ABSTRACT
A direct thin film approach to fabricate large-surface MoS2 nanosheet thin film supercapacitors using the solution-based diffusion of thiourea into an anodized MoO3 thin film was investigated. A dense MoS2 nanosheet thin film electrode (D-MoS2 ) was obtained when the anodized MoO3 thin film was processed in a low thiourea solution concentration, whereas a highly porous MoS2 nanosheet thin film electrode (P-MoS2 ) was formed at a higher thiourea solution concentration. The charge storage performances of the D-MoS2 and P-MoS2 thin films displayed an unusual increase in capacitance on extended cycling, leading to a capacitance as high as around 5-8â mF cm-2 . X-ray diffraction and cross-sectional microscopy revealed the capacitance enhancements of the MoS2 supercapacitors are attributable to the nucleation of a new MoS2-x Ox phase upon cycling. For the D-MoS2 nanosheet thin film, the formation and growth of the MoS2-x Ox phase during cycling was accompanied by a volumetric expansion of the MoS2 layer. For the P-MoS2 thin film, the nucleation and growth of the MoS2-x Ox phase occurred in the pores of the MoS2 layer. The propagation of the MoS2-x Ox phase also shifted the charge storage process in both films from a diffusion-limited process to a capacitive-dominant process.
