Alloying normal and inverse spinel (Zn–Co ferrite) nanostructures via direct precursor pyrolysis for enhanced supercapacitance and water splitting

Abstract

The nanocrystals comprising of multiple redox-active cations are generally proficient electrocatalysts for renewable and sustainable energy applications. Ferrites have rich redox chemistry and crystallographically, they can be classified into normal spinel structures or inverse spinel structures, depending on the type of occupancy at tetrahedral and octahedral sites. Herein, taking advantage of the simplicity and environmental benignity of the solventless method, a series of mixed inverse and normal spinel nanocatalysts (Co1-xZnxFe2O4 (0 = x ≤ 1)) have been successfully synthesized and tested for supercapacitance and overall water splitting. The p-XRD and EDX analyses confirmed the successful nucleation of CoFe2O4 and ZnFe2O4 to form monophasic Co1-xZnxFe2O4 solid solutions over the entire composition range. The solid solutions with composition Co0·4Zn0·6Fe2O4 demonstrated higher discharge time, indicating higher specific capacitance of the material than other electrode compositions. The Co0·8Zn0·2Fe2O4 showed relatively low overpotentials of 317 mV to afford the current density of 10 mA/cm2 for oxygen evolution reaction (OER), while Co0·6Zn0·4Fe2O4 exhibited an overpotential of 169 mV for hydrogen evolution reaction (HER), outperforming most of the electrocatalysts reported in the literature. More impressively, such solid solutions demonstrated negligible deviation between the first and the 1 k cycles, suggesting high durability for the electrolysis of water.