Composition optimization of ternary palladium–iridium–iron alloy catalysts for oxygen reduction reaction in acid medium
Abstract
A series of ternary PdxIrFe/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 PdxIrFe alloy nanoparticles are uniformly distributed on carbon support and Pd is enriched in the surface region of the Pd3IrFe/C catalyst. Among the PdxIrFe/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.