We demonstrate a practical and efficient hybrid triboelectric-piezoelectric energy harvesting structure that consists of a nanopatterned and/or metal-deposited polymer film and a piezoelectric elastomeric sponge. When a polymer (here, polycarbonate (PC)) and an elastomer (here, polydimethylsiloxane (PDMS)) make contact with and detach from each other, triboelectric energy can be harvested. In this case, the PC surface can be nanopatterned by continuous dynamic nanoinscribing and/or coated by a metal (here, Cu) layer for enhanced performance. When a piezoelectric material (here, lead zirconate titanate (PZT)) and sugar powder are mixed with PDMS, and the sugar is later dissolved, a porous piezoelectric elastomeric sponge (PES) can be fabricated. When a PC film and a PES make contact with and detach from each other, both triboelectric and piezoelectric energies can be simultaneously harvested. We systematically study the effect of PES and Cu thicknesses and dynamic nanoinscribed nanopattern on the energy harvesting performance of the hybrid triboelectric–piezoelectric nanogenerator (HTPENG). The performance of the HTPENG can be improved by using the PES of optimal thickness, and by applying the nanopattern and Cu layer. The HTPENG can be utilized in many systems where wireless self-powering is desired, such as wearable devices, flexible sensors, and skin electronics.

In this paper, we develop a cylindrical triboelectric nanogenerator (TENG) for omnidirectional wind energy harvesting, by designing a slanted slit structure along the outer surface of the cylinder. The TENG consists of an inner cylinder based on Al film and a 3D printed outer structure. Wind blowing through the slits of the outer structure causes the inner cylinder to rotate in the slanted direction, and the contact-separation between the Al cylinder and polytetrafluoroethylene attached to the inner surface of the outer structure generates an output voltage. The performance of the harvester with different inner cylinder diameters under various wind speeds is experimentally studied. The results indicate that the TENG with a smaller Al cylinder is suitable for a self-powered wind speed sensor while that with a larger cylinder is optimal for efficient energy harvesting. In addition, the TENG is capable of harvesting wind energy in all directions. Its potential utility to be used as a supplementary power source for small electronic devices is verified through various experiments. Based on its compact size, simple design, and ease of manufacturing, the proposed TENG can be used as a low-cost, portable harvester.

In this study, we demonstrated a triboelectric nanogenerator composed of a vertical column, and a cylindrical shell, for omnidirectional wind energy harvesting. With a simple structure using a metal wire, the height between the two triboelectric materials can be maintained, and the Al coated shell can also be electrically connected to the electrode. When the shell is deformed by wind, its Al layer and Polytetrafluoroethylene (PTFE) on the outside of the column can be triboelectrically charged. Thus, wind energy can be harvested through a triboelectric energy conversion mechanism. In particular, due to the high flexibility of the shell, the nanogenerator operates even at wind speeds as low as 1 m/s. Although the output voltage is asymmetrical depending on the wind direction due to the metal wire, it was experimentally confirmed that the device can harvest wind energy from all directions. The measured output RMS power was approximately 15 μW at a wind speed of 6 m/s.

A major goal of triboelectric generator is to improve its power output by identifying and optimizing the factors contributing to the harvesting capability. In this study, we developed a double-contact triboelectric nanogenerator (DC-TENG) capable of two contact and separation pairs by adding an additional air-gap layer. The voltage and current output was characterized as a function of the contact speed, position, stroke time (ST), standstill time (SST), and the existence of two air-gaps. The voltage and current output increased non-linearly with decreasing the times. The DC-TENG produced the maximum voltage and current output when the ratio of ST to SST was 7 to 3. Our prototype resembling a pavement block was capable of lighting 144 LED lights by producing a maximum output of 650 V, 25 μA at a pressure of 0.5 kgf/cm².