Composition optimization of ternary palladium–iridium–iron alloy catalysts for oxygen reduction reaction in acid medium

Abstract

A series of ternary Pd_xIrFe/C alloy catalysts with Pd : Ir : Fe atomic ratios of 1 : 1 : 1 (denoted as PdIrFe/C), 2 : 1 : 1 (denoted as Pd₂IrFe/C) and 3 : 1 : 1 (denoted as Pd₃IrFe/C) have been prepared through a microwave polyol reduction method for oxygen reduction reaction in acid medium. The morphology, structure, composition and electrochemical properties of the catalysts are analyzed by X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM) equipped with electron diffraction spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and rotating disc electrode (RDE) measurements. It is clearly shown that Pd_xIrFe alloy nanoparticles are uniformly distributed on carbon support and Pd is enriched in the surface region of the Pd₃IrFe/C catalyst. Among the Pd_xIrFe/C catalysts, the ternary Pd₃IrFe/C alloy catalyst exhibits a rather high Pd mass activity that is 11-fold and 5.7-fold higher than that of Pd/C and Pd₃Fe/C catalysts, respectively, at 0.72 V. This activity enhancement is believed to result from the surface segregation of Pd and the modification of electronic structure induced by subsurface Ir, which weakens the binding strength of oxygen-containing intermediates and further enhances their removal from the catalyst surface. Furthermore, the ternary Pd₃IrFe/C alloy catalyst possesses higher methanol tolerance than the Pt/C catalyst. The ternary Pd₃IrFe/C alloy electrocatalyst is a promising ORR catalytic material, especially for DMFCs.