As a 5d transition metal, Pt is located at the lower right of the transition-metal block in the periodic table; therefore, the interaction of Pt with PNP is already lower than most of the other transition metals according to the d-band theory [34]. To further lower the interaction energy, Pt can be doped with 3d transition metals, which reduces the adsorption energy of the catalyst by affecting the electronic structure of Pt (the ligand effect) and the lattice structure at the surface (the strain effect) [33] and [63]. In particular, the strain effect is related to the reduction of interatomic distance. In our experiments, the reduction of interatomic distance upon Ni doping is evident from the reduction of lattice spacing. As shown in Fig. 7, d111 measured from the FFT images in Fig. 2 transitions from the value for Pt toward that for Ni as θ increases [38]. The Pt/Ni nanoalloy having the best performance is associated with an intermediate d111 value, presumably corresponding to the largest change of electronic configuration with the change of lattice structure.