Triboelectric-electromagnetic hybrid nanogenerator for harvesting blue energy and creating an ocean wave warning system.

The abundant water wave energy on Earth stands as one of the most promising renewable blue energy sources, as it exhibits minimal dependence on weather, time and temperature. However, the low fluctuation frequency and extremely irregular nature of the wave energy restrict both the methods and efficiency of energy harvesting. In this study, a packed box-like hybrid nanogenerator was designed, comprising two single-electrode triboelectric nanogenerators (TENGs) and two electromagnetic generators (EMGs). The outputs of both the TENG and EMG were demonstrated under different fluctuation frequencies and swing amplitudes, inspiring the development of a wave warning system. The maximum output voltage, current, and transferred charge of the single TENG, as part of hybrid nanogenerator (HG), reach approximately 110 V, 2.3 µA, and 50 nC, respectively. Its peak power reaches 85.3 µW under a resistance load of 20 MΩ at a frequency of 2 Hz. The EMG component produced maximum output voltages and currents of up to 0.45 V and 1.2 mA, respectively. The peak power is approximately 95.6 µW with a resistance load of 200 Ω. The output performances of the TENG and EMG increase linearly with the increase in the swing angle. Most importantly, a packed box-like hybrid nanogenerator can be conveniently packaged for harvesting energy from water waves. A wave energy collection array floating on the sea is proposed for harvesting blue energy and creating a self-powered ocean wave warning system.

Piezo-phototronic effect regulated broadband photoresponse of a-Ga2O3/ZnO heterojunction.

Amorphous Ga2O3 (a-Ga2O3) films have attracted considerable attention in the field of photodetectors due to their excellent optical absorption response and photoelectric properties. However, there are few studies that have utilized the piezo-phototronic effect to regulate the broadband photoresponse of Ga2O3-based photodetectors. Here, a flexible a-Ga2O3/ZnO heterojunction was constructed, which demonstrated a broadband response range from deep ultraviolet (265 nm) to the near-infrared (1060 nm) and realized a bidirectional adjustable photocurrent response via the piezo-phototronic effect. Under 265 nm illumination and 0.5 V bias, the responsivity and detectivity of the a-Ga2O3/ZnO heterojunction reached up to 12.19 A W-1 and 4.71 × 1011 Jones under 0.164% compressive strain, corresponding to enhancements of 67.7% and 66.8% compared to those under a strain-free state, respectively. Moreover, the broadband photoresponse of the a-Ga2O3/ZnO heterojunction beyond the bandgap limit was tunable under bidirectional strain. The working mechanism of photoresponse performance for the a-Ga2O3/ZnO heterojunction at different wavelengths was elucidated in detail. Oxygen vacancy-assisted carrier generation was found to be influenced by the wavelength of incident light, which mainly determined the broadband photoresponse of the heterojunction. The modulation of the a-Ga2O3/ZnO heterojunction photodetector was interpreted in light of the strain-induced regulation of the barrier height. This work represents an important step toward the development of adjustable broadband photodetectors based on a-Ga2O3 films.

Significantly Enhanced Breakdown Strength and Energy Density in Nanocomposites by Synergic Modulation of Structural Design and Low-Loading Nanofibers.

Polymer-based dielectric nanocomposites have attracted great attention due to the advantages of high-power density and stability. However, due to the limited breakdown strength (Eb) of the dielectrics, the unsatisfactory energy density becomes the bottleneck that restricts their applications. Here, newly designed sandwich-structured nanocomposites are proposed, which includes the introduction of low-loading 0.4BiFeO3-0.6SrTiO3 (BFSTO) nanofibers into the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix as the polarization layer (B-layer) to offer high permittivity and the selection of poly(methylmethacrylate) (PMMA)/P(VDF-HFP) all-organic blend film as the insulation layer (P-layer) to improve Eb of the nanocomposites. The optimized sandwich-structured PBP nanocomposite exhibits significant enhancement in Eb (668.6 MV/m), generating a discharged energy density of 17.2 J/cm3. The dielectric and Kelvin probe force microscope results corroborate that the outer P-layer has a low surface charge density, which can markedly impede the charge injection from the electrode/dielectric interface and thereby suppress the leakage current inside the nanocomposite. Furthermore, both the finite element simulations and capacitive series models demonstrate that the homogenized distribution of electric field in the PBP sandwich-structured nanocomposite favors the improvement of energy storage performance. This work not only provides insightful guidance into the in-depth understanding of the dielectric breakdown mechanism in sandwich-structured nanocomposites but also offers a novel paradigm for the development of polymer-based nanocomposites with high Eb and discharged energy density.

Structure design and wireless transmission application of hybrid nanogenerators for swinging mechanical energy and solar energy harvesting.

With the rapid development of the Internet of Things, the maintenance-free and reliable power supply of widely distributed sensors is still a huge challenge, especially in wireless areas. Wireless power transmission is expected to alleviate the issue that the sensors must be connected by wire to power supply devices. Herein, a novel hybrid nanogenerator combining a triboelectric nanogenerator (TENG) and photovoltaic cell has been demonstrated, which can realize the simultaneous collection and wireless power transmission of swinging mechanical energy and solar energy. The wireless power transmission system based on the hybrid nanogenerator can be actualized through series connection of the TENG and photovoltaic cell with the aid of a specifically designed mechanical switch, enabling the system to generate DC pulses that favor transmitting energies through LC oscillation and a coupled receiver coil. At the receiver coil end, the open-circuit voltage (Voc) of the hybrid nanogenerator can reach 80 V, showing excellent wireless output performance and the rationality of the wireless power transmission circuit. Moreover, the hybrid nanogenerator can wirelessly power a commercial temperature-humidity meter, which indicates the remarkable potential of improving the layout flexibility of sensor nodes. This work successfully realizes the wireless power transmission of hybrid nanogenerator-harvested swinging mechanical energy and solar energy by a simple and feasible circuit design, which can enrich the form of micro/nano energy adapted to wireless energy transmission.

Simultaneously achieving giant piezoelectricity and record coercive field enhancement in relaxor-based ferroelectric crystals.

A large coercive field (EC) and ultrahigh piezoelectricity are essential for ferroelectrics used in high-drive electromechanical applications. The discovery of relaxor-PbTiO3 crystals is a recent breakthrough; they currently afford the highest piezoelectricity, but usually with a low EC. Such performance deterioration occurs because high piezoelectricity is interlinked with an easy polarization rotation, subsequently favoring a dipole switch under small fields. Therefore, the search for ferroelectrics with both a large EC and ultrahigh piezoelectricity has become an imminent challenge. Herein, ternary Pb(Sc1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals are reported, wherein the dispersed local heterogeneity comprises abundant tetragonal phases, affording a EC of 8.2 kV/cm (greater than that of Pb(Mg1/3Nb2/3)O3-PbTiO3 by a factor of three) and ultrahigh piezoelectricity (d33 = 2630 pC/N; d15 = 490 pC/N). The observed EC enhancement is the largest reported for ultrahigh-piezoelectric materials, providing a simple, practical, and universal route for improving functionalities in ferroelectrics with an atomic-level understanding.

Enhanced Output Performance of Piezoelectric Nanogenerators by Tb-Modified (BaCa)(ZrTi)O3 and 3D Core/shell Structure Design with PVDF Composite Spinning for Microenergy Harvesting.

Flexible piezoelectric nanogenerators (PENG) have attracted great attention due to their stable electrical output and promising applications in the Internet of Things. To develop a high-performance PENG, a significant relationship among material, structure, and performance precipitates us to design its rational construction. Herein, Tb-modified (BaCa)(ZrTi)O3 (BCZT) particles have been fabricated into a 3D structure (3D-Tb-BCZT) by the freeze-drying method, and the innovative 3D core/shell structure of 3D-Tb-BCZT-coated 3D-Tb-BCZT/PVDF composite fibers was carried out through the coaxial electrospinning method. The innovative structure can significantly enhance correlation between adjacent piezoelectric particles and improve stress-transfer efficiency, which can be proven by experimental results and COMSOL simulation. As a result, the improved PENG shows a significantly enhanced output of 48.5 V and 3.35 µA as compared to the PENG with the conventional electrospinning process (15.6 V and 1.32 µA). Due to the advantages of light weight, soft flexibility, and high deformation sensitivity of composite fibers, PENG-based fibers can harvest various mechanical energies in daily life such as biological motion, noise vibration, and wind energies. More importantly, the PENG is sufficient enough to power an electronic device for sustained operation by capturing wind energies through power management circuit design, which further promotes the practical application process of a self-powered system.

High-Performance Flexible Piezoelectric Nanogenerator Based on Specific 3D Nano BCZT@Ag Hetero-Structure Design for the Application of Self-Powered Wireless Sensor System.

With the popularity of portable and miniaturized electronic devices in people's live, flexible piezoelectric nanogenerators (PENG) have become a research hotspot for harvesting energy from the living environment to power small-scale electronic equipment and systems because of its stability. For further enhancing output performance of PENG, chemical modification and structural design for piezoelectric fillers are effective ways. Thus, the 3D porous hetero-structure fillers of BCZT@Ag are prepared by freeze-drying method and subsequent chemical seeding reduction. The silicone rubber as matrix is filled into the micro-voids of fillers to prepare specialized composite. The charge transport mechanism and stress transfer efficiency in PENG can be effectively improved through specialized design which is proven by experimental results and multi-physics simulations. The improved PENG exhibit a significantly enhanced output of 38.6 V and 5.85 µA, which is 3.3 and 3.5 times higher than those of PENG without specific design. The prepared PENG can effectively harvest biomechanical energy through walk and joint bending of human body. Moreover, the PENG can be used as a trigger to remotely control wireless collision alarm system, which can acquire rapid response and shows great potential application in Internet of Things.

A stretchable triboelectric nanogenerator made of silver-coated glass microspheres for human motion energy harvesting and self-powered sensing applications.

Wearable triboelectric nanogenerators (TENGs) have recently attracted great interest because they can convert human biomechanical energy into sustainable electricity. However, there is a need for improvement regarding the output performance and the complex fabrication of TENG devices. Here, a triboelectric nanogenerator in single-electrode mode is fabricated by a simple strategy, which involves a sandwich structure of silicone rubber and silver-coated glass microspheres (S-TENG). The S-TENG exhibits a remarkable performance in harvesting human motion energy and as flexible tactile sensor. By optimizing the device parameters and operating conditions, the maximum open-circuit voltage and short-circuit current of the S-TENG can reach up to 370 V and 9.5 µA, respectively. The S-TENG with good stretchability (300%) can be produced in different shapes and placed on various parts of the body to harvest mechanical energy for charging capacitors and powering LED lights or scientific calculators. In addition, the good robustness of the S-TENG satisfies the needs of reliability for flexible tactile sensors in realizing human-machine interfaces. This work expands the potential application of S-TENGs from wearable electronics and smart sensing systems to real-time robotics control and virtual reality/augmented reality interactions.

Self-powered technology based on nanogenerators for biomedical applications.

Biomedical electronic devices have enormous benefits for healthcare and quality of life. Still, the long-term working of those devices remains a great challenge due to the short life and large volume of conventional batteries. Since the nanogenerators (NGs) invention, they have been widely used to convert various ambient mechanical energy sources into electrical energy. The self-powered technology based on NGs is dedicated to harvesting ambient energy to supply electronic devices, which is an effective pathway to conquer the energy insufficiency of biomedical electronic devices. With the aid of this technology, it is expected to develop self-powered biomedical electronic devices with advanced features and distinctive functions. The goal of this review is to summarize the existing self-powered technologies based on NGs and then review the applications based on self-powered technologies in the biomedical field during their rapid development in recent years, including two main directions. The first is the NGs as independent sensors to converts biomechanical energy and heat energy into electrical signals to reflect health information. The second direction is to use the electrical energy produced by NGs to stimulate biological tissues or powering biomedical devices for achieving the purpose of medical application. Eventually, we have analyzed and discussed the remaining challenges and perspectives of the field. We believe that the self-powered technology based on NGs would advance the development of modern biomedical electronic devices.

Enhanced Photovoltaic Performances of La-Doped Bismuth Ferrite/Zinc Oxide Heterojunction by Coupling Piezo-Phototronic Effect and Ferroelectricity.

Ferroelectric materials have drawn widespread attention due to their switchable spontaneous polarization and anomalous photovoltaic effect. The coupling between ferroelectricity and the piezo-phototronic effect may lead to the design of distinctive photoelectric devices with multifunctional features. Here, we report an enhancement of the photovoltaic performances in the ferroelectric p-type La-doped bismuth ferrite film (BLFO)/n-type zinc oxide (ZnO) nanowire array heterojunction by rationally coupling the strain-induced piezoelectricity in ZnO nanowires and the ferroelectricity in BLFO. Under a compressive strain of -2.3% and a 10 V upward poling of the BLFO, the open-circuit voltage (VOC) and short-circuit current density (JSC) of the device increase by 8.4% and 54.7%, respectively. Meanwhile, the rise (/decay) time is modulated from 153.7 (/108.8) to 61.28 (/74.86) ms. Systematical band diagram analysis reveals that the promotion of photogenerated carriers and boost of the photovoltaic performances of the device can be attributed to the modulated carrier transport behaviors at the BLFO/ZnO interface and the superposed driving forces arising from the adding up of the piezoelectric potential and ferroelectric polarization. In addition, COMSOL simulation results of piezopotential distribution in ZnO nanowire arrays and the energy band structure change of the heterojunction further confirm the mechanisms. This work not only presents an approach to design high-performance ferroelectric photovoltaic devices but also further broadens the research scope of piezo-phototronics.

Quantifying and understanding the triboelectric series of inorganic non-metallic materials.

Contact-electrification is a universal effect for all existing materials, but it still lacks a quantitative materials database to systematically understand its scientific mechanisms. Using an established measurement method, this study quantifies the triboelectric charge densities of nearly 30 inorganic nonmetallic materials. From the matrix of their triboelectric charge densities and band structures, it is found that the triboelectric output is strongly related to the work functions of the materials. Our study verifies that contact-electrification is an electronic quantum transition effect under ambient conditions. The basic driving force for contact-electrification is that electrons seek to fill the lowest available states once two materials are forced to reach atomically close distance so that electron transitions are possible through strongly overlapping electron wave functions. We hope that the quantified series could serve as a textbook standard and a fundamental database for scientific research, practical manufacturing, and engineering.

Quantifying the triboelectric series.

Triboelectrification is a well-known phenomenon that commonly occurs in nature and in our lives at any time and any place. Although each and every material exhibits triboelectrification, its quantification has not been standardized. A triboelectric series has been qualitatively ranked with regards to triboelectric polarization. Here, we introduce a universal standard method to quantify the triboelectric series for a wide range of polymers, establishing quantitative triboelectrification as a fundamental materials property. By measuring the tested materials with a liquid metal in an environment under well-defined conditions, the proposed method standardizes the experimental set up for uniformly quantifying the surface triboelectrification of general materials. The normalized triboelectric charge density is derived to reveal the intrinsic character of polymers for gaining or losing electrons. This quantitative triboelectric series may serve as a textbook standard for implementing the application of triboelectrification for energy harvesting and self-powered sensing.

Construction of ZnxCd1-xS/Bi2S3 composite nanospheres with photothermal effect for enhanced photocatalytic activities.

Rational design of photocatalysts with heterostructure is of scientific and technological interest for taking full advantage use of solar energy. Here we demonstrate a facile method to fabricate Zn0.5Cd0.5S/Bi2S3 composite nanospheres, in which Bi2S3 nanorods grown on the surface of Zn0.5Cd0.5S nanospheres. The as-prepared Zn0.5Cd0.5S@ZnS core-shell nanospheres play a vital role in formation of the Zn0.5Cd0.5S@Bi2S3 composite nanospheres. The Zn0.5Cd0.5S/Bi2S3 composites show both excellent photocatalysis and photothermal effect. Nanorods-like Bi2S3 show wide optical absorption from visible to near infrared light and photocurrent response, which enable enhanced full spectrum absorption of the heterostructured photocatalyst and photocurrent for overall photocatalytic performance. Additionally, Bi2S3 nanorods with photothermal effect would synergistically increase the temperature of the micro-environment around the catalysts of ZnxCd1-xS. Thus, the Zn0.5Cd0.5S/Bi2S3 composites exhibit a little better photocatalytic activity than that of pure Zn0.5Cd0.5S. The present study provides a promising strategy for the rational design of efficient sulfide semiconductor heterojunction catalysts for making the utmost of solar fuels in dealing with organic pollutants from wastewater.

Self-Powered Intelligent Water Meter for Electrostatic Scale Preventing, Rust Protection, and Flow Sensor in a Solar Heater System.

Triboelectric nanogenerators (TENGs) have been investigated for mechanical energy harvesting because of their high-energy conversion efficiency, low cost, ease of manufacturing, and so on. This paper deals with designing a kind of water-fluid-driven rotating TENG (WR-TENG) inspired by the structure of a water meter. The designed WR-TENG is effectively integrated into a self-powered electrostatic scale-preventing and rust protection system. The WR-TENG can generate a constant DC voltage up to about 7.6 kV by using a voltage-doubling rectifier circuit (VDRC) to establish a high-voltage electrostatic field in the water tank. A WR-TENG, a VDRC, and an electric water heating tank are the components of the whole system. The system is convenient to be installed in any waterway system, effectively preventing the rusting of stainless steel and restraining the formation of scale when the water is heated to 65 ± 5 °C. Moreover, the approximately linear relationship between the short-circuit current and the rotation rate of the WR-TENG makes employing it as a self-powered water flow sensor possible. This work enables a facile, safe, and effective approach for electrostatic scale prevention, rust protection, and flow sensing in solar heaters, which will enrich the high-voltage applications of TENGs.

Retraction: Comprehensive insights into the charge dynamics process and excellent photoelectric properties of heterojunction solar cells.

Retraction of 'Comprehensive insights into the charge dynamics process and excellent photoelectric properties of heterojunction solar cells' by Xiangyang Liu et al., Phys. Chem. Chem. Phys., 2016, 18, 24299-24306.

Preparation and Characterization of Solution-Processed Nanocrystalline p-Type CuAlO2 Thin-Film Transistors.

The development of p-type metal oxide thin-film transistors (TFTs) is far behind the n-type counterparts. Here, p-type CuAlO2 thin films were deposited by spin coating and annealed in nitrogen atmosphere at different temperature. The effect of post-annealing temperature on the microstructure, chemical compositions, morphology, and optical properties of the thin films was investigated systematically. The phase conversion from a mixture of CuAl2O4 and CuO to nanocrystalline CuAlO2 was achieved when annealing temperature was higher than 900 °C, as well as the transmittance, optical energy band gap, grain size, and surface roughness of the films increase with the increase of annealing temperature. Next, bottom-gate p-type TFTs with CuAlO2 channel layer were fabricated on SiO2/Si substrate. It was found that the TFT performance was strongly dependent on the physical properties and the chemical composition of channel layer. The optimized nanocrystalline CuAlO2 TFT exhibits a threshold voltage of - 1.3 V, a mobility of ~ 0.1 cm2 V-1 s-1, and a current on/off ratio of ~ 103. This report on solution-processed p-type CuAlO2 TFTs represents a significant progress towards low-cost complementary metal oxide semiconductor logic circuits.

A spring-assisted hybrid triboelectric-electromagnetic nanogenerator for harvesting low-frequency vibration energy and creating a self-powered security system.

With the rapid development of portable electronics, exploring sustainable power sources is becoming more and more urgent. Utilizing a nanogenerator to harvest ambient mechanical energy could be an effective approach to solve this challenge. In this work, a novel spring-assisted hybrid nanogenerator (HG) consisting of a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG) was developed for harvesting low-frequency vibration energy. The results show that the TENG with a PTFE surface nanostructure has better output performance than that without the nanostructure. The effect of operating frequency on the open-circuit voltage and short-circuit current of the TENG and EMG is systematically investigated. Under a 2 Hz operating frequency, the EMG and TENG are able to produce a peak power of about 57.6 mW with a resistive load of 2000 Ω and 1682 µW with a resistive load of 50 MΩ, respectively. The impedance matching between the TENG and EMG can be realized by using a transformer to reduce the impedance of the TENG. The charging performance of the HG is much better than that of the individual EMG or TENG. The HG enabled us to develop a self-powered safety system and to power LEDs, and drive some electronic devices. The present work provides a superior solution to improve the output performance of the HG for harvesting low-frequency vibration energy.

Correction: Comprehensive insights into the charge dynamics process and excellent photoelectric properties of heterojunction solar cells.

Correction for 'Comprehensive insights into the charge dynamics process and excellent photoelectric properties of heterojunction solar cells' by Xiangyang Liu et al., Phys. Chem. Chem. Phys., 2016, 18, 24299-24306.

Improvement in the photoelectric conversion efficiency for the flexible fibrous dye-sensitized solar cells.

A dye-sensitized and flexible TiO2 fiber with multilayer structure was prepared by using brush method as the photoanode in the efficient flexible fibrous dye-sensitized solar cells (FFDSSCs) to avoid electronic recombination and improve the electronic capture efficiency. The composite Pt counter electrode, preparation from the surface modification of the electrodeposited Pt wire by using a simple one-step thermal decomposition approach of H2PtCl6 isopropanol and n-butyl alcohol (volume ratio = 1:1) solution, provided a significant improvement in electrocatalytic activity, which was confirmed by extensive electrochemical tests. The FFDSSC assembled with the fiber-shaped TiO2 photoanode and the composite Pt counter electrode achieves an enhanced photoelectric conversion efficiency of 6.35%, higher than that of the FFDSSC with monolayer fibrous TiO2 photoanode and electrodeposited Pt wire counter electrode. More importantly, the photoelectric conversion efficiency of 6.35% is comparable to that of the FFDSSC based on the pure Pt wire counter electrode (6.32%). The FFDSSC with high elasticity, flexibility, and stretchability can adapt to complex mechanical deformations, which is of great significance for the development of wearable electronics in the future.