Guangjie Zhang

A highly shape-adaptive, stretchable design based on conductive liquid for energy harvesting and self-powered biomechanical monitoring

Researchers report a scalable approach for highly deformable and stretchable energy harvesters and self-powered sensors. The rapid growth of deformable and stretchable electronics calls for a deformable and stretchable power source. We report a scalable approach for energy harvesters and self-powered sensors that can be highly deformable and stretchable. With conductive liquid contained in a polymer cover, a shape-adaptive triboelectric nanogenerator (saTENG) unit can effectively harvest energy in various working modes. The saTENG can maintain its performance under a strain of as large as 300%. The saTENG is so flexible that it can be conformed to any three-dimensional and curvilinear surface. We demonstrate applications of the saTENG as a wearable power source and self-powered sensor to monitor biomechanical motion. A bracelet-like saTENG worn on the wrist can light up more than 80 light-emitting diodes. Owing to the highly scalable manufacturing process, the saTENG can be easily applied for large-area energy harvesting. In addition, the saTENG can be extended to extract energy from mechanical motion using flowing water as the electrode. This approach provides a new prospect for deformable and stretchable power sources, as well as self-powered sensors, and has potential applications in various areas such as robotics, biomechanics, physiology, kinesiology, and entertainment.

Electromagnetic wave absorption in reduced graphene oxide functionalized with Fe3O4/Fe nanorings

We report the preparation of nanocomposites of reduced graphene oxide with embedded Fe3O4/Fe nanorings (FeNR@rGO) by chemical hydrothermal growth. We illustrate the use of these nanocomposites as novel electromagnetic wave absorbing materials. The electromagnetic wave absorption properties of the nanocomposites with different compositions were investigated. The preparation procedure and nanocomposite composition were optimized to achieve the best electromagnetic wave absorption properties. Nanocomposites with a GO:α-Fe2O3 mass ratio of 1:1 prepared by annealing in H2/Ar for 3 h exhibited the best properties. This nanocomposite sample (thickness = 4.0 mm) showed a minimum reflectivity of–23.09 dB at 9.16 GHz. The band range was 7.4–11.3 GHz when the reflectivity was less than–10 dB and the spectrum width was up to 3.9 GHz. These figures of merit are typically of the same order of magnitude when compared to the values shown by traditional ferric oxide materials. However, FeNR@rGO can be readily applied as a microwave absorbing material because the production method we propose is highly compatible with mass production standards.

Three-dimensional ordered ZnO/Cu2O nanoheterojunctions for efficient metal-oxide solar cells.

Interface modulation for broad-band light trapping and efficient carrier collection has always been the research focus in solar cells, which provides the most effective way to achieve performance enhancement. In this work, solution-processed 3D ordered ZnO/Cu2O nanoheterojunctions, consisting of patterned n-ZnO nanorod arrays (NRAs) and p-Cu2O films, are elaborately designed and fabricated for the first time. By taking advantage of nanoheterojunctions with square patterned ZnO NRAs, solar cells demonstrate the maximum current density and efficiency of 9.89 mA cm(-2) and 1.52%, which are improved by 201% and 127%, respectively, compared to that of cells without pattern. Experimental analysis and theoretical simulation confirm that this exciting result originates from a more efficient broad-band light trapping and carrier collection of the 3D ordered ZnO/Cu2O nanoheterojunctions. Such 3D ordered nanostructures will have a great potential application for low-cost and all oxide solar energy conversion. Furthermore, the methodology applied in this work can be also generalized to rational design of other efficient nanodevices and nanosystems.

Novel Piezoelectric Paper‐Based Flexible Nanogenerators Composed of BaTiO3 Nanoparticles and Bacterial Cellulose

A piezoelectric paper based on BaTiO3 (BTO) nanoparticles and bacterial cellulose (BC) with excellent output properties for application of nanogenerators (NGs) is reported. A facile and scalable vacuum filtration method is used to fabricate the piezoelectric paper. The BTO/BC piezoelectric paper based NG shows outstanding output performance with open‐circuit voltage of 14 V and short‐circuit current density of 190 nA cm−2. The maximum power density generated by this unique BTO/BC structure is more than ten times higher than BTO/polydimethylsiloxane structure. In bending conditions, the NG device can generate output voltage of 1.5 V, which is capable of driving a liquid crystal display screen. The improved performance can be ascribed to homogeneous distribution of piezoelectric BTO nanoparticles in the BC matrix as well as the enhanced stress on piezoelectric nanoparticles implemented by the unique percolated networks of BC nanofibers. The flexible BTO/BC piezoelectric paper based NG is lightweight, eco‐friendly, and cost‐effective, which holds great promises for achieving wearable or implantable energy harvesters and self‐powered electronics.

Investigation on the optimization, design and microwave absorption properties of reduced graphene oxide/tetrapod-like ZnO composites

A novel microwave absorption composite was fabricated by mixing reduced graphene oxide (RGO) and tetrapod-like ZnO (T-ZnO). The microwave absorption properties of the fabricated composites with different components were investigated. The effects of RGO mass fractions and thickness of composites on microwave absorption properties were studied in the range from 2 to 18 GHz. The electromagnetic parameters showed that the RGO/T-ZnO composites were mainly dependent on dielectric loss. The composites with 5 wt% RGO and 10 wt% T-ZnO had the optimum microwave absorption properties at the thickness of 2.9 mm, and the corresponding minimum reflection loss was −59.50 dB at 14.43 GHz. The bandwidth corresponding to the reflection loss below −20 dB was 8.9 GHz (from 9.1 GHz to 18.0 GHz) when the thickness was in the range of 2.5–4.0 mm. Thus, the composite has a low reflection loss value and wide effective absorption bandwidth in X-band (8–12 GHz) and Ku-band (12–18 GHz), which has great potential for military stealth. The excellent microwave absorption properties were mainly attributed to dielectric relaxation and polarization of RGO, electronic polarization from the needle-like tips of T-ZnO, electrical conduction loss and multiple scattering.

Temperature-dependent electrochemical capacitive performance of the α-Fe2O3 hollow nanoshuttles as supercapacitor electrodes

The design and optimization of supercapacitors electrodes nanostructures are critically important since the properties of supercapacitors can be dramatically enhanced by tunable ion transport channels. Herein, we demonstrate high-performance supercapacitor electrodes materials based on α-Fe2O3 by rationally designing the electrode microstructure. The large solid-liquid reaction interfaces induced by hollow nanoshuttle-like structures not only provide more active sites for faradic reactions but also facilitate the diffusion of the electrolyte into electrodes. These result in the optimized electrodes with high capacitance of 249 F g(-1) at a discharging current density of 0.5 A g(-1) as well as good cycle stability. In addition, the relationship between charge storage and the operating temperature has been researched. The specific capacitance has no significant change when the working temperature increased from 20 °C to 60 °C (e.g. 203 F g(-1) and 234 F g(-1) at 20 °C and 60 °C, respectively), manifesting the electrodes can work stably in a wide temperature range. These findings here elucidate the α-Fe2O3 hollow nanoshuttles can be applied as a promising supercapacitor electrode material for the efficient energy storage at various potential temperatures.

Reduced Graphene Oxide Functionalized with Cobalt Ferrite Nanocomposites for Enhanced Efficient and Lightweight Electromagnetic Wave Absorption

In this paper, reduced graphene oxide functionalized with cobalt ferrite nanocomposites (CoFe@rGO) as a novel type of electromagnetic wave (EW) absorbing materials was successfully prepared by a three-step chemical method including hydrothermal synthesis, annealing process and mixing with paraffin. The effect of the sample thickness and the amount of paraffin on the EW absorption properties of the composites was studied, revealing that the absorption peaks shifted toward the low frequency regions with the increasing thickness while other conditions had little or no effect. It is found that the CoFe@rGO enhanced both dielectric losses and magnetic losses and had the best EW absorption properties and the wide wavelength coverage of the hole Ku-Band when adding only 5wt% composites to paraffin. Therefore, CoFe@rGO could be used as an efficient and lightweight EW absorber. Compared with the research into traditional absorbing materials, this figures of merit are typically of the same order of magnitude, but given the lightweight nature of the material and the high level of compatibility with mass production standards, making use of CoFe@rGO as an electromagnetic absorber material shows great potential for real product applications.

The enhanced performance of piezoelectric nanogenerator via suppressing screening effect with Au particles/ZnO nanoarrays Schottky junction

AbstractThis paper describes a novel strategy to weaken the piezopotential screening effect by forming Schottky junctions on the ZnO surface through the introduction of Au particles onto the surface. With this approach, the piezoelectric-energyconversion performance was greatly enhanced. The output voltage and current density of the Au@ZnO nanoarray-based piezoelectric nanogenerator reached 2 V and 1 μA/cm2, respectively, 10 times higher than the output of pristine ZnO nanoarray-based piezoelectric nanogenerators. We attribute this enhancement to dramatic suppression of the screening effect due to the decreased carrier concentration, as determined by scanning Kelvin probe microscope measurements and impedance analysis. The lowered capacitance of the Au@ZnO nanoarraybased piezoelectric nanogenerator also contributes to the improved output. This work provides a novel method to enhance the performance of piezoelectric nanogenerators and possibly extends to piezotronics and piezophototronics.

Strain-modulation and service behavior of Au–MgO–ZnO ultraviolet photodetector by piezo-phototronic effect

Au–MgO–ZnO (AMZ) ultraviolet (UV) photodetectors were fabricated to enhance their sensitivities by an inserting ultrathin insulating MgO layer. With the insulating layer, the sensitivities of the UV photodetectors were improved via the reduction of the dark current. Furthermore, strain modulation was used to enhance the sensitivities of the AMZ UV photodetectors. The sensitivities of the photodetectors were enhanced by the piezo-phototronic effect. However, there was a limiting value of the applied strains to enhance the sensitivity of the photodetector. When the external strains exceeded the limiting value, the sensitivity decreased because of the tunneling dark current. The external strains loaded on the photodetectors result in the degradation of the photodetectors, and an applied bias can accelerate the process. This work presents a prospective approach to engineer the performance of a UV photodetector. In addition, the study on the service behavior of the photodetectors may offer a strain range and theoretical support for safely using and studying metal–insulator–semiconductor (MIS) UV photodetectors.

Band alignment engineering for high-energy-density solid-state asymmetric supercapacitors with TiO2 insertion at the ZnO/Ni(OH)2 interface

In this paper, an adaptive interface electronic band structure was proposed for improving the capacitance of nano-architectured Ni(OH)2 by introducing a TiO2 embedding layer at the ZnO/Ni(OH)2 interface. A stair-like band alignment was designed to reduce the electron interface transport barrier and induce efficient electron-injection through the interface to the reaction region when it is charging. Consequently, the activation energy of reduction dropped, which further brought about a decreased equilibrium potential (Eeq) depending on the Butler–Volmer model of electrode kinetics. As expected, a superior capacitance of 1981 F g−1 at 2 A g−1 was triggered. After that, this advanced electrode was assembled in an asymmetric cell with a ZnO@Fe2O3 based negative electrode; the as-fabricated device delivered a high energy density of 52.2 W h kg−1 at a power density of 1.3 kW kg−1 within the voltage range of 0–1.6 V as well as a good cycling performance (96.6% capacity retention after 5000 cycles). These features demonstrate that suitable interface engineering may open up new opportunities in the development of high-performance supercapacitors.