Novel catalyst for oxygen reduction reaction in fuel cells

Abstract

A method for making a carbon-metal-nitrogen oxygen reducing cathode catalyst, the method comprising mixing a carbon source with a transition metal precursor to form a metal precursor loaded carbon substrate; adding a nitrogen precursor compound to the metal precursor loaded carbon substrate to form a carbon-metal-nitrogen precursor; and pyrolyzing the carbon-metal-nitrogen precursor in a closed vessel, thereby forming an oxygen reducing cathode catalyst. The carbon-metal-nitrogen catalyst requires no precious metal such as Pt, and also provides benefits such as controlled deposition of catalytically active nitrogenous compounds that can increase the catalytic activity of the catalyst when compared to gaseous deposition of nitrogen to the surface of the carbon support.

1 . A method for making an oxygen reducing cathode catalyst, the method comprising:
 (a) mixing a carbon source with a transition metal precursor to form a metal precursor loaded carbon substrate, wherein the substrate is substantially free of precious metals;   (b) adding a nitrogen precursor compound to the metal precursor loaded carbon substrate to form a carbon-metal-nitrogen precursor; and   (c) pyrolyzing the carbon-metal-nitrogen precursor at an elevated pressure ranging from about 2 bar to about 100 bar, thereby forming the oxygen reducing cathode catalyst.   
     
     
         2 . The method of  claim 1 , wherein the carbon source comprises one or more of Norit® SX Ultra, Ketjenblack®, pyrolyzed perylene tetracarboxylic anhydride (PTCDA), polyacrylonitrile (PAN), Black Pearls®, Printex® XE2, pyrrole black, graphitic powder, acetylene black, Vulcan® XC72, oxidized carbon supports, and metal carbides. 
     
     
         3 . The method of  claim 1 , wherein mixing the carbon source with a transition metal precursor further comprises stirring the carbon source with the transition metal precursor in a solvent for up to 12 hours and evaporating the solvent to form the carbon-metal substrate. 
     
     
         4 . The method of  claim 1 , wherein the transition metal precursor is a transition metal macrocycle, a transition metal salt, or combination thereof. 
     
     
         5 . The method of  claim 4 , wherein the transition metal macrocycle comprises cobalt pthalocyanine, iron pthalocyanine, cobalt tetraazannulene, iron tetramethoxy phenyl porpyrin chloride, tetracarboxylic cobalt, iron pthalocyanine, tetramethoxy phenyl porpyrin chloride, cobalt salen-N,N′ bissalicylidine, ethylenediaminocobalt, cobalt-anten-O-amino, ferrocene, benzaldehyde, ethylenediamino cobalt, iron phenanthroline, or combinations thereof. 
     
     
         6 . The method of  claim 4 , wherein the transition metal salt comprises (1) a cation selected from the group consisting of iron, cobalt, nickel, chromium, cerium, zinc, zirconium, molybdenum, manganese, and mixtures thereof; and (2) an anion selected from the group consisting of acetate, chloride, nitrate, sulfate, and combinations thereof. 
     
     
         7 . The method of  claim 6 , wherein the transition metal salt comprises iron (II) acetate. 
     
     
         8 . The method of  claim 1 , wherein the nominal amount of the metal precursor added to the carbon source to form said metal precursor loaded carbon substrate ranges from about 0.75% to about 10% by weight of the substrate. 
     
     
         9 . The method of  claim 1 , wherein the transition metal precursor is a transition metal macrocycle, a transition metal salt, or combination thereof. 
     
     
         10 . The method of  claim 1 , wherein the nitrogen precursor compound is selected from the group consisting of poly(quinoxaline), nitroaniline, 1,10 phenanthroline, pthalocyanine, pyridine, bipyridine, polyaniline, pyrrole, polyvinyl pyridine, 3-nitrophalimide, p-phenylazophenol, 6-quionoline carboxylic acid, 6-nitrobenzimidazole, 5-amino 6-nitro quinoline, 2,3 naphthalocyanine, 4,4′-azoxydibenzoic acid, 2 amino 5-nitro pyrimidine, hematin, 4,4′ azo-bis[cyanovaleric acid], heamotoporpyrin dihydrochloride, 4,4′ nitrophenyl azo catechol 4,6 dihydroxy pyrimidine, nitrophenyl, benzylamine, 1,6 phenylendiamine, tetracyanoquinodimethane, propylene di-amine, ethylene di-amine, urea, selenourea, thiourea, dimethylformamide, tetrahydrofuran, ammonia, acetonitrile and polymers, and combinations thereof. 
     
     
         11 . The method of  claim 1 , wherein the nitrogen precursor compound comprises melamine. 
     
     
         12 . The method of  claim 10 , wherein the nominal amount of nitrogen in the carbon-metal-nitrogen precursor ranges from about 1.0% to about 15% by weight of the carbon-metal-nitrogen precursor. 
     
     
         13 . The method of  claim 1 , wherein the nitrogen precursor compound is free of carbon. 
     
     
         14 . The method of  claim 1 , wherein the nitrogen precursor compound undergoes a decomposition reaction to form ammonia. 
     
     
         15 . The method of  claim 14 , wherein the nitrogen precursor compound comprises an ammonia generating precursor selected from the group consisting of ammonium hydroxide, urea, ammonium carbamate, or combinations thereof. 
     
     
         16 . The method of  claim 14 , wherein the nitrogen precursor compound comprises an ammonium salt. 
     
     
         17 . The method of  claim 1 , wherein the pyrolyzing step comprises pyrolyzing the carbon-metal-nitrogen precursor at a temperature ranging from about 600° C. to about 900° C. in a closed reaction vessel. 
     
     
         18 . The method of  claim 1 , wherein the reaction vessel comprises quartz. 
     
     
         19 . The method of  claim 1 , wherein the pyrolyzing step further comprises pyrolyzing the carbon-metal-nitrogen precursor using a spray pyrolysis apparatus. 
     
     
         20 . A low temperature fuel cell comprising the oxygen reducing cathode catalyst of  claim 1 . 
     
     
         21 . A method for making a membrane electrode assembly for a fuel cell, comprising:
 (a) providing an ionomeric membrane, the membrane having a first side and a second side;   (b) applying an anode catalyst on at least a portion of the first side of the ionomeric membrane; and   (c) applying a cathode catalyst on at least a portion of the second side of the ionomeric membrane, wherein the cathode catalyst is synthesized by:
 (i) mixing a carbon source with a transition metal precursor to form a metal precursor loaded carbon substrate, wherein the substrate is free of precious metals; 
 (ii) adding a nitrogen precursor compound to the metal precursor loaded carbon substrate to form a carbon-metal-nitrogen precursor; 
 (iii) pyrolyzing the carbon-metal-nitrogen precursor at a pressure ranging from about 2 bar to about 100 bar, thereby forming an oxygen reducing cathode catalyst, and 
 (iv) mixing the oxygen reducing cathode catalyst with a recast ionomer. 
   
     
     
         22 . The method according to  claim 21 , wherein the anode catalyst comprises a catalyst ink having at least one transition metal selected from the group consisting of platinum, ruthenium, palladium, and combinations thereof. 
     
     
         23 . The method according to  claim 21 , wherein the recast ionomer comprises poly(perfluorosulphonic acid). 
     
     
         24 . A method for making a cathode catalyst coated diffusion layer for a fuel cell, comprising:
 (a) providing a gas diffusion layer; and   (b) applying a cathode catalyst on at least a portion of the gas diffusion layer, wherein the cathode catalyst is synthesized by:
 (i) mixing a carbon source with a transition metal precursor to form a metal precursor loaded carbon substrate, wherein the substrate is free of precious metals; 
 (ii) adding a nitrogen precursor compound to the metal precursor loaded carbon substrate to form a carbon-metal-nitrogen precursor; and 
 (iii) pyrolyzing the carbon-metal-nitrogen precursor at a pressure ranging from about 2 bar to about 100 bar, thereby forming an oxygen reducing cathode catalyst. 
   
     
     
         25 . A method for making an oxygen reducing cathode catalyst, the method comprising:
 (a) mixing a carbon source with a transition metal precursor to form a metal precursor loaded carbon substrate substantially free of precious metals;   (b) adding a nitrogen precursor compound having a N:C ratio of at least about 1:1 to the metal precursor loaded carbon substrate to form a carbon-metal-nitrogen precursor; and   (c) pyrolyzing the carbon-metal-nitrogen precursor at an elevated pressure ranging from about 2 bar to about 100 bar, thereby forming the oxygen reducing cathode catalyst.   
     
     
         26 . The method according to  claim 25 , wherein the nitrogen precursor compound has a N:C ratio of at least about 2:1. 
     
     
         27 . The method according to  claim 25 , wherein the nitrogen precursor compound comprises melamine.