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Innovative material design is one of the most plausible routes to sufficiently enhance triboelectric outputs for self-powered electronic devices. Herein, we reported a g-C3N4embedded P(VDF-TrFE) composite as a strong candidate for boosting the output power via simultaneous harvesting of mechanical and light energies. Visible light-responsive g-C3N4nanosheets are chemically bonded to the ferroelectric P(VDF-TrFE) polymer and increase the ferroelectric polarization and dielectric constant of the composite. Kelvin probe force microscopy and photoluminescence measurements reveal that the enhanced triboelectric output is related to the increased workfunction, the reduced recombination rate of electron-hole pairs, and the band bending-induced photocarrier movement. The up-poled g-C3N4@P(VDF-TrFE) composite-based photoactive triboelectric nanogenerator (PA-TENG) generates a power (power density) of 2.0 mW (0.125 mW/cm2) under a blue light illumination, which is 10 times larger than PA-TENG under a dark condition and 54 times larger than bare P(VDF-TrFE)-based TENG. The output power is continued for at least up to 1.5 months in ambient conditions and is enough to power light-emitting diodes, a thermo-hygrometer, and a digital watch, which would be quite useful for individuals in the dark underground. This work provides a novel approach to boost the triboelectric output via a coupling of photocarrier and ferroelectric dipole and a useful hint to realize self-powered small electronics for safety issues in dark environments like caves and tunnels.

We report the microstructure and the ferroelectric properties of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] films grown under various humidity conditions and synthesis times by using a sol-gel method. When the synthesis time under a humid condition was short (approximately 30 min), the moisture in the environment affected only the surface morphology without any loss of ferroelectricity for the P(VDF-TrFE) films. In contrast, when the synthesis time was long (approximately 90 min), the moisture strongly affected the microstructure and the ferroelectric properties of P(VDF-TrFE). The transparent P(VDF-TrFE) film became opaque at high humidity. Scanning electron microscopy revealed numerous pores on the surface of and inside the film. The pores reduced the Young’s modulus considerably from 4.15 to 0.97 GPa for the films grown at 20 and 80% relative humidity, respectively. In addition, the ferroelectric hysteresis loop disappeared at humidities above 60%. This work provides upper limits for the humidity and the synthesis time for the growth of high-quality P(VDF-TrFE) films by using a sol-gel method.

With the rapid development of the Internet of Things and artificial intelligence, smart home has emerged to fulfill the security, convenience, and energy-saving issues of modern life. Self-power, multifunctional, and sensitive sensors are one of the key components for the popularization of smart home systems. Herein, a flexoelectric mica crystal is shown to augment the finger touch-driven triboelectric output enough to operate a wireless and multichannel smart home controller. The smart home controller consists of concave mica films, a hand-grip-type vertical mouse, and an Arduino controller. Strain-gradient-dependent contact potential difference measurement and density functional theory calculation show that flexoelectric charge shifts the workfunction and concave bending reduces the effective electron mass in a mica. A portable hand-grip-type flexoelectrically augmented triboelectric nanogenerator (Flexo-TENG) demonstrates the wireless communication of message in real time and the selective operation of home appliances with various functions via a simple finger touch. This work provides important ingredients for the enhanced triboelectric output via flexoelectricity, and for the realization of a convenient, multifunctional, cost-effective, and adaptable smart home control system without batteries.

Biomaterials and bioproducts have unique characteristics of being renewable, abundant, biodegradable, and having rough surfaces. In order to implement them into highly efficient triboelectric nanogenerator (TENG) applications, the contact electrode should be cheap, flexible, able to withstand outdoor environments, and have a rough surface. Here, microwave-welded single-walled carbon nanotubes (SWCNTs) are shown to effectively harvest the mechanical vibrational energy from biomaterials and bioproducts. Selective and flash microwave heating provides firm welding of SWCNTs to a polycarbonate substrate without significant losses in flexibility, transparency, and electrical conductivity. Microwave-welded SWCNT electrodes were successfully deployed as single-electrode TENGs to harvest energy from cellulose film, hanji paper, and cherry leaf. The cellulose- and paper-based TENGs showed the quite stable triboelectric outputs even after excessive contacts and a long period of time. The leaf-based TENG showed the significantly modified triboelectric outputs due to the moisture evaporation induced shrinkage and roughness of the surface. The SWCNT electrode generated ca. ten- and two-fold larger voltage and current, respectively, than those obtained using an indium-tin oxide (ITO) electrode. Using a fan-shaped leaf-based TENG, multiple light emitting diodes and a cellular phone were successfully powered without a battery. This work implies that the microwave-welded SWCNT electrode with rough pored surface and strong resistance against environmental shocks could be a good candidate for the outdoor biomaterials and indoor bioproducts implemented TENGs to harness random- and low-frequency vibrational energy.

Water waves in wild sea have unique characteristics of being huge, random, irregular, and of low frequency. To effectively harvest such vibrational energy, any devices should be light enough to float, sensitive even to small amplitudes, durable against harsh environmental conditions, easily replaceable after long-term use, and easily linked to form a network. Here, a floating buoy-based triboelectric nanogenerator (FB-TENG) is demonstrated to effectively harvest the vibrational energy with full satisfaction of these requirements. The FB-TENG consisted simply of a power generation unit, which was packed in an acrylic case, and a height-adjustable support, which was attached to a floating buoy. Even for the small amplitude of water waves, the height-adjustable support provides vigorous vibration at the power generation unit; which was sufficient to power 30 light-emitting diodes (LEDs), and operate a digital thermo-hygrometer and an anenometer. Under saltwater (salinity of 40%), thermal shocks (temperature range of 4–60°C), and strong ultraviolet irradiation (power of 10 W), the FB-TENG generates stable electric power by virtue of the acrylic packing of the power generation units. The FB-TENG also generates electric power from the various and mixed amplitudes and frequencies of water waves coming from all directions. Furthermore, the FB-TENG can easily be integrated into a network for high-power generation. This work provides a significant step forward in the harvesting of the blue energy of water waves, and the realization of self-powered sea mark and weather monitoring systems in wild sea.

In operandotechniques have emerged to elucidate the fundamental mechanism of triboelectrification via relevant physical quantity measurement during the physical contact of two materials. Here, a correlation between frictional heat and triboelectric charge is reported in a metal-polymer triboelectric nanogenerator through the in operandotemperature measurement. Fluorine-doped tin oxide (FTO) metal is slid back-and-forth under different contact pressures across polydimethylsiloxane (PDMS) polymers having different degrees of crosslinking, i.e., mixing ratio. Both the triboelectric charge and temperature variation increase and become saturated with different time-constants. Notably, the saturated triboelectric charge increases, while the saturated temperature decreases, with increasing mixing ratio. In contrast, both saturated triboelectric charge and temperature increase with increasing contact pressure. X-ray photoemission spectroscopy reveals that chemical bonds are modified inhomogeneously at the surface, and that charged materials are transferred from PDMS to FTO in accordance with the mixing ratio- and sliding time-dependent triboelectric charges. Frictional heat plays a distributive role in bond rupture and temperature variation, depending on the activation energy and frictional coefficient of PDMS. In operandotemperature variation measurement provides important information on the specific bonds for triboelectrification and detailed charge-transfer process during physical contact.

While ferroelectric polymer-based triboelectric nanogenerators (FE-TENGs) have been regarded as one of the most efficient mechanical energy harvesting devices, their fundamental mechanism is still debated. Here, we propose a dipole charge-shifted work function as the main origin of enhanced performance rather than a piezoelectric charge-increased electrostatic induction. P(VDF-TrFE) FE polymers were contacted with and separated from an ITO metal electrode and another P(VDF-TrFE) FE polymer under the variation of poling voltage, pressure, and temperature. The power outputs of the ITO-P(VDF-TrFE) and P(VDF-TrFE)-P(VDF-TrFE) FE-TENGs increased with poling voltage and pressure, but decreased with temperature; these behaviors are consistent with that of dipole charge rather than piezoelectric charge. Surface-sensitive spectroscopy and microscopy investigations suggested that electrons should be transferred, depending on the dipole direction, in the ITO-P(VDF-TrFE), whereas electrons and material should be transferred, depending on Young’s modulus, in the P(VDF-TrFE)-P(VDF-TrFE). The dipole- and piezoelectric charge-induced electric field plays a crucial role in the overlapped electron cloud model for the triboelectrification of FE-TENGs.