An in situ grown NiFe-based MOF for efficient oxygen evolution in alkaline seawater at high current densities

Abstract

The oxygen evolution reaction (OER) characterized by a four-electron transfer mechanism is inherently limited by significant overpotential requirements and sluggish kinetics. A water-stable NH₂-MIL-88B (Fe₂Ni) metal–organic framework (MOF) was in situ synthesized on nickel foam (NF) with high conductivity (NFN-MOF/NF) for the OER in alkaline electrolytes and alkaline seawater. A NFN-MOF/NF composite material not only exhibited a remarkably low overpotential (η₂₀₀) of merely 286 mV at a current density of 200 mA cm⁻² in 1 M KOH solution, but also maintained impressive OER performance under alkaline seawater conditions, with an η₄₀ of 285 mV. Furthermore, NFN-MOF/NF exhibited only 2.3% and 4.8% chronopotentiometric decay after reacting 100 hours at a high current density of 200 mA cm⁻² in alkaline and alkaline seawater media, demonstrating excellent stability of the composite material. The NFN-MOF/NF‖Pt/C/NF overall water splitting electrolysis system required only an ultra-low battery voltage of 1.58 V to achieve a current density of 10 mA cm⁻². The superior electrochemical performance of the NFN-MOF/NF catalyst can be attributed to the abundance of active sites within the MOF, the positive coupling effect between Ni and Fe ions, and the synergistic interaction between the MOF and the NF substrate.