Evaporative Cooling of Fuel Cells Employing Antifreeze Solution

Abstract

A fuel cell power plant ( 19 ) has a stack of fuel cells ( 20 ) cooled by a mixture of water with a non-volatile, miscible fluid that sufficiently depresses the freezing point, such as polyethylene glycol (PEG). The water and fluid are mixed in a reservoir ( 21 ), a small pump ( 22, 60 ) flows the mixture through coolant channels ( 28 ) in or adjacent water transport plates ( 29 ); heat of the catalytic reaction warms the water transport plates causing water to evaporate therefrom thereby cooling the stack. The PEG is non-volatile at stack operating temperature and does not evaporate; concentrated PEG is returned ( 33 ) to the reservoir ( 21 ). Water in the process air flow channels ( 41 ), including evaporated process water, is recovered in a condensation-rate-controlled ( 53, 54 )) condenser ( 46 ) in communication ( 48 ) with the reservoir ( 21 ) for remixture with the concentrated PEG solution. Hydrophobic gas diffusion layers ( 72 ) shield the proton exchange membrane ( 70 ) from the PEG.

1 . A fuel cell power plant ( 19 ) comprising:
 a stack ( 20 ) of fuel cells ( 63 ), each fuel cell including water transport plates ( 29 ) with coolant channels ( 28 ) formed therein or adjacent thereto and with fuel reactant gas flow field channels ( 65 ) and oxidant reactant gas flow field channels ( 66 ) having inlets and outlets, at least one of said plates being porous and hydrophilic;   a source ( 42 ) of oxidant reactant gas in fluid communication with inlets of said oxidant reactant gas flow field channels;   a source ( 55 ) of fuel reactant gas in fluid communication with inlets of said fuel reactant gas flow field channels;   a coolant reservoir ( 21 ), each of said fuel cell coolant channels being in fluid communication with said coolant reservoir;   a pump ( 22 ,  60 ) for circulating coolant from said reservoir, through said fuel cell coolant channels and back to said reservoir;   characterized by:   said coolant reservoir containing a coolant mixture  23  of water with a miscible, freeze depressing substance; and   a condenser ( 46 ), connected to the outlet of at least one of said oxidant reactant gas flow field channels of said fuel cells, condensate of said condenser in fluid communication ( 48 ) with said reservoir, said coolant mixture migrating from said coolant channels into said at least one hydrophilic, porous water transport plate of each fuel cell and at least some water within said coolant mixture along with some process water evaporating into at least said reactant gas flow field channels of said at least one porous and hydrophilic plates of each fuel cell to cool said fuel cells, at least some of the water vapor in at least one of said reactant gas flow field channels being condensed in said condenser and returned to said reservoir where it mixes with coolant in said reservoir.   
   
   
       2 . A power plant ( 19 ) according to  claim 1  wherein:
 the reactant gas flow field is a fuel channel.   
   
   
       3 . A power plant ( 19 ) according to  claim 1  further characterized by:
 each fuel cell ( 63 ) including membrane electrode assembly (MEA) ( 70 ) having a membrane with catalyst on both surfaces thereof, said MEA configured to provide a wet-proofed barrier between at least one surface of said MEA and said coolant channels.   
   
   
       4 . A power plant ( 19 ) according to  claim 3  wherein said wet-proofed barrier comprises:
 at least one wet-proofed gas diffusion layer ( 72 ) adjacent said MEA ( 70 ) in each of said fuel cells.   
   
   
       5 . A power plant ( 19 ) according to  claim 3  wherein said wet-proofed barrier comprises:
 at least one bilayer ( 70 ) adjacent said MEA in each of said fuel cells.   
   
   
       6 . A power plant ( 19 ) according to  claim 3  wherein said wet-proofed barrier comprises:
 a solid water transport plate ( 29 ) on at least one side of said MEA ( 70 ).   
   
   
       7 . A power plant ( 19 ) according to  claim 1  further characterized by:
 said pump ( 22 ) being disposed at an inlet of said reservoir ( 21 ) receiving ( 33 ) circulating coolant from said coolant channels ( 28 ).   
   
   
       8 . A power plant ( 19 ) according to  claim 1  further characterized by:
 said pump ( 60 ) being disposed in a conduit ( 33 ) interconnecting said coolant channels ( 28 ) with an inlet ( 37 ) of said reservoir ( 21 ).   
   
   
       9 . A power plant ( 19 ) according to  claim 1  further comprising:
 a condenser controller ( 53 ,  54 ) for controlling the rate of condensation of water vapor in said condenser ( 46 ).   
   
   
       10 . A power plant ( 19 ) according to  claim 9  wherein:
 said condenser ( 46 ) is cooled by a stream of air ( 52 ) and said condenser controller is a controller ( 53 ) that varies the speed of an air fan ( 54 ).   
   
   
       11 . A power plant ( 19 ) according to  claim 9  wherein:
 said condenser ( 46 ) is cooled by a controlled flow of freeze-proof coolant through flow passages in said condenser.