In order to have a deeper insight into the electrochemical systems, electrochemical impedance spectroscopy (EIS) was applied from 100 kHz to 10 mHz with an amplitude of 5 mV based on a stabilized open circuit potential (OCP). The Nyquist plots are shown in Figure , both VG-M and VG-S feature nearly vertical curves in low frequency region, indicating their highly capacitive behaviors. Meanwhile, in high frequency region, VG-M shows a smaller resistance than VG-S. Bode plots further reveal the frequency corresponding behaviors of the measured systems. As shown in Figure , VG-M and VG-S exhibit a phase angle of -82.4° and -83.7° respectively at 10 mHz, representing their nearly ideal capacitor behaviors (-90° at low frequency) . In addition, a characteristic frequency (f0) at the phase angle of -45° correlated to the peak frequency in the plot of imaginary capacitance (Figure ) can also be extracted.