Single- and few-layer MoS2 nanoflowers are first discovered to have a piezo-catalyst effect, exhibiting an ultra-high degradation activity in the dark by introducing external mechanical strains. The degradation ratio of the Rhodamine-B dye solution reaches 93% within 60 s under ultrasonic-wave assistance in the dark.

ABSTRACT:We have developed a simple, cost-effective, and scalable approach to fabricate a piezoelectric nanogenerator (NG) with stretchable and flexible characteristics using BaTiO 3 nanotubes, which were synthesized by the hydrothermal method. The NG was fabricated by making a composite of the nanotubes with polymer poly(dimethylsiloxane) (PDMS). The peak open-circuit voltage and short-circuit current of the NG reached a high level of 5.5 V and 350 nA (current density of 350 nA/cm 2 ), respectively. It was used to directly drive a commercial liquid crystal display. The BaTiO 3 nanotubes/PDMS composite is highly transparent and useful for a large-scale (11 × 11 cm) fabrication of lead-free piezoelectric NG. NGs fabricated by PZT nanofibers 16 and nanowires 17 have been demonstrated to provide output voltages of 1.63 and 0.7 V, respectively. However, the component lead in PZT has the concern of toxic effect toward human health and environmental problems.18 Consequently, it has motivated the search for perovskite piezoelectric materials with lead-free properties comparable to PZT with a reduced environmental impact. BaTiO 3 thin-film-based NG fabricated by soft lithographic printing technique can produce an output voltage of 1.0 V and current density of 0.19 μA/cm 2 . 19 Although the abovementioned result is outstanding, there is no report about using BaTiO 3 nanotubes to fabricate a NG. As the size of the piezoelectric materials is reduced to the nanoscale, the conversion efficiency of mechanical energy has been found to be improved dramatically, attributing to the larger piezoelectric coefficients and deformations, which are proportional to the generated potential. 20−22 In this letter, lead-free BaTiO 3 nanotubes were used to fabricate the piezoelectric NG. A large number of high-quality BaTiO 3 nanotubes were synthesized through a hydrothermal method. By forming a composite of BaTiO 3 nanotubes with poly(dimethylsiloxane) (PDMS) polymer, flexible and transparent NG was developed easily after applying a direct poling process. Under periodic external mechanical deformation by a linear motor, we obtained very stable and high output piezoelectric signals, that is, an open-circuit voltage (V oc ) of 5.5 V and short-circuit current (I sc ) exceeding 350 nA. The NG was further demonstrated to be easily scaled-up over 11 × 11 cm and can continuously drive a commercial LCD under the biomechanical movements of a human skin.The NG mainly consists of five layers as schematically shown in Figure 1a. The deposited Au/Cr films act as top and bottom electrodes, and the BaTiO 3 nanotubes and PDMS composite mixed with a 3 wt % ratio serve as the source of piezoelectric potential generation under external stress. The polystyrene (PS) substrate and pure PDMS worked as the supporting and protecting layers to sustain the conformation of NG. Figure 1b shows the cross-sectional scanning electron microscope (SEM) image of a 300 μm thick BaTiO 3 nanotubes/PDMS composite, which demonstrates the flexible property of the developed NG. ...

We demonstrate a thermoelectric nanogenerator (NG) made from a single Sb-doped ZnO micro/nanobelt that generates an output power of about 1.94 nW under a temperature difference of 30 K between the two electrodes. A single Sb-doped ZnO microbelt was bonded at its ends on a glass substrate as a NG, which can give an output voltage of 10 mV and an output current of 194 nA. The single Sb-doped ZnO microbelt shows a Seebeck coefficient of about -350 μV/K and a high power factor of about 3.2 × 10(-4) W/mK(2). The fabricated NG demonstrated its potential to work as a self-powered temperature sensor with a reset time of about 9 s.

We demonstrated a flexible strain sensor based on ZnSnO(3) nanowires/microwires for the first time. High-resolution transmission electron microscopy indicates that the ZnSnO(3) belongs to a rhombohedral structure with an R3c space group and is grown along the [001] axis. On the basis of our experimental observation and theoretical calculation, the characteristic I-V curves of ZnSnO(3) revealed that our strain sensors had ultrahigh sensitivity, which is attributed to the piezopotential-modulated change in Schottky barrier height (SBH), that is, the piezotronic effect. The on/off ratio of our device is ∼587, and a gauge factor of 3740 has been demonstrated, which is 19 times higher than that of Si and three times higher than those of carbon nanotubes and ZnO nanowires.

We demonstrated the first application of a pyroelectric nanogenerator as a self-powered sensor (or active sensor) for detecting a change in temperature. The device consists of a single lead zirconate titanate (PZT) micro/nanowire that is placed on a thin glass substrate and bonded at its two ends, and it is packaged by polydimethylsiloxane (PDMS). By using the device to touch a heat source, the output voltage linearly increases with an increasing rate of change in temperature. The response time and reset time of the fabricated sensor are about 0.9 and 3 s, respectively. The minimum detecting limit of the change in temperature is about 0.4 K at room temperature. The sensor can be used to detect the temperature of a finger tip. The electricity generated under a large change in temperature can light up a liquid crystal display (LCD).

This study is the first to demonstrate that ferroelectric R3c LiNbO 3 -type ZnSnO 3 nanowires (NWs), through the piezocatalysis and piezophototronic process, demonstrate a highly efficient hydrogen evolution reaction (HER). The polarization and electric field curves indicate that ZnSnO 3 NWs exhibit typical ferroelectric hysteresis loops. Time-resolved photoluminescence spectra reveal that the relaxation time increases with the increasing concentration of oxygen vacancies. Moderated 3H-ZnSnO 3 NWs (thermally annealed for 3 h in a hydrogen environment) have the longest extended carrier lifetime of approximately 8.3 ns. The piezoelectricity-induced HER, via the piezocatalysis process (without light irradiation), reaches an optimal H 2 -production rate of approximately 3453.1 µmol g −1 h −1 . Through the synergistic piezophototronic process, the HER reaches approximately 6000 µmol g −1 in 7 h. Crucially, the mechanical force-induced spontaneous polarization functions as a carrier separator, driving the electron and hole in opposite directions in ferroelectric ZnSnO 3 NWs; this separation reduces the recombination rate, enhancing the redox process. This theoretical analysis indicates that the photo catalytic and piezocatalytic effects can synergistically enhance piezophototronic performance through capitalizing on well-modulated oxygen vacancies in ferroelectric semiconductors. This study demonstrates the essential role of this synergy in purifying water pollutants and converting water into hydrogen gas through the piezophototronic process.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201907619. high greenhouse gas emissions, and high energy consumption. Scientists today, being more ecologically conscious, have devised strategies that reduce these negative environmental consequences. Specifically, they have developed catalyst materials that play pivotal roles in the degradation of hazardous pollutants, [1] water splitting, [1][2][3] and energy source conversion. In particular, electrocatalysis [4] and photocatalysis [5] are promising processes for converting solar energy into chemical energy through the irradiation of sunlight. However, challenges remain with respect to improving photoelectrochemical conversion efficiency through doping metal transitions, cocatalysts, [6,7] heterojunction structures, [8,9] and defects states. [10] A sustained effort should be made to accelerate the process of catalyst development using a variety of methods. There has been much recent attention devoted to piezocatalysts, [11][12][13][14] such as MoS 2 , MoSe 2 , and WS 2 , which are made of few-layered 2D materials with unique piezoelectric properties. Specifically, these piezocatalysts have been discovered to have ultrahigh efficiency and to require no light irradiation to convert mechanical energy into chemical energy. [15] Bear this in mind, mechanical energy is naturally available anytime and anywhere. These discoveries have enabled broad engineering applicatio...

We demonstrated a single-microbelt nanogenerator first made using a ZnSnO(3) microbelt that generated an output power of ∼3 nW under a compressive and releasing strain of 0.8-1%. The ZnSnO(3) nanobelts/microbelts were synthesized using a vapor transfer process at 1173 K. The X-ray diffraction pattern shows that the microbelts belong to ZnSnO(3) with rhombohedral structure. An individual ZnSnO(3) microbelt was bonded at its ends on a flexible polystyrene substrate as a nanogenerator, which gives an output voltage and current of 100 mV and 30 nA, respectively, corresponding to an energy conversion efficiency of 4.2-6.6% (based on 0.8-1% strain). Our results show that ZnSnO(3) microbelts are one of the highly promising materials for lead-free piezoelectric energy harvesting.

A flexible and transparent lead-free triangular-belt ZnSnO(3) nanogenerator is demonstrated. When a mechanical deformation of ≈0.1% is applied to the triangular-belt ZnSnO(3) nanogenerator, the output voltage and current reached 5.3 V and 0.13 μA, respectively, which indicated a maximum output power density of ≈11 μW·cm(-3). This is the highest output power that has been demonstrated by lead-free ZnSnO(3) triangular-belts.