*2.2. Characterization and Measurements of NFMs*

The morphology of electrospun NFMs was observed with a scanning electron microscope (SEM, SU8020, Hitachi Ltd., Tokyo, Japan) at an accelerating voltage of 5 kV. ImageJ software (National Institutes of Health, Bethesda, USA) was used to analyze the mean fiber diameter. Tensile testing was done with a tensile test machine (ESM301, Mark-10, Copiague, NY, USA) at room temperature with a cross-head velocity of 10 mm/min. The sample was cut to dumbbell shape (10 mm long and 5 mm wide). The contact angles were recorded employing contact angle goniometer (XG-CAMB1, Xuanzhun co., Ltd, Shanghai, China) by sessile drop method at room temperature. A droplet of deionized water was dropped from the capillary mouth to stop on the membrane surface and the angle of the droplet on the upper surface of the membrane was collected and analyzed. X-ray diffraction (XRD) patterns were done on an X-ray diffractometer (X pert<sup>3</sup> Powder, PANalytical Ltd., Almelo, The Netherlands) and recorded over an angular range from 10◦ to 50◦. Infrared spectra were recorded on a Fourier transform infrared spectrometer (FTIR, VERTEX80v, Bruker Corp., Billerica, MA, USA) from 400 cm−<sup>1</sup> to 1600 cm−1. The polarization-electric field (P-E) hysteresis loops were obtained by precision multiferroic and ferroelectric test systems (Radiant Technologies Inc., Alpharetta, GA, USA ) under a unipolar electric field at a measurement frequency of 10 Hz.

The dynamic piezoelectric coefficient d31 was determined with a homemade measurement system nearly identical to setup described previously [39]. The output voltage of the samples during the process of stretching–relaxing was recorded with a DSP lock-in amplifier (SR830, Stanford Research Systems, Sunnyvale, CA, USA). The piezoelectricity coefficient d33 was measured using a quasi-static d33 measuring instrument (Institute of Acoustics, Chinese Academy of Science, ZJ-4AN, Beijing, China).
