Interfacial charge redistribution boosts β-NiOOH formation for enhanced OER activity of Cu₂S–NiFe-LDH

Heterojunction engineering is a proven strategy for enhancing electrocatalytic oxygen evolution reaction (OER) performance, but the correlation between the evolution of active phases at the interface and the performance enhancement remains poorly understood. Here, we report a Cu₂S–NiFe-LDH heterojunction directly grown on Cu foam by chemical etching and hydrothermal treatment. Spectroscopic characterization verifies interfacial electron donation from Cu₂S to NiFe-LDH, generating Ni sites with elevated electron density. Further, in situ Raman spectroscopy clarifies the influence of interfacial electron transfer on the active phase of OER. Under oxidizing potentials, both NiFe-LDH and the Cu₂S–NiFe-LDH heterostructure undergo transformation into a mixture of γ-NiOOH and β-NiOOH. Cu₂S–NiFe-LDH heterostructure can trigger β-NiOOH at a lower potential and in greater proportion, which is attributed to the lower valence state of Ni induced by interfacial charge redistribution. Furthermore, the construction of the heterointerface reduces the structural disorder of NiFe-LDH, leading to enhanced OER stability. DFT calculations further confirm that β-NiOOH exhibits a lower free energy barrier than γ-NiOOH in the formation process of the ∗OOH intermediate, thereby improving the OER activity. As a result, Cu₂S–NiFe-LDH/CF heterostructure exhibits remarkable alkaline OER performance (286 mV@100 mA cm⁻²), far exceeding that of bare NiFe-LDH (324 mV@100 mA cm⁻²).