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

Abstract

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.