A new mononuclear yttrium(III) complex, [Y(MO)(3)(DMF)(3)(H2O)(2)] (where MO- is methyl orange anion (4-[(4-dimethylamino)phenyldiazenyl]benzenesulfonate)), was synthesized in an aqueous solution. The complex was characterized by elemental analysis, UV/Vis, FT-IR, and single-crystal X-ray crystallography. The yttrium oxysulfate nanoparticles (Y2O2SO4) were then prepared by calcination of [Y(MO)(3)(DMF)(3)(H2O)(2)]. The obtained nanoparticles were characterized by FT-IR, X-ray diffraction analysis (XRD), and field-emission scanning electron microscopy (FE-SEM). The hydrogen adsorption/desorption (H-ads/H-des) behavior of the Y(III) complex and Y2O2SO4 nanoparticles was studied at a carbon paste electrode (CPE) in H2SO4 by cyclic voltammetry (CV). The recorded voltammograms exhibited a pair of peaks corresponding to the adsorption/desorption of hydrogen for the Y(III) complex and Y2O2SO4 nanoparticles. The results show a reversible hydrogen adsorption/desorption reaction for both compounds. The voltammograms of the nanoparticles indicate an excellent cycling stability for the adsorption/desorption of hydrogen. In addition, the linear sweep voltammetry (LSV) technique was used to investigate the electrocatalytic activity of both compounds for the hydrogen adsorption reaction. The linear voltammograms of both compounds demonstrate the excellent electrocatalytic activity for the hydrogen adsorption reaction. (C) 2016 Elsevier B.V. All rights reserved.