Advanced Progress of Non-Stoichiometric Transition Metal Sulfides for Sensing, Catalysis, and Energy Storage

Beyond the extensively studied two-dimensional transition metal dichalcogenides, a wide range of non-stoichiometric transition metal sulfides, such as molybdenum sulfides and tungsten sulfides (Mo₂S₃, W₂S₃, Mo₆S₈, Mo₆S₆, NiMo₃S₄), have attracted significant attention for their promising applications in sensing, catalysis, and energy storage. It is necessary to review the current advanced progress of non-stoichiometric transition metal sulfides for various applications. Here, we systematically summarize the synthesis strategies of the non-stoichiometric transition metal sulfides, encompassing methods such as the molten salt synthesis method, high-metal-content growth strategy, and others. Particular emphasis is placed on how variations in the metal-to-sulfur ratio give rise to distinct crystal structures and electronic properties, and how these features influence their conductivity, stability, and performance. This review will deepen the understanding of the state of the art of non-stoichiometric transition metal sulfides, including the synthesis, characterization, modification, and various applications.