Supercapacitive properties of amorphous MoS3 and crystalline MoS2 nanosheets in an organic electrolyte

Abstract

Molybdenum sulfide materials receive high attention as high-performance electrodes for electrochemical energy storage devices. In this study, we investigate the electrochemical energy storage properties of amorphous MoS₃ and crystalline MoS₂ materials (prepared via thermal decomposition of ammonium tetrathiomolybdate) using an organic liquid electrolyte. Physicochemical characterization using X-ray diffraction pattern and laser Raman analysis confirms the formation of amorphous MoS₃ and crystalline MoS₂, respectively. The energy storage properties of MoS₃ and MoS₂ based symmetric supercapacitor devices were comparatively studied using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge analysis. The cyclic voltammetry analysis reveals the mechanism of charge storage in MoS₃ and MoS₂ is due to the ion-intercalation/de-intercalation pseudocapacitance. Electrochemical impedance spectroscopy studies reveal the better capacitance and charge-transfer nature of the crystalline MoS₂ symmetric supercapacitor compared to that of the amorphous MoS₃ symmetric supercapacitor. The charge–discharge analysis suggests that the MoS₂ symmetric supercapacitor device possesses better electrochemical energy storage properties with a high specific capacity of 20.81 mA h g⁻¹ (24.98 F g⁻¹) and energy density of about 20.69 W h kg⁻¹ with the excellent cyclic stability of about 2000 cycles. The experimental results suggest that the crystalline MoS₂ sheets might be a better choice than amorphous MoS₃ as an electrode material for supercapacitors using an organic liquid electrolyte.