Metal-Organic Framework-Spinel Fe-ZIF-8@NiAl₂O₄ Heterostructures Enabling Efficient and Durable Alkaline Water...

Spinel metal oxides such as NiAl₂O₄ are attractive electrocatalysts for alkaline water splitting but are often limited by low surface area, poor conductivity, and sluggish reaction kinetics. Herein, we report a bifunctional MOF-spinel heterostructured catalyst, Fe-ZIF-8@NiAl₂O₄, constructed by integrating solvothermally synthesized spinel NiAl₂O₄ with iron-doped ZIF-8 without post-synthetic pyrolysis. Benefiting from the porous, nitrogen-rich MOF scaffold and the structurally robust spinel backbone, the composite delivers low overpotentials of 231 mV for the oxygen evolution reaction (OER) and 109 mV for the hydrogen evolution reaction (HER) at 10 mA cm^-2, together with Tafel slopes of 97.45 and 239.29 mV dec^-1, respectively. The enhanced activity originates from synergistic Fe-Ni interfacial interactions that facilitate electronic redistribution, accelerate charge transfer kinetics, and promote the in situ formation of catalytically active NiFe (oxy)hydroxide species during operation. Importantly, Fe-ZIF-8@NiAl₂O₄ exhibits excellent durability and stable overall water splitting performance, retaining bulk crystallinity while undergoing beneficial surface reconstruction under prolonged electrolysis. This work establishes MOF hybridization as an effective strategy to activate Al-based spinel oxides and provides practical design insights for developing cost-effective, noble-metal-free electrocatalysts for sustainable hydrogen production.