Yuxin Nie

Surface free-carrier screening effect on the output of a ZnO nanowire nanogenerator and its potential as a self-powered active gas sensor

The output of a piezoelectric nanogenerator (NG) fabricated using ZnO nanowire arrays is largely influenced by the density of the surface charge carriers at the nanowire surfaces. Adsorption of gas molecules could modify the surface carrier density through a screening effect, thus, the output of the NG is sensitive to the gas concentration. Based on such a mechanism, we first studied the responses of an unpackaged NG to oxygen, H2S and water vapor, and demonstrated its sensitivity to H2S to a level as low as 100 ppm. Therefore, the piezoelectric signal generated by a ZnO NWs NG can act not only as a power source, but also as a response signal to the gas, demonstrating a possible approach as a self-powered active gas sensor.

Biomolecule-adsorption-dependent piezoelectric output of ZnO nanowire nanogenerator and its application as self-powered active biosensor.

Self-powered active biosensor has been realized from ZnO nanowire (NW) nanogenerator (NG). The piezoelectric output generated by ZnO NW NG can act not only as a power source for driving the device, but also as a biosensing signal. After immersing in 10(-3) g ml(-1) human immunoglobulin G (IgG), the piezoelectric output voltage of the device under compressive deformation decreases from 0.203±0.0176 V (without IgG) to 0.038±0.0035 V. Such a self-powered biosensor has higher response than transistor-type biosensor (I-V behavior). The response of self-powered biosensor is in a linear relationship with IgG concentration (logarithm, 10(-7)-10(-3) g ml(-1)) and the limit of detection (LOD) on IgG of the device is about 6.9 ng ml(-1). The adsorption of biomolecules on the surface of ZnO NWs can modify the free-carrier density, which vary the screening effect of free-carriers on the piezoelectric output. The present results demonstrate a feasible approach for actively detecting biomolecules by coupling the piezotronic and biosensing characteristics of ZnO NWs.

CuO/PVDF nanocomposite anode for a piezo-driven self-charging lithium battery

An integrated self-charging power cell (SCPC) is realized from a CuO/PVDF nanocomposite piezo-anode. The efficiency of the integrated SCPC is higher than that of the non-integrated SCPC. The intimate and large contact between CuO and PVDF results in an effective use of the piezoelectric field in the internal piezo-electrochemical process.

PVDF–PZT nanocomposite film based self-charging power cell

A novel PVDF-PZT nanocomposite film has been proposed and used as a piezoseparator in self-charging power cells (SCPCs). The structure, composed of poly(vinylidene fluoride) (PVDF) and lead zirconate titanate (PZT), provides a high piezoelectric output, because PZT in this nanocomposite film can improve the piezopotential compared to the pure PVDF film. The SCPC based on this nanocomposite film can be efficiently charged up by the mechanical deformation in the absence of an external power source. The charge capacity of the PVDF-PZT nanocomposite film based SCPC in 240 s is ∼0.010 μA h, higher than that of a pure PVDF film based SCPC (∼0.004 μA h). This is the first demonstration of using PVDF-PZT nanocomposite film as a piezoseparator for SCPC, and is an important step for the practical applications of SCPC for harvesting and storing mechanical energy.

The conversion of PN-junction influencing the piezoelectric output of a CuO/ZnO nanoarray nanogenerator and its application as a room-temperature self-powered active H2S sensor

Room-temperature, high H2S sensing has been realized from a CuO/ZnO nanoarray self-powered, active gas sensor. The piezoelectric output of CuO/ZnO nanoarrays can act not only as the power source of the device, but also as the H2S sensing signal at room temperature. Upon exposure to 800 ppm H2S at room temperature, the piezoelectric output of the device greatly decreased from 0.738 V (in air) to 0.101 V. The sensitivity increased to 629.8, much higher than bare ZnO nanoarrays. As the device was exposed to H2S, a CuO/ZnO PN-junction was converted into a CuS/ZnO Ohmic contact, which greatly increased the electron density in the nanowire and enhanced the screen effect on the piezoelectric output. Our results can stimulate a research trend on designing new composite piezoelectric material for high-performance self-powered active gas sensors.

Detecting Liquefied Petroleum Gas (LPG) at Room Temperature Using ZnSnO3/ZnO Nanowire Piezo-Nanogenerator as Self-Powered Gas Sensor.

High sensitivity, selectivity, and reliability have been achieved from ZnSnO3/ZnO nanowire (NW) piezo-nanogenerator (NG) as self-powered gas sensor (SPGS) for detecting liquefied petroleum gas (LPG) at room temperature (RT). After being exposed to 8000 ppm LPG, the output piezo-voltage of ZnSnO3/ZnO NW SPGS under compressive deformation is 0.089 V, much smaller than that in air ambience (0.533 V). The sensitivity of the SPGS against 8000 ppm LPG is up to 83.23, and the low limit of detection is 600 ppm. The SPGS has lower sensitivity against H2S, H2, ethanol, methanol and saturated water vapor than LPG, indicating good selectivity for detecting LPG. After two months, the decline of the sensing performance is less than 6%. Such piezo-LPG sensing at RT can be ascribed to the new piezo-surface coupling effect of ZnSnO3/ZnO nanocomposites. The practical application of the device driven by human motion has also been simply demonstrated. This work provides a novel approach to fabricate RT-LPG sensors and promotes the development of self-powered sensing system.

Realizing room-temperature self-powered ethanol sensing of Au/ZnO nanowire arrays by coupling the piezotronics effect of ZnO and the catalysis of noble metal

By coupling the piezotronics effect of ZnO and the catalysis of noble metal, room-temperature self-powered active ethanol sensing was obtained from Au/ZnO nanowire arrays. The piezoelectric output generated by Au/ZnO nanowire arrays acts not only as power source, but also as response signal to ethanol at room temperature. Upon exposure to 1200 ppm ethanol, the piezoelectric output of Au/ZnO nanowire arrays decreased from 1.54 V (in air) to 0.43 V. Our research can stimulate a research trend on the development of the next generation of room-temperature gas sensors and will further expand the scope for self-powered nanosystems.

Template-free assembly of α-Fe2O3–SnO2 core–shell nanorod arrays on titanium foil and their excellent lithium storage performance

α-Fe2O3–SnO2 core–shell nanorod arrays on titanium foil have been assembled by a facile template-free method. At a rate of C/5 (5 h per charging cycle), their reversible capacity is ∼1059.9 mA h g−1, higher than that of pure α-Fe2O3 nanorod array electrodes (∼858.3 mA h g−1). After 30 cycles, the capacity is maintained at 807.1 mA h g−1. Such high performances can be attributed to the synergistic effect between nanostructured SnO2 and α-Fe2O3 and the nanoarray structures. α-Fe2O3 nanostructures with high electrochemical activity can activate the irreversible capacity of SnO2, and the nanoarray structures can provide good contact, short electron transporting paths, a high surface-to-volume ratio and open space in the system. These results indicate that one-dimensional nanocomposite arrays on metal foils are good candidates for high performance lithium ion batteries.

Synthesis of CdS nanorod arrays and their applications in flexible piezo-driven active H2S sensors

A flexible piezo-driven active H2S sensor has been fabricated from CdS nanorod arrays. By coupling the piezoelectric and gas sensing properties of CdS nanorods, the piezoelectric output generated by CdS nanorod arrays acts not only as a power source, but also as a response signal to H2S. Under externally applied compressive force, the piezoelectric output of CdS nanorod arrays is very sensitive to H2S. Upon exposure to 600 ppm H2S, the piezoelectric output of the device decreased from 0.32 V (in air) to 0.12 V. Such a flexible device can be driven by the tiny mechanical energy in our living environment, such as human finger pinching. Our research can stimulate a research trend on designing new material systems and device structures for high-performance piezo-driven active gas sensors.