*3.7. Electrochemical Impedance Spectroscopy (EIS)*

EIS is an excellent technique to investigate the electrochemical behaviors of electrodes. Figure 8 shows the replotted typical Nyquist diagram of the G95 and G70L25 electrodes. The Nyquist plot is generally composed of three parts: the first part in the high-frequency region is x-interference at the semicircle start point, which is considered as an effective ohmic resistance; the second part is a semicircular shape in the mid-frequency region, which is assumed to be a charged transfer resistance (Rct) and is equal to the diameter of the semicircle; the last part is a vertical line at the low-frequency region, which is assumed to be ion transport of diffusion resistance at the electrode/electrolyte interface [41]. In both electrodes, diffusion resistance is similar due to the same electrolyte being used. However, Rct of two electrodes is slightly different. The G70L25 electrode showed slightly larger Rct due to the additional 25 wt% LSMCO causing a decrease of the diffusion pathway accompanied by the reduction in surface area, as shown in Figure 3. The steeper slope of the G95 can explain the higher initial specific capacitance in the CV experiment because it means a faster diffusion.

**Figure 8.** Impedance spectra of the G95 and G70L25 electrodes, measured at an AC amplitude of 10 mV, in H2SO4 electrolyte.

The G70L25 electrode exhibits increasing ohmic resistance, which may originate from the low electrical conductivity of LSMCO perovskite oxide.
