Characterization of Pt-Cu-Fe ternary electrocatalysts supported on carbon black

Abstract

Ternary Pt-Cu-Fe alloy catalysts, useful for low temperature fuel cells, were prepared from aqueous media, followed by heat treatment at 900 °C for various heating periods. Supported metal crystallites were characterized with various techniques including XRD, XPS, TEM and ICP-AES. XRD patterns indicate that the lattice structure of platinum changes from a face-centred cubic to a contracted facecentred tetragonal structure as it forms an alloy. As the heating period increases, the extent of formation of an ordered alloy increases and the formation is completed in 2.5 h, as confirmed by the intensity of superlattice diffraction lines. The presence of different oxidation states is confirmed by XPS and the amount of higher oxidation state is reduced by heat-treatment, but there is no evidence of development of a new photoelectron peak or shift in binding energy by alloy formation. For the electrochemical reduction reaction of oxygen in fuel cell operation, ordered alloys have shown improved catalytic activity compared to platinum alone. After the stability test in hot phosphoric acid, the ordered structure is preserved even though a significant amount of transition metal is dissolved, and some increase in particle size in the heat-treated catalysts is observed.