Deciphering the role of ultra-low-loaded rhodium in NiFe-MIL-53 for superior oxygen evolution reaction

Designing highly active and stable electrocatalysts of oxygen evolution reaction (OER) is one of the crucial challenges. In this study, a novel OER electrocatalyst, NiFe-MIL-53 modified with ultra-low rhodium (Rh@NiFe-MIL-53), is successfully prepared via the hydrothermal method. In-situ Raman spectroscopy and electrochemical impedance spectroscopy reveal that the doped Rh accelerates the phase transformation of NiFe-MIL-53 and the in-situ formed Rh@NiFeOOH is the actual active species. More importantly, the enhanced reversibility of electrochemical reconstruction between NiFeOOH and NiFe(OH) 2 after doping Rh is beneficial for improving the electrochemical stability of the catalyst. X-ray photoelectron spectroscopy spectra show the strong electronic interaction between single-atom Rh and Ni/Fe in Rh@NiFeOOH. Furthermore, theoretical calculations confirm that the integration of single-atom Rh into the NiFeOOH successfully reduces the band gap, regulates the d -band center ( ε d ), accelerates the charge transfer, and optimizes the adsorption behavior of oxygen-containing intermediates, thereby lowering the energy barrier of rate-determining steps. Consequently, the optimized Rh@NiFe-MIL-53 exhibits excellent OER activity (240 mV) with a small Tafel slope of 48.2 mV dec −1 and long-term durability (over 1270 h at 10 mA cm −2 and 110 h at 200 mA cm −2 ). This work presents a new perspective on designing highly efficient OER electrocatalysts.