Engineering of cobalt impregnated sponge like spinel nickel ferrite as an efficient electrocatalyst for sustained overall water splitting

Abstract

The substantial exhaustion of energy resources in the present reality limelight to the exigency for a clean and sustainable energy resource and the key solution for this would be electrocatalytic water splitting to produce clean H₂. For achieving this objective amending noble metals with non-noble metals as electrocatalysts which are cost effective and earth abundant would serve as a better option. Herein, combustion derived nickel ferrite (NiFe₂O₄) and cobalt doped nickel ferrite (NiCo_xFe_2-xO₄) nanoparticles were extensively studied for Oxygen (O₂) and Hydrogen (H₂) evolution reactions respectively. The NiCo_0.01Fe_1.99O₄ and NiCo_0.03Fe_1.97O₄ Co-doped NiFe₂O₄ electrocatalyst exhibits excellent Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) activity in 1.0 M KOH electrolyte requiring a potential of 1.68 V ($\eta$ = 455 mV) vs RHE for OER and −0.167 V ($\eta$ = 167 mV) vs RHE for HER to achieve the benchmark current density of 10 mA cm⁻² and −10 mA cm⁻² for OER and HER respectively. The best performing electrodes (NiCo_0.03Fe_1.97O₄||NiCo_0.01Fe_1.99O₄) were employed for overall water splitting which at a constant current density of 50 mA cm⁻² acquired a cell voltage of around 2.2 V when it was put through the long-term stability test for a stretch of 24 h. Wherein, a slight increase of 30 mV that the initial voltage was spotted after 24 h which is an imperceptible loss. These results demonstrate that the doping of Co metal ions into NiFe₂O₄ nanoparticles has resulted in an efficient noble metal free electrocatalyst for overall water splitting.