Transmission electron microscopy (TEM) was carried out on a FEI Tecnai Osiris electron microscope equipped with a high-brightness field emission gun (XFEG) and an energy dispersive X-ray spectroscopy (EDX) analyzer. The TEM samples were prepared by drop-drying the catalysts on ultrathin carbon coated-copper grids. For atomic resolution imaging, the measurements were performed on an FEI Titan Themis 60-300 instrument that operated at 200 kV with an aberrationcorrected electron probe.