Untapped potential of 2D charge density wave chalcogenides as negative supercapacitor electrode materials

Two-dimensional (2D) materials have opened new avenues for the fabrication of ultrathin, transparent, and flexible functional devices. However, the conventional inorganic graphene analogues are either semiconductors or insulators with low electronic conductivity, hindering their use as supercapacitor electrode materials, which require high conductivity and large surface area. Recently, 2D charge density wave (CDW) materials, such as 2D chalcogenides, have attracted extensive attention as high performance functional nanomaterials in sensors, energy conversion, and spintronic devices. Herein, TaS₂ is investigated as a potential CDW material for supercapacitors. The quantum capacitance (C _Q) of the different TaS₂ polymorphs (1T, 2H, and 3R) was estimated using density functional theory calculations for different numbers of TaS₂ layers and alkali-metal ion (Li, Na and K) intercalants. The results demonstrate the potential of 2H- and 3R-polymorphs as efficient negative electrode materials for supercapacitor devices. The intercalation of K and Na ions in 1T-TaS₂ led to an increase in the C_Q with the intercalation of Li ions resulting in a decrease in the C _Q. In contrast, Li ions were found to be the best intercalant for the 2H-TaS₂ phase (highest C _Q), while K ion intercalation was the best for the 3R-TaS₂ phase. Moreover, increasing the number of layers of the1T-TaS₂ resulted in the highest C_Q. In contrast, C _Q increases upon decreasing the number of layers of 2H-TaS₂. Both 1T-MoS₂ and 2H-TaS₂ can be combined to construct a highly performing supercapacitor device as the positive and negative electrodes, respectively.