4.5. Structural characterizations
The morphology of the samples was observed by SEM JEOL S-4800 using an accelerating voltage of 10 kV and TEM JEM-F200 using an accelerating voltage of 80 kV, which were shown in SEM, TEM, HRTEM, SAED and HAADF images. Furthermore, the preferred growth orientation and crystallinity of the samples were shown by the XRD images provided by the Bruker D8 Advance X-ray diffractometer applying Cu Kα radiation (λ = 0.154 nm). The element distribution/composition and electron population were characterized by TEM mapping, EDS, soft XAS and XPS. Among them, the photoemission end-station (BL10B beamline) of soft XAS was located at the in the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China. In addition, the soft XAS data was normalized by the µ(E) energy mode in Athena software. The device model for XPS has been selected as ESCALAB250Xi with Mg Kα (1486.6 eV) as the radiation source. In addition, the catalyst used to test the potential-dependent quasi-in-situ XPS needs to be pretreated for 8 min under the corresponding potential environment.