Search

The recent use of cryoprotectant replacement method for solving the easy drying problem of hydrogels has attracted increasing research interest. However, the conductivity decrease of organohydrogels due to the induced insulating solvent limited their electronic applications. Herein, we introduce the Hofmeister effect and electrostatic interaction to generate hydrogen and sodium bonds in the hydrogel. Combined with its double network, an effective charge channel that will not be affected by the solvent replacement, is therefore built. The developed organohydrogel-based single-electrode triboelectric nanogenerator (OHS-TENG) shows low conductivity decrease (one order) and high output (1.02-1.81 W/m2), which is much better than reported OHS-TENGs (2-3 orders, 41.2-710 mW/m2). Moreover, replacing water with glycerol in the hydrogel enables the device to exhibit excellent long-term stability (four months) and temperature tolerance (-50-100 °C). The presented strategy and mechanism can be extended to common organohydrogel systems aiming at high performance in electronic applications.

Quartz and clay are substituted gradually by fly ash using a triaxial ceramic formulation under simulated industrial conditions and the effects of fly ash substitution on the macroscopic properties and microstructures of the sintered ceramics are evaluated systematically. With the substitution of 35 wt% (1250 °C), the ceramic sample exhibited optimal properties, including linear shrinkage of 15.61%, bulk density of 2.39 g cm-3, water absorption of 0.62% and flexural strength of 41.70 MPa, due to the accelerated densification and fly ash-spurred needle-shaped mullite. The microstructure analysis shows that the sintered matrix consists of three types of particles, quartz-, clay- and feldspar-like particles showing sintering behavior with respect to filling the glassy matrix with preserved morphology, precipitating mullite crystals, and fusing with the surrounding glassy matrix, respectively. The strength of the fly ash - containing ceramics is analyzed by the dispersion-strengthening mechanism and porosity and the results indicate that the fly ash particles affect the mechanical strength due to Griffith flaws when the total porosity is less than 25% and pores at higher total porosity. This study provides a viable strategy to recycle industrial fly ash in the production of architectural ceramics.

Incorporation of additives into silicon carbide (SiC) ceramics in low temperature, atmospheric pressure sintering is challenging because uniform mixing of additives and raw SiC powders is quite difficult. Herein, an impregnation coating process in which a precise amount of Al 2 O 3 is introduced to raw SiC granules on the nanoscale is described and high-performance SiC ceramics can be processed by atmospheric pressure sintering. The uniform coating promotes densification of SiC via enhanced liquid mass transfer and inhibits grain growth and recombination during sintering. The effects of the doping content on the ceramic structure and mechanical properties are studied. Coating a single layer of Al 2 O 3 nano-particles on SiC particles yield the best interfacial activity, sintering density, and mechanical properties. The SiC sample with 7.5 wt% Al 2 O 3 possesses the best properties such as a relative density of 97.98%, flexural strength of 434.40 MPa, fracture toughness of 5.23 MPa·m 1/2 , and Vickers hardness of 28.21 GPa. The sintering kinetics analyzed by the isothermal sintering method fits the Singh model with an apparent activation energy of 574.64 kJ/mol. The sintering rate is governed by both the interface reaction and diffusion and the model and experimental results provide insights with respect to materials design and commercial batch production.

LiNi0.8Co0.1Mn0.1O2 (NCM811) has a high potential for using as the cathode material for lithium–ion batteries (LIBs) for electric vehicles owing to its high energy density and low cost. However, its poor rate capability and cycling performance have significantly hindered its application. In this study, we successfully design a uniform magnesium oxide (MgO) coating on NCM811 via a wet-chemical coating followed by heat treatment using magnesium ethoxide [Mg (OEt)2] dissolved in ethanol as the Mg source. The effects of MgO coating on the surface states, crystal structure, and electrochemical performances of NCM811 cathode material are studied in detail. After 100 cycles, the capacity retention of MgO-coated NCM811 is 90.1% at room temperature at 1 C, whereas the pristine NCM811 is only 74.5%. Besides, the MgO-coated NCM811 delivers a better rate property than pristine NCM811. Prominent improvements in electrochemical performances are attributed to the fact that the formation of MgO coating layer helps to suppress deleterious side reactions, lower the overpotential on the surface, and facilitate lithium–ion diffusion.

Flexible lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-0.2 mol%Y nanofibers (BCTZY NFs) were synthesized by electrospinning and their corresponding nanogenerators (NGs) with vertical alignments were fabricated. The low-temperature sintering properties of BCTZY NFs were investigated, to optimize their synthesis path and minimize the thermal energy consumption during the sintering process. The continuity, flexibility, and stability of the BCTZ-based NFs were improved by adding Y3+. Moreover, the temperature-evolved Raman spectra displayed a high Curie temperature of 280 °C for BCTZY NFs, which was far higher than that of about 90 °C for BCTZ-based ceramic bulks, owing to the discontinuous physical property of NFs. The dielectric, ferroelectric, and piezoelectric properties of the vertically aligned BCTZY NFs/PDMS were estimated and compared with those of BCTZ NFs/PDMS composites, to verify the advantages of vertical alignments and the donor doping effect of Y3+. Vertically aligned BCTZY NF-based NGs showed an average VOC of 3.0 V and ISC of 85 nA by finger tapping, suggesting their potential applications in tiny energy harvesting.

Using coal fly ash (CFA) as the raw materials in ceramic production is an effective means to realize large-quantity and high-value utilization. An eco-friendly and cleaner process to prepare architectural ceramics from CFA is described in this paper. CFA first undergoes mechanochemical activation and then used to prepare porcelain ceramic tiles with outstanding mechanical properties. The solution after activation is the sole raw materials to produce foamed ceramics with novel thermal insulation properties. The mechanochemical activation mechanism is investigated systematically. During activation, some of the octahedrally coordinated Al3+ ions are converted into tetrahedrally coordinated Al3+, which can substitute for Si4+ in the tetrahedral rendering the silicate structure in activated CFA unstable. Moreover, the preparation mechanism of the foamed ceramics is studied. On the micro-level, solidification of the foamed ceramics can be interpreted as Si-O-Si structural transformation from two-dimensional layers to a three-dimensional network during sintering. The two final products are characterized and the good mechanical properties of as-obtained porcelain ceramic tiles are attributed to the needle-shape mullite derived from activated CFA. The low thermal conductivity of 0.0453 W/m·K of the as-obtained foamed ceramics arises from the unique cavity construction. Finally, the substance flow, gas emission, and heavy metal leaching behavior of the final products are discussed and the results indicate that there is almost no hazardous waste emission in the process. This study provides insights into more efficient and cleaner utilization of CFA as ceramic materials.

With the rapid development of wearable electronics, flexible and sensitive energy harvesters have recently attracted considerable attention. Herein, a novel piezo-triboelectric nanogenerator (PTNG) based on BCZT/PVDF-HFP composite nanofibers (BP-based NFs) is fabricated using silicone rubber as the negative triboelectric counterpart. The introduction of BCZT nanoparticles markedly improves both the piezoelectric and triboelectric properties of the BP-SG PTNG, where the output voltage and current density are 2.5–3 fold higher than those of pure PVDF-HFP PTNG. Owing to the uniform distribution of BCZT particles on the fiber surface via electrospinning, the maximum power density of the device reaches 161.7 mW m−2, representing 5.5-fold improvement compared to that of BaTiO3/PVDF-based composite PTNG. The device shows stable output for 1200 cycles and after three month storage and exhibits high sensitivity to minute body movements as proved by the output response in both two-electrode and single-electrode modes. This study demonstrates a novel approach to fabricate flexible PTNGs with simple structure and high sensitivity for use in self-powered wearable electronics.

The advancement of wearable electronics and environmental awareness requires a wearable triboelectric nanogenerator (TENG) to feature the concepts of sustainability and environmental suitability. While most wearable TENGs are developed based on complex surface modification approaches to avoid the necessity of a physical spacer, herein a nanogap TENG is fabricated based on surface self-modified sustainable polymer films. Compared with poly(lactic acid) (PLA)-based and polycaprolactone (PCL)-based TENGs, the polybutylene succinate (PBS)-based TENG shows the highest output performance, representing up to 3.5-fold that of the reported TENGs based on biodegradable materials with a 0-4 mm spacer, due to the higher content of the ester group and surface roughness resulting from the surface self-modification. The nanogap device is demonstrated as a pressure/angle sensor with acceptable sensitivity for use in health monitoring. More importantly, the environmental suitability of the triboelectric films in air, water, and phosphate buffered saline systems indicates their stability in natural water and saline environments. Moreover, the antibacterial property of the triboelectric films indicates future applications in wearable and implantable electronics. This work demonstrates the potential applications of a biocompatible and environmentally stable TENG in wearable electronics and biomedical systems.

The development of earth-abundant transition-metal-based electrocatalysts with bifunctional properties (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) is crucial to commercial hydrogen production. In this work, layered double hydroxide (LDH)-zinc oxide (ZnO) heterostructures and oxygen vacancies are constructed synchronously by plasma magnetron sputtering of NiFe-LDH. Using the optimal conditions, ZnO nanoparticles are uniformly distributed on the NiFe-LDH nanoflowers, which are prepared uniformly on the three-dimensional porous Ni foam. In the LDH-ZnO heterostructures and oxygen vacancies, electrons are depleted at the Ni cations on the NiFe-LDH surface and the active sites change from Fe cations to Ni cations during OER. Our theoretical assessment confirms the change of active sites after the deposition of ZnO and reveals the charge-transfer mechanism. Owing to the significant improvement in the OER dynamics, overall water splitting can be achieved at only 1.603 V in 1 M KOH when the Ni/LDH-ZnO and Ni/LDH are used as the anode and cathode, respectively. The work reveals a novel design of self-supported catalytic electrodes for efficient water splitting and also provides insights into the surface modification of catalytic materials.

The shrinking unreacted core model has been one of the most widely used models for the uncatalyzed reaction kinetics between the liquid/gas and the solid phases. However, the classical shrinking unreacted core model (CSUC model) is only applicable to spherical particles. Currently, the CSUC model has been used in many studies regardless of its applicable conditions. For example, Wang et al. (2016) investigated the decomposition kinetics of a rod-like residue and deduced the rate-controlling step using the CSUC model. The purpose of this comment is to propose a modified shrinking unreacted core model (shrinking cylinder model) suitable for materials with a high aspect ratio. The authors hope that this work will be helpful for kinetic analysis of rod-shaped and fiber-shaped materials in the uncatalyzed liquid/gas-solid reactions.

BCZT-CuY/rGO/PDMS composites with excellent elasticity and flexibility, and their nanogenerators (NGs) with favorable electrical properties, were fabricated. The impact of rGO on the dispersion of BCZT-CuY, the mechanical properties of BCZT-CuY/rGO/PDMS, and electrical performance of BCZT-CuY/rGO-based NGs were systematically investigated. The results indicated that the distribution of BCZT-CuY in PDMS with added rGO was much more uniform than that without rGO. Moreover, its elastic modulus and elongation at the break increased to 4.6 MPa and 250%, respectively, with the introduction of rGO. Apart from a high d33 at the percolation threshold, the average VOC (1.36 V) and ISC (35nA) achieved by finger tapping BCZT-CuY/rGO-based NGs suggested their considerable potential in harvesting tiny energy.

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-xwt%CuOywt%Y2O3 (BCZT-CuxYy) ceramics with high piezoelectricity were synthesized by the conventional solid-state reaction method. The role of Cu and Y (Cu/Y) in sintering, phase transition, and electrical properties of such ceramics was systematically studied. The results indicated that the sintering temperatures of BCZT-CuxYy decreased by at least 100 °C due to the low melting point of CuO. The promotion effect of Cu/Y on phase transition lied in the improvement of TC by 5–15 °C and the coexistence of O+T phase near room temperature. The contribution of Cu/Y to electrical properties was mainly ascribed to the grains growth, the formed oxygen vacancies and lattice distortions, and the donor doping effect of Y3+. Adding 0.10 wt% Cu2+ and 0.06 wt% Y3+ into BCZT dramatically improved the electrical properties as following: d33 = 552 pC/N, em = 10175, er = 4546, tanδ = 0.016, TC = 100 °C, kp = 0.475, Qm = 157.2, Pr = 10.82 μC/cm2 and EC = 2.33 kV/cm. A plausible mechanism was obtained to explain the reaction process and the favorable performances of BCZT-CuxYy. Co-doping Cu2+ and Y3+ into BCZT could be a promising method to improve and balance the sintering, phase transition, and electrical properties for potential practical applications of lead-free piezoceramics.

Owing to its potential to maximize the power output, hybrid energy harvesting technology has attracted more research interest. Boosting merits such as renewable energy sources and high output, hybrid photovoltaic-triboelectric nanogenerator (HPTNG) is considered as one of the promising power sources for next-generation smart electronics. To date, there is still a lack of a comprehensive review of the latest development and challenges of HPTNGs. Herein, we systematically summarize the recent advances of the hybrid photovoltaic-triboelectric energy-harvesting system. In particular, the structural flexibility and simplification of the hybridized device is described, followed by the detailed discussion from perspectives of the input mechanical energy sources, the output interaction between triboelectric nanogenerators and solar cells, as well as the functions and applications of the HPTNGs. Finally, the main challenges and perspective for the future development of HPTNGs are discussed.

With the rapidly increasing health and environmental awareness, demands for wearable electronics are no longer limited to performance and design, but also safety, health and environment protection. Herein, a sustainable and shape-adaptable skin-like liquid single-electrode TENG (LS-TENG) is developed using aloe vera gel (AVG)@NaCl as the liquid electrode. As an effective network channel for charge transfer, the liquid electrode shows high conductivity and mobility, leading to a high current density that is 2.1–23 folds of reported LS-TENGs. Besides, the size effect of liquid electrode in LS-TENG is firstly investigated, upon which the output parameters are optimized. Consequently, AVG@1wt%NaCl-based LS-TENG shows the highest output reported for LS-TENG with VOC of 157.8 V, JSC of 44.2 mA/m2 and power density of 4.61 W/m2. Moreover, the device shows a high sensitivity to minute face expressions and is suitable for 2D or 3D-shape fabrication, indicating a great potential for use in wearable electronics, such as e-skin and health monitoring.

Accumulation of high-arsenic fly ash (HAFA) poses a serious environmental threat due to the toxicity of As and release of other heavy metals especially Cr. In this work, a novel graphite felt (GF) cathode modified with the nanoscale MoS2/reduced graphene oxide (rGO) heterojunction is prepared by blending with PTFE emulsion for efficient synergistic oxidative dissolution of As(III) and Cr(III) in HAFA. By taking advantage of the p-n junction characteristics of the heterojunction and appropriate hydrophobicity of the PTFE coating, the modified GF efficiently utilizes both dissolved O2 and gaseous O2 in the 2e− oxygen reduction reaction (ORR). Our theoretical assessment indicates that gaseous O2 adsorbs stably on sulfur vacancies and is reduced by electrons transmitted from rGO. Experimentally, the modified GF shows superior ORR catalytic activity as exemplified by a high peak current density of 8.41 mA cm−2 and onset potential of 0.53 V vs. RHE. OH generated by the Cr and Fe-triggered autocatalysis mechanism promotes oxidization of As(III) and Cr(III) in detoxification of HAFA resulting in 96.1% As removal as well as 70.74% Cr removal in 135 min. The modified GF with excellent stability and durability has immense industrial prospect in detoxification of HAFA and treatment of other types of As-containing hazardous wastes.

Li- and Mn-rich materials have high capacities but serious voltage attenuation, whereas Ni-rich materials LiNi0.8Co0.1Mn0.1O2 (NCM) have good rate characteristics but poor stabilities, and they readily to oxidize organic electrolytes. The core–shell strategy with Ni-rich materials as the core and Li- and Mn-rich materials as the shell was expected to balance these merits and drawbacks. In this work, simple and concentration-gradient Li- and Mn-rich shell were successfully synthesized on NCM and critically compared. As expected, a distinct core–shell interface was observed for the simple core–shell cathode, which causes the shell to crack during cycling and exhibits worse electrochemical performance than the single Li- and Mn-rich cathodes and Ni-rich cathodes. In contrast, the fabricated concentration-gradient core–shell cathode shows the uniform fusion of the core and shell at the atomic level, and the overall electrochemical performance is far superior to that of the simple core–shell and pristine cathodes. In addition, it delivers an initial reversible capacity of 226.6 mAh g−1 at a C-rate of 0.1C and 120.2 mAh g−1 at 10.0C, and it retains 86.9% of its capacity after 100 cycles to 4.6 V at 1.0C. Differential capacity versus potential (dQ/dV versus V) and EIS analyses show that the concentration-gradient core–shell cathode has a stable impedance and very stable average voltage. Obviously, the concentration-gradient coating of the Li- and Mn-rich shell can maximize the merits of the core and shell.

Owing to the limited deformability and restricted scalability of traditional triboelectric nanogenerator (TENG), liquid single-electrode TENG based on graphene oxide dispersion (GO LS-TENG) was developed in this study. The device exhibits high short-circuit current density of 18.61 mA m−2 at contact frequency of 3 Hz, being much higher than that of reported LS-TENG based on NaCl solution (1.8 mA m−2, 2.3 Hz) and liquid metal (8.6 mA m−2, 3 Hz). Moreover, its maximum power density can reach 4.97 W m−2 (1.99 mW, 3 Hz), which is higher than that of a reported single-electrode TENG based on GO solid electrode (3.13 W m−2, 5 Hz). On palm tapping the device, 87 green LEDs connected in series can be lit up. Robustness, durability and reproducibility tests show high stability, sensitivity, and potential use of this device in wearable electronics. This work demonstrates a novel approach to fabricate LS-TENG with simple structure, high output and high sensitivity for use in highly flexible and deformable wearable devices.

Metal halide perovskite quantum dots (PQDs), with excellent optical properties and spectacular characteristics of direct and tunable bandgaps, strong light-absorption coefficients, high defect tolerance, and low nonradiative recombination rates, are highly attractive for modern optoelectronic devices. However, the stability issue of PQDs remains a critical challenge of this newly emerged material despite the recent rapid progress. Here, the encapsulation strategies to improve the stability of PQDs are comprehensively reviewed. A special emphasis is put on the effects of encapsulation, ranging from the improvement of chemical stability, to the inhibition of light-induced decomposition, to the enhancement of thermal stability. Particular attention is devoted to summarizing the encapsulation approaches, including the sol-gel method, the template method, physical blending, and microencapsulation. The selection principles of encapsulation materials, including the rigid lattice or porous structure of inorganic compounds, the low penetration rate of oxygen or water, as well as the swelling-deswelling process of polymers, are addressed systematically. Special interest is put on the applications of the encapsulated PQDs with improved stability in white light-emitting diodes, lasers, and biological applications. Finally, the main challenges in encapsulating PQDs and further investigation directions are discussed for future research to promote the development of stable metal halide perovskite materials.

A new kind of acid red 138 (AR138)–calcium fluoride nanosized CaF2/AR138 hybrid adsorbent (CFAR) was prepared. The microstructure of the hybrid adsorbent was characterized and its adsorption capacity to two cationic dyes, methyl blue (MB) and ethyl violet (EV), from aqueous solutions was examined using a batch sorption technique. The adsorption behavior of the MB and EV on CFAR is in good agreement with the Langmiur isotherms. The maximum adsorption capacity (Qm) of CFAR for MB and EV are 370.4 and 131.6 mg/g, respectively. The effects of pH, ionic strength, temperature, and time have been investigated in detail. The CFAR adsorbent was used to treat two dye wastewaters with satisfactory results. In synthesis of the materials, all of the reactants are easily available and harmless to environment as well because AR138 may use a concentrated AR138-producing wastewater instead. Therefore, this paper has developed a simple, eco-friendly and waste treat waste method for large-scale production of a cost...