Real-Time Monitoring of Fe-Induced Stable γ-NiOOH in Binder-Free FeNi MOF Electrocatalysts for Enhanced Oxygen Evolution.

Hydrogen energy is a promising renewable source, and metal-organic frameworks (MOFs) are considered potential electrocatalysts for water electrolysis due to their abundant active sites, high porosity, and large surface area. The synthesis of bimetallic iron-nickel-benzene-1,3,5-tricarboxylate/nickel foam (FeNi-BTC/NF) MOF is reported using a binder-free one-pot method by immersing nickel foam (NF) into a solution of benzene-1,3,5-tricarboxylic acid (BTC), N,N-dimethylformamide (DMF), and iron (Fe) salts. FeNi-BTC/NF exhibits a low overpotential of 276 mV at 100 mA cm- 2, a Tafel slope of 94 mV dec-1, and stability exceeding 120 h. The Fe-Ni interaction facilitates the formation of a stable gamma-nickel oxyhydroxide (γ-NiOOH) phase, preventing its reversion to nickel hydroxyide (Ni(OH)₂), which is crucial for improving oxygen evolution reaction (OER) performance. This phase transition, revealed via in situ Raman spectroelectrochemical analysis, enhances electrocatalytic activity. Additionally, high-valent Fe modulates the electronic structure of Ni, enabling FeNi-BTC/NF to transform into γ-NiOOH at higher potentials, with Fe and γ-NiOOH synergistically boosting OER efficiency. The findings offer insights into Fe/Ni atom interactions and phase transformations in FeNi-BTC/NF MOFs for enhanced water splitting.