Yi Xi

A nanogenerator for harvesting airflow energy and light energy

Harvesting airflow energy and light energy from the ambient environment to build a self-powered system is attractive and challenging work. In this article, an airflow-induced triboelectric nanogenerator (ATNG) has been fabricated that converts wind energy to alternating electricity. The mechanism of ATNG has also been illustrated. The performance of ATNGs with different sizes was studied, from which we discovered that the ATNG (size: 1 cm × 3 cm, electrode gap: 1.5 mm) could easily collect energy from a gentle wind (5.3 m s−1). Due to the relatively high alternating electricity frequency (179.5–1220.9 Hz), an approximately stable output power (of up to 1.5 mW) was obtained from the ATNG (size: 1 cm × 3 cm, electrode gap: 0.5 mm) with 8.35 μC of charge transferred per second. Meanwhile, the fabricated wind energy harvesting device was used to drive 46 commercial green light-emitting diodes (LEDs) connected in series and charge a 220 μF capacitor to 2.5 V over 50 s. When combined with a dye-sensitized solar cell (DSC), the device can individually and simultaneously harvest wind and light energy. This shows the potential applications of this ATNG in self-powered systems.

Airflow-Induced Triboelectric Nanogenerator as a Self-Powered Sensor for Detecting Humidity and Airflow Rate

Humidity sensors are commonly based on the resistance change of metal oxide semiconductors, which show high sensitivity in low humidity but low sensitivity in high humidity. In this work, we design a novel humidity sensor based on the airflow-induced triboelectric nanogenerator (ATNG) that can serve as a self-powered sensor to detect humidity (especially in high humidity) and airflow rate. The output current or voltage change is investigated under different humidity (20-100% relative humidity) at fixed airflow rate and different airflow rates (15-25 L/min) at a fixed humidity. The working principle of the ATNG-based sensor is illustrated. We find that both output current and voltage can serve as a variable for detecting humidity, while only the output current can serve as a variable for determining airflow rate. Our study demonstrates an innovative approach toward detection of humidity and airflow rate with advantages of self-power, multifunction, low cost, simple fabrication, and high sensitivity.

Composite-hydroxide-mediated approach as a general methodology for synthesizing nanostructures

The composite-hydroxide-mediated (CHM) method is based on the use of molten composite hydroxides as a solvent in chemical reactions at ∼200 °C for the synthesis of a wide range of nanostructures. This review focuses on its recent development with an emphasis on its applications for synthesizing materials of complex oxides, hydroxides, simple oxides, sulfides, selenides, tellurides, fluorides and metals. The principle of this synthesis method is introduced, and the key factors that affect the morphology and size are studied. The advantages of its low synthesis temperature, low pressure and low cost are illustrated through the synthesis of functional wires, rods, belts and other nanostructures.

Enhancing Performance of Triboelectric Nanogenerator by Filling High Dielectric Nanoparticles into Sponge PDMS Film

Understanding of the triboelectric charge accumulation from the view of materials plays a critical role in enhancing the output performance of triboelectric nanogenerator (TENG). In this paper, we have designed a feasible approach to modify the tribo-material of TENG by filling it with high permittivity nanoparticles and forming pores. The influence of dielectricity and porosity on the output performance is discussed experimentally and theoretically, which indicates that both the surface charge density and the charge transfer quantity have a close relationship with the relative permittivity and porosity of the tribo-material. A high output performance TENG based on a composite sponge PDMS film (CS-TENG) is fabricated by optimizing both the dielectric properties and the porosity of the tribo-material. With the combination of the enhancement of permittivity and production of pores in the PDMS film, the charge density of ∼19 nC cm(-2), open-circuit voltage of 338 V, and power density of 6.47 W m(-2) are obtained at working frequency of 2.5 Hz with the optimized film consisting of 10% SrTiO3 nanoparticles (∼100 nm in size) and 15% pores in volume, which gives over 5-fold power enhancement compared with the nanogenerator based on the pure PDMS film. This work gives a better understanding of the triboelectricity produced by the TENG from the view of materials and provides a new and effective way to enhance the performance of TENG from the material itself, not just its surface modification.

Eye motion triggered self-powered mechnosensational communication system using triboelectric nanogenerator

A triboelectric eye blinking sensor with robustly high sensitivity achieves prominence as a human-machine interface. Mechnosensational human-machine interfaces (HMIs) can greatly extend communication channels between human and external devices in a natural way. The mechnosensational HMIs based on biopotential signals have been developing slowly owing to the low signal-to-noise ratio and poor stability. In eye motions, the corneal-retinal potential caused by hyperpolarization and depolarization is very weak. However, the mechanical micromotion of the skin around the corners of eyes has never been considered as a good trigger signal source. We report a novel triboelectric nanogenerator (TENG)–based micromotion sensor enabled by the coupling of triboelectricity and electrostatic induction. By using an indium tin oxide electrode and two opposite tribomaterials, the proposed flexible and transparent sensor is capable of effectively capturing eye blink motion with a super-high signal level (~750 mV) compared with the traditional electrooculogram approach (~1 mV). The sensor is fixed on a pair of glasses and applied in two real-time mechnosensational HMIs—the smart home control system and the wireless hands-free typing system with advantages of super-high sensitivity, stability, easy operation, and low cost. This TENG-based micromotion sensor is distinct and unique in its fundamental mechanism, which provides a novel design concept for intelligent sensor technique and shows great potential application in mechnosensational HMIs.

Hierarchical mesoporous NiFe2O4 nanocone forest directly growing on carbon textile for high performance flexible supercapacitors

Binary metal oxides have been considered as promising electrode materials for high performance pseudocapacitors because they offer higher electrochemical activity than mono metal oxides. The rational design of binder free electrode architecture is an efficient solution to the further enhancement of the performance of electrochemical supercapacitors. Herein, we report the synthesis of a hierarchical mesoporous NiFe2O4 (NFO) nanocone forest directly growing on carbon textile with ultra-high surface area by the hydrothermal method. The NiFe2O4 nanocone forest on carbon textile (NFO-CT) was used as a binder free electrode that exhibited the high capacitance of 697 F g−1 at a scan rate of 5 mV s−1 and was further used for the fabrication of a symmetric solid state supercapacitor. The open space between hierarchical nanocones allows easy diffusion for electrolyte ions and the carbon textile ensures fast electron transfer that leads to the remarkable electrochemical performance. The NFO-CT solid state supercapacitor exhibited the high capacitance of 584 F g−1 at a scan rate of 5 mV s−1 and 93.57% capacitance retention after 10 000 cycles with the advantages of being light weight, thin and having good flexibility. A high energy density of 54.9 W h kg−1 at a power density of 300 W kg−1 was achieved, indicating the excellent energy storage features. Furthermore, three charged supercapacitors in series can light 4 red colored LEDs (2 V, 15 mA) for 2 min.

Harvesting heat energy from hot/cold water with a pyroelectric generator

Waste heat has been regarded as one of the most important renewable and green energy sources, and its widespread reclamation could help to reduce the negative impacts of global warming and the energy crisis. In this work, we designed a pyroelectric generator based on a polyvinylidene fluoride film for harvesting the heat energy from hot/cold water, which widely exists in industrial processes. To achieve practical application, the device simply contacts a hot flow and cold flow alternately. The output open-circuit voltage and short-circuit current reached a maximum of 192 V and 12 μA, respectively, under a temperature change of 80 °C. The output power density can reach 14 μW cm, which is a great improvement for thermoelectric devices. The prepared pyroelectric generator can drive 42 green light-emitting diodes or charge a commercial capacitor (100 μF) to 3.3 V in 90 s. This work provides a promising strategy for efficiently harvesting waste heat from water and presents significant progress in thermoelectric conversion technology.

Flexible full-solid state supercapacitors based on zinc sulfide spheres growing on carbon textile with superior charge storage

Nowadays, it is essential for us to design and fabricate efficient and cost-effective electrode materials for energy conversion and storage systems. Nanostructures are remarkable electrode materials due to their high surface area and large number of active sites. Herein zinc sulfide (ZnS) nanospheres with large surface area are hydrothermally grown on a flexible carbon textile (CT). The specific area and porosity are analyzed in detail under different pressures. The electrode based on the ZnS assembled CT (ZnS-CT) exhibits a high capacitance of 747 F g−1 at a scan rate of 5 mV s−1 in the LiCl aqueous electrolyte. The ZnS-CT is directly used as the binder free electrode for the fabrication of the symmetric flexible full solid state supercapacitor. The ZnS-CT supercapacitor shows excellent electrochemical performance along with light weight, thinness and good flexibility. The ZnS-CT supercapacitor demonstrates good capacitive behavior with a high specific capacitance of 540 F g−1 (areal capacitance of 56.25 F cm−2) at a scan rate of 5 mV s−1 with good rate capability and excellent cycling stability (94.6% retention of initial capacitance after 5000 cycles) at a constant current density of 0.8 mA cm−2. A high energy density of 51 W h kg−1 at a power density of 205 W kg−1 is achieved, indicating excellent ion accessibility and charge storage ability. Furthermore, three charged supercapacitors connected in series can light 4 red color light emitting diodes (2.0 V, 15 mA) for 2 min. ZnS nanospheres with large specific surface area combined with flexible carbon textile substrate offer to be a promising material in energy storage devices with high energy.

Flexible interdigital-electrodes-based triboelectric generators for harvesting sliding and rotating mechanical energy

Triboelectric generators have attracted considerable attention due to their rapidly improved electromechanical conversion efficiency. It is a great challenge to design a triboelectric generator to enable practical and effective operations. In this paper, we present a flexible interdigital-electrodes-based triboelectric generator (FITG) for harvesting sliding and rotating mechanical energy. When a film of flexible interdigital electrodes is placed on a plane, it can be used for harvesting sliding energy. When the film of the flexible interdigital electrodes is rolled into a cylinder, it can be used for harvesting rotating energy. In sliding mode, the maximum open-circuit voltage, short-circuit current and peak power density reach up to 400 V, 120 μA (10 mA m−2) and 13 W m−2, respectively, under a sliding velocity of 3.95 m s−1, which can be used to light tens of light-emitting diodes (LEDs) and to charge a commercial capacitor to 7.2 V within 35 s. The FITG can harvest the mechanical energy of mouse operation and traditional printing. In rotating mode, the maximum output voltage of the generator reaches as high as 1020 V at a rotating speed of 240 rpm. The FITG with interdigital electrodes on a flexible substrate has the advantages of light weight, resistance to wear, multifunction and high output power.

A Flexible micro-supercapacitor based on a pen ink-carbon fiber thread

A highly flexible solid-state micro-supercapacitor based on a pen ink-carbon-fiber (Ink-CF) thread structure was fabricated with excellent electrochemical performance such as a high capacitance of 4.31 mF cm−2 and an energy density of 3.8 × 10−7 W h cm−2 at a power density of 5.6 × 10−6 W cm−2. This fabricated structure shows excellent characteristics such as lightweight, small volume, flexibility and portability. By integrating it with a triboelectric nanogenarator, the micro-supercapacitors could be charged and power 8 commercial LEDs, demonstrating its feasibility as an efficient storage component for self-powered micro/nanosystems.