The adsorption and dissociation of O-2 on the supported small nickel clusters with one-, two-, three-Ni atoms on yttria-stabilized zirconia (YSZ) (111) surfaces, as well as those on the bare YSZ(111) and Ni(111) surfaces are comparatively studied using ab initio density functional theory calculations. It is found that the dissociation of O-2 on the YSZ(111) surface is largely enhanced by the supported Ni dimer, which is predicted to be the smallest Ni cluster needed for efficient O-2 dissociation. The results would provide an important reference to improve the activity and efficiency of the Ni/YSZ(111) nanocomposite catalysts in cost-effective materials.(C) 2017 Elsevier B.V. All rights reserved.