Electrodeposition of MoS₂for Charge Storage in Electrochemical Supercapacitors

Mo sulfide thin films were cathodically electrodeposited onto glassy carbon electrodes (GCE) from aqueous electrolytes containing 10 mM (NH 4 ) 2 MoS 4 and 0.2 M KCl. Film adhesion was adequate only for electrodes pretreated by potential cycling in 1.0 M HNO 3 and 0.1 M NaF to enhance the surface roughness and partially oxidize the GCE. Previous studies report direct cathodic electrodeposition of MoS 2 , but energy dispersive X-ray spectroscopy and X-ray diffraction suggest that the as-deposited film is closer in stoichiometry to MoS 3 , which can be converted to MoS 2 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 Na 2 SO 4 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 MoS 2 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. MoS 2 film formed by high temperature annealing in Ar have a charge storage capability about 40 × higher than the as-deposited Mo sulfide films.