Enhanced oxygen evolution reaction over glassy carbon electrode modified with NiO_x and Fe₃O₄

Magnetite iron oxide (Fe₃O₄)/nickel oxide (NiO_x) modified glassy carbon (GC) electrode shows enhancement of oxygen evolution reaction (OER) compared to GC electrode modified with single NiO_x or Fe₃O₄ nanoparticles. Many techniques such as linear and cyclic sweep voltammetry, electrochemical impedance spectroscopy (EIS) have been employed. Field-emission scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) are both used for characterization of the electrocatalysts. Effect of loading amount of both NiO_x and Fe₃O₄ and the order of deposition on the OER was studied. A significant improvement of the electrocatalytic properties of the Fe₃O₄/NiO_x binary catalyst modified GC is obtained when NiO_x is electrodeposited on GC/Fe₃O₄ (i.e. GC/Fe₃O₄/NiO_x) compared to GC/NiO_x/Fe₃O₄ (where NiO_x is deposited first on the GC then Fe₃O₄). The use of GC/Fe₃O₄/NiO_x (where Fe₃O₄ is deposited first on the GC then NiO_x) for OER in alkaline solution support higher currents and consequently negative shifts of the onset potential of OER compared to that of GC/NiO_x or GC/Fe₃O₄. The obtained electrochemical impedance parameters confirmed the above conclusions. Tafel parameters confirm the superior activity of GC/Fe₃O₄/NiO_x and give insight into the mechanism of the OER on the above electrodes.