The long-term stability of Pt electrocatalyst during oxygen reduction reaction (ORR) is a great challenge hampering its use as the cathode of proton exchange membrane fuel cells for automobile applications. A number of researches have reported that the surface oxide formation by diffusion of the atomic oxygen to the sublayer is important to understand its stability. Here, we focused on the study of the effects of the O-2-containing intermediates of ORR such as O-2 and OOH toward the diffusion of the atomic oxygen in the Pt(111) surface by using the density functional theory calculations. Using the climbing image nudged elastic band method, we found that the energy barrier for the diffusion of O in both the forward and the backward directions decreases by the presence of O-2 and OOH on the Pt(111) surface. The reduction of the energy barrier in the forward direction speeds up the diffusion of O into the subsurface and hence speeds up the surface oxide formation, while the reduction of the energy barrier in the backward direction triggers the atomic oxygen moving back to the on-surface that may destroy the Pt(111) surface and therefore affect the stability of the Pt(111) substrate. These results strongly support the previous experiments. Furthermore, the Bader charge analysis suggested that by simultaneously decreasing the charge gain of the atomic oxygen at the initial state (on the surface) and the final state (inside the subsurface) may help increase the stability of the Pt surface. Experiments such as using buffer solutions or corrosion inhibitors are suggested to confirm this prediction. [GRAPHICS]