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

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.