As oxygen are added, the Pt-5d PDOS displays a decreased metallic character as the peak becomes narrower and more localized, indicating a change of the electronic structure towards a platinum-oxide-like cluster. Additionally, the d-band center slightly shifts towards lower energies. In contrast, the O-2p PDOS does not display substantial variations, with only a slight decrease in the peak located at -6.0 eV and the appearance of states above the Additionally, the appearance of the peak on the Pt-5d PDOS possibly signifies a more molecular-like interaction with O-2p states and the formation of a distinct bonding-antibonding pair with these orbitals. The emergence of O-2p states just above the Fermi level with increasing coverage further supports this interpretation, which would likely represent the antibonding molecular-like orbital. In Figure , the states close to the Fermi energy, increasing with coverage, are harder to interpret. Considering the average destabilization of the Pt-O bond with increasing oxidation, we suggest that these states are non-bonding or weakly antibonding states. From the perspective of the Pt-5d PDOS the slight increase in bandwidth indicates that the interaction should retain metallic character. However, the narrow peak close to the Fermi energy suggests that the ionic nature of these bonds develop as oxygen content increases.