Transition metal carbides and nitrides (MXenes), a family of two-dimensional (2D) inorganic compounds, are materials composed of a few atomic layers of transition metal carbides, nitrides, or carbonitrides. Ti₃C₂, the first 2D layered MXene, was isolated in 2011. This material, which is a layered bulk material analogous to graphite, was derived from its 3D phase, Ti₃AlC₂ MAX. Since then, material scientists have either determined or predicted the stable phases of >200 different MXenes based on combinations of various transition metals such as Ti, Mo, V, Cr, and their alloys with C and N. Extensive experimental and theoretical studies have shown their exciting potential for energy conversion and electrochemical storage. To this end, we comprehensively summarize the current advances in MXene research. We begin by reviewing the structure types and morphologies and their fabrication routes. The review then discusses the mechanical, electrical, optical, and electrochemical properties of MXenes. The focus then turns to their exciting potential in energy storage and conversion. Energy storage applications include electrodes in rechargeable lithium- and sodium-ion batteries, lithium–sulfur batteries, and supercapacitors. In terms of energy conversion, photocatalytic fuel production, such as hydrogen evolution from water splitting, and carbon dioxide reduction are presented. The potential of MXenes for the photocatalytic degradation of organic pollutants in water, such as dye waste, is also addressed, along with their promise as catalysts for ammonium synthesis from nitrogen. Finally, their application potential is summarized.

The pioneering exfoliation of monolayer tungsten diselenide has greatly inspired researchers toward semiconducting applications. WSe₂ belongs to a family of transition‐metal dichalcogenides. Similar to graphene, WSe₂ and analogous dichalcogenides have layered structures with weak van der Waals interactions between two adjacent layers. First, the readers are presented with the fundamentals of WSe_2, such as types, morphologies, and properties. Here, we report the characterization principles and practices such as microscopy, spectroscopy, and diffraction. Second, the methods for obtaining high‐quality WSe₂, such as exfoliation, hydrothermal and chemical vapor deposition, are briefly listed. With advantages of light weight, flexibility, and high quantum efficiency, 2D materials may have a niche in optoelectronics as building blocks in p‐n junctions. Therefore, we introduce a state‐of‐the‐art demonstration of heterostructure devices employing the p‐type WSe₂ semiconductor. The device architectures include field‐effect transistors, photodetectors, gas sensors, and photovoltaic solar cells. Due to its unique electronic, optical, and energy band properties, WSe₂ has been increasingly investigated due to the conductivity of the p‐type charge carrier upon palladium contact. Eventually, the dynamic research on WSe₂ and van der Waals heterostructures is summarized to arouse the passion of the 2D research community. image