# Lotus Root Type Nickel Oxide-Carbon Nanofibers: A Hybrid Supercapacitor Electrode Material
## 3 Results and Discussion
Figure S1a depict the adsorption isotherm, pore distribution, and BET plots for each sample, while Figure S2 summarizes the data in Table S1. The specific surface area for LC, LCN-35, LCN-40, LCN 45, LCN-48, and LN is 124.71 m\({}^{2}\) g\({}^{-1}\), 209.89 m\({}^{2}\) g\({}^{-1}\), 122.91 m\({}^{2}\) g\({}^{-1}\), 133.34 m\({}^{2}\) g\({}^{-1}\), and 205.68 m\({}^{2}\) g\({}^{-1}\), respectiviely. In the LCN series, the specific surface area equaled or exceeded that of the LC sample. This increase can be attributed to the deepening of surface curvature resulting from the heat treatment process of the sample containing the nickel source. Figure S1a presents the adsorption isotherm curve, indicating the pore size and volume distribution within each sample. All samples, including the LC, LCN series, and LN, exhibited a sharp increase in the latter, with the isotherm line rising above 0.9, indicative of a porous structure [24]. Figure S1b illustrates the BJH analysis results, portraying the pore size distribution graph for each sample, spanning a range of 2 to 185 nm. Overall, pore sizes exhibited non-uniformity, with various pore sizes present. LC primarily featured pores around 80 nm, the LCN series displayed an even distribution around 90 nm, and LN exhibited an even distribution around 100 nm. Mostly, it has been reported that a large specific surface area can enhance capacitance performance by facilitating electrolyte diffusion to the redox reaction's active site. Meanwhile, it has been recently reported that specific surface area alone does not exclusively dictate a capacitance increase [25]. Figure 2: SEM images of **(a)** LC, **(b)** LCN-35, **(c)** LCN-40, **(d)** LCN-45, **(e)** LCN-48, and **(f)** LN. The electrochemical properties of the LC, LCN series, and LN samples, classified based on NiO content through TGA and XRD analysis, were analyzed through Cyclic voltammetry (CV), Galvanostatic Charge/Discharge (GCD), and Electric Impedance Spectroscopy (EIS). CV was conducted using a 6 M KOH electrolyte and a three-electrode system. All electrodes were analyzed by selecting a voltage range (0.25-0.5 V) wherein oxidation/reduction reactions occur at a fixed scanning speed of 2 mV s\({}^{-1}\). As the curve area increased, so did the capacitance values [26]. In Figure 4a, the CV curve for LC exhibits a distorted rectangular shape with an unclear redox reaction, whereas the CV curve for LN displayed a distinct redox peak attributed to the reversible Faradaic transition of nickel, indicating typical pseudocapacitive behavior. In Figure 4b, the CV curves for LCN series samples exhibited a distorted rectangular shape coupled to a distinct pseudo-capacitance behavior attributed to the Faradaic redox reaction. The reason for the different positioning of redox peaks among LCN series might be attributed to the synthetic electrochemical interference between NiO and carbon. Among the LCN series, the highest capacitance was calculated for the LCN-45 sample. Figure 4c shows the CV curves within the voltage range of 0.25 to 0.5 V for the LCN-45 sample. CV was also used to measure chemical changes in the electrode at the scanning speed ranging from 2 to 100 mV s\({}^{-1}\). An increase in the scanning speed resulted in an expanded curve area, demonstrating the potential for improved charge storage capability. Figure 4d shows specific capacitance values derived from CV conducted at various voltage scan rates for LCN-45. This highlights the charge storage mechanism of the NiO/C electrode, resulting from faradic redox reactions [27]. The highest capacitance for the LCN-45, measured at 2 mV s\({}^{-1}\), reached 92.52 F g\({}^{-1}\) (0.18504 C g\({}^{-1}\)), with corresponding energy and power density of 2.89 Wh kg\({}^{-1}\) and 46.05 W kg\({}^{-1}\), respectively.