Structural transformation of carbon-supported Pt₃Cr nanoparticles from a disordered to an ordered phase as a durable...

The sluggish oxygen reduction kinetics and insufficient durability of cathode catalysts restrict the practical application of proton exchange membrane fuel cells. This study focuses on the structural transformation of carbon-supported Pt₃Cr from a disordered to an ordered phase and on the effect of such structural transformation on oxygen reduction reaction (ORR) activity and durability. X-ray diffraction and transmission electron microscopy results confirm the formation of carbon-supported Pt₃Cr intermetallic nanoparticles with a mean particle size of ca. 7.2 nm. Line scanning EDX reveals that the practical Pt-Cr atomic ratio is approximately 3 : 1. X-ray photoelectron spectroscopy results indicate that the proportion of metallic Pt increases while the binding energy of Pt 4f decreases with such structural transformation. The Pt₃Cr/C intermetallic nanoparticles exhibit enhanced mass and specific activities toward the ORR compared with commercial Pt/C but slightly lower mass activity than the disordered Pt₃Cr/C alloy nanoparticles. After the accelerated durability test for 5000 cycles, the Pt₃Cr intermetallic nanoparticles displayed negligible decay in ORR mass activity; however the ORR mass activity on the isordered Pt₃Cr alloy decreases to ca. 50%. Much enhanced durability of the Pt₃Cr/C intermetallic nanoparticles toward the ORR is definitely caused by the much higher structural and compositional stabilities of the Pt₃Cr/C intermetallic nanoparticles than that of the disordered Pt3Cr/C alloy nanoparticles, suggesting that the Pt₃Cr intermetallic nanoparticles may serve as highly active and durable ORR electrocatalysts for practical application.