Catalyst for fuel cell, membrane-electrode assembly, method of manufacturing the assembly, and fuel cell using the assembly

Abstract

A membrane-electrode assembly comprising a cathode catalyst layer for reducing an oxidant gas, a polymer electrolyte membrane and an anode catalyst layer, the polymer electrolyte membrane being sandwiched between the catalyst layers, wherein the cathode catalyst layer exhibits super-water-repellency. The disclosure is also concerned with a method of manufacturing the membrane-electrode assembly and a fuel cell using the membrane-electrode assembly.

1 . A membrane-electrode assembly comprising a cathode catalyst layer for reducing an oxidant gas, a polymer electrolyte membrane and an anode catalyst layer, the polymer electrolyte membrane being sandwiched between the catalyst layers, wherein the cathode catalyst layer exhibits super-water-repellency.  
     
     
         2 . The membrane-electrode assembly according to  claim 1 , wherein the super-water-repellency is imparted by at least one member selected from the group consisting of silicon compounds having perfluoropolyether chains, silicon compound having perfluoroalkyl chains and silicon compounds having fluoroalkyl chains.  
     
     
         3 . The membrane-electrode assembly according to  claim 2 , wherein the silicon compounds are present in the vicinity of the surface of the catalyst layer.  
     
     
         4 . The membrane-electrode assembly according to  claim 2 , wherein at least one of the silicon compounds represented by the (1) following formula is contained in the cathode catalyst layer:  
         [F{CF(CF 3 )—CF 2 O} n —CF(CF 3 )]—X—Si(OR 1 ) 3 ,  {F(CF 2 CF 2 CF 2 O) n }—X—Si(OR 2 ) 3 ,  {H(CF 2 ) n }—Y—Si(OR 3 ) 3 , and  {F(CF 2 ) n }—Y—Si(OR 4 ) 3   formula (1)  wherein X is a connecting group between a perfluoropolyether chain and an alkoxysilane redidue, Y is a connecting group between a perfluoroalkyl chain and an alkoxysilane residue, and R 1 , R 2 , R 3  and R 4  are alkyl groups.    
     
     
         5 . A method of manufacturing an electrode-membrane assembly, which comprises irradiating oxygen plasma with the surface of a cathode catalyst layer supported on carbon, contacting the treated surface of the catalyst layer with at least one fluorine-containing compound represented by the following formula (1), and heating the treated catalyst layer:  
         [F{CF(CF 3 )—CF 2 O} n —CF(CF 3 )]—X—Si(OR1) 3 ,  {F(CF 2 CF 2 CF 2 O) n }—X—Si(OR 2 ) 3 ,  {H(CF 2 ) n }—Y—Si(OR 3 ) 3 , and  {F(CF 2 ) n }—Y—Si(OR 4 ) 3   formula (1)  wherein X is a connecting group between a perfluoropolyether chain and an alkoxysilane redidue, Y is a connecting group between a perfluoroalkyl chain and an alkoxysilane residue, and R 1 , R 2 , R 3  and R 4  are alkyl groups.    
     
     
         6 . A fuel cell comprising at least one unit cell the electrode-membrane assembly defined in  claim 1 , a pair of gas diffusion layers each in contact with the cathode catalyst layer and the anode catalyst layer, and a pair of separator each in contact with the gas diffusion layers.  
     
     
         7 . A catalyst for a fuel cell treated with at least one member selected from the group consisting of silicon compounds having perfluoropolyether chains, silicon compound having perfluoroalkyl chains and silicon compounds having fluoroalkyl chains.  
     
     
         8 . The catalyst for a fuel cell according to  claim 7 , wherein the silicon compounds are one represented by the following formula (1):  
         [F{CF(CF 3 )—CF 2 O} n —CF(CF 3 )]—X—Si(OR 1 ) 3 ,  {F(CF 2 CF 2 CF 2 O) n }—X—Si(OR 2 ) 3 ,  {H(CF 2 ) n }—Y—Si(OR 3 ) 3 , and  {F(CF 2 ) n }—Y—Si(OR 4 ) 3   formula (1)  wherein X is a connecting group between a perfluoropolyether chain and an alkoxysilane redidue, Y is a connecting group between a perfluoroalkyl chain and an alkoxysilane residue, and R 1 , R 2 , R 3  and R 4  are alkyl groups.    
     
     
         9 . A method of manufacturing a catalyst for a fuel cell, which comprises: irradiating a catalyst supported on carbon with oxygen plasma, contacting the treated catalyst with a silicon compound represented by the following formula (1), and heating the treated catalyst:  
         [F{CF(CF 3 )—CF 2 O} n —CF(CF 3 )]—X—Si(OR 1 ) 3 ,  {F(CF 2 CF 2 CF 2 O) n }—X—Si(OR 2 ) 3 ,  {H(CF 2 ) n }—Y—Si(OR 3 ) 3 , and  {F(CF 2 ) n }—Y—Si(OR 4 ) 3   formula (1)  wherein X is a connecting group between a perfluoropolyether chain and an alkoxysilane redidue, Y is a connecting group between a perfluoroalkyl chain and an alkoxysilane residue, and R 1 , R 2 , R 3  and R 4  are alkyl groups.    
     
     
         10 . A fuel cell according to  claim 6 , wherein the fuel is methanol aqueous solution.  
     
     
         11 . The fuel cell according to  claim 6 , wherein the fuel is hydrogen, which is supplied from a hydrogen storage-supply system that performs hydrogenation reaction by a hydrogen storage of an aromatic compound and de-hydrogenation reaction of a hydrogen storage material of hydrogenated derivatives of the aromatic compound.