Fe₃O₄@NiFe_<i>x</i>O_<i>y</i> Nanoparticles with Enhanced Electrocatalytic Properties for Oxygen Evolution in Carbonate Electrolyte

The design and engineering of earth-abundant catalysts that are both cost-effective and highly active for water splitting are crucial challenges in a number of energy conversion and storage technologies. In this direction, herein we report the synthesis of Fe₃O₄@NiFe_<i>x</i>O_<i>y</i> core–shell nanoheterostructures and the characterization of their electrocatalytic performance toward the oxygen evolution reaction (OER). Such nanoparticles (NPs) were produced by a two-step synthesis procedure involving the colloidal synthesis of Fe₃O₄ nanocubes with a defective shell and the posterior diffusion of nickel cations within this defective shell. Fe₃O₄@NiFe_<i>x</i>O_<i>y</i> NPs were subsequently spin-coated over ITO-covered glass and their electrocatalytic activity toward water oxidation in carbonate electrolyte was characterized. Fe₃O₄@NiFe_<i>x</i>O_<i>y</i> catalysts reached current densities above 1 mA/cm² with a 410 mV overpotential and Tafel slopes of 48 mV/dec, which is among the best electrocatalytic performances reported in carbonate electrolyte