@article{Li2025, 
author = {Bin Li and Yanming Yu and Yihao Wang and Ming Xu and Guanjie Li and Si-Min Xu and Wei Wei and Tingting Cui},
title = {Spin-regulated Ni sites with optimal d-orbital occupancy unlocking unprecedented oxygen evolution activity},
year = {2025},
journal = {Nano Research},
volume = {18},
number = {5},
pages = {94907361},
keywords = {low-spin Ni sites, oxygen evolution reaction, defect engineering, optimal d-orbital occupancy, unprecedented performance},
url = {https://www.sciopen.com/article/10.26599/NR.2025.94907361},
doi = {10.26599/NR.2025.94907361},
abstract = {Nickel-based layered double hydroxides (LDHs) are widely recognized as promising substitutes for noble metal catalysts in the oxygen evolution reaction (OER). However, conventional Ni2+ sites exhibit a high-spin configuration ( dxz2dyz2dxy2dx2−y21dz21) with excessive frontier-orbital occupancy, resulting in weak binding strength toward oxygen intermediates, which dramatically limits their OER performance. Herein, we first report the successful construction of low-spin state Ni2+ ( dxz2dyz2dxy2dx2−y22dz20) in NiCoFe-LDH (LS-NCF) through oxygen defect engineering. LS-NCF exhibits a splendid OER activity with an ultra-low overpotential of 241 mV at the current density of 1 A·cm−2, which is 79 mV lower than that of the conventional NiCoFe-LDH with high-spin Ni2+ (HS-NCF), significantly outperforming previously reported transition metal-based catalysts. Comprehensive studies reveal that LS Ni2+ with reduced  dz2 orbital occupancy effectively enhances oxygen intermediates adsorption through reinforcing the orbital hybridization between Ni 3d and O 2p. Moreover, the d-band center of LS Ni2+ is closer to the Fermi level compared to that of HS Ni2+, thus accelerating electron transfer. Consequently, the strengthened adsorption of *O intermediate and accelerated electron transfer in LS-NCF efficiently lower the reaction energy barrier of the rate-determining step (*O → *OOH), thereby greatly boosting its OER performance. This work provides valuable insights into designing high-performance Ni-based electrocatalysts via spintronic-level engineering.}
}