RESUMO
Flexible membranes with ultrathin thickness and excellent mechanical properties have shown great potential for broad uses in solid polymer electrolytes (SPEs), on-skin electronics, etc. However, an ultrathin membrane (<5 µm) is rarely reported in the above applications due to the inherent trade-off between thickness and antifailure ability. We discover a protic solvent penetration strategy to prepare ultrathin, ultrastrong layered films through a continuous interweaving of aramid nanofibers (ANFs) with the assistance of simultaneous protonation and penetration of a protic solvent. The thickness of a pure ANF film can be controlled below 5 µm, with a tensile strength of 556.6 MPa, allowing us to produce the thinnest SPE (3.4 µm). The resultant SPEs enable Li-S batteries to cycle over a thousand times at a high rate of 1C due to the small ionic impedance conferred by the ultrathin characteristic and regulated ionic transportation. Besides, a high loading of the sulfur cathode (4 mg cm-2) with good sulfur utilization was achieved at a mild temperature (35 °C), which is difficult to realize in previously reported solid-state Li-S batteries. Through a simple laminating process at the wet state, the thicker film (tens of micrometers) obtained exhibits mechanical properties comparable to those of thin films and possesses the capability to withstand high-velocity projectile impacts, indicating that our technique features a high degree of thickness controllability. We believe that it can serve as a valuable tool to assemble nanomaterials into ultrathin, ultrastrong membranes for various applications.
RESUMO
Currently, the only thermoelectric (TE) materials commercially available at room temperature are those based on bismuth telluride. However, their widespread application is limited due to their inferior thermoelectric and mechanical properties. In this study, a strategy of growing a rigid second phase of MoSe2 is employed, in situ within the matrix phase to achieve n-type bismuth telluride-based materials with exceptional mechanical and thermoelectric properties. The in situ grown second phase contributes to both the electronic and lattice thermal conductivities. This is primarily attributed to the strong energy filtering effect, as the second phase forms a semi-common lattice interfacial structure with the matrix phase during growth. Furthermore, for composites containing 2 wt% MoSe2, a maximum zT value of 1.24 at 373 K can be achieved. On this basis, 8-pair TE module is fabricated and 1-pair TE module is optimized using a homemade p-type material. The optimized 1-pair TE module generates a maximum output power of 13.6 µW, which is twice that of the 8-pair TE module and four times more than the 8-pair TE module fabricated by commercial material. This work facilitates the development of the TE module by presenting a novel approach to obtaining bismuth telluride-based thermoelectric materials with superior thermoelectric and mechanical properties.
RESUMO
The Tibetan Plateau (TP) is crucial for global climate change and China's ecological security. Given recent drastic changes in vegetation from climate change and human activities, long-term vegetation monitoring is urgently required. This study produced the vegetation maps of the TP from 1990 to 2020 every ten years using random forest classifier and Landsat imagery. We selected the same stable samples and features for mapping to reduce errors between years and proposed spatial filtering to further improve the accuracy. The overall accuracy surpassed 95.00%, with all Kappa coefficients exceeding 0.95. A further assessment based on sampling sites from literature and field survey was higher than 80%. The importance ranking results indicated that in the TP, climate factors and terrain factors are the most important factors in the vegetation mapping. This study provides a method for mapping vegetation in alpine areas and data support for researching the dynamic change of vegetation on the TP and evaluating its response to climate change.