Electrochemically Synthesized and Converted Bimetallic NiO–FeOOH Nanowires on Copper Foil for Enhanced Oxygen Evolution Reaction in an Alkaline Medium

Developing an efficient cost-effective electrocatalyst for a kinetically sluggish oxygen evolution reaction (OER) is important for hydrogen fuel generation by water electrolysis. Herein, we report the fabrication of NiO–FeOOH heteronanostructures directly on a conductive copper foil electrode by an electrochemical method and used for electrocatalytic OER activity in an alkaline medium. The electrochemical deposition produced Ni(OH)2–FeOOH on copper foil initially, and Ni(OH)2 was converted to NiO by further electrochemical activation. The formation of heteronanostructures was confirmed by X-ray photoelectron spectroscopy analysis. Scanning electron microscopy (SEM) studies showed the formation of aggregated Ni(OH)2 nanoparticles on the thick layer of FeOOH. The aggregated Ni(OH)2 nanoparticles were converted to NiO nanowires by electrochemical activation, but FeOOH remained unchanged. The electrochemically converted bimetallic NiO–FeOOH showed strong electrocatalytic OER activity and required a low overpotential (220 mV) to produce a 10 mA/cm2 current density. The individual NiO and FeOOH required high overpotentials (320 (NiO) and 390 mV (FeOOH)) to produce a 10 mA/cm2 current density. Tafel analysis revealed a low Tafel slope (48 mV/dec) and suggested fast reaction kinetics in the bimetallic electrode interface. Electrochemical impedance spectra further indicated the improved charge transfer and contributed for enhanced OER activity. The catalyst showed good stability over 6 h. After catalysis, SEM analysis revealed the same morphology of NiO–FeOOH heteronanostructures and further supported the stability of the catalyst. The method was extended to grow NiO–FeOOH on nickel foam, which also showed highly enhanced OER activity. It required only a 209 mV overpotential to produce a 10 mA/cm2 current density and exhibited good stability over 15 h. This indicated the broader applicability of the present method in developing a highly active electrocatalyst by electrochemical deposition.