Electrode for solid polymer type fuel cell

Abstract

An electrode for solid polymer electrolyte fuel cell comprising a catalyst layer comprising at least electrocatalyst particles ( 3 ), a supporting substance therefor ( 4 ) and proton-conductive polymers ( 1 ) and ( 2 ), wherein the proton-conductive polymer ( 1 ) is present in a primary presence state in which the proton-conductive polymer ( 1 ) covers the electrocatalyst particles ( 3 ) or the supporting substance therefor ( 4 ), or both at least partly; the proton-conductive polymer ( 2 ) is present in a secondary presence state in which the proton-conductive polymer ( 2 ) binds the electrocatalyst particles ( 3 ) to one another or binds particles of the supporting substance ( 4 ) to one another or to the solid polymer electrolyte membrane; and the melt viscosity of the proton-conductive polymer ( 1 ) is lower than the melt viscosity of the proton-conductive polymer ( 2 ).

1 . An electrode for solid polymer electrolyte fuel cell comprising a catalyst layer comprising at least electrocatalyst particles ( 3 ), a supporting substance therefor ( 4 ) and proton-conductive polymers ( 1 ) and ( 2 ), wherein the proton-conductive polymer ( 1 ) is present in a primary presence state in which the proton-conductive polymer ( 1 ) covers the electrocatalyst particles ( 3 ) or the catalyst-supporting substance therefor ( 4 ), or both at least partly; the proton-conductive polymer ( 2 ) is present in a secondary presence state in which a large portion of the proton-conductive polymer ( 2 ) binds particles of the catalyst-supporting substance ( 4 ) containing the electrocatalyst particles ( 3 ) to one another or to a solid polymer electrolyte membrane; and the melt viscosity of the proton-conductive polymer ( 1 ) is lower than the melt viscosity of the proton-conductive polymer ( 2 ).  
     
     
         2 . An electrode for fuel cell according to  claim 1 , wherein the MI (melt index measured at 270° C., according to ASTM standard D1238) value of a precursor of the proton-conductive polymer ( 1 ) is 10 or more and is higher than the MI (melt index measured at 270° C., according to ASTM standard D1238) value of a precursor of the proton-conductive polymer ( 2 ), and the MI value of the precursor of the proton-conductive polymer ( 2 ) ranges from 0.1 to 100.  
     
     
         3 . An electrode for fuel cell according to  claim 1 , wherein the MI (melt index measured at 150° C., according to ASTM standard D1238) value of a precursor of the proton-conductive polymer ( 1 ) is 10 or more and is higher than the MI (melt index measured at 270° C., according to ASTM standard D1238) value of a precursor of the proton-conductive polymer ( 2 ), and the MI value of the precursor of the proton-conductive polymer ( 2 ) to be allowed to assume the secondary presence state ranges from 0.1 to 100.  
     
     
         4 . An electrode for fuel cell according to  claim 1 , wherein the equivalent weight value and melt viscosity of the proton-conductive polymer ( 1 ) are lower than those of the proton-conductive polymer ( 2 ).  
     
     
         5 . An electrode for fuel cell according to  claim 1 , wherein the EW value of the proton-conductive polymer ( 1 ) ranges from 500 to 1200, and the EW value of the proton-conductive polymer ( 2 ) ranges from 850 to 1500.  
     
     
         6 . An electrode for fuel cell according to  claim 1 , wherein the proton-conductive polymers ( 1 ) and ( 2 ) are perfluorocarbon copolymers having sulfonic acid groups.  
     
     
         7 . An electrode for fuel cell according to  claim 1 , wherein the proton-conductive polymer ( 1 ) is insoluble or slightly soluble in water or methanol.  
     
     
         8 . An electrode for fuel cell according to  claim 1 , wherein the amount of the proton-conductive polymer ( 1 ) adhered is smaller than the amount of the proton-conductive polymer ( 2 ) adhered.  
     
     
         9 . A process for producing an electrode for solid polymer electrolyte fuel cell comprising forming the electrode by fixing a mixture of solutions or dispersions of proton-conductive polymers, respectively, electrocatalyst particles and a catalyst-supporting substance therefor, which comprises a step of mixing a solution of the proton-conductive polymer ( 1 ) in water or a solvent, a dispersion of the proton-conductive polymer ( 2 ) dispersed in the form of micelles in water or a solvent, the electrocatalyst particles ( 3 ) and the catalyst-supporting substance therefor ( 4 ).  
     
     
         10 . A process for producing an electrode for solid polymer electrolyte fuel cell comprising forming the electrode by fixing a mixture of dispersions of proton-conductive polymers, electrocatalyst particles and a catalyst-supporting substance therefor, which comprises a step of mixing a dispersion of the proton-conductive polymer ( 1 ) dispersed in water or a solvent so as to have a size of dispersed particles which is smaller than that of the proton-conductive polymer ( 2 ), a dispersion of the proton-conductive polymer ( 2 ), and at least the electrocatalyst particles ( 3 ) and the catalyst-supporting substance therefor ( 4 ).  
     
     
         11 . A process for producing an electrode for solid polymer electrolyte fuel cell comprising forming the electrode by fixing a mixture of solutions or dispersions of proton-conductive polymers, electrocatalyst particles and a catalyst-supporting substance therefor, which comprises (a) a step of mixing a solution or dispersion in water or a solvent of the proton-conductive polymer ( 1 ) which has an MI value higher than that of the proton-conductive polymer ( 2 ) and a precursor of which has an MI (melt index measured at 270° C., according to ASTM standard D1238) value of 10 or more, the electrocatalyst particles ( 3 ) and the catalyst-supporting substance therefor ( 4 ), to produce a catalyst at least partly covered with the proton-conductive polymer ( 1 ), and (b) a step of mixing the catalyst obtained in the step (a) with a dispersion in water or a solvent of the proton-conductive polymer ( 2 ) a precursor of which has an MI (melt index measured at 270° C., according to ASTM standard D1238) value in a range of 0.1 to 100.  
     
     
         12 . A process for producing an electrode for solid polymer electrolyte fuel cell according to  claim 11 , wherein the MI (melt index measured at 270° C., according to ASTM standard D1238) value of the precursor of the proton-conductive polymer ( 1 ) is more than 100.  
     
     
         13 . A process for producing an electrode for solid polymer electrolyte fuel cell comprising forming the electrode by fixing a mixture of solutions or dispersions of proton-conductive polymers, electrocatalyst particles and a catalyst-supporting substance therefor, which comprises the steps of mixing a dispersion of the proton-conductive polymer ( 1 ) dispersed in water or a solvent so as to have a size of dispersed particles which is smaller than that of the proton-conductive polymer ( 2 ), and at least the electrocatalyst particles ( 3 ) and the catalyst-supporting substance therefor ( 4 ), and then mixing a dispersion of the proton-conductive polymer ( 2 ) therewith.  
     
     
         14 . A process for producing an electrode for solid polymer electrolyte fuel cell according to any one of  claims 9  to  13 , characterized in that the proton-conductive polymers ( 1 ) and ( 2 ) are perfluorocarbon copolymers having sulfonic acid groups.  
     
     
         15 . A process for producing an electrode for solid polymer electrolyte fuel cell comprising forming the electrode by fixing a mixture of solutions or dispersions of proton-conductive polymers, electrocatalyst particles and a catalyst-supporting substance therefor, which comprises (a) a step of mixing a solution or dispersion of the proton-conductive polymer ( 1 ) in water or a solvent, the electrocatalyst particles ( 3 ) and the catalyst-supporting substance therefor ( 4 ), 
 (b) a step of making the proton-conductive polymer ( 1 ) on the catalyst obtained in the step (a) insoluble or slightly soluble, and    (c) a step of mixing a dispersion of a proton-conductive polymer ( 2 ) with the catalyst obtained in the step (b).