Axial coordination engineering of FeNi catalysts for oxygen evolution reaction

Oxygen evolution, recognized as a significant half-reaction in the processes of water decomposition and carbon dioxide reduction, has garnered considerable attention in the scientific community. However, the conversion efficiency of renewable energy sources is limited by the oxygen evolution reaction's slow kinetics. Therefore, it is urgent to develop efficient and stable catalysts for oxygen evolution. Accordingly, a wet chemical synthesis of halogen-doped FeNi bimetallic oxygen evolution reaction (OER) catalyst (FeNi-X/NC, X = F, Cl and Br) has been reported. Among them, the FeNi-Cl/NC catalyst is rich in Ni-Cl/O sites where Ni is coordinated with a subsurface axial Cl atom. Ni-Cl active sites were verified to be present in FeNi-Cl/NC by X-ray absorption spectroscopy (XAS). Besides, the Cl-doped FeNi bimetallic catalyst exhibits 265 mV translocation at the current density of 10 mA cm^-2, which is superior to the F and Br-doped FeNi bimetallic catalysts. The experimental results show that Cl affects electron migration in FeNi metal. Meanwhile, density functional theory (DFT) confirms that the introduction of F, Cl and Br reduces the Gibbs free energy of the decision speed step in the OER process. Our findings provide a new idea for the preparation of high quality OER electrocatalysts by heteroatom doping, and accelerate the development of FeNi based OER catalysts.