fig2

Figure 2. (A) Raman spectra of NiCrS and NiCrS/CN; (B) XRD result, (C and D) SEM images, (E) Element mapping images and (F) HRTEM result of NiCrS/CN. SEM: Scanning electron microscope; HRTEM: high-resolution transmission electron microscopy; XRD: X-ray diffraction; NiCrS/CN: nickel-chromium sulfide with nitrogen-doped carbon shell.