Iron Doped Nickel Oxide Nanocrystals as Highly Efficient Electrocatalysts for Alkaline Water Splitting

Abstract

Efficient electrochemical water splitting to hydrogen and oxygen is considered a promising technology to overcome our dependency on fossil fuels. Searching for novel catalytic materials for electrochemical oxygen generation is essential for improving the total efficiency of water splitting processes. We report the synthesis, structural characterization, and electrochemical performance in the oxygen evolution reaction of Fe-doped NiO nanocrystals. The facile solvothermal synthesis in <i>tert</i>-butanol leads to the formation of ultrasmall crystalline and highly dispersible Fe_<i>x</i>Ni_1–<i>x</i>O nanoparticles with dopant concentrations of up to 20%. The increase in Fe content is accompanied by a decrease in particle size, resulting in nonagglomerated nanocrystals of 1.5–3.8 nm in size. The Fe content and composition of the nanoparticles are determined by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy measurements, while Mössbauer and extended X-ray absorption fine structure analyses reveal a substitutional incorporation of Fe(III) into the NiO rock salt structure. The excellent dispersibility of the nanoparticles in ethanol allows for the preparation of homogeneous <i>ca</i>. 8 nm thin films with a smooth surface on various substrates. The turnover frequencies (TOF) of these films could be precisely calculated using a quartz crystal microbalance. Fe_0.1Ni_0.9O was found to have the highest electrocatalytic water oxidation activity in basic media with a TOF of 1.9 s^–1 at the overpotential of 300 mV. The current density of 10 mA cm^–2 is reached at an overpotential of 297 mV with a Tafel slope of 37 mV dec^–1. The extremely high catalytic activity, facile preparation, and low cost of the single crystalline Fe_<i>x</i>Ni_1–<i>x</i>O nanoparticles make them very promising catalysts for the oxygen evolution reaction