A dynamic supercritical carbon dioxide foaming method for fabricating wrinkled surface to enhance triboelectric nanogenerator performance

Triboelectric nanogenerator (TENG) is a promising energy harvester to overcome the energy depletion issue. The surface structure has been considered as an effective way to enhance the triboelectric performance. Herein, a dynamic supercritical carbon dioxide (scCO₂) foaming method, which introduced a scCO₂ flow field during scCO₂ saturation, was proposed to fabricate thermoplastic polyurethane (TPU) foams with surface wrinkly structures. The size of the surface wrinkles could be regulated in the range of 1.8–10 μm by varying the foaming pressure. The surface wrinkled TPU film with wrinkle wave length of 2.4 μm demonstrated an excellent enhancement in output voltage (130%), current (180%), and maximum transfer charge (130%) when paired with surface structured polydimethylsiloxane film in a TENG. Due to the excellent durability and flexibility of the composing materials, the developed TENG showed outstanding stability in long-term continuous operation. With a high power density of 0.5 W/m² achieved on a 10⁷ Ω external load, the flexible TENG could be used to charge capacitors, power light-emitting-diodes, and served as a self-powered sensor to detect various human movement behaviors. This work provides a new path for the fabrication of surface wrinkled films for the sustainable development of high performance TENGs.     

Integrated energy storage system based on triboelectric nanogenerator in electronic devices

The emergence of electronic devices has brought earth-shaking changes to people's life.However,an extemal power source may become indispensable to the electronie devices due to the limited capacity of batteries.As one of the possible solutions for the extermal power sources,the triboelectric nanogenerator(TENG)provides a novel idea to the increasing mumber of personal electronic devices.TENG is a new type of energy ollector,which has become a hot spot in the field of nanotechnology.It is widely used at the acquisition and conversion of mechan-ical enegy to electrice energy through the principle of electrostatic induction.On this basis,the TENG could be integrated with the energy stonage system into a self-powered system,W hich can supply power to the electronic devices and make them work continuously.In this review,TENG's basic structure as well as its working process and working mode are firstly discussed.The integration method of TENGs with enegy storage systems and the related research status are then introduced in detail.At the end of this paper,we put forward some problems and discuss the prospect in the future.     

Interior-architectured ZnO nanostructure for enhanced electrical conductivity via stepwise fabrication process

Fabrication of ZnO nanostructure via direct patterning based on sol-gel process has advantages of low-cost, vacuum-free, and rapid process and producibility on flexible or non-uniform substrates. Recently, it has been applied in light-emitting devices and advanced nanopatterning. However, application as an electrically conducting layer processed at low temperature has been limited by its high resistivity due to interior structure. In this paper, we report interior-architecturing of sol-gel-based ZnO nanostructure for the enhanced electrical conductivity. Stepwise fabrication process combining the nanoimprint lithography (NIL) process with an additional growth process was newly applied. Changes in morphology, interior structure, and electrical characteristics of the fabricated ZnO nanolines were analyzed. It was shown that filling structural voids in ZnO nanolines with nanocrystalline ZnO contributed to reducing electrical resistivity. Both rigid and flexible substrates were adopted for the device implementation, and the robustness of ZnO nanostructure on flexible substrate was verified. Interior-architecturing of ZnO nanostructure lends itself well to the tunability of morphological, electrical, and optical characteristics of nanopatterned inorganic materials with the large-area, low-cost, and low-temperature producibility.     

PREPARATION AND ELECTROCHEMICAL PROPERTIES OF NANOSCALE POROUS CARBON ELECTRODE MATERIALS BASED ON RICE PLANT SOOT

Supercapacitors are a kind of novel energy storage devices with long cycle stability and high power density. Electrode materials selection is one of the key factors that affect the properties of supercapacitors. Biomass-derived electrode materials – being low cost, renewable and environmentally friendly – are therefore attracting researchers’ attention. In this work, we adopted a simple process of carbonization and activation with rice plant soot, a common biomass material, as carbon source, and finally obtained the nanoscale porous carbon electrode (NPCE) materials. Then, the electrochemical properties of the as-prepared NPCE materials were tested in 6 M KOH, and the results indicated that the specific capacitance could reach 216?Fg^?1. Therefore, this low-cost, highly efficient technique is a significant milepost towards environmentally sustainable and commercially feasible fabrication of carbon electrode materials from biomass sources.     

Facile Fabrication of Binder-Free CoZn LDH/CFP Electrode with Enhanced Capacitive Properties for Asymmetric Supercapacitor

CoZn layered double hydroxide (LDH) or Co(OH)₂ pseudocapacitive material has been prepared on the current collector of carbon fiber paper (CFP) using an eco-friendly one-step electrodeposition. Benefiting from its unique structural feature, the binder-free CoZn LDH/CFP electrode material realizes high specific capacitance of 1156 Fg^?1 at a current density of 1 Ag^?1 and excellent rate capability of 80% retention with 16 fold current density increment, which is much better than that of Co(OH)₂ (617 Fg^?1, 65%). Notably, the CoZn LDH/CFP can retain an outstanding electrochemical stability with a capacitance degradation of only 6% after 6000 charge–discharge cycles at 32 Ag^?1. Moreover, an asymmetric supercapacitor (ASC) using CoZn LDH/CFP as a positive electrode and AC/CFP as a negative electrode has been assembled. The ASC exhibits a superior energy density of 30.0 Whkg^?1 at a power density of 800 Wkg^?1 with a specific capacitance up to 84.4 Fg^?1 and a potential window wide to 1.6 V. These encouraging results indicate that CoZn LDH/CFP composite material has a great potential for next-generation energy conversion/storage devices.

     

Broadband anti-reflective properties of grown ZnO nanopyramidal structure on Si substrate via low-temperature electrochemical deposition

Anti-reflection coatings (ARCs) are widely used in various optical and optoelectronic devices to minimize the reflection of light. In this study, we demonstrated the fabrication of ZnO nanopyramidal structures on Si substrate via low-temperature electrochemical deposition. We also investigated the anti-reflection (AR) properties of these nanostructures compared with nanorods and planar ZnO texture on Si substrates. We changed the growth conditions, namely, growth temperature and applied current density, to modify the shape of the ZnO nanorod tips. Nanopyramidal structures with continuously varying refractive index profiles in a single layer were obtained. Reflectance spectra show that the nanopyramid-based texture reduced the reflection of light in a broad spectral range from 380 nm to 1000 nm and is much more effective than nanorod and planar textures. For nanopyramid arrays (NPAs) with average tip diameter of 20 nm, we achieved a 6.5% reflectance over a wide range of wavelengths, which is superior to an optimized single-layer ARC such as SiO₂ or TiO₂. These textured ZnO ARCs may be applied to a wide variety of photovoltaic devices and other anti-reflection applications with large areas because of their low temperature, fast growth, and simple fabrication.     

Well-integrated ZnO nanorod arrays on conductive textiles by electrochemical synthesis and their physical properties

We reported well-integrated zinc oxide (ZnO) nanorod arrays (NRAs) on conductive textiles (CTs) and their structural and optical properties. The integrated ZnO NRAs were synthesized by cathodic electrochemical deposition on the ZnO seed layer-coated CT substrate in ultrasonic bath. The ZnO NRAs were regularly and densely grown as well as vertically aligned on the overall surface of CT substrate, in comparison with the grown ZnO NRAs without ZnO seed layer or ultrasonication. Additionally, their morphologies and sizes can be efficiently controlled by changing the external cathodic voltage between the ZnO seed-coated CT substrate and the counter electrode. At an external cathodic voltage of −2 V, the photoluminescence property of ZnO NRAs was optimized with good crystallinity and high density.     

Electroluminescent Characteristics of DBPPV–ZnO Nanocomposite Polymer Light Emitting Devices

We have demonstrated that fabrication and characterization of nanocomposite polymer light emitting devices with metal Zinc Oxide (ZnO) nanoparticles and 2,3-dibutoxy-1,4-poly(phenylenevinylene) (DBPPV). The current and luminance characteristics of devices with ZnO nanoparticles are much better than those of device with pure DBPPV. Optimized maximum luminance efficiencies of DBPPV–ZnO (3:1 wt%) before annealing (1.78 cd/A) and after annealing (2.45 cd/A) having a brightness 643 and 776 cd/m² at a current density of 36.16 and 31.67 mA/cm² are observed, respectively. Current density–voltage and brightness–voltage characteristics indicate that addition of ZnO nanoparticles can facilitate electrical injection and charge transport. The thermal annealing is thought to result in the formation of an interfacial layer between emissive polymer film and cathode.     

Layer-by-layer construction of multi-walled carbon nanotubes, zinc oxide, and gold nanoparticles integrated composite electrode for nitrite detection

A novel composite electrode of Au/ZnO/MWCNTs/GC has been constructed for the electrochemical detection of nitrite, where ZnO thin film and Au nanoparticles are electrodeposited through layer-by-layer onto MWCNTs/GC substrate. The resulting electrode is characterized by scanning electron microscopy and energy-dispersed X-ray spectroscopy. Its electrocatalytic activity toward the electro-oxidation of nitrite has been examined and compared to various modified electrodes, including MWCNTs/GC, Au/ZnO/GC, Au/MWCNTs/GC, and ZnO/MWCNTs/GC via cyclic voltammetry. The electrodeposition time for ZnO and the Au loading amount together with the solution pH are investigated to achieve optimal conditions for the electrode fabrication and nitrite detection. Linear relationship between current response and nitrite concentration is observed in the range from 7.8 × 10⁻⁷ to 4.0 × 10⁻⁴ M and the limit of the detection is 4.0 × 10⁻⁷ M (S/N = 3). The influence of various anions and cations on the nitrite detection has been studied. The proposed method is also employed for the determination of nitrite in real samples.     

Electrochemical behaviors of graphene-ZnO and graphene-SnO2 composite films for supercapacitors

Graphene, graphene-ZnO and graphene-SnO₂ films were successfully synthesized and used as electrode materials for electrochemical supercapacitors, respectively. The screen-printing approach was employed to fabricate graphene film on graphite substrate while the ZnO and SnO₂ were deposited on graphene films by ultrasonic spray pyrolysis. The electrochemical performances of these electrodes were comparatively analyzed through electrochemical impedance spectrometry, cyclic voltammetry and chronopotentiometry tests. The results showed that the incorporation of ZnO or SnO₂ improved the capacitive performance of graphene electrode. Graphene-ZnO composite electrode exhibited higher capacitance value (61.7 F/g) and maximum power density (4.8 kW/kg) as compared with graphene-SnO₂ and pure graphene electrodes.     

Decorating carbon nanosheets with copper oxide nanoparticles for boosting the electrochemical performance of symmetric coin cell supercapacitor with different electrolytes

The synergetic combination of double-layer capacitor carbon nanosheets and pseudocapacitive CuO particles with enhanced electrochemical properties had been proposed. Herein, CuO/carbon nanosheets electrode material with outstanding electrochemistry performance was successfully synthesized via a low-cost and controllable strategy. Such rational architecture integrates high-conductivity carbon nanosheets with rich-chemical-activity CuO particles. The surface-functional carbon nanosheets serve as a conductive substrate, provide an efficient pathway and accelerate the fast diffusion of electrons. This electrode material depicts high specific capacitance up to 183.9 and 371.1 F g⁻¹ at 1 A g⁻¹ in Na₂SO₄ and KOH electrolyte using three-electrode tests, respectively. Moreover, two symmetric devices using this CuO/carbon nanosheets electrode material were assembled with different electrolytes. The as-fabricated device with KOH electrolyte delivers remarkable energy density of 19.36 W h kg⁻¹ at power density of 355.6 W kg⁻¹ and still maintains 12.06 W h kg⁻¹ at 1750.7 W kg⁻¹. The as-fabricated device with Na₂SO₄ electrolyte achieves the maximum energy density of 12.46 W h kg⁻¹ at 355.6 W kg⁻¹. The capacitance retention rate is maintained at 94.4% after 2000 cycles in the as-fabricated coin cell supercapacitor with Na₂SO₄ electrolyte, showing outstanding long-cycling life. Herein, the strategic integration of CuO particles with two-dimensional functional carbon nanosheets as the electrode material provides superior electrochemical performance for supercapacitors.     

Number Density and Diameter Control of Chemical Bath Deposition of ZnO Nanorods on FTO by Forced Hydrolysis of Seed Crystals

ZnO nanorods have been studied extensively due to facile synthesis and useful optoelectronic properties for applications in nanoscale devices. In a common two‐step procedure, an ethanolic Zn²⁺ precursor solution is used to deposit ZnO seed crystals on a substrate, which is then immersed in an aqueous Zn²⁺ precursor solution to grow the nanorods. Here, a forced hydrolysis technique was employed based on additions of water and heat to the seed precursor solution before depositing the seeds on commercial fluorine‐doped tin oxide (FTO)/glass substrates. ZnO nanorods were then grown from these seeds by chemical bath deposition. Analyses showed that the forced hydrolysis resulted in an increase in seed crystallite size and a decrease in the number of seeds deposited. With increasing seed size, the number density of nanorods decreased, while the length and diameter of each rod increased. These findings offer a simple method for exerting control over the number density of ZnO nanorods that is compatible with the rough FTO surface, unlike other methods that require smoother substrates.     

High performance of a solid-state flexible asymmetric supercapacitor based on graphene films

Solid-state flexible energy storage devices hold the key to realizing portable and flexible electronic devices. Achieving fully flexible energy storage devices requires that all of the essential components (i.e., electrodes, separator, and electrolyte) with specific electrochemical and interfacial properties are integrated into a single solid-state and mechanically flexible unit. In this study, we describe the fabrication of solid-state flexible asymmetric supercapacitors based on an ionic liquid functionalized-chemically modified graphene (IL-CMG) film (as the negative electrode) and a hydrous RuO(2)-IL-CMG composite film (as the positive electrode), separated with polyvinyl alcohol-H(2)SO(4) electrolyte. The highly ordered macroscopic layer structures of these films arising through direct flow self-assembly make them simultaneously excellent electrical conductors and mechanical supports, allowing them to serve as flexible electrodes and current collectors in supercapacitor devices. Our asymmetric supercapacitors have been optimized with a maximum cell voltage up to 1.8 V and deliver a high energy density (19.7 W h kg(-1)) and power density (6.8 kW g(-1)), higher than those of symmetric supercapacitors based on IL-CMG films. They can operate even under an extremely high rate of 10 A g(-1) with 79.4% retention of specific capacitance. Their superior flexibility and cycling stability are evident in their good performance stability over 2000 cycles under harsh mechanical conditions including twisted and bent states. These solid-state flexible asymmetric supercapacitors with their simple cell configuration could offer new design and fabrication opportunities for flexible energy storage devices that can combine high energy and power densities, high rate capability, and long-term cycling stability.     

Low-temperature precipitation synthesis of flower-like ZnO with lignin amine and its optical properties

A facile precipitation method has been developed to synthesize ZnO with [bis(2-aminoethyl)amino]methyl lignin (lignin amine) that is chemically modified from low-cost pulp industrial lignin. The obtained ZnO crystallites have been characterized to exhibit a hexagonal wurtzite structure, and their sizes have been determined at ca. 24 nm (mean value). These ZnO nanocrystallites are of high purity and well crystallized. Our present synthetic approach apparently exempts the commonly used calcining purification procedure. It is found that the morphology of ZnO and its specific surface area are capable of being tuned by varying the added lignin amine amount. Using the optimal 10 mL lignin amine, the synthesized ZnO exhibits flower-like morphology with proper specific surface area. Additionally, photoluminescence property of the obtainable ZnO displays two emissive bands at 383 nm (sharp) and in the range of 480 to 600 nm (broad) at room temperature. Their intensities were revealed to depend on the added lignin amine amount as well as on the molar ratio of Zn²⁺/OH^-. The present investigation demonstrates that our method is simple, eco-friendly, and cost-effective for the synthesis of small-size ZnO materials.     

Nanodiamond lateral field emitter devices on thick insulator substrates for reliable high power applications

Nanocrystalline diamond field emitter array devices on a thick insulator substrate are being developed for high power applications. These monolithic lateral emitter diodes in comb array configurations demonstrate potential for high emission current applications. A 640 μm-thick aluminium nitride insulating substrate has been integrated with nanodiamond for device electrode isolation. The fabrication process and preliminary field emission characterization results are discussed. The nanodiamond lateral vacuum device may be a superior way to achieve reliable high-speed and high-power electronics.     

Lead-free BiFeO3 film on glass fiber fabric: Wearable hybrid piezoelectric-triboelectric nanogenerator

Constructing hybrid nanogenerators (NGs) based on triboelectric effect and piezoelectric effect can combine the merits of the individual type of NG thus have drawn great attention in flexible wearable electronics. Herein, we prepared flexible BiFeO₃ (BFO) film in a simple and cost-effective way, which was used to fabricate a wearable hybrid piezoelectric-triboelectric nanogenerator (H–P/TENG) with silk fiber. By optimizing the experimental conditions, the highest open-circuit voltage of 110 V and short-circuit current density of 3.67 μA/cm² were achieved under 1 Hz contact-separation movement. The device also showed the best output power density of 151.42 μW/cm² with load resistance of 250 MΩ. Stimulating by moving body, the fabricated H–P/TENG successively realized the harvest and conversion of mechanical energy into electric energy, demonstrating great potential to monitor posture and establish a self-powered system. Moreover, the proposed H–P/TENG exhibited great stable output after 1800 contact-separation cycles, indicating the outstanding structure stability and fatigue resistance. This work will provide not only a facile and viable way to realize the application of ferroelectric materials in H–P/TENG but also new opportunities for developing monitor posture and self-powered systems.     

Aqueous Solution‐Processable,Flexible Thin‐Film Transistors Based on Crosslinked Chitosan Dielectric Thin Films

The hydrophilic character of chitosan (CS) limits its use as a gate dielectric material in thin‐film transistors (TFTs) based on aqueous solution‐processable semiconductor materials. In this study, this drawback is overcome through controlled crosslinking of CS and report, for the first time, its application to aqueous solution‐processable TFTs. In comparison to natural CS thin films, crosslinked chitosan (Cr‐CS) thin films are hydrophobic. The dielectric properties of Cr‐CS thin films are explored through fabrication of metal–insulator–metal devices on a flexible substrate. Compared to natural CS, the Cr‐CS dielectric thin films show enhanced environmental and water stabilities, with a high breakdown voltage (10 V) and low leakage current (0.02 nA). The compatibility of Cr‐CS dielectric thin films with aqueous solution‐processable semiconductors is demonstrated by growing ZnO nanorods via a hydrothermal method to fabricate flexible TFT devices. The ZnO nanorod‐based TFTs show a high field‐effect mobility (linear regime) of 10.48 cm² V^?1 s^?1. Low temperature processing conditions (below 100 °C) and water as the solvent are utilized to ensure the process is environmental friendly to address the e‐waste problem.     

ZnO纳米线阵列的籽晶控制生长及其紫外探测性能

分别利用磁控溅射沉积、溶胶-凝胶浸涂及旋涂等方法在氧化铟锡(indium tin oxide,ITO)导电玻璃上得到籽晶层,然后通过低温水热法获得了ZnO纳米线阵列。通过X射线衍射、扫描电镜、透射电镜、光致发光谱等测试手段对不同方法获得的ZnO籽晶和纳米线阵列进行了表征和研究。进而在光刻有银电极的ITO玻璃基片上制备出紫外探测原型器件,测试了其紫外响应特性,并结合ZnO纳米线表面特性讨论了器件的紫外响应机理。结果表明:溶胶-凝胶旋涂获得的籽晶最小,生长出的纳米线长径比最高,直径最细,取向性也最好。对应的室温光致发光谱在近带边有优良的激发峰,而可见区的发光峰受到明显抑制。旋涂和浸涂籽晶获得的紫外探测样品响应迅速,但恢复较慢;磁控溅射籽晶样品有较优的响应和恢复特性,但信号强度较低。     

A flexible UV nanosensor based on reduced graphene oxide decorated ZnO nanostructures

A low-cost, compatible with flexible electronics, high performance UV sensor has been achieved from a reduced graphene oxide (RGO) decorated hydrangea-like ZnO film on a PDMS substrate. The hydrangea-like ZnO UV sensor has the best UV sensing performance among devices made of three kinds of ZnO nanostructures synthesized by a hydrothermal method, and demonstrated a dramatic enhancement in on/off ratio and photoresponse current by introducing an appropriate weight ratio of RGO. The on/off ratio of the 0.05% RGO/ZnO sensor increases almost one order of magnitude compared to that of a pristine hydrangea-like ZnO UV sensor. While for the 5% RGO decorated ZnO sensor, the photoresponse current reaches as high as ～1 μA and exceeds 700 times that of a ZnO UV sensor. These results indicate that RGO is an appropriate material to enhance the performance of ZnO nanostructure UV sensors based on its unique features, especially the high optical transparency and excellent electronic conductivity. Our findings will make RGO/ZnO nanohybrids extraordinarily promising in optoelectronics, flexible electronics and sensor applications.     

Controllable synthesis of branched ZnO/Si nanowire arrays with hierarchical structure

A rational approach for creating branched ZnO/Si nanowire arrays with hierarchical structure was developed based on a combination of three simple and cost-effective synthesis pathways. The crucial procedure included growth of crystalline Si nanowire arrays as backbones by chemical etching of Si substrates, deposition of ZnO thin film as a seed layer by magnetron sputtering, and fabrication of ZnO nanowire arrays as branches by hydrothermal growth. The successful synthesis of ZnO/Si heterogeneous nanostructures was confirmed by morphologic, structural, and optical characterizations. The roles of key experimental parameters, such as the etchant solution, the substrate direction, and the seed layer on the hierarchical nanostructure formation, were systematically investigated. It was demonstrated that an etchant solution with an appropriate redox potential of the oxidant was crucial for a moderate etching speed to achieve a well-aligned Si nanowire array with solid and round surface. Meanwhile, the presence of gravity gradient was a key issue for the growth of branched ZnO nanowire arrays. The substrate should be placed vertically or facedown in contrast to the solution surface during the hydrothermal growth. Otherwise, only the condensation of the ZnO nanoparticles took place in a form of film on the substrate surface. The seed layer played another important role in the growth of ZnO nanowire arrays, as it provided nucleation sites and determined the growing direction and density of the nanowire arrays for reducing the thermodynamic barrier. The results of this study might provide insight on the synthesis of hierarchical three-dimensional nanostructure materials and offer an approach for the development of complex devices and advanced applications.