Core–shell Pt modified Pd/C as an active and durable electrocatalyst for the oxygen reduction reaction in PEMFCs

Abstract

A series of Pt modified Pd/C catalysts (Pt/Pd/C) with different Pt/Pd molar ratio (Pt:Pd=1:4, 1:2 and 1:1) are synthesized by a chemical reduction method for oxygen reduction reaction (ORR). X-ray diffraction (XRD), transmission electron microscope (TEM) and cyclic voltammetry (CV) measurements confirm that Pt is deposited on the Pd nanoparticles and the Pt/Pd/C catalysts have a Pdcore@Ptshell structure. In the half cell testing, the catalytic ORR activity of Pt1/Pd2/C and Pt1/Pd4/C are superior to commercial Pt/C. Moreover, the electrochemical durability to potential cycling of Pt1/Pd2/C and Pt1/Pd1/C catalysts is better than Pt/C catalysts. The improved durability is believed to be associated with the dissolution of Pd and the corresponding structure transformation from core–shell structure to Pt-Pd alloy with Pt rich surface. The structure change is confirmed by TEM, CV, XRD and X-ray photoelectron spectroscopy (XPS). In addition, the electrochemical active surface area (ECSA) loss and polarization behavior in the single cell testing also suggest that the Pt/Pd/C show a much better durability than Pt/C catalysts. Similarly, the dissolution of Pd is observed by CV and scanning electron microscope-energy dispersive X-ray spectra (SEM-EDX). The Pt/Pd/C electrocatalysts have high ORR activity and this high activity can be further improved during potential cycling, that is, the activity and durability can be obtained simultaneously. This Pdcore@Ptshell structure allows for the development of highly active and durable ORR electrocatalysts, with potential for the application in proton exchange membrane fuel cells (PEMFCs).