# Ag-Cellulose Hybrid Filler for Boosting the Power Output of a Triboelectric Nanogenerator
## 3 Results and Discussion  
The fabrication process of the NR-CF@Ag TENG is summarized as illustrated in the schematic in Figure 1. The physical appearances of the prepared CF@Ag suspensions were relatively different in color, where the yellow color became darker, indicating that the number of Ag particles formed increased as the AgNO\({}_{3}\) concentration increased. However, when the CF@Ag fillers were incorporated into NR, no significant difference was observed among the prepared NR-CF@Ag_1-3 and NR film, as shown in the digital photographs in Figure 2. This was attributed to the fact that the CF@Ag content in all the composite samples was fixed at 0.2 wt% of NR, which was the optimized ratio, as reported in our previous study [21]. The SEM images in Figure 3 reveal the morphologies of the synthesized CF and the internal (cross-sectioned) structures of the NR, NR-CF, and NR-CF@Ag_1-3 composite films. Cellulose fibers with diameters of a few tens of microns were detected in all the NR-CF composites, including the NR-CF and NR-CF@Ag_1-3 specimens. A small amount of CF was observed in the NR-CF, NR-CF@Ag specimens. This was because the CF content was controlled at 0.20 wt% of NR in all the samples. It was also observed that the fiber sizes were relatively large, which could cause the non-uniform dispersion of the fiber in the NR polymer. Ag nanoparticles were not observed in the SEM images, but the presence of Ag in the CF@Ag specimens was confirmed by the EDX elemental analysis, which was found to increase with increasing AgNO\({}_{3}\) concentrations, as displayed in Figure 4. The Ag contents in the CF@Ag_1, CF@Ag_2, and CF@Ag_3 were 1.37, 2.22, and 4.38 wt%, respectively. Figure 1: Schematic illustration of the fabrication process of NR-CF@Ag TENG. Figure 2: Photographs of all the fabricated TENG including NR, NR-CF, and NR-CF@Ag_1-3. XRD and FTIR spectra of the NR-CF@Ag_1-3 films compared to those of the pristine NR and NR-CF samples are displayed in Figure 5. XRD patterns of all the specimens indicated that the films had an amorphous structure, with the prominent broad diffraction peak at 20-18\({}^{\circ}\) (Figure 5a), similar to those of NR reported elsewhere [38; 39; 40]. No additional filler material peaks were observed, since the amount of CF and Ag nanoparticles were relatively small compared to NR, as discussed above. Figure 4: EDX-SEM elemental analysis confirming the presence of Ag nanoparticles in the CF@Ag_1–3 films. Figure 3: SEM images of the CF and cross-sectional structures of NR, NR-CF, and NR-CF@Ag_1–3 films. The FTIR spectra of all the NR-CF and NR-CF@Ag films were relatively alike and similar to that of pristine NR, as revealed in Figure 5b. The FTIR absorption peaks at 840 and 1662 cm\({}^{-1}\), which corresponded to the out-of-plane bending vibration of the C-H and C=C stretching of cis-1,4-polyisoprene, respectively [41]. The peaks at 1373 and 1444 cm\({}^{-1}\) are associated with the CH\({}_{2}\) deformation, and the multiple peaks at and 2850, 2912, and 2960 cm\({}^{-1}\) correspond to the asymmetric-symmetric stretching vibration of CH\({}_{2}\) and C-H in the NR molecule, respectively [42]. The FTIR absorption peak of cellulose was not clearly observed; however, the broad band centered at around 3320 cm\({}^{-1}\), which corresponded to the stretching vibration of O-H, was found to gain absorption intensity in the NR-CF and NR-CF@Ag films compared to that of the NR sample, indicating the presence of cellulose in the NR-CF-based samples. Among four basic working modes of TENG--vertical contact-separation mode, single-electrode mode, lateral sliding mode, and freestanding mode--the single electrode mode is easy to fabricate. In this mode, the conductive electrode is attached to one triboelectric material, whereas the contact material is free to move. Thus, the wiring between two triboelectrodes is not required; thus, a single electrode TENG is suitable for scavenging mechanical energy from contact electrification effects from various types of materials [43].