Halogen-Modified Iron-Based Metal–Organic Frameworks for Remarkably Improved Electrocatalytic Oxygen Evolution

Iron-based metal–organic frameworks (MOFs) have shown potential as catalysts for the electrocatalysis oxygen evolution reaction (OER). Despite numerous methods being employed to enhance the OER performance of MOFs, the influence of halogen-containing linkers on the electronic structure of iron-based MOF catalysts remains unexplored. In this study, a series of Fe-based MOFs (denoted as MOF-R, where R = H, Cl, or Br) with comparable structures are synthesized by changing the organic linkers coordinated with the Fe metal active center, with the aim of investigating the influence of halogen-containing linkers on the OER activity. Significantly, MOF-Br exhibited superior OER activity compared to MOF-Cl and MOF-H. Density functional theory calculations reveal that the tuning of halogen groups on organic linkers can modulate the electronic structure of the metal active sites and effectively regulate the adsorption behavior of key intermediates near the optimal d-band center, leading to the enhancement of electroactivity. Notably, the bromine-substituted MOF-Br catalyst displayed remarkable intrinsic OER activity, including a low overpotential of 251.2 mV at a current density of 10 mA cm^–2 and a low Tafel slope of 44.5 mV dec^–1, surpassing the halogen-unsubstituted MOF-H (262.6 mV and 63.4 mV dec^–1) and commercial IrO₂ (335.3 mV and 98.6 mV dec^–1). Moreover, the high turnover frequency at an overpotential of 300 mV was measured to be 0.537 s^–1, which is 30 times greater than that of the commercial IrO₂ catalyst (0.018 s^–1). This research offers a potential strategy for designing MOF electrocatalysts with superior OER activity, laying a solid foundation for the rational design and synthesis of excellent OER electrocatalysts in the future.