Fig. 2. The SEM images of the NGM/CP electrodes. The inset in each image shows the thickness of the NGM on the NGM/CP electrode (scale bar, 30 μm). (A) CP (heated at 1000 °C in an argon (Ar) atmosphere for 2 h), (B) NGM-1/CP, (C) NGM-2/CP, (D) NGM-3/CP, (E) NGM-4/CP and (F) NGM-5/CP.