Surface metal-EDTA coordination layer activates Ni_xFe_3-xO₄ spinel as an outstanding electrocatalyst for oxygen evolution reaction

Nickel-iron oxides are competitive electrocatalysts for oxygen evolution reaction, but their practical applications are restricted by the less-than-desirable intrinsic activity and working stability. To tackle the challenge, surface coordination chemistry is applied to the nickel-iron oxides through a complex-assisted in-situ crystal growth strategy. The ethylenediaminetetraacetate (EDTA) coordinated Ni_xFe_3-xO₄ (Ni_xFe_3-xO₄-EDTA) is prepared by a simple one-pot hydrothermal process. The coordinated EDTA molecules can deeply alter the surface coordination structure of the Ni_xFe_3-xO₄. The Ni_xFe_3-xO₄-EDTA demonstrates outstanding intrinsic activity towards oxygen evolution reaction, requiring only a small overpotential of 180 mV to reach 10 mA cm^-2 in 1.0 M KOH. Moreover, the Ni_xFe_3-xO₄-EDTA exhibits extremely stable long-term working stability. Density functional theory calculations show that the highly enhanced intrinsic activity is attributed to the surface coordinated EDTA-induced favorable electronic structure and coordination environment, which tunes the adsorption strength of the intermediates and optimizes the energetics of the elementary steps, while the high stability is ascribed to the strong coordination ability of EDTA.