For a variety of mechanical energy harvesting as well as biomedical device applications, flexible energy devices are useful which require the development of environment-friendly and robust materials and devices. In this manuscript, we demonstrate a lead-free, facile, low-cost, sol–gel-processed reduced graphene oxide (rGO)/P­(VDF-TrFE) nanocomposite with multipurpose capability demonstration as a piezoelectric nanogenerator (PENG) and hybrid piezoelectric triboelectric nanogenerator (HPTENG) devices. The structural analysis of the materials shows that the interactions between the rGO and P­(VDF-TrFE) matrix help in breaking the centrosymmetry of rGO, resulting in a strong enhancement in the piezoelectric, ferroelectric, and triboelectric properties of composites over pristine P­(VDF-TrFE) films. In the case of PENG, the composite devices showed >22 times improvement in the piezoelectric output voltage over the pristine P­(VDF-TrFE) PENG device with the highest output voltage of 89.7 V for the 0.5 wt % rGO composite. Also, HPTENG devices based on composite films generated an average V OC of 227 V, much higher than the pristine P­(VDF-TrFE)-based devices. Maximum output power densities measured were 0.28 W/cm3 and 0.34 mW/cm3 for hybrid piezoelectric–triboelectric and piezoelectric devices, respectively. The triboelectric devices demonstrated lighting of 45 blue light-emitting diodes directly, connected in series, by harvesting mechanical energy generated by repeated finger tapping. The study highlights the promise of rGO/P­(VDF-TrFE) composites for PENG and HPTENG devices with dramatically improved electrical output.

Conventional ceramic based piezoelectric materials are brittle, which restricts their use in energy harvesting where flexibility is required. Polymer counterparts are flexible but exhibit comparatively reduced electrical output. Here, we provide a method that overcomes these challenges through design of composites comprised of a piezoelectric polymer matrix (PVDF-TrFE) and filler nanoparticles (niobium-doped Pb­(Zr,Ti)­O3). Nanoparticles were functionalized with trimethoxysilylpropyl methacrylate (TMSPM) that promotes linkage between filler and the matrix to achieve effective local dipole–dipole interaction. An enhanced remnant polarization of 9.1 μC/cm2 at 100 Hz and high longitudinal piezoelectric coefficient of 101 pm/V are obtained. Using this composite, a piezoelectric nanogenerator (PENG) is demonstrated that delivers an output of 10 V in response to mechanical bending. Our composite devices show an output which is greater than 200% in comparison to polymeric PVDF-TrFE film based devices. These composites were also implemented in a triboelectric nanogenerator (TENG) device that can power 10 commercial red LEDs. This novel hybrid piezoelectric and triboelectric nanogenerator device has promise for powering wireless sensor nodes and wearable medical devices.

Propelled by the development of the Internet of things and other low-power devices such as in health care or sensing applications, there is growing emphasis on development of energy harvesting devices based on piezoelectric and triboelectric harvesting. We demonstrate a highly flexible and transparent triboelectric nanogenerator (TENG) prepared by incorporating maghemite (γ-Fe2O3) fillers in polyvinylidene fluoride (PVDF) with polyethylene terephthalate (PET) as a triboelectric counterpart for potential application in powering wearable electronic devices. Addition of γ-Fe2O3 fillers in the PVDF matrix results in a power output with an average open circuit voltage of 250 V and short circuit current of 5 μA, which is substantially higher than that from only-PVDF-based TENG. With manually applied force, the lightweight TENG device (area ∼14.5 cm2 and weight ∼1 g) can induce a maximum power output of 0.17 mW with a power density of 0.117 W m–2. In addition, this device is extremely robust with excellent long-term stability for approximately 3000 s. We harvested biomechanical motion in the form of slow and fast foot movement by attaching this device to the sole of footwear. Moreover, the TENG device could continuously supply enough power to light up 108 light-emitting diodes (LEDs) connected in series, without the use of a capacitor and has potential applications in self-powered wearable and portable electronics obviating the use of batteries. Moreover, this device is shown to harvest energy from the rotary pump to charge a 1 μF capacitor to a value of ∼30 V in just 90 s. In addition, a thick magnetic γ-Fe2O3/PVDF nanocomposite film was also successfully tested as a magneto-triboelectric nanogenerator (M-TENG) in noncontact mode showing potential for harvesting of the stray magnetic field.

In this study, we report on the development of triboelectric energy generators (TEGs) made of porous polyvinylidene fluoride (PVDF) and bacterial cellulose (BC) layers and their demonstration as a self-powered...

The growth of good quality bulk single crystals of bismuth selenide by employing a high-temperature vertical Bridgman technique with a specially designed ampoule having a provision for a necking process is reported. Several growth experiments were performed and reproducible results were obtained. The crystal structure and lattice dimensions were confirmed by powder X-ray diffraction (PXRD), the bulk crystalline perfection was assessed using highresolution X-ray diffractometry and the good bulk crystalline perfection with an indication of layered structure was confirmed. Transmission electron microscopy (TEM) was carried out for the grown single crystal and confirmed the layered structure. High-resolution TEM (HRTEM) was also used to further assess the crystalline perfection. The direct measurement of d spacing obtained from HRTEM imaging was found to be in good agreement with the data obtained from PXRD. The thermal behavior was examined by differential scanning calorimetry and a sharp melting was found at 983 K, which revealed the purity of the bismuth selenide. The Seebeck coefficient and electrical and thermal conductivities were measured, and a thermoelectric figure of merit was calculated in order to assess the suitability of the crystal for thermoelectric applications such as refrigeration and portable power generation. Nanoindentation analysis was also performed for the first time.

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We have demonstrated an in situ route to design barium titanate (BT)@polyvinyl pyrrolidone (PVP) nanoparticles (NPs) in PVP/polyvinylidene fluoride (PVDF) blends. Thus, the PVP simultaneously acted as a linker and a part of the polymer matrix. We have hydrothermally synthesized the tetragonal phase of BT NPs (~150 nm). The BT NPs content was varied from 0 to 15 vol%. The resulting polymer nanocomposites generated enormous interfaces because of homogeneously dispersed BT@PVP NPs. Furthermore, the PVP simultaneously tailored the interfacial properties surrounding the BT NPs and bulk of the polymer matrix. Therefore, we achieved an enhanced maximum polarization (P max ) and energy density (U d ) of 27.9 μC cm À2 and 13.4 J cm À3 (2261 kV cm À1 ), respectively, at 7.5 vol% BT NPs loadings. At the same time, PVP/PVDF blends showed P max and U d of only 3.9 μC cm À2 and 4.6 J cm À3 (3369 kV cm À1 ), respectively. This simple approach of in situ nanomaterials modification will lead to development of lowcost and time-efficient dielectric capacitors.

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