Emerging as a critical technology for atmospheric carbon dioxide (CO2) removal, the mass deployment of direct air capture (DAC) demands breakthrough innovations in efficient and stable adsorbent materials that simultaneously achieve high capacity, oxidative durability, and low cost. Herein, a hydroxyl‐rich Mg0.55Al layered double hydroxide (LDH) support is developed via aqueous miscible organic solvent treatment, circumventing energy‐intensive calcination while engineering mesopores for efficient polyethyleneimine (PEI) loading. The optimized 60 wt.% PEI modified Mg0.55Al‐CO3 AMO‐LDH achieves a CO2 uptake of 3.92 mmol g−1 under simulated wet air at 25 °C and retains 90.8% capacity over 20 cycles. Crucially, the abundant surface hydroxyls of uncalcined LDH, validated by 1H Nuclear Magnetic Resonance and in situ X‐ray Photoelectron Spectroscopy, form hydrogen bonds with PEI, suppressing oxidative degradation. After 3 h at 120 °C in simulated air, PEI‐LDH retains a CO2 capacity of 1.06 mmol g−1, significantly outperforming PEI/mixed metal oxide and conventional silica‐based adsorbents. In situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy further reveals that hydroxyl‐mediated amine anchoring minimizes water co‐adsorption. This work establishes a dual strategy of hydroxyl preservation and mesopore engineering to design cost‐effective DAC adsorbents, achieving both high capacity and exceptional stability under realistic operating conditions
