The sluggish kinetics of the oxygen reduction reaction (ORR) and insufficient durability of the catalysts restrict the practical application of proton exchange membrane fuel cells (PEMFCs), including direct methanol fuel cell. Pt alloy electrocatalysts have been extensively investigated to address the issue of both sluggish ORR kinetics and high-cost of Pt catalysts. Previous results have shown that Pt alloy catalysts do enhance the ORR activity in comparison to pure Pt/C, which may be resulted from the d-orbital coupling effect between metals. However, the durability of previously reported disordered Pt-based alloy (i.e. solid solution ) catalysts does not meet the requirement for the practical application because of possible dissolution of transition metal within the catalysts for long-term operation. In this regard, recent research efforts have focused on the development of Pt-based intermetallic compounds as the durable ORR catalysts, since they allow a greater degree over their structural, geometric and electronic properties.

In this work, we focus on the structural transformation of carbon-supported PtNi intermetallic nanoparticles from disordered to an ordered phase and on the effects of such a structural transformation on the ORR activity and durability. Both XRD and TEM results reveal that the obtained ordered PtNi catalysts present a single-phase of intermetallic compound structure with a mean particle size of ca. 7.5nm. The PtNi intermetallic nanoparticles are more active and durable towards the ORR than both disordered PtNi alloy and commercial Pt/C. After accelerated durability test (ADT) for 5000 cycles, the ordered PtNi catalyst presents only slight decrease in mass activity of the ORR, while the ORR activity on disordered PtNi decreases to ca.50%. In comparative growing of particle size and leaching out of Ni for disordered PtNi, no obvious change in particle size and structure for the ordered PtNi phase before and after ADT. This phenomenon could be due to the Pt enrichment on the shell of the nanoparticles. The enhanced ORR activity and durability may be ascribed to the compositional effects and an ordered atomic structure.