Tailoring the catalytic activity of nickel sites in NiFe2O4 by cobalt substitution for highly enhanced oxygen evolution reaction

Abstract

Density functional theory (DFT) calculations predict that the Fe sites of NiFe₂O₄ are the preferred active centers for the OER, while Ni centers are activated at higher potentials. Tuning the local electronic environment of Ni in NiFe₂O₄ is expected to be an efficient approach to alter the electronic properties and tailor the intrinsic activity of Ni sites. Herein, a series of Ni_1−xCo_xFe₂O₄ (x = 0.01, 0.02, 0.05, and 0.1) were synthesized through a one-pot hydrothermal process, aiming to tune the electronic structure of nickel ferrite and to offer insights into the design of highly active nickel ferrite-based catalysts. TEM and XPS characterization experiments show that the partial substitution of Ni by Co decreases the particle size and alters the electronic properties, respectively. Electrochemical measurements show that the dopant concentration plays a key role in tailoring the catalytic performance of nickel ferrite towards the OER, and that the optimized Ni_1−xCo_xFe₂O₄ displays a small overpotential of 227 mV at 10 mA cm⁻² in 1 M KOH. DFT calculations show that the incorporation of Co changes the rate-determining step and promotes the catalytic activity of Ni because of the Ni–Co interaction-induced change in electronic properties. This study offers new insights into the active sites of nickel ferrite and the design of advanced nickel ferrite catalysts.