A NiFe-based monolithic electrocatalyst for pleiotropic-efficiency water oxidation

Abstract

NiFe-based catalysts have attracted great attention due to their high activity in alkaline water oxidation. However, potential metal dissolution, in particular Fe, causes gradual deactivation during oxygen evolution reaction (OER). In this work, a monolithic catalyst of FeS₂–Ni₃S₂ heterostructures and FeNi₃ nanoparticles embedded within porous S, N co-doped carbon nanofibers was synthesized via in situ electrospinning. Such an integrated catalyst exhibits excellent OER activity with an overpotential of 270 mV to gain 10 mA cm⁻². Under high-potential operations, the surficial reconstructed FeOOH and Ni(OH)₂ active phases were detected by in situ Raman spectroscopy. The high Fe content maintains the low oxidation state of Ni at Ni²⁺, and conversely Ni has a positive effect on the intrinsic activity of the Fe site. The covalent interaction between Ni(OH)₂ and the carbon encapsulation structure enhances the stability of FeOOH species. FeOOH and Ni(OH)₂ synergistically catalyze the OER process assisted by conductive FeNi₃ and S, N co-doped carbon. Such ingredients and monolithic structure not only alleviate Fe leaching, but also establish self-supportive ability to allow the anode reaction using a direct electrode without any additional substrates, which is conducive to adequate electrolyte infiltration and rapid O₂ liberation. Taking advantage of the above-described pleiotropic properties, this monolithic catalyst realizes an appreciable stability of 50 h for successive O₂ generation without any damage to the electrode structure.