Electronic structure modulation with ultrafine Fe₃O₄ nanoparticles on 2D Ni-based metal-organic framework layers for enhanced oxygen evolution reaction

Two-dimensional (2D) metal organic frameworks (MOFs) are emerging as low-cost oxygen evolution reaction (OER) electrocatalysts, however, suffering aggregation and poor operation stability. Herein, ultrafine Fe₃O₄ nanoparticles (diameter: 6 ± 2 nm) are homogeneously immobilized on 2D Ni based MOFs (Ni-BDC, thickness: 5 ± 1 nm) to improve the OER stability. Electronic structure modulation for enhanced catalytic activity is studied via adjusting the amount of Fe₃O₄ nanoparticles on Ni-BDC. The optimal Fe₃O₄/Ni-BDC achieves the best OER performance with an overpotential of 295 mV at 10 mA cm^-2, a Tafel slope of 47.8 mV dec^-1 and a considerable catalytic durability of more than 40 h (less than 5 h for Ni-BDC alone). DFT calculations confirm that the active sites for Fe₃O₄/Ni-BDC are mainly contributed by Fe species with a higher oxidation state, and the potential-determining step (PDS) is the formation of the adsorbed O* species, which are facilitated in the composite.