Publications

Switching the wires: p-Type α-Fe2O3 nanowires with ordered oxygen vacancies were synthesized without additional annealing. After a process of annealing in a reductive ambient, a p-type to n-type transition was achieved in a nanowire device (see graph and image). The observation of a p–n transition suggests potential applications for these nanowires in future nanodevice technologies. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2296/2007/z700004_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

The use of triboelectric nanogenerators (TENG) is a highly effective technology for harvesting ambient mechanical energy to produce electricity. In this work, a theoretical model of rotary freestanding TENG with grating structure is constructed, including the conductor‐to‐dielectric and dielectric‐to‐dielectric categories. The finite element simulations are performed to capture the fundamental physics of rotary freestanding TENG. Based on the simulations and derivations of approximate analytical equations, the real‐time output characteristics of TENG with arbitrary load resistance are calculated. Furthermore, the influences of structural parameters of TENG and rotation rate on the output performance are investigated. The theory presented here facilitates a deep understanding of the working mechanism of rotary freestanding TENG and provides useful guidance for designing high performance TENG for energy harvesting applications.

People have shown increasing interests in outdoor activities in recent years. However, the development of smart outdoor clothing for sophisticated health monitoring and multifunctional interaction remains challenging. Here, we develop a thermal-insulating textile based TENG (TI-TENG) composed of multiple functional layers, including the crucial triboelectrification layer, Ag-coated Nylon electrodes, windproof outer textile, and inner textile lining. The triboelectric output properties of the TI-TENG can be enhanced by material modification and structural optimization. The prepared TI-TENG is demonstrated with multifunctionality (e.g., thermal insulation and antibacterial properties) and intelligences (e.g., sensing and energy harvesting function). In addition, an intelligent human motion monitoring as well as an outdoor wireless signal transmission system are developed by employing the TI-TENGs as self-powered wearable sensors and human-machine interactive interfaces, which are ready for one-button call for emergency rescue during the outdoor activities. The available large-scale production of TI-textile also promise TENG with great commercial potentials, offering a new research direction for multifunctional wearable devices toward self-powered sensing, energy harvesting, and human-machine interaction.

Abstract Owing to the advantages of integration and being magnet-free and light-weight, the switched-capacitor-convertor plays an increasing role compared to traditional transformer in some specific power supply systems. However, the high output impedance and switching loss largely reduces its power efficiency, due to imperfect topology and transistors. Herein, we propose a fractal-design based switched-capacitor-convertors with characteristics including high conversion efficiency, minimum output impedance, and electrostatic voltage applicability. As a double-function output power management system for triboelectric nanogenerators, it delivers over 67 times charge boosting and 954 W m −2 power density in pulse mode, and achieves over 94% total energy transfer efficiency in constant mode. The establishment of the fractal-design switched-capacitor-convertors provides significant guidance for the development of power management toward multi-functional output for numerous applications. The successful demonstration in triboelectric nanogenerators also declares its great potential in electric vehicles, DC micro-grids etc.

We report the first flexible hybrid energy cell that is capable of simultaneously or individually harvesting thermal, mechanical, and solar energies to power some electronic devices. For having both the pyroelectric and piezoelectric properties, a polarized poly(vinylidene fluoride) (PVDF) film-based nanogenerator (NG) was used to harvest thermal and mechanical energies. Using aligned ZnO nanowire arrays grown on the flexible polyester (PET) substrate, a ZnO-poly(3-hexylthiophene) (P3HT) heterojunction solar cell was designed for harvesting solar energy. By integrating the NGs and the solar cells, a hybrid energy cell was fabricated to simultaneously harvest three different types of energies. With the use of a Li-ion battery as the energy storage, the harvested energy can drive four red light-emitting diodes (LEDs).

Mechanical vibrations are ubiquitous and enriched energy sources found in everyday environments. However, harvesting these energies, such as from water flowing in the ocean and wind energy, remains a significant challenge due to their irregular, discontinuous, low-vibration frequencies. The triboelectric nanogenerator (TENG) exhibits an effective approach to convert these low frequency mechanical energies into electrical energy. In this work, a new triboelectric and electromagnetic hybrid nanogenerator is fabricated by designing a crankshaft system that consists of a delicate crankshaft and a piston based off the physical vibration characteristics of tidal energy, wind energy, and other rotational energies. This newly designed hybrid nanogenerator demonstrates a high efficiency to harvest rotary energy and a wide range of other rotational energies using the vertical contact–separation mode nanogenerator with much lower friction. The device delivers an output power of 0.08 mW cm−2, and an electromagnetic generator is added to widen the capacity of the device to also collect energies with higher vibration frequencies. Moreover, this hybrid device can be employed in many fields, such as harvesting rotational energy from the wind and ocean. This device can replace the conventional linear motor to avoid or reduce electromagnetic interferences during precise microdevice testing processing.

Nanowires of up to 1 cm in length and approximately 30 nm in diameter were synthesized through a simple chemical vapor deposition process. Scanning electron microscopy (SEM) data showed that these nanowires were well-aligned and grew in the direction along the flow of the carrier gas. Through transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis, the nanowires were found to be composed of a single-crystalline ZnS core and amorphous SiO2 shell. Gold catalyst particles were found at the tips of the nanowires and completely encased by a silica shell. Photoluminescence (PL) measurements were performed on nanowire samples in which the synthesis time was systematically varied to provide information regarding growth dynamics. After a systematic study on the structure, we propose that the core−shell nanowires were formed via a distinct volume and surface diffusion process occurring simultaneously for different chemical species in and on the gold catalyst particle.

We have monitored the phase transformation from a Sandia octahedral molecular sieve Na2Nb2O6–H2O to a piezoelectric NaNbO3 nanowire through in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements at high temperatures. After dehydration at 288 °C, the Na2Nb2O6–H2O becomes significantly destabilized and transforms into NaNbO3 with the increase of time. The phase transformation time is exponentially proportional to the inverse of temperature, for example, ∼105 s at 300 °C and ∼101 s at 500 °C, and follows an Arrhenius equation with the activation energy of 2.0 eV. Real time TEM investigation directly reveals that the phase transformation occurs through a thermally excited atomic rearrangement due to the small difference of Gibbs free energy between two phases. This work may provide a clue of kinetic control for the development of high piezoelectric lead-free alkaline niobates and a deep insight for the crystallization of oxide nanostructures during a hydrothermal process.

As an energy harvesting technology, triboelectric nanogenerator (TENG) plays an increasingly important role in achieving the goal of green, low-carbon, and renewable development. In practical application, a power management circuit that matches the TENG with the load is also necessary. In this article, a synchronized charge accumulation circuit (SCAC) is designed, which improves the output current of TENG and the charging rate of capacitor, achieving efficient energy storage. The experimental results demonstrate that the energy conversion efficiency of SCAC is calculated to be 88.89%, the output peak current reaches the mA level (from 1 to 12 mA), the maximum output peak current is 240 times higher than the original current of TENG, and can light up 1280 parallel LEDs, compared with the original signal, the number of lights is increased by six times. At the same time, when charging the capacitor, the charging rate with SCAC is 10 times that without SCAC, this charging rate can stably and continuously supply power to the hygrothermograph and calculator. This article improves the energy storage rate of TENG and provides an effective method for the energy management and practical application of TENG.