Electrochemistry of Nickelocene-Ferrocene Organometallic Complexes for Electrodeposition of Nickel–Iron–Based Nanostructured Film under Ambient Conditions for Oxygen Evolution Reaction

Abstract

This study explores the interesting redox chemistry of organometallic complexes nickelocene (Nc) and ferrocene (Fc) as well as their instability as metal inorganic complexs in electrolytes on the application of bias to derive bimetallic NiFe-based nanostructured films at room temperature conditions in the presence of atmospheric oxygen. The cyclic voltammogram of the two complexes under optimized conditions revealed that the redox peaks for Fc lie between the two redox peaks of Nc, which gave us the freedom of individual potential windows for the deposition of Ni and Fe in one step. The transformation of the metal inorganic complex to the respective nanostructured oxides was investigated using in situ UV–visible spectroscopy method, and the electrodeposited product was characterized using XRD, TEM, Raman, and XPS techniques. Furthermore, the bimetallic films were tested for their catalytic activity toward oxygen evolution reaction (OER) and urea oxidation reaction (UOR). The optimized nanoscale thicknesses of Ni and NiFe films deposited in 15 cyclic voltammetry (CV) cycles showed the best performance toward both urea and water oxidation, respectively. The NiFe-15 showed only 258 mV overpotential to achieve a current density of 10 mAcm^–2 and an impressive TOF of 1.02 s^–1 at 300 mV overpotential. Electrocatalytic studies reveal that the presence of iron increases the OER efficiency and adversely affects UOR. In-situ ultraviolet–visible (UV–vis) spectroscopy combined with in situ Raman spectroscopy revealed that the active site for the OER is higher valence oxo species of NiOOH while for UOR, NiOOH was found to be an active species. Our research reports an improved, user-friendly approach for electrode fabrication of an NiFe-based catalyst but also opens a different pathway toward the application of organometallic complexes for the design of catalysts for the oxygen evolution reaction.