Abstract
Water splitting electrolysis is a promising sustainable methodology to produce clean and green hydrogen fuel, which is considered as a prominent replacement for conventional fossil fuels. Developing highly active, stable and low-cost electrocatalysts plays a critical role for achieving efficient production of hydrogen by electrolysis for practical applications. Herein, we report the synthesis of Co3O4 spinel oxides by simple calcination of commercially available cobalt salts at different temperatures (400, 600 and 800 degrees C) and the disordered structure induced highly enhanced hydrogen evolution reaction (HER) in an alkaline medium (1.0 M KOH). Powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) indicated the formation of a normal spinel Co3O4 structure at 400 (Co3O4-400) and 600 degrees C (Co3O4-600) calcination, whereas disordered Co3O4 at 800 degrees C (Co3O4-800). HR-TEM analysis revealed the formation of spherical crystalline particles in Co3O4-400 and featureless aggregated crystalline particles at higher temperatures. The d-spacing analysis using PXRD and the lattice fringe pattern showed a decrease of the spacing with increasing calcination temperature, which suggested higher strain for Co3O4-800. The electrocatalytic HER activity of Co3O4-400 and Co3O4-600 in an alkaline medium showed moderate activity. Co3O4-400 and Co3O4-600 required an overpotential of 293 and 240 mV, respectively, to achieve a geometric current density of 10 mA cm(-2). In contrast, disordered Co3O4-800 required a very low overpotential (93 mV) for producing the geometric current density of 10 mA cm(-2). Electrochemical impedance studies showed faster kinetics and charge transfer for disordered spinel Co3O4-800 and supported the enhanced HER activity. The electrocatalytic stability studies for Co3O4-800 were tested up to 48 h at 100 mA cm(-2) current density and confirmed the excellent stability. Thus, a low-cost earth abundant HER electrocatalyst was fabricated by a simple method.