Pt is still the most used catalyst for various electrocatalytic reactions. But its high cost and scarcity hinder its wide application. In order to address this problem, researchers found that alloying Pt with one or more transition metals such as Ni, Fe or Co can enhance its activity via maximizing the exposure of (111) facets.¹ Octahedral Pt-Ni nanoparticles have been regarded as promising electrocatalyst for various reactions.^2-4 It has been found that post heat annealing on the Pt-Ni octahedra plays a significant role in altering their activity and durability during oxygen reduction reaction. ⁵

In this study, the structure evolution and compositional segregation were systematically studied during annealing in various atmosphere (vacuum, N₂, H₂, Ar and air) by XRD, TEM, XPS and electrochemical techniques. The impact of the heat treatment on the activities toward oxygen reduction reaction, hydrogen evolution reaction, and ethanol electro-oxidation reaction were assessed. It is interesting to find that the carbon support might be unstable in certain atmosphere, for example, Ar, and can be deposited on the catalyst surface. Figure 1 compares the CVs of Pt-Ni treated in Ar and N₂ at 400 °C with the unannealed one. It is clear that the surface area of Pt-Ni treated in Ar diminished due to carbon coating.

In this talk, the composition and structural evolution result upon annealing will be presented. Their effects on various electrochemical reaction activities will be discussed.

Figure 1. Comparisons of cyclic voltammograms of Pt-Ni annealed in N₂ (blue), Ar (red) at 400°C for 30 min, and un-annealed one in an N₂-saturated 0.1 M HClO₄ solution.

Reference:

1. Stamenkovic, V. R.; Fowler, B.; Mun, B. S.; Wang, G.; Ross, P. N.; Lucas, C. A.; Marković, N. M. Science 2007, 315 (5811), 493-497.

2. Sulaiman, J. E.; Zhu, S.; Xing, Z.; Chang, Q.; Shao, M. ACS Catalysis 2017, 7 (8), 5134-5141.

3. Choi, S.-I.; Xie, S.; Shao, M.; Odell, J. H.; Lu, N.; Peng, H.-C.; Protsailo, L.; Guerrero, S.; Park, J.; Xia, X.Nano letters 2013, 13 (7), 3420-3425.

4. Kavian, R.; Choi, S.-I.; Park, J.; Liu, T.; Peng, H.-C.; Lu, N.; Wang, J.; Kim, M. J.; Xia, Y.; Lee, S. W. Journal of Materials Chemistry A 2016, 4 (32), 12392-12397.

5. Gan, L.; Heggen, M.; Cui, C.; Strasser, P.ACS catalysis 2015, 6 (2), 692-695.