The present study aims to gain molecular insights into how peroxomonosulfate (PMS) reacts with ethylenediaminetetraacetic acid (EDTA)-Ni II at alkaline pH by conducting experimental tests and density functional theory (DFT) calculations. We first show experimental evidence that the decomplexation of EDTA-Ni II and simultaneous formation of Ni hydroxide precipitates can be successfully achieved with the addition of PMS under alkaline conditions. At pH 11.0 or above, the aqueous Ni concentration is substantially reduced from 2.0 to below 0.1 mg L −1 within 60 min. We then propose an alternative reaction pathway in which Ni II rather than EDTA is attacked by PMS, leading to the production of high-valent Ni species (in the form of EDTA-Ni IV =O). This is a key and highly oxidative species being further self-decomplexed to Ni III hydroxides. Our findings suggest that the involvement of Ni IV species might be a viable redox pathway that plays an important role in promoting decomplexation.
Active site exposure and intrinsic catalytic performance are considered important aspects of oxygen evolution reaction catalyst design. In this work, the coordination capacity of tributylphosphine is utilized to construct cationic vacancy defects on NiFe-LDH nanosheets. As-prepared defective NiFe-LDH nanosheets show not only the optimization of the exposure ability of the active site but also the intrinsic catalytic capacity is improved by construction of cationic vacancy defect to tune local electronic structure. The x-ray photoelectron spectroscopy results revealed that after reconstruction of the prepared d-NiFe-LDH, high-valence Ni and Fe can stably appear on the surface of the material. The presence of high-valence Ni and Fe is considered to be the main reason to improve the intrinsic catalytic capacity of catalysts. Finally, d-NiFe-LDH nanosheets show excellent catalytic performance (η10 = 243 mV) and remarkable long-term stability.
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.
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