Comparison of Nucleation, Chemical State, and Energetics of Ni and Co Nanoparticles on CeO₂(111)

The nucleation, growth, and chemical states of Ni nanoparticles (NPs) over CeO2(111) thin film surfaces have been studied by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations in comparison to Co NPs. At a very low coverage of ∼0.10 ML, Ni NPs are present in both Ni2+ and metallic states on CeO2(111), while Co NPs are found in the Co2+ state. STM results show that Ni grows as small particles with an average height and diameter of 2.1 ± 0.7 and 17.6 ± 4.4 Å, while Co particles exhibit an average height and diameter of 1.8 ± 0.5 and 17.0 ± 3.2 Å, respectively, indicating a slightly stronger metal–ceria relative to metal–metal interaction for Co than for Ni at this scale. This is corroborated by DFT calculations, which predict a more rapid stabilization of metal atoms in the NPs with increasing size of the NPs for Ni than for Co.