Fig. 1: Formation of PtOx layer on Pt(111) under NO2.

a, In situ SEM images obtained during the oxidation of Pt(111) by 1 mbar NO2 under 1,000 K. b, Change in intensity in region A (shown in a). c, Evolution of the O1s spectra during the oxidation process on a Pt(111) surface under 1 mbar NO2 from 300 to 1,000 K. d, Pt4f spectra of the PtOx collected with various photon energies, demonstrating that PtOx was located at the topmost surface. The red arrows indicate identical positions on the Pt surface. A complete oxidation process is shown in Supplementary Videos 1 and 2.