Iron-based binary metal-organic framework nanorods as an efficient catalyst for the oxygen evolution reaction

First-row transition metal compounds have been widely explored as oxygen evolution reaction (OER) electrocatalysts due to their impressive performance in this application. However, the activity trends of these electrocatalysts remain elusive due to the effect of inevitable iron impurities in alkaline electrolytes on the OER; the inhomogeneous structure of iron-based (oxy)hydroxides further complicates this situation. Bimetallic metal-organic frameworks (MOFs) have the advantages of well-defined and uniform atomic structures and the tunable coordination environments, allowing the structure-activity relationships of bimetallic sites to be precisely explored. Therefore, we prepared a series of iron-based bimetallic MOFs (denoted as Fe2M-MIL-88B, M = Mn, Co, or Ni) and systematically compared their electrocatalytic performance in the OER in this work. All the bimetallic MOFs exhibited higher OER activity than their monometallic iron-based counterpart, with their activity following the order FeNi > FeCo > FeMn. In an alkaline electrolyte, Fe2Ni-MIL-88B showed the lowest overpotential to achieve a current density of 10 mA cm−2 (307 mV) and the smallest Tafel slope (38 mV dec−1). The experimental and calculated results demonstrated that iron and nickel exhibited the strongest coupling effect in the series, leading to modification of the electronic structure, which is crucial for tuning the electrocatalytic activity.