Amine oxide coating compositions

Abstract

An aqueous coating composition is provided comprising carbon particles, one or more highly fluorinated polymers and one or more amine oxide surfactants, typically an amine oxide surfactant according to formula I: where n is 9 to 19. The coating composition is advantageously used in a method of making a gas diffusion layer for an electrochemical cell comprising the steps of: a) coating a electrically conductive porous substrate with the aqueous coating composition, and b) heating the electrically conductive porous substrate to a temperature sufficient to decompose the amine oxide surfactants. In another aspect, a gas diffusion layer for an electrochemical cell is provided which is advantageously free of surfactant.

We claim:  
     
         1 . An aqueous coating composition comprising carbon particles, one or more highly fluorinated polymers and one or more amine oxide surfactants.  
     
     
         2 . The composition according to  claim 1  wherein said amine oxide surfactants have a decomposition temperature of less than 200° C.  
     
     
         3 . The composition according to  claim 1  wherein said amine oxide surfactants are alkyl dimethylamine oxides according to formula II:  
       R 3 N→O  (II)  
       where each R is independently selected from alkyl groups containing 1-20 carbons which may include ether oxygens, which may be substituted with alcohol groups, and which may be additionally substituted.  
     
     
         4 . The composition according to  claim 3  wherein said amine oxide surfactants have a decomposition temperature of less than 200° C.  
     
     
         5 . The composition according to  claim 1  wherein said amine oxide surfactants are alkyl dimethylamine oxides according to formula I:  
       
         
           
           
               
               
           
         
         wherein n is 9 to 19, and which is optionally substituted.  
       
     
     
         6 . The composition according to  claim 5  wherein said amine oxide surfactants have a decomposition temperature of less than 200° C.  
     
     
         7 . The composition according to  claim 5  wherein n is 11 to 15.  
     
     
         8 . The composition according to  claim 7  comprising: 
 1-50% by weight carbon particles;  
 0.1-15% by weight highly fluorinated polymers; and  
 0.1-15% by weight amine oxide surfactant.  
 
     
     
         9 . The composition of  claim 1  wherein said highly fluorinated polymers have a sintering temperature and wherein said amine oxide surfactants have a decomposition temperature which is lower than said sintering temperature by at least 5° C.  
     
     
         10 . A method of making a gas diffusion layer for an electrochemical cell comprising the steps of: 
 a) coating a electrically conductive porous substrate with the aqueous coating composition according to  claim 1;  and    b) heating the electrically conductive porous substrate to a temperature sufficient to decompose said amine oxide surfactants.    
     
     
         11 . The method according to  claim 10  wherein said electrically conductive porous substrate comprises carbon fiber.  
     
     
         12 . The method according to  claim 10  wherein said highly fluorinated polymers have a sintering temperature and wherein said amine oxide surfactants have a decomposition temperature which is lower than said sintering temperature by at least 5° C.  
     
     
         13 . The method according to  claim 10  wherein said step of heating the electrically conductive porous substrate comprises heating the electrically conductive porous substrate to a temperature sufficient to sinter said highly fluorinated polymers.  
     
     
         14 . The method according to  claim 12  wherein said step of heating the electrically conductive porous substrate comprises heating the electrically conductive porous substrate to a temperature sufficient to sinter said highly fluorinated polymers.  
     
     
         15 . A gas diffusion layer for an electrochemical cell made according to the method of  claim 10 .  
     
     
         16 . A gas diffusion layer for an electrochemical cell according to  claim 15  which comprises essentially no surfactant.  
     
     
         17 . A membrane electrode assembly for an electrochemical cell comprising the gas diffusion layer according to  claim 15 .  
     
     
         18 . A membrane electrode assembly for an electrochemical cell comprising the gas diffusion layer according to  claim 16.