*3.3. BET*

BET nitrogen adsorption/desorption isotherm measurements were used to determine the surface area, pore diameter, and pore volume. Figure 3 corresponds to type II with unrestricted mono-multilayer characteristics in the classification of adsorption isotherms. The specific surface area has 441.83 and 317.17 m2/g for G95 and G70L25, respectively. The average pore diameter was around 8.5 nm for both G95 and G70L25. The total pore volume is 0.9483 and 0.6935 cm3/g, respectively, for G95 and G70L25.

**Figure 2.** XRD pattern of comparing G70L25, G95, pure graphene nanoplatelets, and pure LSMCO; The DIFFRAC.EVA program was used to identify the data.

**Figure 3.** Nitrogen adsorption and desorption isotherms for (**a**) G95 and (**b**) G70L25.

### *3.4. XPS*

The chemical composition of samples was analyzed by using X-ray photoelectron spectroscopy (XPS). The full XPS spectrum of G95 reveals the presence of C elements along with a small quantity of O elements. The G7025 electrode includes the perovskite LSMCO elements along with the above-mentioned elements. Figure 4b–f shows an XPS spectrum of core levels of C1s and O1s from the G95 and G70L25 electrodes, each of which can be decomposed into three peaks. Binding energy values were analyzed by reference to previous literature [34,35]. The detailed analysis of the C1s spectrum is as follows: sp2 carbon at 248.6 eV (Ca), alcohol and ether groups at ~286.4 eV (Cb), and ester and carboxyl groups at ~289.04 eV (Cc) both for G70L25 and G95 electrodes. The deconvoluted spectrum of G70L25's O1s was shown to be three peaks: a carbon-oxygen double bond at ~531.95 eV (Ob), carbon-oxygen single-bonds in hydroxyl groups at ~533.68eV (Od), and quinine or pyridone groups at ~530.16 eV (Oa). However, for G95, single bonds such as carbon-oxygen ether at 532.33 eV (Oc) or absorbed water or oxygen at 535.23 eV (Oe) appears. The same combination type appears in the G70L25 for two measurements, but different combination types appear in the G95. Additionally, the oxygen content of G70L25 is higher than G95.

**Figure 4.** (**a**) XPS fully scanned spectrum of G95 and G70L25; fitted results of XPS C1s spectra of (**b**) G95 and (**c**) G70L25; fitted results of XPS O1s spectra of (**d**,**e**) G95 and (**f**) G70L25.
