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

Abstract

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 (CQ) 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 CQ with the intercalation of Li ions resulting in a decrease in the CQ. In contrast, Li ions were found to be the best intercalant for the 2H-TaS2 phase (highest CQ), 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 CQ. In contrast, CQ 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.