Nanosegregated Surfaces As Catalysts for Fuel Cells

Abstract

A method of preparing a nanosegregated Pt alloy having enhanced catalytic properties. The method includes providing a sample of Pt and one or more of a transition metal in a substantially inert environment, and annealing the sample in such an environment for a period of time and at a temperature profile to form a nanosegregated Pt alloy having a Pt-skin on a surface. The resulting alloy is characterized by a plurality of compositionally oscillatory atomic layers resulting in an advantageous electronic structure with enhanced catalytic properties.

1 . A method of preparing a nanosegregated Pt alloy having enhanced catalytic properties, comprising:
 providing a sample comprising Pt and one or more of a transition metal;   providing a substantially inert and/or reductive environment; and   annealing the sample in the substantially inert environment for a period and at a temperature profile to form a nanosegregated Pt alloy having a Pt-skin on a surface.   
     
     
         2 . The method of  claim 1 , wherein the one or more transition metals are alloyed with Pt and selected from the group consisting of: Co, Ni, Fe, Ti, Cr, V, Zr and Mn. 
     
     
         3 . The method of  claim 2 , wherein the period is from about 120 minutes to about 1000 minutes 
     
     
         4 . The method of  claim 2 , wherein the temperature profile is a substantially constant temperature between about 350° C. to about 1000° C. 
     
     
         5 . The method of  claim 4 , wherein the period is from about 20 minutes to about 360 minutes 
     
     
         6 . The method of  2  wherein, the environment comprises an atmosphere of N 2 , H 2 , or Ar gas and mixtures thereof or vacuum conditions. 
     
     
         7 . The method of  claim 1 , wherein the sample comprises a Pt 3 Ni single crystal, and wherein the period and temperature are selected to obtain the nanosegregated Pt alloy with a first layer composed substantially of Pt, a second layer having an elevated level of Ni, and a third layer having an elevated level of Pt. 
     
     
         8 . The method of  claim 7 , wherein the content of the second layer is from about 30 percent to about 70 percent Ni, and wherein the content of the third layer is from about 75 percent to about 95 percent Pt. 
     
     
         9 . The method of  claim 1 , wherein the period and temperature are selected such that the nanosegregated Pt alloy is characterized by a contraction of the first layer at a potential of at least about 0.8 V. 
     
     
         10 . The method of  claim 1 , wherein the period and temperature are selected such that the nanosegregated Pt alloy is characterized by a surface activity of at least about 2.0 mA/cm 2  at 0.9V. 
     
     
         11 . The method of  claim 1 , further comprising: disposing the nanosegregated Pt alloy on one or more substrates for use in a fuel cell, wherein the substrates are selected from the group consisting of: carbon, metal oxides, metals, carbon nanotubes, and nanowires. 
     
     
         12 . A nanosegregated Pt alloy having enhanced catalytic properties, comprising:
 an alloy of Pt and one or more of a transition metal, the alloy including one or more layers proximate to a surface of the alloy, each of the one or more layers having a concentration of Pt varying from the bulk concentration of Pt in the alloy, wherein the surface layer comprises a Pt-skin.   
     
     
         13 . The nanosegregated Pt alloy of  claim 12 , wherein the one or more transition metals is selected from the group consisting of: Co, Ni, Fe, Ti, Cr, V, Zr and Mn. 
     
     
         14 . The nanosegregated Pt alloy of  claim 13 , wherein the alloy comprises PtNi characterized by a crystallographic orientation of one or more of a {100}, {110} and {111} orientation. 
     
     
         15 . The nanosegregated Pt alloy of  claim 14 , wherein the alloy comprises PtNi characterized by a substantially {111} crystallographic orientation. 
     
     
         16 . The nanosegregated Pt alloy of  claim 12 , wherein the one or more layers include a first surface layer composed of substantially pure Pt, a second layer having an elevated level of Ni, and a third layer having an elevated level of Pt. 
     
     
         17 . The nanosegregated Pt alloy of  claim 16 , wherein the content of the second layer is from about 30 percent to about 60 percent Ni, and wherein the content of the third layer is from about 75 percent to about 95 percent Pt. 
     
     
         18 . The nanosegregated Pt alloy of  claim 16 , wherein the first layer is characterized by a contraction at a potential of at least about 0.8 V. 
     
     
         19 . The nanosegregated Pt alloy of  claim 12 , wherein the nanosegregated Pt alloy is in a form comprising a thin film or a nano-cluster. 
     
     
         20 . The nanosegregated Pt alloy of  claim 12 , wherein the nanosegregated Pt alloy in the form of nanoparticles is disposed in a high surface area carbon substrate.