A 2H-MoS2/carbon cloth composite for high-performance all-solid-state supercapacitors derived from a molybdenum dithiocarbamate complex

Reactant conversion-intercalation strategy toward interlayer-expanded MoS2 microflowers with superior supercapacitor performance

In order to avoid the complicated control and fussy procedure associated with foreign species and templates in conventional synthesis strategies, a simple reactant conversion-intercalation strategy is developed to synthesize interlayer-expanded MoS₂ (E-MoS₂) by employing ammonium thiocyanate converted from a thiourea reactant as intercalator. In this strategy, the thiourea plays a bifunctionality role as reactant and intercalator precursor to ensure in situ embedding into the interlayers of MoS₂ to expand the interlayer spacing. The optimal E-MoS₂ obtained presents superior supercapacitor performance with a specific capacity of 246.8 F g^-1 at 0.5 A g^-1 in 1 M Na₂SO₄ electrolyte in a three-electrode system, outperforming pristine MoS₂ prepared by a conventional hydrothermal method (42.5 F g^-1 at 0.5 A g^-1). Furthermore, a symmetric supercapacitor based on an E-MoS₂ electrode delivers a high specific capacity of 261.3 F g^-1 and energy density of 13.3 W h kg^-1 at 0.5 A g^-1, and excellent cycling life with 81.7% capacity retention after 3000 cycles at 2 A g^-1. Density functional theory calculations reveal that the NH₄⁺ and SCN^- can be effectively adsorbed on the surface to be inserted into the interlayers during the growth of MoS₂, resulting in an expanded interlayer spacing of 9.4 Å, and the favorable electrochemical performance stems from the large Na⁺ adsorption capacitance and low diffusion barrier of the E-MoS₂. This work offers a novel intercalation strategy that may be generally applicable to other layer-structured materials, shedding some light on the development of high-performance electrode materials via interface engineering for energy applications.

High-Performance MnO2 Nanowire/MoS2 Nanosheet Composite for a Symmetrical Solid-State Supercapacitor

To improve the production rate of MoS₂ nanosheets as an excellent supercapacitor (SC) material and enhance the performance of the MoS₂-based solid-state SC, a liquid phase exfoliation method is used to prepare MoS₂ nanosheets on a large scale. Then, the MnO₂ nanowire sample is synthesized by a one-step hydrothermal method to make a composite with the as-synthesized MoS₂ nanosheets to achieve a better performance of the solid-state SC. The interaction between the MoS₂ nanosheets and MnO₂ nanowires produces a synergistic effect, resulting in a decent energy storage performance. For practical applications, all-solid-state SC devices are fabricated with different molar ratios of MoS₂ nanosheets and MnO₂ nanowires. From the experimental results, it can be seen that the synthesized nanocomposite with a 1:4 M ratio of MoS₂ nanosheets and MnO₂ nanowires exhibits a high Brunauer-Emmett-Teller surface area (∼118 m²/g), optimum pore size distribution, a specific capacitance value of 212 F/g at 0.8 A/g, an energy density of 29.5 W h/kg, and a power density of 1316 W/kg. Besides, cyclic charging-discharging and retention tests manifest significant cycling stability with 84.1% capacitive retention after completing 5000 rapid charge-discharge cycles. It is believed that this unique, symmetric, lightweight, solid-state SC device may help accomplish a scalable approach toward powering forthcoming portable energy storage applications.