Pt-Decorated\nComposition-Tunable Pd–Fe@Pd/C\nCore–Shell Nanoparticles with Enhanced Electrocatalytic Activity\ntoward the Oxygen Reduction Reaction

Abstract

Design of electrocatalysts with both\na high-Pt-utilization efficiency\nand enhanced electrochemical activity is still the key challenge in\nthe development of proton exchange membrane fuel cells. In the present\nwork, Pd–Fe/C bimetallic nanoparticles (NPs) with an optimal\nFe composition and decorated with Pt are introduced as promising catalysts\ntoward the oxygen reduction reaction. These bimetallic nanoparticles\nhave a Pd–Fe@Pd core–shell structure with a surface\nPt decoration as established through the use of electron energy loss\nspectroscopy (EELS) and energy-dispersive X-ray (EDX) spectroscopy.\nThese catalysts exhibit excellent electrocatalytic activity (<i>E</i>_1/2 = 0.866 V vs RHE), increasing the mass activity\nby more than 70% over that of Pt/C in terms of the total mass of Pt\nand Pd and by 14 times if only Pt is considered. Simple geometrical\ncalculations, based on spherical core–shell models, indicate\nthat Pd–Fe@Pt has a surface Pt decoration rather than a complete\nPt monolayer. Such calculations applied to other examples in the literature\npoint out the need for careful and rigorous arguments about claimed\n“Pt monolayer/multilayers”. Such calculations must be\nbased on not only elemental mapping data but also on the Pt/Pd and\nother metal atomic ratios in the precursors. Our analysis predicts\na minimal Pt/Pd atomic ratio in order to achieve a complete Pt monolayer\non the surface of the core materials.