Enhancing stability of octahedral PtNi nanoparticles for oxygen reduction reaction by halide treatment

• Published in: Journal of power sources 2016-03, Vol.307, p.883-890
• Main Authors: Choi, Juhyuk, Lee, Youhan, Kim, Jihan, Lee, Hyunjoo
• Format: Article
• Language: English
• Subjects: Alloys; Halides; Leaching; Oxygen reduction reaction; PtNi nanoparticles; Stability
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2016.01.063

Because a reduction in the amount of Pt catalysts is essential for the commercialization of fuel cells, various approaches have been tested to maximize the mass activity of Pt-based catalysts. Among these, the most successful results so far were obtained using shaped PtNi alloy nanoparticles, preferably with PtNi(111) facets. However, these nanoparticles typically suffer from much lower activity after the durability tests due to the leaching out of the surface Ni during the oxygen reduction reaction (ORR), which leads to the disappearance of the activity-enhancing effect caused by electronic structure modification. Here, we showed that halide treatment of the octahedral PtNi nanoparticles could significantly enhance their durability. Halides are adsorbed on surface Ni more strongly than on surface Pt, and the surface halides are found to preserve the surface Ni that induces the ORR activity enhancement. Especially, Br can preserve the surface Ni effectively. Durability testing by repeating cyclic voltammetry 10,000 times in the 0.6–1.1 V range showed that the mass activity decreased by 52.6% for the as-prepared PtNi octahedral nanoparticles, whereas the mass activity decreased by only 15.0% for the Br-treated PtNi nanoparticles. The simple treatment significantly enhanced the long-term stability of the highly active PtNi alloy nano-octahedra. [Display omitted] •PtNi octahedral nanoparticles showed high activity for oxygen reduction reaction (ORR).•The surface Ni is leached out in acidic solution degrading the activity for the ORR.•Halides can be adsorbed on Ni sites more strongly than Pt sites.•Br adsorbed on the nanoparticle surface protected Ni from being leached out.•The Br-treated PtNi nanoparticles preserved the shape with high activity even after ADT.