This invention relates to managing gases within the fuel cell, which need to be released to the atmosphere while retaining the water within the fuel cell.
A hydrogen fuel cell uses a cathode and anode that receive an oxidant such as air and a fuel such as hydrogen, respectively, and generate an electrochemical reaction that produces electricity, as is well known. The reactant gases are fed to the membrane electrode assembly via reactant flow fields. The fuel cell typically includes numerous cells that form a stack. A means to cool the fuel cell is also provided, typically coolant flow fields interspersed among the cells forming the stack. The coolant may be water in some fuel cell systems. The cells typically include separator plates to prevent reactant gases from commingling. The separator plates may be solid or porous. Porous separator plates, referred to as water transport plates, permit through-plane movement of water but have a pore size and structure so as to restrict through-plane gas transfer. The through-plane movement of water permits membrane hydration and enables removal of product water on the cathode side, which is generated from the electrochemical reaction.
The volume of water within the stack must be managed to maintain a desired amount of water, for example, for membrane hydration and cooling. In one type of cooling system, water is evaporated and then condensed to return liquid water to the fuel cell. Evaporatively cooled fuel cells have far less water than similar fuel cells using other types of cooling strategies. Gases may become entrained in the coolant flow field passages due to leakage from ambient surroundings, or reactant crossover through the seals or the pores of the water transport plates, on the order of one cubic centimeter per minute per cell in the stack in one example. Entrained gases inhibit the replenishment of liquid water to the coolant flow field, which can cause operational problems with the fuel cell. The gases must be expelled from the fuel cell to maintain desired operation of the fuel cell.
What is needed is a simple method and apparatus of releasing gases from the fuel cell without losing water.
A fuel cell includes a water transport plate providing a water flow field. The water flow field includes water having gas. A vent is in fluid communication with the water flow field. The vent includes a membrane that obstructs flow of water past the membrane while permitting the flow of gas past the membrane. The membrane can include a pore size between approximately 0.1μ to 10.0μ, which enables gases to pass through the pores while blocking water. In one example, the membrane can be hydrophobic, for example, Teflon, to prevent the passage of water through the membrane. A fluid can also be arranged on the membrane to act as a check valve. In another example, the fluid is hydrophilic, attracting any water away from the membrane.
Accordingly, gases can be released from the fuel cell without undesirably reducing the volume of water within the fuel cell.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
A water transport plate 44 provides a water flow field 24 (
A cooling loop 28 receives evaporated water from the cathode exhaust that is produced by the heat generated from the cells. The water vapor is condensed with a condenser 30 and fan 32, or similar arrangement. Liquid water 36 is collected in a separator 34 and gases are vented through an exit 40 in the separator 34. A return line 38 supplies the liquid water 36 back to the fuel cell 10.
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Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US06/49645 | 12/29/2006 | WO | 00 | 6/2/2009 |