Fe ²⁺ ‐ Induced Activation of Single and Dual Metal Site—Lattice Oxygen Mechanism in Fe Rich NiFe‐LDHs for Oxygen Evolution Reaction

Developing a durable and efficient oxygen evolution reaction (OER) catalyst without noble metals is essential for the economical and sustainable production of hydrogen by alkaline water electrolysis. Recent studies have advocated triggering the lattice oxygen mechanism (LOM) to reduce the overpotential of catalysis and overcome the inherent limitations of the adsorbate evolution mechanism (AEM). Herein, we explored a facile and scalable method for synthesizing an iron-rich nickel-layered double hydroxide (NiFe-LDH) with a unique hollow nanocapsule morphology using a metal-organic framework (MOF) MIL-88A as a sacrificial template for OER. The transformation of the MOF into hollow NiFe-LDH provides abundant lattice oxygen defects and alters the Fermi level of O 2p, triggering LOM. As a result, the material exhibited outstanding OER performance, with a low overpotential of 244 mV at 10 mAcm^-2, and excellent long-term durability. Ex-situ X-ray Photoelectron Spectroscopy (XPS) analysis of the catalyst before and after the OER reaction revealed a high density of surface oxygen defects in the Fe-rich NiFe-LDH, which is a prerequisite for LOM activation. Also, through in-situ Raman spectroscopy, which monitored the appearance of superoxide intermediates (1040-1250 cm^-1), revealed strong evidence for the involvement of the single metal site LOM and dual metal site LOM pathways in the OER. The presence of Fe²⁺ and Fe³⁺ in Fe-rich NiFe-LDH and the possible LOM mechanism were further evaluated using computational analyses.