Unveiling a robust and high-temperature-stable two-dimensional ZnAl layered double hydroxide nanosheet based flexible triboelectric nanogenerator.

Triboelectric nanogenerators have the ability to harvest low- and mid-frequency vibrational energy from the environment; however, achieving stable performance of the nanogenerator device in high-temperature conditions remains challenging. In this work, a flexible and temperature-stable polyvinyl alcohol (PVA)/layered double hydroxides (LDH) nanocomposite-based triboelectric nanogenerator was developed to harvest unexploited vibrational energy for the first time. Crystalline ZnAl LDH nanosheets grown by a hydrothermal route are used to fabricate the high-performance flexible nanogenerator. The ZnAl LDH exhibits fire-retardancy and high-temperature stability (∼500 °C). A triboelectric nanogenerator based on the ZnAl LDH-PVA nanocomposite generated a very high output voltage of 60 V even under a low vertical pressure of 1 kgf. Surprisingly, the developed device shows ultra-stable output performance even up to a temperature of 200 °C. In addition, a ZnAl LDH-nanosheet-reinforced PVA nanocomposite film shows very high dielectric constant of about 5 × 105 at the low-frequency side. The tremendous increase in the output voltage and stable performance are discussed in terms of the high dielectric constant and synergistic effect of the LDH nanosheets and PVA. Furthermore, the device was also used to monitor human body movements such as finger and wrist bending to develop self-powered sensors.

Paddy-Straw-Derived Graphene Quantum Dots Reinforced Vertical Aligned Zinc Oxide Nanosheet-Based Flexible Triboelectric Nanogenerator for Self-Powered UV Sensors and Tribotronics Application.

Herein, we report the paddy-straw-derived graphene quantum dots (GQDs)-reinforced vertical-aligned two-dimensional (2D) ZnO nanosheet-based flexible triboelectric nanogenerator (FTNG) for scavenging mechanical energy for the first time. The GQDs (diameter ∼5-7 nm) and ZnO nanosheets were grown using a hydrothermal method and seed-assisted chemical route, respectively. The X-ray diffraction and electron microscopy results confirmed the formation of a hexagonal wurtzite crystal structure and vertical-aligned morphology of 2D ZnO nanosheets. The GQD-reinforced ZnO-nanosheet-based FTNG device generated an output voltage of 40 V and current density of 2 µA/cm2, respectively, whereas pristine vertical-aligned ZnO-nanosheet-based device produced an output voltage of only 16 V and a current density of 0.36 µA/cm2, respectively. The performance of the GQD-ZnO nanosheet FTNG device was also measured under illumination of the UV light, and a drastic increase in the output voltage is observed as compared to a pristine ZnO-nanosheet-based device. The GQD-reinforced ZnO nanosheets exhibited very high dielectric constant of 40 at low frequency side. The current finding suggested a novel approach to efficiently harvest mechanical energy and a novel method to fabricate the self-powered UV sensors and tribotronics devices using agrowaste-derived GQDs and ZnO nanosheets.

Humidity Sustainable Hydrophobic Poly(vinylidene fluoride)-Carbon Nanotubes Foam Based Piezoelectric Nanogenerator.

Light weight lead free, polymer, and carbon nanotubes based flexible piezoelectric nanogenerators have prompted widespread concern for harvesting mechanical energy and powering next generation electronics devices. Herein, lightweight polyvinylidene fluoride (PVDF)-carbon nanotube (CNT) foam was prepared to fabricate humid resistant hydrophobic flexible piezoelectric nanogenerator to converts mechanical energy into electricity for the first time. Hydrophobic piezoelectric PVDF-CNT foam with density of 0.15 g/cm3 was prepared by solution route. PVDF-CNT foam exhibited crystalline and a well-defined chain likes structure with 65% fraction of ß-phase. Self-poled PVDF-CNT foam shows piezoelectric charge coefficient (d33) of 9.4 pC/N. High d33 of PVDF-CNT foam is caused by dipole alignment induced by local electric field of CNT in the microcellular structure of PVDF. The developed foam exhibits ultrahigh dielectric constant (ε') ∼ 3048 at 150 Hz. Flexible piezoelectric PVDF-CNT foam based nanogenerator was fabricated, which generates high output voltage ∼12 V and current density of 30 nA/cm2 at small compressive pressure of 0.02 kgf. Piezoelectric output performance was measured under different humid condition and an output voltage up to 8 V was achieved even under 60% RH condition. PVDF-CNT foam exhibited hydrophobic behavior and high surface water contact angle of 139°. Such high output voltage even under small pressure, without applying electrical poling and under humid condition was originated though CNT induced self-alignment of electric dipoles in PVDF polymer. These excellent performances of developed foam based device confirmed its potential application in organic based ultrasensitive self-powered nanosensors and nanosystems.

A high performance flexible two dimensional vertically aligned ZnO nanodisc based piezoelectric nanogenerator via surface passivation.

Herein, we present the growth of pristine vertically aligned flexible two dimensional (2D) pure ZnO nanodiscs via a simple seed assisted solution route and their use in the fabrication of a piezoelectric nanogenerator. The preferred growth direction and morphology of wurtzite ZnO nanodiscs were investigated using X-ray diffraction and field emission scanning electron microscopy (FESEM) studies. A flexible piezoelectric nanogenerator was fabricated using the vertically aligned ZnO nanodiscs as the active piezoelectric material and a carbon nanotube-polydimethylsiloxane (CNT : PDMS) film as the top electrode. This unique 2D-type ZnO nanodisc-based nanogenerator generated a direct current (DC) type output voltage and current density of about 2.5 V and 30 nA cm-2 under compressive vertical strain, respectively. Significant enhancement of the piezoelectric output voltage from the flexible nanogenerator based on the vertically aligned two dimensional (2D) zinc oxide (ZnO) nanodiscs was achieved via thermal annealing. An output voltage and current density of 17 V and 150 nA cm-2 were detected from the thermally annealed 2D ZnO nanodisc based nanogenerator which is approximately 8 times higher (voltage) than that from the pristine nanogenerator. It is proposed that the output performance of the vertically aligned ZnO nanodisc based nanogenerators increases due to surface passivation and reduction of oxygen vacancies.