Polymer based composites are the backbone of piezoelectric flexible devices, but the use of toxic compounds or requirement of high voltage poling are the Achilles’ heel of this field. Herein, a lead-free, self-poled, flexible, high performance piezoelectric nanogenerator (PENG) is demonstrated based on a poly­(vinylidene fluoride) (PVDF)–ZnSnO3–MoS2 free-standing electrospun nanofiber mat. ZnSnO3 and MoS2 were synthesized by a hydrothermal route, and a composite nanofiber mat was prepared by the electrospinning method. The structural study revealed an enhancement of the electroactive β-phase of PVDF due to inclusion of MoS2. With the optimized concentration of MoS2, the fabricated piezoelectric device can generate open-circuit voltage, short circuit current, and an instantaneous power density of 26 V, 0.5 μA, and 28.9 mW m–2, respectively, with gentle finger tapping. This power density is almost 18 times more than that of PENG made out of pristine PVDF, and the enhancement in the performance is attributed to the synergistic effect of interfacial action due to the piezoceramic (ZnSnO3) and MoS2 in the PVDF matrix. Both ZnSnO3 and MoS2 interact with −CF and −CH dipoles of PVDF to mobilize the bonds to enhance the electroactive phase of PVDF. Biomechanical energy harvesting, sensing of movement of different body parts, and real-time application such as charging capacitors and powering a calculator were demonstrated using the as-fabricated nanogenerator. The device showed reliable performance when tested for 3000 cycles and durability over 50 days of storage. This superior performance and robustness of the device make the PVDF–ZnSnO3–MoS2 based electrospun nanofiber mat an ideal candidate for energy harvesting and sensing applications.

Flexible nanofiber-based composites have been widely explored because of their light weight, high surface area, scalability, and tunable physical and mechanical properties. In this work, we report electrospun 2D-Bi2S3 incorporated PVDF/PPy nanofibers as a versatile platform for ultrasensitive pressure, strain, and temperature sensing. Detailed characterization studies revealed the formation of ultrathin nanofibers and characteristic Raman and IR vibration modes of PPy, 2D-Bi2S3, β-phased PVDF. The fabricated pressure sensor exhibited a sensitivity of 1.51 kPa–1 in the wide linear range of 1–50 kPa and a response time of 0.04 s. The practical ability of pressure sensor was tested by successfully detecting pulse rate of human radial arteries. Further, the BS- PVDF/PPy composite was employed as a strain sensor in the range of 3.1–61.5%, displayed a gauge factor (GF) of 45.45 and a response time of 0.1 s. The wearable sensor was capable of detecting minute changes in hand gestures by recognizing the microstrains applied to the device. The sensing mechanism can be attributed to the excellent piezoelectric property of β- phase PVDF, electron transport property of PPy nanoparticles and tensile strength of the BS nanoparticles embedded in the polymer matrix. When used as a wearable temperature sensor, the versatile device demonstrated a linear range of detection 24- 48 °C with a response time of 0.33 s and Temperature coefficient of resistance (TCR) of −0.1117 °C–1 that can be attributed to the phonon-assisted hoping mechanism. The nanofiber composite dissolved in volatile organic solvent acetone in 5 days with the least impact on the surrounding environment thus making this a promising strategy to develop transient technologies aimed at zero-waste, green electronics.

Polymer-based piezoelectric nanogenerators (PENG) produce satisfactory voltage but low current outputs. Herein, a flexible, multilayered PENG with a high power density is demonstrated based on poly­(vinylidene fluoride) (PVDF)-[0.67­(BiFeO3)-0.33­(BaTiO3)] (BF33BT) electrospun nanofiber mats. With a maximum β-phase and piezoresponse, the optimized composite with 30 wt % BF33BT was used to fabricate the multilayered PENG (MPENG). The MPENG, comprising three layers, shows an open-circuit voltage, short-circuit current, and instantaneous power density of 83 V, 1.62 μA, and 142 mW m–2, respectively, by applying a compressive force of 0.1 kgf at 3 Hz frequency. This power density is almost three times more than that of a single-layer composite-based PENG and 65 times more than that of a single-layer PENG of pristine PVDF. The exceptional piezoresponse is due to the combined effect of the piezoceramic and multilayered structures. The MPENG was used to charge a supercapacitor (0.047 F) up to 1.5 V in 660 s to power a calculator. The device showed no performance degradation for more than 5000 cycles, thus opening up promising avenues for sustainable energy harvesting applications.

Monitoring of personal healthcare requires multifunctional sensors that can sense both chemical and physical stimuli. One of the possible solutions is the fabrication of low-cost, disposable "one time use" functional nanomaterials based sensors that can sense multiple health parameters, and the sensor data can be wirelessly transmitted to the smartphone for further processing. This report is a first demonstration of the direct growth of NiSe 2 on cellulose paper by the solution processed hydrothermal method and its application for a smart personal healthcare monitoring system that includes a noninvasive periodontal diagnosis to monitor oral health by the use of human saliva, a breath analyzer for various breath-related diseases, and a gesture sensor for deaf, dumb, and aurally challenged patients to communicate with the world. The fabricated sensor can be customized for a specific sensing with a dedicated user-friendly Android application which can be accessed remotely by a smartphone. The detailed sensing mechanism of each sensor is explained in terms of charge transport and electron transfer mechanisms. Furthermore, the sensing performance does not fluctuate even after 500 bending cycles for both chemical and physical stimuli, thus enabling low-cost yet robust and reliable monitoring. Successful development of such a versatile platform finds wide applications in the field of smart healthcare, medical devices, and the internet of things.

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