Spin-regulated Ni sites with optimal d-orbital occupancy unlocking unprecedented oxygen evolution activity

Bin Li; Yanming Yu; Yihao Wang; Ming Xu; Guanjie Li; Si-Min Xu; Wei Wei; Tingting Cui

doi:10.26599/NR.2025.94907361

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Research Article | Open Access

Spin-regulated Ni sites with optimal d-orbital occupancy unlocking unprecedented oxygen evolution activity

Bin Li^{¹^,^§}, Yanming Yu^{¹^,^§}, Yihao Wang^{¹^,^§}, Ming Xu^¹

(), Guanjie Li^¹, Si-Min Xu^², Wei Wei^³

(), Tingting Cui^¹

()

1College of Chemistry, Chemical Engineering and Resource Utilization, Center for Innovative Research in Synthetic Chemistry and Resource Utilization, Northeast Forestry University, Harbin 150040, China

2College of Chemistry and Chemical Engineering, Gannan Normal University, Ganzhou 341000, China

3Vacuum Interconnected Nanotech Workstation, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China

^§ Bin Li, Yanming Yu, and Yihao Wang contributed equally to this work.

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Low-spin state Ni²⁺ (d_xz²d_yz²d_xy²d_x²−y²²d_z²⁰) was successfully constructed in NiCoFe-layered double hydroxide (NiCoFe-LDH), denoted as LS-NCF, through oxygen defect engineering, which enhanced oxygen intermediates adsorption and electron transfer, thereby significantly accelerating oxygen evolution reaction (OER) kinetics.

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 ( $d_{x z}^{2} d_{y z}^{2} d_{x y}^{2} d_{x^{2} - y^{2}}^{1} d_{z^{2}}^{1}$ ) 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⁺ ( $d_{x z}^{2} d_{y z}^{2} d_{x y}^{2} d_{x^{2} - y^{2}}^{2} d_{z^{2}}^{0}$ ) 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 $d_{z^{2}}$ 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.

Keywords

low-spin Ni sites oxygen evolution reaction defect engineering optimal d-orbital occupancy unprecedented performance

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References

[1]

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