Liquid Nitrogen Quenching‐Induced Orbital Occupancy Modulation for Optimized Intermediate Adsorption for Efficient Anion Exchange Membrane Water Electrolyzers

ABSTRACT The inherent stress in heterostructures destabilizes the crystal lattice, distorts intermediate adsorption, and increases the energy barrier of the potential‐determining step in anion exchange membrane water electrolyzers (AEMWE). Herein, an innovative liquid nitrogen quenching strategy is developed to induce a high‐spin to low‐spin transition in NiS x ‐based heterostructures through nitrogen incorporation, where the electron‐withdrawing effect modifies the local electronic valence state to optimize intermediate adsorption/desorption energetics and significantly reduce the energy barrier of the potential‐determining step. Consequently, the low‐spin state NiS x nanosheets demonstrate superior electrocatalytic performance, delivering low overpotentials of 78.1 mV for hydrogen evolution reaction (HER) and 210.0 mV for oxygen evolution reaction (OER) at ±10 mA cm −2 , respectively, while enabling efficient overall water splitting with a cell voltage of 1.59 V at 10 mA cm −2 . Meanwhile, the AEMWE with LNQ‐NiS x /NF anode maintains stable operation at 1.25 A cm −2 for over 150 h, showing merely 1.13 mV h −1 potential degradation. In situ characterization confirms robust structural stability and enhanced adsorption of reactive intermediates, while density functional theory (DFT) calculations verify the critical role of low‐spin state in reducing energy barriers. Overall, this work provides a rational design strategy for advanced water electrolyzer electrocatalysts by elucidating the spin state‐activity relationship.