Two-dimensional (2D) transitional metal oxides (TMOs) are an attractive class of materials due to the combined advantages of high active surface area, enhanced electrochemical properties, and stability. Among the 2D TMOs, 2D tungsten oxide (WO) nanosheets possess great potential in electrochemical applications, particularly in electrochromic (EC) devices. However, feasible production of 2D WO nanosheets is challenging due to the innate 3D crystallographic structure of WO. Here we report a novel solution-phase synthesis of 2D WO nanosheets through simple oxidation from 2D tungsten disulfide (WS) nanosheets exfoliated from bulk WS powder. The complete conversion from WS into WO was confirmed through crystallographic and elemental analyses, followed by validation of the 2D WO nanosheets applied in the EC device. The EC device showed color modulation of 62.57% at 700 nm wavelength, which is 3.43 times higher than the value of the conventional device using bulk WO powder, while also showing enhancement of ∼46.62% and ∼62.71% in switching response-time (coloration and bleaching). The mechanism of enhancement was rationalized through comparative analysis based on the thickness of the WO components. In the future, 2D WO nanosheets could also be used for other promising applications such as sensors, catalysis, thermoelectric, and energy conversion.

The insufficient strategies to improve electronic transport, the poor intrinsic chemical activities, and limited active site densities are all factors inhibiting MXenes from their electrocatalytic applications in terms of hydrogen production. Herein, these limitations are overcome by tunable interfacial chemical doping with a nonmetallic electron donor, i.e., phosphorization through simple heattreatment with triphenyl phosphine (TPP) as a phosphorous source in 2D vanadium carbide MXene. Through this process, substitution, and/or doping of phosphorous occurs at the basal plane with controllable chemical compositions (3.83-4.84 at%). Density functional theory (DFT) calculations demonstrate that the PC bonding shows the lowest surface formation energy (ΔG Surf ) of 0.027 eV Å −2 and Gibbs free energy (ΔG H ) of -0.02 eV, whereas others such as P-oxide and PV (phosphide) show highly positive ΔG H . The P3-V 2 CT x treated at 500 °C shows the highest concentration of PC bonds, and exhibits the lowest onset overpotential of -28 mV, Tafel slope of 74 mV dec −1 , and the smallest overpotential of −163 mV at 10 mA cm −2 in 0.5 m H 2 SO 4 . The first strategy for electrocatalytically accelerating hydrogen evolution activity of V 2 CT x MXene by simple interfacial doping will open the possibility of manipulating the catalytic performance of various MXenes.

Identifying effective means to improve the electrocatalytic performance of transition metal dichalcogenides in alkaline electrolytes is a significant challenge. Herein, an advanced electrocatalyst possessing shells of molybdenum disulfide (MoS2) on molybdenum carbide (Mo2C) for efficient electrocatalytic activity in alkaline electrolytes is reported. The strained sheets of curved MoS2 surround the surface of Mo2C, turning the inactive basal planes of MoS2 into highly active electrocatalytic sites in the alkaline electrolyte. The van der Waals layers, which even possess van der Waals epitaxy along (100) facets of MoS2 and Mo2C, enhance the spin coupling between MoS2 and Mo2C, providing an easy electron transfer path for excellent electrocatalytic activity in alkaline electrolytes and solving the stability issue. In addition, it is found that curved MoS2 sheets on Mo2C show 3.45% tensile strain in the lattice, producing excellent catalytic activity for both oxygen reduction reaction (ORR) (with E1/2 = 0.60 V vs RHE) and oxygen evolution reaction (OER) (overpotential = 1.51 V vs RHE at 10 mA cm−2) with 60 times higher electrochemical active area than pristine MoS2. The unique structure and synthesis route outlined here provide a novel and efficient approach toward designing highly active, durable, and cost‐effective ORR and OER electrocatalysts.

Recent progress and research trends for 2D and 3D nanostructures in thermoelectric applications.