Electron Modulation in Cr-Doped NiFeOOH Enhances Oxygen Evolution Reaction Activity and Stabilizes Cr Dopant

NiFe(oxy)hydroxide (NiFeOOH) has been widely studied as a catalyst for oxygen evolution reaction (OER), but its activity is still not satisfactory. Although metal doping has been employed as a promising strategy for addressing this issue, the instability and leaching of the high-valence dopant metals remain considerable challenges. Herein, an array of Cr-doped NiFeOOH nanosheets was in situ synthesized on nickel foam via a one-step hydrothermal method. The doping of NiFeOOH with Cr was found to induce partial electron transfer from Ni and Fe to Cr atoms, thereby modulating the electronic structure of the catalyst and enhancing its intrinsic activity. Electrochemical and in situ Raman spectroscopy analyses showed that Fe active sites with lower charge density enhance the adsorption of *OH and reduce the formation energy barrier of the *OOH intermediate during OER, thereby accelerating the OER. Moreover, Fe was found to promote the transfer of additional electrons to Cr, leading to electron accumulation at Cr sites. This electron accumulation effectively prevents Cr from excessive oxidation and leaching under anode potentials, thereby maintaining the structural stability of the catalyst. The optimized Cr-doped NiFeOOH self-supported electrode exhibited a current density of 50 mA/cm 2 with an overpotential of only 239 mV and remained stable for 100 h at 600 mA/cm 2 in 1 mol/L KOH.