Noble metals have been widely applied as catalysts in chemical production, energy conversion, and emission control [1-3], but their high cost and scarcity are major obstacles for any large-scale practical applications. It is therefore of great interest to explore new active material systems that require less mass loading of noble metal catalysts but with even better performance. Recently, intense research has been devoted towards downsizing the noble metals into single-atom catalysts (SACs) [4,5]. SACs, with single-atom active centers, were first reported by Qiao et al. . They synthesized a single Pt atom catalyst supported on FeOx (Pt1/FeOx), which offered extremely high efficiency on an atomic percent basis and showed excellent performance towards CO oxidation.