Chemistem

The XRD characterization was conducted with a Rigaku Miniflex600. Raman and PL spectra were performed with a laser micro-Raman spectrometer (Renishaw in Via, 532 nm excitation wavelength). SEM images were obtained on a ZEISS Merlin Compact SEM. The AFM images were taken with an NT–MDT Ntegra Spectra. The XPS measurements were carried out using a Thermo Scientific, ESCALAB 250Xi. The XPS depth analysis was performed at 3 keV with a spot size of 2 mm × 2 mm and the binding energies were calibrated by referencing the C 1 s peak (284.8 eV). The TEM images were obtained using an aberration-corrected transmission electron microscope (FEI Titan Thermis 60–300) operated at 300 kV. The STEM images were obtained using a probe Cs-corrected transmission electron microscope (FEI Titan ChemiSTEM) operating at 200 kV. The positive ion TOF-SIMS spectra were acquired with an ION TOF ToF SIMS 5-100.

The transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) images were achieved from a Hitachi HT-7700 microscope operated at 100 kV and a FEI Tecnai G2 F20 microscope operated at 200 kV, respectively. A FEI Titan ChemiSTEM equipped with a probe-corrector and a Super-X EDX detector system was employed to obtain the high-angle annular dark-field scanning TEM (HAADF-STEM) and energy dispersive X-ray (EDX) mapping images. The X-ray diffraction (XRD) characterization was performed on a Rigaku Ultima Ⅳ x-ray diffractometer with graphite monochromatized Cu Kα radiation (λ = 1.54178 Å). The chemical states of samples were characterized by a Shimadzu AXIS Supra X-ray photoelectron Spectroscopy (XPS) with Al Kα radiation. The percentage of each element in the electrocatalysts was recorded by a Thermofisher iCAP Pro Ⅹ inductively coupled plasma atomic emission spectrometer (ICP-AES).

The morphology of the as-prepared samples was characterized via field emission scanning electron microscopy (FESEM, HITACH S4800) and transmission electron microscopy (TEM, PHILIPS F200). Energy dispersive spectroscopy (EDS) mapping images and line scanning images were recorded by a FEI Titan ChemiS TEM equipped with a probe-corrector and a Super-X EDS detector system. X-ray photoelectron spectroscopy (XPS) was performed by employing a Thermo ESCALAB 250Xi spectrometer with a monochromatic Al Kα line (1486.6 eV). The crystal structures of the materials were determined using a high power X-ray diffractometer (XRD) on a Rigaku D/max-ga X-ray diffractometer, where the Cu Kα radiation was 1.54 Å.