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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation-in-part of U.S. patent application Ser. No. 12 / 583,532, filed on Aug. 21, 2009, which claims the benefit of U.S. Provisional Patent Application No. 61 / 090,780, filed Aug. 21, 2008. The entire disclosure of each of the above applications is incorporated herein by reference.INTRODUCTION[0002]The present technology relates to methods for producing improved metal, nitrogen, and carbon containing catalysts effective for the reduction of oxygen in low temperature fuel cells and other electrochemical reactions and cathode catalysts produced by these methods.[0003]There is an increasing interest to replace platinum (Pt) based electro-catalysts with cost-effective non-noble catalysts for the oxygen reduction reaction (“ORR”) in low-temperature fuel cells, such as Polymer Electrolyte Fuel Cells (PEFCs) and Direct Methanol Fuel Cells (“DMFCs”) etc. Non-noble metal catalysts based on iron (Fe) and cobalt (Co) ions a...

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Benefits of technology

[0003]There is an increasing interest to replace platinum (Pt) based electro-catalysts with cost-effective non-noble catalysts for the oxygen reduction reaction (“ORR”) in low-temperature fuel cells, such as Polymer Electrolyte Fuel Cells (PEFCs) and Direct Methanol Fuel Cells (“DMFCs”) etc. Non-noble metal catalysts based on iron (Fe) and cobalt (Co) ions are among the possible candidates for replacement of Pt based catalyst metals for ORR. These catalysts are active towards ORR and exhibit selectivity towards ORR in the presence of a fuel, thereby increasing the volumetric energy density of a DMFC.

[0005]Recently, investigators have ball-milled highly-ordered synthetic graphite for use as a carbon support as it contains low levels of iron as impurities and low surface area (3.5 m2 / g), Pyrolysis of the milled material with an iron source in ammonia environment produced catalysts with nitrogen content as high as 4 atom %. These nitrogen containing catalysts demonstrate that the catalytic activity increases as a result of decreasing metal crystallite size, increasing degree of disorder, nitrogen content, and microporous (<22 Å) specific surface area. Others in the field have also suggested that active sites containing pyridinic nitrogen can be responsible for the catalytic activity for ORR and reported low levels of H2O2 production while reducing oxygen in an acidic medium.

[0008]The present technology provides methods for making non-precious metal electrochemical cathode catalysts for the reduction of molecular oxygen, for example, in a fuel cell. In addition, the present technology provides for a method to control the anchoring of a nitrogen containing compound on a high surface area carbon surface, which actively contributes to the catalytic activity of the cathode catalyst over preexisting methods of depositing nitrogen, thereby effectively increasing the catalytic activity per unit mass of catalytic material on a substrate. The cathode catalyst material produced in accordance with the present technology lowers the cost for producing the catalyst material and follows a simple synthesis method compared to platinum / carbon catalysts and other non-precious metal catalysts conventionally used in fuel cell designs.

Problems solved by technology

The thermal treatment can comprise heating the coated substrate for 15 minutes or so at temperatures of at least 600-900° C. However, the deposition of the nitrogen source is not readily controllable.

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