Hydrothermal synthesis of monoclinic WO 3 nanoplates and nanorods used as an electrocatalyst for hydrogen evolution reactions from water

Abstract

Monoclinic WO 3 (m-WO 3) nanoplates and nanorods were successfully synthesized by a simple hydrothermal process using sodium tungstate dihydrate (Na 2WO 4·2H 2O), ammonium nitrate (NH 4NO 3) and polyethylene glycol (PEG) as initial precursors. Phase, morphologies and electrochemical properties of the products were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM, TEM), high-resolution transmission electron microscopy (HRTEM), cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The effect of NH 4NO 3 concentration on the formation of the pure phase of m-WO 3 nanomaterial was studied. The product synthesized under NH 4NO 3-free condition was pure orthorhombic WO 3·0.33H 2O (o-WO 3·0.33H 2O) phase. By adding and increasing the amount of NH 4NO 3 to the solution, m-WO 3 phase started to form and became pure m-WO 3 phase when 1.50 g NH 4NO 3 was used. The morphology of m-WO 3 was nanoplates, and became nanorods by PEG adding. The nanostructured m-WO 3 showed much higher electrocatalytic activity for hydrogen evolution from water than that of the commercial bulk m-WO 3, including the m-WO 3 nanorods with slightly better than the m-WO 3 nanoplates.