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Organic solid electrolytes for rechargeable batteries are usually produced by dissolving or suspending all components and casting. For decades, acetonitrile has been widely used despite its rapid reaction with alkali metals, forming toxic products such as cyanide. Using large amounts of acetonitrile for industrial applications may pose health and environmental concerns. In addition, researchers claim that even if the solid electrolyte membranes contain residual trace water, this may positively affect the transport properties of Na ions in PEO, and those batteries with electrolytes containing trace water showed significantly improved electrochemical performance. Here, an aqueous medium was considered for casting solid polymer electrolyte membranes. Na ions conducting membranes produced with water were characterized and compared to traditional ones, produced with organic solvents. Spectral studies and electrochemical measurements of symmetric cells with Na metal electrodes under static and dynamic conditions and all-solid-state Na batteries showed that the membranes cast from aqueous media are similar to their counterparts, cast from organic volatile solvents. Surprisingly, the water-cast membranes exhibit better performance as solid electrolytes than similar membranes prepared with organic solvents.

We report a facile and robust room-temperature NO2sensor fabricated using bi- and multi-layered 2H variant of tungsten di-selenide (2H-WSe2) nanosheets, exhibiting high sensing characteristics. A simple liquid-assisted exfoliation of 2H-WSe2, prepared using ambient pressure chemical vapor deposition, allows smooth integration of these nanosheets on transducers. Three sensor batches are fabricated by modulating the total number of layers (L) obtained from the total number of droplets from a homogeneous 2H-WSe2dispersion, such as ∼2L, ∼5–6L, and ∼13–17L, respectively. The gas-sensing attributes of 2H-WSe2nanosheets are investigated thoroughly. Room temperature (RT) experiments show that these devices are specifically tailored for NO2detection. 2L WSe2nanosheets deliver the best rapid response compared to ∼5–6L or ∼13–17L. The response of 2L WSe2at RT is 250, 328, and 361% to 2, 4, and 6 ppm NO2, respectively. The sensor showed nearly the same response toward low NO2concentration even after 9 months of testing, confirming its remarkable long-term stability. A selectivity study, performed at three working temperatures (RT, 100, and 150 °C), shows high selectivity at 150 and 100 °C. Full selectivity toward NO2at RT confirms that 2H-WSe2nanosheet-based sensors are ideal candidates for NO2gas detection.

Low-wavenumber Raman (LWR) spectroscopy determines signatures in structural information and layer-to-layer dependency of transition metal dichalcogenides (TMDCs). It supports proper 2D TMDC analysis and subsequent layer verification. The nondestructive nature and ultrafast detection make LWR measurements imperative for layer variations and defect investigations. Interference-enhanced Raman scattering utilizes a metal–dielectric layer to enhance the Raman signal. This has been used to study graphene, C60,and Te. Here, we investigate using Al/Al2O3coatings to enhance the LWR scattering of different 2H-WS2layers and understand the structures of these large-area nanosheets. Phase-pure WS2is synthesized by CVD, and the layers are exfoliated via ultrasonication at 80 kHz. Layers were drop-casted on Al/Al2O3coatings of different thicknesses of Al2O3to study differences in bilayers up to a few layers of 2H-WS2. We observe an enhancement of 30 times in the Raman signal (356 cm–1) corresponding to a quarter wave-thick 80 nm Al2O3and characterize these 2H-WS2films for their defects. Transfer-matrix calculations confirm the observed behavior to field enhancement. Our work shows how the structures and weaknesses of 2D materials such as WS2can be better identified, provided an enhancing substrate is chosen.

Among the most reliable techniques for exfoliation of two-dimensional (2D) layered materials, sonication-assisted liquid-phase exfoliation (LPE) is considered as a cost-effective and straightforward method for preparing graphene and its 2D inorganic counterparts at reasonable sizes and acceptable levels of defects. Although there were rapid advances in this field, the effect and outcome of the sonication frequency are poorly understood and often ignored, resulting in a low exfoliation efficiency. Here, we demonstrate that simple mild bath sonication at a higher frequency and low power positively contributes to the thickness, size, and quality of the final exfoliated products. We show that monolayer graphene flakes can be directly exfoliated from graphite using ethanol as a solvent by increasing the frequency of the bath sonication from 37 to 80 kHz. The statistical analysis shows that ∼77% of the measured graphene flakes have a thickness below three layers with an average lateral size of 13 μm. We demonstrate that this approach works for digenite (Cu9S5) and silver sulfide (Ag2S), thus indicating that this exfoliation technique can be applied to other inorganic 2D materials to obtain high-quality few-layered flakes. This simple and effective method facilitates the formation of monolayer/few layers of graphene and transition metal chalcogenides for a wide range of applications.