Recent progress on transition metal diselenides from formation and modification to applications.

The development of graphene promotes the research of similar two-dimensional (2D) materials, especially 2D transition metal dichalcogenides (TMDCs) with semiconductor properties. Monolayer or few-layer TMDCs have several advantages, such as direct band gap, weak interlayer van der Waals force, large interlayer spacing, and abundant marginal active sites, which make them widely used in catalysis, optoelectronics, as well as energy conversion and storage devices. In addition, transition metal diselenides (TMDSs) also possess many intriguing characteristics. For instance, transition metal diselenides (e.g., MoSe2) have a more stable 1T phase, larger interlayer spacing, smaller band gap, and more obvious metallic property of Se than TMDCs (e.g., MoS2). Thus, it has become one of the most attractive research topics branching out from TMDCs. Herein, this review unveils the structures, synthesis, properties, modifications, applications, and perspectives for TMDSs.