The adjacent Fe oxidation greatly enhancing OER activity on the Ni active site: S plays the role in optimizing local coordination and electronic structure

Oxygen evolution reaction (OER) is the bottleneck process of water splitting, and finding efficient, durable, low-cost, and earth-abundant electrocatalysts remains a major challenge. Here, FeNi₂-400-S is to be a promising OER electrocatalyst which exhibits a low overpotential of 214 mV at a current density of 10 mA/cm². X-ray analysis indicates that the introduction of S leads to a mismatch in bond distance between the metal-sulfur bond and the metal-metal bond, which can change the local electronic structure and favorably control the electronic oxidation. The active site position of FeNi₂-400-S has been further confirmed by DFT, which the ∗OOH can stably adsorb on the Ni site of the oxidized Fe-Ni-S benefitting from the synergetic effect of the Ni site and the adjacent oxidized O on the Fe atom. Our findings demonstrate that the internal reconstruction of catalyst can make the optimization of local coordination and electronic structure, in which the in-situ generated vacancy can enable the outstanding OER performance.