## 3 Results and Discussion  
The amount of PANI in composite fibers is a significant factor for the electrochemical performance of the flexible supercapacitors. This work reports composite fibers with different loading amounts of PANI. The PANI/GF prepared with 0.2 g PANI suspension displays the best electrochemical performance, and the following characterizations are obtained from the composite fibers with 0.2 g PANI suspension. Figure 2 shows the TGA profiles of PANI, GF, and PANI/GF. The mass decreasing around 100 \({}^{\circ}\)C in the PANI curve is ascribed to the loss of the H\({}_{2}\)O molecular, and a sharp change at about 500 \({}^{\circ}\)C exists in the TGA curve of the PANI [33; 34; 35; 36]. The pure PANI still maintains 45% weight at 1000 \({}^{\circ}\)C, suggesting the carbonization of phenyl [37]. After the same procedure, the weight loss of the GF and PANI/GF is approximately 35.6% and 39.2%, respectively. Therefore, the corresponding PANI weight ratio of PANI/GF is 18.6%. This result is consistent with that calculated by adding the amount of PANI in the synthesis process. In Figure 3, SEM shows the detailed morphology and architecture of the as-synthesized GF and PANI/GF. The diameter of GF is approximately 160 \(\upmu\)m, and the GF possess a coarse surface with a wrinkled and crumpled architecture (Figure 3a,b). The cross-section morphology of GF exhibits a hierarchical structure (Figure 3c). These morphological and structure features help in the transportation and storage of massive electrons, which can fully utilize the electrical double layer capacitance to improve electrochemical performance. In Figure 3d-f, PANI/GF exhibits approximate surface morphology and architecture at the microscale compared with GF. PANI nanomaterials can be found on the surface and cross section of the composite fibers, and the existence of PANI nanomaterials in the composite fibers changes the hierarchical structure (Figure 3g,h). Energy-dispersive X-ray spectroscopic element distribution maps of C, N, and O clearly verify the uniform distribution of the PANI nanomaterials in the composite fibers, as shown in Figure 3i. Figure 3: Surface (**a,b**) and cross-sectional (**c**) SEM images of GF, and surface (**d–f**) and cross-sectional (**g,h**) SEM images of PANI/GF at low and high magnifications. (**i**) SEM image and EDS element distribution mapping of C, N, and O.  
Figure 2: Thermal gravimetric analysis (TGA) profiles of PANI/GF, GF, and PANI. In Figure 4, there are two characteristic peaks of D and G associated with graphene nanosheets in the Raman curves of GO, GF, and PANI/GF, which are ascribed to the reduction in the size of the in-plane vibration of sp \({}^{2}\) carbon atoms and the K-point phonons of A\({}_{1\text{g}}\) symmetry [38; 39]. The information corresponding to carbon structural changes can be obtained from Raman spectra [40]. For the PANI/GF, besides the D and G bands of GF, the typical peaks at 575 cm\({}^{-1}\) and 1169 cm\({}^{-1}\) relate to the out-of-plane C-H deformation and C-H binding of the quinoid ring, respectively [25; 32; 35]. As shown in Figure 5, the XRD patterns of GO, GF, and PANI/GF are analyzed. GO has a typical diffraction peak (001) located at 11.6\({}^{\circ}\), while GF shows a characteristic peak at 25.5\({}^{\circ}\) related to the (002) plane of stacked graphene sheets [29; 41]. The XRD pattern of PANI/GF and GF indicate similar features, and the (002) diffraction peak reveals the superimposed intensity of GF and PANI, which is due to a typical peak near 25\({}^{\circ}\) for both [25; 42]. Figure 4: Raman curves of GO, GF, and PANI/GF. Figure 5: XRD spectra of GO, GF, and PANI/GF. Additionally, high-resolution XPS of the C1s and N1s peaks can show electronic states between elements. In Figure 6a, the peaks at 284.7, 286, 287, and 288.3 eV were assigned to the C-C in the aromatic rings, C-O of epoxy, C=O, and O=C-OH groups, respectively [43]. Compared with the GO spectrum, the oxygen content in GF and PANI/GF are decreased significantly (Figure 6b,c).