Sol-gel derived MgCr2O4 nanoparticles for aqueous supercapacitor and alkaline OER and HER bi-functional electrocatalyst applications

Abstract

Metal oxides with spinel structure exhibit interesting electrochemical properties, arising from their unique crystal structure and presence of multiple redox centers. In this investigation, MgCr2O4 nanoparticles were synthesized by a chemical sol-gel reaction process to explore its improved aqueous supercapacitor and alkaline electrocatalyst applications. We obtain a polycrystalline sample with spherical morphology, with an average particle size of 12–20 nm. These nanoparticles of MgCr2O4 are suitable for electrochemical operations. The hollow and porous microstructure of these MgCr2O4 nanoparticles enabled efficient ionic diffusion and electrons’ movement during electrochemical measurements. In the presence of aqueous 1 M Li2SO4 electrolyte system, we observed the value of capacitance of about 17 F/g (at 0.25 A/g), an energy density of about 11 Wh/kg, and a power density of about 275 W/kg. On the other hand, in presence of aqueous 1 M NaClO4 electrolyte systems, approximately C = 21 F/g (at 0.5 A/g), E = 14 Wh/kg and P = 550 W/kg, were found. Capacitance retention of more than 84% after undergoing 1000 charge-discharge cycles was observed in both cases, indicating long term cyclic stability performance of the system. These qualities make MgCr2O4 nanoparticles a suitable electrode material for future aqueous energy storage devices. MgCr2O4 also showed promising performance as alkaline water splitting electrocatalyst. As an Oxygen Evolution Reaction (OER) catalyst, it showed an overpotential of 1.174 V, and a Tafel slope of about 349 mV/dec was recorded. As a Hydrogen Evolution Reaction (HER) electrocatalyst, an overpotential of 631 mV was observed, and a Tafel slope of about 169 mV/dec was recorded. Our analysis clearly showed that the chemically synthesized MgCr2O4 nanoparticles are very promising for aqueous supercapacitor and alkaline OER and HER bi-functional electrocatalyst applications.