Recent advances in fabricating high-performance triboelectric nanogenerators via modulating surface charge density

Triboelectric nanogenerators(TENGs),a type of promising micro/nano energy source,have been arousing tremendous research interest since their inception and have been the subject of many striking developments,including defining the fundamental physical mechanisms,expanding applications in mechanical to electric power conversion and self-powered sensors,etc.TENGs with a superior surface charge density at the interfaces of the electrodes and dielectrics are found to be crucial to the enhancement of the performance of the devices.Here,an overview of recent advances,including material optimization,circuit design,and strategy conjunction,in developing TENGs through surface charge enhancement is presented.In these topics,different strategies are retrospected in terms of charge transport and trapping mechanisms,technical merits,and limitations.Additionally,the current challenges in high-performance TENG research and the perspectives in this field are discussed.

Promoted surface charge density from interlayer Zn–N_(4) configuration in carbon nitride for enhanced CO_(2) photoreduction

The solar-driven reduction of CO_(2) into valuable products is a promising method to alleviate global environmental problems and energy crises.However,the low surface charge density limits the photocatalytic conversion performance of CO_(2).Herein,a polymeric carbon nitride(PCN)photocatalyst with Zn single atoms(Zn1/CN)was designed and synthesized for CO_(2) photoreduction.The results of the CO_(2) photoreduction studies show that the CO and CH_(4) yields of Zn1/CN increased fivefold,reaching 76.9 and 22.9μmol/(g·h),respectively,in contrast to the unmodified PCN.Ar+plasma-etched X-ray photoelectron spectroscopy and synchrotron radiation-based X-ray absorption fine structure results reveal that Zn single atom is mainly present in the interlayer space of PCN in the Zn–N_(4) configuration.Photoelectrochemical characterizations indicate that the interlayer Zn–N_(4) configuration can amplify light absorption and establish an interlayer charge transfer channel.Light-assisted Kelvin probe force microscopy confirms that more photogenerated electrons are delivered to the catalyst surface through interlayer Zn–N_(4) configuration,which increases its surface charge density.Further,in-situ infrared spectroscopy combined with density functional theory calculation reveals that promoted surface charge density accelerates key intermediates(*COOH)conversion,thus achieving efficient CO_(2) conversion.This work elucidates the role of internal single atoms in catalytic surface reactions,which provides important implications for the design of single-atom catalysts.

Optimization of Out-of-Plane Vibration Energy Harvesters Employing Electret

This paper investigated the dependence of out-of-plane electret-based vibration energy harvesters’output power,frequency bandwidth,and resonance frequency on surface charge density and load resistance.As the external acceleration amplitude and electret size were held constant,the following results are predicted by the numerical investigation：（1）An optimum value exists in the surface charge density to maximize the output power.As the surface charge density is increasing,electrostatic forces are enhanced,which emphasizes that the soft spring effect widens the frequency bandwidth and lowers the resonance frequency.（2）Different surface charge densities correspond to different optimum initial air gaps,resonance frequency,and optimum load resistance.（3）With the attenuation of the surface potential,the output power,frequency drift,and frequency bandwidth decreased.（4）An optimum value exists in the load resistance to maximize the output power.As the load resistance is decreasing,electrostatic force is enhanced,which lowers the resonance frequency.（5）A maximum frequency bandwidth exists with further load resistance increasing,and the initial air gap is smaller,the greater the frequency bandwidth.

BREAK-UP MECHANISM OF METAL DROPLETS GENERATED BY AN ELECTROHYDRODYNAMIC TECHNIQUE

Nanometer powders can be produced by an electrohydrodynamic technique. The breakup mechanism of the metal droplets generated by the electrohydrodynamic technique was analysed. It showed that the applied voltage, the electric field Btrength, the properties of the molten metal and the volumetric flow rate of the molten metal directly effect the breat-up extent of the metal droplets.

Solution of the Poisson-Boltzmann Equation for a Cylindrical Particle with a Limited Length: Functional Theoretical Approach

With the help of the method of separation of variables and the Debye-Hüchel approximation, the Poisson-Boltzmann equation that describes the distribution of the potential in the electrical double layer of a cylindrical particle with a limited length has been firstly solved under a very low potential condition. Then with the help of the functional analysis theory this equation has been further analytically solved under general potential conditions and consequently, the corresponding surface charge densities have been obtained. Both the potential and the surface charge densities cointide with those results obtained from the Debye-Hüchel approximation when the very low potential of zeψ〈〈kT is introduced.

Flexible and transparent triboelectric nanogenerator based on high performance well-ordered porous PDMS dielectric film

A flexible and transparent triboelectric nanogenerator （FT-TENG） has great potential for application in self-powered biosensor systems, electronic skin and wearable electronic devices. However, improving the output performance with little damage to its optical properties is challenging. Herein, we have developed an FT-TENG that has a well-ordered nest-like porous polydimethylsiloxane （NP-PDMS） film and graphene transparent electrodes. The NP-PDMS film with ordered pores is fabricated by hydrochloric acid etching of 500 nm sized ZnO spheres made of aggregated nanoparticles, having a light transmittance of 81.8% and a water contact angle of 118.62°. The FT-TENG based on the NP-PDMS film with a porosity of 12%, gives a maximum output of 271 V and 7.8 μA, which are respectively, 3.7 and 2.1-fold of those of a TENG with a flat PDMS film. The peak output power reaches 0.39 mW with a load resistance of 9.01 MΩ. The dielectric constant and effective thickness of the NP-PDMS film and the capacitance and charge transfer of the FT-TENG are systematically investigated. This work provides a novel and effective method to enhance the performance of FT-TENGs with little damage to their optical properties.

Au nanocomposite enhanced electret film for triboelectric nanogenerator

A triboelectric nanogenerator （TENG） with an organic nanocomposite electret thin film as the triboelectric layer for mechanical energy harvesting was investigated systematically. In combination with corona charging, a TENG was fabricated by using embedded-nanocapacitor-structure polytetrafluoroethylene （PTFE） impregnated with gold nanoparticles （Au-NPs）. The output performances, stability, and durability of the TENGs with Au-PTFE nanocomposite films were characterized after being washed in water. It was found that the output current increases by 70% and the equivalent surface charge density （ESCD） reaches 85 μC/m^2 in comparison to the virgin PTFE film. Such outstanding performance is likely due to the equivalent nanocapacitors between the Au-NPs and PTFE molecules, which serve as nano charge traps in the nanocomposite electret film under negative high-voltage corona charging. This work not only expands the practical applications of TENGs, but also opens up new possibilities for the development of high performance triboelectric materials.

Sequence identification, structure prediction and validation of tannase from Aspergillusniger N5-5

Tannases produced by filamentous fungi are in a family of important hydrolases of gallotannins and have broad industry applications.But until now,the 3-D structures of fungi tannases have not been reported.The protein sequence deduced from the cDNA sequence obtained using RT-PCR amplification was identified as tannase through sequence alignment and phylogenetic analysis.Structure models based on the tannase sequence were collected using I-TASSER,and the model with the best match to the surface charge density-pH titration profile was selected as the final structure for tannase from Aspergillusniger N5-5.This work provides an effective method for protein structure research.The structure constructed in this work should be very important to understand the enzyme bioactivities and further developments of fungi tannases.