[en] Highlights: • A simple process has been developed to incorporate liquid metal particles into PAN nanofibers uniformly. • Liquid metal has been used as nanoparticle dopants to improve the TENG performance significantly • The charge trapping at the liquid metal surface oxide plays the key role for the performance improvement of TENGs. -- Abstract: Liquid metal (LM) has been used as flexible electrodes for high performance triboelectric nanogenerators (TENGs), however it is unclear how the LM in tribo-layers would affect the performance of TENGs. Here, we report the investigation on the effects of LM particles incorporated into a tribo-layer on the performance of TENGs. The TENGs consist of a polyacrylonitrile (PAN) electrospinning nanofiber membrane, and a polytetrafluoroethylene (PTFE) thin film. LM particles with different concentrations are incorporated into PAN polymer matrix, and used to make the PAN nanofibers membranes by electrospinning. Result shows that the outputs of TENGs become much larger with the increase in LM content. Specifically, the current density increases by about 40%, and both the charge density and output voltage increase by nearly 70%. The overall output power is approximately 2 times higher for the TENG with 1.5 wt% LM concentration, as compared to those of TENGs with pure PAN tribo-layer. However, the output of PAN/LM-PTFE TENGs deteriorates drastically when the LM mass content is increased to 2.5 wt%, at which the composite contains a high density of LM spheroid and spindle particles, deteriorating the generation of triboelectric charge.

[en] Highlights: • We report a high-performance hybrid piezo/triboelectric nanogenerator utilizing few-layered hexagonal boron nitride nanosheets . • The BNNS-PDMS/PA6 PTEG demonstrates ultrahigh power density and stability with superior energy conversion efficiency. • The enhanced performance originates the synergy of the piezoelectric effects and the increased negative triboelectric properties of BNNS-PDMS composite membranes. The hexagonal boron nitride nanosheets (BNNSs) are one of the 2-dimensional(2D) materials, and have been explored for their applications in nanoelectronics etc, owing to their unique properties. Here, BNNSs are utilized to develop a high-performance hybrid piezo/triboelectric nanogenerator (PTEG). BNNSs of a few percentages in weight are incorporated into polydimethylsiloxane (PDMS) to form composites that are able to produce piezoelectric voltages up to ~ 5.4 V with $d_{33}$ ~ 12 pC/N. A PTEG composed of BNNS-PDMS and polyamide-6 (PA6) membranes ($20\times 20{\mathrm{mm}}^2$) demonstrates a current density of ~ 230 mA ${\mathrm{m}}^{-2}$, an output voltage of ~ 1870 V and a maximum power density of ~ 103.7 $\mathrm{W}{\mathrm{m}}^{-2}$, more than three times higher than those of the control PDMS/PA6 nanogenerator. Electric polarization of the BNNS-PDMS membranes can further enhance the output of PTEGs. Detailed investigation reveals that the dramatically enhanced performance originates from the synergy of piezoelectric effect of BNNSs and increased electron affinity of BNNS-PDMS membranes, demonstrates the excellent potential of BNNS-based PTEGs.

[en] Highlights: • Different types of electrolytes have been utilized to dope and modulate PVA based solid polymer electrolytes tribolayer to achieve much enhanced transferred charge density of 210 μC m⁻². • The PTFE/PVA-LiCl TENG demonstrates much enhanced triboelectric performance and stability, achieving a high power density of 83 W m⁻². • Electrolyte addition enhances the triboelectric property of PVA based SPE as a positive triboelectric material. • Enhanced interaction between triboelectric layers further improves the outputs of TENGs significantly. -- Abstract: Triboelectric nanogenerators (TENGs), as a promising energy harvesting technology, have attracted considerable attention and various approaches have been developed to improve their output performance. An innovative strategy was proposed recently by using solid polymer electrolyte (SPE) with asymmetric pairing ions as the friction layer, showing excellent potential to achieve high-performance TENGs. However, it is far from clear what are the effects of SPE on TENG performance as only one electrolyte, CaCl₂, was used for the investigation. Herein, PTFE/PVA-MCl_x TENGs based on SPEs with different types of electrolytes, including LiCl, ZnCl₂, CaCl₂, FeCl₃, and AlCl₃, were fabricated and their performances were investigated. All the devices demonstrated superior output performance than that of the control PTFE/PVA TENG. Specifically, the PTFE/PVA-LiCl TENG exhibited remarkably enhanced triboelectric performance with an output voltage of ~1345 V, a short-circuit current density of ~260 mA m⁻² and a maximum power density of ~83 W m⁻², four times higher than that of the control PTFE/PVA TENG. Detailed investigations revealed that in combination with improved triboelectric property, the enhanced interaction of SPEs with opposite triboelectric layers further significantly boost the triboelectric outputs. This work presents a new method to increase the interaction between triboelectric layers to effectively improve the outputs of TENGs, and to facilitate the development of high performance TENGs.

[en] The increased public concerns on healthcare, the environment and sustainable development inspired the development of biodegradable and biocompatible electronics that could be used as degradable electronics in implants. In this work, a fully biodegradable and flexible resistance random access memory (RRAM) was developed with low-cost biomaterial gelatin as the dielectric layer and the biodegradable polymer poly(lactide-coglycolide) acid (PLGA) as the substrate. PLGA can be synthesized by a simple solution process, and the PLGA substrate can be peeled off the handling substrate for operation once the devices are fabricated. The fabricated memory devices exhibited reliable nonvolatile resistive switching characteristics with a long retention time over 10⁴ s and a near-constant on/off resistance ratio of 10² even after 200 bending cycles, showing the promising potential for application in flexible electronics. Degradation of the devices in deionized water and in phosphate buffered saline (PBS) solution showed that the whole devices can be completely degraded in water. The dissolution time of the metals and the gelatin layer was a few days, while that for PLGA is about 6 months, and can be modified by changing the synthesis conditions of the film, thus allowing the development of biodegradable electronics with designed dissolution time. (paper)

[en] An extremely effortless method was applied for successful synthesis of mesoporous carbonaceous materials (MCMs) using well-ordered mesoporous silica as template. Various characterizations (scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman, X-ray photoelectron spectroscopy (XPS), Brunner-Emmet-Teller (BET) and Zeta potential) confirmed that MCMs had large surface area, uniform pore size distribution, and abundant oxygen-containing functional groups. The batch techniques were employed to study U(VI) adsorption on MCMs under a wide range of experiment conditions. The adsorption kinetics of U(VI) onto MCMs were well-fitted by pseudo-second-order kinetic model, indicating a chemisorption process. The excellent adsorption capacity of MCMs calculated from the Langmuir model was 293.95 mg g⁻¹ at pH 4.0. The FT-IR and XPS analyses further evidenced that the binding of U(VI) onto MCMs was ascribed to the plentiful adsorption sites (–OH and –COOH groups) in the internal mesoporous structure, which could efficiently trap guest U(VI) ions. The results presented herein revealed that MCMs were ideal adsorbents in the efficient elimination of uranium or other lanthanides/actinides from aqueous solutions, which would play an important role in environmental pollution management application.

[en] Highlights: • The developmental timeline of MOFs-containing membranes for water treatment are summarized. • The synthesis strategies of various MOFs-containing membranes are introduced. • The removal performances of MOFs-containing membranes for various pollutants are determined. • The mechanisms mainly ascribe to size-exclusion, π-π stacking interaction, electrostatic interaction, hydrogen bonding. • Multi-factor influences demonstrate the practical application potential of MOFs-containing membranes. Among many separation membranes reported to date, the favorable polymer affinity and unique physio-chemical performances of metal-organic frameworks (MOFs) including ultra-high surface area, regular and highly controlled porosity have drawn widespread attention in industrial and academic communities. In this comprehensive review, the developmental timeline of MOF containing membranes for water treatment were clarified. The removal efficiencies, elimination mechanisms, as well as possible influencing factors of various MOF containing membranes that applied to water treatment were systematically summarized. The excellent removal performances of MOF containing membranes for various pollutants were determined by the size-exclusion, π-π stacking interaction, electrostatic interaction, hydrogen bonding and so on. Since the progress of engineered MOF containing membranes for practical wastewater treatment applications lags, we further analyzed the potential environmental application of MOF containing membranes from four aspects (stability of MOFs, antifouling performance of membranes, compatibility between MOF fillers and polymer matrix, dispersity of MOF nanoparticles in matrix), hoping to provide some meaningful insights.

[en] Highlights: • An effective strategy that simultaneously optimizes the chemical composition and surface microstructure of triboelectric materials is proposed to fabricate high performance TENGs. • Flat PVDF/G films and PVDF/G nanofibers have been prepared and investigated as negative triboelectric materials for the first time. • The PVDF/G nanofibers based PVDF/G NF-PA6 TENGs demonstrate much enhanced triboelectric performance and superior stability, achieving a maximum output power density of ~130.2 W m⁻². • Both graphene nanosheets addition and micro/nanostructure construction enhance the triboelectric property of PVDF/G composite nanofiber and make it to be a promising negative triboelectric material for energy harvesting. As a promising sustainable power source for intelligent electronics, triboelectric nanogenerator (TENG) has attracted remarkable attention and various strategies have been sought to improve its output performance. However, most of these approaches for triboelectric materials optimization only focus on either chemical composition modulation or surface microstructure fabrication. In this work, both aspects are considered and an effective strategy is proposed to construct high performance TENGs based on polyvinylidene fluoride (PVDF) via graphene nanosheets incorporation in conjunction with electrospinning technology. Hence, a 20 × 20 mm² TENG comprising of PVDF/G nanofibers and polyamide-6 (PA6) films demonstrates superior triboelectric performance with an output voltage of ~1511 V, a short-circuit current density of ~189 mA m⁻², and a maximum peak power density of ~130.2 W m⁻², nearly eight times higher than that of the PVDF-PA6 TENG. Additionally, under impedance matching condition, the PVDF/G-PA6 TENG can harvest ~74.13 μJ energy per cycle, with a time-averaged output power density of 926.65 mW m⁻². Detail investigation reveals that both composition modulation with graphene and nanofiber structure fabricated through electrospinning contribute to the triboelectric performance enhancement of PVDF/G NF films. This work provides an effective strategy of simultaneously optimizing the chemical composition and surface microstructure of triboelectric materials to significantly improve the output performance of TENGs, and to further promote the widespread application of TENGs.

[en] Highlights: • Surface electrical properties can be detected by polymer-based contact electrification probe with quantitative model. • Different polarization effects in hybrid perovskite can be either enhanced or suppressed from each other depending on the polarization configuration. • Polarization effects are beneficial for hybrid perovskite based photovoltaic devices. Surface electrical properties is of great significance for developing high-performance organic-inorganic hybrid perovskite based electronic devices. The photovoltage-induced ions transport and redistribution at the surface region have been well studied, but their contributions to the surface electrical properties are still lack of experimental evidences. In this article, a self-powered polymer-based contact electrification probe (PCE-probe) is proposed to investigate the photovoltage- or applied bias-induced ion transport polarization (P_I) and ferroelectric polarization (P_F) inside the methylammonium lead iodide films (MAPI). Results show that both the P_I- and P_F-induced ion transport and redistribution create a similar local ion-doping region near the surface. Positive or negative ion-doping produces a n-type or p-type layer, which enhances the interficial junction inside MAPI-based solar cells and benefits the seperation and transfer of photogenerated carriers or excitons. The P_I and P_F effects can be added up or subtracted from each other depending on the polarization configuration. A qualitative relationship between the PCE-probe output and CE-effect, P_I- and P_F-induced transferred surface charges is investigated. These results can help to understand the polarization nature inside and the high power conversion efficiency of MAPI-based photovoltaic devices, and provide a feasible analysis method of PCE-probe for detecting surface electrical properties.

[en] Highlights: • Under strain the material positions shifts on the triboelectric series scale. • New result obsolete static triboelectric series for the dynamic characterizations. • New quasi-equilibrium states were discovered during the CE. • A self-powered nanoscale thickness monitoring proof-of-concept is demonstrated. Contact electrification has been a debatable topic in the last few years and newer theories have accounted for the recent developments. In recent times, triboelectricity is proposed to be a newer alternative among the ubiquitous energy resources which makes it indispensable to understand the technique in vivid details. Here in this research work, the dynamic triboelectric nature of materials under strain was observed and studied in detail. On account of this, soft material like nylon and Teflon tends to shift their respective positions on the triboelectric series scale upon the applied strain. The detailed investigation using advanced techniques allowed us to probe and discover new quasi-equilibrium states during the contact and separation cycle of nylon when contacted with aluminum oxide. The new results obsolete the existing static triboelectric series scale for the dynamic characterizations for the nanogenerator applications. Additionally, recent charge transfer models of contact electrifications were investigated in detail to probe the intricate mechanism further. Here, in this research, a novel self-powered nanoscale thickness monitoring system application is demonstrated with a resolution of 5 nm (for ALD grown aluminum oxide films). We believe this work will help the researchers to understand the contact-electrification phenomenon in detail.

[en] This work presents the development of flexible dual-mode surface acoustic wave (SAW) sensor based on single crystalline thin film lithium niobate (TF-LN). Numerical modeling is conducted to investigate the SAW propagation and the effects on strain sensitivity. The dependence of strain sensitivity on angles between the applied strain and SAW propagation direction is analyzed numerically and experimentally, showing that the maximum strain sensitivity is at 45° rather than longitudinal direction. 128° Y-cut TF-LN (∼50 µm), obtained by micromachining technique, is utilized as the piezoelectric substrate to fabricate the SAW strain sensors with dual-mode, namely Rayleigh mode and thickness shear mode. The sensor has excellent flexibility and demonstrates remarkable capability for an ultra-wide range strain measurement up to  ±3000 . Temperature effects on resonant frequency and strain sensitivity are investigated in the range of 25 °C–100 °C, and similar temperature characteristics are observed for the dual modes. A method of beat frequency between the dual modes is introduced which is able to eliminate the temperature effect on strain sensing, an on-chip temperature influence removing capability. All the results clearly show that this sensor exhibits great potential for applications in flexible electronics and microsystems. (paper)