This work reports the synthesis, electrocatalytic performance and structure-dependent catalytic activity of Pt₂Ni alloy@Pt core–shell nanoarchitectures (denoted as Pt₂Ni alloy@Pt). The core–shell nanoarchitecture of Pt₂Ni alloy@Pt catalyst is confirmed as consisting of a single concave-tetrahedral alloy nanocrystal core decorated with nanodendritic Pt particles. The oxygen reduction reaction (ORR) activity measurement indicates that the Pt₂Ni alloy@Pt nanoarchitecture can enhance the ORR activity, accelerate the catalytic reaction and improve the durability of the catalyst during the electrocatalytic process. The atomic ratio between Pt and Ni is tuned to obtain various Pt_xNi_1−x bimetallic nanostructures, and used for elucidation of structure dependence of catalytic activity. The resultant different Pt_xNi_1−x catalysts exhibit considerable structure-dependent catalytic activity. The measurement results indicate that the order of ORR activity is as follows: cubic alloy nanocrystals (PtNi₂) < cubic alloy crystal@Pt particles (PtNi₂@Pt) < concave-tetrahedral alloy nanocrystals (Pt₂Ni) < Pt₂Ni alloy@Pt. Accordingly, the considerable ORR activity of Pt₂Ni alloy@Pt catalyst is achieved by introducing an optimal amount of Ni atoms into Pt_xNi_1−x catalyst and formulating the bimetallic crystal into a core–shell nanoarchitecture. In this integrated core–shell nanoarchitecture, the extended Pt nanoparticles shell provides high surface area, rich adsorption sites, and favorable surface permeability. Furthermore, the concave-tetrahedral alloy crystal core suppresses the activity loss derived from the agglomeration and/or corrosion of Pt active sites. Therefore, the two different components (alloy crystal core and extended Pt particles shell) contribute to different functions and further generate a synergistic effect towards ORR activity.