Exploring the role of iron in Fe5Ni4S8 toward oxygen evolution through modulation of electronic orbital occupancy

Ni-Fe-based catalysts are considered to be among the most active catalysts for the oxygen evolution reaction (OER) under alkaline conditions, with Fe playing a crucial role. However, Fe leaching occurs during the reaction due to thermodynamic instability, which has resulted in conflicting reports within the literature regarding its role. To clarify this point, we propose a strategy consisting of modulating the electronic orbital occupancy to suppress the extensive loss of Fe atoms during the OER process. Theoretical calculations, in-situ X-ray photoelectron spectroscopy, molecular dynamics simulations, and a series of characterization showed that the stable presence of Fe not only accelerates the electron transfer process but also optimizes the reaction barriers of the oxygen evolution intermediates, promoting the phase transition of Fe5Ni4S8 to highly active catalytic species. The modulated Fe5Ni4S8-based pre-catalysts exhibit improved OER activity and long-term durability. This study provides a novel perspective for understanding the role of Fe in the OER process.