Abstract: Hydrogen (H₂) has emerged as a pivotal clean energy carrier due to its zero-carbon emissions and high energy density, while seawater electrolysis presents a promising route for H₂ production. However, the complex ionic environment of seawater poses significant challenges for stable and efficient catalytic electrodes. Herein, we develop a spin-state engineering strategy that stabilizes low-spin metallic Ni centers within N-doped graphitic carbon through H₂-assisted pyrolysis (Ni/CN-AH). Density functional theory (DFT) reveals graphitization and low-spin Ni synergistically downshift the d-band center by 0.69 eV, achieving optimal H* adsorption while weakening chlorine binding. The strong d-p hybridization at the interface and charge delocalization from low-spin Ni to carbon enhances reaction kinetics. The catalyst exhibits outstanding HER activity and durability in both 1 M KOH and alkaline seawater, while simultaneously suppressing Cl^- adsorption and preventing Ca²⁺/Mg²⁺ precipitation. This work establishes a new pathway for developing durable seawater-splitting catalysts through atomic-scale spin control and nanoscale carbon engineering.

Key words: Hydrogen evolution, Seawater electrolysis, Spin-state engineering, Graphitization carbon matrix, Concentration gradient