a conventional direct methanol fuel cell system as the system operates in a cycle between an operation and a stop.

FIG. 2 is a block diagram of a direct methanol fuel cell system according to a first embodiment of the present invention.

FIG. 3 is a flowchart showing operation of the direct methanol fuel cell system according to the first embodiment of the present invention.

FIG. 4 is a graph showing a performance change of the direct methanol fuel cell system according to the first embodiment of the present invention.

FIG. 5 is a block diagram of a direct methanol fuel cell system according to a second embodiment of the present invention.

FIG. 6 is a flowchart showing operation of the direct methanol fuel cell system according to the second embodiment of the present invention.

FIG. 7 is a schematic view of one embodiment of a fuel cell main body employed in the direct methanol fuel cell system according to the first and second embodiments of the present invention.

FIG. 8 is a block diagram of a direct methanol fuel cell system according to a third embodiment of the present invention.

FIG. 9 is a schematic view of one embodiment of a fuel cell main body employed in the direct methanol fuel cell system according to the third embodiment of the present invention.

FIG. 10A is a perspective view of a concentration sensor employed in the direct methanol fuel cell system according to an embodiment of the present invention.

FIG. 10B is a graph showing an expansion coefficient of the concentration sensor of FIG. 10A according to molar concentration and temperature.

Claims

1. A direct methanol fuel cell system comprising: a fuel cell main body including at least one membrane-electrode assembly having an electrolyte membrane, and an anode and a cathode positioned on opposite sides of the electrolyte membrane;a fuel-supplying unit feeding a mixing tank with high concentration fuel;the mixing tank mixing and/or storing the fuel fed from the fuel-supplying unit and an outlet stream discharged from the fuel cell main body;a fuel feeder supplying mixed fuel stored in the mixing tank to the fuel cell main body; anda controller controlling the fuel-supplying unit to stop operating in response to a stop request signal, and controlling the fuel feeder to operate to circulate the mixed fuel via the anode of the fuel cell main body until a fuel concentration of the mixed fuel is less than or equal to a reference concentration.

2. The direct methanol fuel cell system according to claim 1, wherein the mixed fuel is a methanol solution, and the reference concentration ranges from 0 to 0.3 mol.

3. The direct methanol fuel cell system according to claim 1, further comprising a concentration sensor to detect the fuel concentration of the mixed fuel.

4. The direct methanol fuel cell system according to claim 1, further comprising a timer that is set to operate for a time taken to lower the fuel concentration of the mixed fuel to less than or equal to the reference concentration, the timer stopping the fuel feeder when the timer stops operating.

5. The direct methanol fuel cell system according to claim 4, wherein the timer operates in response to the stop request signal.

6. The direct methanol fuel cell system according to claim 1, further comprising a soft switch type stop button generating the stop request signal, wherein the controller is adapted to receive the stop request signal from the soft switch type stop button and to control the fuel-supplying unit to stop operating in response to the stop request signal.

7. The direct methanol fuel cell system according to claim 6, wherein the soft switch type stop button is coupled to an external load.

8. The direct methanol fuel cell system according to claim 1, wherein the at least one membrane-electrode assembly is a plurality of membrane-electrode assemblies, and wherein the fuel cell main body comprises a separator electrically connecting the plurality of membrane-electrode assemblies in series and defining a channel allowing a fluid flow.

9. The direct methanol fuel cell system according to claim 8, further comprising an oxidant-supplying unit to feed the fuel cell main body with an oxidant, wherein the controller controls the oxidant-supplying unit to stop operating at or after a time when the fuel feeder stops operating.

10. The direct methanol fuel cell system according to claim 1, wherein the fuel cell main body employs air contacting the cathode as an oxidant.

11. The direct methanol fuel cell system according to claim 1, further comprising an electricity storage device electrically connected to the fuel cell main body, the fuel-supplying unit, the fuel feeder, and the controller.

12. The direct methanol fuel cell system according to claim 11, wherein the controller controls the electricity storage device to be charged with electricity generated in the fuel cell main body.

13. The direct methanol fuel cell system according to claim 12, further comprising a switching unit electrically disconnecting an external load from the fuel cell main body, and electrically connecting the electricity storage device with the fuel cell main body.

14. The direct methanol fuel cell system according to claim 1, the outlet stream includes unreacted fuel and/or water.

15. A method of operating a direct methanol fuel cell system having a mixing tank storing fuel supplied from a fuel-supplying unit and unreacted fuel and water discharged from a fuel cell main body, and a fuel feeder supplying mixed fuel stored in the mixing tank to the fuel cell main body, the method comprising: receiving a stop request signal for stopping the direct methanol fuel cell system; andcontrolling the fuel-supplying unit to stop operating in response to the stop request signal, and controlling the fuel feeder to operate to circulate the mixed fuel via an anode of the fuel cell main body until a fuel concentration of the mixed fuel is less than or equal to a reference concentration.

16. The method according to claim 15, wherein the mixed fuel is a methanol solution, and the reference concentration ranges from 0 to 0.3 mol.

17. The method according to claim 15, further comprising sensing the fuel concentration of the mixed fuel.

18. The method according to claim 15, further comprising operating a timer for a time taken to lower the fuel concentration of the mixed fuel to less than or equal to the reference concentration, and stopping the fuel feeder when the timer stops operating.

19. The method according to claim 18, wherein the operating the timer comprises operating the timer in response to the stop request signal.

20. The method according to claim 15, wherein the receiving the stop request signal comprises receiving a signal generated by a soft switch type stop button coupled to the direct methanol fuel cell system or an external load.

21. The method according to claim 15, further comprising controlling an electricity storage device to be charged with electricity generated in the fuel cell main body.

22. The method according to claim 15, further comprising stopping an oxidant-supplying unit feeding the fuel cell main body with an oxidant at or after a time when the fuel feeder stops operating.