Electrodeposition of MoS2 for Charge Storage in Electrochemical Supercapacitors

Abstract

Mo sulfide thin films were cathodically electrodeposited onto glassy carbon electrodes (GCE) from aqueous electrolytes containing 10 mM (NH4)2MoS4 and 0.2 M KCl. Film adhesion was adequate only for electrodes pretreated by potential cycling in 1.0 M HNO3 and 0.1 M NaF to enhance the surface roughness and partially oxidize the GCE. Previous studies report direct cathodic electrodeposition of MoS2, but energy dispersive X-ray spectroscopy and X-ray diffraction suggest that the as-deposited film is closer in stoichiometry to MoS3, which can be converted to MoS2 by annealing in Ar at 600°C for one hour. The charge storage capability of electrodeposited Mo sulfide films is studied here for the first time in 1.0 M Na2SO4 over the thickness range 50 nm to 5 μm, and before and after high temperature annealing. The highest capacitance is obtained for 50 nm thick MoS2 films is 330 F/g measured by galvanostatic charge discharge at 0.75 A/g, and 360 F/g measured by cyclic voltammetry at 10 mV/sec. The capacitance per unit mass decreases with increasing film thickness due to reduced electrochemical accessibility. MoS2 film formed by high temperature annealing in Ar have a charge storage capability about 40× higher than the as-deposited Mo sulfide films.