Powder X-ray diffraction (XRD) measurements were carried out on an X'Pert Philips diffractometer in Bragg-Brentano geometry with monochromatic CuKα radiation (0.1541 nm) and a fast Si-PIN multi-strip detector. The step size was 0.02 degree s -1 . Transmission electron microscopy (TEM) was performed on an FEI Talos-S operated at 200 kV high tension. Elemental energy dispersive X-ray spectroscopy (EDXS) mapping was used for elemental characterization, with simultaneously acquired high-angular annular dark field scanning transmission electron microscopy (HAADF-STEM) images showing atomic number and thickness contrast. For atomic resolution imaging, the measurements were performed on an FEI Titan Themis 60-300 operated at 200 kV with an aberration-corrected electron probe and using HAADF-STEM conditions. Samples for TEM were prepared by drop-drying the samples from their diluted ethanol suspensions onto carbon-coated copper grids. X-ray photoelectron spectroscopy (XPS) measurements were performed on a PHI5000 VersaProbe II XPS system by Physical Electronics (PHI) with a detection limit of 1 atomic percent. Monochromatic X-rays were generated by an Al Kα source (1486.7 eV). The diameter of the analyzed area is 10 µm. Raman spectrum was recorded on a LabRAM high resolution Raman spectrometer. The power of laser was set as 0.1% in order to alleviate the damage of carbon matrix caused by stronger laser beam. ICP-AES (Inductively coupled plasma -Atomic Emission Spectroscopy) results were obtained by a NexIon 350 (Perkin Elmer) machine. Before dissolving in ultra-pure nitric acid (65%, Merck KGaA), all the samples were put in muffle oven and then heated at 600 °C for 12 h in air to remove carbon support and make sure all of the metal ions were exposed to be digested by nitric acid. N2physisorption measurements were performed on a Micromeritics 3Flex apparatus at liquid nitrogen temperature between 10 -5 and 0.99 relative N2 pressure. Samples (ca. 100 mg) were dried at 120°C under vacuum (< 10 -3 mbar) for 4 h and a leak test was performed prior to analysis.