Formation Process of Pt Subnano-Clusters on Graphene Nanosheets
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The formation mechanism of Pt subnano-clusters composed of 5−40 Pt atoms on graphene nanosheets (GNS) has been studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscope (TEM). The exchange of Cl− ion by OH− ion and the reduction of Pt4+ to Pt2+ are examined by XPS in the reduction of an H2PtCl6 catalyst precursor by ethanol at different pH. XPS and TEM results show that particles of Pt2+-containing compounds with the sizes of 2−7 nm are first formed on GNS by the reduction of H2PtCl6 with ethanol, which are then fully reduced to Pt subnano-clusters by H2 at 400 °C. The proposed mechanism for the Pt subnano-cluster formation includes two pivotal surface reactions: the reduction of Pt2+ particles into isolated Pt atoms by H2 on the GNS surface, followed by the formation of Pt subnano-clusters by collision of the Pt single atom migrating on GNS.