## 3 Results and Discussion
As shown in Figure 6d, the N1s of PANI/GF contains three kinds electronic states of the quinoid mimic (-N=) at 398.5, the benzenoid amine (-NH-) at 399.1, and the nitrogen cationic radical (N\({}^{+}\)) at 400.5 eV, respectively [26; 44]. The XPS results and the XRD spectra indicate the PANI structure in the composite fibers. We evaluated in detail the electrochemical properties of fiber-shaped flexible supercapacitors assembled by covering the gel-state polyvinyl alcohol supported H2 SO4 electrolyte on the as-synthesized graphene-based composite fibers in a two-electrode system. Figure 7a-c show cyclic voltammogram (CV) profiles of the flexible supercapacitors constructed by GF and PANI/GF, which are measured in a narrow electrochemical window of 0-0.8 V at various scan rates of 10 mVs\({}^{-1}\), 20 mVs\({}^{-1}\), 30 mVs\({}^{-1}\), 40 mVs\({}^{-1}\), and 50 mVs\({}^{-1}\). The CV analysis is beneficial to further understanding of the electrochemical behavior and stability during electrochemical measurement processes [45]. As shown in Figure 7a,b, with scan rates increasing, the CV curves of the GF also display an approximate rectangular shape (Figure 7a), indicating apparent electrochemical double-layer capacitive behavior. Figure 7b shows the typical redox peaks and rectangle shape in the CV curves of PANI/GF, and the capacitance of the as-constructed flexible energy storage devices consists of pseudocapacitance and double-layer capacitance [43]. Notably, the area of the CV curves of PANI/GF almost increases with the scan rate in the proportion, revealing that the specific capacitance of PANI/GF is not influenced by the scan rate. Figure 7c displays the CV profiles of GF and PANI/GF at 10 mVs\({}^{-1}\). The CV profiles of PANI/GF display a larger integrated CV area with obvious redox peaks compared with those of GF, indicating faster ion diffusion and higher energy storage properties. The enhanced electrochemical performance of PANI/GF is mainly ascribed to the more internal electroactive sites and the structural stability of PANI/GF [46]. In addition, Figure 7d shows EIS of GF and PANI/GF to evaluate the ion transport mechanisms, which can indicate the contact between the  
Figure 6: XPS C1s spectra of GO (**a**), GF (**b**), and PANI/GF (**c**), as well as XPS N1s curve of PANI/GF (**d**). electrode and electrolyte. In the high frequency region, the x-intercept of PANI/GF is significantly smaller than that of GF. This is because the doping of conductive polymer increases its conductivity and reduces the corresponding equivalent resistance value. The low frequency curve of PANI/GF has a larger slope [9; 10; 47]. The greater slope of the curve of PANI/GF implies better capacitive behavior and fast ion migration capability, improving the electrochemical performance [17; 32; 48]. Figure 8a displays the GCD profiles of GF and PANI/GF with different PANI content at a current density of 0.05 mA cm\({}^{-2}\). PANI/GF prepared with 19% PANI displays the largest capacitance (370.2 mF cm\({}^{-2}\)) at a current density of 0.05 mA cm\({}^{-2}\), which is better than those of PANI/GF1 (196.4 mF cm\({}^{-2}\)), PANI/GF3 (85 mF cm\({}^{-2}\)), and GF (68.8 mF cm\({}^{-2}\)). The specific capacitances derived from the discharge profiles (Figure 8a) are displayed in Figure 8b. The GCD curves of PANI/GF-based fiber-shaped supercapacitors are symmetric and indicate approximately electrochemical behavior at different current densities (Figure 8c), indicating an excellent reversibility and efficient ion/charge transport of the fiber-shaped supercapacitors [48]. The fiber-shaped supercapacitors fabricated by PANI/GF display specific areal capacitances of 370.2, 330.8, 229.6, 145.2, and 96.0 mF cm\({}^{-2}\) (104.8, 93.7, 65.0, and 27.2 F cm\({}^{-3}\) for specific volumetric capacitances) at 0.05, 0.1, 0.2, 0.3, and 0.4 mA cm\({}^{-2}\), respectively, as shown in Figure 8d.