Fig. 2: Structural characterization of the CuNa-CF catalyst.

a Scanning electron microscope image of the CuNa-CF membrane. b Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) image, some of Cu atoms are marked by red circles. c HAADF-STEM image of the CuNa-CF catalyst and the corresponding energy dispersive X-ray spectroscopy elemental mapping images for C, N, O, Cu, and Na. d HAADF-STEM image of the CuNa-CF catalyst and the corresponding scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) mapping (e) taken from the orange boxed area in (d). f the corresponding EELS spectrum of the 0.5 nm × 0.5 nm selected small area in (e).