In Situ Raman Study of Surface Reconstruction of FeOOH/Ni₃S₂ Oxygen Evolution Reaction Electrocatalysts

Construction of heterojunctions is an effective strategy to enhanced electrocatalytic oxygen evolution reaction (OER), but the structural evolution of the active phases and synergistic mechanism still lack in-depth understanding. Here, an FeOOH/Ni₃S₂ heterostructure supported on nickel foam (NF) through a two-step hydrothermal-chemical etching method is reported. In situ Raman spectroscopy study of the surface reconstruction behaviors of FeOOH/Ni₃S₂/NF indicates that Ni₃S₂ can be rapidly converted to NiOOH, accompanied by the phase transition from α-FeOOH to β-FeOOH during the OER process. Importantly, a deep analysis of Ni─O bond reveals that the phase transition of FeOOH can regulate the lattice disorder of NiOOH for improved catalytic activity. Density functional theory (DFT) calculations further confirm that NiOOH/FeOOH heterostructure possess strengthened adsorption for O-containing intermediates, as well as lower energy barrier toward the OER. As a result, FeOOH/Ni₃S₂/NF exhibits promising OER activity and stability in alkaline conditions, requiring an overpotential of 268 mV @ 100 mA cm⁻² and long-term stability over 200 h at a current density of 200 mA cm⁻². This work provides a new perspective for understanding the synergistic mechanism of heterogeneous electrocatalysts during the OER process.