Method for producing alloy catalyst for fuel cells using silica coating

Abstract

Disclosed is a method for producing an alloy catalyst supported on carbon, including the steps of: dispersing alloy particles into a mixed solution of water with alcohol, introducing a silica precursor thereto, and carrying out sol-gel reaction in the presence of a basic catalyst to obtain silica-coated alloy particles; supporting the silica-coated alloy particles onto a carbon carrier to obtain silica-coated alloy particles supported on carbon; heat treating the silica-coated alloy particles supported on carbon to increase an alloying degree; and removing silica coating by using inorganic base solution and a surfactant. The method for producing an alloy catalyst provides a high-quality and high-durability alloy catalyst by increasing the alloying degree of a catalyst through a heat treatment step, while forming a silica coating layer effectively on small alloy particles having a size of several nanometers to inhibit growth of the size of alloy particles. In addition, the catalyst may be used advantageously as an electrode for fuel cells.

1 . A method for producing an alloy catalyst supported on carbon, comprising the steps of:
 (1) dispersing alloy particles into a mixed solution of water with alcohol, introducing a silica precursor thereto, and carrying out sol-gel reaction in the presence of a basic catalyst to obtain silica-coated alloy particles;   (2) supporting the silica-coated alloy particles onto a carbon carrier to obtain silica-coated alloy particles supported on carbon;   (3) heat treating the silica-coated alloy particles supported on carbon to increase an alloying degree; and   (4) removing silica coating by using aqueous hydrofluoric acid (HF) solution or inorganic base solution and a surfactant.   
     
     
         2 . The method for producing an alloy catalyst supported on carbon according to  claim 1 , wherein the alloy particle comprises an alloy of at least two metals selected from platinum, palladium, gold, iridium, ruthenium, vanadium, chrome, manganese, iron, cobalt, nickel, copper, zinc and titanium. 
     
     
         3 . The method for producing an alloy catalyst supported on carbon according to  claim 1 , wherein the silica precursor is selected from TEOS (tetraethyl orthosilicate), TMOS (tetramethyl orthosilicate), TBOS (tetrabutyl orthosilicate) and a mixture thereof. 
     
     
         4 . The method for producing an alloy catalyst supported on carbon according to  claim 1 , wherein the alloy particles have a size of 2-10 nm and the silica coating layer has a thickness of 3-50 nm. 
     
     
         5 . The method for producing an alloy catalyst supported on carbon according to  claim 1 , wherein the basic catalyst in the sol-gel reaction is selected from aqueous ammonia, sodium hydroxide and potassium hydroxide. 
     
     
         6 . The method for producing an alloy catalyst supported on carbon according to  claim 1 , the sol-gel reaction is carried out at 10-50° C. for 3-48 hours under agitation. 
     
     
         7 . The method for producing an alloy catalyst supported on carbon according to  claim 1 , wherein the carbon carrier is at least one selected from carbon black, carbon nanotubes, carbon nanofibers, carbon nanocoils and carbon nanocages. 
     
     
         8 . The method for producing an alloy catalyst supported on carbon according to  claim 1 , wherein the heat treatment in step (3) is carried out under inert gas atmosphere of argon or nitrogen, or mixed gas atmosphere of argon or nitrogen with hydrogen at 400-1000° C. for 2-4 hours to increase an alloying degree. 
     
     
         9 . The method for producing an alloy catalyst supported on carbon according to  claim 1 , wherein the aqueous inorganic base solution is aqueous sodium hydroxide (NaOH) solution or aqueous potassium hydroxide (KOH) solution. 
     
     
         10 . The method for producing an alloy catalyst supported on carbon according to  claim 1 , wherein the surfactant is a non-ionic surfactant selected from polyoxyethylene glycol sorbitan fatty acid esters, sorbitan fatty acid esters, aliphatic alcohols and polyoxyethylene alkyl ethers. 
     
     
         11 . The method for producing an alloy catalyst supported on carbon according to  claim 1 , which comprises, instead of step (2), supporting the alloy particles from which the silica coating is removed onto a carbon carrier after step (4). 
     
     
         12 . An alloy catalyst supported on carbon, obtained by a method comprising the steps of:
 (1) dispersing alloy particles into a mixed solution of water with alcohol, introducing a silica precursor thereto, and carrying out sol-gel reaction in the presence of a basic catalyst to obtain silica-coated alloy particles;   (2) supporting the silica-coated alloy particles onto a carbon carrier to obtain silica-coated alloy particles supported on carbon;   (3) heat treating the silica-coated alloy particles supported on carbon to increase an alloying degree; and   (4) removing silica coating by using aqueous hydrofluoric acid (HF) solution or inorganic base solution and a surfactant.   
     
     
         13 . The alloy catalyst supported on carbon according to  claim 12 , which has a particle size of 2-10 nm. 
     
     
         14 . An electrode for fuel cells, comprising an alloy catalyst supported on carbon, said alloy catalyst obtained by a method comprising the steps of:
 (1) dispersing alloy particles into a mixed solution of water with alcohol, introducing a silica precursor thereto, and carrying out sol-gel reaction in the presence of a basic catalyst to obtain silica-coated alloy particles;   (2) supporting the silica-coated alloy particles onto a carbon carrier to obtain silica-coated alloy particles supported on carbon;   (3) heat treating the silica-coated alloy particles supported on carbon to increase an alloying degree; and   (4) removing silica coating by using aqueous hydrofluoric acid (HF) solution or inorganic base solution and a surfactant.   
     
     
         15 . A fuel cell comprising an electrode for fuel cells comprising an alloy catalyst supported on carbon, said alloy catalyst obtained by a method comprising the steps of:
 (1) dispersing alloy particles into a mixed solution of water with alcohol, introducing a silica precursor thereto, and carrying out sol-gel reaction in the presence of a basic catalyst to obtain silica-coated alloy particles;   (2) supporting the silica-coated alloy particles onto a carbon carrier to obtain silica-coated alloy particles supported on carbon;   (3) heat treating the silica-coated alloy particles supported on carbon to increase an alloying degree; and   (4) removing silica coating by using aqueous hydrofluoric acid (HF) solution or inorganic base solution and a surfactant.