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 (NO, PO, SO, and SeO) into the NiFeOOH substrate, improving its resistance to bond breakage. And the NiFeOOH-NO- electrocatalyst was found to be optimal, achieving an overpotential of 311 mV and stable performance at 1 A cm for several hundred hours. Consequently, NiFeOOH-NO 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 NO in NiFeOOH effectively mitigates Fe segregation, leading to a fourfold enhancement in long-term stability relative to that of NiFeOOH without NO modification. Theoretical calculations show that the introduction of NO 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.