NPG films were prepared by electrochemically reducing similar Au oxide electrodes to those presented in the previous section. Here, we also first focus on electrodes prepared by HV electrolysis at 540 V. Optical microscope and SEM images of electrochemically reduced Au POSCs after 250 ms, 15 s and 30 s are shown in Fig. . Additional optical microscope and SEM images for different electrolysis times are provided in Fig. . Although the Au POSCs in the optical microscope images tend to appear golden to some extent, they exhibit a black coloration, especially at electrolysis times longer than 500 ms. The black color is distinct for the formation of a NPG film. 21,22,26,27, From the optical microscope and SEM images of the entire Au POSC in Fig. and Fig. it is apparent that after HV electrolysis at 540 V for 15 s (and more) and subsequent electrochemical reduction, the resulting NPG film randomly exfoliates from the surface. In some cases, exfoliation is also observed to some degree in the SEM images of the entire POSC in experiments with 2 s and 4 s electrolysis time.