Fuel cell with randomly-dispersed carbon fibers in a backing layer

Abstract

A fuel cell ( 40 ) includes first and second catalysts ( 12 ′), ( 14 ′) secured to opposed surfaces of an electrolyte ( 16 ′); a first flow field ( 26 ′) secured in fluid communication with the first catalyst ( 12 ′) defining a plurality of flow channels ( 30 A′, 30 B′, 30 C′, 30 D′) between a plurality of ribs ( 32 A′, 32 B′, 32 C′, 32 D′, 32 E′) of the first flow field ( 26 ′); and a backing layer ( 42 ) secured between the first flow field ( 26 ′) and the first catalyst ( 12 ′). The backing layer ( 42 ) includes a carbon black, a hydrophobic polymer, and randomly-dispersed carbon fibers ( 44 ). The carbon fibers ( 44 ) are at least twice as long as a width (46) of the flow channels ( 30 A′, 30 B′, 30 C′, 30 D′) defined in the adjacent first flow field ( 26 ′). The backing layer ( 42 ) replaces a known substrate ( 22 ) and diffusion layer ( 18 ).

1 . A fuel cell ( 40 ) for producing electricity from reducing fluid and oxygen containing oxidant reactant streams, the fuel cell ( 40 ) comprising: 
 a. a first catalyst ( 12 ′) and a second catalyst ( 14 ′) secured to opposed surfaces of an electrolyte ( 16 ′);    b. a first flow field ( 26 ′) secured in fluid communication with the first catalyst ( 12 ′), the first flow field ( 26 ′) defining a plurality of flow channels ( 30 A′,  30 B′,  30 C′,  30 D′) between a plurality of ribs ( 32 A′,  32 B′,  32 C′,  32 D′,  32 E′) of the first flow field ( 26 ′);    c. a backing layer ( 42 ) secured between and in fluid communication with the first flow field ( 26 ′) and the first catalyst ( 12 ′); and,    d. wherein, the backing layer ( 42 ) includes: 
 i. between 5 wt % and 25 wt % carbon black;  
 ii. between 50 wt % and 90 wt % carbon fibers ( 44 ), where the carbon fibers ( 44 ) have a length that is at least twice as long as a width ( 46 ) of a widest flow channel ( 30 ′D), wherein the width ( 46 ) of the widest flow channel ( 30 ′D) is a shortest distance between flow field ribs ( 32 D′,  32 E′) defining the widest flow channel ( 30 D′) of the first flow field ( 26 ′);  
 iii. between 5 wt % and 25 wt % of a hydrophobic polymer; and,  
 iv. the carbon fibers ( 44 ) being randomly dispersed with the carbon black and hydrophobic polymer so that the resulting backing layer ( 42 ) has a thickness between the first catalyst ( 12 ′) and the first flow field ( 26 ′) of between about 25 and 250 microns, and a compressive strength greater than 5 Kgf/cm 2 .  
   
   
   
       2 . The fuel cell ( 40 ) of  claim 1 , wherein the first catalyst ( 12 ′) is an anode catalyst and the second catalyst ( 14 ′) is a cathode catalyst secured to a cathode diffusion layer ( 20 ′) that is secured to a cathode substrate ( 24 ′).  
   
   
       3 . The fuel cell ( 40 ) of  claim 1 , further comprising a second backing layer secured between the second catalyst ( 14 ′) and second flow field ( 28 ′).  
   
   
       4 . The fuel cell ( 40 ) of  claim 1  wherein the first catalyst ( 12 ′) is a cathode catalyst and the second catalyst ( 14 ′) is an anode catalyst secured to an anode diffusion layer ( 20 ′) that is secured to an anode substrate ( 24 ′).  
   
   
       5 . The fuel cell ( 40 ) of  claim 1 , wherein the electrolyte ( 16 ′) is a proton exchange membrane.  
   
   
       6 . A method of manufacturing a backing layer ( 42 ) for use adjacent a catalyst ( 12 ′,  14 ′) in a fuel cell ( 40 ), the method comprising the steps of: 
 a. randomly dispersing a carbon black, carbon fibers ( 44 ), and a hydrophobic polymer in an aqueous suspension, wherein the carbon fibers ( 44 ) have a length that is at least twice as long as a width ( 46 ) of a widest flow channel ( 30 ′D) of a flow field ( 26 ′) secured in fluid communication with the catalysts ( 12 ′,  14 ′);    b. removing the water from the aqueous suspension;    c. thermally processing the carbon black, carbon fibers ( 44 ), and hydrophobic polymer of the layer ( 42 ) to melt the hydrophobic polymer.    
   
   
       7 . A method of manufacturing a fuel cell ( 40 ) comprising the steps of: 
 a. securing a cathode diffusion layer ( 20 ′) to a cathode substrate ( 24 ′);    b. securing an anode catalyst ( 12 ′) and a cathode catalyst ( 14 ′) to opposed surfaces of an electrolyte ( 16 ′) to form a membrane electrode assembly;    c. bonding the cathode catalyst ( 14 ′) to the cathode diffusion layer ( 20 ′); and,    d. bonding the backing layer ( 42 ) of  claim 1  to the anode catalyst ( 12 ′).