Structure of Pt n Ni Nanoparticles Electrocatalysts Investigated by X‑ray Absorption Spectroscopy

Carbon supported Pt–Ni nanoparticles (NPs) electrocatalysts with nominal Pt/Ni atomic ratios of 3:1, 2:1, and 1:1, denoted as Pt3Ni/C, Pt2Ni/C, and Pt1Ni/C, respectively, were obtained by a modified polyol process. The structure of Pt n Ni/C (n = 3, 2, 1) electrocatalysts was studied by using an X-ray absorption spectroscopy technique combined with X-ray diffraction and transmission electron microscopy. Significantly, the NPs of Pt3Ni/C in air are demonstrated to have a quasi core–shell structure consisting of a core of metallic Pt surrounded by many small NiO x clusters. In contrast, both Pt2Ni/C and Pt1Ni/C are demonstrated to have an alloy structure with partial oxidation on the surface. Under the atmosphere of H2 at 393 K, the Pt n Ni/C became the expected bimetallic alloy. At last, we discuss the effect of Ni amount on the structure of Pt n Ni/C and estimate their possible catalytic activity for methanol oxidation reaction. Our results further confirmed that the structure of Pt–Ni NPs can be influenced by Ni amount and this effect may be enlarged by environment effects.