Fig. 2: The characterization of Fe-NCv catalysts by AC-STEM and in situ ETEM measurements.

a–e High-resolution AC-STEM images of Fe-NCv catalysts. f, g The in situ ETEM images during pyrolysis of Fe-NCv-600 at 500 °C and 700 °C, respectively. h The lattice spacing of Zn NPs measured by AC-STEM image.