## 4 Results and Discussion  
The schematic diagram shows the fabrication of piezoelectric nanofiber (Figure 1A). A facile and modest electrospinning technique was used to fabricate the electrospun piezoelectric PVDF mats in aligned and random orientation. It has been already reported that the nanofibers (NFs) alignment also play crucial role in determining the crystalline structure and thereby piezoelectric properties of the samples [39]. In order to enhance the piezoelectric \(\beta\) phase nucleation, GO was selected as a filler due to its active interaction with the PVDF matrix as well as its higher dielectric constant. Different concentrations (2, 5 and 7 wt.%) of GO were added with PVDF and electrospun to obtain the random (PGRNF) as well as aligned (PGANF) composite nanofibers. The optimization of the GO concentration has been done by analysing the surface morphologies of the composite nanofibers along with the pristine PVDF NF using the FESEM studies. The FESEM results reveals that the 5 wt.% GO encapsulated PVDF nanofibers showed better fibre morphology (Figure 1D,E) compared to the rest of the samples (Figure 1A-C of the supporting information (SI)). Moreover, the composite nanofiber possesses even rough morphology compared to the quite smooth surface of the pure PVDF nanofibers (Figure 1B,C), confirming the uniform encapsulation of GO throughout the nanofiber without any agglomeration. The pristine and composite nanofibers fabricated in aligned orientation significantly exhibits a highly ordered arrangement compared to their random counterparts, revealing the successful orientation of the NF in an aligned fashion, since our first priority was to fabricate the piezoelectric nanofibers with better morphology for higher piezoelectric performance. In case of nanofiber-based FENGs, the morphology plays a crucial role in determining their performance and hence the beaded nanofibers or distorted fiber morphologies will hinder the material performance [40; 41]. Considering the results obtained, we selected 5 wt.% GO encapsulated PVDF nanofibers as the final material for FENG fabrication. The structural properties and crystallization behaviour of the NFs were confirmed by XRD and FTIR. The XRD pattern (Figure 2A) clearly shows that the PVDF powder possess the characteristic peaks of the non-polar \(\alpha\) phase at 20 = 17.6, 18.3, 19.9 and 26.5 corresponding to the reflection planes (100), (020), (110) and (021) planes [31]. However, a more intense single peak is seen at 20= 20.4-20.6, relating to the (200)/(110) plane for the electrospun nanofiber samples, revealing the polarized \(\beta\) phase formation after electrospinning. It is also observed that the peaks assigned to the \(\beta\) phase are significantly stronger and sharper in the PGANF compared to the randomly oriented NFs. In order to confirm the \(\beta\) phase enhancement due to the nanofiber alignment and GO addition, the relative proportion of the \(\beta\) phase formation is assessed as per Equation (1) provided in the experimental section, and the relative \(\beta\) phase formation is found to be highest in the PGANF (\(\sim\) 67%) and lowest in the pristine PVDF NF (PNF) (\(\sim\) 55.7%). PGRNF (\(\sim\) 59.4%) exhibits an intermediate value for the relative \(\beta\) phase formation. Figure 2B represents the FTIR spectra of PVDF powered, pristine PVDF NF and the GO composite nanofibers in different alignments. The peculiar peaks associated with GO such as the bands at 1038, 1157 and 1356 cm\({}^{-1}\) for the C-O stretching, C-O-C stretching, and the C-O-H deformation, respectively, are visible in both the composite nanofibers, clearly confirming the presence of GO in the NF system (Figure S2 of SI) [37]. The characteristic peaks for the \(\alpha\) phase in PVDF at 491, 515, 530, 615, 746, 796, 839, 978 and 1272 cm\({}^{-1}\) are clearly visible in the PVDF powder sample whereas the absorption bands for \(\beta\) phase at 509, 839 and 1273 cm\({}^{-1}\) started appearing for the electrospun sample (Figure 2B), showing the in situ polarization [37].