Surface segregation of Pd_xNi_100-x alloy nanoparticles

Alloy nanoparticles of Pd_xNi_100-x (x = 20, 30, 70, and 80) were prepared by the coprecipitation method. The surface segregation of nanoparticles, driven by the surface energy, strain energy, and reduction potential, was studied systematically. The surface composition, surface species, and alloy structure of as-prepared Pd_xNi_100-x and heated Pd₃₀Ni₇₀ alloy nanoparticles was characterized by ESCA, TPR, and XRD, respectively. The structure of as-prepared Pd_xNi _100-x alloy nanoparticles is not homogeneous and changes with the alloy content x. The surface is Pd enriched for as-prepared Pd ₈₀Ni₂₀ alloy due to the strain energy effect. In contrast, the surface is Ni enriched for as-prepared Pd_xNi_100-x alloy with x = 20, 30, and 70 due to the reduction potential effect. In addition, a combinatory process of surface segregation and homogenization during the heat treatment was observed on the surface of Pd₃₀Ni ₇₀ alloy nanoparticles after heating at T > 620 K.