fig5

Figure 5. TEM characterizations of CS sample. (A) Low-magnification and (B) HRTEM images of CS sample before HER test. (C) Low-magnification and (E) HRTEM images of CS sample after HER test, where the white arrows indicate the hydrogen blisters formed. (D) A schematic diagram illustrating the position of the hydrogen blisters, which are formed at the grain boundaries. (F) FFT pattern transformed from the white square region in (E). The inset of (E) is an FFT image transformed from (F).