Figure 2 Structural characterizations of SA-Cu-NC (A) X-ray diffraction (XRD) patterns of NC and SA-Cu-NC. (B) High-resolution transmission electron microscopy (HRTEM) image of SA-Cu-NC. (C) Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of SA-Cu-NC. (D–G) Energy-dispersive X-ray (EDX) images of SA-Cu-NC.