This work reports on the general electrodeposition mechanism of tetrachalcogenmetallates from 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Both tetrathio- and tetraselenomolybdate underwent anodic electrodeposition and cathodic corrosion reactions as determined by UV-vis spectroelectrochemistry. Electrodeposition was carried out by cycling the potential between the anodic and cathodic regimes. This resulted in a film of densely packed nanoparticles of amorphous MoSx or MoSex as determined by SEM, Raman, and XPS. The films were shown to have high activity for the hydrogen evolution reaction. The onset potential (J = 1 mA/cm(2)) of the MoSx film was E = -0.208 V vs RHE, and that of MoSex was E = -0.230 V vs RHE. The Tafel slope of MoSx was 42 mV/decade, and that of MoSex was 59 mV/decade.