Flexible self-powered humidity sensors with high response and good flexibility have attracted extensive interest in wearable electronics, motion monitoring and personal healthcare. In this work, we ...reported a high-performance flexible tin disulfide nanoflowers/reduced graphene oxide (SnS2/RGO) nanohybrid-based humidity sensor driven by a poly(tetrafluoroethylene) triboelectric nanogenerator (TENG). The humidity sensitive film of SnS2/RGO was screen-printed on a flexible PET substrate with Au interdigital electrodes. The TENG has a peak-to-peak voltage of 500 V and maximum output power of 378 μW. The tribotronic constant voltage source is achieved by integrating TENG with voltage rectifier and stabilizer circuits to steadily power the humidity sensor. The performance of the self-powered triboelectric humidity sensor (TEHS) at different humidity levels was systematically investigated, which exhibits high steady output voltage (0–24 V), fast response/recovery time (4 s/3 s for 33%RH, 6 s/15 s for 97%RH), wide sensing range (0–97%RH), great stability, and ultralow power consumption (29.78 μW). Furthermore, the TEHS demonstrated the potential ability of monitoring human breath with differ frequency, human cough, and finger approach in various applications for humidity sensing. This work provides a novel thought to design the self-powered humidity sensor, and also proposes the promising applications of TENG for the self-powered electronic devices.
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•A flexible poly(tetrafluoroethylene) triboelectric nanogenerator (TENG) was fabricated and used as energy harvester.•A flexible SnS2 nanoflowers/reduced graphene oxide (SnS2/RGO) nanohybrid based humidity sensor was fabricated.•The self-powered triboelectric humidity sensor (TEHS) was proposed by integrating the TENG with the humidity sensor.•The TEHS demonstrates excellent humidity sensing properties and ultralow power consumption in a wide RH range.•The TEHS is capable of monitoring human breath, cough, and finger approach for multifunctional applications.
It is crucial to determine the optimal number of clusters for the clustering quality in cluster analysis. From the standpoint of sample geometry, two concepts, i.e., the sample clustering dispersion ...degree and the sample clustering synthesis degree, are defined, and a new clustering validity index is designed. Moreover, a method for determining the optimal number of clusters based on an agglomerative hierarchical clustering (AHC) algorithm is proposed. The new index and the method can evaluate the clustering results produced by the AHC and determine the optimal number of clusters for multiple types of datasets, such as linear, manifold, annular, and convex structures. Theoretical research and experimental results indicate the validity and good performance of the proposed index and the method.
Efficient thermal energy harvesting using phase‐change materials (PCMs) has great potential for cost‐effective thermal management and energy storage applications. However, the low thermal ...conductivity of PCMs (KPCM) is a long‐standing bottleneck for high‐power‐density energy harvesting. Although PCM‐based nanocomposites with an enhanced thermal conductivity can address this issue, achieving a higher K (>10 W m−1 K−1) at filler loadings below 50 wt% remains challenging. A strategy for synthesizing highly thermally conductive phase‐change composites (PCCs) by compression‐induced construction of large aligned graphite sheets inside PCCs is demonstrated. The millimeter‐sized graphite sheet consists of lateral van‐der‐Waals‐bonded and oriented graphite nanoplatelets at the micro/nanoscale, which together with a thin PCM layer between the sheets synergistically enhance KPCM in the range of 4.4–35.0 W m−1 K−1 at graphite loadings below 40.0 wt%. The resulting PCCs also demonstrate homogeneity, no leakage, and superior phase change behavior, which can be easily engineered into devices for efficient thermal energy harvesting by coordinating the sheet orientation with the thermal transport direction. This method offers a promising route to high‐power‐density and low‐cost applications of PCMs in large‐scale thermal energy storage, thermal management of electronics, etc.
A method for synthesizing high‐performance thermally conductive phase‐ change composites is demonstrated. Large aligned graphite sheets inside the composite are generated from worm‐like expanded graphite. The aligned and interconnected graphite framework enhances KPCM up to 4.4–35.0 W m−1 K−1 at graphite loadings below 40.0 wt%, which may accelerate the high‐power‐density, low‐cost, and large‐scale applications of phase‐change materials.
Recent advances in thermally localized solar evaporation hold significant promise for vapor generation, seawater desalination, wastewater treatment, and medical sterilization. However, salt ...accumulation is one of the key bottlenecks for reliable adoption. Here, we demonstrate highly efficient (>80% solar-to-vapor conversion efficiency) and salt rejecting (20 weight % salinity) solar evaporation by engineering the fluidic flow in a wick-free confined water layer. With mechanistic modeling and experimental characterization of salt transport, we show that natural convection can be triggered in the confined water. More notably, there exists a regime enabling simultaneous thermal localization and salt rejection, i.e., natural convection significantly accelerates salt rejection while inducing negligible additional heat loss. Furthermore, we show the broad applicability by integrating this confined water layer with a recently developed contactless solar evaporator and report an improved efficiency. This work elucidates the fundamentals of salt transport and offers a low-cost strategy for high-performance solar evaporation.
Passive vapor generation systems with interfacial solar heat localization enable high-efficiency low-cost desalination. In particular, recent progress combining interfacial solar heating and ...vaporization enthalpy recycling through a capillary-fed multistage architecture, known as the thermally-localized multistage solar still (TMSS), significantly improves the performance of passive solar desalination. Yet, state-of-the-art experimental demonstrations of solar-to-vapor conversion efficiency are still limited since the dominant factors and the general design principle for TMSS were not well-understood. In this work, we show optimizing the overall heat and mass transport in a multistage configuration plays a key role for further improving the performance. This understanding also increases the flexibility of material choices for the TMSS design. Using a low-cost and free-of-salt accumulation TMSS architecture, we experimentally demonstrated a record-high solar-to-vapor conversion efficiency of 385% with a production rate of 5.78 L m
−2
h
−1
under one-sun illumination, where more than 75% of the total production was collected through condensation. This work not only significantly improves the performance of existing passive solar desalination technologies for portable and affordable drinking water, but also provides a comprehensive physical understanding and optimization principle for TMSS systems.
A palladium-catalyzed chelation-assisted ortho-nitration of aryl C–H bond is described. A range of azaarenes such as 2-arylquinoxalines, pyridines, quinoline, and pyrazoles were nitrated with ...excellent chemo- and regioselectivity. Using the O-methyl oximyl group as a removable directing group, the regiospecific synthesis of a variety of o-nitro aryl ketones was achieved starting from aryl ketones via a three-step process involving the Pd-catalyzed ipso-nitration of C–H bond as a key step. Mechanistic investigations support a silver-mediated radical mechanism involving Pd((II/III) and/or Pd(II/IV) catalytic cycles under oxidizing conditions.
Absorption heat pump attracts increasing attention due to its advantages in low grade thermal energy utilization. It can be applied for waste heat reuse to save energy consumption, reduce environment ...pollution, and bring considerable economic benefit. In this paper, three important aspects for absorption heat pump for waste heat reuse are reviewed. In the first part, different absorption heat pump cycles are classified and introduced. Absorption heat pumps for heat amplification and absorption heat transformer for temperature upgrading are included. Both basic single effect cycles and advanced cycles for better performance are introduced. In the second part, different working pairs, including the water based working pairs, ammonia based working pairs, alcohol based working pairs, and halogenated hydrocarbon based working pairs, for absorption heat pump are classified based on the refrigerant. In the third part, the applications of the absorption heat pump and absorption heat transformer for waste heat reuse in different industries are introduced. Based on the reviews in the three aspects, essential summary and future perspective are presented at last.
A mild and efficient protocol for the synthesis of fluorinated pyrazoles has been developed via gold(I)-catalyzed tandem aminofluorination of alkynes in the presence of Selectfluor. This method ...offers a broad substrate scope.
•IL absorbents for NH3 and H2O are evaluated in thermal storage and transmission.•A screening method is proposed via relating VLE data with energy density.•Change in excess enthalpy during absorption ...is considered in the modeling.•Improvement in both COP and energy density could be achieved by IL absorbents.
Efficient thermal energy storage and transmission are considered as two of the most significant challenges for decarbonisation in thermal energy utilization. The liquid-gas absorption thermal energy storage/transmission system is promising approach to tackle these challenges, owing to the long-term stability, flexibility in heat/cooling output, and liquid medium. At present, the shortcomings of conventional absorption working fluids have triggered considerable interest in searching for novel working pairs, such as ionic liquids (ILs). However, it is still unknown whether ILs can work effectively in thermal energy transmission with long distance. In this study, the absorption thermal energy storage/transmission systems using IL absorbents are theoretically investigated. modeling frameworks for working pairs screening and performance evaluation are proposed. Results show that the IL-based working pairs present better or comparable performance than conventional working pairs (including H2O/Salts and NH3/Salts). Among the investigated IL-based working pairs, H2O/EMIMEtSO4 presents highest COP (around 0.62) and exergy efficiency (around 0.32), and is relatively close to H2O/LiBr. As for energy storage density, H2O/EMIMAc performs better than H2O/LiBr, presenting 137.4 kWh/m3 with a desorption temperature of 115 °C. The present work provides a straightforward screening of IL absorbents for thermal energy storage and transmission purposes.
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Three-axis atomic magnetometers have great advantages for interpreting information conveyed by magnetic fields. Here, we demonstrate a compact construction of a three-axis vector atomic magnetometer. ...The magnetometer is operated with a single laser beam and with a specially designed triangular 87Rb vapor cell (side length is 5 mm). The ability of three-axis measurement is realized by reflecting the light beam in the cell chamber under high pressure, so that the atoms before and after reflection are polarized along two different directions. It achieves a sensitivity of 40 fT/Hz in x-axis, 20 fT/Hz in y-axis, and 30 fT/Hz in z-axis under spin-exchange relaxation-free regime. The crosstalk effect between different axes is proven to be little in this configuration. The sensor configuration here is expected to form further values, especially for vector biomagnetism measurement, clinical diagnosis, and field source reconstruction.
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