A Sol–Gel–Hydrothermal Interfacial Regulation Strategy for Sulfate Intercalation in NiFe-LDH to Promote High-Valent Ni Formation and LOM-Type OER

Modulating the electronic state of nickel is a crucial strategy for activating lattice oxygen participation in the oxygen evolution reaction (OER). Herein, a sol–gel-assisted hydrothermal strategy is employed to synthesize sulfate-intercalated NiFe-LDH (SG-S-NiFe-LDH), where SO42– anions are stably incorporated into the interlayer galleries to modulate Ni oxidation states. This interfacial regulation reconstructs the local electronic environment, enabling the formation of high-valent Ni species and favoring a lattice-oxygen-mediated (LOM) pathway. Structural characterizations confirm successful anion incorporation, while post-OER XPS evidences Ni3+/Ni4+ enrichment. Mechanistic studies, including pH-dependent kinetics and O–O intermediate trapping, further validate LOM dominance. SG-S-NiFe-LDH exhibits outstanding activity with a low overpotential of 177 mV at 10 mA cm–2, a Tafel slope of 32.98 mV dec–1, and long-term durability exceeding 170 h. Post-OER HRTEM and ICP confirm structural robustness and minimal Ni loss. Density functional theory calculations reveal that sulfate intercalation raises the Ni d-band center, strengthens *OOH adsorption, and reduces the *OOH → *OO barrier to 0.53 eV. Moreover, a water-splitting device using SG-S-NiFe-LDH as the anode achieves 100 mA cm–2 at 1.66 V with stable 28 h operation. Faradaic efficiency above 98% with an O2:H2 ratio of 1:2 confirms high reaction selectivity. This work demonstrates a targeted anion intercalation strategy to modulate transition-metal states, unlock lattice oxygen reactivity, and advance efficient and durable water electrolysis.