Membrane-electrode assembly for fuel cell and fuel cell system comprising same

Abstract

A membrane-electrode assembly for a fuel cell of the present invention includes an anode and a cathode facing each other, and a polymer electrolyte membrane interposed therebetween. At least one of the anode and the cathode includes a catalyst layer and an electrode substrate. The catalyst layer includes a catalyst and a porous ionomer. The polymer electrolyte membrane contacts one side of the catalyst layer and the electrode substrate contacts the other side of the catalyst layer.

1 . A membrane-electrode assembly for a fuel cell, comprising: 
 an anode and a cathode facing each other, at least one of the anode and the cathode comprising: 
 a catalyst layer comprising a catalyst and a porous ionomer layer; and  
 an electrode substrate enabling a reactant to diffuse into the catalyst layer; and  
   a polymer electrolyte membrane interposed between the anode and the cathode.    
     
     
         2 . The membrane-electrode assembly of  claim 1 , wherein the porous ionomer layer has a porosity ranging from about 40 volume % to about 80 volume %.  
     
     
         3 . The membrane-electrode assembly of  claim 1 , wherein the porous ionomer layer has a pore size ranging from about 10 nm to about 1,000 nm.  
     
     
         4 . The membrane-electrode assembly of  claim 1 , wherein the porous ionomer layer is present on a surface of the catalyst.  
     
     
         5 . The membrane-electrode assembly of  claim 1 , wherein the catalyst comprises a metal catalyst supported on a carrier.  
     
     
         6 . The membrane-electrode assembly of  claim 1 , wherein the electrode substrate comprises a conductive substrate selected from the group consisting of a water-repellent treated carbon paper and carbon cloth.  
     
     
         7 . A fuel cell system, comprising: 
 at least one electricity generating element for generating electricity through oxidation of fuel and reduction of an oxidant, comprising: 
 a membrane-electrode assembly comprising: 
 an anode and a cathode facing each other, at least one of the anode and the cathode comprising: 
 a catalyst layer comprising a catalyst and a porous ionomer layer; and  
 an electrode substrate enabling the fuel or the oxidant to diffuse into the catalyst layer; and  
 
 a polymer electrolyte membrane interposed between the anode and the cathode; and  
 
 separators positioned at both sides of the membrane-electrode assembly;  
   a fuel supplier providing the fuel to the electricity generating element; and    an oxidant supplier supplying the oxidant to the electricity generating element.    
     
     
         8 . The fuel cell system of  claim 7 , wherein the porous ionomer layer has a porosity ranging from about 40 volume % to about 80 volume %.  
     
     
         9 . The fuel cell system of  claim 7 , wherein the porous ionomer layer has a pore size ranging from about 10 nm to about 1,000 nm.  
     
     
         10 . The fuel cell system of  claim 7 , wherein the porous ionomer layer is present on a surface of the catalyst.  
     
     
         11 . A method for manufacturing a membrane-electrode assembly, comprising: 
 preparing an anode and a cathode, at least one of the anode and the cathode comprising: 
 a catalyst layer comprising a catalyst and a porous ionomer layer; and  
 an electrode substrate enabling a reactant to diffuse into the catalyst layer; and  
   preparing a polymer electrolyte membrane interposed between the anode and the cathode.    
     
     
         12 . The method of  claim 11 , wherein the catalyst layer is formed by a process comprising: 
 coating a composition including the catalyst, an ionomer and a plasticizer onto the electrode substrate; and    extracting the plasticizer.    
     
     
         13 . The method of  claim 12 , wherein the plasticizer is at least one polymer selected from the group consisting of a C1 to C10 polyalkyleneglycol; a C1 to C10 polyalkyleneoxide; a C1 to C10 poly(alkyl)acrylic acid; an aromatic or fluorine polymer having a sulfonic acid group; and a cellulose-based polymer.  
     
     
         14 . The method of  claim 12 , wherein the plasticizer is extracted by dipping the coated composition onto the electrode substrate in an extraction solvent.  
     
     
         15 . The method of  claim 14 , wherein the extraction solvent is selected from the group consisting of an alcohol-based solvent, an ether-based solvent, tetrahydrofuran, and a mixture thereof.  
     
     
         16 . The method of  claim 12 , wherein the weight ratio of the plasticizer to the ionomer ranges from about 20:80 to 70:30.  
     
     
         17 . The method of  claim 11 , wherein the catalyst layer is formed by a process comprising: 
 coating a composition including the catalyst, an ionomer and fumed silica onto the electrode substrate; and    firing the coated composition.    
     
     
         18 . The method of  claim 17 , wherein the weight ratio of the fumed silica to the ionomer ranges from about 10:90 to 50:50.  
     
     
         19 . An membrane-electrode assembly manufactured according to  claim 12 .  
     
     
         20 . The fuel cell system comprising the membrane-electrode assembly of  claim 19 .  
     
     
         21 . A membrane-electrode assembly for a fuel cell, comprising: 
 an anode and a cathode facing each other, at least one of the anode and the cathode formed by coating a composition including a catalyst, an ionomer and one of a plasticizer or fumed silica onto an electrode substrate, and extracting the plasticizer when the plasticizer is used or firing the coated composition when the fumed silica is used; and    a polymer electrolyte membrane interposed between the anode and the cathode.    
     
     
         22 . The membrane-electrode assembly of  claim 21 , wherein the plasticizer is at least one polymer selected from the group consisting of a C1 to C10 polyalkyleneglycol; a C1 to C10 polyalkyleneoxide; a C1 to C10 poly(alkyl)acrylic acid; an aromatic or fluorine polymer having a sulfonic acid group; and a cellulose-based polymer.  
     
     
         23 . The membrane-electrode assembly of  claim 21 , wherein the plasticizer is extracted by dipping the coated composition onto the electrode substrate in an extraction solvent.  
     
     
         24 . The membrane-electrode assembly of  claim 21 , wherein the weight ratio of the plasticizer to the ionomer ranges from about 20:80 to 70:30.  
     
     
         25 . The membrane-electrode assembly of  claim 21 , wherein the plasticizer has a number average molecular weight ranging from 200 to 50,000.  
     
     
         26 . The membrane-electrode assembly of  claim 21 , wherein the weight ratio of the fumed silica to the ionomer ranges from about 10:90 to 50:50.  
     
     
         27 . The membrane-electrode assembly of  claim 21 , wherein the fumed silica has a specific surface area ranging from 100 to 1,200 m 2 /g and a particle size of 10 nm to 1,000 nm.