Optimizing the stability of NiFeOOH via oxyanion intercalation for water oxidation at large current densities

In alkaline water splitting, transition metals (Ni, Fe) have received extensive attention, and NiFe-oxyhydroxide (NiFeOOH) is regarded as an exceptionally active electrocatalysts for oxygen evolution reaction (OER). However, maintaining the long-term stability of NiFeOOH at high current densities is challenging due to Fe segregation and catalyst degradation. Herein, this study proposes an approach to enhancing the stability of the Ni/Fe-O covalent bond by intercalating oxyanions (NO₃^-, PO₄^3-, SO₄^2-, and SeO₄^2-) into the NiFeOOH substrate, improving its resistance to bond breakage. And the NiFeOOH-NO₃- electrocatalyst was found to be optimal, achieving an overpotential of 311 mV and stable performance at 1 A cm^-2 for several hundred hours. Consequently, NiFeOOH-NO₃^- exhibited a significantly improved OER stability, with a mere 3.33 % stability attenuation after 100 h, compared to 13.19 % for pristine NiFeOOH. Notably, the presence of NO₃^- in NiFeOOH effectively mitigates Fe segregation, leading to a fourfold enhancement in long-term stability relative to that of NiFeOOH without NO₃^- modification. Theoretical calculations show that the introduction of NO₃^- effectively shifts metal 3d band centers of NiFeOOH closer to the Fermi level. It is suggested that the oxyanions lead to increased strength of the Ni/Fe-O bonds, thereby inhibiting the dissolution of Fe and enhancing the stability of NiFeOOH phase. This research represents a significant advance in controlling Fe segregation to stabilize NiFe-based electrocatalysts for high-current-density water oxidation.