Oxygen Nucleation of MoS2 Nanosheet Thin Film Supercapacitor Electrodes for Enhanced Electrochemical Energy Storage

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 5-8 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-xOx phase upon cycling. For the D-MoS2 nanosheet thin film, the formation and growth of the MoS2-xOx 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-xOx phase occurred in the pores of the MoS2 layer. The propagation of the MoS2-xOx phase also shifted the charge storage process in both films from a diffusion-limited process to a capacitive-dominant process.

Automated summary

A direct thin film approach was used to fabricate large-surface MoS2 nanosheet thin film supercapacitors. The charge storage performances of the thin films exhibited an unusual increase in capacitance on extended cycling. This enhancement in capacitance was attributed to the nucleation of a new MoS2-xOx phase during cycling, shifting the charge storage process from diffusion-limited to capacitive-dominant.