Amorphous molybdenum sulfide (MoSx) materials have been considered as cheap and promising catalysts for hydrogen evolution reaction (HER). In this contribution, we report that the amorphous MoSx catalysts prepared by the low temperature thermolysis of the (NH4)(2)MoS4 precursors on carbon clothes (catalyst loading: 3.2 mg/cm(2)) exhibit a Tefal slope of 50.5 mV/dec and a high exchange current density of 1.5 x 10(-3) mA/cm(2) in 0.5 M H2SO4 solutions. Spectroscopic studies of the amorphous MoSx catalysts show that the increase of HER efficiency is positively correlated to the concentration of S-2(2-) species, providing strong evidence to support the argument that S-2(2-) is an active species for electrocatalytic HER. Additionally, the method for preparing catalysts is simple, scalable and applicable for large-scale production. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.