Scalable Synthesis of Few-Layered 2D Tungsten Diselenide (2H-WSe₂) Nanosheets Directly Grown on Tungsten (W) Foil Using Ambient-Pressure Chemical Vapor Deposition for Reversible Li-Ion Storage

Abstract

We report a facile two-furnace APCVD synthesis of 2H-WSe 2 . A systematic study of the process parameters is performed to show the formation of the phase-pure material. Extensive characterization of the bulk and exfoliated material confirm that 2H-WSe 2 is layered (i.e., 2D). X-ray diffraction (XRD) confirms the phase, while high-resolution scanning electron microscopy (HRSEM), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM) clarify the morphology of the material. Focused ion beam scanning electron microscopy (FIB-SEM) estimates the depth of the 2H-WSe 2 formed on W foil to be around 5–8 μm, and Raman/UV–vis measurements prove the quality of the exfoliated 2H-WSe 2 . Studies on the redox processes of lithium-ion batteries (LiBs) show an increase in capacity up to 500 cycles. On prolonged cycling, the discharge capacity up to the 50th cycle at 250 mA/g of the material shows a stable value of 550 mAh/g. These observations indicate that exfoliated 2H-WSe 2 has promising applications as an LiB electrode material.

Robust Room-Temperature NO2 Sensors from Exfoliated 2D Few-Layered CVD-Grown Bulk Tungsten Di-selenide (2H-WSe2)

“…This ultimately leads to a variation in response to the NO 2 gas sensing. This particular study, according to the best of our knowledge, is the first report of APCVD-grown LPE 2H-WSe 2 from bulk 2H-WSe 2 grown on tungsten (W) foil, as per our recent report on 2H-WSe 2 growth 41 acting as a chemical sensor for NO 2 detection (primarily based on sensing concerning droplet modulation). The pristine 2H-WSe 2 is prepared according to our previous work, where a surface reaction between W foil and elemental Se (in the absence of any reductant) drives the formation of 2H-WSe 2 on the exposed part of the W foil.…”

“…Starting from two droplets, we obtained two layers of 2H-WSe 2 (∼1.7 ± 0.3 nm), which is very consistent with our previous report. 41 Increasing the number of droplets to 8 and 12 gave us consecutive height profiles of ∼5.5 ± 0.3 nm (indicating ∼6L) and ∼11 ± 0.3 nm (indicating ∼13L), respectively. We also performed a similar measurement for exfoliation and drop-casting of 2H-WSe 2 at 37 kHz, which provided us a similar variation.…”

“…The exfoliation parameters of the pristine 2H-WSe 2 also varied according to our previous report. 41 Since both ethanol and isopropanol proved to be ideal low-boiling solvents for our exfoliation experiments, further analyses in ethanol dispersions were carried out. The main idea was to find out the optimal stability of the dispersions obtained after exfoliations because it would help in subsequent simple integration of the 2H-WSe 2 flakes into the sensor-based system.…”

“…The synthetic procedure is the same as per our previous reports of growing bulk 2H-WSe 2 on W foil using elemental Se (Alfa Aesar, 99.999% purity) and W foil (Alfa Aesar, 99.999% purity) in an AP-CVD-assisted process. 41 We prepared the pristine W foil after etching it in dilute hydrochloric acid (0.01 M) and sonicating it in isopropanol (for removing the native oxide layer on the exposed W foil’s surface). The W foil was introduced into the furnace (F2) at 900 °C.…”

“…The pristine 2H-WSe 2 is prepared according to our previous work, where a surface reaction between W foil and elemental Se (in the absence of any reductant) drives the formation of 2H-WSe 2 on the exposed part of the W foil. 41 The bulk 2H-WSe 2 is then exfoliated following the already-optimized parameters (at two frequencies of 37 and 80 kHz). The stability of the as-prepared dispersions was previously checked in different solvents.…”